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1    -----------------------------------------------------------------------------
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
# Line 5  synopses of each function in the library Line 6  synopses of each function in the library
6  separate text files for the pcregrep and pcretest commands.  separate text files for the pcregrep and pcretest commands.
7  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
8    
 NAME  
      PCRE - Perl-compatible regular expressions  
9    
10    PCRE(3)                                                                PCRE(3)
11    
 DESCRIPTION  
12    
13       The PCRE library is a set of functions that implement  regu-  NAME
14       lar  expression  pattern  matching using the same syntax and         PCRE - Perl-compatible regular expressions
      semantics as Perl, with just a few differences. The  current  
      implementation  of  PCRE  (release 4.x) corresponds approxi-  
      mately with Perl 5.8, including support  for  UTF-8  encoded  
      strings.    However,  this  support  has  to  be  explicitly  
      enabled; it is not the default.  
   
      PCRE is written in C and released as a C library. However, a  
      number  of  people  have  written wrappers and interfaces of  
      various kinds. A C++ class is included  in  these  contribu-  
      tions,  which  can  be found in the Contrib directory at the  
      primary FTP site, which is:  
   
      ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre  
   
      Details of exactly which Perl  regular  expression  features  
      are  and  are  not  supported  by PCRE are given in separate  
      documents. See the pcrepattern and pcrecompat pages.  
   
      Some features of PCRE can be included, excluded, or  changed  
      when  the library is built. The pcre_config() function makes  
      it possible for a client  to  discover  which  features  are  
      available.  Documentation  about  building  PCRE for various  
      operating systems can be found in the  README  file  in  the  
      source distribution.  
15    
16    
17  USER DOCUMENTATION  INTRODUCTION
18    
19       The user documentation for PCRE has been  split  up  into  a         The  PCRE  library is a set of functions that implement regular expres-
20       number  of  different sections. In the "man" format, each of         sion pattern matching using the same syntax and semantics as Perl, with
21       these is a separate "man page". In the HTML format, each  is         just  a  few differences. (Certain features that appeared in Python and
22       a  separate  page,  linked from the index page. In the plain         PCRE before they appeared in Perl are also available using  the  Python
23       text format, all the sections are concatenated, for ease  of         syntax.)
24       searching. The sections are as follows:  
25           The  current  implementation of PCRE (release 7.x) corresponds approxi-
26         pcre              this document         mately with Perl 5.10, including support for UTF-8 encoded strings  and
27         pcreapi           details of PCRE's native API         Unicode general category properties. However, UTF-8 and Unicode support
28         pcrebuild         options for building PCRE         has to be explicitly enabled; it is not the default. The Unicode tables
29         pcrecallout       details of the callout feature         correspond to Unicode release 5.0.0.
30         pcrecompat        discussion of Perl compatibility  
31         pcregrep          description of the pcregrep command         In  addition to the Perl-compatible matching function, PCRE contains an
32         pcrepattern       syntax and semantics of supported         alternative matching function that matches the same  compiled  patterns
33                             regular expressions         in  a different way. In certain circumstances, the alternative function
34         pcreperform       discussion of performance issues         has some advantages. For a discussion of the two  matching  algorithms,
35         pcreposix         the POSIX-compatible API         see the pcrematching page.
36         pcresample        discussion of the sample program  
37         pcretest          the pcretest testing command         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       In addition, in the "man" and HTML formats, there is a short         Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
40       page  for  each  library function, listing its arguments and         included as part of the PCRE distribution. The pcrecpp page has details
41       results.         of  this  interface.  Other  people's contributions can be found in the
42           Contrib directory at the primary FTP site, which is:
43    
44           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  LIMITATIONS  USER DOCUMENTATION
68    
69       There are some size limitations in PCRE but it is hoped that         The user documentation for PCRE comprises a number  of  different  sec-
70       they will never in practice be relevant.         tions.  In the "man" format, each of these is a separate "man page". In
71           the HTML format, each is a separate page, linked from the  index  page.
72           In  the  plain text format, all the sections are concatenated, for ease
73           of searching. The sections are as follows:
74    
75             pcre              this document
76             pcre-config       show PCRE installation configuration information
77             pcreapi           details of PCRE's native C API
78             pcrebuild         options for building PCRE
79             pcrecallout       details of the callout feature
80             pcrecompat        discussion of Perl compatibility
81             pcrecpp           details of the C++ wrapper
82             pcregrep          description of the pcregrep command
83             pcrematching      discussion of the two matching algorithms
84             pcrepartial       details of the partial matching facility
85             pcrepattern       syntax and semantics of supported
86                                 regular expressions
87             pcresyntax        quick syntax reference
88             pcreperform       discussion of performance issues
89             pcreposix         the POSIX-compatible C API
90             pcreprecompile    details of saving and re-using precompiled patterns
91             pcresample        discussion of the sample program
92             pcrestack         discussion of stack usage
93             pcretest          description of the pcretest testing command
94    
95       The maximum length of a  compiled  pattern  is  65539  (sic)         In  addition,  in the "man" and HTML formats, there is a short page for
96       bytes  if PCRE is compiled with the default internal linkage         each C library function, listing its arguments and results.
      size of 2. If you want to process regular  expressions  that  
      are  truly  enormous,  you can compile PCRE with an internal  
      linkage size of 3 or 4 (see the README file  in  the  source  
      distribution  and  the pcrebuild documentation for details).  
      If these cases the limit is substantially larger.   However,  
      the speed of execution will be slower.  
   
      All values in repeating quantifiers must be less than 65536.  
      The maximum number of capturing subpatterns is 65535.  
   
      There is no limit to the  number  of  non-capturing  subpat-  
      terns,  but  the  maximum  depth  of nesting of all kinds of  
      parenthesized subpattern, including  capturing  subpatterns,  
      assertions, and other types of subpattern, is 200.  
   
      The maximum length of a subject string is the largest  posi-  
      tive number that an integer variable can hold. However, PCRE  
      uses recursion to handle subpatterns and indefinite  repeti-  
      tion.  This  means  that the available stack space may limit  
      the size of a subject string that can be processed  by  cer-  
      tain patterns.  
97    
98    
99  UTF-8 SUPPORT  LIMITATIONS
100    
101       Starting at release 3.3, PCRE has had some support for char-         There are some size limitations in PCRE but it is hoped that they  will
102       acter  strings  encoded in the UTF-8 format. For release 4.0         never in practice be relevant.
      this has been greatly extended to cover most common require-  
      ments.  
   
      In order process UTF-8  strings,  you  must  build  PCRE  to  
      include  UTF-8  support  in  the code, and, in addition, you  
      must call pcre_compile() with  the  PCRE_UTF8  option  flag.  
      When  you  do this, both the pattern and any subject strings  
      that are matched against it are  treated  as  UTF-8  strings  
      instead of just strings of bytes.  
   
      If you compile PCRE with UTF-8 support, but do not use it at  
      run  time,  the  library will be a bit bigger, but the addi-  
      tional run time overhead is limited to testing the PCRE_UTF8  
      flag in several places, so should not be very large.  
   
      The following comments apply when PCRE is running  in  UTF-8  
      mode:  
   
      1. PCRE assumes that the strings it is given  contain  valid  
      UTF-8  codes. It does not diagnose invalid UTF-8 strings. If  
      you pass invalid UTF-8 strings  to  PCRE,  the  results  are  
      undefined.  
   
      2. In a pattern, the escape sequence \x{...}, where the con-  
      tents  of  the  braces is a string of hexadecimal digits, is  
      interpreted as a UTF-8 character whose code  number  is  the  
      given  hexadecimal  number, for example: \x{1234}. If a non-  
      hexadecimal digit appears between the braces,  the  item  is  
      not  recognized.  This escape sequence can be used either as  
      a literal, or within a character class.  
   
      3. The original hexadecimal escape sequence, \xhh, matches a  
      two-byte UTF-8 character if the value is greater than 127.  
   
      4. Repeat quantifiers apply to  complete  UTF-8  characters,  
      not to individual bytes, for example: \x{100}{3}.  
   
      5. The dot metacharacter matches one UTF-8 character instead  
      of a single byte.  
   
      6. The escape sequence \C can be used to match a single byte  
      in UTF-8 mode, but its use can lead to some strange effects.  
   
      7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  
      correctly test characters of any code value, but the charac-  
      ters that PCRE recognizes as digits, spaces, or word charac-  
      ters  remain  the  same  set as before, all with values less  
      than 256.  
   
      8. Case-insensitive  matching  applies  only  to  characters  
      whose  values  are  less than 256. PCRE does not support the  
      notion of "case" for higher-valued characters.  
103    
104       9. PCRE does not support the use of Unicode tables and  pro-         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
105       perties or the Perl escapes \p, \P, and \X.         is compiled with the default internal linkage size of 2. If you want to
106           process  regular  expressions  that are truly enormous, you can compile
107           PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
108           the  source  distribution and the pcrebuild documentation for details).
109           In these cases the limit is substantially larger.  However,  the  speed
110           of execution is slower.
111    
112           All values in repeating quantifiers must be less than 65536.
113    
114           There is no limit to the number of parenthesized subpatterns, but there
115           can be no more than 65535 capturing subpatterns.
116    
117           The maximum length of name for a named subpattern is 32 characters, and
118           the maximum number of named subpatterns is 10000.
119    
120           The  maximum  length of a subject string is the largest positive number
121           that an integer variable can hold. However, when using the  traditional
122           matching function, PCRE uses recursion to handle subpatterns and indef-
123           inite repetition.  This means that the available stack space may  limit
124           the size of a subject string that can be processed by certain patterns.
125           For a discussion of stack issues, see the pcrestack documentation.
126    
127    
128    UTF-8 AND UNICODE PROPERTY SUPPORT
129    
130           From release 3.3, PCRE has  had  some  support  for  character  strings
131           encoded  in the UTF-8 format. For release 4.0 this was greatly extended
132           to cover most common requirements, and in release 5.0  additional  sup-
133           port for Unicode general category properties was added.
134    
135           In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
136           support in the code, and, in addition,  you  must  call  pcre_compile()
137           with  the PCRE_UTF8 option flag. When you do this, both the pattern and
138           any subject strings that are matched against it are  treated  as  UTF-8
139           strings instead of just strings of bytes.
140    
141           If  you compile PCRE with UTF-8 support, but do not use it at run time,
142           the library will be a bit bigger, but the additional run time  overhead
143           is limited to testing the PCRE_UTF8 flag occasionally, so should not be
144           very big.
145    
146           If PCRE is built with Unicode character property support (which implies
147           UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
148           ported.  The available properties that can be tested are limited to the
149           general  category  properties such as Lu for an upper case letter or Nd
150           for a decimal number, the Unicode script names such as Arabic  or  Han,
151           and  the  derived  properties  Any  and L&. A full list is given in the
152           pcrepattern documentation. Only the short names for properties are sup-
153           ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-
154           ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
155           optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
156           does not support this.
157    
158       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  AUTHOR  AUTHOR
247    
248       Philip Hazel <ph10@cam.ac.uk>         Philip Hazel
249       University Computing Service,         University Computing Service
250       Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
251       Phone: +44 1223 334714  
252           Putting  an actual email address here seems to have been a spam magnet,
253           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    REVISION
258    
259           Last updated: 09 August 2007
260           Copyright (c) 1997-2007 University of Cambridge.
261    ------------------------------------------------------------------------------
262    
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         --enable-utf8  UNICODE CHARACTER PROPERTY SUPPORT
314    
315       to the configure command. Of itself, this does not make PCRE         UTF-8 support allows PCRE to process character values greater than  255
316       treat  strings as UTF-8. As well as compiling PCRE with this         in  the  strings that it handles. On its own, however, it does not pro-
317       option, you also have have to set the PCRE_UTF8 option  when         vide any facilities for accessing the properties of such characters. If
318       you call the pcre_compile() function.         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-unicode-properties
322    
323           to the configure command. This implies UTF-8 support, even if you  have
324           not explicitly requested it.
325    
326           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
399       stack is no longer used is 10; it can be changed by adding a  
400       setting such as           --with-posix-malloc-threshold=20
401    
402         --with-posix-malloc-threshold=20         to the configure command.
403    
404       to the configure command.  
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  SYNOPSIS OF PCRE API         there are three possible answers. The standard algorithm finds only one
566           of them, whereas the alternative algorithm finds all three.
567    
      #include <pcre.h>  
568    
569       pcre *pcre_compile(const char *pattern, int options,  REGULAR EXPRESSIONS AS TREES
           const char **errptr, int *erroffset,  
           const unsigned char *tableptr);  
570    
571       pcre_extra *pcre_study(const pcre *code, int options,         The set of strings that are matched by a regular expression can be rep-
572            const char **errptr);         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    
      int pcre_exec(const pcre *code, const pcre_extra *extra,  
           const char *subject, int length, int startoffset,  
           int options, int *ovector, int ovecsize);  
579    
580       int pcre_copy_named_substring(const pcre *code,  THE STANDARD MATCHING ALGORITHM
           const char *subject, int *ovector,  
           int stringcount, const char *stringname,  
           char *buffer, int buffersize);  
581    
582       int pcre_copy_substring(const char *subject, int *ovector,         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
583            int stringcount, int stringnumber, char *buffer,         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
584            int buffersize);         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       int pcre_get_named_substring(const pcre *code,         If a leaf node is reached, a matching string has  been  found,  and  at
595            const char *subject, int *ovector,         that  point the algorithm stops. Thus, if there is more than one possi-
596            int stringcount, const char *stringname,         ble match, this algorithm returns the first one that it finds.  Whether
597            const char **stringptr);         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       int pcre_get_stringnumber(const pcre *code,         Because  it  ends  up  with a single path through the tree, it is rela-
602            const char *name);         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_get_substring(const char *subject, int *ovector,  
           int stringcount, int stringnumber,  
           const char **stringptr);  
606    
607       int pcre_get_substring_list(const char *subject,  THE ALTERNATIVE MATCHING ALGORITHM
           int *ovector, int stringcount, const char ***listptr);  
608    
609       void pcre_free_substring(const char *stringptr);         This algorithm conducts a breadth-first search of  the  tree.  Starting
610           from  the  first  matching  point  in the subject, it scans the subject
611           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       void pcre_free_substring_list(const char **stringptr);         The scan continues until either the end of the subject is  reached,  or
618           there  are  no more unterminated paths. At this point, terminated paths
619           represent the different matching possibilities (if there are none,  the
620           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       const unsigned char *pcre_maketables(void);         Note that all the matches that are found start at the same point in the
626           subject. If the pattern
627    
628       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,           cat(er(pillar)?)
           int what, void *where);  
629    
630           is  matched  against the string "the caterpillar catchment", the result
631           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       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         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       int pcre_config(int what, void *where);         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       char *pcre_version(void);           ^a++\w!
645    
646       void *(*pcre_malloc)(size_t);         This  pattern matches "aaab!" but not "aaa!", which would be matched by
647           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       void (*pcre_free)(void *);         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_callout)(pcre_callout_block *);         3.  Because no substrings are captured, back references within the pat-
659           tern are not supported, and cause errors if encountered.
660    
661           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  PCRE API         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       PCRE has its own native API,  which  is  described  in  this         6.  Callouts  are  supported, but the value of the capture_top field is
671       document.  There  is  also  a  set of wrapper functions that         always 1, and the value of the capture_last field is always -1.
      correspond to the POSIX regular expression API.   These  are  
      described in the pcreposix documentation.  
672    
673       The native API function prototypes are defined in the header         7. The \C escape sequence, which (in the standard algorithm) matches  a
674       file  pcre.h,  and  on  Unix  systems  the library itself is         single  byte, even in UTF-8 mode, is not supported because the alterna-
675       called libpcre.a, so can be accessed by adding -lpcre to the         tive algorithm moves through the subject  string  one  character  at  a
676       command  for  linking  an  application  which  calls it. The         time, for all active paths through the tree.
      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.  
677    
678       The functions pcre_compile(), pcre_study(), and  pcre_exec()         8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-
679       are  used  for compiling and matching regular expressions. A         ported.
      sample program that demonstrates the simplest way  of  using  
      them  is  given in the file pcredemo.c. The pcresample docu-  
      mentation describes how to run it.  
680    
      There are convenience functions for extracting captured sub-  
      strings from a matched subject string. They are:  
681    
682         pcre_copy_substring()  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
        pcre_copy_named_substring()  
        pcre_get_substring()  
        pcre_get_named_substring()  
        pcre_get_substring_list()  
683    
684       pcre_free_substring()  and  pcre_free_substring_list()   are         Using the alternative matching algorithm provides the following  advan-
685       also  provided,  to  free  the  memory  used  for  extracted         tages:
      strings.  
686    
687       The function pcre_maketables() is used (optionally) to build         1. All possible matches (at a single point in the subject) are automat-
688       a  set of character tables in the current locale for passing         ically found, and in particular, the longest match is  found.  To  find
689       to pcre_compile().         more than one match using the standard algorithm, you have to do kludgy
690           things with callouts.
691    
692       The function pcre_fullinfo() is used to find out information         2. There is much better support for partial matching. The  restrictions
693       about a compiled pattern; pcre_info() is an obsolete version         on  the content of the pattern that apply when using the standard algo-
694       which returns only some of the available information, but is         rithm for partial matching do not apply to the  alternative  algorithm.
695       retained   for   backwards   compatibility.    The  function         For  non-anchored patterns, the starting position of a partial match is
696       pcre_version() returns a pointer to a string containing  the         available.
      version of PCRE and its date of release.  
697    
698       The global variables  pcre_malloc  and  pcre_free  initially         3. Because the alternative algorithm  scans  the  subject  string  just
699       contain the entry points of the standard malloc() and free()         once,  and  never  needs to backtrack, it is possible to pass very long
700       functions respectively. PCRE  calls  the  memory  management         subject strings to the matching function in  several  pieces,  checking
701       functions  via  these  variables,  so  a calling program can         for partial matching each time.
      replace them if it  wishes  to  intercept  the  calls.  This  
      should be done before calling any PCRE functions.  
702    
703       The global variable pcre_callout initially contains NULL. It  
704       can be set by the caller to a "callout" function, which PCRE  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
705       will then call at specified points during a matching  opera-  
706       tion. Details are given in the pcrecallout documentation.         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    
738    
739    PCRE NATIVE API
740    
741           #include <pcre.h>
742    
743           pcre *pcre_compile(const char *pattern, int options,
744                const char **errptr, int *erroffset,
745                const unsigned char *tableptr);
746    
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 client to dis-
969           cover which optional features have been compiled into the PCRE library.
970           The  pcrebuild documentation has more details about these optional fea-
971           tures.
972    
973           The first argument for pcre_config() is an  integer,  specifying  which
974           information is required; the second argument is a pointer to a variable
975           into which the information is  placed.  The  following  information  is
976           available:
977    
978             PCRE_CONFIG_UTF8
979    
980           The  output is an integer that is set to one if UTF-8 support is avail-
981           able; otherwise it is set to zero.
982    
983             PCRE_CONFIG_UNICODE_PROPERTIES
984    
985       The function pcre_config() makes  it  possible  for  a  PCRE         The output is an integer that is set to  one  if  support  for  Unicode
986       client  to  discover  which optional features have been com-         character properties is available; otherwise it is set to zero.
      piled into the PCRE library. The pcrebuild documentation has  
      more details about these optional features.  
987    
988       The first argument for pcre_config() is an integer, specify-           PCRE_CONFIG_NEWLINE
      ing  which information is required; the second argument is a  
      pointer to a variable into which the information is  placed.  
      The following information is available:  
989    
990         PCRE_CONFIG_UTF8         The  output  is  an integer whose value specifies the default character
991           sequence that is recognized as meaning "newline". The four values  that
992           are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
993           and -1 for ANY. The default should normally be  the  standard  sequence
994           for your operating system.
995    
996       The output is an integer that is set to one if UTF-8 support           PCRE_CONFIG_BSR
      is available; otherwise it is set to zero.  
997    
998         PCRE_CONFIG_NEWLINE         The output is an integer whose value indicates what character sequences
999           the \R escape sequence matches by default. A value of 0 means  that  \R
1000           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       The output is an integer that is set to  the  value  of  the           PCRE_CONFIG_LINK_SIZE
      code  that  is  used for the newline character. It is either  
      linefeed (10) or carriage return (13), and  should  normally  
      be the standard character for your operating system.  
1005    
1006         PCRE_CONFIG_LINK_SIZE         The  output  is  an  integer that contains the number of bytes used for
1007           internal linkage in compiled regular expressions. The value is 2, 3, or
1008           4.  Larger  values  allow larger regular expressions to be compiled, at
1009           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       The output is an integer that contains the number  of  bytes           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
      used  for  internal linkage in compiled regular expressions.  
      The value is 2, 3, or 4. Larger values allow larger  regular  
      expressions  to be compiled, at the expense of slower match-  
      ing. The default value of 2 is sufficient for  all  but  the  
      most  massive patterns, since it allows the compiled pattern  
      to be up to 64K in size.  
1014    
1015         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD         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       The output is an integer that contains the  threshold  above           PCRE_CONFIG_MATCH_LIMIT
      which  the POSIX interface uses malloc() for output vectors.  
      Further details are given in the pcreposix documentation.  
1020    
1021         PCRE_CONFIG_MATCH_LIMIT         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       The output is an integer that gives the  default  limit  for           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1026       the   number  of  internal  matching  function  calls  in  a  
1027       pcre_exec()  execution.  Further  details  are  given   with         The output is an integer that gives the default limit for the depth  of
1028       pcre_exec() below.         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.  An explicit match is either a literal CR or LF character, or
1569           \r or \n.
1570         PCRE_INFO_NAMECOUNT  
1571         PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_JCHANGED
1572         PCRE_INFO_NAMETABLE  
1573           Return 1 if the (?J) option setting is used in the  pattern,  otherwise
1574       PCRE supports the use of named as well as numbered capturing         0. The fourth argument should point to an int variable. The (?J) inter-
1575       parentheses. The names are just an additional way of identi-         nal option setting changes the local PCRE_DUPNAMES option.
1576       fying the parentheses,  which  still  acquire  a  number.  A  
1577       caller  that  wants  to extract data from a named subpattern           PCRE_INFO_LASTLITERAL
1578       must convert the name to a number in  order  to  access  the  
1579       correct  pointers  in  the  output  vector  (described  with         Return the value of the rightmost literal byte that must exist  in  any
1580       pcre_exec() below). In order to do this, it must  first  use         matched  string,  other  than  at  its  start,  if such a byte has been
1581       these  three  values  to  obtain  the name-to-number mapping         recorded. The fourth argument should point to an int variable. If there
1582       table for the pattern.         is  no such byte, -1 is returned. For anchored patterns, a last literal
1583           byte is recorded only if it follows something of variable  length.  For
1584       The  map  consists  of  a  number  of  fixed-size   entries.         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1585       PCRE_INFO_NAMECOUNT   gives   the  number  of  entries,  and         /^a\dz\d/ the returned value is -1.
1586       PCRE_INFO_NAMEENTRYSIZE gives the size of each  entry;  both  
1587       of  these return an int value. The entry size depends on the           PCRE_INFO_NAMECOUNT
1588       length of the longest name.  PCRE_INFO_NAMETABLE  returns  a           PCRE_INFO_NAMEENTRYSIZE
1589       pointer to the first entry of the table (a pointer to char).           PCRE_INFO_NAMETABLE
1590       The first two bytes of each entry are the number of the cap-  
1591       turing parenthesis, most significant byte first. The rest of         PCRE supports the use of named as well as numbered capturing  parenthe-
1592       the entry is the corresponding name,  zero  terminated.  The         ses.  The names are just an additional way of identifying the parenthe-
1593       names  are  in alphabetical order. For example, consider the         ses, which still acquire numbers. Several convenience functions such as
1594       following pattern (assume PCRE_EXTENDED  is  set,  so  white         pcre_get_named_substring()  are  provided  for extracting captured sub-
1595       space - including newlines - is ignored):         strings by name. It is also possible to extract the data  directly,  by
1596           first  converting  the  name to a number in order to access the correct
1597         (?P<date> (?P<year>(\d\d)?\d\d) -         pointers in the output vector (described with pcre_exec() below). To do
1598         (?P<month>\d\d) - (?P<day>\d\d) )         the  conversion,  you  need  to  use  the  name-to-number map, which is
1599           described by these three values.
1600       There are four named subpatterns,  so  the  table  has  four  
1601       entries,  and  each  entry in the table is eight bytes long.         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1602       The table is as follows, with non-printing  bytes  shows  in         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1603       hex, and undefined bytes shown as ??:         of each entry; both of these  return  an  int  value.  The  entry  size
1604           depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1605         00 01 d  a  t  e  00 ??         a pointer to the first entry of the table  (a  pointer  to  char).  The
1606         00 05 d  a  y  00 ?? ??         first two bytes of each entry are the number of the capturing parenthe-
1607         00 04 m  o  n  t  h  00         sis, most significant byte first. The rest of the entry is  the  corre-
1608         00 02 y  e  a  r  00 ??         sponding  name,  zero  terminated. The names are in alphabetical order.
1609           When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1610       When writing code to extract data  from  named  subpatterns,         theses  numbers.  For  example,  consider the following pattern (assume
1611       remember  that the length of each entry may be different for         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1612       each compiled pattern.         ignored):
1613    
1614         PCRE_INFO_OPTIONS           (?<date> (?<year>(\d\d)?\d\d) -
1615             (?<month>\d\d) - (?<day>\d\d) )
1616       Return a copy of the options with which the pattern was com-  
1617       piled.  The fourth argument should point to an unsigned long         There  are  four  named subpatterns, so the table has four entries, and
1618       int variable. These option bits are those specified  in  the         each entry in the table is eight bytes long. The table is  as  follows,
1619       call  to  pcre_compile(),  modified  by any top-level option         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1620       settings within the pattern itself.         as ??:
1621    
1622       A pattern is automatically anchored by PCRE if  all  of  its           00 01 d  a  t  e  00 ??
1623       top-level alternatives begin with one of the following:           00 05 d  a  y  00 ?? ??
1624             00 04 m  o  n  t  h  00
1625         ^     unless PCRE_MULTILINE is set           00 02 y  e  a  r  00 ??
1626         \A    always  
1627         \G    always         When writing code to extract data  from  named  subpatterns  using  the
1628         .*    if PCRE_DOTALL is set and there are no back         name-to-number  map,  remember that the length of the entries is likely
1629                 references to the subpattern in which .* appears         to be different for each compiled pattern.
1630    
1631       For such patterns, the  PCRE_ANCHORED  bit  is  set  in  the           PCRE_INFO_OKPARTIAL
1632       options returned by pcre_fullinfo().  
1633           Return 1 if the pattern can be used for partial matching, otherwise  0.
1634         PCRE_INFO_SIZE         The  fourth  argument  should point to an int variable. The pcrepartial
1635           documentation lists the restrictions that apply to patterns  when  par-
1636       Return the size of the compiled pattern, that is, the  value         tial matching is used.
1637       that  was  passed as the argument to pcre_malloc() when PCRE  
1638       was getting memory in which to place the compiled data.  The           PCRE_INFO_OPTIONS
1639       fourth argument should point to a size_t variable.  
1640           Return  a  copy of the options with which the pattern was compiled. The
1641         PCRE_INFO_STUDYSIZE         fourth argument should point to an unsigned long  int  variable.  These
1642           option bits are those specified in the call to pcre_compile(), modified
1643       Returns the size  of  the  data  block  pointed  to  by  the         by any top-level option settings at the start of the pattern itself. In
1644       study_data  field  in a pcre_extra block. That is, it is the         other  words,  they are the options that will be in force when matching
1645       value that was passed to pcre_malloc() when PCRE was getting         starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1646       memory into which to place the data created by pcre_study().         the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1647       The fourth argument should point to a size_t variable.         and PCRE_EXTENDED.
1648    
1649           A pattern is automatically anchored by PCRE if  all  of  its  top-level
1650           alternatives begin with one of the following:
1651    
1652             ^     unless PCRE_MULTILINE is set
1653             \A    always
1654             \G    always
1655             .*    if PCRE_DOTALL is set and there are no back
1656                     references to the subpattern in which .* appears
1657    
1658           For such patterns, the PCRE_ANCHORED bit is set in the options returned
1659           by pcre_fullinfo().
1660    
1661             PCRE_INFO_SIZE
1662    
1663           Return the size of the compiled pattern, that is, the  value  that  was
1664           passed as the argument to pcre_malloc() when PCRE was getting memory in
1665           which to place the compiled data. The fourth argument should point to a
1666           size_t variable.
1667    
1668             PCRE_INFO_STUDYSIZE
1669    
1670           Return the size of the data block pointed to by the study_data field in
1671           a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1672           pcre_malloc() when PCRE was getting memory into which to place the data
1673           created by pcre_study(). The fourth argument should point to  a  size_t
1674           variable.
1675    
1676    
1677  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1678    
1679       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1680    
1681       The pcre_info() function is now obsolete because its  inter-         The  pcre_info()  function is now obsolete because its interface is too
1682       face  is  too  restrictive  to return all the available data         restrictive to return all the available data about a compiled  pattern.
1683       about  a  compiled  pattern.   New   programs   should   use         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1684       pcre_fullinfo()  instead.  The  yield  of pcre_info() is the         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1685       number of capturing subpatterns, or  one  of  the  following         lowing negative numbers:
1686       negative numbers:  
1687             PCRE_ERROR_NULL       the argument code was NULL
1688         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1689         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1690           If  the  optptr  argument is not NULL, a copy of the options with which
1691       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
1692       with which the pattern was compiled is placed in the integer         PCRE_INFO_OPTIONS above).
1693       it points to (see PCRE_INFO_OPTIONS above).  
1694           If  the  pattern  is  not anchored and the firstcharptr argument is not
1695       If the pattern is not anchored and the firstcharptr argument         NULL, it is used to pass back information about the first character  of
1696       is  not  NULL, it is used to pass back information about the         any matched string (see PCRE_INFO_FIRSTBYTE above).
1697       first    character    of    any    matched    string    (see  
1698       PCRE_INFO_FIRSTBYTE above).  
1699    REFERENCE COUNTS
1700    
1701           int pcre_refcount(pcre *code, int adjust);
1702    
1703           The  pcre_refcount()  function is used to maintain a reference count in
1704           the data block that contains a compiled pattern. It is provided for the
1705           benefit  of  applications  that  operate  in an object-oriented manner,
1706           where different parts of the application may be using the same compiled
1707           pattern, but you want to free the block when they are all done.
1708    
1709           When a pattern is compiled, the reference count field is initialized to
1710           zero.  It is changed only by calling this function, whose action is  to
1711           add  the  adjust  value  (which may be positive or negative) to it. The
1712           yield of the function is the new value. However, the value of the count
1713           is  constrained to lie between 0 and 65535, inclusive. If the new value
1714           is outside these limits, it is forced to the appropriate limit value.
1715    
1716           Except when it is zero, the reference count is not correctly  preserved
1717           if  a  pattern  is  compiled on one host and then transferred to a host
1718           whose byte-order is different. (This seems a highly unlikely scenario.)
1719    
1720    
1721    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1722    
1723           int pcre_exec(const pcre *code, const pcre_extra *extra,
1724                const char *subject, int length, int startoffset,
1725                int options, int *ovector, int ovecsize);
1726    
1727           The  function pcre_exec() is called to match a subject string against a
1728           compiled pattern, which is passed in the code argument. If the  pattern
1729           has been studied, the result of the study should be passed in the extra
1730           argument. This function is the main matching facility of  the  library,
1731           and it operates in a Perl-like manner. For specialist use there is also
1732           an alternative matching function, which is described below in the  sec-
1733           tion about the pcre_dfa_exec() function.
1734    
1735           In  most applications, the pattern will have been compiled (and option-
1736           ally studied) in the same process that calls pcre_exec().  However,  it
1737           is possible to save compiled patterns and study data, and then use them
1738           later in different processes, possibly even on different hosts.  For  a
1739           discussion about this, see the pcreprecompile documentation.
1740    
1741           Here is an example of a simple call to pcre_exec():
1742    
1743             int rc;
1744             int ovector[30];
1745             rc = pcre_exec(
1746               re,             /* result of pcre_compile() */
1747               NULL,           /* we didn't study the pattern */
1748               "some string",  /* the subject string */
1749               11,             /* the length of the subject string */
1750               0,              /* start at offset 0 in the subject */
1751               0,              /* default options */
1752               ovector,        /* vector of integers for substring information */
1753               30);            /* number of elements (NOT size in bytes) */
1754    
1755       Extra data for pcre_exec()
1756    
1757           If  the  extra argument is not NULL, it must point to a pcre_extra data
1758           block. The pcre_study() function returns such a block (when it  doesn't
1759           return  NULL), but you can also create one for yourself, and pass addi-
1760           tional information in it. The pcre_extra block contains  the  following
1761           fields (not necessarily in this order):
1762    
1763             unsigned long int flags;
1764             void *study_data;
1765             unsigned long int match_limit;
1766             unsigned long int match_limit_recursion;
1767             void *callout_data;
1768             const unsigned char *tables;
1769    
1770           The  flags  field  is a bitmap that specifies which of the other fields
1771           are set. The flag bits are:
1772    
1773             PCRE_EXTRA_STUDY_DATA
1774             PCRE_EXTRA_MATCH_LIMIT
1775             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1776             PCRE_EXTRA_CALLOUT_DATA
1777             PCRE_EXTRA_TABLES
1778    
1779           Other flag bits should be set to zero. The study_data field is  set  in
1780           the  pcre_extra  block  that is returned by pcre_study(), together with
1781           the appropriate flag bit. You should not set this yourself, but you may
1782           add  to  the  block by setting the other fields and their corresponding
1783           flag bits.
1784    
1785           The match_limit field provides a means of preventing PCRE from using up
1786           a  vast amount of resources when running patterns that are not going to
1787           match, but which have a very large number  of  possibilities  in  their
1788           search  trees.  The  classic  example  is  the  use of nested unlimited
1789           repeats.
1790    
1791           Internally, PCRE uses a function called match() which it calls  repeat-
1792           edly  (sometimes  recursively). The limit set by match_limit is imposed
1793           on the number of times this function is called during  a  match,  which
1794           has  the  effect  of  limiting the amount of backtracking that can take
1795           place. For patterns that are not anchored, the count restarts from zero
1796           for each position in the subject string.
1797    
1798           The  default  value  for  the  limit can be set when PCRE is built; the
1799           default default is 10 million, which handles all but the  most  extreme
1800           cases.  You  can  override  the  default by suppling pcre_exec() with a
1801           pcre_extra    block    in    which    match_limit    is    set,     and
1802           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1803           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1804    
1805           The match_limit_recursion field is similar to match_limit, but  instead
1806           of limiting the total number of times that match() is called, it limits
1807           the depth of recursion. The recursion depth is a  smaller  number  than
1808           the  total number of calls, because not all calls to match() are recur-
1809           sive.  This limit is of use only if it is set smaller than match_limit.
1810    
1811           Limiting  the  recursion  depth  limits the amount of stack that can be
1812           used, or, when PCRE has been compiled to use memory on the heap instead
1813           of the stack, the amount of heap memory that can be used.
1814    
1815           The  default  value  for  match_limit_recursion can be set when PCRE is
1816           built; the default default  is  the  same  value  as  the  default  for
1817           match_limit.  You can override the default by suppling pcre_exec() with
1818           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1819           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1820           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1821    
1822           The pcre_callout field is used in conjunction with the  "callout"  fea-
1823           ture, which is described in the pcrecallout documentation.
1824    
1825           The  tables  field  is  used  to  pass  a  character  tables pointer to
1826           pcre_exec(); this overrides the value that is stored with the  compiled
1827           pattern.  A  non-NULL value is stored with the compiled pattern only if
1828           custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1829           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1830           PCRE's internal tables to be used. This facility is  helpful  when  re-
1831           using  patterns  that  have been saved after compiling with an external
1832           set of tables, because the external tables  might  be  at  a  different
1833           address  when  pcre_exec() is called. See the pcreprecompile documenta-
1834           tion for a discussion of saving compiled patterns for later use.
1835    
1836       Option bits for pcre_exec()
1837    
1838           The unused bits of the options argument for pcre_exec() must  be  zero.
1839           The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1840           PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1841           PCRE_PARTIAL.
1842    
1843             PCRE_ANCHORED
1844    
1845           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1846           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1847           turned  out to be anchored by virtue of its contents, it cannot be made
1848           unachored at matching time.
1849    
1850             PCRE_BSR_ANYCRLF
1851             PCRE_BSR_UNICODE
1852    
1853           These options (which are mutually exclusive) control what the \R escape
1854           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1855           or to match any Unicode newline sequence. These  options  override  the
1856           choice that was made or defaulted when the pattern was compiled.
1857    
1858             PCRE_NEWLINE_CR
1859             PCRE_NEWLINE_LF
1860             PCRE_NEWLINE_CRLF
1861             PCRE_NEWLINE_ANYCRLF
1862             PCRE_NEWLINE_ANY
1863    
1864           These  options  override  the  newline  definition  that  was chosen or
1865           defaulted when the pattern was compiled. For details, see the  descrip-
1866           tion  of  pcre_compile()  above.  During  matching,  the newline choice
1867           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1868           ters.  It may also alter the way the match position is advanced after a
1869           match failure for an unanchored pattern.
1870    
1871           When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
1872           set,  and a match attempt for an unanchored pattern fails when the cur-
1873           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1874           explicit  matches  for  CR  or  LF  characters,  the  match position is
1875           advanced by two characters instead of one, in other words, to after the
1876           CRLF.
1877    
1878           The above rule is a compromise that makes the most common cases work as
1879           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1880           option is not set), it does not match the string "\r\nA" because, after
1881           failing at the start, it skips both the CR and the LF before  retrying.
1882           However,  the  pattern  [\r\n]A does match that string, because it con-
1883           tains an explicit CR or LF reference, and so advances only by one char-
1884           acter after the first failure.
1885    
1886           An explicit match for CR of LF is either a literal appearance of one of
1887           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1888           matches  such  as [^X] do not count, nor does \s (which includes CR and
1889           LF in the characters that it matches).
1890    
1891           Notwithstanding the above, anomalous effects may still occur when  CRLF
1892           is a valid newline sequence and explicit \r or \n escapes appear in the
1893           pattern.
1894    
1895             PCRE_NOTBOL
1896    
1897           This option specifies that first character of the subject string is not
1898           the  beginning  of  a  line, so the circumflex metacharacter should not
1899           match before it. Setting this without PCRE_MULTILINE (at compile  time)
1900           causes  circumflex  never to match. This option affects only the behav-
1901           iour of the circumflex metacharacter. It does not affect \A.
1902    
1903             PCRE_NOTEOL
1904    
1905           This option specifies that the end of the subject string is not the end
1906           of  a line, so the dollar metacharacter should not match it nor (except
1907           in multiline mode) a newline immediately before it. Setting this  with-
1908           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1909           option affects only the behaviour of the dollar metacharacter. It  does
1910           not affect \Z or \z.
1911    
1912             PCRE_NOTEMPTY
1913    
1914           An empty string is not considered to be a valid match if this option is
1915           set. If there are alternatives in the pattern, they are tried.  If  all
1916           the  alternatives  match  the empty string, the entire match fails. For
1917           example, if the pattern
1918    
1919             a?b?
1920    
1921           is applied to a string not beginning with "a" or "b",  it  matches  the
1922           empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
1923           match is not valid, so PCRE searches further into the string for occur-
1924           rences of "a" or "b".
1925    
1926           Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1927           cial case of a pattern match of the empty  string  within  its  split()
1928           function,  and  when  using  the /g modifier. It is possible to emulate
1929           Perl's behaviour after matching a null string by first trying the match
1930           again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1931           if that fails by advancing the starting offset (see below)  and  trying
1932           an ordinary match again. There is some code that demonstrates how to do
1933           this in the pcredemo.c sample program.
1934    
1935             PCRE_NO_UTF8_CHECK
1936    
1937           When PCRE_UTF8 is set at compile time, the validity of the subject as a
1938           UTF-8  string is automatically checked when pcre_exec() is subsequently
1939           called.  The value of startoffset is also checked  to  ensure  that  it
1940           points  to  the start of a UTF-8 character. There is a discussion about
1941           the validity of UTF-8 strings in the section on UTF-8  support  in  the
1942           main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
1943           pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
1944           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1945    
1946           If  you  already  know that your subject is valid, and you want to skip
1947           these   checks   for   performance   reasons,   you   can    set    the
1948           PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
1949           do this for the second and subsequent calls to pcre_exec() if  you  are
1950           making  repeated  calls  to  find  all  the matches in a single subject
1951           string. However, you should be  sure  that  the  value  of  startoffset
1952           points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
1953           set, the effect of passing an invalid UTF-8 string as a subject,  or  a
1954           value  of startoffset that does not point to the start of a UTF-8 char-
1955           acter, is undefined. Your program may crash.
1956    
1957             PCRE_PARTIAL
1958    
1959           This option turns on the  partial  matching  feature.  If  the  subject
1960           string  fails to match the pattern, but at some point during the match-
1961           ing process the end of the subject was reached (that  is,  the  subject
1962           partially  matches  the  pattern and the failure to match occurred only
1963           because there were not enough subject characters), pcre_exec()  returns
1964           PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1965           used, there are restrictions on what may appear in the  pattern.  These
1966           are discussed in the pcrepartial documentation.
1967    
1968       The string to be matched by pcre_exec()
1969    
1970           The  subject string is passed to pcre_exec() as a pointer in subject, a
1971           length in length, and a starting byte offset in startoffset.  In  UTF-8
1972           mode,  the  byte  offset  must point to the start of a UTF-8 character.
1973           Unlike the pattern string, the subject may contain binary  zero  bytes.
1974           When  the starting offset is zero, the search for a match starts at the
1975           beginning of the subject, and this is by far the most common case.
1976    
1977           A non-zero starting offset is useful when searching for  another  match
1978           in  the same subject by calling pcre_exec() again after a previous suc-
1979           cess.  Setting startoffset differs from just passing over  a  shortened
1980           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
1981           with any kind of lookbehind. For example, consider the pattern
1982    
1983             \Biss\B
1984    
1985           which finds occurrences of "iss" in the middle of  words.  (\B  matches
1986           only  if  the  current position in the subject is not a word boundary.)
1987           When applied to the string "Mississipi" the first call  to  pcre_exec()
1988           finds  the  first  occurrence. If pcre_exec() is called again with just
1989           the remainder of the subject,  namely  "issipi",  it  does  not  match,
1990           because \B is always false at the start of the subject, which is deemed
1991           to be a word boundary. However, if pcre_exec()  is  passed  the  entire
1992           string again, but with startoffset set to 4, it finds the second occur-
1993           rence of "iss" because it is able to look behind the starting point  to
1994           discover that it is preceded by a letter.
1995    
1996           If  a  non-zero starting offset is passed when the pattern is anchored,
1997           one attempt to match at the given offset is made. This can only succeed
1998           if  the  pattern  does  not require the match to be at the start of the
1999           subject.
2000    
2001       How pcre_exec() returns captured substrings
2002    
2003           In general, a pattern matches a certain portion of the subject, and  in
2004           addition,  further  substrings  from  the  subject may be picked out by
2005           parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2006           this  is  called "capturing" in what follows, and the phrase "capturing
2007           subpattern" is used for a fragment of a pattern that picks out  a  sub-
2008           string.  PCRE  supports several other kinds of parenthesized subpattern
2009           that do not cause substrings to be captured.
2010    
2011           Captured substrings are returned to the caller via a vector of  integer
2012           offsets  whose  address is passed in ovector. The number of elements in
2013           the vector is passed in ovecsize, which must be a non-negative  number.
2014           Note: this argument is NOT the size of ovector in bytes.
2015    
2016           The  first  two-thirds of the vector is used to pass back captured sub-
2017           strings, each substring using a pair of integers. The  remaining  third
2018           of  the  vector is used as workspace by pcre_exec() while matching cap-
2019           turing subpatterns, and is not available for passing back  information.
2020           The  length passed in ovecsize should always be a multiple of three. If
2021           it is not, it is rounded down.
2022    
2023           When a match is successful, information about  captured  substrings  is
2024           returned  in  pairs  of integers, starting at the beginning of ovector,
2025           and continuing up to two-thirds of its length at the  most.  The  first
2026           element of a pair is set to the offset of the first character in a sub-
2027           string, and the second is set to the  offset  of  the  first  character
2028           after  the  end  of  a  substring. The first pair, ovector[0] and ovec-
2029           tor[1], identify the portion of  the  subject  string  matched  by  the
2030           entire  pattern.  The next pair is used for the first capturing subpat-
2031           tern, and so on. The value returned by pcre_exec() is one more than the
2032           highest numbered pair that has been set. For example, if two substrings
2033           have been captured, the returned value is 3. If there are no  capturing
2034           subpatterns,  the return value from a successful match is 1, indicating
2035           that just the first pair of offsets has been set.
2036    
2037           If a capturing subpattern is matched repeatedly, it is the last portion
2038           of the string that it matched that is returned.
2039    
2040           If  the vector is too small to hold all the captured substring offsets,
2041           it is used as far as possible (up to two-thirds of its length), and the
2042           function  returns a value of zero. In particular, if the substring off-
2043           sets are not of interest, pcre_exec() may be called with ovector passed
2044           as  NULL  and  ovecsize  as zero. However, if the pattern contains back
2045           references and the ovector is not big enough to  remember  the  related
2046           substrings,  PCRE has to get additional memory for use during matching.
2047           Thus it is usually advisable to supply an ovector.
2048    
2049           The pcre_info() function can be used to find  out  how  many  capturing
2050           subpatterns  there  are  in  a  compiled pattern. The smallest size for
2051           ovector that will allow for n captured substrings, in addition  to  the
2052           offsets of the substring matched by the whole pattern, is (n+1)*3.
2053    
2054           It  is  possible for capturing subpattern number n+1 to match some part
2055           of the subject when subpattern n has not been used at all. For example,
2056           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
2057           return from the function is 4, and subpatterns 1 and 3 are matched, but
2058           2  is  not.  When  this happens, both values in the offset pairs corre-
2059           sponding to unused subpatterns are set to -1.
2060    
2061           Offset values that correspond to unused subpatterns at the end  of  the
2062           expression  are  also  set  to  -1. For example, if the string "abc" is
2063           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
2064           matched.  The  return  from the function is 2, because the highest used
2065           capturing subpattern number is 1. However, you can refer to the offsets
2066           for  the  second  and third capturing subpatterns if you wish (assuming
2067           the vector is large enough, of course).
2068    
2069           Some convenience functions are provided  for  extracting  the  captured
2070           substrings as separate strings. These are described below.
2071    
2072       Error return values from pcre_exec()
2073    
2074           If  pcre_exec()  fails, it returns a negative number. The following are
2075           defined in the header file:
2076    
2077             PCRE_ERROR_NOMATCH        (-1)
2078    
2079           The subject string did not match the pattern.
2080    
2081             PCRE_ERROR_NULL           (-2)
2082    
2083           Either code or subject was passed as NULL,  or  ovector  was  NULL  and
2084           ovecsize was not zero.
2085    
2086             PCRE_ERROR_BADOPTION      (-3)
2087    
2088           An unrecognized bit was set in the options argument.
2089    
2090             PCRE_ERROR_BADMAGIC       (-4)
2091    
2092           PCRE  stores a 4-byte "magic number" at the start of the compiled code,
2093           to catch the case when it is passed a junk pointer and to detect when a
2094           pattern that was compiled in an environment of one endianness is run in
2095           an environment with the other endianness. This is the error  that  PCRE
2096           gives when the magic number is not present.
2097    
2098             PCRE_ERROR_UNKNOWN_OPCODE (-5)
2099    
2100           While running the pattern match, an unknown item was encountered in the
2101           compiled pattern. This error could be caused by a bug  in  PCRE  or  by
2102           overwriting of the compiled pattern.
2103    
2104             PCRE_ERROR_NOMEMORY       (-6)
2105    
2106           If  a  pattern contains back references, but the ovector that is passed
2107           to pcre_exec() is not big enough to remember the referenced substrings,
2108           PCRE  gets  a  block of memory at the start of matching to use for this
2109           purpose. If the call via pcre_malloc() fails, this error is given.  The
2110           memory is automatically freed at the end of matching.
2111    
2112             PCRE_ERROR_NOSUBSTRING    (-7)
2113    
2114           This  error is used by the pcre_copy_substring(), pcre_get_substring(),
2115           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2116           returned by pcre_exec().
2117    
2118             PCRE_ERROR_MATCHLIMIT     (-8)
2119    
2120           The  backtracking  limit,  as  specified  by the match_limit field in a
2121           pcre_extra structure (or defaulted) was reached.  See  the  description
2122           above.
2123    
2124             PCRE_ERROR_CALLOUT        (-9)
2125    
2126           This error is never generated by pcre_exec() itself. It is provided for
2127           use by callout functions that want to yield a distinctive  error  code.
2128           See the pcrecallout documentation for details.
2129    
2130             PCRE_ERROR_BADUTF8        (-10)
2131    
2132           A  string  that contains an invalid UTF-8 byte sequence was passed as a
2133           subject.
2134    
2135             PCRE_ERROR_BADUTF8_OFFSET (-11)
2136    
2137           The UTF-8 byte sequence that was passed as a subject was valid, but the
2138           value  of startoffset did not point to the beginning of a UTF-8 charac-
2139           ter.
2140    
2141             PCRE_ERROR_PARTIAL        (-12)
2142    
2143           The subject string did not match, but it did match partially.  See  the
2144           pcrepartial documentation for details of partial matching.
2145    
2146             PCRE_ERROR_BADPARTIAL     (-13)
2147    
2148           The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
2149           items that are not supported for partial matching. See the  pcrepartial
2150           documentation for details of partial matching.
2151    
2152             PCRE_ERROR_INTERNAL       (-14)
2153    
2154           An  unexpected  internal error has occurred. This error could be caused
2155           by a bug in PCRE or by overwriting of the compiled pattern.
2156    
2157             PCRE_ERROR_BADCOUNT       (-15)
2158    
2159           This error is given if the value of the ovecsize argument is  negative.
2160    
2161             PCRE_ERROR_RECURSIONLIMIT (-21)
2162    
2163           The internal recursion limit, as specified by the match_limit_recursion
2164           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2165           description above.
2166    
2167             PCRE_ERROR_BADNEWLINE     (-23)
2168    
2169  MATCHING A PATTERN         An invalid combination of PCRE_NEWLINE_xxx options was given.
2170    
2171       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.  
2172    
2173    
2174  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2175    
2176       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_copy_substring(const char *subject, int *ovector,
2177            int stringcount, int stringnumber, char *buffer,              int stringcount, int stringnumber, char *buffer,
2178            int buffersize);              int buffersize);
2179    
2180       int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
2181            int stringcount, int stringnumber,              int stringcount, int stringnumber,
2182            const char **stringptr);              const char **stringptr);
2183    
2184       int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2185            int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2186    
2187       Captured substrings can be accessed directly  by  using  the         Captured  substrings  can  be  accessed  directly  by using the offsets
2188       offsets returned by pcre_exec() in ovector. For convenience,         returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2189       the functions  pcre_copy_substring(),  pcre_get_substring(),         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2190       and  pcre_get_substring_list()  are  provided for extracting         string_list() are provided for extracting captured substrings  as  new,
2191       captured  substrings  as  new,   separate,   zero-terminated         separate,  zero-terminated strings. These functions identify substrings
2192       strings.  These functions identify substrings by number. The         by number. The next section describes functions  for  extracting  named
2193       next section describes functions for extracting  named  sub-         substrings.
2194       strings.   A  substring  that  contains  a  binary  zero  is  
2195       correctly extracted and has a further zero added on the end,         A  substring that contains a binary zero is correctly extracted and has
2196       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
2197           string.   However,  you  can  process such a string by referring to the
2198       The first three arguments are the  same  for  all  three  of         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2199       these  functions:   subject  is the subject string which has         string().  Unfortunately, the interface to pcre_get_substring_list() is
2200       just been successfully matched, ovector is a pointer to  the         not adequate for handling strings containing binary zeros, because  the
2201       vector  of  integer  offsets that was passed to pcre_exec(),         end of the final string is not independently indicated.
2202       and stringcount is the number of substrings that  were  cap-  
2203       tured by the match, including the substring that matched the         The  first  three  arguments  are the same for all three of these func-
2204       entire regular expression. This is  the  value  returned  by         tions: subject is the subject string that has  just  been  successfully
2205       pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()         matched, ovector is a pointer to the vector of integer offsets that was
2206       returned zero, indicating that it ran out of space in  ovec-         passed to pcre_exec(), and stringcount is the number of substrings that
2207       tor,  the  value passed as stringcount should be the size of         were  captured  by  the match, including the substring that matched the
2208       the vector divided by three.         entire regular expression. This is the value returned by pcre_exec() if
2209           it  is greater than zero. If pcre_exec() returned zero, indicating that
2210       The functions pcre_copy_substring() and pcre_get_substring()         it ran out of space in ovector, the value passed as stringcount  should
2211       extract a single substring, whose number is given as string-         be the number of elements in the vector divided by three.
2212       number. A value of zero extracts the substring that  matched  
2213       the entire pattern, while higher values extract the captured         The  functions pcre_copy_substring() and pcre_get_substring() extract a
2214       substrings. For pcre_copy_substring(), the string is  placed         single substring, whose number is given as  stringnumber.  A  value  of
2215       in  buffer,  whose  length is given by buffersize, while for         zero  extracts  the  substring that matched the entire pattern, whereas
2216       pcre_get_substring() a new block of memory is  obtained  via         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2217       pcre_malloc,  and its address is returned via stringptr. The         string(),  the  string  is  placed  in buffer, whose length is given by
2218       yield of the function is  the  length  of  the  string,  not         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2219       including the terminating zero, or one of         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2220           The yield of the function is the length of the  string,  not  including
2221         PCRE_ERROR_NOMEMORY       (-6)         the terminating zero, or one of these error codes:
2222    
2223       The buffer was too small for pcre_copy_substring(),  or  the           PCRE_ERROR_NOMEMORY       (-6)
2224       attempt to get memory failed for pcre_get_substring().  
2225           The  buffer  was too small for pcre_copy_substring(), or the attempt to
2226         PCRE_ERROR_NOSUBSTRING    (-7)         get memory failed for pcre_get_substring().
2227    
2228       There is no substring whose number is stringnumber.           PCRE_ERROR_NOSUBSTRING    (-7)
2229    
2230       The pcre_get_substring_list() function extracts  all  avail-         There is no substring whose number is stringnumber.
2231       able  substrings  and builds a list of pointers to them. All  
2232       this is done in a single block of memory which  is  obtained         The pcre_get_substring_list()  function  extracts  all  available  sub-
2233       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
2234       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
2235       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
2236       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
2237           pointer.  The  yield  of  the function is zero if all went well, or the
2238         PCRE_ERROR_NOMEMORY       (-6)         error code
2239    
2240       if the attempt to get the memory block failed.           PCRE_ERROR_NOMEMORY       (-6)
2241    
2242       When any of these functions encounter a  substring  that  is         if the attempt to get the memory block failed.
2243       unset, which can happen when capturing subpattern number n+1  
2244       matches some part of the subject, but subpattern n  has  not         When any of these functions encounter a substring that is unset,  which
2245       been  used  at all, they return an empty string. This can be         can  happen  when  capturing subpattern number n+1 matches some part of
2246       distinguished  from  a  genuine  zero-length  substring   by         the subject, but subpattern n has not been used at all, they return  an
2247       inspecting the appropriate offset in ovector, which is nega-         empty string. This can be distinguished from a genuine zero-length sub-
2248       tive for unset substrings.         string by inspecting the appropriate offset in ovector, which is  nega-
2249           tive for unset substrings.
2250       The  two  convenience  functions  pcre_free_substring()  and  
2251       pcre_free_substring_list()  can  be  used to free the memory         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2252       returned by  a  previous  call  of  pcre_get_substring()  or         string_list() can be used to free the memory  returned  by  a  previous
2253       pcre_get_substring_list(),  respectively.  They  do  nothing         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2254       more than call the function pointed to by  pcre_free,  which         tively. They do nothing more than  call  the  function  pointed  to  by
2255       of  course  could  be called directly from a C program. How-         pcre_free,  which  of course could be called directly from a C program.
2256       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-
2257       a  special  interface  to another programming language which         cial   interface  to  another  programming  language  that  cannot  use
2258       cannot use pcre_free directly; it is for  these  cases  that         pcre_free directly; it is for these cases that the functions  are  pro-
2259       the functions are provided.         vided.
2260    
2261    
2262  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2263    
2264       int pcre_copy_named_substring(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
2265            const char *subject, int *ovector,              const char *name);
2266            int stringcount, const char *stringname,  
2267            char *buffer, int buffersize);         int pcre_copy_named_substring(const pcre *code,
2268                const char *subject, int *ovector,
2269       int pcre_get_stringnumber(const pcre *code,              int stringcount, const char *stringname,
2270            const char *name);              char *buffer, int buffersize);
2271    
2272       int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2273            const char *subject, int *ovector,              const char *subject, int *ovector,
2274            int stringcount, const char *stringname,              int stringcount, const char *stringname,
2275            const char **stringptr);              const char **stringptr);
2276    
2277       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-
2278       ciated    number.    This    can    be   done   by   calling         ber.  For example, for this pattern
2279       pcre_get_stringnumber(). The first argument is the  compiled  
2280       pattern,  and  the second is the name. For example, for this           (a+)b(?<xxx>\d+)...
2281       pattern  
2282           the number of the subpattern called "xxx" is 2. If the name is known to
2283         ab(?<xxx>\d+)...         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2284           name by calling pcre_get_stringnumber(). The first argument is the com-
2285       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
2286       number,  you can then extract the substring directly, or use         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2287       one of the functions described in the previous section.  For         subpattern of that name.
2288       convenience,  there are also two functions that do the whole  
2289       job.         Given the number, you can extract the substring directly, or use one of
2290           the functions described in the previous section. For convenience, there
2291       Most of the  arguments  of  pcre_copy_named_substring()  and         are also two functions that do the whole job.
2292       pcre_get_named_substring()  are  the  same  as those for the  
2293       functions that  extract  by  number,  and  so  are  not  re-         Most    of    the    arguments   of   pcre_copy_named_substring()   and
2294       described here. There are just two differences.         pcre_get_named_substring() are the same  as  those  for  the  similarly
2295           named  functions  that extract by number. As these are described in the
2296       First, instead of a substring number, a  substring  name  is         previous section, they are not re-described here. There  are  just  two
2297       given.  Second,  there  is  an  extra argument, given at the         differences:
2298       start, which is a pointer to the compiled pattern.  This  is  
2299       needed  in order to gain access to the name-to-number trans-         First,  instead  of a substring number, a substring name is given. Sec-
2300       lation table.         ond, there is an extra argument, given at the start, which is a pointer
2301           to  the compiled pattern. This is needed in order to gain access to the
2302       These functions  call  pcre_get_stringnumber(),  and  if  it         name-to-number translation table.
2303       succeeds,    they   then   call   pcre_copy_substring()   or  
2304       pcre_get_substring(), as appropriate.         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2305           then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2306           ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2307           behaviour may not be what you want (see the next section).
2308    
2309    
2310    DUPLICATE SUBPATTERN NAMES
2311    
2312           int pcre_get_stringtable_entries(const pcre *code,
2313                const char *name, char **first, char **last);
2314    
2315           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2316           subpatterns are not required to  be  unique.  Normally,  patterns  with
2317           duplicate  names  are such that in any one match, only one of the named
2318           subpatterns participates. An example is shown in the pcrepattern  docu-
2319           mentation.
2320    
2321           When    duplicates   are   present,   pcre_copy_named_substring()   and
2322           pcre_get_named_substring() return the first substring corresponding  to
2323           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2324           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2325           function  returns one of the numbers that are associated with the name,
2326           but it is not defined which it is.
2327    
2328           If you want to get full details of all captured substrings for a  given
2329           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2330           first argument is the compiled pattern, and the second is the name. The
2331           third  and  fourth  are  pointers to variables which are updated by the
2332           function. After it has run, they point to the first and last entries in
2333           the  name-to-number  table  for  the  given  name.  The function itself
2334           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2335           there  are none. The format of the table is described above in the sec-
2336           tion entitled Information about a  pattern.   Given  all  the  relevant
2337           entries  for the name, you can extract each of their numbers, and hence
2338           the captured data, if any.
2339    
2340    
2341    FINDING ALL POSSIBLE MATCHES
2342    
2343           The traditional matching function uses a  similar  algorithm  to  Perl,
2344           which stops when it finds the first match, starting at a given point in
2345           the subject. If you want to find all possible matches, or  the  longest
2346           possible  match,  consider using the alternative matching function (see
2347           below) instead. If you cannot use the alternative function,  but  still
2348           need  to  find all possible matches, you can kludge it up by making use
2349           of the callout facility, which is described in the pcrecallout documen-
2350           tation.
2351    
2352           What you have to do is to insert a callout right at the end of the pat-
2353           tern.  When your callout function is called, extract and save the  cur-
2354           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2355           backtrack and try other alternatives. Ultimately, when it runs  out  of
2356           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2357    
2358    
2359    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2360    
2361           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2362                const char *subject, int length, int startoffset,
2363                int options, int *ovector, int ovecsize,
2364                int *workspace, int wscount);
2365    
2366           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2367           against a compiled pattern, using a matching algorithm that  scans  the
2368           subject  string  just  once, and does not backtrack. This has different
2369           characteristics to the normal algorithm, and  is  not  compatible  with
2370           Perl.  Some  of the features of PCRE patterns are not supported. Never-
2371           theless, there are times when this kind of matching can be useful.  For
2372           a discussion of the two matching algorithms, see the pcrematching docu-
2373           mentation.
2374    
2375           The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2376           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2377           ent way, and this is described below. The other  common  arguments  are
2378           used  in  the  same way as for pcre_exec(), so their description is not
2379           repeated here.
2380    
2381           The two additional arguments provide workspace for  the  function.  The
2382           workspace  vector  should  contain at least 20 elements. It is used for
2383           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2384           workspace  will  be  needed for patterns and subjects where there are a
2385           lot of potential matches.
2386    
2387           Here is an example of a simple call to pcre_dfa_exec():
2388    
2389             int rc;
2390             int ovector[10];
2391             int wspace[20];
2392             rc = pcre_dfa_exec(
2393               re,             /* result of pcre_compile() */
2394               NULL,           /* we didn't study the pattern */
2395               "some string",  /* the subject string */
2396               11,             /* the length of the subject string */
2397               0,              /* start at offset 0 in the subject */
2398               0,              /* default options */
2399               ovector,        /* vector of integers for substring information */
2400               10,             /* number of elements (NOT size in bytes) */
2401               wspace,         /* working space vector */
2402               20);            /* number of elements (NOT size in bytes) */
2403    
2404       Option bits for pcre_dfa_exec()
2405    
2406           The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2407           zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2408           LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2409           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2410           three of these are the same as for pcre_exec(), so their description is
2411           not repeated here.
2412    
2413             PCRE_PARTIAL
2414    
2415           This  has  the  same general effect as it does for pcre_exec(), but the
2416           details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2417           pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2418           PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2419           been no complete matches, but there is still at least one matching pos-
2420           sibility. The portion of the string that provided the partial match  is
2421           set as the first matching string.
2422    
2423             PCRE_DFA_SHORTEST
2424    
2425           Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2426           stop as soon as it has found one match. Because of the way the alterna-
2427           tive  algorithm  works, this is necessarily the shortest possible match
2428           at the first possible matching point in the subject string.
2429    
2430             PCRE_DFA_RESTART
2431    
2432           When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2433           returns  a  partial  match, it is possible to call it again, with addi-
2434           tional subject characters, and have it continue with  the  same  match.
2435           The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2436           workspace and wscount options must reference the same vector as  before
2437           because  data  about  the  match so far is left in them after a partial
2438           match. There is more discussion of this  facility  in  the  pcrepartial
2439           documentation.
2440    
2441       Successful returns from pcre_dfa_exec()
2442    
2443           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2444           string in the subject. Note, however, that all the matches from one run
2445           of  the  function  start  at the same point in the subject. The shorter
2446           matches are all initial substrings of the longer matches. For  example,
2447           if the pattern
2448    
2449             <.*>
2450    
2451           is matched against the string
2452    
2453             This is <something> <something else> <something further> no more
2454    
2455           the three matched strings are
2456    
2457             <something>
2458             <something> <something else>
2459             <something> <something else> <something further>
2460    
2461           On  success,  the  yield of the function is a number greater than zero,
2462           which is the number of matched substrings.  The  substrings  themselves
2463           are  returned  in  ovector. Each string uses two elements; the first is
2464           the offset to the start, and the second is the offset to  the  end.  In
2465           fact,  all  the  strings  have the same start offset. (Space could have
2466           been saved by giving this only once, but it was decided to retain  some
2467           compatibility  with  the  way pcre_exec() returns data, even though the
2468           meaning of the strings is different.)
2469    
2470           The strings are returned in reverse order of length; that is, the long-
2471           est  matching  string is given first. If there were too many matches to
2472           fit into ovector, the yield of the function is zero, and the vector  is
2473           filled with the longest matches.
2474    
2475       Error returns from pcre_dfa_exec()
2476    
2477           The  pcre_dfa_exec()  function returns a negative number when it fails.
2478           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2479           described  above.   There are in addition the following errors that are
2480           specific to pcre_dfa_exec():
2481    
2482             PCRE_ERROR_DFA_UITEM      (-16)
2483    
2484           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2485           tern  that  it  does not support, for instance, the use of \C or a back
2486           reference.
2487    
2488             PCRE_ERROR_DFA_UCOND      (-17)
2489    
2490           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2491           that  uses  a back reference for the condition, or a test for recursion
2492           in a specific group. These are not supported.
2493    
2494             PCRE_ERROR_DFA_UMLIMIT    (-18)
2495    
2496           This return is given if pcre_dfa_exec() is called with an  extra  block
2497           that contains a setting of the match_limit field. This is not supported
2498           (it is meaningless).
2499    
2500             PCRE_ERROR_DFA_WSSIZE     (-19)
2501    
2502           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2503           workspace vector.
2504    
2505             PCRE_ERROR_DFA_RECURSE    (-20)
2506    
2507           When  a  recursive subpattern is processed, the matching function calls
2508           itself recursively, using private vectors for  ovector  and  workspace.
2509           This  error  is  given  if  the output vector is not large enough. This
2510           should be extremely rare, as a vector of size 1000 is used.
2511    
2512    
2513    SEE ALSO
2514    
2515           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2516           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2517    
2518    
2519    AUTHOR
2520    
2521           Philip Hazel
2522           University Computing Service
2523           Cambridge CB2 3QH, England.
2524    
2525    
2526    REVISION
2527    
2528           Last updated: 11 September 2007
2529           Copyright (c) 1997-2007 University of Cambridge.
2530    ------------------------------------------------------------------------------
2531    
2532    
2533    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2534    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2535    
2536  NAME  NAME
2537       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2538    
2539    
2540  PCRE CALLOUTS  PCRE CALLOUTS
2541    
2542       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.  
2543    
2544           PCRE provides a feature called "callout", which is a means of temporar-
2545           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2546           matching.  The  caller of PCRE provides an external function by putting
2547           its entry point in the global variable pcre_callout. By  default,  this
2548           variable contains NULL, which disables all calling out.
2549    
2550           Within  a  regular  expression,  (?C) indicates the points at which the
2551           external function is to be called.  Different  callout  points  can  be
2552           identified  by  putting  a number less than 256 after the letter C. The
2553           default value is zero.  For  example,  this  pattern  has  two  callout
2554           points:
2555    
2556             (?C1)abc(?C2)def
2557    
2558           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2559           called, PCRE automatically  inserts  callouts,  all  with  number  255,
2560           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2561           used with the pattern
2562    
2563             A(\d{2}|--)
2564    
2565           it is processed as if it were
2566    
2567           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2568    
2569           Notice that there is a callout before and after  each  parenthesis  and
2570           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2571           progress of pattern matching. The pcretest command has an  option  that
2572           sets  automatic callouts; when it is used, the output indicates how the
2573           pattern is matched. This is useful information when you are  trying  to
2574           optimize the performance of a particular pattern.
2575    
2576    
2577    MISSING CALLOUTS
2578    
2579           You  should  be  aware  that,  because of optimizations in the way PCRE
2580           matches patterns, callouts sometimes do not happen. For example, if the
2581           pattern is
2582    
2583             ab(?C4)cd
2584    
2585           PCRE knows that any matching string must contain the letter "d". If the
2586           subject string is "abyz", the lack of "d" means that  matching  doesn't
2587           ever  start,  and  the  callout is never reached. However, with "abyd",
2588           though the result is still no match, the callout is obeyed.
2589    
2590    
2591    THE CALLOUT INTERFACE
2592    
2593           During matching, when PCRE reaches a callout point, the external  func-
2594           tion  defined by pcre_callout is called (if it is set). This applies to
2595           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2596           only  argument  to  the callout function is a pointer to a pcre_callout
2597           block. This structure contains the following fields:
2598    
2599             int          version;
2600             int          callout_number;
2601             int         *offset_vector;
2602             const char  *subject;
2603             int          subject_length;
2604             int          start_match;
2605             int          current_position;
2606             int          capture_top;
2607             int          capture_last;
2608             void        *callout_data;
2609             int          pattern_position;
2610             int          next_item_length;
2611    
2612           The version field is an integer containing the version  number  of  the
2613           block  format. The initial version was 0; the current version is 1. The
2614           version number will change again in future  if  additional  fields  are
2615           added, but the intention is never to remove any of the existing fields.
2616    
2617           The callout_number field contains the number of the  callout,  as  com-
2618           piled  into  the pattern (that is, the number after ?C for manual call-
2619           outs, and 255 for automatically generated callouts).
2620    
2621           The offset_vector field is a pointer to the vector of offsets that  was
2622           passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2623           pcre_exec() is used, the contents can be inspected in order to  extract
2624           substrings  that  have  been  matched  so  far,  in the same way as for
2625           extracting substrings after a match has completed. For  pcre_dfa_exec()
2626           this field is not useful.
2627    
2628           The subject and subject_length fields contain copies of the values that
2629           were passed to pcre_exec().
2630    
2631           The start_match field normally contains the offset within  the  subject
2632           at  which  the  current  match  attempt started. However, if the escape
2633           sequence \K has been encountered, this value is changed to reflect  the
2634           modified  starting  point.  If the pattern is not anchored, the callout
2635           function may be called several times from the same point in the pattern
2636           for different starting points in the subject.
2637    
2638           The  current_position  field  contains the offset within the subject of
2639           the current match pointer.
2640    
2641           When the pcre_exec() function is used, the capture_top  field  contains
2642           one  more than the number of the highest numbered captured substring so
2643           far. If no substrings have been captured, the value of  capture_top  is
2644           one.  This  is always the case when pcre_dfa_exec() is used, because it
2645           does not support captured substrings.
2646    
2647           The capture_last field contains the number of the  most  recently  cap-
2648           tured  substring. If no substrings have been captured, its value is -1.
2649           This is always the case when pcre_dfa_exec() is used.
2650    
2651           The callout_data field contains a value that is passed  to  pcre_exec()
2652           or  pcre_dfa_exec() specifically so that it can be passed back in call-
2653           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2654           structure.  If  no such data was passed, the value of callout_data in a
2655           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2656           structure in the pcreapi documentation.
2657    
2658           The  pattern_position field is present from version 1 of the pcre_call-
2659           out structure. It contains the offset to the next item to be matched in
2660           the pattern string.
2661    
2662           The  next_item_length field is present from version 1 of the pcre_call-
2663           out structure. It contains the length of the next item to be matched in
2664           the  pattern  string. When the callout immediately precedes an alterna-
2665           tion bar, a closing parenthesis, or the end of the pattern, the  length
2666           is  zero.  When the callout precedes an opening parenthesis, the length
2667           is that of the entire subpattern.
2668    
2669           The pattern_position and next_item_length fields are intended  to  help
2670           in  distinguishing between different automatic callouts, which all have
2671           the same callout number. However, they are set for all callouts.
2672    
2673    
2674  RETURN VALUES  RETURN VALUES
2675    
2676       The callout function returns an integer.  If  the  value  is         The external callout function returns an integer to PCRE. If the  value
2677       zero,  matching  proceeds as normal. If the value is greater         is  zero,  matching  proceeds  as  normal. If the value is greater than
2678       than zero, matching fails at the current  point,  but  back-         zero, matching fails at the current point, but  the  testing  of  other
2679       tracking  to test other possibilities goes ahead, just as if         matching possibilities goes ahead, just as if a lookahead assertion had
2680       a lookahead assertion had failed. If the value is less  than         failed. If the value is less than zero, the  match  is  abandoned,  and
2681       zero,  the  match  is abandoned, and pcre_exec() returns the         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2682       value.  
2683           Negative   values   should   normally   be   chosen  from  the  set  of
2684       Negative values should normally be chosen from  the  set  of         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2685       PCRE_ERROR_xxx  values.  In  particular,  PCRE_ERROR_NOMATCH         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2686       forces a standard "no  match"  failure.   The  error  number         reserved for use by callout functions; it will never be  used  by  PCRE
2687       PCRE_ERROR_CALLOUT is reserved for use by callout functions;         itself.
2688       it will never be used by PCRE itself.  
2689    
2690    AUTHOR
2691    
2692           Philip Hazel
2693           University Computing Service
2694           Cambridge CB2 3QH, England.
2695    
2696    
2697    REVISION
2698    
2699           Last updated: 29 May 2007
2700           Copyright (c) 1997-2007 University of Cambridge.
2701    ------------------------------------------------------------------------------
2702    
2703    
2704    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2705    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2706    
2707  NAME  NAME
2708       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2709    
2710    
2711  DIFFERENCES FROM PERL  DIFFERENCES BETWEEN PCRE AND PERL
2712    
2713       This document describes the differences  in  the  ways  that         This  document describes the differences in the ways that PCRE and Perl
2714       PCRE  and  Perl  handle regular expressions. The differences         handle regular expressions. The differences described here  are  mainly
2715       described here are with respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2716           some features that are expected to be in the forthcoming Perl 5.10.
2717       1. PCRE does  not  allow  repeat  quantifiers  on  lookahead  
2718       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
2719       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
2720       next  three characters are not "a". It just asserts that the         main pcre page.
2721       next character is not "a" three times.  
2722           2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2723       2. Capturing subpatterns that occur inside  negative  looka-         permits  them,  but they do not mean what you might think. For example,
2724       head  assertions  are  counted,  but  their  entries  in the         (?!a){3} does not assert that the next three characters are not "a". It
2725       offsets vector are never set. Perl sets its numerical  vari-         just asserts that the next character is not "a" three times.
2726       ables  from  any  such  patterns that are matched before the  
2727       assertion fails to match something (thereby succeeding), but         3.  Capturing  subpatterns  that occur inside negative lookahead asser-
2728       only  if  the negative lookahead assertion contains just one         tions are counted, but their entries in the offsets  vector  are  never
2729       branch.         set.  Perl sets its numerical variables from any such patterns that are
2730           matched before the assertion fails to match something (thereby succeed-
2731       3. Though binary zero characters are supported in  the  sub-         ing),  but  only  if the negative lookahead assertion contains just one
2732       ject  string,  they  are  not  allowed  in  a pattern string         branch.
2733       because it is passed as a normal  C  string,  terminated  by  
2734       zero. The escape sequence "\0" can be used in the pattern to         4. Though binary zero characters are supported in the  subject  string,
2735       represent a binary zero.         they are not allowed in a pattern string because it is passed as a nor-
2736           mal C string, terminated by zero. The escape sequence \0 can be used in
2737       4. The following Perl escape sequences  are  not  supported:         the pattern to represent a binary zero.
2738       \l,  \u,  \L,  \U,  \P, \p, and \X. In fact these are imple-  
2739       mented by Perl's general string-handling and are not part of         5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2740       its pattern matching engine. If any of these are encountered         \U, and \N. In fact these are implemented by Perl's general string-han-
2741       by PCRE, an error is generated.         dling  and are not part of its pattern matching engine. If any of these
2742           are encountered by PCRE, an error is generated.
2743       5. PCRE does support the \Q...\E  escape  for  quoting  sub-  
2744       strings. Characters in between are treated as literals. This         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2745       is slightly different from Perl in that $  and  @  are  also         is  built  with Unicode character property support. The properties that
2746       handled  as  literals inside the quotes. In Perl, they cause         can be tested with \p and \P are limited to the general category  prop-
2747       variable interpolation (but of course  PCRE  does  not  have         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2748       variables). Note the following examples:         derived properties Any and L&.
2749    
2750           Pattern            PCRE matches      Perl matches         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2751           ters  in  between  are  treated as literals. This is slightly different
2752           \Qabc$xyz\E        abc$xyz           abc followed by the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2753                                                  contents of $xyz         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2754           \Qabc\$xyz\E       abc\$xyz          abc\$xyz         does not have variables). Note the following examples:
2755           \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz  
2756               Pattern            PCRE matches      Perl matches
2757       In PCRE, the \Q...\E mechanism is not  recognized  inside  a  
2758       character class.             \Qabc$xyz\E        abc$xyz           abc followed by the
2759                                                      contents of $xyz
2760       8. Fairly obviously, PCRE does not support the (?{code}) and             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2761       (?p{code})  constructions. However, there is some experimen-             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2762       tal support for recursive patterns using the non-Perl  items  
2763       (?R),  (?number)  and  (?P>name).  Also,  the PCRE "callout"         The \Q...\E sequence is recognized both inside  and  outside  character
2764       feature allows an external function to be called during pat-         classes.
2765       tern matching.  
2766           8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2767       9. There are some differences that are  concerned  with  the         constructions. However, there is support for recursive  patterns.  This
2768       settings  of  captured  strings  when  part  of a pattern is         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2769       repeated. For example, matching "aba"  against  the  pattern         "callout" feature allows an external function to be called during  pat-
2770       /^(a(b)?)+$/  in Perl leaves $2 unset, but in PCRE it is set         tern matching. See the pcrecallout documentation for details.
2771       to "b".  
2772           9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2773       10. PCRE  provides  some  extensions  to  the  Perl  regular         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2774       expression facilities:         unlike Perl.
2775    
2776       (a) Although lookbehind assertions must match  fixed  length         10.  There are some differences that are concerned with the settings of
2777       strings,  each  alternative branch of a lookbehind assertion         captured strings when part of  a  pattern  is  repeated.  For  example,
2778       can match a different length of string. Perl  requires  them         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2779       all to have the same length.         unset, but in PCRE it is set to "b".
2780    
2781       (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is  not         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2782