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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
5  synopses of each function in the library have not been included. There are  synopses of each function in the library have not been included. Neither has
6  separate text files for the pcregrep and pcretest commands.  the pcredemo program. There are separate text files for the pcregrep and
7    pcretest commands.
8  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
9    
 NAME  
      PCRE - Perl-compatible regular expressions  
10    
11    PCRE(3)                                                                PCRE(3)
12    
 DESCRIPTION  
13    
14       The PCRE library is a set of functions that implement  regu-  NAME
15       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.  
16    
17    
18  USER DOCUMENTATION  INTRODUCTION
19    
20       The user documentation for PCRE has been  split  up  into  a         The  PCRE  library is a set of functions that implement regular expres-
21       number  of  different sections. In the "man" format, each of         sion pattern matching using the same syntax and semantics as Perl, with
22       these is a separate "man page". In the HTML format, each  is         just  a few differences. Some features that appeared in Python and PCRE
23       a  separate  page,  linked from the index page. In the plain         before they appeared in Perl are also available using the  Python  syn-
24       text format, all the sections are concatenated, for ease  of         tax,  there  is  some  support for one or two .NET and Oniguruma syntax
25       searching. The sections are as follows:         items, and there is an option for requesting some  minor  changes  that
26           give better JavaScript compatibility.
27         pcre              this document  
28         pcreapi           details of PCRE's native API         The  current implementation of PCRE corresponds approximately with Perl
29         pcrebuild         options for building PCRE         5.12, including support for UTF-8 encoded strings and  Unicode  general
30         pcrecallout       details of the callout feature         category  properties.  However,  UTF-8  and  Unicode  support has to be
31         pcrecompat        discussion of Perl compatibility         explicitly enabled; it is not the default. The  Unicode  tables  corre-
32         pcregrep          description of the pcregrep command         spond to Unicode release 6.0.0.
33         pcrepattern       syntax and semantics of supported  
34                             regular expressions         In  addition to the Perl-compatible matching function, PCRE contains an
35         pcreperform       discussion of performance issues         alternative function that matches the same compiled patterns in a  dif-
36         pcreposix         the POSIX-compatible API         ferent way. In certain circumstances, the alternative function has some
37         pcresample        discussion of the sample program         advantages.  For a discussion of the two matching algorithms,  see  the
38         pcretest          the pcretest testing command         pcrematching page.
39    
40       In addition, in the "man" and HTML formats, there is a short         PCRE  is  written  in C and released as a C library. A number of people
41       page  for  each  library function, listing its arguments and         have written wrappers and interfaces of various kinds.  In  particular,
42       results.         Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
43           included as part of the PCRE distribution. The pcrecpp page has details
44           of  this  interface.  Other  people's contributions can be found in the
45  LIMITATIONS         Contrib directory at the primary FTP site, which is:
46    
47       There are some size limitations in PCRE but it is hoped that         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
48       they will never in practice be relevant.  
49           Details of exactly which Perl regular expression features are  and  are
50       The maximum length of a  compiled  pattern  is  65539  (sic)         not supported by PCRE are given in separate documents. See the pcrepat-
51       bytes  if PCRE is compiled with the default internal linkage         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
52       size of 2. If you want to process regular  expressions  that         page.
53       are  truly  enormous,  you can compile PCRE with an internal  
54       linkage size of 3 or 4 (see the README file  in  the  source         Some  features  of  PCRE can be included, excluded, or changed when the
55       distribution  and  the pcrebuild documentation for details).         library is built. The pcre_config() function makes it  possible  for  a
56       If these cases the limit is substantially larger.   However,         client  to  discover  which  features are available. The features them-
57       the speed of execution will be slower.         selves are described in the pcrebuild page. Documentation about  build-
58           ing  PCRE  for various operating systems can be found in the README and
59       All values in repeating quantifiers must be less than 65536.         NON-UNIX-USE files in the source distribution.
60       The maximum number of capturing subpatterns is 65535.  
61           The library contains a number of undocumented  internal  functions  and
62       There is no limit to the  number  of  non-capturing  subpat-         data  tables  that  are  used by more than one of the exported external
63       terns,  but  the  maximum  depth  of nesting of all kinds of         functions, but which are not intended  for  use  by  external  callers.
64       parenthesized subpattern, including  capturing  subpatterns,         Their  names  all begin with "_pcre_", which hopefully will not provoke
65       assertions, and other types of subpattern, is 200.         any name clashes. In some environments, it is possible to control which
66           external  symbols  are  exported when a shared library is built, and in
67       The maximum length of a subject string is the largest  posi-         these cases the undocumented symbols are not exported.
      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.  
68    
69    
70  UTF-8 SUPPORT  USER DOCUMENTATION
71    
72       Starting at release 3.3, PCRE has had some support for char-         The user documentation for PCRE comprises a number  of  different  sec-
73       acter  strings  encoded in the UTF-8 format. For release 4.0         tions.  In the "man" format, each of these is a separate "man page". In
74       this has been greatly extended to cover most common require-         the HTML format, each is a separate page, linked from the  index  page.
75       ments.         In  the  plain  text format, all the sections, except the pcredemo sec-
76           tion, are concatenated, for ease of searching. The sections are as fol-
77       In order process UTF-8  strings,  you  must  build  PCRE  to         lows:
78       include  UTF-8  support  in  the code, and, in addition, you  
79       must call pcre_compile() with  the  PCRE_UTF8  option  flag.           pcre              this document
80       When  you  do this, both the pattern and any subject strings           pcre-config       show PCRE installation configuration information
81       that are matched against it are  treated  as  UTF-8  strings           pcreapi           details of PCRE's native C API
82       instead of just strings of bytes.           pcrebuild         options for building PCRE
83             pcrecallout       details of the callout feature
84       If you compile PCRE with UTF-8 support, but do not use it at           pcrecompat        discussion of Perl compatibility
85       run  time,  the  library will be a bit bigger, but the addi-           pcrecpp           details of the C++ wrapper
86       tional run time overhead is limited to testing the PCRE_UTF8           pcredemo          a demonstration C program that uses PCRE
87       flag in several places, so should not be very large.           pcregrep          description of the pcregrep command
88             pcrejit           discussion of the just-in-time optimization support
89       The following comments apply when PCRE is running  in  UTF-8           pcrelimits        details of size and other limits
90       mode:           pcrematching      discussion of the two matching algorithms
91             pcrepartial       details of the partial matching facility
92       1. PCRE assumes that the strings it is given  contain  valid           pcrepattern       syntax and semantics of supported
93       UTF-8  codes. It does not diagnose invalid UTF-8 strings. If                               regular expressions
94       you pass invalid UTF-8 strings  to  PCRE,  the  results  are           pcreperform       discussion of performance issues
95       undefined.           pcreposix         the POSIX-compatible C API
96             pcreprecompile    details of saving and re-using precompiled patterns
97       2. In a pattern, the escape sequence \x{...}, where the con-           pcresample        discussion of the pcredemo program
98       tents  of  the  braces is a string of hexadecimal digits, is           pcrestack         discussion of stack usage
99       interpreted as a UTF-8 character whose code  number  is  the           pcresyntax        quick syntax reference
100       given  hexadecimal  number, for example: \x{1234}. If a non-           pcretest          description of the pcretest testing command
101       hexadecimal digit appears between the braces,  the  item  is           pcreunicode       discussion of Unicode and UTF-8 support
      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.  
102    
103       9. PCRE does not support the use of Unicode tables and  pro-         In  addition,  in the "man" and HTML formats, there is a short page for
104       perties or the Perl escapes \p, \P, and \X.         each C library function, listing its arguments and results.
105    
106    
107  AUTHOR  AUTHOR
108    
109       Philip Hazel <ph10@cam.ac.uk>         Philip Hazel
110       University Computing Service,         University Computing Service
111       Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
112       Phone: +44 1223 334714  
113           Putting an actual email address here seems to have been a spam  magnet,
114           so  I've  taken  it away. If you want to email me, use my two initials,
115           followed by the two digits 10, at the domain cam.ac.uk.
116    
117    
118    REVISION
119    
120           Last updated: 24 August 2011
121           Copyright (c) 1997-2011 University of Cambridge.
122    ------------------------------------------------------------------------------
123    
124    
125    PCREBUILD(3)                                                      PCREBUILD(3)
126    
 Last updated: 04 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
127    
128  NAME  NAME
129       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
130    
131    
132  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
133    
134       This document describes the optional features of  PCRE  that         This  document  describes  the  optional  features  of PCRE that can be
135       can  be  selected when the library is compiled. They are all         selected when the library is compiled. It assumes use of the  configure
136       selected, or deselected, by providing options to the config-         script,  where the optional features are selected or deselected by pro-
137       ure  script  which  is run before the make command. The com-         viding options to configure before running the make  command.  However,
138       plete list of options  for  configure  (which  includes  the         the  same  options  can be selected in both Unix-like and non-Unix-like
139       standard  ones  such  as  the  selection of the installation         environments using the GUI facility of cmake-gui if you are using CMake
140       directory) can be obtained by running         instead of configure to build PCRE.
141    
142         ./configure --help         There  is  a  lot more information about building PCRE in non-Unix-like
143           environments in the file called NON_UNIX_USE, which is part of the PCRE
144       The following sections describe certain options whose  names         distribution.  You  should consult this file as well as the README file
145       begin  with  --enable  or  --disable. These settings specify         if you are building in a non-Unix-like environment.
146       changes to the defaults for the configure  command.  Because  
147       of  the  way  that  configure  works, --enable and --disable         The complete list of options for configure (which includes the standard
148       always come in pairs, so  the  complementary  option  always         ones  such  as  the  selection  of  the  installation directory) can be
149       exists  as  well, but as it specifies the default, it is not         obtained by running
150       described.  
151             ./configure --help
152    
153           The following sections include  descriptions  of  options  whose  names
154           begin with --enable or --disable. These settings specify changes to the
155           defaults for the configure command. Because of the way  that  configure
156           works,  --enable  and --disable always come in pairs, so the complemen-
157           tary option always exists as well, but as it specifies the default,  it
158           is not described.
159    
160    
161    BUILDING SHARED AND STATIC LIBRARIES
162    
163           The  PCRE building process uses libtool to build both shared and static
164           Unix libraries by default. You can suppress one of these by adding  one
165           of
166    
167             --disable-shared
168             --disable-static
169    
170           to the configure command, as required.
171    
172    
173    C++ SUPPORT
174    
175           By default, the configure script will search for a C++ compiler and C++
176           header files. If it finds them, it automatically builds the C++ wrapper
177           library for PCRE. You can disable this by adding
178    
179             --disable-cpp
180    
181           to the configure command.
182    
183    
184  UTF-8 SUPPORT  UTF-8 SUPPORT
185    
186       To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
187    
188             --enable-utf8
189    
190           to  the  configure  command.  Of  itself, this does not make PCRE treat
191           strings as UTF-8. As well as compiling PCRE with this option, you  also
192           have  have to set the PCRE_UTF8 option when you call the pcre_compile()
193           or pcre_compile2() functions.
194    
195           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
196           expects its input to be either ASCII or UTF-8 (depending on the runtime
197           option). It is not possible to support both EBCDIC and UTF-8  codes  in
198           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
199           --enable-ebcdic are mutually exclusive.
200    
201    
202    UNICODE CHARACTER PROPERTY SUPPORT
203    
204         --enable-utf8         UTF-8 support allows PCRE to process character values greater than  255
205           in  the  strings that it handles. On its own, however, it does not pro-
206           vide any facilities for accessing the properties of such characters. If
207           you  want  to  be able to use the pattern escapes \P, \p, and \X, which
208           refer to Unicode character properties, you must add
209    
210       to the configure command. Of itself, this does not make PCRE           --enable-unicode-properties
211       treat  strings as UTF-8. As well as compiling PCRE with this  
212       option, you also have have to set the PCRE_UTF8 option  when         to the configure command. This implies UTF-8 support, even if you  have
213       you call the pcre_compile() function.         not explicitly requested it.
214    
215           Including  Unicode  property  support  adds around 30K of tables to the
216           PCRE library. Only the general category properties such as  Lu  and  Nd
217           are supported. Details are given in the pcrepattern documentation.
218    
219    
220  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
221    
222       By default, PCRE treats character 10 (linefeed) as the  new-         By  default,  PCRE interprets the linefeed (LF) character as indicating
223       line  character.  This  is  the  normal newline character on         the end of a line. This is the normal newline  character  on  Unix-like
224       Unix-like systems. You can compile PCRE to use character  13         systems.  You  can compile PCRE to use carriage return (CR) instead, by
225       (carriage return) instead by adding         adding
   
        --enable-newline-is-cr  
   
      to the configure command. For completeness there is  also  a  
      --enable-newline-is-lf  option,  which  explicitly specifies  
      linefeed as the newline character.  
226    
227             --enable-newline-is-cr
228    
229  BUILDING SHARED AND STATIC LIBRARIES         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
230           option, which explicitly specifies linefeed as the newline character.
231    
232           Alternatively, you can specify that line endings are to be indicated by
233           the two character sequence CRLF. If you want this, add
234    
235             --enable-newline-is-crlf
236    
237           to the configure command. There is a fourth option, specified by
238    
239             --enable-newline-is-anycrlf
240    
241       The PCRE building process uses libtool to build both  shared         which causes PCRE to recognize any of the three sequences  CR,  LF,  or
242       and  static  Unix libraries by default. You can suppress one         CRLF as indicating a line ending. Finally, a fifth option, specified by
      of these by adding one of  
243    
244         --disable-shared           --enable-newline-is-any
        --disable-static  
245    
246       to the configure command, as required.         causes PCRE to recognize any Unicode newline sequence.
247    
248           Whatever  line  ending convention is selected when PCRE is built can be
249           overridden when the library functions are called. At build time  it  is
250           conventional to use the standard for your operating system.
251    
252    
253    WHAT \R MATCHES
254    
255           By  default,  the  sequence \R in a pattern matches any Unicode newline
256           sequence, whatever has been selected as the line  ending  sequence.  If
257           you specify
258    
259             --enable-bsr-anycrlf
260    
261           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
262           ever is selected when PCRE is built can be overridden when the  library
263           functions are called.
264    
265    
266  POSIX MALLOC USAGE  POSIX MALLOC USAGE
267    
268       When PCRE is called through the  POSIX  interface  (see  the         When PCRE is called through the POSIX interface (see the pcreposix doc-
269       pcreposix  documentation),  additional  working  storage  is         umentation), additional working storage is  required  for  holding  the
270       required for holding the pointers  to  capturing  substrings         pointers  to capturing substrings, because PCRE requires three integers
271       because  PCRE requires three integers per substring, whereas         per substring, whereas the POSIX interface provides only  two.  If  the
272       the POSIX interface provides only  two.  If  the  number  of         number of expected substrings is small, the wrapper function uses space
273       expected  substrings  is  small,  the  wrapper function uses         on the stack, because this is faster than using malloc() for each call.
274       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
275       loc()  for  each call. The default threshold above which the         can be changed by adding a setting such as
276       stack is no longer used is 10; it can be changed by adding a  
277       setting such as           --with-posix-malloc-threshold=20
278    
279           to the configure command.
280    
        --with-posix-malloc-threshold=20  
281    
282       to the configure command.  HANDLING VERY LARGE PATTERNS
283    
284           Within a compiled pattern, offset values are used  to  point  from  one
285           part  to another (for example, from an opening parenthesis to an alter-
286           nation metacharacter). By default, two-byte values are used  for  these
287           offsets,  leading  to  a  maximum size for a compiled pattern of around
288           64K. This is sufficient to handle all but the most  gigantic  patterns.
289           Nevertheless,  some  people do want to process truyl enormous patterns,
290           so it is possible to compile PCRE to use three-byte or  four-byte  off-
291           sets by adding a setting such as
292    
293             --with-link-size=3
294    
295           to  the  configure  command.  The value given must be 2, 3, or 4. Using
296           longer offsets slows down the operation of PCRE because it has to  load
297           additional bytes when handling them.
298    
299    
300    AVOIDING EXCESSIVE STACK USAGE
301    
302           When matching with the pcre_exec() function, PCRE implements backtrack-
303           ing by making recursive calls to an internal function  called  match().
304           In  environments  where  the size of the stack is limited, this can se-
305           verely limit PCRE's operation. (The Unix environment does  not  usually
306           suffer from this problem, but it may sometimes be necessary to increase
307           the maximum stack size.  There is a discussion in the  pcrestack  docu-
308           mentation.)  An alternative approach to recursion that uses memory from
309           the heap to remember data, instead of using recursive  function  calls,
310           has  been  implemented to work round the problem of limited stack size.
311           If you want to build a version of PCRE that works this way, add
312    
313             --disable-stack-for-recursion
314    
315           to the configure command. With this configuration, PCRE  will  use  the
316           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
317           ment functions. By default these point to malloc() and free(), but  you
318           can replace the pointers so that your own functions are used instead.
319    
320           Separate  functions  are  provided  rather  than  using pcre_malloc and
321           pcre_free because the  usage  is  very  predictable:  the  block  sizes
322           requested  are  always  the  same,  and  the blocks are always freed in
323           reverse order. A calling program might be able to  implement  optimized
324           functions  that  perform  better  than  malloc()  and free(). PCRE runs
325           noticeably more slowly when built in this way. This option affects only
326           the pcre_exec() function; it is not relevant for pcre_dfa_exec().
327    
328    
329  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
330    
331       Internally, PCRE has a  function  called  match()  which  it         Internally,  PCRE has a function called match(), which it calls repeat-
332       calls  repeatedly  (possibly  recursively) when performing a         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
333       matching operation. By limiting the  number  of  times  this         pcre_exec()  function.  By controlling the maximum number of times this
334       function  may  be  called,  a  limit  can  be  placed on the         function may be called during a single matching operation, a limit  can
335       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
336       can  be  changed  at  run  time, as described in the pcreapi         limit can be changed at run time, as described in the pcreapi  documen-
337       documentation. The default is 10 million, but  this  can  be         tation.  The default is 10 million, but this can be changed by adding a
338       changed by adding a setting such as         setting such as
339    
340         --with-match-limit=500000           --with-match-limit=500000
341    
342       to the configure command.         to  the  configure  command.  This  setting  has  no  effect   on   the
343           pcre_dfa_exec() matching function.
344    
345           In  some  environments  it is desirable to limit the depth of recursive
346           calls of match() more strictly than the total number of calls, in order
347           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
348           for-recursion is specified) that is used. A second limit controls this;
349           it  defaults  to  the  value  that is set for --with-match-limit, which
350           imposes no additional constraints. However, you can set a  lower  limit
351           by adding, for example,
352    
353  HANDLING VERY LARGE PATTERNS           --with-match-limit-recursion=10000
354    
355       Within a compiled pattern, offset values are used  to  point         to  the  configure  command.  This  value can also be overridden at run
356       from  one  part  to  another  (for  example, from an opening         time.
357       parenthesis to an  alternation  metacharacter).  By  default  
358       two-byte  values  are  used  for these offsets, leading to a  
359       maximum size for a compiled pattern of around 64K.  This  is  CREATING CHARACTER TABLES AT BUILD TIME
360       sufficient  to  handle  all  but the most gigantic patterns.  
361       Nevertheless, some people do want to process  enormous  pat-         PCRE uses fixed tables for processing characters whose code values  are
362       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
363       or four-byte offsets by adding a setting such as         distributed in the file pcre_chartables.c.dist. These  tables  are  for
364           ASCII codes only. If you add
365         --with-link-size=3  
366             --enable-rebuild-chartables
367       to the configure command. The value given must be 2,  3,  or  
368       4.  Using  longer  offsets  slows down the operation of PCRE         to  the  configure  command, the distributed tables are no longer used.
369       because it has to load additional bytes when handling them.         Instead, a program called dftables is compiled and  run.  This  outputs
370           the source for new set of tables, created in the default locale of your
371       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
372       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
373       of these tests is a representation of the compiled  pattern,         you need to create alternative tables when cross  compiling,  you  will
374       and this changes with the link size.         have to do so "by hand".)
375    
376    
377    USING EBCDIC CODE
378    
379           PCRE  assumes  by  default that it will run in an environment where the
380           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
381           This  is  the  case for most computer operating systems. PCRE can, how-
382           ever, be compiled to run in an EBCDIC environment by adding
383    
384             --enable-ebcdic
385    
386           to the configure command. This setting implies --enable-rebuild-charta-
387           bles.  You  should  only  use  it if you know that you are in an EBCDIC
388           environment (for example,  an  IBM  mainframe  operating  system).  The
389           --enable-ebcdic option is incompatible with --enable-utf8.
390    
391    
392    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
393    
394           By default, pcregrep reads all files as plain text. You can build it so
395           that it recognizes files whose names end in .gz or .bz2, and reads them
396           with libz or libbz2, respectively, by adding one or both of
397    
398             --enable-pcregrep-libz
399             --enable-pcregrep-libbz2
400    
401           to the configure command. These options naturally require that the rel-
402           evant libraries are installed on your system. Configuration  will  fail
403           if they are not.
404    
405    
406    PCREGREP BUFFER SIZE
407    
408           pcregrep  uses  an internal buffer to hold a "window" on the file it is
409           scanning, in order to be able to output "before" and "after" lines when
410           it  finds  a match. The size of the buffer is controlled by a parameter
411           whose default value is 20K. The buffer itself is three times this size,
412           but because of the way it is used for holding "before" lines, the long-
413           est line that is guaranteed to be processable is  the  parameter  size.
414           You can change the default parameter value by adding, for example,
415    
416             --with-pcregrep-bufsize=50K
417    
418           to the configure command. The caller of pcregrep can, however, override
419           this value by specifying a run-time option.
420    
421    
422    PCRETEST OPTION FOR LIBREADLINE SUPPORT
423    
424           If you add
425    
426             --enable-pcretest-libreadline
427    
428           to the configure command,  pcretest  is  linked  with  the  libreadline
429           library,  and  when its input is from a terminal, it reads it using the
430           readline() function. This provides line-editing and history facilities.
431           Note that libreadline is GPL-licensed, so if you distribute a binary of
432           pcretest linked in this way, there may be licensing issues.
433    
434           Setting this option causes the -lreadline option to  be  added  to  the
435           pcretest  build.  In many operating environments with a sytem-installed
436           libreadline this is sufficient. However, in some environments (e.g.  if
437           an  unmodified  distribution version of readline is in use), some extra
438           configuration may be necessary. The INSTALL file for  libreadline  says
439           this:
440    
441             "Readline uses the termcap functions, but does not link with the
442             termcap or curses library itself, allowing applications which link
443             with readline the to choose an appropriate library."
444    
445           If  your environment has not been set up so that an appropriate library
446           is automatically included, you may need to add something like
447    
448             LIBS="-ncurses"
449    
450           immediately before the configure command.
451    
452    
453    SEE ALSO
454    
455           pcreapi(3), pcre_config(3).
456    
457    
458    AUTHOR
459    
460           Philip Hazel
461           University Computing Service
462           Cambridge CB2 3QH, England.
463    
464    
465    REVISION
466    
467           Last updated: 02 August 2011
468           Copyright (c) 1997-2011 University of Cambridge.
469    ------------------------------------------------------------------------------
470    
471    
472    PCREMATCHING(3)                                                PCREMATCHING(3)
473    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
474    
475  NAME  NAME
476       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
477    
478    
479    PCRE MATCHING ALGORITHMS
480    
481           This document describes the two different algorithms that are available
482           in PCRE for matching a compiled regular expression against a given sub-
483           ject  string.  The  "standard"  algorithm  is  the  one provided by the
484           pcre_exec() function.  This works in the same was  as  Perl's  matching
485           function, and provides a Perl-compatible matching operation.
486    
487           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
488           this operates in a different way, and is not  Perl-compatible.  It  has
489           advantages  and disadvantages compared with the standard algorithm, and
490           these are described below.
491    
492           When there is only one possible way in which a given subject string can
493           match  a pattern, the two algorithms give the same answer. A difference
494           arises, however, when there are multiple possibilities. For example, if
495           the pattern
496    
497             ^<.*>
498    
499           is matched against the string
500    
501             <something> <something else> <something further>
502    
503           there are three possible answers. The standard algorithm finds only one
504           of them, whereas the alternative algorithm finds all three.
505    
506    
507    REGULAR EXPRESSIONS AS TREES
508    
509           The set of strings that are matched by a regular expression can be rep-
510           resented  as  a  tree structure. An unlimited repetition in the pattern
511           makes the tree of infinite size, but it is still a tree.  Matching  the
512           pattern  to a given subject string (from a given starting point) can be
513           thought of as a search of the tree.  There are two  ways  to  search  a
514           tree:  depth-first  and  breadth-first, and these correspond to the two
515           matching algorithms provided by PCRE.
516    
 SYNOPSIS OF PCRE API  
517    
518       #include <pcre.h>  THE STANDARD MATCHING ALGORITHM
519    
520       pcre *pcre_compile(const char *pattern, int options,         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
521            const char **errptr, int *erroffset,         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
522            const unsigned char *tableptr);         depth-first search of the pattern tree. That is, it  proceeds  along  a
523           single path through the tree, checking that the subject matches what is
524           required. When there is a mismatch, the algorithm  tries  any  alterna-
525           tives  at  the  current point, and if they all fail, it backs up to the
526           previous branch point in the  tree,  and  tries  the  next  alternative
527           branch  at  that  level.  This often involves backing up (moving to the
528           left) in the subject string as well.  The  order  in  which  repetition
529           branches  are  tried  is controlled by the greedy or ungreedy nature of
530           the quantifier.
531    
532       pcre_extra *pcre_study(const pcre *code, int options,         If a leaf node is reached, a matching string has  been  found,  and  at
533            const char **errptr);         that  point the algorithm stops. Thus, if there is more than one possi-
534           ble match, this algorithm returns the first one that it finds.  Whether
535           this  is the shortest, the longest, or some intermediate length depends
536           on the way the greedy and ungreedy repetition quantifiers are specified
537           in the pattern.
538    
539       int pcre_exec(const pcre *code, const pcre_extra *extra,         Because  it  ends  up  with a single path through the tree, it is rela-
540            const char *subject, int length, int startoffset,         tively straightforward for this algorithm to keep  track  of  the  sub-
541            int options, int *ovector, int ovecsize);         strings  that  are  matched  by portions of the pattern in parentheses.
542           This provides support for capturing parentheses and back references.
543    
      int pcre_copy_named_substring(const pcre *code,  
           const char *subject, int *ovector,  
           int stringcount, const char *stringname,  
           char *buffer, int buffersize);  
544    
545       int pcre_copy_substring(const char *subject, int *ovector,  THE ALTERNATIVE MATCHING ALGORITHM
           int stringcount, int stringnumber, char *buffer,  
           int buffersize);  
546    
547       int pcre_get_named_substring(const pcre *code,         This algorithm conducts a breadth-first search of  the  tree.  Starting
548            const char *subject, int *ovector,         from  the  first  matching  point  in the subject, it scans the subject
549            int stringcount, const char *stringname,         string from left to right, once, character by character, and as it does
550            const char **stringptr);         this,  it remembers all the paths through the tree that represent valid
551           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
552           though  it is not implemented as a traditional finite state machine (it
553           keeps multiple states active simultaneously).
554    
555       int pcre_get_stringnumber(const pcre *code,         Although the general principle of this matching algorithm  is  that  it
556            const char *name);         scans  the subject string only once, without backtracking, there is one
557           exception: when a lookaround assertion is encountered,  the  characters
558           following  or  preceding  the  current  point  have to be independently
559           inspected.
560    
561       int pcre_get_substring(const char *subject, int *ovector,         The scan continues until either the end of the subject is  reached,  or
562            int stringcount, int stringnumber,         there  are  no more unterminated paths. At this point, terminated paths
563            const char **stringptr);         represent the different matching possibilities (if there are none,  the
564           match  has  failed).   Thus,  if there is more than one possible match,
565           this algorithm finds all of them, and in particular, it finds the long-
566           est.  The  matches are returned in decreasing order of length. There is
567           an option to stop the algorithm after the first match (which is  neces-
568           sarily the shortest) is found.
569    
570       int pcre_get_substring_list(const char *subject,         Note that all the matches that are found start at the same point in the
571            int *ovector, int stringcount, const char ***listptr);         subject. If the pattern
572    
573       void pcre_free_substring(const char *stringptr);           cat(er(pillar)?)?
574    
575       void pcre_free_substring_list(const char **stringptr);         is matched against the string "the caterpillar catchment",  the  result
576           will  be the three strings "caterpillar", "cater", and "cat" that start
577           at the fifth character of the subject. The algorithm does not automati-
578           cally move on to find matches that start at later positions.
579    
580       const unsigned char *pcre_maketables(void);         There are a number of features of PCRE regular expressions that are not
581           supported by the alternative matching algorithm. They are as follows:
582    
583       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         1. Because the algorithm finds all  possible  matches,  the  greedy  or
584            int what, void *where);         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and
585           ungreedy quantifiers are treated in exactly the same way. However, pos-
586           sessive  quantifiers can make a difference when what follows could also
587           match what is quantified, for example in a pattern like this:
588    
589             ^a++\w!
590    
591       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         This pattern matches "aaab!" but not "aaa!", which would be matched  by
592           a  non-possessive quantifier. Similarly, if an atomic group is present,
593           it is matched as if it were a standalone pattern at the current  point,
594           and  the  longest match is then "locked in" for the rest of the overall
595           pattern.
596    
597       int pcre_config(int what, void *where);         2. When dealing with multiple paths through the tree simultaneously, it
598           is  not  straightforward  to  keep track of captured substrings for the
599           different matching possibilities, and  PCRE's  implementation  of  this
600           algorithm does not attempt to do this. This means that no captured sub-
601           strings are available.
602    
603       char *pcre_version(void);         3. Because no substrings are captured, back references within the  pat-
604           tern are not supported, and cause errors if encountered.
605    
606       void *(*pcre_malloc)(size_t);         4.  For  the same reason, conditional expressions that use a backrefer-
607           ence as the condition or test for a specific group  recursion  are  not
608           supported.
609    
610       void (*pcre_free)(void *);         5.  Because  many  paths  through the tree may be active, the \K escape
611           sequence, which resets the start of the match when encountered (but may
612           be  on  some  paths  and not on others), is not supported. It causes an
613           error if encountered.
614    
615       int (*pcre_callout)(pcre_callout_block *);         6. Callouts are supported, but the value of the  capture_top  field  is
616           always 1, and the value of the capture_last field is always -1.
617    
618           7.  The \C escape sequence, which (in the standard algorithm) matches a
619           single byte, even in UTF-8 mode, is not supported because the  alterna-
620           tive  algorithm  moves  through  the  subject string one character at a
621           time, for all active paths through the tree.
622    
623  PCRE API         8. Except for (*FAIL), the backtracking control verbs such as  (*PRUNE)
624           are  not  supported.  (*FAIL)  is supported, and behaves like a failing
625           negative assertion.
626    
      PCRE has its own native API,  which  is  described  in  this  
      document.  There  is  also  a  set of wrapper functions that  
      correspond to the POSIX regular expression API.   These  are  
      described in the pcreposix documentation.  
627    
628       The native API function prototypes are defined in the header  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
      file  pcre.h,  and  on  Unix  systems  the library itself is  
      called libpcre.a, so can be accessed by adding -lpcre to the  
      command  for  linking  an  application  which  calls it. The  
      header file defines the macros PCRE_MAJOR and PCRE_MINOR  to  
      contain the major and minor release numbers for the library.  
      Applications can use these to include support for  different  
      releases.  
629    
630       The functions pcre_compile(), pcre_study(), and  pcre_exec()         Using the alternative matching algorithm provides the following  advan-
631       are  used  for compiling and matching regular expressions. A         tages:
      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.  
632    
633       There are convenience functions for extracting captured sub-         1. All possible matches (at a single point in the subject) are automat-
634       strings from a matched subject string. They are:         ically found, and in particular, the longest match is  found.  To  find
635           more than one match using the standard algorithm, you have to do kludgy
636           things with callouts.
637    
638         pcre_copy_substring()         2. Because the alternative algorithm  scans  the  subject  string  just
639         pcre_copy_named_substring()         once,  and  never  needs to backtrack, it is possible to pass very long
640         pcre_get_substring()         subject strings to the matching function in  several  pieces,  checking
641         pcre_get_named_substring()         for  partial  matching  each time. Although it is possible to do multi-
642         pcre_get_substring_list()         segment matching using the standard algorithm (pcre_exec()), by retain-
643           ing  partially matched substrings, it is more complicated. The pcrepar-
644           tial documentation gives details  of  partial  matching  and  discusses
645           multi-segment matching.
646    
      pcre_free_substring()  and  pcre_free_substring_list()   are  
      also  provided,  to  free  the  memory  used  for  extracted  
      strings.  
647    
648       The function pcre_maketables() is used (optionally) to build  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
      a  set of character tables in the current locale for passing  
      to pcre_compile().  
649    
650       The function pcre_fullinfo() is used to find out information         The alternative algorithm suffers from a number of disadvantages:
      about a compiled pattern; pcre_info() is an obsolete version  
      which returns only some of the available information, but is  
      retained   for   backwards   compatibility.    The  function  
      pcre_version() returns a pointer to a string containing  the  
      version of PCRE and its date of release.  
651    
652       The global variables  pcre_malloc  and  pcre_free  initially         1.  It  is  substantially  slower  than the standard algorithm. This is
653       contain the entry points of the standard malloc() and free()         partly because it has to search for all possible matches, but  is  also
654       functions respectively. PCRE  calls  the  memory  management         because it is less susceptible to optimization.
      functions  via  these  variables,  so  a calling program can  
      replace them if it  wishes  to  intercept  the  calls.  This  
      should be done before calling any PCRE functions.  
655    
656       The global variable pcre_callout initially contains NULL. It         2. Capturing parentheses and back references are not supported.
657       can be set by the caller to a "callout" function, which PCRE  
658       will then call at specified points during a matching  opera-         3. Although atomic groups are supported, their use does not provide the
659       tion. Details are given in the pcrecallout documentation.         performance advantage that it does for the standard algorithm.
660    
661    
662    AUTHOR
663    
664           Philip Hazel
665           University Computing Service
666           Cambridge CB2 3QH, England.
667    
668    
669    REVISION
670    
671           Last updated: 17 November 2010
672           Copyright (c) 1997-2010 University of Cambridge.
673    ------------------------------------------------------------------------------
674    
675    
676    PCREAPI(3)                                                          PCREAPI(3)
677    
678    
679    NAME
680           PCRE - Perl-compatible regular expressions
681    
682    
683    PCRE NATIVE API
684    
685           #include <pcre.h>
686    
687           pcre *pcre_compile(const char *pattern, int options,
688                const char **errptr, int *erroffset,
689                const unsigned char *tableptr);
690    
691           pcre *pcre_compile2(const char *pattern, int options,
692                int *errorcodeptr,
693                const char **errptr, int *erroffset,
694                const unsigned char *tableptr);
695    
696           pcre_extra *pcre_study(const pcre *code, int options,
697                const char **errptr);
698    
699           int pcre_exec(const pcre *code, const pcre_extra *extra,
700                const char *subject, int length, int startoffset,
701                int options, int *ovector, int ovecsize);
702    
703           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
704                const char *subject, int length, int startoffset,
705                int options, int *ovector, int ovecsize,
706                int *workspace, int wscount);
707    
708           int pcre_copy_named_substring(const pcre *code,
709                const char *subject, int *ovector,
710                int stringcount, const char *stringname,
711                char *buffer, int buffersize);
712    
713           int pcre_copy_substring(const char *subject, int *ovector,
714                int stringcount, int stringnumber, char *buffer,
715                int buffersize);
716    
717           int pcre_get_named_substring(const pcre *code,
718                const char *subject, int *ovector,
719                int stringcount, const char *stringname,
720                const char **stringptr);
721    
722           int pcre_get_stringnumber(const pcre *code,
723                const char *name);
724    
725           int pcre_get_stringtable_entries(const pcre *code,
726                const char *name, char **first, char **last);
727    
728           int pcre_get_substring(const char *subject, int *ovector,
729                int stringcount, int stringnumber,
730                const char **stringptr);
731    
732           int pcre_get_substring_list(const char *subject,
733                int *ovector, int stringcount, const char ***listptr);
734    
735           void pcre_free_substring(const char *stringptr);
736    
737           void pcre_free_substring_list(const char **stringptr);
738    
739           const unsigned char *pcre_maketables(void);
740    
741           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
742                int what, void *where);
743    
744           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
745    
746           int pcre_refcount(pcre *code, int adjust);
747    
748           int pcre_config(int what, void *where);
749    
750           char *pcre_version(void);
751    
752           void *(*pcre_malloc)(size_t);
753    
754           void (*pcre_free)(void *);
755    
756           void *(*pcre_stack_malloc)(size_t);
757    
758           void (*pcre_stack_free)(void *);
759    
760           int (*pcre_callout)(pcre_callout_block *);
761    
762    
763    PCRE API OVERVIEW
764    
765           PCRE has its own native API, which is described in this document. There
766           are also some wrapper functions that correspond to  the  POSIX  regular
767           expression  API.  These  are  described in the pcreposix documentation.
768           Both of these APIs define a set of C function calls. A C++  wrapper  is
769           distributed with PCRE. It is documented in the pcrecpp page.
770    
771           The  native  API  C  function prototypes are defined in the header file
772           pcre.h, and on Unix systems the library itself is called  libpcre.   It
773           can normally be accessed by adding -lpcre to the command for linking an
774           application  that  uses  PCRE.  The  header  file  defines  the  macros
775           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
776           bers for the library.  Applications can use these  to  include  support
777           for different releases of PCRE.
778    
779           In a Windows environment, if you want to statically link an application
780           program against a non-dll pcre.a  file,  you  must  define  PCRE_STATIC
781           before  including  pcre.h or pcrecpp.h, because otherwise the pcre_mal-
782           loc()   and   pcre_free()   exported   functions   will   be   declared
783           __declspec(dllimport), with unwanted results.
784    
785           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
786           pcre_exec() are used for compiling and matching regular expressions  in
787           a  Perl-compatible  manner. A sample program that demonstrates the sim-
788           plest way of using them is provided in the file  called  pcredemo.c  in
789           the PCRE source distribution. A listing of this program is given in the
790           pcredemo documentation, and the pcresample documentation describes  how
791           to compile and run it.
792    
793           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
794           ble, is also provided. This uses a different algorithm for  the  match-
795           ing.  The  alternative algorithm finds all possible matches (at a given
796           point in the subject), and scans the subject just  once  (unless  there
797           are  lookbehind  assertions).  However,  this algorithm does not return
798           captured substrings. A description of the two matching  algorithms  and
799           their  advantages  and disadvantages is given in the pcrematching docu-
800           mentation.
801    
802           In addition to the main compiling and  matching  functions,  there  are
803           convenience functions for extracting captured substrings from a subject
804           string that is matched by pcre_exec(). They are:
805    
806             pcre_copy_substring()
807             pcre_copy_named_substring()
808             pcre_get_substring()
809             pcre_get_named_substring()
810             pcre_get_substring_list()
811             pcre_get_stringnumber()
812             pcre_get_stringtable_entries()
813    
814           pcre_free_substring() and pcre_free_substring_list() are also provided,
815           to free the memory used for extracted strings.
816    
817           The  function  pcre_maketables()  is  used  to build a set of character
818           tables  in  the  current  locale   for   passing   to   pcre_compile(),
819           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
820           provided for specialist use.  Most  commonly,  no  special  tables  are
821           passed,  in  which case internal tables that are generated when PCRE is
822           built are used.
823    
824           The function pcre_fullinfo() is used to find out  information  about  a
825           compiled  pattern; pcre_info() is an obsolete version that returns only
826           some of the available information, but is retained for  backwards  com-
827           patibility.   The function pcre_version() returns a pointer to a string
828           containing the version of PCRE and its date of release.
829    
830           The function pcre_refcount() maintains a  reference  count  in  a  data
831           block  containing  a compiled pattern. This is provided for the benefit
832           of object-oriented applications.
833    
834           The global variables pcre_malloc and pcre_free  initially  contain  the
835           entry  points  of  the  standard malloc() and free() functions, respec-
836           tively. PCRE calls the memory management functions via these variables,
837           so  a  calling  program  can replace them if it wishes to intercept the
838           calls. This should be done before calling any PCRE functions.
839    
840           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
841           indirections  to  memory  management functions. These special functions
842           are used only when PCRE is compiled to use  the  heap  for  remembering
843           data, instead of recursive function calls, when running the pcre_exec()
844           function. See the pcrebuild documentation for  details  of  how  to  do
845           this.  It  is  a non-standard way of building PCRE, for use in environ-
846           ments that have limited stacks. Because of the greater  use  of  memory
847           management,  it  runs  more  slowly. Separate functions are provided so
848           that special-purpose external code can be  used  for  this  case.  When
849           used,  these  functions  are always called in a stack-like manner (last
850           obtained, first freed), and always for memory blocks of the same  size.
851           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
852           mentation.
853    
854           The global variable pcre_callout initially contains NULL. It can be set
855           by  the  caller  to  a "callout" function, which PCRE will then call at
856           specified points during a matching operation. Details are given in  the
857           pcrecallout documentation.
858    
859    
860    NEWLINES
861    
862           PCRE  supports five different conventions for indicating line breaks in
863           strings: a single CR (carriage return) character, a  single  LF  (line-
864           feed) character, the two-character sequence CRLF, any of the three pre-
865           ceding, or any Unicode newline sequence. The Unicode newline  sequences
866           are  the  three just mentioned, plus the single characters VT (vertical
867           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
868           separator, U+2028), and PS (paragraph separator, U+2029).
869    
870           Each  of  the first three conventions is used by at least one operating
871           system as its standard newline sequence. When PCRE is built, a  default
872           can  be  specified.  The default default is LF, which is the Unix stan-
873           dard. When PCRE is run, the default can be overridden,  either  when  a
874           pattern is compiled, or when it is matched.
875    
876           At compile time, the newline convention can be specified by the options
877           argument of pcre_compile(), or it can be specified by special  text  at
878           the start of the pattern itself; this overrides any other settings. See
879           the pcrepattern page for details of the special character sequences.
880    
881           In the PCRE documentation the word "newline" is used to mean "the char-
882           acter  or pair of characters that indicate a line break". The choice of
883           newline convention affects the handling of  the  dot,  circumflex,  and
884           dollar metacharacters, the handling of #-comments in /x mode, and, when
885           CRLF is a recognized line ending sequence, the match position  advance-
886           ment for a non-anchored pattern. There is more detail about this in the
887           section on pcre_exec() options below.
888    
889           The choice of newline convention does not affect the interpretation  of
890           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
891           which is controlled in a similar way, but by separate options.
892    
893    
894  MULTITHREADING  MULTITHREADING
895    
896       The PCRE functions can be used in  multi-threading  applica-         The PCRE functions can be used in  multi-threading  applications,  with
897       tions, with the proviso that the memory management functions         the  proviso  that  the  memory  management  functions  pointed  to  by
898       pointed to by pcre_malloc and  pcre_free,  and  the  callout         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
899       function  pointed  to  by  pcre_callout,  are  shared by all         callout function pointed to by pcre_callout, are shared by all threads.
900       threads.  
901           The  compiled form of a regular expression is not altered during match-
902       The compiled form of a regular  expression  is  not  altered         ing, so the same compiled pattern can safely be used by several threads
903       during  matching, so the same compiled pattern can safely be         at once.
904       used by several threads at once.  
905    
906    SAVING PRECOMPILED PATTERNS FOR LATER USE
907    
908           The compiled form of a regular expression can be saved and re-used at a
909           later time, possibly by a different program, and even on a  host  other
910           than  the  one  on  which  it  was  compiled.  Details are given in the
911           pcreprecompile documentation. However, compiling a  regular  expression
912           with  one version of PCRE for use with a different version is not guar-
913           anteed to work and may cause crashes.
914    
915    
916  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
917    
918       int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
919    
920           The function pcre_config() makes it possible for a PCRE client to  dis-
921           cover which optional features have been compiled into the PCRE library.
922           The pcrebuild documentation has more details about these optional  fea-
923           tures.
924    
925           The  first  argument  for pcre_config() is an integer, specifying which
926           information is required; the second argument is a pointer to a variable
927           into  which  the  information  is  placed. The following information is
928           available:
929    
930       The function pcre_config() makes  it  possible  for  a  PCRE           PCRE_CONFIG_UTF8
      client  to  discover  which optional features have been com-  
      piled into the PCRE library. The pcrebuild documentation has  
      more details about these optional features.  
931    
932       The first argument for pcre_config() is an integer, specify-         The output is an integer that is set to one if UTF-8 support is  avail-
933       ing  which information is required; the second argument is a         able; otherwise it is set to zero.
      pointer to a variable into which the information is  placed.  
      The following information is available:  
934    
935         PCRE_CONFIG_UTF8           PCRE_CONFIG_UNICODE_PROPERTIES
936    
937       The output is an integer that is set to one if UTF-8 support         The  output  is  an  integer  that is set to one if support for Unicode
938       is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
939    
940         PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
941    
942       The output is an integer that is set to  the  value  of  the         The output is an integer whose value specifies  the  default  character
943       code  that  is  used for the newline character. It is either         sequence  that is recognized as meaning "newline". The four values that
944       linefeed (10) or carriage return (13), and  should  normally         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
945       be the standard character for your operating system.         and  -1  for  ANY.  Though they are derived from ASCII, the same values
946           are returned in EBCDIC environments. The default should normally corre-
947           spond to the standard sequence for your operating system.
948    
949         PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_BSR
950    
951       The output is an integer that contains the number  of  bytes         The output is an integer whose value indicates what character sequences
952       used  for  internal linkage in compiled regular expressions.         the \R escape sequence matches by default. A value of 0 means  that  \R
953       The value is 2, 3, or 4. Larger values allow larger  regular         matches  any  Unicode  line ending sequence; a value of 1 means that \R
954       expressions  to be compiled, at the expense of slower match-         matches only CR, LF, or CRLF. The default can be overridden when a pat-
955       ing. The default value of 2 is sufficient for  all  but  the         tern is compiled or matched.
      most  massive patterns, since it allows the compiled pattern  
      to be up to 64K in size.  
956    
957         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_LINK_SIZE
958    
959       The output is an integer that contains the  threshold  above         The  output  is  an  integer that contains the number of bytes used for
960       which  the POSIX interface uses malloc() for output vectors.         internal linkage in compiled regular expressions. The value is 2, 3, or
961       Further details are given in the pcreposix documentation.         4.  Larger  values  allow larger regular expressions to be compiled, at
962           the expense of slower matching. The default value of  2  is  sufficient
963           for  all  but  the  most massive patterns, since it allows the compiled
964           pattern to be up to 64K in size.
965    
966         PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
967    
968       The output is an integer that gives the  default  limit  for         The output is an integer that contains the threshold  above  which  the
969       the   number  of  internal  matching  function  calls  in  a         POSIX  interface  uses malloc() for output vectors. Further details are
970       pcre_exec()  execution.  Further  details  are  given   with         given in the pcreposix documentation.
971       pcre_exec() below.  
972             PCRE_CONFIG_MATCH_LIMIT
973    
974           The output is a long integer that gives the default limit for the  num-
975           ber  of  internal  matching  function calls in a pcre_exec() execution.
976           Further details are given with pcre_exec() below.
977    
978             PCRE_CONFIG_MATCH_LIMIT_RECURSION
979    
980           The output is a long integer that gives the default limit for the depth
981           of   recursion  when  calling  the  internal  matching  function  in  a
982           pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
983           below.
984    
985             PCRE_CONFIG_STACKRECURSE
986    
987           The  output is an integer that is set to one if internal recursion when
988           running pcre_exec() is implemented by recursive function calls that use
989           the  stack  to remember their state. This is the usual way that PCRE is
990           compiled. The output is zero if PCRE was compiled to use blocks of data
991           on  the  heap  instead  of  recursive  function  calls.  In  this case,
992           pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
993           blocks on the heap, thus avoiding the use of the stack.
994    
995    
996  COMPILING A PATTERN  COMPILING A PATTERN
997    
998       pcre *pcre_compile(const char *pattern, int options,         pcre *pcre_compile(const char *pattern, int options,
999            const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
1000            const unsigned char *tableptr);              const unsigned char *tableptr);
1001    
1002       The function pcre_compile() is called to compile  a  pattern         pcre *pcre_compile2(const char *pattern, int options,
1003       into  an internal form. The pattern is a C string terminated              int *errorcodeptr,
1004       by a binary zero, and is passed in the argument  pattern.  A              const char **errptr, int *erroffset,
1005       pointer  to  a  single  block of memory that is obtained via              const unsigned char *tableptr);
1006       pcre_malloc is returned. This contains the compiled code and  
1007       related  data.  The  pcre  type  is defined for the returned         Either of the functions pcre_compile() or pcre_compile2() can be called
1008       block; this is a typedef for a structure whose contents  are         to compile a pattern into an internal form. The only difference between
1009       not  externally  defined. It is up to the caller to free the         the  two interfaces is that pcre_compile2() has an additional argument,
1010       memory when it is no longer required.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1011           avoid  too  much repetition, we refer just to pcre_compile() below, but
1012       Although the compiled code of a PCRE regex  is  relocatable,         the information applies equally to pcre_compile2().
1013       that is, it does not depend on memory location, the complete  
1014       pcre data block is not fully relocatable,  because  it  con-         The pattern is a C string terminated by a binary zero, and is passed in
1015       tains  a  copy of the tableptr argument, which is an address         the  pattern  argument.  A  pointer to a single block of memory that is
1016       (see below).         obtained via pcre_malloc is returned. This contains the  compiled  code
1017       The options argument contains independent bits  that  affect         and related data. The pcre type is defined for the returned block; this
1018       the  compilation.  It  should  be  zero  if  no  options are         is a typedef for a structure whose contents are not externally defined.
1019       required. Some of the options, in particular, those that are         It is up to the caller to free the memory (via pcre_free) when it is no
1020       compatible  with Perl, can also be set and unset from within         longer required.
1021       the pattern (see the detailed description of regular expres-  
1022       sions  in the pcrepattern documentation). For these options,         Although the compiled code of a PCRE regex is relocatable, that is,  it
1023       the contents of the options argument specifies their initial         does not depend on memory location, the complete pcre data block is not
1024       settings  at  the  start  of  compilation and execution. The         fully relocatable, because it may contain a copy of the tableptr  argu-
1025       PCRE_ANCHORED option can be set at the time of  matching  as         ment, which is an address (see below).
1026       well as at compile time.  
1027           The options argument contains various bit settings that affect the com-
1028       If errptr is NULL, pcre_compile() returns NULL  immediately.         pilation. It should be zero if no options are required.  The  available
1029       Otherwise, if compilation of a pattern fails, pcre_compile()         options  are  described  below. Some of them (in particular, those that
1030       returns NULL, and sets the variable pointed to by errptr  to         are compatible with Perl, but some others as well) can also be set  and
1031       point  to a textual error message. The offset from the start         unset  from  within  the  pattern  (see the detailed description in the
1032       of  the  pattern  to  the  character  where  the  error  was         pcrepattern documentation). For those options that can be different  in
1033       discovered   is   placed  in  the  variable  pointed  to  by         different  parts  of  the pattern, the contents of the options argument
1034       erroffset, which must not be NULL. If it  is,  an  immediate         specifies their settings at the start of compilation and execution. The
1035       error is given.         PCRE_ANCHORED,  PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and
1036           PCRE_NO_START_OPT options can be set at the time of matching as well as
1037       If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a         at compile time.
1038       default  set  of character tables which are built when it is  
1039       compiled, using the default C  locale.  Otherwise,  tableptr         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1040       must  be  the result of a call to pcre_maketables(). See the         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1041       section on locale support below.         sets the variable pointed to by errptr to point to a textual error mes-
1042           sage. This is a static string that is part of the library. You must not
1043       This code fragment shows a typical straightforward  call  to         try  to  free it. Normally, the offset from the start of the pattern to
1044       pcre_compile():         the byte that was being processed when  the  error  was  discovered  is
1045           placed  in the variable pointed to by erroffset, which must not be NULL
1046         pcre *re;         (if it is, an immediate error is given). However, for an invalid  UTF-8
1047         const char *error;         string,  the offset is that of the first byte of the failing character.
1048         int erroffset;         Also, some errors are not detected until checks are  carried  out  when
1049         re = pcre_compile(         the  whole  pattern  has been scanned; in these cases the offset passed
1050           "^A.*Z",          /* the pattern */         back is the length of the pattern.
1051           0,                /* default options */  
1052           &error,           /* for error message */         Note that the offset is in bytes, not characters, even in  UTF-8  mode.
1053           &erroffset,       /* for error offset */         It may sometimes point into the middle of a UTF-8 character.
1054           NULL);            /* use default character tables */  
1055           If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1056       The following option bits are defined:         codeptr argument is not NULL, a non-zero error code number is  returned
1057           via  this argument in the event of an error. This is in addition to the
1058         PCRE_ANCHORED         textual error message. Error codes and messages are listed below.
1059    
1060       If this bit is set, the pattern is forced to be  "anchored",         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1061       that is, it is constrained to match only at the first match-         character  tables  that  are  built  when  PCRE  is compiled, using the
1062       ing point in the string which is being searched  (the  "sub-         default C locale. Otherwise, tableptr must be an address  that  is  the
1063       ject string"). This effect can also be achieved by appropri-         result  of  a  call to pcre_maketables(). This value is stored with the
1064       ate constructs in the pattern itself, which is the only  way         compiled pattern, and used again by pcre_exec(), unless  another  table
1065       to do it in Perl.         pointer is passed to it. For more discussion, see the section on locale
1066           support below.
1067         PCRE_CASELESS  
1068           This code fragment shows a typical straightforward  call  to  pcre_com-
1069       If this bit is set, letters in the pattern match both  upper         pile():
1070       and  lower  case  letters.  It  is  equivalent  to Perl's /i  
1071       option, and it can be changed within a  pattern  by  a  (?i)           pcre *re;
1072       option setting.           const char *error;
1073             int erroffset;
1074         PCRE_DOLLAR_ENDONLY           re = pcre_compile(
1075               "^A.*Z",          /* the pattern */
1076       If this bit is set, a dollar metacharacter  in  the  pattern             0,                /* default options */
1077       matches  only at the end of the subject string. Without this             &error,           /* for error message */
1078       option, a dollar also matches immediately before  the  final             &erroffset,       /* for error offset */
1079       character  if it is a newline (but not before any other new-             NULL);            /* use default character tables */
1080       lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if  
1081       PCRE_MULTILINE is set. There is no equivalent to this option         The  following  names  for option bits are defined in the pcre.h header
1082       in Perl, and no way to set it within a pattern.         file:
1083    
1084         PCRE_DOTALL           PCRE_ANCHORED
1085    
1086       If this bit is  set,  a  dot  metacharater  in  the  pattern         If this bit is set, the pattern is forced to be "anchored", that is, it
1087       matches all characters, including newlines. Without it, new-         is  constrained to match only at the first matching point in the string
1088       lines are excluded. This option is equivalent to  Perl's  /s         that is being searched (the "subject string"). This effect can also  be
1089       option,  and  it  can  be changed within a pattern by a (?s)         achieved  by appropriate constructs in the pattern itself, which is the
1090       option setting. A negative class such as [^a] always matches         only way to do it in Perl.
1091       a  newline  character,  independent  of  the setting of this  
1092       option.           PCRE_AUTO_CALLOUT
1093    
1094         PCRE_EXTENDED         If this bit is set, pcre_compile() automatically inserts callout items,
1095           all  with  number  255, before each pattern item. For discussion of the
1096       If this bit is set, whitespace data characters in  the  pat-         callout facility, see the pcrecallout documentation.
1097       tern  are  totally  ignored  except when escaped or inside a  
1098       character class. Whitespace does not include the VT  charac-           PCRE_BSR_ANYCRLF
1099       ter  (code 11). In addition, characters between an unescaped           PCRE_BSR_UNICODE
1100       # outside a character class and the next newline  character,  
1101       inclusive, are also ignored. This is equivalent to Perl's /x         These options (which are mutually exclusive) control what the \R escape
1102       option, and it can be changed within a  pattern  by  a  (?x)         sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1103       option setting.         or to match any Unicode newline sequence. The default is specified when
1104           PCRE is built. It can be overridden from within the pattern, or by set-
1105       This option makes it possible  to  include  comments  inside         ting an option when a compiled pattern is matched.
1106       complicated patterns.  Note, however, that this applies only  
1107       to data characters. Whitespace characters may  never  appear           PCRE_CASELESS
1108       within special character sequences in a pattern, for example  
1109       within the sequence (?( which introduces a conditional  sub-         If this bit is set, letters in the pattern match both upper  and  lower
1110       pattern.         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1111           changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1112         PCRE_EXTRA         always  understands the concept of case for characters whose values are
1113           less than 128, so caseless matching is always possible. For  characters
1114       This option was invented in  order  to  turn  on  additional         with  higher  values,  the concept of case is supported if PCRE is com-
1115       functionality of PCRE that is incompatible with Perl, but it         piled with Unicode property support, but not otherwise. If you want  to
1116       is currently of very little use. When set, any backslash  in         use  caseless  matching  for  characters 128 and above, you must ensure
1117       a  pattern  that is followed by a letter that has no special         that PCRE is compiled with Unicode property support  as  well  as  with
1118       meaning causes an error, thus reserving  these  combinations         UTF-8 support.
1119       for  future  expansion.  By default, as in Perl, a backslash  
1120       followed by a letter with no special meaning is treated as a           PCRE_DOLLAR_ENDONLY
1121       literal.  There  are at present no other features controlled  
1122       by this option. It can also be set by a (?X) option  setting         If  this bit is set, a dollar metacharacter in the pattern matches only
1123       within a pattern.         at the end of the subject string. Without this option,  a  dollar  also
1124           matches  immediately before a newline at the end of the string (but not
1125         PCRE_MULTILINE         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1126           if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1127       By default, PCRE treats the subject string as consisting  of         Perl, and no way to set it within a pattern.
1128       a  single "line" of characters (even if it actually contains  
1129       several newlines). The "start  of  line"  metacharacter  (^)           PCRE_DOTALL
1130       matches  only  at the start of the string, while the "end of  
1131       line" metacharacter ($) matches  only  at  the  end  of  the         If this bit is set, a dot metacharacter in the pattern matches a  char-
1132       string,    or   before   a   terminating   newline   (unless         acter of any value, including one that indicates a newline. However, it
1133       PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.         only ever matches one character, even if newlines are  coded  as  CRLF.
1134           Without  this option, a dot does not match when the current position is
1135       When PCRE_MULTILINE it is set, the "start of line" and  "end         at a newline. This option is equivalent to Perl's /s option, and it can
1136       of  line"  constructs match immediately following or immedi-         be  changed within a pattern by a (?s) option setting. A negative class
1137       ately before any newline  in  the  subject  string,  respec-         such as [^a] always matches newline characters, independent of the set-
1138       tively,  as  well  as  at  the  very  start and end. This is         ting of this option.
1139       equivalent to Perl's /m option, and it can be changed within  
1140       a  pattern  by  a  (?m) option setting. If there are no "\n"           PCRE_DUPNAMES
1141       characters in a subject string, or no occurrences of ^ or  $  
1142       in a pattern, setting PCRE_MULTILINE has no effect.         If  this  bit is set, names used to identify capturing subpatterns need
1143           not be unique. This can be helpful for certain types of pattern when it
1144         PCRE_NO_AUTO_CAPTURE         is  known  that  only  one instance of the named subpattern can ever be
1145           matched. There are more details of named subpatterns  below;  see  also
1146       If this option is set, it disables the use of numbered  cap-         the pcrepattern documentation.
1147       turing  parentheses  in the pattern. Any opening parenthesis  
1148       that is not followed by ? behaves as if it were followed  by           PCRE_EXTENDED
1149       ?:  but  named  parentheses  can still be used for capturing  
1150       (and they acquire numbers in the usual  way).  There  is  no         If  this  bit  is  set,  whitespace  data characters in the pattern are
1151       equivalent of this option in Perl.         totally ignored except when escaped or inside a character class. White-
1152           space does not include the VT character (code 11). In addition, charac-
1153         PCRE_UNGREEDY         ters between an unescaped # outside a character class and the next new-
1154           line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1155       This option inverts the "greediness" of the  quantifiers  so         option, and it can be changed within a pattern by a  (?x)  option  set-
1156       that  they  are  not greedy by default, but become greedy if         ting.
1157       followed by "?". It is not compatible with Perl. It can also  
1158       be set by a (?U) option setting within the pattern.         Which  characters  are  interpreted  as  newlines  is controlled by the
1159           options passed to pcre_compile() or by a special sequence at the  start
1160         PCRE_UTF8         of  the  pattern, as described in the section entitled "Newline conven-
1161           tions" in the pcrepattern documentation. Note that the end of this type
1162       This option causes PCRE to regard both the pattern  and  the         of  comment  is  a  literal  newline  sequence  in  the pattern; escape
1163       subject  as  strings  of UTF-8 characters instead of single-         sequences that happen to represent a newline do not count.
1164       byte character strings. However, it  is  available  only  if  
1165       PCRE  has  been  built to include UTF-8 support. If not, the         This option makes it possible to include  comments  inside  complicated
1166       use of this option provokes an error. Details  of  how  this         patterns.   Note,  however,  that this applies only to data characters.
1167       option  changes  the behaviour of PCRE are given in the sec-         Whitespace  characters  may  never  appear  within  special   character
1168       tion on UTF-8 support in the main pcre page.         sequences in a pattern, for example within the sequence (?( that intro-
1169           duces a conditional subpattern.
1170    
1171             PCRE_EXTRA
1172    
1173           This option was invented in order to turn on  additional  functionality
1174           of  PCRE  that  is  incompatible with Perl, but it is currently of very
1175           little use. When set, any backslash in a pattern that is followed by  a
1176           letter  that  has  no  special  meaning causes an error, thus reserving
1177           these combinations for future expansion. By  default,  as  in  Perl,  a
1178           backslash  followed by a letter with no special meaning is treated as a
1179           literal. (Perl can, however, be persuaded to give an error for this, by
1180           running  it with the -w option.) There are at present no other features
1181           controlled by this option. It can also be set by a (?X) option  setting
1182           within a pattern.
1183    
1184             PCRE_FIRSTLINE
1185    
1186           If  this  option  is  set,  an  unanchored pattern is required to match
1187           before or at the first  newline  in  the  subject  string,  though  the
1188           matched text may continue over the newline.
1189    
1190             PCRE_JAVASCRIPT_COMPAT
1191    
1192           If this option is set, PCRE's behaviour is changed in some ways so that
1193           it is compatible with JavaScript rather than Perl. The changes  are  as
1194           follows:
1195    
1196           (1)  A  lone  closing square bracket in a pattern causes a compile-time
1197           error, because this is illegal in JavaScript (by default it is  treated
1198           as a data character). Thus, the pattern AB]CD becomes illegal when this
1199           option is set.
1200    
1201           (2) At run time, a back reference to an unset subpattern group  matches
1202           an  empty  string (by default this causes the current matching alterna-
1203           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1204           set  (assuming  it can find an "a" in the subject), whereas it fails by
1205           default, for Perl compatibility.
1206    
1207             PCRE_MULTILINE
1208    
1209           By default, PCRE treats the subject string as consisting  of  a  single
1210           line  of characters (even if it actually contains newlines). The "start
1211           of line" metacharacter (^) matches only at the  start  of  the  string,
1212           while  the  "end  of line" metacharacter ($) matches only at the end of
1213           the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1214           is set). This is the same as Perl.
1215    
1216           When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1217           constructs match immediately following or immediately  before  internal
1218           newlines  in  the  subject string, respectively, as well as at the very
1219           start and end. This is equivalent to Perl's /m option, and  it  can  be
1220           changed within a pattern by a (?m) option setting. If there are no new-
1221           lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1222           setting PCRE_MULTILINE has no effect.
1223    
1224             PCRE_NEWLINE_CR
1225             PCRE_NEWLINE_LF
1226             PCRE_NEWLINE_CRLF
1227             PCRE_NEWLINE_ANYCRLF
1228             PCRE_NEWLINE_ANY
1229    
1230           These  options  override the default newline definition that was chosen
1231           when PCRE was built. Setting the first or the second specifies  that  a
1232           newline  is  indicated  by a single character (CR or LF, respectively).
1233           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1234           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1235           that any of the three preceding sequences should be recognized. Setting
1236           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1237           recognized. The Unicode newline sequences are the three just mentioned,
1238           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1239           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1240           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1241           UTF-8 mode.
1242    
1243           The newline setting in the  options  word  uses  three  bits  that  are
1244           treated as a number, giving eight possibilities. Currently only six are
1245           used (default plus the five values above). This means that if  you  set
1246           more  than one newline option, the combination may or may not be sensi-
1247           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1248           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1249           cause an error.
1250    
1251           The only time that a line break in a pattern  is  specially  recognized
1252           when  compiling  is when PCRE_EXTENDED is set. CR and LF are whitespace
1253           characters, and so are ignored in this mode. Also, an unescaped #  out-
1254           side  a  character class indicates a comment that lasts until after the
1255           next line break sequence. In other circumstances, line break  sequences
1256           in patterns are treated as literal data.
1257    
1258           The newline option that is set at compile time becomes the default that
1259           is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1260    
1261             PCRE_NO_AUTO_CAPTURE
1262    
1263           If this option is set, it disables the use of numbered capturing paren-
1264           theses  in the pattern. Any opening parenthesis that is not followed by
1265           ? behaves as if it were followed by ?: but named parentheses can  still
1266           be  used  for  capturing  (and  they acquire numbers in the usual way).
1267           There is no equivalent of this option in Perl.
1268    
1269             NO_START_OPTIMIZE
1270    
1271           This is an option that acts at matching time; that is, it is really  an
1272           option  for  pcre_exec()  or  pcre_dfa_exec().  If it is set at compile
1273           time, it is remembered with the compiled pattern and assumed at  match-
1274           ing  time.  For  details  see  the discussion of PCRE_NO_START_OPTIMIZE
1275           below.
1276    
1277             PCRE_UCP
1278    
1279           This option changes the way PCRE processes \B, \b, \D, \d, \S, \s,  \W,
1280           \w,  and  some  of  the POSIX character classes. By default, only ASCII
1281           characters are recognized, but if PCRE_UCP is set,  Unicode  properties
1282           are  used instead to classify characters. More details are given in the
1283           section on generic character types in the pcrepattern page. If you  set
1284           PCRE_UCP,  matching  one of the items it affects takes much longer. The
1285           option is available only if PCRE has been compiled with  Unicode  prop-
1286           erty support.
1287    
1288             PCRE_UNGREEDY
1289    
1290           This  option  inverts  the "greediness" of the quantifiers so that they
1291           are not greedy by default, but become greedy if followed by "?". It  is
1292           not  compatible  with Perl. It can also be set by a (?U) option setting
1293           within the pattern.
1294    
1295             PCRE_UTF8
1296    
1297           This option causes PCRE to regard both the pattern and the  subject  as
1298           strings  of  UTF-8 characters instead of single-byte character strings.
1299           However, it is available only when PCRE is built to include UTF-8  sup-
1300           port.  If not, the use of this option provokes an error. Details of how
1301           this option changes the behaviour of PCRE are given in the  pcreunicode
1302           page.
1303    
1304             PCRE_NO_UTF8_CHECK
1305    
1306           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1307           automatically checked. There is a  discussion  about  the  validity  of
1308           UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1309           bytes is found, pcre_compile() returns an error. If  you  already  know
1310           that your pattern is valid, and you want to skip this check for perfor-
1311           mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1312           set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1313           undefined. It may cause your program to crash. Note  that  this  option
1314           can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1315           UTF-8 validity checking of subject strings.
1316    
1317    
1318    COMPILATION ERROR CODES
1319    
1320           The following table lists the error  codes  than  may  be  returned  by
1321           pcre_compile2(),  along with the error messages that may be returned by
1322           both compiling functions. As PCRE has developed, some error codes  have
1323           fallen out of use. To avoid confusion, they have not been re-used.
1324    
1325              0  no error
1326              1  \ at end of pattern
1327              2  \c at end of pattern
1328              3  unrecognized character follows \
1329              4  numbers out of order in {} quantifier
1330              5  number too big in {} quantifier
1331              6  missing terminating ] for character class
1332              7  invalid escape sequence in character class
1333              8  range out of order in character class
1334              9  nothing to repeat
1335             10  [this code is not in use]
1336             11  internal error: unexpected repeat
1337             12  unrecognized character after (? or (?-
1338             13  POSIX named classes are supported only within a class
1339             14  missing )
1340             15  reference to non-existent subpattern
1341             16  erroffset passed as NULL
1342             17  unknown option bit(s) set
1343             18  missing ) after comment
1344             19  [this code is not in use]
1345             20  regular expression is too large
1346             21  failed to get memory
1347             22  unmatched parentheses
1348             23  internal error: code overflow
1349             24  unrecognized character after (?<
1350             25  lookbehind assertion is not fixed length
1351             26  malformed number or name after (?(
1352             27  conditional group contains more than two branches
1353             28  assertion expected after (?(
1354             29  (?R or (?[+-]digits must be followed by )
1355             30  unknown POSIX class name
1356             31  POSIX collating elements are not supported
1357             32  this version of PCRE is not compiled with PCRE_UTF8 support
1358             33  [this code is not in use]
1359             34  character value in \x{...} sequence is too large
1360             35  invalid condition (?(0)
1361             36  \C not allowed in lookbehind assertion
1362             37  PCRE does not support \L, \l, \N{name}, \U, or \u
1363             38  number after (?C is > 255
1364             39  closing ) for (?C expected
1365             40  recursive call could loop indefinitely
1366             41  unrecognized character after (?P
1367             42  syntax error in subpattern name (missing terminator)
1368             43  two named subpatterns have the same name
1369             44  invalid UTF-8 string
1370             45  support for \P, \p, and \X has not been compiled
1371             46  malformed \P or \p sequence
1372             47  unknown property name after \P or \p
1373             48  subpattern name is too long (maximum 32 characters)
1374             49  too many named subpatterns (maximum 10000)
1375             50  [this code is not in use]
1376             51  octal value is greater than \377 (not in UTF-8 mode)
1377             52  internal error: overran compiling workspace
1378             53  internal error: previously-checked referenced subpattern
1379                   not found
1380             54  DEFINE group contains more than one branch
1381             55  repeating a DEFINE group is not allowed
1382             56  inconsistent NEWLINE options
1383             57  \g is not followed by a braced, angle-bracketed, or quoted
1384                   name/number or by a plain number
1385             58  a numbered reference must not be zero
1386             59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1387             60  (*VERB) not recognized
1388             61  number is too big
1389             62  subpattern name expected
1390             63  digit expected after (?+
1391             64  ] is an invalid data character in JavaScript compatibility mode
1392             65  different names for subpatterns of the same number are
1393                   not allowed
1394             66  (*MARK) must have an argument
1395             67  this version of PCRE is not compiled with PCRE_UCP support
1396             68  \c must be followed by an ASCII character
1397             69  \k is not followed by a braced, angle-bracketed, or quoted name
1398    
1399           The  numbers  32  and 10000 in errors 48 and 49 are defaults; different
1400           values may be used if the limits were changed when PCRE was built.
1401    
1402    
1403  STUDYING A PATTERN  STUDYING A PATTERN
1404    
1405       pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1406            const char **errptr);              const char **errptr);
1407    
1408       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
1409       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
1410       the time taken for matching. The function pcre_study() takes         matching. The function pcre_study() takes a pointer to a compiled  pat-
1411       a  pointer  to  a compiled pattern as its first argument. If         tern as its first argument. If studying the pattern produces additional
1412       studing the pattern  produces  additional  information  that         information that will help speed up matching,  pcre_study()  returns  a
1413       will  help speed up matching, pcre_study() returns a pointer         pointer  to a pcre_extra block, in which the study_data field points to
1414       to a pcre_extra block, in which the study_data field  points         the results of the study.
1415       to the results of the study.  
1416           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1417       The  returned  value  from  a  pcre_study()  can  be  passed         pcre_exec()  or  pcre_dfa_exec(). However, a pcre_extra block also con-
1418       directly  to pcre_exec(). However, the pcre_extra block also         tains other fields that can be set by the caller before  the  block  is
1419       contains other fields that can be set by the  caller  before         passed; these are described below in the section on matching a pattern.
1420       the  block is passed; these are described below. If studying  
1421       the pattern does not  produce  any  additional  information,         If  studying  the  pattern  does  not  produce  any useful information,
1422       pcre_study() returns NULL. In that circumstance, if the cal-         pcre_study() returns NULL. In that circumstance, if the calling program
1423       ling program wants to pass  some  of  the  other  fields  to         wants   to   pass   any   of   the   other  fields  to  pcre_exec()  or
1424       pcre_exec(), it must set up its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1425    
1426       The second argument contains option  bits.  At  present,  no         The second argument of pcre_study() contains option bits.  At  present,
1427       options  are  defined  for  pcre_study(),  and this argument         no options are defined, and this argument should always be zero.
1428       should always be zero.  
1429           The  third argument for pcre_study() is a pointer for an error message.
1430       The third argument for pcre_study()  is  a  pointer  for  an         If studying succeeds (even if no data is  returned),  the  variable  it
1431       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
1432       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
1433       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
1434       fore  test  the  error  pointer  for  NULL   after   calling         after calling pcre_study(), to be sure that it has run successfully.
1435       pcre_study(), to be sure that it has run successfully.  
1436           This is a typical call to pcre_study():
1437       This is a typical call to pcre_study():  
1438             pcre_extra *pe;
1439         pcre_extra *pe;           pe = pcre_study(
1440         pe = pcre_study(             re,             /* result of pcre_compile() */
1441           re,             /* result of pcre_compile() */             0,              /* no options exist */
1442           0,              /* no options exist */             &error);        /* set to NULL or points to a message */
1443           &error);        /* set to NULL or points to a message */  
1444           Studying a pattern does two things: first, a lower bound for the length
1445       At present, studying a  pattern  is  useful  only  for  non-         of subject string that is needed to match the pattern is computed. This
1446       anchored  patterns  that do not have a single fixed starting         does not mean that there are any strings of that length that match, but
1447       character. A  bitmap  of  possible  starting  characters  is         it  does  guarantee that no shorter strings match. The value is used by
1448       created.         pcre_exec() and pcre_dfa_exec() to avoid  wasting  time  by  trying  to
1449           match  strings  that are shorter than the lower bound. You can find out
1450           the value in a calling program via the pcre_fullinfo() function.
1451    
1452           Studying a pattern is also useful for non-anchored patterns that do not
1453           have  a  single fixed starting character. A bitmap of possible starting
1454           bytes is created. This speeds up finding a position in the  subject  at
1455           which to start matching.
1456    
1457           The  two  optimizations  just  described can be disabled by setting the
1458           PCRE_NO_START_OPTIMIZE   option    when    calling    pcre_exec()    or
1459           pcre_dfa_exec().  You  might  want  to do this if your pattern contains
1460           callouts or (*MARK), and you want to make use of  these  facilities  in
1461           cases  where  matching fails. See the discussion of PCRE_NO_START_OPTI-
1462           MIZE below.
1463    
1464    
1465  LOCALE SUPPORT  LOCALE SUPPORT
1466    
1467       PCRE handles caseless matching, and determines whether char-         PCRE handles caseless matching, and determines whether  characters  are
1468       acters  are  letters, digits, or whatever, by reference to a         letters,  digits, or whatever, by reference to a set of tables, indexed
1469       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
1470       to characters with codes less than 256. The library contains         characters  with  codes  less than 128. By default, higher-valued codes
1471       a default set of tables that is created  in  the  default  C         never match escapes such as \w or \d, but they can be tested with \p if
1472       locale  when  PCRE  is compiled. This is used when the final         PCRE  is  built with Unicode character property support. Alternatively,
1473       argument of pcre_compile() is NULL, and  is  sufficient  for         the PCRE_UCP option can be set at compile  time;  this  causes  \w  and
1474       many applications.         friends to use Unicode property support instead of built-in tables. The
1475           use of locales with Unicode is discouraged. If you are handling charac-
1476       An alternative set of tables can, however, be supplied. Such         ters  with codes greater than 128, you should either use UTF-8 and Uni-
1477       tables  are built by calling the pcre_maketables() function,         code, or use locales, but not try to mix the two.
1478       which has no arguments, in the relevant locale.  The  result  
1479       can  then be passed to pcre_compile() as often as necessary.         PCRE contains an internal set of tables that are used  when  the  final
1480       For example, to build and use tables  that  are  appropriate         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1481       for  the French locale (where accented characters with codes         applications.  Normally, the internal tables recognize only ASCII char-
1482       greater than 128 are treated as letters), the following code         acters. However, when PCRE is built, it is possible to cause the inter-
1483       could be used:         nal tables to be rebuilt in the default "C" locale of the local system,
1484           which may cause them to be different.
1485         setlocale(LC_CTYPE, "fr");  
1486         tables = pcre_maketables();         The  internal tables can always be overridden by tables supplied by the
1487         re = pcre_compile(..., tables);         application that calls PCRE. These may be created in a different locale
1488           from  the  default.  As more and more applications change to using Uni-
1489       The  tables  are  built  in  memory  that  is  obtained  via         code, the need for this locale support is expected to die away.
1490       pcre_malloc.  The  pointer that is passed to pcre_compile is  
1491       saved with the compiled pattern, and  the  same  tables  are         External tables are built by calling  the  pcre_maketables()  function,
1492       used via this pointer by pcre_study() and pcre_exec(). Thus,         which  has no arguments, in the relevant locale. The result can then be
1493       for any single pattern, compilation, studying  and  matching         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1494       all happen in the same locale, but different patterns can be         example,  to  build  and use tables that are appropriate for the French
1495       compiled in different locales. It is the caller's  responsi-         locale (where accented characters with  values  greater  than  128  are
1496       bility  to  ensure  that  the  memory  containing the tables         treated as letters), the following code could be used:
1497       remains available for as long as it is needed.  
1498             setlocale(LC_CTYPE, "fr_FR");
1499             tables = pcre_maketables();
1500             re = pcre_compile(..., tables);
1501    
1502           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1503           if you are using Windows, the name for the French locale is "french".
1504    
1505           When pcre_maketables() runs, the tables are built  in  memory  that  is
1506           obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1507           that the memory containing the tables remains available for as long  as
1508           it is needed.
1509    
1510           The pointer that is passed to pcre_compile() is saved with the compiled
1511           pattern, and the same tables are used via this pointer by  pcre_study()
1512           and normally also by pcre_exec(). Thus, by default, for any single pat-
1513           tern, compilation, studying and matching all happen in the same locale,
1514           but different patterns can be compiled in different locales.
1515    
1516           It  is  possible to pass a table pointer or NULL (indicating the use of
1517           the internal tables) to pcre_exec(). Although  not  intended  for  this
1518           purpose,  this facility could be used to match a pattern in a different
1519           locale from the one in which it was compiled. Passing table pointers at
1520           run time is discussed below in the section on matching a pattern.
1521    
1522    
1523  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
1524    
1525       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1526            int what, void *where);              int what, void *where);
1527    
1528       The pcre_fullinfo() function  returns  information  about  a         The  pcre_fullinfo() function returns information about a compiled pat-
1529       compiled pattern. It replaces the obsolete pcre_info() func-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1530       tion, which is nevertheless retained for backwards compabil-         less retained for backwards compability (and is documented below).
1531       ity (and is documented below).  
1532           The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1533       The first argument for pcre_fullinfo() is a pointer  to  the         pattern. The second argument is the result of pcre_study(), or NULL  if
1534       compiled  pattern.  The  second  argument  is  the result of         the  pattern  was not studied. The third argument specifies which piece
1535       pcre_study(), or NULL if the pattern was  not  studied.  The         of information is required, and the fourth argument is a pointer  to  a
1536       third  argument  specifies  which  piece  of  information is         variable  to  receive  the  data. The yield of the function is zero for
1537       required, and the fourth argument is a pointer to a variable         success, or one of the following negative numbers:
1538       to  receive  the data. The yield of the function is zero for  
1539       success, or one of the following negative numbers:           PCRE_ERROR_NULL       the argument code was NULL
1540                                   the argument where was NULL
1541         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1542                               the argument where was NULL           PCRE_ERROR_BADOPTION  the value of what was invalid
1543         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1544         PCRE_ERROR_BADOPTION  the value of what was invalid         The "magic number" is placed at the start of each compiled  pattern  as
1545           an  simple check against passing an arbitrary memory pointer. Here is a
1546       Here is a typical call of  pcre_fullinfo(),  to  obtain  the         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1547       length of the compiled pattern:         pattern:
1548    
1549         int rc;           int rc;
1550         unsigned long int length;           size_t length;
1551         rc = pcre_fullinfo(           rc = pcre_fullinfo(
1552           re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1553           pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1554           PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1555           &length);         /* where to put the data */             &length);         /* where to put the data */
1556    
1557       The possible values for the third argument  are  defined  in         The  possible  values for the third argument are defined in pcre.h, and
1558       pcre.h, and are as follows:         are as follows:
1559    
1560         PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1561    
1562       Return the number of the highest back reference in the  pat-         Return the number of the highest back reference  in  the  pattern.  The
1563       tern.  The  fourth argument should point to an int variable.         fourth  argument  should  point to an int variable. Zero is returned if
1564       Zero is returned if there are no back references.         there are no back references.
1565    
1566         PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1567    
1568       Return the number of capturing subpatterns in  the  pattern.         Return the number of capturing subpatterns in the pattern.  The  fourth
1569       The fourth argument should point to an int variable.         argument should point to an int variable.
1570    
1571         PCRE_INFO_FIRSTBYTE           PCRE_INFO_DEFAULT_TABLES
1572    
1573       Return information about  the  first  byte  of  any  matched         Return  a pointer to the internal default character tables within PCRE.
1574       string,  for a non-anchored pattern. (This option used to be         The fourth argument should point to an unsigned char *  variable.  This
1575       called PCRE_INFO_FIRSTCHAR; the old name is still recognized         information call is provided for internal use by the pcre_study() func-
1576       for backwards compatibility.)         tion. External callers can cause PCRE to use  its  internal  tables  by
1577           passing a NULL table pointer.
1578       If there is a fixed first byte, e.g. from a pattern such  as  
1579       (cat|cow|coyote),  it  is returned in the integer pointed to           PCRE_INFO_FIRSTBYTE
1580       by where. Otherwise, if either  
1581           Return  information  about  the first byte of any matched string, for a
1582       (a) the pattern was compiled with the PCRE_MULTILINE option,         non-anchored pattern. The fourth argument should point to an int  vari-
1583       and every branch starts with "^", or         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1584           is still recognized for backwards compatibility.)
1585       (b) every  branch  of  the  pattern  starts  with  ".*"  and  
1586       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
1587       anchored),         (cat|cow|coyote), its value is returned. Otherwise, if either
1588    
1589       -1 is returned, indicating that the pattern matches only  at         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1590       the  start  of  a subject string or after any newline within         branch starts with "^", or
1591       the string. Otherwise -2 is returned. For anchored patterns,  
1592       -2 is returned.         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1593           set (if it were set, the pattern would be anchored),
1594         PCRE_INFO_FIRSTTABLE  
1595           -1  is  returned, indicating that the pattern matches only at the start
1596       If the pattern was studied, and this resulted  in  the  con-         of a subject string or after any newline within the  string.  Otherwise
1597       struction of a 256-bit table indicating a fixed set of bytes         -2 is returned. For anchored patterns, -2 is returned.
1598       for the first byte in any matching string, a pointer to  the  
1599       table  is  returned.  Otherwise NULL is returned. The fourth           PCRE_INFO_FIRSTTABLE
1600       argument should point to an unsigned char * variable.  
1601           If  the pattern was studied, and this resulted in the construction of a
1602         PCRE_INFO_LASTLITERAL         256-bit table indicating a fixed set of bytes for the first byte in any
1603           matching  string, a pointer to the table is returned. Otherwise NULL is
1604       Return the value of the rightmost  literal  byte  that  must         returned. The fourth argument should point to an unsigned char *  vari-
1605       exist  in  any  matched  string, other than at its start, if         able.
1606       such a byte has been recorded. The  fourth  argument  should  
1607       point  to  an  int variable. If there is no such byte, -1 is           PCRE_INFO_HASCRORLF
1608       returned. For anchored patterns,  a  last  literal  byte  is  
1609       recorded  only  if  it follows something of variable length.         Return  1  if  the  pattern  contains any explicit matches for CR or LF
1610       For example, for the pattern /^a\d+z\d+/ the returned  value         characters, otherwise 0. The fourth argument should  point  to  an  int
1611       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
1612           \r or \n.
1613         PCRE_INFO_NAMECOUNT  
1614         PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_JCHANGED
1615         PCRE_INFO_NAMETABLE  
1616           Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1617       PCRE supports the use of named as well as numbered capturing         otherwise  0. The fourth argument should point to an int variable. (?J)
1618       parentheses. The names are just an additional way of identi-         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1619       fying the parentheses,  which  still  acquire  a  number.  A  
1620       caller  that  wants  to extract data from a named subpattern           PCRE_INFO_LASTLITERAL
1621       must convert the name to a number in  order  to  access  the  
1622       correct  pointers  in  the  output  vector  (described  with         Return the value of the rightmost literal byte that must exist  in  any
1623       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
1624       these  three  values  to  obtain  the name-to-number mapping         recorded. The fourth argument should point to an int variable. If there
1625       table for the pattern.         is  no such byte, -1 is returned. For anchored patterns, a last literal
1626           byte is recorded only if it follows something of variable  length.  For
1627       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
1628       PCRE_INFO_NAMECOUNT   gives   the  number  of  entries,  and         /^a\dz\d/ the returned value is -1.
1629       PCRE_INFO_NAMEENTRYSIZE gives the size of each  entry;  both  
1630       of  these return an int value. The entry size depends on the           PCRE_INFO_MINLENGTH
1631       length of the longest name.  PCRE_INFO_NAMETABLE  returns  a  
1632       pointer to the first entry of the table (a pointer to char).         If the pattern was studied and a minimum length  for  matching  subject
1633       The first two bytes of each entry are the number of the cap-         strings  was  computed,  its  value is returned. Otherwise the returned
1634       turing parenthesis, most significant byte first. The rest of         value is -1. The value is a number of characters, not bytes  (this  may
1635       the entry is the corresponding name,  zero  terminated.  The         be  relevant in UTF-8 mode). The fourth argument should point to an int
1636       names  are  in alphabetical order. For example, consider the         variable. A non-negative value is a lower bound to the  length  of  any
1637       following pattern (assume PCRE_EXTENDED  is  set,  so  white         matching  string.  There  may not be any strings of that length that do
1638       space - including newlines - is ignored):         actually match, but every string that does match is at least that long.
1639    
1640         (?P<date> (?P<year>(\d\d)?\d\d) -           PCRE_INFO_NAMECOUNT
1641         (?P<month>\d\d) - (?P<day>\d\d) )           PCRE_INFO_NAMEENTRYSIZE
1642             PCRE_INFO_NAMETABLE
1643       There are four named subpatterns,  so  the  table  has  four  
1644       entries,  and  each  entry in the table is eight bytes long.         PCRE supports the use of named as well as numbered capturing  parenthe-
1645       The table is as follows, with non-printing  bytes  shows  in         ses.  The names are just an additional way of identifying the parenthe-
1646       hex, and undefined bytes shown as ??:         ses, which still acquire numbers. Several convenience functions such as
1647           pcre_get_named_substring()  are  provided  for extracting captured sub-
1648         00 01 d  a  t  e  00 ??         strings by name. It is also possible to extract the data  directly,  by
1649         00 05 d  a  y  00 ?? ??         first  converting  the  name to a number in order to access the correct
1650         00 04 m  o  n  t  h  00         pointers in the output vector (described with pcre_exec() below). To do
1651         00 02 y  e  a  r  00 ??         the  conversion,  you  need  to  use  the  name-to-number map, which is
1652           described by these three values.
1653       When writing code to extract data  from  named  subpatterns,  
1654       remember  that the length of each entry may be different for         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1655       each compiled pattern.         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1656           of each entry; both of these  return  an  int  value.  The  entry  size
1657         PCRE_INFO_OPTIONS         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1658           a pointer to the first entry of the table  (a  pointer  to  char).  The
1659       Return a copy of the options with which the pattern was com-         first two bytes of each entry are the number of the capturing parenthe-
1660       piled.  The fourth argument should point to an unsigned long         sis, most significant byte first. The rest of the entry is  the  corre-
1661       int variable. These option bits are those specified  in  the         sponding name, zero terminated.
1662       call  to  pcre_compile(),  modified  by any top-level option  
1663       settings within the pattern itself.         The  names are in alphabetical order. Duplicate names may appear if (?|
1664           is used to create multiple groups with the same number, as described in
1665       A pattern is automatically anchored by PCRE if  all  of  its         the  section  on  duplicate subpattern numbers in the pcrepattern page.
1666       top-level alternatives begin with one of the following:         Duplicate names for subpatterns with different  numbers  are  permitted
1667           only  if  PCRE_DUPNAMES  is  set. In all cases of duplicate names, they
1668         ^     unless PCRE_MULTILINE is set         appear in the table in the order in which they were found in  the  pat-
1669         \A    always         tern.  In  the  absence  of (?| this is the order of increasing number;
1670         \G    always         when (?| is used this is not necessarily the case because later subpat-
1671         .*    if PCRE_DOTALL is set and there are no back         terns may have lower numbers.
1672                 references to the subpattern in which .* appears  
1673           As  a  simple  example of the name/number table, consider the following
1674       For such patterns, the  PCRE_ANCHORED  bit  is  set  in  the         pattern (assume PCRE_EXTENDED is set, so white space -  including  new-
1675       options returned by pcre_fullinfo().         lines - is ignored):
1676    
1677         PCRE_INFO_SIZE           (?<date> (?<year>(\d\d)?\d\d) -
1678             (?<month>\d\d) - (?<day>\d\d) )
1679       Return the size of the compiled pattern, that is, the  value  
1680       that  was  passed as the argument to pcre_malloc() when PCRE         There  are  four  named subpatterns, so the table has four entries, and
1681       was getting memory in which to place the compiled data.  The         each entry in the table is eight bytes long. The table is  as  follows,
1682       fourth argument should point to a size_t variable.         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1683           as ??:
1684         PCRE_INFO_STUDYSIZE  
1685             00 01 d  a  t  e  00 ??
1686       Returns the size  of  the  data  block  pointed  to  by  the           00 05 d  a  y  00 ?? ??
1687       study_data  field  in a pcre_extra block. That is, it is the           00 04 m  o  n  t  h  00
1688       value that was passed to pcre_malloc() when PCRE was getting           00 02 y  e  a  r  00 ??
1689       memory into which to place the data created by pcre_study().  
1690       The fourth argument should point to a size_t variable.         When writing code to extract data  from  named  subpatterns  using  the
1691           name-to-number  map,  remember that the length of the entries is likely
1692           to be different for each compiled pattern.
1693    
1694             PCRE_INFO_OKPARTIAL
1695    
1696           Return 1  if  the  pattern  can  be  used  for  partial  matching  with
1697           pcre_exec(),  otherwise  0.  The fourth argument should point to an int
1698           variable. From  release  8.00,  this  always  returns  1,  because  the
1699           restrictions  that  previously  applied  to  partial matching have been
1700           lifted. The pcrepartial documentation gives details of  partial  match-
1701           ing.
1702    
1703             PCRE_INFO_OPTIONS
1704    
1705           Return  a  copy of the options with which the pattern was compiled. The
1706           fourth argument should point to an unsigned long  int  variable.  These
1707           option bits are those specified in the call to pcre_compile(), modified
1708           by any top-level option settings at the start of the pattern itself. In
1709           other  words,  they are the options that will be in force when matching
1710           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1711           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1712           and PCRE_EXTENDED.
1713    
1714           A pattern is automatically anchored by PCRE if  all  of  its  top-level
1715           alternatives begin with one of the following:
1716    
1717             ^     unless PCRE_MULTILINE is set
1718             \A    always
1719             \G    always
1720             .*    if PCRE_DOTALL is set and there are no back
1721                     references to the subpattern in which .* appears
1722    
1723           For such patterns, the PCRE_ANCHORED bit is set in the options returned
1724           by pcre_fullinfo().
1725    
1726             PCRE_INFO_SIZE
1727    
1728           Return the size of the compiled pattern, that is, the  value  that  was
1729           passed as the argument to pcre_malloc() when PCRE was getting memory in
1730           which to place the compiled data. The fourth argument should point to a
1731           size_t variable.
1732    
1733             PCRE_INFO_STUDYSIZE
1734    
1735           Return the size of the data block pointed to by the study_data field in
1736           a pcre_extra block. If pcre_extra is NULL, or there is no  study  data,
1737           zero  is  returned.  The fourth argument should point to a size_t vari-
1738           able.  The study_data field is set by pcre_study() to  record  informa-
1739           tion  that will speed up matching (see the section entitled "Studying a
1740           pattern" above). The format of the study_data block is private, but its
1741           length  is  made  available via this option so that it can be saved and
1742           restored (see the pcreprecompile documentation for details).
1743    
1744    
1745  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1746    
1747       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1748    
1749       The pcre_info() function is now obsolete because its  inter-         The pcre_info() function is now obsolete because its interface  is  too
1750       face  is  too  restrictive  to return all the available data         restrictive  to return all the available data about a compiled pattern.
1751       about  a  compiled  pattern.   New   programs   should   use         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1752       pcre_fullinfo()  instead.  The  yield  of pcre_info() is the         pcre_info()  is the number of capturing subpatterns, or one of the fol-
1753       number of capturing subpatterns, or  one  of  the  following         lowing negative numbers:
1754       negative numbers:  
1755             PCRE_ERROR_NULL       the argument code was NULL
1756         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1757         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1758           If the optptr argument is not NULL, a copy of the  options  with  which
1759       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
1760       with which the pattern was compiled is placed in the integer         PCRE_INFO_OPTIONS above).
1761       it points to (see PCRE_INFO_OPTIONS above).  
1762           If the pattern is not anchored and the  firstcharptr  argument  is  not
1763       If the pattern is not anchored and the firstcharptr argument         NULL,  it is used to pass back information about the first character of
1764       is  not  NULL, it is used to pass back information about the         any matched string (see PCRE_INFO_FIRSTBYTE above).
1765       first    character    of    any    matched    string    (see  
1766       PCRE_INFO_FIRSTBYTE above).  
1767    REFERENCE COUNTS
1768    
1769           int pcre_refcount(pcre *code, int adjust);
1770    
1771           The pcre_refcount() function is used to maintain a reference  count  in
1772           the data block that contains a compiled pattern. It is provided for the
1773           benefit of applications that  operate  in  an  object-oriented  manner,
1774           where different parts of the application may be using the same compiled
1775           pattern, but you want to free the block when they are all done.
1776    
1777           When a pattern is compiled, the reference count field is initialized to
1778           zero.   It is changed only by calling this function, whose action is to
1779           add the adjust value (which may be positive or  negative)  to  it.  The
1780           yield of the function is the new value. However, the value of the count
1781           is constrained to lie between 0 and 65535, inclusive. If the new  value
1782           is outside these limits, it is forced to the appropriate limit value.
1783    
1784           Except  when it is zero, the reference count is not correctly preserved
1785           if a pattern is compiled on one host and then  transferred  to  a  host
1786           whose byte-order is different. (This seems a highly unlikely scenario.)
1787    
1788    
1789    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1790    
1791           int pcre_exec(const pcre *code, const pcre_extra *extra,
1792                const char *subject, int length, int startoffset,
1793                int options, int *ovector, int ovecsize);
1794    
1795           The  function pcre_exec() is called to match a subject string against a
1796           compiled pattern, which is passed in the code argument. If the  pattern
1797           was  studied,  the  result  of  the study should be passed in the extra
1798           argument. This function is the main matching facility of  the  library,
1799           and it operates in a Perl-like manner. For specialist use there is also
1800           an alternative matching function, which is described below in the  sec-
1801           tion about the pcre_dfa_exec() function.
1802    
1803           In  most applications, the pattern will have been compiled (and option-
1804           ally studied) in the same process that calls pcre_exec().  However,  it
1805           is possible to save compiled patterns and study data, and then use them
1806           later in different processes, possibly even on different hosts.  For  a
1807           discussion about this, see the pcreprecompile documentation.
1808    
1809           Here is an example of a simple call to pcre_exec():
1810    
1811             int rc;
1812             int ovector[30];
1813             rc = pcre_exec(
1814               re,             /* result of pcre_compile() */
1815               NULL,           /* we didn't study the pattern */
1816               "some string",  /* the subject string */
1817               11,             /* the length of the subject string */
1818               0,              /* start at offset 0 in the subject */
1819               0,              /* default options */
1820               ovector,        /* vector of integers for substring information */
1821               30);            /* number of elements (NOT size in bytes) */
1822    
1823       Extra data for pcre_exec()
1824    
1825           If  the  extra argument is not NULL, it must point to a pcre_extra data
1826           block. The pcre_study() function returns such a block (when it  doesn't
1827           return  NULL), but you can also create one for yourself, and pass addi-
1828           tional information in it. The pcre_extra block contains  the  following
1829           fields (not necessarily in this order):
1830    
1831             unsigned long int flags;
1832             void *study_data;
1833             unsigned long int match_limit;
1834             unsigned long int match_limit_recursion;
1835             void *callout_data;
1836             const unsigned char *tables;
1837             unsigned char **mark;
1838    
1839           The  flags  field  is a bitmap that specifies which of the other fields
1840           are set. The flag bits are:
1841    
1842             PCRE_EXTRA_STUDY_DATA
1843             PCRE_EXTRA_MATCH_LIMIT
1844             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1845             PCRE_EXTRA_CALLOUT_DATA
1846             PCRE_EXTRA_TABLES
1847             PCRE_EXTRA_MARK
1848    
1849           Other flag bits should be set to zero. The study_data field is  set  in
1850           the  pcre_extra  block  that is returned by pcre_study(), together with
1851           the appropriate flag bit. You should not set this yourself, but you may
1852           add  to  the  block by setting the other fields and their corresponding
1853           flag bits.
1854    
1855           The match_limit field provides a means of preventing PCRE from using up
1856           a  vast amount of resources when running patterns that are not going to
1857           match, but which have a very large number  of  possibilities  in  their
1858           search  trees. The classic example is a pattern that uses nested unlim-
1859           ited repeats.
1860    
1861           Internally, PCRE uses a function called match() which it calls  repeat-
1862           edly  (sometimes  recursively). The limit set by match_limit is imposed
1863           on the number of times this function is called during  a  match,  which
1864           has  the  effect  of  limiting the amount of backtracking that can take
1865           place. For patterns that are not anchored, the count restarts from zero
1866           for each position in the subject string.
1867    
1868           The  default  value  for  the  limit can be set when PCRE is built; the
1869           default default is 10 million, which handles all but the  most  extreme
1870           cases.  You  can  override  the  default by suppling pcre_exec() with a
1871           pcre_extra    block    in    which    match_limit    is    set,     and
1872           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1873           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1874    
1875           The match_limit_recursion field is similar to match_limit, but  instead
1876           of limiting the total number of times that match() is called, it limits
1877           the depth of recursion. The recursion depth is a  smaller  number  than
1878           the  total number of calls, because not all calls to match() are recur-
1879           sive.  This limit is of use only if it is set smaller than match_limit.
1880    
1881           Limiting the recursion depth limits the amount of  stack  that  can  be
1882           used, or, when PCRE has been compiled to use memory on the heap instead
1883           of the stack, the amount of heap memory that can be used.
1884    
1885           The default value for match_limit_recursion can be  set  when  PCRE  is
1886           built;  the  default  default  is  the  same  value  as the default for
1887           match_limit. You can override the default by suppling pcre_exec()  with
1888           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1889           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1890           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1891    
1892           The  callout_data  field is used in conjunction with the "callout" fea-
1893           ture, and is described in the pcrecallout documentation.
1894    
1895           The tables field  is  used  to  pass  a  character  tables  pointer  to
1896           pcre_exec();  this overrides the value that is stored with the compiled
1897           pattern. A non-NULL value is stored with the compiled pattern  only  if
1898           custom  tables  were  supplied to pcre_compile() via its tableptr argu-
1899           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1900           PCRE's  internal  tables  to be used. This facility is helpful when re-
1901           using patterns that have been saved after compiling  with  an  external
1902           set  of  tables,  because  the  external tables might be at a different
1903           address when pcre_exec() is called. See the  pcreprecompile  documenta-
1904           tion for a discussion of saving compiled patterns for later use.
1905    
1906           If  PCRE_EXTRA_MARK  is  set in the flags field, the mark field must be
1907           set to point to a char * variable. If the pattern  contains  any  back-
1908           tracking  control verbs such as (*MARK:NAME), and the execution ends up
1909           with a name to pass back, a pointer to the  name  string  (zero  termi-
1910           nated)  is  placed  in  the  variable pointed to by the mark field. The
1911           names are within the compiled pattern; if you wish  to  retain  such  a
1912           name  you must copy it before freeing the memory of a compiled pattern.
1913           If there is no name to pass back, the variable pointed to by  the  mark
1914           field  set  to NULL. For details of the backtracking control verbs, see
1915           the section entitled "Backtracking control" in the pcrepattern documen-
1916           tation.
1917    
1918       Option bits for pcre_exec()
1919    
1920           The  unused  bits of the options argument for pcre_exec() must be zero.
1921           The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
1922           PCRE_NOTBOL,    PCRE_NOTEOL,    PCRE_NOTEMPTY,   PCRE_NOTEMPTY_ATSTART,
1923           PCRE_NO_START_OPTIMIZE,  PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,   and
1924           PCRE_PARTIAL_HARD.
1925    
1926             PCRE_ANCHORED
1927    
1928           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1929           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1930           turned  out to be anchored by virtue of its contents, it cannot be made
1931           unachored at matching time.
1932    
1933             PCRE_BSR_ANYCRLF
1934             PCRE_BSR_UNICODE
1935    
1936           These options (which are mutually exclusive) control what the \R escape
1937           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1938           or to match any Unicode newline sequence. These  options  override  the
1939           choice that was made or defaulted when the pattern was compiled.
1940    
1941             PCRE_NEWLINE_CR
1942             PCRE_NEWLINE_LF
1943             PCRE_NEWLINE_CRLF
1944             PCRE_NEWLINE_ANYCRLF
1945             PCRE_NEWLINE_ANY
1946    
1947           These  options  override  the  newline  definition  that  was chosen or
1948           defaulted when the pattern was compiled. For details, see the  descrip-
1949           tion  of  pcre_compile()  above.  During  matching,  the newline choice
1950           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1951           ters.  It may also alter the way the match position is advanced after a
1952           match failure for an unanchored pattern.
1953    
1954           When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
1955           set,  and a match attempt for an unanchored pattern fails when the cur-
1956           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1957           explicit  matches  for  CR  or  LF  characters,  the  match position is
1958           advanced by two characters instead of one, in other words, to after the
1959           CRLF.
1960    
1961           The above rule is a compromise that makes the most common cases work as
1962           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1963           option is not set), it does not match the string "\r\nA" because, after
1964           failing at the start, it skips both the CR and the LF before  retrying.
1965           However,  the  pattern  [\r\n]A does match that string, because it con-
1966           tains an explicit CR or LF reference, and so advances only by one char-
1967           acter after the first failure.
1968    
1969           An explicit match for CR of LF is either a literal appearance of one of
1970           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1971           matches  such  as [^X] do not count, nor does \s (which includes CR and
1972           LF in the characters that it matches).
1973    
1974           Notwithstanding the above, anomalous effects may still occur when  CRLF
1975           is a valid newline sequence and explicit \r or \n escapes appear in the
1976           pattern.
1977    
1978             PCRE_NOTBOL
1979    
1980           This option specifies that first character of the subject string is not
1981           the  beginning  of  a  line, so the circumflex metacharacter should not
1982           match before it. Setting this without PCRE_MULTILINE (at compile  time)
1983           causes  circumflex  never to match. This option affects only the behav-
1984           iour of the circumflex metacharacter. It does not affect \A.
1985    
1986             PCRE_NOTEOL
1987    
1988           This option specifies that the end of the subject string is not the end
1989           of  a line, so the dollar metacharacter should not match it nor (except
1990           in multiline mode) a newline immediately before it. Setting this  with-
1991           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1992           option affects only the behaviour of the dollar metacharacter. It  does
1993           not affect \Z or \z.
1994    
1995             PCRE_NOTEMPTY
1996    
1997           An empty string is not considered to be a valid match if this option is
1998           set. If there are alternatives in the pattern, they are tried.  If  all
1999           the  alternatives  match  the empty string, the entire match fails. For
2000           example, if the pattern
2001    
2002             a?b?
2003    
2004           is applied to a string not beginning with "a" or  "b",  it  matches  an
2005           empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
2006           match is not valid, so PCRE searches further into the string for occur-
2007           rences of "a" or "b".
2008    
2009             PCRE_NOTEMPTY_ATSTART
2010    
2011           This  is  like PCRE_NOTEMPTY, except that an empty string match that is
2012           not at the start of  the  subject  is  permitted.  If  the  pattern  is
2013           anchored, such a match can occur only if the pattern contains \K.
2014    
2015           Perl     has    no    direct    equivalent    of    PCRE_NOTEMPTY    or
2016           PCRE_NOTEMPTY_ATSTART, but it does make a special  case  of  a  pattern
2017           match  of  the empty string within its split() function, and when using
2018           the /g modifier. It is  possible  to  emulate  Perl's  behaviour  after
2019           matching a null string by first trying the match again at the same off-
2020           set with PCRE_NOTEMPTY_ATSTART and  PCRE_ANCHORED,  and  then  if  that
2021           fails, by advancing the starting offset (see below) and trying an ordi-
2022           nary match again. There is some code that demonstrates how to  do  this
2023           in  the  pcredemo sample program. In the most general case, you have to
2024           check to see if the newline convention recognizes CRLF  as  a  newline,
2025           and  if so, and the current character is CR followed by LF, advance the
2026           starting offset by two characters instead of one.
2027    
2028             PCRE_NO_START_OPTIMIZE
2029    
2030           There are a number of optimizations that pcre_exec() uses at the  start
2031           of  a  match,  in  order to speed up the process. For example, if it is
2032           known that an unanchored match must start with a specific character, it
2033           searches  the  subject  for that character, and fails immediately if it
2034           cannot find it, without actually running the  main  matching  function.
2035           This means that a special item such as (*COMMIT) at the start of a pat-
2036           tern is not considered until after a suitable starting  point  for  the
2037           match  has been found. When callouts or (*MARK) items are in use, these
2038           "start-up" optimizations can cause them to be skipped if the pattern is
2039           never  actually  used.  The start-up optimizations are in effect a pre-
2040           scan of the subject that takes place before the pattern is run.
2041    
2042           The PCRE_NO_START_OPTIMIZE option disables the start-up  optimizations,
2043           possibly  causing  performance  to  suffer,  but ensuring that in cases
2044           where the result is "no match", the callouts do occur, and  that  items
2045           such as (*COMMIT) and (*MARK) are considered at every possible starting
2046           position in the subject string. If  PCRE_NO_START_OPTIMIZE  is  set  at
2047           compile time, it cannot be unset at matching time.
2048    
2049           Setting  PCRE_NO_START_OPTIMIZE  can  change  the outcome of a matching
2050           operation.  Consider the pattern
2051    
2052             (*COMMIT)ABC
2053    
2054           When this is compiled, PCRE records the fact that a  match  must  start
2055           with  the  character  "A".  Suppose the subject string is "DEFABC". The
2056           start-up optimization scans along the subject, finds "A" and  runs  the
2057           first  match attempt from there. The (*COMMIT) item means that the pat-
2058           tern must match the current starting position, which in this  case,  it
2059           does.  However,  if  the  same match is run with PCRE_NO_START_OPTIMIZE
2060           set, the initial scan along the subject string  does  not  happen.  The
2061           first  match  attempt  is  run  starting  from "D" and when this fails,
2062           (*COMMIT) prevents any further matches  being  tried,  so  the  overall
2063           result  is  "no  match". If the pattern is studied, more start-up opti-
2064           mizations may be used. For example, a minimum length  for  the  subject
2065           may be recorded. Consider the pattern
2066    
2067             (*MARK:A)(X|Y)
2068    
2069           The  minimum  length  for  a  match is one character. If the subject is
2070           "ABC", there will be attempts to  match  "ABC",  "BC",  "C",  and  then
2071           finally  an empty string.  If the pattern is studied, the final attempt
2072           does not take place, because PCRE knows that the subject is too  short,
2073           and  so  the  (*MARK) is never encountered.  In this case, studying the
2074           pattern does not affect the overall match result, which  is  still  "no
2075           match", but it does affect the auxiliary information that is returned.
2076    
2077             PCRE_NO_UTF8_CHECK
2078    
2079           When PCRE_UTF8 is set at compile time, the validity of the subject as a
2080           UTF-8 string is automatically checked when pcre_exec() is  subsequently
2081           called.   The  value  of  startoffset is also checked to ensure that it
2082           points to the start of a UTF-8 character. There is a  discussion  about
2083           the  validity  of  UTF-8 strings in the section on UTF-8 support in the
2084           main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,
2085           pcre_exec()  returns  the  error  PCRE_ERROR_BADUTF8  or,  if PCRE_PAR-
2086           TIAL_HARD is set and the problem is a truncated UTF-8 character at  the
2087           end  of  the  subject, PCRE_ERROR_SHORTUTF8. In both cases, information
2088           about the precise nature of the error may also  be  returned  (see  the
2089           descriptions  of these errors in the section entitled Error return val-
2090           ues from pcre_exec() below).  If startoffset contains a value that does
2091           not  point to the start of a UTF-8 character (or to the end of the sub-
2092           ject), PCRE_ERROR_BADUTF8_OFFSET is returned.
2093    
2094           If you already know that your subject is valid, and you  want  to  skip
2095           these    checks    for   performance   reasons,   you   can   set   the
2096           PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
2097           do  this  for the second and subsequent calls to pcre_exec() if you are
2098           making repeated calls to find all  the  matches  in  a  single  subject
2099           string.  However,  you  should  be  sure  that the value of startoffset
2100           points to the start of a UTF-8 character (or the end of  the  subject).
2101           When  PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8
2102           string as a subject or an invalid value of  startoffset  is  undefined.
2103           Your program may crash.
2104    
2105             PCRE_PARTIAL_HARD
2106             PCRE_PARTIAL_SOFT
2107    
2108           These  options turn on the partial matching feature. For backwards com-
2109           patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A  partial
2110           match  occurs if the end of the subject string is reached successfully,
2111           but there are not enough subject characters to complete the  match.  If
2112           this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set,
2113           matching continues by testing any remaining alternatives.  Only  if  no
2114           complete  match  can be found is PCRE_ERROR_PARTIAL returned instead of
2115           PCRE_ERROR_NOMATCH. In other words,  PCRE_PARTIAL_SOFT  says  that  the
2116           caller  is  prepared to handle a partial match, but only if no complete
2117           match can be found.
2118    
2119           If PCRE_PARTIAL_HARD is set, it overrides  PCRE_PARTIAL_SOFT.  In  this
2120           case,  if  a  partial  match  is found, pcre_exec() immediately returns
2121           PCRE_ERROR_PARTIAL, without  considering  any  other  alternatives.  In
2122           other  words, when PCRE_PARTIAL_HARD is set, a partial match is consid-
2123           ered to be more important that an alternative complete match.
2124    
2125           In both cases, the portion of the string that was  inspected  when  the
2126           partial match was found is set as the first matching string. There is a
2127           more detailed discussion of partial and  multi-segment  matching,  with
2128           examples, in the pcrepartial documentation.
2129    
2130       The string to be matched by pcre_exec()
2131    
2132           The  subject string is passed to pcre_exec() as a pointer in subject, a
2133           length (in bytes) in length, and a starting byte offset in startoffset.
2134           If  this  is  negative  or  greater  than  the  length  of the subject,
2135           pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting  offset  is
2136           zero,  the  search  for a match starts at the beginning of the subject,
2137           and this is by far the most common case. In UTF-8 mode, the byte offset
2138           must  point  to  the start of a UTF-8 character (or the end of the sub-
2139           ject). Unlike the pattern string, the subject may contain  binary  zero
2140           bytes.
2141    
2142           A  non-zero  starting offset is useful when searching for another match
2143           in the same subject by calling pcre_exec() again after a previous  suc-
2144           cess.   Setting  startoffset differs from just passing over a shortened
2145           string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
2146           with any kind of lookbehind. For example, consider the pattern
2147    
2148             \Biss\B
2149    
2150           which  finds  occurrences  of "iss" in the middle of words. (\B matches
2151           only if the current position in the subject is not  a  word  boundary.)
2152           When  applied  to the string "Mississipi" the first call to pcre_exec()
2153           finds the first occurrence. If pcre_exec() is called  again  with  just
2154           the  remainder  of  the  subject,  namely  "issipi", it does not match,
2155           because \B is always false at the start of the subject, which is deemed
2156           to  be  a  word  boundary. However, if pcre_exec() is passed the entire
2157           string again, but with startoffset set to 4, it finds the second occur-
2158           rence  of "iss" because it is able to look behind the starting point to
2159           discover that it is preceded by a letter.
2160    
2161           Finding all the matches in a subject is tricky  when  the  pattern  can
2162           match an empty string. It is possible to emulate Perl's /g behaviour by
2163           first  trying  the  match  again  at  the   same   offset,   with   the
2164           PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED  options,  and  then  if that
2165           fails, advancing the starting  offset  and  trying  an  ordinary  match
2166           again. There is some code that demonstrates how to do this in the pcre-
2167           demo sample program. In the most general case, you have to check to see
2168           if  the newline convention recognizes CRLF as a newline, and if so, and
2169           the current character is CR followed by LF, advance the starting offset
2170           by two characters instead of one.
2171    
2172           If  a  non-zero starting offset is passed when the pattern is anchored,
2173           one attempt to match at the given offset is made. This can only succeed
2174           if  the  pattern  does  not require the match to be at the start of the
2175           subject.
2176    
2177       How pcre_exec() returns captured substrings
2178    
2179           In general, a pattern matches a certain portion of the subject, and  in
2180           addition,  further  substrings  from  the  subject may be picked out by
2181           parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2182           this  is  called "capturing" in what follows, and the phrase "capturing
2183           subpattern" is used for a fragment of a pattern that picks out  a  sub-
2184           string.  PCRE  supports several other kinds of parenthesized subpattern
2185           that do not cause substrings to be captured.
2186    
2187           Captured substrings are returned to the caller via a vector of integers
2188           whose  address is passed in ovector. The number of elements in the vec-
2189           tor is passed in ovecsize, which must be a non-negative  number.  Note:
2190           this argument is NOT the size of ovector in bytes.
2191    
2192           The  first  two-thirds of the vector is used to pass back captured sub-
2193           strings, each substring using a pair of integers. The  remaining  third
2194           of  the  vector is used as workspace by pcre_exec() while matching cap-
2195           turing subpatterns, and is not available for passing back  information.
2196           The  number passed in ovecsize should always be a multiple of three. If
2197           it is not, it is rounded down.
2198    
2199           When a match is successful, information about  captured  substrings  is
2200           returned  in  pairs  of integers, starting at the beginning of ovector,
2201           and continuing up to two-thirds of its length at the  most.  The  first
2202           element  of  each pair is set to the byte offset of the first character
2203           in a substring, and the second is set to the byte offset of  the  first
2204           character  after  the end of a substring. Note: these values are always
2205           byte offsets, even in UTF-8 mode. They are not character counts.
2206    
2207           The first pair of integers, ovector[0]  and  ovector[1],  identify  the
2208           portion  of  the subject string matched by the entire pattern. The next
2209           pair is used for the first capturing subpattern, and so on.  The  value
2210           returned by pcre_exec() is one more than the highest numbered pair that
2211           has been set.  For example, if two substrings have been  captured,  the
2212           returned  value is 3. If there are no capturing subpatterns, the return
2213           value from a successful match is 1, indicating that just the first pair
2214           of offsets has been set.
2215    
2216           If a capturing subpattern is matched repeatedly, it is the last portion
2217           of the string that it matched that is returned.
2218    
2219           If the vector is too small to hold all the captured substring  offsets,
2220           it is used as far as possible (up to two-thirds of its length), and the
2221           function returns a value of zero. If the substring offsets are  not  of
2222           interest,  pcre_exec()  may  be  called with ovector passed as NULL and
2223           ovecsize as zero. However, if the pattern contains back references  and
2224           the  ovector is not big enough to remember the related substrings, PCRE
2225           has to get additional memory for use during matching. Thus it  is  usu-
2226           ally advisable to supply an ovector.
2227    
2228           The pcre_fullinfo() function can be used to find out how many capturing
2229           subpatterns there are in a compiled  pattern.  The  smallest  size  for
2230           ovector  that  will allow for n captured substrings, in addition to the
2231           offsets of the substring matched by the whole pattern, is (n+1)*3.
2232    
2233           It is possible for capturing subpattern number n+1 to match  some  part
2234           of the subject when subpattern n has not been used at all. For example,
2235           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
2236           return from the function is 4, and subpatterns 1 and 3 are matched, but
2237           2 is not. When this happens, both values in  the  offset  pairs  corre-
2238           sponding to unused subpatterns are set to -1.
2239    
2240           Offset  values  that correspond to unused subpatterns at the end of the
2241           expression are also set to -1. For example,  if  the  string  "abc"  is
2242           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
2243           matched. The return from the function is 2, because  the  highest  used
2244           capturing  subpattern  number  is 1, and the offsets for for the second
2245           and third capturing subpatterns (assuming the vector is  large  enough,
2246           of course) are set to -1.
2247    
2248           Note: Elements of ovector that do not correspond to capturing parenthe-
2249           ses in the pattern are never changed. That is, if a pattern contains  n
2250           capturing parentheses, no more than ovector[0] to ovector[2n+1] are set
2251           by pcre_exec(). The other elements retain whatever values  they  previ-
2252           ously had.
2253    
2254           Some  convenience  functions  are  provided for extracting the captured
2255           substrings as separate strings. These are described below.
2256    
2257       Error return values from pcre_exec()
2258    
2259           If pcre_exec() fails, it returns a negative number. The  following  are
2260           defined in the header file:
2261    
2262             PCRE_ERROR_NOMATCH        (-1)
2263    
2264           The subject string did not match the pattern.
2265    
2266             PCRE_ERROR_NULL           (-2)
2267    
2268           Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2269           ovecsize was not zero.
2270    
2271             PCRE_ERROR_BADOPTION      (-3)
2272    
2273           An unrecognized bit was set in the options argument.
2274    
2275             PCRE_ERROR_BADMAGIC       (-4)
2276    
2277           PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2278           to catch the case when it is passed a junk pointer and to detect when a
2279           pattern that was compiled in an environment of one endianness is run in
2280           an  environment  with the other endianness. This is the error that PCRE
2281           gives when the magic number is not present.
2282    
2283             PCRE_ERROR_UNKNOWN_OPCODE (-5)
2284    
2285           While running the pattern match, an unknown item was encountered in the
2286           compiled  pattern.  This  error  could be caused by a bug in PCRE or by
2287           overwriting of the compiled pattern.
2288    
2289             PCRE_ERROR_NOMEMORY       (-6)
2290    
2291           If a pattern contains back references, but the ovector that  is  passed
2292           to pcre_exec() is not big enough to remember the referenced substrings,
2293           PCRE gets a block of memory at the start of matching to  use  for  this
2294           purpose.  If the call via pcre_malloc() fails, this error is given. The
2295           memory is automatically freed at the end of matching.
2296    
2297           This error is also given if pcre_stack_malloc() fails  in  pcre_exec().
2298           This  can happen only when PCRE has been compiled with --disable-stack-
2299           for-recursion.
2300    
2301             PCRE_ERROR_NOSUBSTRING    (-7)
2302    
2303           This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2304           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2305           returned by pcre_exec().
2306    
2307             PCRE_ERROR_MATCHLIMIT     (-8)
2308    
2309           The backtracking limit, as specified by  the  match_limit  field  in  a
2310           pcre_extra  structure  (or  defaulted) was reached. See the description
2311           above.
2312    
2313             PCRE_ERROR_CALLOUT        (-9)
2314    
2315           This error is never generated by pcre_exec() itself. It is provided for
2316           use  by  callout functions that want to yield a distinctive error code.
2317           See the pcrecallout documentation for details.
2318    
2319             PCRE_ERROR_BADUTF8        (-10)
2320    
2321           A string that contains an invalid UTF-8 byte sequence was passed  as  a
2322           subject,  and the PCRE_NO_UTF8_CHECK option was not set. If the size of
2323           the output vector (ovecsize) is at least 2,  the  byte  offset  to  the
2324           start  of  the  the invalid UTF-8 character is placed in the first ele-
2325           ment, and a reason code is placed in the  second  element.  The  reason
2326           codes are listed in the following section.  For backward compatibility,
2327           if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8  char-
2328           acter   at   the   end   of   the   subject  (reason  codes  1  to  5),
2329           PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
2330    
2331             PCRE_ERROR_BADUTF8_OFFSET (-11)
2332    
2333           The UTF-8 byte sequence that was passed as a subject  was  checked  and
2334           found  to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the
2335           value of startoffset did not point to the beginning of a UTF-8  charac-
2336           ter or the end of the subject.
2337    
2338             PCRE_ERROR_PARTIAL        (-12)
2339    
2340           The  subject  string did not match, but it did match partially. See the
2341           pcrepartial documentation for details of partial matching.
2342    
2343             PCRE_ERROR_BADPARTIAL     (-13)
2344    
2345           This code is no longer in  use.  It  was  formerly  returned  when  the
2346           PCRE_PARTIAL  option  was used with a compiled pattern containing items
2347           that were  not  supported  for  partial  matching.  From  release  8.00
2348           onwards, there are no restrictions on partial matching.
2349    
2350             PCRE_ERROR_INTERNAL       (-14)
2351    
2352           An  unexpected  internal error has occurred. This error could be caused
2353           by a bug in PCRE or by overwriting of the compiled pattern.
2354    
2355             PCRE_ERROR_BADCOUNT       (-15)
2356    
2357           This error is given if the value of the ovecsize argument is negative.
2358    
2359             PCRE_ERROR_RECURSIONLIMIT (-21)
2360    
2361           The internal recursion limit, as specified by the match_limit_recursion
2362           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2363           description above.
2364    
2365             PCRE_ERROR_BADNEWLINE     (-23)
2366    
2367           An invalid combination of PCRE_NEWLINE_xxx options was given.
2368    
2369             PCRE_ERROR_BADOFFSET      (-24)
2370    
2371           The value of startoffset was negative or greater than the length of the
2372           subject, that is, the value in length.
2373    
2374             PCRE_ERROR_SHORTUTF8      (-25)
2375    
2376           This  error  is returned instead of PCRE_ERROR_BADUTF8 when the subject
2377           string ends with a truncated UTF-8 character and the  PCRE_PARTIAL_HARD
2378           option  is  set.   Information  about  the  failure  is returned as for
2379           PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this  case,  but
2380           this  special error code for PCRE_PARTIAL_HARD precedes the implementa-
2381           tion of returned information; it is retained for backwards  compatibil-
2382           ity.
2383    
2384             PCRE_ERROR_RECURSELOOP    (-26)
2385    
2386           This error is returned when pcre_exec() detects a recursion loop within
2387           the pattern. Specifically, it means that either the whole pattern or  a
2388           subpattern  has been called recursively for the second time at the same
2389           position in the subject string. Some simple patterns that might do this
2390           are  detected  and faulted at compile time, but more complicated cases,
2391           in particular mutual recursions between two different subpatterns, can-
2392           not be detected until run time.
2393    
2394           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2395    
2396       Reason codes for invalid UTF-8 strings
2397    
2398           When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT-
2399           UTF8, and the size of the output vector (ovecsize) is at least  2,  the
2400           offset  of  the  start  of the invalid UTF-8 character is placed in the
2401           first output vector element (ovector[0]) and a reason code is placed in
2402           the  second  element  (ovector[1]). The reason codes are given names in
2403           the pcre.h header file:
2404    
2405             PCRE_UTF8_ERR1
2406             PCRE_UTF8_ERR2
2407             PCRE_UTF8_ERR3
2408             PCRE_UTF8_ERR4
2409             PCRE_UTF8_ERR5
2410    
2411           The string ends with a truncated UTF-8 character;  the  code  specifies
2412           how  many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8
2413           characters to be no longer than 4 bytes, the  encoding  scheme  (origi-
2414           nally  defined  by  RFC  2279)  allows  for  up to 6 bytes, and this is
2415           checked first; hence the possibility of 4 or 5 missing bytes.
2416    
2417             PCRE_UTF8_ERR6
2418             PCRE_UTF8_ERR7
2419             PCRE_UTF8_ERR8
2420             PCRE_UTF8_ERR9
2421             PCRE_UTF8_ERR10
2422    
2423           The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of
2424           the  character  do  not have the binary value 0b10 (that is, either the
2425           most significant bit is 0, or the next bit is 1).
2426    
2427             PCRE_UTF8_ERR11
2428             PCRE_UTF8_ERR12
2429    
2430           A character that is valid by the RFC 2279 rules is either 5 or 6  bytes
2431           long; these code points are excluded by RFC 3629.
2432    
2433             PCRE_UTF8_ERR13
2434    
2435           A  4-byte character has a value greater than 0x10fff; these code points
2436           are excluded by RFC 3629.
2437    
2438             PCRE_UTF8_ERR14
2439    
2440           A 3-byte character has a value in the  range  0xd800  to  0xdfff;  this
2441           range  of code points are reserved by RFC 3629 for use with UTF-16, and
2442           so are excluded from UTF-8.
2443    
2444             PCRE_UTF8_ERR15
2445             PCRE_UTF8_ERR16
2446             PCRE_UTF8_ERR17
2447             PCRE_UTF8_ERR18
2448             PCRE_UTF8_ERR19
2449    
2450           A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it  codes
2451           for  a  value that can be represented by fewer bytes, which is invalid.
2452           For example, the two bytes 0xc0, 0xae give the value 0x2e,  whose  cor-
2453           rect coding uses just one byte.
2454    
2455             PCRE_UTF8_ERR20
2456    
2457           The two most significant bits of the first byte of a character have the
2458           binary value 0b10 (that is, the most significant bit is 1 and the  sec-
2459           ond  is  0). Such a byte can only validly occur as the second or subse-
2460           quent byte of a multi-byte character.
2461    
2462             PCRE_UTF8_ERR21
2463    
2464  MATCHING A PATTERN         The first byte of a character has the value 0xfe or 0xff. These  values
2465           can never occur in a valid UTF-8 string.
      int pcre_exec(const pcre *code, const pcre_extra *extra,  
           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.  
2466    
2467    
2468  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2469    
2470       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_copy_substring(const char *subject, int *ovector,
2471            int stringcount, int stringnumber, char *buffer,              int stringcount, int stringnumber, char *buffer,
2472            int buffersize);              int buffersize);
2473    
2474       int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
2475            int stringcount, int stringnumber,              int stringcount, int stringnumber,
2476            const char **stringptr);              const char **stringptr);
2477    
2478       int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2479            int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2480    
2481       Captured substrings can be accessed directly  by  using  the         Captured  substrings  can  be  accessed  directly  by using the offsets
2482       offsets returned by pcre_exec() in ovector. For convenience,         returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2483       the functions  pcre_copy_substring(),  pcre_get_substring(),         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2484       and  pcre_get_substring_list()  are  provided for extracting         string_list() are provided for extracting captured substrings  as  new,
2485       captured  substrings  as  new,   separate,   zero-terminated         separate,  zero-terminated strings. These functions identify substrings
2486       strings.  These functions identify substrings by number. The         by number. The next section describes functions  for  extracting  named
2487       next section describes functions for extracting  named  sub-         substrings.
2488       strings.   A  substring  that  contains  a  binary  zero  is  
2489       correctly extracted and has a further zero added on the end,         A  substring that contains a binary zero is correctly extracted and has
2490       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
2491           string.   However,  you  can  process such a string by referring to the
2492       The first three arguments are the  same  for  all  three  of         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2493       these  functions:   subject  is the subject string which has         string().  Unfortunately, the interface to pcre_get_substring_list() is
2494       just been successfully matched, ovector is a pointer to  the         not adequate for handling strings containing binary zeros, because  the
2495       vector  of  integer  offsets that was passed to pcre_exec(),         end of the final string is not independently indicated.
2496       and stringcount is the number of substrings that  were  cap-  
2497       tured by the match, including the substring that matched the         The  first  three  arguments  are the same for all three of these func-
2498       entire regular expression. This is  the  value  returned  by         tions: subject is the subject string that has  just  been  successfully
2499       pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()         matched, ovector is a pointer to the vector of integer offsets that was
2500       returned zero, indicating that it ran out of space in  ovec-         passed to pcre_exec(), and stringcount is the number of substrings that
2501       tor,  the  value passed as stringcount should be the size of         were  captured  by  the match, including the substring that matched the
2502       the vector divided by three.         entire regular expression. This is the value returned by pcre_exec() if
2503           it  is greater than zero. If pcre_exec() returned zero, indicating that
2504       The functions pcre_copy_substring() and pcre_get_substring()         it ran out of space in ovector, the value passed as stringcount  should
2505       extract a single substring, whose number is given as string-         be the number of elements in the vector divided by three.
2506       number. A value of zero extracts the substring that  matched  
2507       the entire pattern, while higher values extract the captured         The  functions pcre_copy_substring() and pcre_get_substring() extract a
2508       substrings. For pcre_copy_substring(), the string is  placed         single substring, whose number is given as  stringnumber.  A  value  of
2509       in  buffer,  whose  length is given by buffersize, while for         zero  extracts  the  substring that matched the entire pattern, whereas
2510       pcre_get_substring() a new block of memory is  obtained  via         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2511       pcre_malloc,  and its address is returned via stringptr. The         string(),  the  string  is  placed  in buffer, whose length is given by
2512       yield of the function is  the  length  of  the  string,  not         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2513       including the terminating zero, or one of         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2514           The yield of the function is the length of the  string,  not  including
2515         PCRE_ERROR_NOMEMORY       (-6)         the terminating zero, or one of these error codes:
2516    
2517       The buffer was too small for pcre_copy_substring(),  or  the           PCRE_ERROR_NOMEMORY       (-6)
2518       attempt to get memory failed for pcre_get_substring().  
2519           The  buffer  was too small for pcre_copy_substring(), or the attempt to
2520         PCRE_ERROR_NOSUBSTRING    (-7)         get memory failed for pcre_get_substring().
2521    
2522       There is no substring whose number is stringnumber.           PCRE_ERROR_NOSUBSTRING    (-7)
2523    
2524       The pcre_get_substring_list() function extracts  all  avail-         There is no substring whose number is stringnumber.
2525       able  substrings  and builds a list of pointers to them. All  
2526       this is done in a single block of memory which  is  obtained         The pcre_get_substring_list()  function  extracts  all  available  sub-
2527       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
2528       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
2529       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
2530       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
2531           pointer.  The  yield  of  the function is zero if all went well, or the
2532         PCRE_ERROR_NOMEMORY       (-6)         error code
2533    
2534       if the attempt to get the memory block failed.           PCRE_ERROR_NOMEMORY       (-6)
2535    
2536       When any of these functions encounter a  substring  that  is         if the attempt to get the memory block failed.
2537       unset, which can happen when capturing subpattern number n+1  
2538       matches some part of the subject, but subpattern n  has  not         When any of these functions encounter a substring that is unset,  which
2539       been  used  at all, they return an empty string. This can be         can  happen  when  capturing subpattern number n+1 matches some part of
2540       distinguished  from  a  genuine  zero-length  substring   by         the subject, but subpattern n has not been used at all, they return  an
2541       inspecting the appropriate offset in ovector, which is nega-         empty string. This can be distinguished from a genuine zero-length sub-
2542       tive for unset substrings.         string by inspecting the appropriate offset in ovector, which is  nega-
2543           tive for unset substrings.
2544       The  two  convenience  functions  pcre_free_substring()  and  
2545       pcre_free_substring_list()  can  be  used to free the memory         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2546       returned by  a  previous  call  of  pcre_get_substring()  or         string_list() can be used to free the memory  returned  by  a  previous
2547       pcre_get_substring_list(),  respectively.  They  do  nothing         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2548       more than call the function pointed to by  pcre_free,  which         tively. They do nothing more than  call  the  function  pointed  to  by
2549       of  course  could  be called directly from a C program. How-         pcre_free,  which  of course could be called directly from a C program.
2550       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-
2551       a  special  interface  to another programming language which         cial   interface  to  another  programming  language  that  cannot  use
2552       cannot use pcre_free directly; it is for  these  cases  that         pcre_free directly; it is for these cases that the functions  are  pro-
2553       the functions are provided.         vided.
2554    
2555    
2556  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2557    
2558       int pcre_copy_named_substring(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
2559            const char *subject, int *ovector,              const char *name);
2560            int stringcount, const char *stringname,  
2561            char *buffer, int buffersize);         int pcre_copy_named_substring(const pcre *code,
2562                const char *subject, int *ovector,
2563       int pcre_get_stringnumber(const pcre *code,              int stringcount, const char *stringname,
2564            const char *name);              char *buffer, int buffersize);
2565    
2566       int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2567            const char *subject, int *ovector,              const char *subject, int *ovector,
2568            int stringcount, const char *stringname,              int stringcount, const char *stringname,
2569            const char **stringptr);              const char **stringptr);
2570    
2571       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-
2572       ciated    number.    This    can    be   done   by   calling         ber.  For example, for this pattern
2573       pcre_get_stringnumber(). The first argument is the  compiled  
2574       pattern,  and  the second is the name. For example, for this           (a+)b(?<xxx>\d+)...
2575       pattern  
2576           the number of the subpattern called "xxx" is 2. If the name is known to
2577         ab(?<xxx>\d+)...         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2578           name by calling pcre_get_stringnumber(). The first argument is the com-
2579       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
2580       number,  you can then extract the substring directly, or use         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2581       one of the functions described in the previous section.  For         subpattern of that name.
2582       convenience,  there are also two functions that do the whole  
2583       job.         Given the number, you can extract the substring directly, or use one of
2584           the functions described in the previous section. For convenience, there
2585       Most of the  arguments  of  pcre_copy_named_substring()  and         are also two functions that do the whole job.
2586       pcre_get_named_substring()  are  the  same  as those for the  
2587       functions that  extract  by  number,  and  so  are  not  re-         Most    of    the    arguments   of   pcre_copy_named_substring()   and
2588       described here. There are just two differences.         pcre_get_named_substring() are the same  as  those  for  the  similarly
2589           named  functions  that extract by number. As these are described in the
2590       First, instead of a substring number, a  substring  name  is         previous section, they are not re-described here. There  are  just  two
2591       given.  Second,  there  is  an  extra argument, given at the         differences:
2592       start, which is a pointer to the compiled pattern.  This  is  
2593       needed  in order to gain access to the name-to-number trans-         First,  instead  of a substring number, a substring name is given. Sec-
2594       lation table.         ond, there is an extra argument, given at the start, which is a pointer
2595           to  the compiled pattern. This is needed in order to gain access to the
2596       These functions  call  pcre_get_stringnumber(),  and  if  it         name-to-number translation table.
2597       succeeds,    they   then   call   pcre_copy_substring()   or  
2598       pcre_get_substring(), as appropriate.         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2599           then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2600           ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2601           behaviour may not be what you want (see the next section).
2602    
2603           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2604           terns with the same number, as described in the  section  on  duplicate
2605           subpattern  numbers  in  the  pcrepattern page, you cannot use names to
2606           distinguish the different subpatterns, because names are  not  included
2607           in  the compiled code. The matching process uses only numbers. For this
2608           reason, the use of different names for subpatterns of the  same  number
2609           causes an error at compile time.
2610    
2611    
2612    DUPLICATE SUBPATTERN NAMES
2613    
2614           int pcre_get_stringtable_entries(const pcre *code,
2615                const char *name, char **first, char **last);
2616    
2617           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2618           subpatterns are not required to be unique. (Duplicate names are  always
2619           allowed  for subpatterns with the same number, created by using the (?|
2620           feature. Indeed, if such subpatterns are named, they  are  required  to
2621           use the same names.)
2622    
2623           Normally, patterns with duplicate names are such that in any one match,
2624           only one of the named subpatterns participates. An example is shown  in
2625           the pcrepattern documentation.
2626    
2627           When    duplicates   are   present,   pcre_copy_named_substring()   and
2628           pcre_get_named_substring() return the first substring corresponding  to
2629           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2630           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2631           function  returns one of the numbers that are associated with the name,
2632           but it is not defined which it is.
2633    
2634           If you want to get full details of all captured substrings for a  given
2635           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2636           first argument is the compiled pattern, and the second is the name. The
2637           third  and  fourth  are  pointers to variables which are updated by the
2638           function. After it has run, they point to the first and last entries in
2639           the  name-to-number  table  for  the  given  name.  The function itself
2640           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2641           there  are none. The format of the table is described above in the sec-
2642           tion entitled Information about a pattern above.  Given all  the  rele-
2643           vant  entries  for the name, you can extract each of their numbers, and
2644           hence the captured data, if any.
2645    
2646    
2647    FINDING ALL POSSIBLE MATCHES
2648    
2649           The traditional matching function uses a  similar  algorithm  to  Perl,
2650           which stops when it finds the first match, starting at a given point in
2651           the subject. If you want to find all possible matches, or  the  longest
2652           possible  match,  consider using the alternative matching function (see
2653           below) instead. If you cannot use the alternative function,  but  still
2654           need  to  find all possible matches, you can kludge it up by making use
2655           of the callout facility, which is described in the pcrecallout documen-
2656           tation.
2657    
2658           What you have to do is to insert a callout right at the end of the pat-
2659           tern.  When your callout function is called, extract and save the  cur-
2660           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2661           backtrack and try other alternatives. Ultimately, when it runs  out  of
2662           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2663    
2664    
2665    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2666    
2667           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2668                const char *subject, int length, int startoffset,
2669                int options, int *ovector, int ovecsize,
2670                int *workspace, int wscount);
2671    
2672           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2673           against a compiled pattern, using a matching algorithm that  scans  the
2674           subject  string  just  once, and does not backtrack. This has different
2675           characteristics to the normal algorithm, and  is  not  compatible  with
2676           Perl.  Some  of the features of PCRE patterns are not supported. Never-
2677           theless, there are times when this kind of matching can be useful.  For
2678           a  discussion  of  the  two matching algorithms, and a list of features
2679           that pcre_dfa_exec() does not support, see the pcrematching  documenta-
2680           tion.
2681    
2682           The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2683           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2684           ent  way,  and  this is described below. The other common arguments are
2685           used in the same way as for pcre_exec(), so their  description  is  not
2686           repeated here.
2687    
2688           The  two  additional  arguments provide workspace for the function. The
2689           workspace vector should contain at least 20 elements. It  is  used  for
2690           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2691           workspace will be needed for patterns and subjects where  there  are  a
2692           lot of potential matches.
2693    
2694           Here is an example of a simple call to pcre_dfa_exec():
2695    
2696             int rc;
2697             int ovector[10];
2698             int wspace[20];
2699             rc = pcre_dfa_exec(
2700               re,             /* result of pcre_compile() */
2701               NULL,           /* we didn't study the pattern */
2702               "some string",  /* the subject string */
2703               11,             /* the length of the subject string */
2704               0,              /* start at offset 0 in the subject */
2705               0,              /* default options */
2706               ovector,        /* vector of integers for substring information */
2707               10,             /* number of elements (NOT size in bytes) */
2708               wspace,         /* working space vector */
2709               20);            /* number of elements (NOT size in bytes) */
2710    
2711       Option bits for pcre_dfa_exec()
2712    
2713           The  unused  bits  of  the options argument for pcre_dfa_exec() must be
2714           zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2715           LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2716           PCRE_NOTEMPTY_ATSTART,      PCRE_NO_UTF8_CHECK,       PCRE_BSR_ANYCRLF,
2717           PCRE_BSR_UNICODE,  PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR-
2718           TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART.  All but  the  last
2719           four  of  these  are  exactly  the  same  as  for pcre_exec(), so their
2720           description is not repeated here.
2721    
2722             PCRE_PARTIAL_HARD
2723             PCRE_PARTIAL_SOFT
2724    
2725           These have the same general effect as they do for pcre_exec(), but  the
2726           details  are  slightly  different.  When  PCRE_PARTIAL_HARD  is set for
2727           pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of  the  sub-
2728           ject  is  reached  and there is still at least one matching possibility
2729           that requires additional characters. This happens even if some complete
2730           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2731           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2732           of  the  subject  is  reached, there have been no complete matches, but
2733           there is still at least one matching possibility. The  portion  of  the
2734           string  that  was inspected when the longest partial match was found is
2735           set as the first matching string  in  both  cases.   There  is  a  more
2736           detailed  discussion  of partial and multi-segment matching, with exam-
2737           ples, in the pcrepartial documentation.
2738    
2739             PCRE_DFA_SHORTEST
2740    
2741           Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2742           stop as soon as it has found one match. Because of the way the alterna-
2743           tive algorithm works, this is necessarily the shortest  possible  match
2744           at the first possible matching point in the subject string.
2745    
2746             PCRE_DFA_RESTART
2747    
2748           When pcre_dfa_exec() returns a partial match, it is possible to call it
2749           again, with additional subject characters, and have  it  continue  with
2750           the  same match. The PCRE_DFA_RESTART option requests this action; when
2751           it is set, the workspace and wscount options must  reference  the  same
2752           vector  as  before  because data about the match so far is left in them
2753           after a partial match. There is more discussion of this facility in the
2754           pcrepartial documentation.
2755    
2756       Successful returns from pcre_dfa_exec()
2757    
2758           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2759           string in the subject. Note, however, that all the matches from one run
2760           of  the  function  start  at the same point in the subject. The shorter
2761           matches are all initial substrings of the longer matches. For  example,
2762           if the pattern
2763    
2764             <.*>
2765    
2766           is matched against the string
2767    
2768             This is <something> <something else> <something further> no more
2769    
2770           the three matched strings are
2771    
2772             <something>
2773             <something> <something else>
2774             <something> <something else> <something further>
2775    
2776           On  success,  the  yield of the function is a number greater than zero,
2777           which is the number of matched substrings.  The  substrings  themselves
2778           are  returned  in  ovector. Each string uses two elements; the first is
2779           the offset to the start, and the second is the offset to  the  end.  In
2780           fact,  all  the  strings  have the same start offset. (Space could have
2781           been saved by giving this only once, but it was decided to retain  some
2782           compatibility  with  the  way pcre_exec() returns data, even though the
2783           meaning of the strings is different.)
2784    
2785           The strings are returned in reverse order of length; that is, the long-
2786           est  matching  string is given first. If there were too many matches to
2787           fit into ovector, the yield of the function is zero, and the vector  is
2788           filled with the longest matches.
2789    
2790       Error returns from pcre_dfa_exec()
2791    
2792           The  pcre_dfa_exec()  function returns a negative number when it fails.
2793           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2794           described  above.   There are in addition the following errors that are
2795           specific to pcre_dfa_exec():
2796    
2797             PCRE_ERROR_DFA_UITEM      (-16)
2798    
2799           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2800           tern  that  it  does not support, for instance, the use of \C or a back
2801           reference.
2802    
2803             PCRE_ERROR_DFA_UCOND      (-17)
2804    
2805           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2806           that  uses  a back reference for the condition, or a test for recursion
2807           in a specific group. These are not supported.
2808    
2809             PCRE_ERROR_DFA_UMLIMIT    (-18)
2810    
2811           This return is given if pcre_dfa_exec() is called with an  extra  block
2812           that contains a setting of the match_limit field. This is not supported
2813           (it is meaningless).
2814    
2815             PCRE_ERROR_DFA_WSSIZE     (-19)
2816    
2817           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2818           workspace vector.
2819    
2820             PCRE_ERROR_DFA_RECURSE    (-20)
2821    
2822           When  a  recursive subpattern is processed, the matching function calls
2823           itself recursively, using private vectors for  ovector  and  workspace.
2824           This  error  is  given  if  the output vector is not large enough. This
2825           should be extremely rare, as a vector of size 1000 is used.
2826    
2827    
2828    SEE ALSO
2829    
2830           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2831           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2832    
2833    
2834    AUTHOR
2835    
2836           Philip Hazel
2837           University Computing Service
2838           Cambridge CB2 3QH, England.
2839    
2840    
2841