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1    -----------------------------------------------------------------------------
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
# Line 5  synopses of each function in the library Line 6  synopses of each function in the library
6  separate text files for the pcregrep and pcretest commands.  separate text files for the pcregrep and pcretest commands.
7  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
8    
9  NAME  PCRE(3)                                                                PCRE(3)
      PCRE - Perl-compatible regular expressions  
   
10    
 DESCRIPTION  
11    
      The PCRE library is a set of functions that implement  regu-  
      lar  expression  pattern  matching using the same syntax and  
      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.  
12    
13    NAME
14           PCRE - Perl-compatible regular expressions
15    
16  USER DOCUMENTATION  INTRODUCTION
17    
18       The user documentation for PCRE has been  split  up  into  a         The  PCRE  library is a set of functions that implement regular expres-
19       number  of  different sections. In the "man" format, each of         sion pattern matching using the same syntax and semantics as Perl, with
20       these is a separate "man page". In the HTML format, each  is         just  a  few  differences.  The current implementation of PCRE (release
21       a  separate  page,  linked from the index page. In the plain         5.x) corresponds approximately with Perl  5.8,  including  support  for
22       text format, all the sections are concatenated, for ease  of         UTF-8 encoded strings and Unicode general category properties. However,
23       searching. The sections are as follows:         this support has to be explicitly enabled; it is not the default.
24    
25         pcre              this document         PCRE is written in C and released as a C library. A  number  of  people
26         pcreapi           details of PCRE's native API         have  written  wrappers and interfaces of various kinds. A C++ class is
27         pcrebuild         options for building PCRE         included in these contributions, which can  be  found  in  the  Contrib
28         pcrecallout       details of the callout feature         directory at the primary FTP site, which is:
29         pcrecompat        discussion of Perl compatibility  
30         pcregrep          description of the pcregrep command         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
31         pcrepattern       syntax and semantics of supported  
32                             regular expressions         Details  of  exactly which Perl regular expression features are and are
33         pcreperform       discussion of performance issues         not supported by PCRE are given in separate documents. See the pcrepat-
34         pcreposix         the POSIX-compatible API         tern and pcrecompat pages.
35         pcresample        discussion of the sample program  
36         pcretest          the pcretest testing command         Some  features  of  PCRE can be included, excluded, or changed when the
37           library is built. The pcre_config() function makes it  possible  for  a
38       In addition, in the "man" and HTML formats, there is a short         client  to  discover  which  features are available. The features them-
39       page  for  each  library function, listing its arguments and         selves are described in the pcrebuild page. Documentation about  build-
40       results.         ing  PCRE for various operating systems can be found in the README file
41           in the source distribution.
42    
43    
44  LIMITATIONS  USER DOCUMENTATION
45    
46       There are some size limitations in PCRE but it is hoped that         The user documentation for PCRE comprises a number  of  different  sec-
47       they will never in practice be relevant.         tions.  In the "man" format, each of these is a separate "man page". In
48           the HTML format, each is a separate page, linked from the  index  page.
49           In  the  plain text format, all the sections are concatenated, for ease
50           of searching. The sections are as follows:
51    
52             pcre              this document
53             pcreapi           details of PCRE's native API
54             pcrebuild         options for building PCRE
55             pcrecallout       details of the callout feature
56             pcrecompat        discussion of Perl compatibility
57             pcregrep          description of the pcregrep command
58             pcrepartial       details of the partial matching facility
59             pcrepattern       syntax and semantics of supported
60                                 regular expressions
61             pcreperform       discussion of performance issues
62             pcreposix         the POSIX-compatible API
63             pcreprecompile    details of saving and re-using precompiled patterns
64             pcresample        discussion of the sample program
65             pcretest          description of the pcretest testing command
66    
67       The maximum length of a  compiled  pattern  is  65539  (sic)         In  addition,  in the "man" and HTML formats, there is a short page for
68       bytes  if PCRE is compiled with the default internal linkage         each library function, listing its arguments and results.
      size of 2. If you want to process regular  expressions  that  
      are  truly  enormous,  you can compile PCRE with an internal  
      linkage size of 3 or 4 (see the README file  in  the  source  
      distribution  and  the pcrebuild documentation for details).  
      If these cases the limit is substantially larger.   However,  
      the speed of execution will be slower.  
   
      All values in repeating quantifiers must be less than 65536.  
      The maximum number of capturing subpatterns is 65535.  
   
      There is no limit to the  number  of  non-capturing  subpat-  
      terns,  but  the  maximum  depth  of nesting of all kinds of  
      parenthesized subpattern, including  capturing  subpatterns,  
      assertions, and other types of subpattern, is 200.  
   
      The maximum length of a subject string is the largest  posi-  
      tive number that an integer variable can hold. However, PCRE  
      uses recursion to handle subpatterns and indefinite  repeti-  
      tion.  This  means  that the available stack space may limit  
      the size of a subject string that can be processed  by  cer-  
      tain patterns.  
69    
70    
71  UTF-8 SUPPORT  LIMITATIONS
72    
73       Starting at release 3.3, PCRE has had some support for char-         There are some size limitations in PCRE but it is hoped that they  will
74       acter  strings  encoded in the UTF-8 format. For release 4.0         never in practice be relevant.
      this has been greatly extended to cover most common require-  
      ments.  
   
      In order process UTF-8  strings,  you  must  build  PCRE  to  
      include  UTF-8  support  in  the code, and, in addition, you  
      must call pcre_compile() with  the  PCRE_UTF8  option  flag.  
      When  you  do this, both the pattern and any subject strings  
      that are matched against it are  treated  as  UTF-8  strings  
      instead of just strings of bytes.  
   
      If you compile PCRE with UTF-8 support, but do not use it at  
      run  time,  the  library will be a bit bigger, but the addi-  
      tional run time overhead is limited to testing the PCRE_UTF8  
      flag in several places, so should not be very large.  
   
      The following comments apply when PCRE is running  in  UTF-8  
      mode:  
   
      1. PCRE assumes that the strings it is given  contain  valid  
      UTF-8  codes. It does not diagnose invalid UTF-8 strings. If  
      you pass invalid UTF-8 strings  to  PCRE,  the  results  are  
      undefined.  
   
      2. In a pattern, the escape sequence \x{...}, where the con-  
      tents  of  the  braces is a string of hexadecimal digits, is  
      interpreted as a UTF-8 character whose code  number  is  the  
      given  hexadecimal  number, for example: \x{1234}. If a non-  
      hexadecimal digit appears between the braces,  the  item  is  
      not  recognized.  This escape sequence can be used either as  
      a literal, or within a character class.  
   
      3. The original hexadecimal escape sequence, \xhh, matches a  
      two-byte UTF-8 character if the value is greater than 127.  
   
      4. Repeat quantifiers apply to  complete  UTF-8  characters,  
      not to individual bytes, for example: \x{100}{3}.  
   
      5. The dot metacharacter matches one UTF-8 character instead  
      of a single byte.  
   
      6. The escape sequence \C can be used to match a single byte  
      in UTF-8 mode, but its use can lead to some strange effects.  
   
      7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  
      correctly test characters of any code value, but the charac-  
      ters that PCRE recognizes as digits, spaces, or word charac-  
      ters  remain  the  same  set as before, all with values less  
      than 256.  
   
      8. Case-insensitive  matching  applies  only  to  characters  
      whose  values  are  less than 256. PCRE does not support the  
      notion of "case" for higher-valued characters.  
75    
76       9. PCRE does not support the use of Unicode tables and  pro-         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
77       perties or the Perl escapes \p, \P, and \X.         is compiled with the default internal linkage size of 2. If you want to
78           process  regular  expressions  that are truly enormous, you can compile
79           PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
80           the  source  distribution and the pcrebuild documentation for details).
81           In these cases the limit is substantially larger.  However,  the  speed
82           of execution will be slower.
83    
84           All values in repeating quantifiers must be less than 65536.  The maxi-
85           mum number of capturing subpatterns is 65535.
86    
87           There is no limit to the number of non-capturing subpatterns,  but  the
88           maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,
89           including capturing subpatterns, assertions, and other types of subpat-
90           tern, is 200.
91    
92           The  maximum  length of a subject string is the largest positive number
93           that an integer variable can hold. However, PCRE uses recursion to han-
94           dle  subpatterns  and indefinite repetition. This means that the avail-
95           able stack space may limit the size of a subject  string  that  can  be
96           processed by certain patterns.
97    
98    
99    UTF-8 AND UNICODE PROPERTY SUPPORT
100    
101           From  release  3.3,  PCRE  has  had  some support for character strings
102           encoded in the UTF-8 format. For release 4.0 this was greatly  extended
103           to  cover  most common requirements, and in release 5.0 additional sup-
104           port for Unicode general category properties was added.
105    
106           In order process UTF-8 strings, you must build PCRE  to  include  UTF-8
107           support  in  the  code,  and, in addition, you must call pcre_compile()
108           with the PCRE_UTF8 option flag. When you do this, both the pattern  and
109           any  subject  strings  that are matched against it are treated as UTF-8
110           strings instead of just strings of bytes.
111    
112           If you compile PCRE with UTF-8 support, but do not use it at run  time,
113           the  library will be a bit bigger, but the additional run time overhead
114           is limited to testing the PCRE_UTF8 flag in several places,  so  should
115           not be very large.
116    
117           If PCRE is built with Unicode character property support (which implies
118           UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
119           ported.  The available properties that can be tested are limited to the
120           general category properties such as Lu for an upper case letter  or  Nd
121           for  a decimal number. A full list is given in the pcrepattern documen-
122           tation. The PCRE library is increased in size by about 90K when Unicode
123           property support is included.
124    
125           The following comments apply when PCRE is running in UTF-8 mode:
126    
127           1.  When you set the PCRE_UTF8 flag, the strings passed as patterns and
128           subjects are checked for validity on entry to the  relevant  functions.
129           If an invalid UTF-8 string is passed, an error return is given. In some
130           situations, you may already know  that  your  strings  are  valid,  and
131           therefore want to skip these checks in order to improve performance. If
132           you set the PCRE_NO_UTF8_CHECK flag at compile time  or  at  run  time,
133           PCRE  assumes  that  the  pattern or subject it is given (respectively)
134           contains only valid UTF-8 codes. In this case, it does not diagnose  an
135           invalid  UTF-8 string. If you pass an invalid UTF-8 string to PCRE when
136           PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may
137           crash.
138    
139           2. In a pattern, the escape sequence \x{...}, where the contents of the
140           braces is a string of hexadecimal digits, is  interpreted  as  a  UTF-8
141           character  whose code number is the given hexadecimal number, for exam-
142           ple: \x{1234}. If a non-hexadecimal digit appears between  the  braces,
143           the item is not recognized.  This escape sequence can be used either as
144           a literal, or within a character class.
145    
146           3. The original hexadecimal escape sequence, \xhh, matches  a  two-byte
147           UTF-8 character if the value is greater than 127.
148    
149           4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
150           vidual bytes, for example: \x{100}{3}.
151    
152           5. The dot metacharacter matches one UTF-8 character instead of a  sin-
153           gle byte.
154    
155           6.  The  escape sequence \C can be used to match a single byte in UTF-8
156           mode, but its use can lead to some strange effects.
157    
158           7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly
159           test  characters of any code value, but the characters that PCRE recog-
160           nizes as digits, spaces, or word characters  remain  the  same  set  as
161           before, all with values less than 256. This remains true even when PCRE
162           includes Unicode property support, because to do otherwise  would  slow
163           down  PCRE in many common cases. If you really want to test for a wider
164           sense of, say, "digit", you must use Unicode  property  tests  such  as
165           \p{Nd}.
166    
167           8.  Similarly,  characters that match the POSIX named character classes
168           are all low-valued characters.
169    
170           9. Case-insensitive matching applies only to  characters  whose  values
171           are  less than 128, unless PCRE is built with Unicode property support.
172           Even when Unicode property support is available, PCRE  still  uses  its
173           own  character  tables when checking the case of low-valued characters,
174           so as not to degrade performance.  The Unicode property information  is
175           used only for characters with higher values.
176    
177    
178  AUTHOR  AUTHOR
179    
180       Philip Hazel <ph10@cam.ac.uk>         Philip Hazel <ph10@cam.ac.uk>
181       University Computing Service,         University Computing Service,
182       Cambridge CB2 3QG, England.         Cambridge CB2 3QG, England.
183       Phone: +44 1223 334714         Phone: +44 1223 334714
184    
185  Last updated: 04 February 2003  Last updated: 09 September 2004
186  Copyright (c) 1997-2003 University of Cambridge.  Copyright (c) 1997-2004 University of Cambridge.
187  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
188    
189  NAME  PCRE(3)                                                                PCRE(3)
      PCRE - Perl-compatible regular expressions  
190    
191    
192    
193    NAME
194           PCRE - Perl-compatible regular expressions
195    
196  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
197    
198       This document describes the optional features of  PCRE  that         This  document  describes  the  optional  features  of PCRE that can be
199       can  be  selected when the library is compiled. They are all         selected when the library is compiled. They are all selected, or  dese-
200       selected, or deselected, by providing options to the config-         lected, by providing options to the configure script that is run before
201       ure  script  which  is run before the make command. The com-         the make command. The complete list of  options  for  configure  (which
202       plete list of options  for  configure  (which  includes  the         includes  the  standard  ones such as the selection of the installation
203       standard  ones  such  as  the  selection of the installation         directory) can be obtained by running
204       directory) can be obtained by running  
205             ./configure --help
206         ./configure --help  
207           The following sections describe certain options whose names begin  with
208       The following sections describe certain options whose  names         --enable  or  --disable. These settings specify changes to the defaults
209       begin  with  --enable  or  --disable. These settings specify         for the configure command. Because of the  way  that  configure  works,
210       changes to the defaults for the configure  command.  Because         --enable  and  --disable  always  come  in  pairs, so the complementary
211       of  the  way  that  configure  works, --enable and --disable         option always exists as well, but as it specifies the  default,  it  is
212       always come in pairs, so  the  complementary  option  always         not described.
      exists  as  well, but as it specifies the default, it is not  
      described.  
213    
214    
215  UTF-8 SUPPORT  UTF-8 SUPPORT
216    
217       To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 character strings, add
218    
219             --enable-utf8
220    
221           to  the  configure  command.  Of  itself, this does not make PCRE treat
222           strings as UTF-8. As well as compiling PCRE with this option, you  also
223           have  have to set the PCRE_UTF8 option when you call the pcre_compile()
224           function.
225    
        --enable-utf8  
226    
227       to the configure command. Of itself, this does not make PCRE  UNICODE CHARACTER PROPERTY SUPPORT
228       treat  strings as UTF-8. As well as compiling PCRE with this  
229       option, you also have have to set the PCRE_UTF8 option  when         UTF-8 support allows PCRE to process character values greater than  255
230       you call the pcre_compile() function.         in  the  strings that it handles. On its own, however, it does not pro-
231           vide any facilities for accessing the properties of such characters. If
232           you  want  to  be able to use the pattern escapes \P, \p, and \X, which
233           refer to Unicode character properties, you must add
234    
235             --enable-unicode-properties
236    
237           to the configure command. This implies UTF-8 support, even if you  have
238           not explicitly requested it.
239    
240           Including  Unicode  property  support  adds around 90K of tables to the
241           PCRE library, approximately doubling its size. Only the  general  cate-
242           gory  properties  such as Lu and Nd are supported. Details are given in
243           the pcrepattern documentation.
244    
245    
246  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
247    
248       By default, PCRE treats character 10 (linefeed) as the  new-         By default, PCRE treats character 10 (linefeed) as the newline  charac-
249       line  character.  This  is  the  normal newline character on         ter. This is the normal newline character on Unix-like systems. You can
250       Unix-like systems. You can compile PCRE to use character  13         compile PCRE to use character 13 (carriage return) instead by adding
251       (carriage return) instead by adding  
252             --enable-newline-is-cr
253         --enable-newline-is-cr  
254           to the configure command. For completeness there is  also  a  --enable-
255       to the configure command. For completeness there is  also  a         newline-is-lf  option,  which explicitly specifies linefeed as the new-
256       --enable-newline-is-lf  option,  which  explicitly specifies         line character.
      linefeed as the newline character.  
257    
258    
259  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
260    
261       The PCRE building process uses libtool to build both  shared         The PCRE building process uses libtool to build both shared and  static
262       and  static  Unix libraries by default. You can suppress one         Unix  libraries by default. You can suppress one of these by adding one
263       of these by adding one of         of
264    
265         --disable-shared           --disable-shared
266         --disable-static           --disable-static
267    
268       to the configure command, as required.         to the configure command, as required.
269    
270    
271  POSIX MALLOC USAGE  POSIX MALLOC USAGE
272    
273       When PCRE is called through the  POSIX  interface  (see  the         When PCRE is called through the POSIX interface (see the pcreposix doc-
274       pcreposix  documentation),  additional  working  storage  is         umentation),  additional  working  storage  is required for holding the
275       required for holding the pointers  to  capturing  substrings         pointers to capturing substrings, because PCRE requires three  integers
276       because  PCRE requires three integers per substring, whereas         per  substring,  whereas  the POSIX interface provides only two. If the
277       the POSIX interface provides only  two.  If  the  number  of         number of expected substrings is small, the wrapper function uses space
278       expected  substrings  is  small,  the  wrapper function uses         on the stack, because this is faster than using malloc() for each call.
279       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
280       loc()  for  each call. The default threshold above which the         can be changed by adding a setting such as
      stack is no longer used is 10; it can be changed by adding a  
      setting such as  
281    
282         --with-posix-malloc-threshold=20           --with-posix-malloc-threshold=20
283    
284       to the configure command.         to the configure command.
285    
286    
287  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
288    
289       Internally, PCRE has a  function  called  match()  which  it         Internally,  PCRE has a function called match(), which it calls repeat-
290       calls  repeatedly  (possibly  recursively) when performing a         edly (possibly recursively) when matching a pattern. By controlling the
291       matching operation. By limiting the  number  of  times  this         maximum  number  of  times  this function may be called during a single
292       function  may  be  called,  a  limit  can  be  placed on the         matching operation, a limit can be placed on the resources  used  by  a
293       resources used by a single call to  pcre_exec().  The  limit         single  call  to  pcre_exec(). The limit can be changed at run time, as
294       can  be  changed  at  run  time, as described in the pcreapi         described in the pcreapi documentation. The default is 10 million,  but
295       documentation. The default is 10 million, but  this  can  be         this can be changed by adding a setting such as
      changed by adding a setting such as  
296    
297         --with-match-limit=500000           --with-match-limit=500000
298    
299       to the configure command.         to the configure command.
300    
301    
302  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
303    
304       Within a compiled pattern, offset values are used  to  point         Within  a  compiled  pattern,  offset values are used to point from one
305       from  one  part  to  another  (for  example, from an opening         part to another (for example, from an opening parenthesis to an  alter-
306       parenthesis to an  alternation  metacharacter).  By  default         nation  metacharacter).  By default, two-byte values are used for these
307       two-byte  values  are  used  for these offsets, leading to a         offsets, leading to a maximum size for a  compiled  pattern  of  around
308       maximum size for a compiled pattern of around 64K.  This  is         64K.  This  is sufficient to handle all but the most gigantic patterns.
309       sufficient  to  handle  all  but the most gigantic patterns.         Nevertheless, some people do want to process enormous patterns,  so  it
310       Nevertheless, some people do want to process  enormous  pat-         is  possible  to compile PCRE to use three-byte or four-byte offsets by
311       terns,  so  it is possible to compile PCRE to use three-byte         adding a setting such as
312       or four-byte offsets by adding a setting such as  
313             --with-link-size=3
314         --with-link-size=3  
315           to the configure command. The value given must be 2,  3,  or  4.  Using
316       to the configure command. The value given must be 2,  3,  or         longer  offsets slows down the operation of PCRE because it has to load
317       4.  Using  longer  offsets  slows down the operation of PCRE         additional bytes when handling them.
318       because it has to load additional bytes when handling them.  
319           If you build PCRE with an increased link size, test 2 (and  test  5  if
320       If you build PCRE with an increased link size, test  2  (and         you  are using UTF-8) will fail. Part of the output of these tests is a
321       test 5 if you are using UTF-8) will fail. Part of the output         representation of the compiled pattern, and this changes with the  link
322       of these tests is a representation of the compiled  pattern,         size.
323       and this changes with the link size.  
324    
325    AVOIDING EXCESSIVE STACK USAGE
326    
327           PCRE  implements  backtracking while matching by making recursive calls
328           to an internal function called match(). In environments where the  size
329           of the stack is limited, this can severely limit PCRE's operation. (The
330           Unix environment does not usually suffer from this problem.) An  alter-
331           native  approach  that  uses  memory  from  the  heap to remember data,
332           instead of using recursive function calls, has been implemented to work
333           round  this  problem. If you want to build a version of PCRE that works
334           this way, add
335    
336             --disable-stack-for-recursion
337    
338           to the configure command. With this configuration, PCRE  will  use  the
339           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
340           ment functions. Separate functions are provided because  the  usage  is
341           very  predictable:  the  block sizes requested are always the same, and
342           the blocks are always freed in reverse order. A calling  program  might
343           be  able  to implement optimized functions that perform better than the
344           standard malloc() and  free()  functions.  PCRE  runs  noticeably  more
345           slowly when built in this way.
346    
347    
348    USING EBCDIC CODE
349    
350           PCRE  assumes  by  default that it will run in an environment where the
351           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
352           PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by
353           adding
354    
355             --enable-ebcdic
356    
357  Last updated: 21 January 2003         to the configure command.
358  Copyright (c) 1997-2003 University of Cambridge.  
359    Last updated: 09 September 2004
360    Copyright (c) 1997-2004 University of Cambridge.
361  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
362    
363    PCRE(3)                                                                PCRE(3)
364    
365    
366    
367  NAME  NAME
368       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
369    
370    PCRE NATIVE API
371    
372           #include <pcre.h>
373    
374  SYNOPSIS OF PCRE API         pcre *pcre_compile(const char *pattern, int options,
375                const char **errptr, int *erroffset,
376                const unsigned char *tableptr);
377    
378       #include <pcre.h>         pcre_extra *pcre_study(const pcre *code, int options,
379                const char **errptr);
380    
381       pcre *pcre_compile(const char *pattern, int options,         int pcre_exec(const pcre *code, const pcre_extra *extra,
382            const char **errptr, int *erroffset,              const char *subject, int length, int startoffset,
383            const unsigned char *tableptr);              int options, int *ovector, int ovecsize);
384    
385       pcre_extra *pcre_study(const pcre *code, int options,         int pcre_copy_named_substring(const pcre *code,
386            const char **errptr);              const char *subject, int *ovector,
387                int stringcount, const char *stringname,
388                char *buffer, int buffersize);
389    
390       int pcre_exec(const pcre *code, const pcre_extra *extra,         int pcre_copy_substring(const char *subject, int *ovector,
391            const char *subject, int length, int startoffset,              int stringcount, int stringnumber, char *buffer,
392            int options, int *ovector, int ovecsize);              int buffersize);
393    
394       int pcre_copy_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
395            const char *subject, int *ovector,              const char *subject, int *ovector,
396            int stringcount, const char *stringname,              int stringcount, const char *stringname,
397            char *buffer, int buffersize);              const char **stringptr);
398    
399       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_get_stringnumber(const pcre *code,
400            int stringcount, int stringnumber, char *buffer,              const char *name);
           int buffersize);  
401    
402       int pcre_get_named_substring(const pcre *code,         int pcre_get_substring(const char *subject, int *ovector,
403            const char *subject, int *ovector,              int stringcount, int stringnumber,
404            int stringcount, const char *stringname,              const char **stringptr);
           const char **stringptr);  
405    
406       int pcre_get_stringnumber(const pcre *code,         int pcre_get_substring_list(const char *subject,
407            const char *name);              int *ovector, int stringcount, const char ***listptr);
408    
409       int pcre_get_substring(const char *subject, int *ovector,         void pcre_free_substring(const char *stringptr);
           int stringcount, int stringnumber,  
           const char **stringptr);  
410    
411       int pcre_get_substring_list(const char *subject,         void pcre_free_substring_list(const char **stringptr);
           int *ovector, int stringcount, const char ***listptr);  
412    
413       void pcre_free_substring(const char *stringptr);         const unsigned char *pcre_maketables(void);
414    
415       void pcre_free_substring_list(const char **stringptr);         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
416                int what, void *where);
417    
418       const unsigned char *pcre_maketables(void);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
419    
420       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_config(int what, void *where);
           int what, void *where);  
421    
422           char *pcre_version(void);
423    
424       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         void *(*pcre_malloc)(size_t);
425    
426       int pcre_config(int what, void *where);         void (*pcre_free)(void *);
427    
428       char *pcre_version(void);         void *(*pcre_stack_malloc)(size_t);
429    
430       void *(*pcre_malloc)(size_t);         void (*pcre_stack_free)(void *);
431    
432       void (*pcre_free)(void *);         int (*pcre_callout)(pcre_callout_block *);
433    
      int (*pcre_callout)(pcre_callout_block *);  
434    
435    PCRE API OVERVIEW
436    
437  PCRE API         PCRE has its own native API, which is described in this document. There
438           is also a set of wrapper functions that correspond to the POSIX regular
439           expression API.  These are described in the pcreposix documentation.
440    
441       PCRE has its own native API,  which  is  described  in  this         The  native  API  function  prototypes  are  defined in the header file
442       document.  There  is  also  a  set of wrapper functions that         pcre.h, and on Unix systems the library itself is  called  libpcre.  It
443       correspond to the POSIX regular expression API.   These  are         can normally be accessed by adding -lpcre to the command for linking an
444       described in the pcreposix documentation.         application  that  uses  PCRE.  The  header  file  defines  the  macros
445           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
446           bers for the library.  Applications can use these  to  include  support
447           for different releases of PCRE.
448    
449       The native API function prototypes are defined in the header         The  functions  pcre_compile(),  pcre_study(), and pcre_exec() are used
450       file  pcre.h,  and  on  Unix  systems  the library itself is         for compiling and matching regular expressions. A sample  program  that
451       called libpcre.a, so can be accessed by adding -lpcre to the         demonstrates  the  simplest  way  of using them is provided in the file
452       command  for  linking  an  application  which  calls it. The         called pcredemo.c in the source distribution. The pcresample documenta-
453       header file defines the macros PCRE_MAJOR and PCRE_MINOR  to         tion describes how to run it.
      contain the major and minor release numbers for the library.  
      Applications can use these to include support for  different  
      releases.  
454    
455       The functions pcre_compile(), pcre_study(), and  pcre_exec()         In  addition  to  the  main compiling and matching functions, there are
456       are  used  for compiling and matching regular expressions. A         convenience functions for extracting captured substrings from a matched
457       sample program that demonstrates the simplest way  of  using         subject string.  They are:
      them  is  given in the file pcredemo.c. The pcresample docu-  
      mentation describes how to run it.  
458    
459       There are convenience functions for extracting captured sub-           pcre_copy_substring()
460       strings from a matched subject string. They are:           pcre_copy_named_substring()
461             pcre_get_substring()
462             pcre_get_named_substring()
463             pcre_get_substring_list()
464             pcre_get_stringnumber()
465    
466         pcre_copy_substring()         pcre_free_substring() and pcre_free_substring_list() are also provided,
467         pcre_copy_named_substring()         to free the memory used for extracted strings.
        pcre_get_substring()  
        pcre_get_named_substring()  
        pcre_get_substring_list()  
468    
469       pcre_free_substring()  and  pcre_free_substring_list()   are         The function pcre_maketables() is used to  build  a  set  of  character
470       also  provided,  to  free  the  memory  used  for  extracted         tables   in  the  current  locale  for  passing  to  pcre_compile()  or
471       strings.         pcre_exec().  This is an optional facility that is  provided  for  spe-
472           cialist use. Most commonly, no special tables are passed, in which case
473           internal tables that are generated when PCRE is built are used.
474    
475       The function pcre_maketables() is used (optionally) to build         The function pcre_fullinfo() is used to find out  information  about  a
476       a  set of character tables in the current locale for passing         compiled  pattern; pcre_info() is an obsolete version that returns only
477       to pcre_compile().         some of the available information, but is retained for  backwards  com-
478           patibility.   The function pcre_version() returns a pointer to a string
479           containing the version of PCRE and its date of release.
480    
481       The function pcre_fullinfo() is used to find out information         The global variables pcre_malloc and pcre_free  initially  contain  the
482       about a compiled pattern; pcre_info() is an obsolete version         entry  points  of  the  standard malloc() and free() functions, respec-
483       which returns only some of the available information, but is         tively. PCRE calls the memory management functions via these variables,
484       retained   for   backwards   compatibility.    The  function         so  a  calling  program  can replace them if it wishes to intercept the
485       pcre_version() returns a pointer to a string containing  the         calls. This should be done before calling any PCRE functions.
      version of PCRE and its date of release.  
486    
487       The global variables  pcre_malloc  and  pcre_free  initially         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
488       contain the entry points of the standard malloc() and free()         indirections  to  memory  management functions. These special functions
489       functions respectively. PCRE  calls  the  memory  management         are used only when PCRE is compiled to use  the  heap  for  remembering
490       functions  via  these  variables,  so  a calling program can         data,  instead  of recursive function calls. This is a non-standard way
491       replace them if it  wishes  to  intercept  the  calls.  This         of building PCRE, for use in environments  that  have  limited  stacks.
492       should be done before calling any PCRE functions.         Because  of  the greater use of memory management, it runs more slowly.
493           Separate functions are provided so that special-purpose  external  code
494           can be used for this case. When used, these functions are always called
495           in a stack-like manner (last obtained, first  freed),  and  always  for
496           memory blocks of the same size.
497    
498       The global variable pcre_callout initially contains NULL. It         The global variable pcre_callout initially contains NULL. It can be set
499       can be set by the caller to a "callout" function, which PCRE         by the caller to a "callout" function, which PCRE  will  then  call  at
500       will then call at specified points during a matching  opera-         specified  points during a matching operation. Details are given in the
501       tion. Details are given in the pcrecallout documentation.         pcrecallout documentation.
502    
503    
504  MULTITHREADING  MULTITHREADING
505    
506       The PCRE functions can be used in  multi-threading  applica-         The PCRE functions can be used in  multi-threading  applications,  with
507       tions, with the proviso that the memory management functions         the  proviso  that  the  memory  management  functions  pointed  to  by
508       pointed to by pcre_malloc and  pcre_free,  and  the  callout         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
509       function  pointed  to  by  pcre_callout,  are  shared by all         callout function pointed to by pcre_callout, are shared by all threads.
510       threads.  
511           The compiled form of a regular expression is not altered during  match-
512       The compiled form of a regular  expression  is  not  altered         ing, so the same compiled pattern can safely be used by several threads
513       during  matching, so the same compiled pattern can safely be         at once.
514       used by several threads at once.  
515    
516    SAVING PRECOMPILED PATTERNS FOR LATER USE
517    
518           The compiled form of a regular expression can be saved and re-used at a
519           later  time,  possibly by a different program, and even on a host other
520           than the one on which  it  was  compiled.  Details  are  given  in  the
521           pcreprecompile documentation.
522    
523    
524  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
525    
526       int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
527    
528           The  function pcre_config() makes it possible for a PCRE client to dis-
529           cover which optional features have been compiled into the PCRE library.
530           The  pcrebuild documentation has more details about these optional fea-
531           tures.
532    
533       The function pcre_config() makes  it  possible  for  a  PCRE         The first argument for pcre_config() is an  integer,  specifying  which
534       client  to  discover  which optional features have been com-         information is required; the second argument is a pointer to a variable
535       piled into the PCRE library. The pcrebuild documentation has         into which the information is  placed.  The  following  information  is
536       more details about these optional features.         available:
537    
538       The first argument for pcre_config() is an integer, specify-           PCRE_CONFIG_UTF8
      ing  which information is required; the second argument is a  
      pointer to a variable into which the information is  placed.  
      The following information is available:  
539    
540         PCRE_CONFIG_UTF8         The  output is an integer that is set to one if UTF-8 support is avail-
541           able; otherwise it is set to zero.
542    
543       The output is an integer that is set to one if UTF-8 support           PCRE_CONFIG_UNICODE_PROPERTIES
      is available; otherwise it is set to zero.  
544    
545         PCRE_CONFIG_NEWLINE         The output is an integer that is set to  one  if  support  for  Unicode
546           character properties is available; otherwise it is set to zero.
547    
548       The output is an integer that is set to  the  value  of  the           PCRE_CONFIG_NEWLINE
      code  that  is  used for the newline character. It is either  
      linefeed (10) or carriage return (13), and  should  normally  
      be the standard character for your operating system.  
549    
550         PCRE_CONFIG_LINK_SIZE         The  output  is an integer that is set to the value of the code that is
551           used for the newline character. It is either linefeed (10) or  carriage
552           return  (13),  and  should  normally be the standard character for your
553           operating system.
554    
555       The output is an integer that contains the number  of  bytes           PCRE_CONFIG_LINK_SIZE
      used  for  internal linkage in compiled regular expressions.  
      The value is 2, 3, or 4. Larger values allow larger  regular  
      expressions  to be compiled, at the expense of slower match-  
      ing. The default value of 2 is sufficient for  all  but  the  
      most  massive patterns, since it allows the compiled pattern  
      to be up to 64K in size.  
556    
557         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD         The output is an integer that contains the number  of  bytes  used  for
558           internal linkage in compiled regular expressions. The value is 2, 3, or
559           4. Larger values allow larger regular expressions to  be  compiled,  at
560           the  expense  of  slower matching. The default value of 2 is sufficient
561           for all but the most massive patterns, since  it  allows  the  compiled
562           pattern to be up to 64K in size.
563    
564       The output is an integer that contains the  threshold  above           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
      which  the POSIX interface uses malloc() for output vectors.  
      Further details are given in the pcreposix documentation.  
565    
566         PCRE_CONFIG_MATCH_LIMIT         The  output  is  an integer that contains the threshold above which the
567           POSIX interface uses malloc() for output vectors. Further  details  are
568           given in the pcreposix documentation.
569    
570       The output is an integer that gives the  default  limit  for           PCRE_CONFIG_MATCH_LIMIT
571       the   number  of  internal  matching  function  calls  in  a  
572       pcre_exec()  execution.  Further  details  are  given   with         The output is an integer that gives the default limit for the number of
573       pcre_exec() below.         internal matching function calls in a  pcre_exec()  execution.  Further
574           details are given with pcre_exec() below.
575    
576             PCRE_CONFIG_STACKRECURSE
577    
578           The  output  is  an integer that is set to one if internal recursion is
579           implemented by recursive function calls that use the stack to  remember
580           their state. This is the usual way that PCRE is compiled. The output is
581           zero if PCRE was compiled to use blocks of data on the heap instead  of
582           recursive   function   calls.   In  this  case,  pcre_stack_malloc  and
583           pcre_stack_free are called to manage memory blocks on  the  heap,  thus
584           avoiding the use of the stack.
585    
586    
587  COMPILING A PATTERN  COMPILING A PATTERN
588    
589       pcre *pcre_compile(const char *pattern, int options,         pcre *pcre_compile(const char *pattern, int options,
590            const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
591            const unsigned char *tableptr);              const unsigned char *tableptr);
592    
593       The function pcre_compile() is called to compile  a  pattern         The  function  pcre_compile()  is  called  to compile a pattern into an
594       into  an internal form. The pattern is a C string terminated         internal form. The pattern is a C string terminated by a  binary  zero,
595       by a binary zero, and is passed in the argument  pattern.  A         and  is  passed in the pattern argument. A pointer to a single block of
596       pointer  to  a  single  block of memory that is obtained via         memory that is obtained via pcre_malloc is returned. This contains  the
597       pcre_malloc is returned. This contains the compiled code and         compiled  code  and  related  data.  The  pcre  type is defined for the
598       related  data.  The  pcre  type  is defined for the returned         returned block; this is a typedef for a structure  whose  contents  are
599       block; this is a typedef for a structure whose contents  are         not  externally defined. It is up to the caller to free the memory when
600       not  externally  defined. It is up to the caller to free the         it is no longer required.
601       memory when it is no longer required.  
602           Although the compiled code of a PCRE regex is relocatable, that is,  it
603       Although the compiled code of a PCRE regex  is  relocatable,         does not depend on memory location, the complete pcre data block is not
604       that is, it does not depend on memory location, the complete         fully relocatable, because it may contain a copy of the tableptr  argu-
605       pcre data block is not fully relocatable,  because  it  con-         ment, which is an address (see below).
606       tains  a  copy of the tableptr argument, which is an address  
607       (see below).         The options argument contains independent bits that affect the compila-
608       The options argument contains independent bits  that  affect         tion. It should be zero if  no  options  are  required.  The  available
609       the  compilation.  It  should  be  zero  if  no  options are         options  are  described  below. Some of them, in particular, those that
610       required. Some of the options, in particular, those that are         are compatible with Perl, can also be set and  unset  from  within  the
611       compatible  with Perl, can also be set and unset from within         pattern  (see  the  detailed  description in the pcrepattern documenta-
612       the pattern (see the detailed description of regular expres-         tion). For these options, the contents of the options  argument  speci-
613       sions  in the pcrepattern documentation). For these options,         fies  their initial settings at the start of compilation and execution.
614       the contents of the options argument specifies their initial         The PCRE_ANCHORED option can be set at the time of matching as well  as
615       settings  at  the  start  of  compilation and execution. The         at compile time.
616       PCRE_ANCHORED option can be set at the time of  matching  as  
617       well as at compile time.         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
618           if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
619       If errptr is NULL, pcre_compile() returns NULL  immediately.         sets the variable pointed to by errptr to point to a textual error mes-
620       Otherwise, if compilation of a pattern fails, pcre_compile()         sage. The offset from the start of the pattern to the  character  where
621       returns NULL, and sets the variable pointed to by errptr  to         the  error  was  discovered  is  placed  in  the variable pointed to by
622       point  to a textual error message. The offset from the start         erroffset, which must not be NULL. If it  is,  an  immediate  error  is
623       of  the  pattern  to  the  character  where  the  error  was         given.
624       discovered   is   placed  in  the  variable  pointed  to  by  
625       erroffset, which must not be NULL. If it  is,  an  immediate         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of
626       error is given.         character tables that are  built  when  PCRE  is  compiled,  using  the
627           default  C  locale.  Otherwise, tableptr must be an address that is the
628       If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a         result of a call to pcre_maketables(). This value is  stored  with  the
629       default  set  of character tables which are built when it is         compiled  pattern,  and used again by pcre_exec(), unless another table
630       compiled, using the default C  locale.  Otherwise,  tableptr         pointer is passed to it. For more discussion, see the section on locale
631       must  be  the result of a call to pcre_maketables(). See the         support below.
632       section on locale support below.  
633           This  code  fragment  shows a typical straightforward call to pcre_com-
634       This code fragment shows a typical straightforward  call  to         pile():
635       pcre_compile():  
636             pcre *re;
637         pcre *re;           const char *error;
638         const char *error;           int erroffset;
639         int erroffset;           re = pcre_compile(
640         re = pcre_compile(             "^A.*Z",          /* the pattern */
641           "^A.*Z",          /* the pattern */             0,                /* default options */
642           0,                /* default options */             &error,           /* for error message */
643           &error,           /* for error message */             &erroffset,       /* for error offset */
644           &erroffset,       /* for error offset */             NULL);            /* use default character tables */
645           NULL);            /* use default character tables */  
646           The following names for option bits are defined in  the  pcre.h  header
647       The following option bits are defined:         file:
648    
649         PCRE_ANCHORED           PCRE_ANCHORED
650    
651       If this bit is set, the pattern is forced to be  "anchored",         If this bit is set, the pattern is forced to be "anchored", that is, it
652       that is, it is constrained to match only at the first match-         is constrained to match only at the first matching point in the  string
653       ing point in the string which is being searched  (the  "sub-         that  is being searched (the "subject string"). This effect can also be
654       ject string"). This effect can also be achieved by appropri-         achieved by appropriate constructs in the pattern itself, which is  the
655       ate constructs in the pattern itself, which is the only  way         only way to do it in Perl.
656       to do it in Perl.  
657             PCRE_AUTO_CALLOUT
658         PCRE_CASELESS  
659           If this bit is set, pcre_compile() automatically inserts callout items,
660       If this bit is set, letters in the pattern match both  upper         all with number 255, before each pattern item. For  discussion  of  the
661       and  lower  case  letters.  It  is  equivalent  to Perl's /i         callout facility, see the pcrecallout documentation.
662       option, and it can be changed within a  pattern  by  a  (?i)  
663       option setting.           PCRE_CASELESS
664    
665         PCRE_DOLLAR_ENDONLY         If  this  bit is set, letters in the pattern match both upper and lower
666           case letters. It is equivalent to Perl's  /i  option,  and  it  can  be
667       If this bit is set, a dollar metacharacter  in  the  pattern         changed  within  a  pattern  by  a (?i) option setting. When running in
668       matches  only at the end of the subject string. Without this         UTF-8 mode, case support for high-valued characters is  available  only
669       option, a dollar also matches immediately before  the  final         when PCRE is built with Unicode character property support.
670       character  if it is a newline (but not before any other new-  
671       lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if           PCRE_DOLLAR_ENDONLY
672       PCRE_MULTILINE is set. There is no equivalent to this option  
673       in Perl, and no way to set it within a pattern.         If  this bit is set, a dollar metacharacter in the pattern matches only
674           at the end of the subject string. Without this option,  a  dollar  also
675         PCRE_DOTALL         matches  immediately before the final character if it is a newline (but
676           not before any  other  newlines).  The  PCRE_DOLLAR_ENDONLY  option  is
677       If this bit is  set,  a  dot  metacharater  in  the  pattern         ignored if PCRE_MULTILINE is set. There is no equivalent to this option
678       matches all characters, including newlines. Without it, new-         in Perl, and no way to set it within a pattern.
679       lines are excluded. This option is equivalent to  Perl's  /s  
680       option,  and  it  can  be changed within a pattern by a (?s)           PCRE_DOTALL
681       option setting. A negative class such as [^a] always matches  
682       a  newline  character,  independent  of  the setting of this         If this bit is set, a dot metacharater in the pattern matches all char-
683       option.         acters,  including  newlines.  Without  it, newlines are excluded. This
684           option is equivalent to Perl's /s option, and it can be changed  within
685         PCRE_EXTENDED         a  pattern  by  a  (?s)  option  setting. A negative class such as [^a]
686           always matches a newline character, independent of the setting of  this
687       If this bit is set, whitespace data characters in  the  pat-         option.
688       tern  are  totally  ignored  except when escaped or inside a  
689       character class. Whitespace does not include the VT  charac-           PCRE_EXTENDED
690       ter  (code 11). In addition, characters between an unescaped  
691       # outside a character class and the next newline  character,         If  this  bit  is  set,  whitespace  data characters in the pattern are
692       inclusive, are also ignored. This is equivalent to Perl's /x         totally ignored except  when  escaped  or  inside  a  character  class.
693       option, and it can be changed within a  pattern  by  a  (?x)         Whitespace  does  not  include the VT character (code 11). In addition,
694       option setting.         characters between an unescaped # outside a  character  class  and  the
695           next newline character, inclusive, are also ignored. This is equivalent
696       This option makes it possible  to  include  comments  inside         to Perl's /x option, and it can be changed within a pattern by  a  (?x)
697       complicated patterns.  Note, however, that this applies only         option setting.
698       to data characters. Whitespace characters may  never  appear  
699       within special character sequences in a pattern, for example         This  option  makes  it possible to include comments inside complicated
700       within the sequence (?( which introduces a conditional  sub-         patterns.  Note, however, that this applies only  to  data  characters.
701       pattern.         Whitespace   characters  may  never  appear  within  special  character
702           sequences in a pattern, for  example  within  the  sequence  (?(  which
703         PCRE_EXTRA         introduces a conditional subpattern.
704    
705       This option was invented in  order  to  turn  on  additional           PCRE_EXTRA
706       functionality of PCRE that is incompatible with Perl, but it  
707       is currently of very little use. When set, any backslash  in         This  option  was invented in order to turn on additional functionality
708       a  pattern  that is followed by a letter that has no special         of PCRE that is incompatible with Perl, but it  is  currently  of  very
709       meaning causes an error, thus reserving  these  combinations         little  use. When set, any backslash in a pattern that is followed by a
710       for  future  expansion.  By default, as in Perl, a backslash         letter that has no special meaning  causes  an  error,  thus  reserving
711       followed by a letter with no special meaning is treated as a         these  combinations  for  future  expansion.  By default, as in Perl, a
712       literal.  There  are at present no other features controlled         backslash followed by a letter with no special meaning is treated as  a
713       by this option. It can also be set by a (?X) option  setting         literal.  There  are  at  present  no other features controlled by this
714       within a pattern.         option. It can also be set by a (?X) option setting within a pattern.
715    
716         PCRE_MULTILINE           PCRE_MULTILINE
717    
718       By default, PCRE treats the subject string as consisting  of         By default, PCRE treats the subject string as consisting  of  a  single
719       a  single "line" of characters (even if it actually contains         line  of characters (even if it actually contains newlines). The "start
720       several newlines). The "start  of  line"  metacharacter  (^)         of line" metacharacter (^) matches only at the  start  of  the  string,
721       matches  only  at the start of the string, while the "end of         while  the  "end  of line" metacharacter ($) matches only at the end of
722       line" metacharacter ($) matches  only  at  the  end  of  the         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
723       string,    or   before   a   terminating   newline   (unless         is set). This is the same as Perl.
724       PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.  
725           When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
726       When PCRE_MULTILINE it is set, the "start of line" and  "end         constructs match immediately following or immediately before  any  new-
727       of  line"  constructs match immediately following or immedi-         line  in the subject string, respectively, as well as at the very start
728       ately before any newline  in  the  subject  string,  respec-         and end. This is equivalent to Perl's /m option, and it can be  changed
729       tively,  as  well  as  at  the  very  start and end. This is         within a pattern by a (?m) option setting. If there are no "\n" charac-
730       equivalent to Perl's /m option, and it can be changed within         ters in a subject string, or no occurrences of ^ or  $  in  a  pattern,
731       a  pattern  by  a  (?m) option setting. If there are no "\n"         setting PCRE_MULTILINE has no effect.
732       characters in a subject string, or no occurrences of ^ or  $  
733       in a pattern, setting PCRE_MULTILINE has no effect.           PCRE_NO_AUTO_CAPTURE
734    
735         PCRE_NO_AUTO_CAPTURE         If this option is set, it disables the use of numbered capturing paren-
736           theses in the pattern. Any opening parenthesis that is not followed  by
737       If this option is set, it disables the use of numbered  cap-         ?  behaves as if it were followed by ?: but named parentheses can still
738       turing  parentheses  in the pattern. Any opening parenthesis         be used for capturing (and they acquire  numbers  in  the  usual  way).
739       that is not followed by ? behaves as if it were followed  by         There is no equivalent of this option in Perl.
740       ?:  but  named  parentheses  can still be used for capturing  
741       (and they acquire numbers in the usual  way).  There  is  no           PCRE_UNGREEDY
742       equivalent of this option in Perl.  
743           This  option  inverts  the "greediness" of the quantifiers so that they
744         PCRE_UNGREEDY         are not greedy by default, but become greedy if followed by "?". It  is
745           not  compatible  with Perl. It can also be set by a (?U) option setting
746       This option inverts the "greediness" of the  quantifiers  so         within the pattern.
747       that  they  are  not greedy by default, but become greedy if  
748       followed by "?". It is not compatible with Perl. It can also           PCRE_UTF8
749       be set by a (?U) option setting within the pattern.  
750           This option causes PCRE to regard both the pattern and the  subject  as
751         PCRE_UTF8         strings  of  UTF-8 characters instead of single-byte character strings.
752           However, it is available only when PCRE is built to include UTF-8  sup-
753       This option causes PCRE to regard both the pattern  and  the         port.  If not, the use of this option provokes an error. Details of how
754       subject  as  strings  of UTF-8 characters instead of single-         this option changes the behaviour of PCRE are given in the  section  on
755       byte character strings. However, it  is  available  only  if         UTF-8 support in the main pcre page.
756       PCRE  has  been  built to include UTF-8 support. If not, the  
757       use of this option provokes an error. Details  of  how  this           PCRE_NO_UTF8_CHECK
758       option  changes  the behaviour of PCRE are given in the sec-  
759       tion on UTF-8 support in the main pcre page.         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
760           automatically checked. If an invalid UTF-8 sequence of bytes is  found,
761           pcre_compile()  returns an error. If you already know that your pattern
762           is valid, and you want to skip this check for performance reasons,  you
763           can  set  the  PCRE_NO_UTF8_CHECK option. When it is set, the effect of
764           passing an invalid UTF-8 string as a pattern is undefined. It may cause
765           your  program  to  crash.   Note that this option can also be passed to
766           pcre_exec(),  to  suppress  the  UTF-8  validity  checking  of  subject
767           strings.
768    
769    
770  STUDYING A PATTERN  STUDYING A PATTERN
771    
772       pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options,
773            const char **errptr);              const char **errptr);
774    
775       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
776       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
777       the time taken for matching. The function pcre_study() takes         matching.  The function pcre_study() takes a pointer to a compiled pat-
778       a  pointer  to  a compiled pattern as its first argument. If         tern as its first argument. If studying the pattern produces additional
779       studing the pattern  produces  additional  information  that         information  that  will  help speed up matching, pcre_study() returns a
780       will  help speed up matching, pcre_study() returns a pointer         pointer to a pcre_extra block, in which the study_data field points  to
781       to a pcre_extra block, in which the study_data field  points         the results of the study.
782       to the results of the study.  
783           The  returned  value  from  pcre_study()  can  be  passed  directly  to
784       The  returned  value  from  a  pcre_study()  can  be  passed         pcre_exec(). However, a pcre_extra block  also  contains  other  fields
785       directly  to pcre_exec(). However, the pcre_extra block also         that  can  be  set  by the caller before the block is passed; these are
786       contains other fields that can be set by the  caller  before         described below in the section on matching a pattern.
787       the  block is passed; these are described below. If studying  
788       the pattern does not  produce  any  additional  information,         If studying the pattern does not produce  any  additional  information,
789       pcre_study() returns NULL. In that circumstance, if the cal-         pcre_study() returns NULL. In that circumstance, if the calling program
790       ling program wants to pass  some  of  the  other  fields  to         wants to pass any of the other fields to pcre_exec(), it  must  set  up
791       pcre_exec(), it must set up its own pcre_extra block.         its own pcre_extra block.
792    
793       The second argument contains option  bits.  At  present,  no         The  second  argument of pcre_study() contains option bits. At present,
794       options  are  defined  for  pcre_study(),  and this argument         no options are defined, and this argument should always be zero.
795       should always be zero.  
796           The third argument for pcre_study() is a pointer for an error  message.
797       The third argument for pcre_study()  is  a  pointer  for  an         If  studying  succeeds  (even  if no data is returned), the variable it
798       error  message.  If  studying  succeeds  (even if no data is         points to is set to NULL. Otherwise it points to a textual  error  mes-
799       returned), the variable it points to is set to NULL.  Other-         sage.  You should therefore test the error pointer for NULL after call-
800       wise it points to a textual error message. You should there-         ing pcre_study(), to be sure that it has run successfully.
801       fore  test  the  error  pointer  for  NULL   after   calling  
802       pcre_study(), to be sure that it has run successfully.         This is a typical call to pcre_study():
803    
804       This is a typical call to pcre_study():           pcre_extra *pe;
805             pe = pcre_study(
806         pcre_extra *pe;             re,             /* result of pcre_compile() */
807         pe = pcre_study(             0,              /* no options exist */
808           re,             /* result of pcre_compile() */             &error);        /* set to NULL or points to a message */
809           0,              /* no options exist */  
810           &error);        /* set to NULL or points to a message */         At present, studying a pattern is useful only for non-anchored patterns
811           that  do not have a single fixed starting character. A bitmap of possi-
812       At present, studying a  pattern  is  useful  only  for  non-         ble starting bytes is created.
      anchored  patterns  that do not have a single fixed starting  
      character. A  bitmap  of  possible  starting  characters  is  
      created.  
813    
814    
815  LOCALE SUPPORT  LOCALE SUPPORT
816    
817       PCRE handles caseless matching, and determines whether char-         PCRE handles caseless matching, and determines whether  characters  are
818       acters  are  letters, digits, or whatever, by reference to a         letters,  digits, or whatever, by reference to a set of tables, indexed
819       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
820       to characters with codes less than 256. The library contains         characters  with  codes  less than 128. Higher-valued codes never match
821       a default set of tables that is created  in  the  default  C         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
822       locale  when  PCRE  is compiled. This is used when the final         with Unicode character property support.)
823       argument of pcre_compile() is NULL, and  is  sufficient  for  
824       many applications.         An  internal set of tables is created in the default C locale when PCRE
825           is built. This is used when the final  argument  of  pcre_compile()  is
826       An alternative set of tables can, however, be supplied. Such         NULL,  and  is  sufficient for many applications. An alternative set of
827       tables  are built by calling the pcre_maketables() function,         tables can, however, be supplied. These may be created in  a  different
828       which has no arguments, in the relevant locale.  The  result         locale  from the default. As more and more applications change to using
829       can  then be passed to pcre_compile() as often as necessary.         Unicode, the need for this locale support is expected to die away.
830       For example, to build and use tables  that  are  appropriate  
831       for  the French locale (where accented characters with codes         External tables are built by calling  the  pcre_maketables()  function,
832       greater than 128 are treated as letters), the following code         which  has no arguments, in the relevant locale. The result can then be
833       could be used:         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
834           example,  to  build  and use tables that are appropriate for the French
835         setlocale(LC_CTYPE, "fr");         locale (where accented characters with  values  greater  than  128  are
836         tables = pcre_maketables();         treated as letters), the following code could be used:
837         re = pcre_compile(..., tables);  
838             setlocale(LC_CTYPE, "fr_FR");
839       The  tables  are  built  in  memory  that  is  obtained  via           tables = pcre_maketables();
840       pcre_malloc.  The  pointer that is passed to pcre_compile is           re = pcre_compile(..., tables);
841       saved with the compiled pattern, and  the  same  tables  are  
842       used via this pointer by pcre_study() and pcre_exec(). Thus,         When  pcre_maketables()  runs,  the  tables are built in memory that is
843       for any single pattern, compilation, studying  and  matching         obtained via pcre_malloc. It is the caller's responsibility  to  ensure
844       all happen in the same locale, but different patterns can be         that  the memory containing the tables remains available for as long as
845       compiled in different locales. It is the caller's  responsi-         it is needed.
846       bility  to  ensure  that  the  memory  containing the tables  
847       remains available for as long as it is needed.         The pointer that is passed to pcre_compile() is saved with the compiled
848           pattern,  and the same tables are used via this pointer by pcre_study()
849           and normally also by pcre_exec(). Thus, by default, for any single pat-
850           tern, compilation, studying and matching all happen in the same locale,
851           but different patterns can be compiled in different locales.
852    
853           It is possible to pass a table pointer or NULL (indicating the  use  of
854           the  internal  tables)  to  pcre_exec(). Although not intended for this
855           purpose, this facility could be used to match a pattern in a  different
856           locale from the one in which it was compiled. Passing table pointers at
857           run time is discussed below in the section on matching a pattern.
858    
859    
860  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
861    
862       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
863            int what, void *where);              int what, void *where);
864    
865       The pcre_fullinfo() function  returns  information  about  a         The pcre_fullinfo() function returns information about a compiled  pat-
866       compiled pattern. It replaces the obsolete pcre_info() func-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
867       tion, which is nevertheless retained for backwards compabil-         less retained for backwards compability (and is documented below).
868       ity (and is documented below).  
869           The first argument for pcre_fullinfo() is a  pointer  to  the  compiled
870       The first argument for pcre_fullinfo() is a pointer  to  the         pattern.  The second argument is the result of pcre_study(), or NULL if
871       compiled  pattern.  The  second  argument  is  the result of         the pattern was not studied. The third argument specifies  which  piece
872       pcre_study(), or NULL if the pattern was  not  studied.  The         of  information  is required, and the fourth argument is a pointer to a
873       third  argument  specifies  which  piece  of  information is         variable to receive the data. The yield of the  function  is  zero  for
874       required, and the fourth argument is a pointer to a variable         success, or one of the following negative numbers:
875       to  receive  the data. The yield of the function is zero for  
876       success, or one of the following negative numbers:           PCRE_ERROR_NULL       the argument code was NULL
877                                   the argument where was NULL
878         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
879                               the argument where was NULL           PCRE_ERROR_BADOPTION  the value of what was invalid
880         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
881         PCRE_ERROR_BADOPTION  the value of what was invalid         The  "magic  number" is placed at the start of each compiled pattern as
882           an simple check against passing an arbitrary memory pointer. Here is  a
883       Here is a typical call of  pcre_fullinfo(),  to  obtain  the         typical  call  of pcre_fullinfo(), to obtain the length of the compiled
884       length of the compiled pattern:         pattern:
885    
886         int rc;           int rc;
887         unsigned long int length;           unsigned long int length;
888         rc = pcre_fullinfo(           rc = pcre_fullinfo(
889           re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
890           pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
891           PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
892           &length);         /* where to put the data */             &length);         /* where to put the data */
893    
894       The possible values for the third argument  are  defined  in         The possible values for the third argument are defined in  pcre.h,  and
895       pcre.h, and are as follows:         are as follows:
896    
897         PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
898    
899       Return the number of the highest back reference in the  pat-         Return  the  number  of  the highest back reference in the pattern. The
900       tern.  The  fourth argument should point to an int variable.         fourth argument should point to an int variable. Zero  is  returned  if
901       Zero is returned if there are no back references.         there are no back references.
902    
903         PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
904    
905       Return the number of capturing subpatterns in  the  pattern.         Return  the  number of capturing subpatterns in the pattern. The fourth
906       The fourth argument should point to an int variable.         argument should point to an int variable.
907    
908         PCRE_INFO_FIRSTBYTE           PCRE_INFO_DEFAULTTABLES
909    
910       Return information about  the  first  byte  of  any  matched         Return a pointer to the internal default character tables within  PCRE.
911       string,  for a non-anchored pattern. (This option used to be         The  fourth  argument should point to an unsigned char * variable. This
912       called PCRE_INFO_FIRSTCHAR; the old name is still recognized         information call is provided for internal use by the pcre_study() func-
913       for backwards compatibility.)         tion.  External  callers  can  cause PCRE to use its internal tables by
914           passing a NULL table pointer.
915       If there is a fixed first byte, e.g. from a pattern such  as  
916       (cat|cow|coyote),  it  is returned in the integer pointed to           PCRE_INFO_FIRSTBYTE
917       by where. Otherwise, if either  
918           Return information about the first byte of any matched  string,  for  a
919       (a) the pattern was compiled with the PCRE_MULTILINE option,         non-anchored    pattern.    (This    option    used    to   be   called
920       and every branch starts with "^", or         PCRE_INFO_FIRSTCHAR; the old name is  still  recognized  for  backwards
921           compatibility.)
922       (b) every  branch  of  the  pattern  starts  with  ".*"  and  
923       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
924       anchored),         (cat|cow|coyote), it is returned in the integer pointed  to  by  where.
925           Otherwise, if either
926       -1 is returned, indicating that the pattern matches only  at  
927       the  start  of  a subject string or after any newline within         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
928       the string. Otherwise -2 is returned. For anchored patterns,         branch starts with "^", or
929       -2 is returned.  
930           (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
931         PCRE_INFO_FIRSTTABLE         set (if it were set, the pattern would be anchored),
932    
933       If the pattern was studied, and this resulted  in  the  con-         -1  is  returned, indicating that the pattern matches only at the start
934       struction of a 256-bit table indicating a fixed set of bytes         of a subject string or after any newline within the  string.  Otherwise
935       for the first byte in any matching string, a pointer to  the         -2 is returned. For anchored patterns, -2 is returned.
936       table  is  returned.  Otherwise NULL is returned. The fourth  
937       argument should point to an unsigned char * variable.           PCRE_INFO_FIRSTTABLE
938    
939         PCRE_INFO_LASTLITERAL         If  the pattern was studied, and this resulted in the construction of a
940           256-bit table indicating a fixed set of bytes for the first byte in any
941       Return the value of the rightmost  literal  byte  that  must         matching  string, a pointer to the table is returned. Otherwise NULL is
942       exist  in  any  matched  string, other than at its start, if         returned. The fourth argument should point to an unsigned char *  vari-
943       such a byte has been recorded. The  fourth  argument  should         able.
944       point  to  an  int variable. If there is no such byte, -1 is  
945       returned. For anchored patterns,  a  last  literal  byte  is           PCRE_INFO_LASTLITERAL
946       recorded  only  if  it follows something of variable length.  
947       For example, for the pattern /^a\d+z\d+/ the returned  value         Return  the  value of the rightmost literal byte that must exist in any
948       is "z", but for /^a\dz\d/ the returned value is -1.         matched string, other than at its  start,  if  such  a  byte  has  been
949           recorded. The fourth argument should point to an int variable. If there
950         PCRE_INFO_NAMECOUNT         is no such byte, -1 is returned. For anchored patterns, a last  literal
951         PCRE_INFO_NAMEENTRYSIZE         byte  is  recorded only if it follows something of variable length. For
952         PCRE_INFO_NAMETABLE         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
953           /^a\dz\d/ the returned value is -1.
954       PCRE supports the use of named as well as numbered capturing  
955       parentheses. The names are just an additional way of identi-           PCRE_INFO_NAMECOUNT
956       fying the parentheses,  which  still  acquire  a  number.  A           PCRE_INFO_NAMEENTRYSIZE
957       caller  that  wants  to extract data from a named subpattern           PCRE_INFO_NAMETABLE
958       must convert the name to a number in  order  to  access  the  
959       correct  pointers  in  the  output  vector  (described  with         PCRE  supports the use of named as well as numbered capturing parenthe-
960       pcre_exec() below). In order to do this, it must  first  use         ses. The names are just an additional way of identifying the  parenthe-
961       these  three  values  to  obtain  the name-to-number mapping         ses,  which  still  acquire  numbers.  A  convenience  function  called
962       table for the pattern.         pcre_get_named_substring() is provided  for  extracting  an  individual
963           captured  substring  by  name.  It is also possible to extract the data
964       The  map  consists  of  a  number  of  fixed-size   entries.         directly, by first converting the name to a number in order  to  access
965       PCRE_INFO_NAMECOUNT   gives   the  number  of  entries,  and         the  correct  pointers in the output vector (described with pcre_exec()
966       PCRE_INFO_NAMEENTRYSIZE gives the size of each  entry;  both         below). To do the conversion, you need to use the  name-to-number  map,
967       of  these return an int value. The entry size depends on the         which is described by these three values.
968       length of the longest name.  PCRE_INFO_NAMETABLE  returns  a  
969       pointer to the first entry of the table (a pointer to char).         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
970       The first two bytes of each entry are the number of the cap-         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
971       turing parenthesis, most significant byte first. The rest of         of  each  entry;  both  of  these  return  an int value. The entry size
972       the entry is the corresponding name,  zero  terminated.  The         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
973       names  are  in alphabetical order. For example, consider the         a  pointer  to  the  first  entry of the table (a pointer to char). The
974       following pattern (assume PCRE_EXTENDED  is  set,  so  white         first two bytes of each entry are the number of the capturing parenthe-
975       space - including newlines - is ignored):         sis,  most  significant byte first. The rest of the entry is the corre-
976           sponding name, zero terminated. The names are  in  alphabetical  order.
977         (?P<date> (?P<year>(\d\d)?\d\d) -         For  example,  consider  the following pattern (assume PCRE_EXTENDED is
978         (?P<month>\d\d) - (?P<day>\d\d) )         set, so white space - including newlines - is ignored):
979    
980       There are four named subpatterns,  so  the  table  has  four           (?P<date> (?P<year>(\d\d)?\d\d) -
981       entries,  and  each  entry in the table is eight bytes long.           (?P<month>\d\d) - (?P<day>\d\d) )
982       The table is as follows, with non-printing  bytes  shows  in  
983       hex, and undefined bytes shown as ??:         There are four named subpatterns, so the table has  four  entries,  and
984           each  entry  in the table is eight bytes long. The table is as follows,
985         00 01 d  a  t  e  00 ??         with non-printing bytes shows in hexadecimal, and undefined bytes shown
986         00 05 d  a  y  00 ?? ??         as ??:
987         00 04 m  o  n  t  h  00  
988         00 02 y  e  a  r  00 ??           00 01 d  a  t  e  00 ??
989             00 05 d  a  y  00 ?? ??
990       When writing code to extract data  from  named  subpatterns,           00 04 m  o  n  t  h  00
991       remember  that the length of each entry may be different for           00 02 y  e  a  r  00 ??
992       each compiled pattern.  
993           When  writing  code  to  extract  data from named subpatterns using the
994         PCRE_INFO_OPTIONS         name-to-number map, remember that the length of each entry is likely to
995           be different for each compiled pattern.
996       Return a copy of the options with which the pattern was com-  
997       piled.  The fourth argument should point to an unsigned long           PCRE_INFO_OPTIONS
998       int variable. These option bits are those specified  in  the  
999       call  to  pcre_compile(),  modified  by any top-level option         Return  a  copy of the options with which the pattern was compiled. The
1000       settings within the pattern itself.         fourth argument should point to an unsigned long  int  variable.  These
1001           option bits are those specified in the call to pcre_compile(), modified
1002       A pattern is automatically anchored by PCRE if  all  of  its         by any top-level option settings within the pattern itself.
1003       top-level alternatives begin with one of the following:  
1004           A pattern is automatically anchored by PCRE if  all  of  its  top-level
1005         ^     unless PCRE_MULTILINE is set         alternatives begin with one of the following:
1006         \A    always  
1007         \G    always           ^     unless PCRE_MULTILINE is set
1008         .*    if PCRE_DOTALL is set and there are no back           \A    always
1009                 references to the subpattern in which .* appears           \G    always
1010             .*    if PCRE_DOTALL is set and there are no back
1011       For such patterns, the  PCRE_ANCHORED  bit  is  set  in  the                   references to the subpattern in which .* appears
1012       options returned by pcre_fullinfo().  
1013           For such patterns, the PCRE_ANCHORED bit is set in the options returned
1014         PCRE_INFO_SIZE         by pcre_fullinfo().
1015    
1016       Return the size of the compiled pattern, that is, the  value           PCRE_INFO_SIZE
1017       that  was  passed as the argument to pcre_malloc() when PCRE  
1018       was getting memory in which to place the compiled data.  The         Return the size of the compiled pattern, that is, the  value  that  was
1019       fourth argument should point to a size_t variable.         passed as the argument to pcre_malloc() when PCRE was getting memory in
1020           which to place the compiled data. The fourth argument should point to a
1021         PCRE_INFO_STUDYSIZE         size_t variable.
1022    
1023       Returns the size  of  the  data  block  pointed  to  by  the           PCRE_INFO_STUDYSIZE
1024       study_data  field  in a pcre_extra block. That is, it is the  
1025       value that was passed to pcre_malloc() when PCRE was getting         Return the size of the data block pointed to by the study_data field in
1026       memory into which to place the data created by pcre_study().         a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1027       The fourth argument should point to a size_t variable.         pcre_malloc() when PCRE was getting memory into which to place the data
1028           created by pcre_study(). The fourth argument should point to  a  size_t
1029           variable.
1030    
1031    
1032  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1033    
1034       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1035    
1036       The pcre_info() function is now obsolete because its  inter-         The  pcre_info()  function is now obsolete because its interface is too
1037       face  is  too  restrictive  to return all the available data         restrictive to return all the available data about a compiled  pattern.
1038       about  a  compiled  pattern.   New   programs   should   use         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1039       pcre_fullinfo()  instead.  The  yield  of pcre_info() is the         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1040       number of capturing subpatterns, or  one  of  the  following         lowing negative numbers:
1041       negative numbers:  
1042             PCRE_ERROR_NULL       the argument code was NULL
1043         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1044         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1045           If  the  optptr  argument is not NULL, a copy of the options with which
1046       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
1047       with which the pattern was compiled is placed in the integer         PCRE_INFO_OPTIONS above).
1048       it points to (see PCRE_INFO_OPTIONS above).  
1049           If  the  pattern  is  not anchored and the firstcharptr argument is not
1050       If the pattern is not anchored and the firstcharptr argument         NULL, it is used to pass back information about the first character  of
1051       is  not  NULL, it is used to pass back information about the         any matched string (see PCRE_INFO_FIRSTBYTE above).
      first    character    of    any    matched    string    (see  
      PCRE_INFO_FIRSTBYTE above).  
1052    
1053    
1054  MATCHING A PATTERN  MATCHING A PATTERN
1055    
1056       int pcre_exec(const pcre *code, const pcre_extra *extra,         int pcre_exec(const pcre *code, const pcre_extra *extra,
1057            const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1058            int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1059    
1060       The function pcre_exec() is called to match a subject string         The  function pcre_exec() is called to match a subject string against a
1061       against  a pre-compiled pattern, which is passed in the code         compiled pattern, which is passed in the code argument. If the  pattern
1062       argument. If the pattern has been studied, the result of the         has been studied, the result of the study should be passed in the extra
1063       study should be passed in the extra argument.         argument.
1064    
1065       Here is an example of a simple call to pcre_exec():         In most applications, the pattern will have been compiled (and  option-
1066           ally  studied)  in the same process that calls pcre_exec(). However, it
1067         int rc;         is possible to save compiled patterns and study data, and then use them
1068         int ovector[30];         later  in  different processes, possibly even on different hosts. For a
1069         rc = pcre_exec(         discussion about this, see the pcreprecompile documentation.
1070           re,             /* result of pcre_compile() */  
1071           NULL,           /* we didn't study the pattern */         Here is an example of a simple call to pcre_exec():
1072           "some string",  /* the subject string */  
1073           11,             /* the length of the subject string */           int rc;
1074           0,              /* start at offset 0 in the subject */           int ovector[30];
1075           0,              /* default options */           rc = pcre_exec(
1076           ovector,        /* vector for substring information */             re,             /* result of pcre_compile() */
1077           30);            /* number of elements in the vector */             NULL,           /* we didn't study the pattern */
1078               "some string",  /* the subject string */
1079       If the extra argument is  not  NULL,  it  must  point  to  a             11,             /* the length of the subject string */
1080       pcre_extra  data  block.  The  pcre_study() function returns             0,              /* start at offset 0 in the subject */
1081       such a block (when it doesn't return NULL), but you can also             0,              /* default options */
1082       create  one for yourself, and pass additional information in             ovector,        /* vector of integers for substring information */
1083       it. The fields in the block are as follows:             30);            /* number of elements in the vector  (NOT  size  in
1084           bytes) */
1085         unsigned long int flags;  
1086         void *study_data;     Extra data for pcre_exec()
1087         unsigned long int match_limit;  
1088         void *callout_data;         If  the  extra argument is not NULL, it must point to a pcre_extra data
1089           block. The pcre_study() function returns such a block (when it  doesn't
1090       The flags field is a bitmap  that  specifies  which  of  the         return  NULL), but you can also create one for yourself, and pass addi-
1091       other fields are set. The flag bits are:         tional information in it. The fields in a pcre_extra block are as  fol-
1092           lows:
1093         PCRE_EXTRA_STUDY_DATA  
1094         PCRE_EXTRA_MATCH_LIMIT           unsigned long int flags;
1095         PCRE_EXTRA_CALLOUT_DATA           void *study_data;
1096             unsigned long int match_limit;
1097       Other flag bits should be set to zero. The study_data  field           void *callout_data;
1098       is   set  in  the  pcre_extra  block  that  is  returned  by           const unsigned char *tables;
1099       pcre_study(), together with the appropriate  flag  bit.  You  
1100       should  not  set this yourself, but you can add to the block         The  flags  field  is a bitmap that specifies which of the other fields
1101       by setting the other fields.         are set. The flag bits are:
1102    
1103       The match_limit field provides a means  of  preventing  PCRE           PCRE_EXTRA_STUDY_DATA
1104       from  using  up a vast amount of resources when running pat-           PCRE_EXTRA_MATCH_LIMIT
1105       terns that are not going to match, but  which  have  a  very           PCRE_EXTRA_CALLOUT_DATA
1106       large  number  of  possibilities  in their search trees. The           PCRE_EXTRA_TABLES
1107       classic example is the  use  of  nested  unlimited  repeats.  
1108       Internally,  PCRE  uses  a  function called match() which it         Other flag bits should be set to zero. The study_data field is  set  in
1109       calls  repeatedly  (sometimes  recursively).  The  limit  is         the  pcre_extra  block  that is returned by pcre_study(), together with
1110       imposed  on the number of times this function is called dur-         the appropriate flag bit. You should not set this yourself, but you may
1111       ing a match, which has the effect of limiting the amount  of         add  to  the  block by setting the other fields and their corresponding
1112       recursion and backtracking that can take place. For patterns         flag bits.
1113       that are not anchored, the count starts from zero  for  each  
1114       position in the subject string.         The match_limit field provides a means of preventing PCRE from using up
1115           a  vast amount of resources when running patterns that are not going to
1116       The default limit for the library can be set  when  PCRE  is         match, but which have a very large number  of  possibilities  in  their
1117       built;  the default default is 10 million, which handles all         search  trees.  The  classic  example  is  the  use of nested unlimited
1118       but the most extreme cases. You can reduce  the  default  by         repeats.
1119       suppling  pcre_exec()  with  a  pcre_extra  block  in  which  
1120       match_limit   is   set   to    a    smaller    value,    and         Internally, PCRE uses a function called match() which it calls  repeat-
1121       PCRE_EXTRA_MATCH_LIMIT  is  set  in  the flags field. If the         edly  (sometimes  recursively).  The  limit is imposed on the number of
1122       limit      is      exceeded,       pcre_exec()       returns         times this function is called during a match, which has the  effect  of
1123       PCRE_ERROR_MATCHLIMIT.         limiting  the amount of recursion and backtracking that can take place.
1124           For patterns that are not anchored, the count starts from zero for each
1125       The pcre_callout field is used in conjunction with the "cal-         position in the subject string.
1126       lout"  feature,  which is described in the pcrecallout docu-  
1127       mentation.         The  default  limit  for the library can be set when PCRE is built; the
1128           default default is 10 million, which handles all but the  most  extreme
1129       The PCRE_ANCHORED option can be passed in the options  argu-         cases.  You  can  reduce  the  default  by  suppling pcre_exec() with a
1130       ment,   whose   unused   bits  must  be  zero.  This  limits         pcre_extra block in which match_limit is set to a  smaller  value,  and
1131       pcre_exec() to matching at the first matching position. How-         PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1132       ever,  if  a  pattern  was  compiled  with PCRE_ANCHORED, or         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1133       turned out to be anchored by virtue of its contents, it can-  
1134       not be made unachored at matching time.         The pcre_callout field is used in conjunction with the  "callout"  fea-
1135           ture, which is described in the pcrecallout documentation.
1136       There are also three further options that can be set only at  
1137       matching time:         The  tables  field  is  used  to  pass  a  character  tables pointer to
1138           pcre_exec(); this overrides the value that is stored with the  compiled
1139         PCRE_NOTBOL         pattern.  A  non-NULL value is stored with the compiled pattern only if
1140           custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1141       The first character of the string is not the beginning of  a         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1142       line,  so  the  circumflex  metacharacter  should  not match         PCRE's internal tables to be used. This facility is  helpful  when  re-
1143       before it. Setting this without PCRE_MULTILINE  (at  compile         using  patterns  that  have been saved after compiling with an external
1144       time) causes circumflex never to match.         set of tables, because the external tables  might  be  at  a  different
1145           address  when  pcre_exec() is called. See the pcreprecompile documenta-
1146         PCRE_NOTEOL         tion for a discussion of saving compiled patterns for later use.
1147    
1148       The end of the string is not the end of a line, so the  dol-     Option bits for pcre_exec()
1149       lar  metacharacter should not match it nor (except in multi-  
1150       line mode) a newline immediately  before  it.  Setting  this         The unused bits of the options argument for pcre_exec() must  be  zero.
1151       without PCRE_MULTILINE (at compile time) causes dollar never         The   only  bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NOTBOL,
1152       to match.         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.
1153    
1154         PCRE_NOTEMPTY           PCRE_ANCHORED
1155    
1156       An empty string is not considered to be  a  valid  match  if         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
1157       this  option  is  set. If there are alternatives in the pat-         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
1158       tern, they are tried. If  all  the  alternatives  match  the         turned out to be anchored by virtue of its contents, it cannot be  made
1159       empty  string,  the  entire match fails. For example, if the         unachored at matching time.
1160       pattern  
1161             PCRE_NOTBOL
1162         a?b?  
1163           This option specifies that first character of the subject string is not
1164       is applied to a string not beginning with  "a"  or  "b",  it         the beginning of a line, so the  circumflex  metacharacter  should  not
1165       matches  the  empty string at the start of the subject. With         match  before it. Setting this without PCRE_MULTILINE (at compile time)
1166       PCRE_NOTEMPTY set, this match is not valid, so PCRE searches         causes  circumflex  never  to  match.  This  option  affects  only  the
1167       further into the string for occurrences of "a" or "b".         behaviour of the circumflex metacharacter. It does not affect \A.
1168    
1169       Perl has no direct equivalent of PCRE_NOTEMPTY, but it  does           PCRE_NOTEOL
1170       make  a  special case of a pattern match of the empty string  
1171       within its split() function, and when using the /g modifier.         This option specifies that the end of the subject string is not the end
1172       It  is possible to emulate Perl's behaviour after matching a         of a line, so the dollar metacharacter should not match it nor  (except
1173       null string by first trying the  match  again  at  the  same         in  multiline mode) a newline immediately before it. Setting this with-
1174       offset  with  PCRE_NOTEMPTY  set,  and then if that fails by         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1175       advancing the starting offset  (see  below)  and  trying  an         option  affects only the behaviour of the dollar metacharacter. It does
1176       ordinary match again.         not affect \Z or \z.
1177    
1178       The subject string is passed to pcre_exec() as a pointer  in           PCRE_NOTEMPTY
1179       subject,  a length in length, and a starting offset in star-  
1180       toffset. Unlike the pattern string, the subject may  contain         An empty string is not considered to be a valid match if this option is
1181       binary  zero  bytes.  When  the starting offset is zero, the         set.  If  there are alternatives in the pattern, they are tried. If all
1182       search for a match starts at the beginning of  the  subject,         the alternatives match the empty string, the entire  match  fails.  For
1183       and this is by far the most common case.         example, if the pattern
1184    
1185       If the pattern was compiled with the PCRE_UTF8  option,  the           a?b?
1186       subject  must  be  a sequence of bytes that is a valid UTF-8  
1187       string.  If  an  invalid  UTF-8  string  is  passed,  PCRE's         is  applied  to  a string not beginning with "a" or "b", it matches the
1188       behaviour is not defined.         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
1189           match is not valid, so PCRE searches further into the string for occur-
1190       A non-zero starting offset  is  useful  when  searching  for         rences of "a" or "b".
1191       another  match  in  the  same subject by calling pcre_exec()  
1192       again after a previous success.  Setting startoffset differs         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1193       from  just  passing  over  a  shortened  string  and setting         cial  case  of  a  pattern match of the empty string within its split()
1194       PCRE_NOTBOL in the case of a pattern that  begins  with  any         function, and when using the /g modifier. It  is  possible  to  emulate
1195       kind of lookbehind. For example, consider the pattern         Perl's behaviour after matching a null string by first trying the match
1196           again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1197         \Biss\B         if  that  fails by advancing the starting offset (see below) and trying
1198           an ordinary match again. There is some code that demonstrates how to do
1199       which finds occurrences of "iss" in the middle of words. (\B         this in the pcredemo.c sample program.
1200       matches only if the current position in the subject is not a  
1201       word boundary.) When applied to the string "Mississipi"  the           PCRE_NO_UTF8_CHECK
1202       first  call  to  pcre_exec()  finds the first occurrence. If  
1203       pcre_exec() is called again with just the remainder  of  the         When PCRE_UTF8 is set at compile time, the validity of the subject as a
1204       subject,  namely  "issipi", it does not match, because \B is         UTF-8 string is automatically checked when pcre_exec() is  subsequently
1205       always false at the start of the subject, which is deemed to         called.   The  value  of  startoffset is also checked to ensure that it
1206       be  a  word  boundary. However, if pcre_exec() is passed the         points to the start of a UTF-8 character. If an invalid UTF-8  sequence
1207       entire string again, but with startoffset set to 4, it finds         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1208       the  second  occurrence  of "iss" because it is able to look         startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is
1209       behind the starting point to discover that it is preceded by         returned.
1210       a letter.  
1211           If  you  already  know that your subject is valid, and you want to skip
1212       If a non-zero starting offset is passed when the pattern  is         these   checks   for   performance   reasons,   you   can    set    the
1213       anchored, one attempt to match at the given offset is tried.         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
1214       This can only succeed if the pattern does  not  require  the         do this for the second and subsequent calls to pcre_exec() if  you  are
1215       match to be at the start of the subject.         making  repeated  calls  to  find  all  the matches in a single subject
1216           string. However, you should be  sure  that  the  value  of  startoffset
1217       In general, a pattern matches a certain portion of the  sub-         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
1218       ject,  and  in addition, further substrings from the subject         set, the effect of passing an invalid UTF-8 string as a subject,  or  a
1219       may be picked out by parts of  the  pattern.  Following  the         value  of startoffset that does not point to the start of a UTF-8 char-
1220       usage  in  Jeffrey Friedl's book, this is called "capturing"         acter, is undefined. Your program may crash.
1221       in what follows, and the phrase  "capturing  subpattern"  is  
1222       used for a fragment of a pattern that picks out a substring.           PCRE_PARTIAL
1223       PCRE supports several other kinds of  parenthesized  subpat-  
1224       tern that do not cause substrings to be captured.         This option turns on the  partial  matching  feature.  If  the  subject
1225           string  fails to match the pattern, but at some point during the match-
1226       Captured substrings are returned to the caller via a  vector         ing process the end of the subject was reached (that  is,  the  subject
1227       of  integer  offsets whose address is passed in ovector. The         partially  matches  the  pattern and the failure to match occurred only
1228       number of elements in the vector is passed in ovecsize.  The         because there were not enough subject characters), pcre_exec()  returns
1229       first two-thirds of the vector is used to pass back captured         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1230       substrings, each substring using a  pair  of  integers.  The         used, there are restrictions on what may appear in the  pattern.  These
1231       remaining  third  of  the  vector  is  used  as workspace by         are discussed in the pcrepartial documentation.
1232       pcre_exec() while matching capturing subpatterns, and is not  
1233       available for passing back information. The length passed in     The string to be matched by pcre_exec()
1234       ovecsize should always be a multiple of three. If it is not,  
1235       it is rounded down.         The  subject string is passed to pcre_exec() as a pointer in subject, a
1236           length in length, and a starting byte offset in startoffset.  In  UTF-8
1237       When a match has been successful, information about captured         mode,  the  byte  offset  must point to the start of a UTF-8 character.
1238       substrings is returned in pairs of integers, starting at the         Unlike the pattern string, the subject may contain binary  zero  bytes.
1239       beginning of ovector, and continuing up to two-thirds of its         When  the starting offset is zero, the search for a match starts at the
1240       length  at  the  most. The first element of a pair is set to         beginning of the subject, and this is by far the most common case.
1241       the offset of the first character in a  substring,  and  the  
1242       second is set to the offset of the first character after the         A non-zero starting offset is useful when searching for  another  match
1243       end of a substring. The first  pair,  ovector[0]  and  ovec-         in  the same subject by calling pcre_exec() again after a previous suc-
1244       tor[1],  identify  the portion of the subject string matched         cess.  Setting startoffset differs from just passing over  a  shortened
1245       by the entire pattern. The next pair is used for  the  first         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
1246       capturing  subpattern,  and  so  on.  The  value returned by         with any kind of lookbehind. For example, consider the pattern
1247       pcre_exec() is the number of pairs that have  been  set.  If  
1248       there  are no capturing subpatterns, the return value from a           \Biss\B
1249       successful match is 1, indicating that just the  first  pair  
1250       of offsets has been set.         which finds occurrences of "iss" in the middle of  words.  (\B  matches
1251           only  if  the  current position in the subject is not a word boundary.)
1252       Some convenience functions are provided for  extracting  the         When applied to the string "Mississipi" the first call  to  pcre_exec()
1253       captured substrings as separate strings. These are described         finds  the  first  occurrence. If pcre_exec() is called again with just
1254       in the following section.         the remainder of the subject,  namely  "issipi",  it  does  not  match,
1255           because \B is always false at the start of the subject, which is deemed
1256       It is possible for an capturing  subpattern  number  n+1  to         to be a word boundary. However, if pcre_exec()  is  passed  the  entire
1257       match  some  part  of  the subject when subpattern n has not         string again, but with startoffset set to 4, it finds the second occur-
1258       been used at all.  For  example,  if  the  string  "abc"  is         rence of "iss" because it is able to look behind the starting point  to
1259       matched  against the pattern (a|(z))(bc) subpatterns 1 and 3         discover that it is preceded by a letter.
1260       are matched, but 2 is not. When this  happens,  both  offset  
1261       values corresponding to the unused subpattern are set to -1.         If  a  non-zero starting offset is passed when the pattern is anchored,
1262           one attempt to match at the given offset is made. This can only succeed
1263       If a capturing subpattern is matched repeatedly, it  is  the         if  the  pattern  does  not require the match to be at the start of the
1264       last  portion  of  the  string  that  it  matched  that gets         subject.
1265       returned.  
1266       How pcre_exec() returns captured substrings
1267       If the vector is too small to hold  all  the  captured  sub-  
1268       strings,  it is used as far as possible (up to two-thirds of         In general, a pattern matches a certain portion of the subject, and  in
1269       its length), and the function returns a value  of  zero.  In         addition,  further  substrings  from  the  subject may be picked out by
1270       particular,  if  the  substring offsets are not of interest,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
1271       pcre_exec() may be called with ovector passed  as  NULL  and         this  is  called "capturing" in what follows, and the phrase "capturing
1272       ovecsize  as  zero.  However,  if  the pattern contains back         subpattern" is used for a fragment of a pattern that picks out  a  sub-
1273       references and the ovector isn't big enough to remember  the         string.  PCRE  supports several other kinds of parenthesized subpattern
1274       related  substrings,  PCRE  has to get additional memory for         that do not cause substrings to be captured.
1275       use during matching. Thus it is usually advisable to  supply  
1276       an ovector.         Captured substrings are returned to the caller via a vector of  integer
1277           offsets  whose  address is passed in ovector. The number of elements in
1278       Note that pcre_info() can be used to find out how many  cap-         the vector is passed in ovecsize, which must be a non-negative  number.
1279       turing  subpatterns  there  are  in  a compiled pattern. The         Note: this argument is NOT the size of ovector in bytes.
1280       smallest size for ovector that will  allow  for  n  captured  
1281       substrings,  in  addition  to  the  offsets of the substring         The  first  two-thirds of the vector is used to pass back captured sub-
1282       matched by the whole pattern, is (n+1)*3.         strings, each substring using a pair of integers. The  remaining  third
1283           of  the  vector is used as workspace by pcre_exec() while matching cap-
1284       If pcre_exec() fails, it returns a negative number. The fol-         turing subpatterns, and is not available for passing back  information.
1285       lowing are defined in the header file:         The  length passed in ovecsize should always be a multiple of three. If
1286           it is not, it is rounded down.
1287         PCRE_ERROR_NOMATCH        (-1)  
1288           When a match is successful, information about  captured  substrings  is
1289       The subject string did not match the pattern.         returned  in  pairs  of integers, starting at the beginning of ovector,
1290           and continuing up to two-thirds of its length at the  most.  The  first
1291         PCRE_ERROR_NULL           (-2)         element of a pair is set to the offset of the first character in a sub-
1292           string, and the second is set to the  offset  of  the  first  character
1293       Either code or subject was passed as NULL,  or  ovector  was         after  the  end  of  a  substring. The first pair, ovector[0] and ovec-
1294       NULL and ovecsize was not zero.         tor[1], identify the portion of  the  subject  string  matched  by  the
1295           entire  pattern.  The next pair is used for the first capturing subpat-
1296         PCRE_ERROR_BADOPTION      (-3)         tern, and so on. The value returned by pcre_exec()  is  the  number  of
1297           pairs  that  have  been set. If there are no capturing subpatterns, the
1298       An unrecognized bit was set in the options argument.         return value from a successful match is 1,  indicating  that  just  the
1299           first pair of offsets has been set.
1300         PCRE_ERROR_BADMAGIC       (-4)  
1301           Some  convenience  functions  are  provided for extracting the captured
1302       PCRE stores a 4-byte "magic number" at the start of the com-         substrings as separate strings. These are described  in  the  following
1303       piled  code,  to  catch  the  case  when it is passed a junk         section.
1304       pointer. This is the error it gives when  the  magic  number  
1305       isn't present.         It  is  possible  for  an capturing subpattern number n+1 to match some
1306           part of the subject when subpattern n has not been  used  at  all.  For
1307         PCRE_ERROR_UNKNOWN_NODE   (-5)         example, if the string "abc" is matched against the pattern (a|(z))(bc)
1308           subpatterns 1 and 3 are matched, but 2 is not. When this happens,  both
1309       While running the pattern match, an unknown item was encoun-         offset values corresponding to the unused subpattern are set to -1.
1310       tered in the compiled pattern. This error could be caused by  
1311       a bug in PCRE or by overwriting of the compiled pattern.         If a capturing subpattern is matched repeatedly, it is the last portion
1312           of the string that it matched that is returned.
1313         PCRE_ERROR_NOMEMORY       (-6)  
1314           If the vector is too small to hold all the captured substring  offsets,
1315       If a pattern contains back references, but the ovector  that         it is used as far as possible (up to two-thirds of its length), and the
1316       is  passed  to pcre_exec() is not big enough to remember the         function returns a value of zero. In particular, if the substring  off-
1317       referenced substrings, PCRE gets a block of  memory  at  the         sets are not of interest, pcre_exec() may be called with ovector passed
1318       start  of  matching to use for this purpose. If the call via         as NULL and ovecsize as zero. However, if  the  pattern  contains  back
1319       pcre_malloc() fails, this error  is  given.  The  memory  is         references  and  the  ovector is not big enough to remember the related
1320       freed at the end of matching.         substrings, PCRE has to get additional memory for use during  matching.
1321           Thus it is usually advisable to supply an ovector.
1322         PCRE_ERROR_NOSUBSTRING    (-7)  
1323           Note  that  pcre_info() can be used to find out how many capturing sub-
1324       This   error   is   used   by   the   pcre_copy_substring(),         patterns there are in a compiled pattern. The smallest size for ovector
1325       pcre_get_substring(),  and  pcre_get_substring_list()  func-         that  will  allow for n captured substrings, in addition to the offsets
1326       tions (see below). It is never returned by pcre_exec().         of the substring matched by the whole pattern, is (n+1)*3.
1327    
1328         PCRE_ERROR_MATCHLIMIT     (-8)     Return values from pcre_exec()
1329    
1330       The recursion and backtracking limit, as  specified  by  the         If pcre_exec() fails, it returns a negative number. The  following  are
1331       match_limit  field  in a pcre_extra structure (or defaulted)         defined in the header file:
1332       was reached. See the description above.  
1333             PCRE_ERROR_NOMATCH        (-1)
1334         PCRE_ERROR_CALLOUT        (-9)  
1335           The subject string did not match the pattern.
1336       This error is never generated by pcre_exec() itself.  It  is  
1337       provided  for  use by callout functions that want to yield a           PCRE_ERROR_NULL           (-2)
1338       distinctive error code. See  the  pcrecallout  documentation  
1339       for details.         Either  code  or  subject  was  passed as NULL, or ovector was NULL and
1340           ovecsize was not zero.
1341    
1342             PCRE_ERROR_BADOPTION      (-3)
1343    
1344           An unrecognized bit was set in the options argument.
1345    
1346             PCRE_ERROR_BADMAGIC       (-4)
1347    
1348           PCRE stores a 4-byte "magic number" at the start of the compiled  code,
1349           to catch the case when it is passed a junk pointer and to detect when a
1350           pattern that was compiled in an environment of one endianness is run in
1351           an  environment  with the other endianness. This is the error that PCRE
1352           gives when the magic number is not present.
1353    
1354             PCRE_ERROR_UNKNOWN_NODE   (-5)
1355    
1356           While running the pattern match, an unknown item was encountered in the
1357           compiled  pattern.  This  error  could be caused by a bug in PCRE or by
1358           overwriting of the compiled pattern.
1359    
1360             PCRE_ERROR_NOMEMORY       (-6)
1361    
1362           If a pattern contains back references, but the ovector that  is  passed
1363           to pcre_exec() is not big enough to remember the referenced substrings,
1364           PCRE gets a block of memory at the start of matching to  use  for  this
1365           purpose.  If the call via pcre_malloc() fails, this error is given. The
1366           memory is automatically freed at the end of matching.
1367    
1368             PCRE_ERROR_NOSUBSTRING    (-7)
1369    
1370           This error is used by the pcre_copy_substring(),  pcre_get_substring(),
1371           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
1372           returned by pcre_exec().
1373    
1374             PCRE_ERROR_MATCHLIMIT     (-8)
1375    
1376           The recursion and backtracking limit, as specified by  the  match_limit
1377           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
1378           description above.
1379    
1380             PCRE_ERROR_CALLOUT        (-9)
1381    
1382           This error is never generated by pcre_exec() itself. It is provided for
1383           use  by  callout functions that want to yield a distinctive error code.
1384           See the pcrecallout documentation for details.
1385    
1386             PCRE_ERROR_BADUTF8        (-10)
1387    
1388           A string that contains an invalid UTF-8 byte sequence was passed  as  a
1389           subject.
1390    
1391             PCRE_ERROR_BADUTF8_OFFSET (-11)
1392    
1393           The UTF-8 byte sequence that was passed as a subject was valid, but the
1394           value of startoffset did not point to the beginning of a UTF-8  charac-
1395           ter.
1396    
1397             PCRE_ERROR_PARTIAL (-12)
1398    
1399           The  subject  string did not match, but it did match partially. See the
1400           pcrepartial documentation for details of partial matching.
1401    
1402             PCRE_ERROR_BAD_PARTIAL (-13)
1403    
1404           The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
1405           items  that are not supported for partial matching. See the pcrepartial
1406           documentation for details of partial matching.
1407    
1408             PCRE_ERROR_INTERNAL (-14)
1409    
1410           An unexpected internal error has occurred. This error could  be  caused
1411           by a bug in PCRE or by overwriting of the compiled pattern.
1412    
1413             PCRE_ERROR_BADCOUNT (-15)
1414    
1415           This  error is given if the value of the ovecsize argument is negative.
1416    
1417    
1418  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
1419    
1420       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_copy_substring(const char *subject, int *ovector,
1421            int stringcount, int stringnumber, char *buffer,              int stringcount, int stringnumber, char *buffer,
1422            int buffersize);              int buffersize);
1423    
1424       int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
1425            int stringcount, int stringnumber,              int stringcount, int stringnumber,
1426            const char **stringptr);              const char **stringptr);
1427    
1428       int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
1429            int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
1430    
1431       Captured substrings can be accessed directly  by  using  the         Captured substrings can be  accessed  directly  by  using  the  offsets
1432       offsets returned by pcre_exec() in ovector. For convenience,         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
1433       the functions  pcre_copy_substring(),  pcre_get_substring(),         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
1434       and  pcre_get_substring_list()  are  provided for extracting         string_list()  are  provided for extracting captured substrings as new,
1435       captured  substrings  as  new,   separate,   zero-terminated         separate, zero-terminated strings. These functions identify  substrings
1436       strings.  These functions identify substrings by number. The         by  number.  The  next section describes functions for extracting named
1437       next section describes functions for extracting  named  sub-         substrings. A substring  that  contains  a  binary  zero  is  correctly
1438       strings.   A  substring  that  contains  a  binary  zero  is         extracted  and  has  a further zero added on the end, but the result is
1439       correctly extracted and has a further zero added on the end,         not, of course, a C string.
1440       but the result is not, of course, a C string.  
1441           The first three arguments are the same for all  three  of  these  func-
1442       The first three arguments are the  same  for  all  three  of         tions:  subject  is  the subject string that has just been successfully
1443       these  functions:   subject  is the subject string which has         matched, ovector is a pointer to the vector of integer offsets that was
1444       just been successfully matched, ovector is a pointer to  the         passed to pcre_exec(), and stringcount is the number of substrings that
1445       vector  of  integer  offsets that was passed to pcre_exec(),         were captured by the match, including the substring  that  matched  the
1446       and stringcount is the number of substrings that  were  cap-         entire regular expression. This is the value returned by pcre_exec() if
1447       tured by the match, including the substring that matched the         it is greater than zero. If pcre_exec() returned zero, indicating  that
1448       entire regular expression. This is  the  value  returned  by         it  ran out of space in ovector, the value passed as stringcount should
1449       pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()         be the number of elements in the vector divided by three.
1450       returned zero, indicating that it ran out of space in  ovec-  
1451       tor,  the  value passed as stringcount should be the size of         The functions pcre_copy_substring() and pcre_get_substring() extract  a
1452       the vector divided by three.         single  substring,  whose  number  is given as stringnumber. A value of
1453           zero extracts the substring that matched the  entire  pattern,  whereas
1454       The functions pcre_copy_substring() and pcre_get_substring()         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
1455       extract a single substring, whose number is given as string-         string(), the string is placed in buffer,  whose  length  is  given  by
1456       number. A value of zero extracts the substring that  matched         buffersize,  while  for  pcre_get_substring()  a new block of memory is
1457       the entire pattern, while higher values extract the captured         obtained via pcre_malloc, and its address is  returned  via  stringptr.
1458       substrings. For pcre_copy_substring(), the string is  placed         The  yield  of  the function is the length of the string, not including
1459       in  buffer,  whose  length is given by buffersize, while for         the terminating zero, or one of
1460       pcre_get_substring() a new block of memory is  obtained  via  
1461       pcre_malloc,  and its address is returned via stringptr. The           PCRE_ERROR_NOMEMORY       (-6)
1462       yield of the function is  the  length  of  the  string,  not  
1463       including the terminating zero, or one of         The buffer was too small for pcre_copy_substring(), or the  attempt  to
1464           get memory failed for pcre_get_substring().
1465         PCRE_ERROR_NOMEMORY       (-6)  
1466             PCRE_ERROR_NOSUBSTRING    (-7)
1467       The buffer was too small for pcre_copy_substring(),  or  the  
1468       attempt to get memory failed for pcre_get_substring().         There is no substring whose number is stringnumber.
1469    
1470         PCRE_ERROR_NOSUBSTRING    (-7)         The  pcre_get_substring_list()  function  extracts  all  available sub-
1471           strings and builds a list of pointers to them. All this is  done  in  a
1472       There is no substring whose number is stringnumber.         single block of memory that is obtained via pcre_malloc. The address of
1473           the memory block is returned via listptr, which is also  the  start  of
1474       The pcre_get_substring_list() function extracts  all  avail-         the  list  of  string pointers. The end of the list is marked by a NULL
1475       able  substrings  and builds a list of pointers to them. All         pointer. The yield of the function is zero if all went well, or
1476       this is done in a single block of memory which  is  obtained  
1477       via pcre_malloc. The address of the memory block is returned           PCRE_ERROR_NOMEMORY       (-6)
1478       via listptr, which is also the start of the list  of  string  
1479       pointers.  The  end of the list is marked by a NULL pointer.         if the attempt to get the memory block failed.
1480       The yield of the function is zero if all went well, or  
1481           When any of these functions encounter a substring that is unset,  which
1482         PCRE_ERROR_NOMEMORY       (-6)         can  happen  when  capturing subpattern number n+1 matches some part of
1483           the subject, but subpattern n has not been used at all, they return  an
1484       if the attempt to get the memory block failed.         empty string. This can be distinguished from a genuine zero-length sub-
1485           string by inspecting the appropriate offset in ovector, which is  nega-
1486       When any of these functions encounter a  substring  that  is         tive for unset substrings.
1487       unset, which can happen when capturing subpattern number n+1  
1488       matches some part of the subject, but subpattern n  has  not         The  two convenience functions pcre_free_substring() and pcre_free_sub-
1489       been  used  at all, they return an empty string. This can be         string_list() can be used to free the memory  returned  by  a  previous
1490       distinguished  from  a  genuine  zero-length  substring   by         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
1491       inspecting the appropriate offset in ovector, which is nega-         tively. They do nothing more than  call  the  function  pointed  to  by
1492       tive for unset substrings.         pcre_free,  which  of course could be called directly from a C program.
1493           However, PCRE is used in some situations where it is linked via a  spe-
1494       The  two  convenience  functions  pcre_free_substring()  and         cial  interface  to  another  programming  language  which  cannot  use
1495       pcre_free_substring_list()  can  be  used to free the memory         pcre_free directly; it is  for  these  cases  that  the  functions  are
1496       returned by  a  previous  call  of  pcre_get_substring()  or         provided.
      pcre_get_substring_list(),  respectively.  They  do  nothing  
      more than call the function pointed to by  pcre_free,  which  
      of  course  could  be called directly from a C program. How-  
      ever, PCRE is used in some situations where it is linked via  
      a  special  interface  to another programming language which  
      cannot use pcre_free directly; it is for  these  cases  that  
      the functions are provided.  
1497    
1498    
1499  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
1500    
1501       int pcre_copy_named_substring(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
1502            const char *subject, int *ovector,              const char *name);
1503            int stringcount, const char *stringname,  
1504            char *buffer, int buffersize);         int pcre_copy_named_substring(const pcre *code,
1505                const char *subject, int *ovector,
1506       int pcre_get_stringnumber(const pcre *code,              int stringcount, const char *stringname,
1507            const char *name);              char *buffer, int buffersize);
1508    
1509       int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
1510            const char *subject, int *ovector,              const char *subject, int *ovector,
1511            int stringcount, const char *stringname,              int stringcount, const char *stringname,
1512            const char **stringptr);              const char **stringptr);
1513    
1514       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-
1515       ciated    number.    This    can    be   done   by   calling         ber.  For example, for this pattern
1516       pcre_get_stringnumber(). The first argument is the  compiled  
1517       pattern,  and  the second is the name. For example, for this           (a+)b(?<xxx>\d+)...
1518       pattern  
1519           the number of the subpattern called "xxx" is 2. You can find the number
1520         ab(?<xxx>\d+)...         from the name by calling pcre_get_stringnumber(). The first argument is
1521           the compiled pattern, and the second is the  name.  The  yield  of  the
1522       the number of the subpattern called "xxx" is  1.  Given  the         function  is  the  subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if
1523       number,  you can then extract the substring directly, or use         there is no subpattern of that name.
1524       one of the functions described in the previous section.  For  
1525       convenience,  there are also two functions that do the whole         Given the number, you can extract the substring directly, or use one of
1526       job.         the functions described in the previous section. For convenience, there
1527           are also two functions that do the whole job.
1528       Most of the  arguments  of  pcre_copy_named_substring()  and  
1529       pcre_get_named_substring()  are  the  same  as those for the         Most   of   the   arguments    of    pcre_copy_named_substring()    and
1530       functions that  extract  by  number,  and  so  are  not  re-         pcre_get_named_substring()  are  the  same  as  those for the similarly
1531       described here. There are just two differences.         named functions that extract by number. As these are described  in  the
1532           previous  section,  they  are not re-described here. There are just two
1533       First, instead of a substring number, a  substring  name  is         differences:
1534       given.  Second,  there  is  an  extra argument, given at the  
1535       start, which is a pointer to the compiled pattern.  This  is         First, instead of a substring number, a substring name is  given.  Sec-
1536       needed  in order to gain access to the name-to-number trans-         ond, there is an extra argument, given at the start, which is a pointer
1537       lation table.         to the compiled pattern. This is needed in order to gain access to  the
1538           name-to-number translation table.
1539       These functions  call  pcre_get_stringnumber(),  and  if  it  
1540       succeeds,    they   then   call   pcre_copy_substring()   or         These  functions call pcre_get_stringnumber(), and if it succeeds, they
1541       pcre_get_substring(), as appropriate.         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
1542           ate.
1543    
1544  Last updated: 03 February 2003  Last updated: 09 September 2004
1545  Copyright (c) 1997-2003 University of Cambridge.  Copyright (c) 1997-2004 University of Cambridge.
1546  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
1547    
1548  NAME  PCRE(3)                                                                PCRE(3)
      PCRE - Perl-compatible regular expressions  
1549    
1550    
 PCRE CALLOUTS  
1551    
1552       int (*pcre_callout)(pcre_callout_block *);  NAME
1553           PCRE - Perl-compatible regular expressions
1554    
1555    PCRE CALLOUTS
1556    
1557       PCRE provides a feature called "callout", which is  a  means         int (*pcre_callout)(pcre_callout_block *);
      of  temporarily passing control to the caller of PCRE in the  
      middle of pattern matching. The caller of PCRE  provides  an  
      external  function  by putting its entry point in the global  
      variable pcre_callout. By default,  this  variable  contains  
      NULL, which disables all calling out.  
   
      Within a regular expression, (?C) indicates  the  points  at  
      which  the external function is to be called. Different cal-  
      lout points can be identified by putting a number less  than  
      256  after  the  letter  C.  The default value is zero.  For  
      example, this pattern has two callout points:  
   
        (?C1)9abc(?C2)def  
   
      During matching, when PCRE  reaches  a  callout  point  (and  
      pcre_callout  is  set), the external function is called. Its  
      only argument is a pointer to  a  pcre_callout  block.  This  
      contains the following variables:  
   
        int          version;  
        int          callout_number;  
        int         *offset_vector;  
        const char  *subject;  
        int          subject_length;  
        int          start_match;  
        int          current_position;  
        int          capture_top;  
        int          capture_last;  
        void        *callout_data;  
   
      The version field  is  an  integer  containing  the  version  
      number of the block format. The current version is zero. The  
      version number may change in future if additional fields are  
      added,  but  the  intention  is  never  to remove any of the  
      existing fields.  
   
      The callout_number field contains the number of the callout,  
      as compiled into the pattern (that is, the number after ?C).  
   
      The offset_vector field  is  a  pointer  to  the  vector  of  
      offsets  that  was  passed by the caller to pcre_exec(). The  
      contents can be inspected in  order  to  extract  substrings  
      that  have  been  matched  so  far,  in  the same way as for  
      extracting substrings after a match has completed.  
      The subject and subject_length  fields  contain  copies  the  
      values that were passed to pcre_exec().  
   
      The start_match field contains the offset within the subject  
      at  which  the current match attempt started. If the pattern  
      is not anchored, the callout function may be called  several  
      times for different starting points.  
   
      The current_position field contains the  offset  within  the  
      subject of the current match pointer.  
   
      The capture_top field contains the  number  of  the  highest  
      captured substring so far.  
   
      The capture_last field  contains  the  number  of  the  most  
      recently captured substring.  
   
      The callout_data field contains a value that  is  passed  to  
      pcre_exec()  by  the  caller  specifically so that it can be  
      passed back in callouts. It is passed  in  the  pcre_callout  
      field  of the pcre_extra data structure. If no such data was  
      passed, the value of callout_data in a pcre_callout block is  
      NULL.  There is a description of the pcre_extra structure in  
      the pcreapi documentation.  
1558    
1559           PCRE provides a feature called "callout", which is a means of temporar-
1560           ily passing control to the caller of PCRE  in  the  middle  of  pattern
1561           matching.  The  caller of PCRE provides an external function by putting
1562           its entry point in the global variable pcre_callout. By  default,  this
1563           variable contains NULL, which disables all calling out.
1564    
1565           Within  a  regular  expression,  (?C) indicates the points at which the
1566           external function is to be called.  Different  callout  points  can  be
1567           identified  by  putting  a number less than 256 after the letter C. The
1568           default value is zero.  For  example,  this  pattern  has  two  callout
1569           points:
1570    
1571             (?C1)eabc(?C2)def
1572    
1573           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
1574           called, PCRE automatically  inserts  callouts,  all  with  number  255,
1575           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
1576           used with the pattern
1577    
1578             A(\d{2}|--)
1579    
1580           it is processed as if it were
1581    
1582           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
1583    
1584           Notice that there is a callout before and after  each  parenthesis  and
1585           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
1586           progress of pattern matching. The pcretest command has an  option  that
1587           sets  automatic callouts; when it is used, the output indicates how the
1588           pattern is matched. This is useful information when you are  trying  to
1589           optimize the performance of a particular pattern.
1590    
1591    
1592    MISSING CALLOUTS
1593    
1594           You  should  be  aware  that,  because of optimizations in the way PCRE
1595           matches patterns, callouts sometimes do not happen. For example, if the
1596           pattern is
1597    
1598             ab(?C4)cd
1599    
1600           PCRE knows that any matching string must contain the letter "d". If the
1601           subject string is "abyz", the lack of "d" means that  matching  doesn't
1602           ever  start,  and  the  callout is never reached. However, with "abyd",
1603           though the result is still no match, the callout is obeyed.
1604    
1605    
1606    THE CALLOUT INTERFACE
1607    
1608           During matching, when PCRE reaches a callout point, the external  func-
1609           tion  defined  by pcre_callout is called (if it is set). The only argu-
1610           ment is a pointer to a pcre_callout block. This structure contains  the
1611           following fields:
1612    
1613             int          version;
1614             int          callout_number;
1615             int         *offset_vector;
1616             const char  *subject;
1617             int          subject_length;
1618             int          start_match;
1619             int          current_position;
1620             int          capture_top;
1621             int          capture_last;
1622             void        *callout_data;
1623             int          pattern_position;
1624             int          next_item_length;
1625    
1626           The  version  field  is an integer containing the version number of the
1627           block format. The initial version was 0; the current version is 1.  The
1628           version  number  will  change  again in future if additional fields are
1629           added, but the intention is never to remove any of the existing fields.
1630    
1631           The  callout_number  field  contains the number of the callout, as com-
1632           piled into the pattern (that is, the number after ?C for  manual  call-
1633           outs, and 255 for automatically generated callouts).
1634    
1635           The  offset_vector field is a pointer to the vector of offsets that was
1636           passed by the caller to pcre_exec(). The contents can be  inspected  in
1637           order  to extract substrings that have been matched so far, in the same
1638           way as for extracting substrings after a match has completed.
1639    
1640           The subject and subject_length fields contain copies of the values that
1641           were passed to pcre_exec().
1642    
1643           The  start_match  field contains the offset within the subject at which
1644           the current match attempt started. If the pattern is not anchored,  the
1645           callout function may be called several times from the same point in the
1646           pattern for different starting points in the subject.
1647    
1648           The current_position field contains the offset within  the  subject  of
1649           the current match pointer.
1650    
1651           The  capture_top field contains one more than the number of the highest
1652           numbered captured substring so far. If no  substrings  have  been  cap-
1653           tured, the value of capture_top is one.
1654    
1655           The  capture_last  field  contains the number of the most recently cap-
1656           tured substring. If no substrings have been captured, its value is  -1.
1657    
1658           The  callout_data  field contains a value that is passed to pcre_exec()
1659           by the caller specifically so that it can be passed back  in  callouts.
1660           It  is  passed  in the pcre_callout field of the pcre_extra data struc-
1661           ture. If no such data was  passed,  the  value  of  callout_data  in  a
1662           pcre_callout  block  is  NULL. There is a description of the pcre_extra
1663           structure in the pcreapi documentation.
1664    
1665           The pattern_position field is present from version 1 of the  pcre_call-
1666           out structure. It contains the offset to the next item to be matched in
1667           the pattern string.
1668    
1669           The next_item_length field is present from version 1 of the  pcre_call-
1670           out structure. It contains the length of the next item to be matched in
1671           the pattern string. When the callout immediately precedes  an  alterna-
1672           tion  bar, a closing parenthesis, or the end of the pattern, the length
1673           is zero. When the callout precedes an opening parenthesis,  the  length
1674           is that of the entire subpattern.
1675    
1676           The  pattern_position  and next_item_length fields are intended to help
1677           in distinguishing between different automatic callouts, which all  have
1678           the same callout number. However, they are set for all callouts.
1679    
1680    
1681  RETURN VALUES  RETURN VALUES
1682    
1683       The callout function returns an integer.  If  the  value  is         The  external callout function returns an integer to PCRE. If the value
1684       zero,  matching  proceeds as normal. If the value is greater         is zero, matching proceeds as normal. If  the  value  is  greater  than
1685       than zero, matching fails at the current  point,  but  back-         zero,  matching  fails  at  the current point, but backtracking to test
1686       tracking  to test other possibilities goes ahead, just as if         other matching possibilities goes ahead, just as if a lookahead  asser-
1687       a lookahead assertion had failed. If the value is less  than         tion  had  failed.  If  the value is less than zero, the match is aban-
1688       zero,  the  match  is abandoned, and pcre_exec() returns the         doned, and pcre_exec() returns the negative value.
1689       value.  
1690           Negative  values  should  normally  be   chosen   from   the   set   of
1691       Negative values should normally be chosen from  the  set  of         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
1692       PCRE_ERROR_xxx  values.  In  particular,  PCRE_ERROR_NOMATCH         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is
1693       forces a standard "no  match"  failure.   The  error  number         reserved  for  use  by callout functions; it will never be used by PCRE
1694       PCRE_ERROR_CALLOUT is reserved for use by callout functions;         itself.
      it will never be used by PCRE itself.  
1695    
1696  Last updated: 21 January 2003  Last updated: 09 September 2004
1697  Copyright (c) 1997-2003 University of Cambridge.  Copyright (c) 1997-2004 University of Cambridge.
1698  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
1699    
1700    PCRE(3)                                                                PCRE(3)
1701    
1702    
1703    
1704  NAME  NAME
1705       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
1706    
1707    DIFFERENCES BETWEEN PCRE AND PERL
1708    
1709           This  document describes the differences in the ways that PCRE and Perl
1710           handle regular expressions. The differences  described  here  are  with
1711           respect to Perl 5.8.
1712    
1713           1.  PCRE does not have full UTF-8 support. Details of what it does have
1714           are given in the section on UTF-8 support in the main pcre page.
1715    
1716           2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
1717           permits  them,  but they do not mean what you might think. For example,
1718           (?!a){3} does not assert that the next three characters are not "a". It
1719           just asserts that the next character is not "a" three times.
1720    
1721           3.  Capturing  subpatterns  that occur inside negative lookahead asser-
1722           tions are counted, but their entries in the offsets  vector  are  never
1723           set.  Perl sets its numerical variables from any such patterns that are
1724           matched before the assertion fails to match something (thereby succeed-
1725           ing),  but  only  if the negative lookahead assertion contains just one
1726           branch.
1727    
1728           4. Though binary zero characters are supported in the  subject  string,
1729           they are not allowed in a pattern string because it is passed as a nor-
1730           mal C string, terminated by zero. The escape sequence \0 can be used in
1731           the pattern to represent a binary zero.
1732    
1733           5.  The  following Perl escape sequences are not supported: \l, \u, \L,
1734           \U, and \N. In fact these are implemented by Perl's general string-han-
1735           dling  and are not part of its pattern matching engine. If any of these
1736           are encountered by PCRE, an error is generated.
1737    
1738           6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
1739           is  built  with Unicode character property support. The properties that
1740           can be tested with \p and \P are limited to the general category  prop-
1741           erties such as Lu and Nd.
1742    
1743           7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
1744           ters in between are treated as literals.  This  is  slightly  different
1745           from  Perl  in  that  $  and  @ are also handled as literals inside the
1746           quotes. In Perl, they cause variable interpolation (but of course  PCRE
1747           does not have variables). Note the following examples:
1748    
1749               Pattern            PCRE matches      Perl matches
1750    
1751               \Qabc$xyz\E        abc$xyz           abc followed by the
1752                                                      contents of $xyz
1753               \Qabc\$xyz\E       abc\$xyz          abc\$xyz
1754               \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
1755    
1756           The  \Q...\E  sequence  is recognized both inside and outside character
1757           classes.
1758    
1759           8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})
1760           constructions.  However,  there is support for recursive patterns using
1761           the non-Perl items (?R),  (?number),  and  (?P>name).  Also,  the  PCRE
1762           "callout"  feature allows an external function to be called during pat-
1763           tern matching. See the pcrecallout documentation for details.
1764    
1765           9. There are some differences that are concerned with the  settings  of
1766           captured  strings  when  part  of  a  pattern is repeated. For example,
1767           matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
1768           unset, but in PCRE it is set to "b".
1769    
1770           10. PCRE provides some extensions to the Perl regular expression facil-
1771           ities:
1772    
1773           (a) Although lookbehind assertions must  match  fixed  length  strings,
1774           each alternative branch of a lookbehind assertion can match a different
1775           length of string. Perl requires them all to have the same length.
1776    
1777           (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $
1778           meta-character matches only at the very end of the string.
1779    
1780           (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
1781           cial meaning is faulted.
1782    
1783           (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
1784           fiers is inverted, that is, by default they are not greedy, but if fol-
1785           lowed by a question mark they are.
1786    
1787           (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
1788           tried only at the first matching position in the subject string.
1789    
1790           (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
1791           TURE options for pcre_exec() have no Perl equivalents.
1792    
1793  DIFFERENCES FROM PERL         (g) The (?R), (?number), and (?P>name) constructs allows for  recursive
1794           pattern  matching  (Perl  can  do  this using the (?p{code}) construct,
1795           which PCRE cannot support.)
1796    
1797       This document describes the differences  in  the  ways  that         (h) PCRE supports named capturing substrings, using the Python  syntax.
      PCRE  and  Perl  handle regular expressions. The differences  
      described here are with respect to Perl 5.8.  
   
      1. PCRE does  not  allow  repeat  quantifiers  on  lookahead  
      assertions. Perl permits them, but they do not mean what you  
      might think. For example, (?!a){3} does not assert that  the  
      next  three characters are not "a". It just asserts that the  
      next character is not "a" three times.  
   
      2. Capturing subpatterns that occur inside  negative  looka-  
      head  assertions  are  counted,  but  their  entries  in the  
      offsets vector are never set. Perl sets its numerical  vari-  
      ables  from  any  such  patterns that are matched before the  
      assertion fails to match something (thereby succeeding), but  
      only  if  the negative lookahead assertion contains just one  
      branch.  
   
      3. Though binary zero characters are supported in  the  sub-  
      ject  string,  they  are  not  allowed  in  a pattern string  
      because it is passed as a normal  C  string,  terminated  by  
      zero. The escape sequence "\0" can be used in the pattern to  
      represent a binary zero.  
   
      4. The following Perl escape sequences  are  not  supported:  
      \l,  \u,  \L,  \U,  \P, \p, and \X. In fact these are imple-  
      mented by Perl's general string-handling and are not part of  
      its pattern matching engine. If any of these are encountered  
      by PCRE, an error is generated.  
   
      5. PCRE does support the \Q...\E  escape  for  quoting  sub-  
      strings. Characters in between are treated as literals. This  
      is slightly different from Perl in that $  and  @  are  also  
      handled  as  literals inside the quotes. In Perl, they cause  
      variable interpolation (but of course  PCRE  does  not  have  
      variables). Note the following examples:  
   
          Pattern            PCRE matches      Perl matches  
   
          \Qabc$xyz\E        abc$xyz           abc followed by the  
                                                 contents of $xyz  
          \Qabc\$xyz\E       abc\$xyz          abc\$xyz  
          \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz  
   
      In PCRE, the \Q...\E mechanism is not  recognized  inside  a  
      character class.  
   
      8. Fairly obviously, PCRE does not support the (?{code}) and  
      (?p{code})  constructions. However, there is some experimen-  
      tal support for recursive patterns using the non-Perl  items  
      (?R),  (?number)  and  (?P>name).  Also,  the PCRE "callout"  
      feature allows an external function to be called during pat-  
      tern matching.  
   
      9. There are some differences that are  concerned  with  the  
      settings  of  captured  strings  when  part  of a pattern is  
      repeated. For example, matching "aba"  against  the  pattern  
      /^(a(b)?)+$/  in Perl leaves $2 unset, but in PCRE it is set  
      to "b".  
   
      10. PCRE  provides  some  extensions  to  the  Perl  regular  
      expression facilities:  
   
      (a) Although lookbehind assertions must match  fixed  length  
      strings,  each  alternative branch of a lookbehind assertion  
      can match a different length of string. Perl  requires  them  
      all to have the same length.  
   
      (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is  not  
      set,  the  $  meta-character matches only at the very end of  
      the string.  
   
      (c) If PCRE_EXTRA is set, a backslash followed by  a  letter  
      with no special meaning is faulted.  
   
      (d) If PCRE_UNGREEDY is set, the greediness of  the  repeti-  
      tion  quantifiers  is inverted, that is, by default they are  
      not greedy, but if followed by a question mark they are.  
   
      (e) PCRE_ANCHORED can be used to force a pattern to be tried  
      only at the first matching position in the subject string.  
   
      (f)  The  PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   and  
      PCRE_NO_AUTO_CAPTURE  options  for  pcre_exec() have no Perl  
      equivalents.  
   
      (g) The (?R), (?number), and (?P>name) constructs allows for  
      recursive  pattern  matching  (Perl  can  do  this using the  
      (?p{code}) construct, which PCRE cannot support.)  
   
      (h) PCRE supports  named  capturing  substrings,  using  the  
      Python syntax.  
   
      (i) PCRE supports the  possessive  quantifier  "++"  syntax,  
      taken from Sun's Java package.  
1798    
1799       (j) The (R) condition, for  testing  recursion,  is  a  PCRE         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from
1800       extension.         Sun's Java package.
1801    
1802       (k) The callout facility is PCRE-specific.         (j) The (R) condition, for testing recursion, is a PCRE extension.
1803    
1804  Last updated: 03 February 2003         (k) The callout facility is PCRE-specific.
1805  Copyright (c) 1997-2003 University of Cambridge.  
1806           (l) The partial matching facility is PCRE-specific.
1807    
1808           (m) Patterns compiled by PCRE can be saved and re-used at a later time,
1809           even on different hosts that have the other endianness.
1810    
1811    Last updated: 09 September 2004
1812    Copyright (c) 1997-2004 University of Cambridge.
1813  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
1814    
1815  NAME  PCRE(3)                                                                PCRE(3)
1816       PCRE - Perl-compatible regular expressions  
1817    
1818    
1819    NAME
1820           PCRE - Perl-compatible regular expressions
1821    
1822  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
1823    
1824       The syntax and semantics of  the  regular  expressions  sup-         The  syntax  and semantics of the regular expressions supported by PCRE
1825       ported  by PCRE are described below. Regular expressions are         are described below. Regular expressions are also described in the Perl
1826       also described in the Perl documentation and in a number  of         documentation  and  in  a  number  of books, some of which have copious
1827       other  books,  some  of which have copious examples. Jeffrey         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published
1828       Friedl's  "Mastering  Regular  Expressions",  published   by         by  O'Reilly, covers regular expressions in great detail. This descrip-
1829       O'Reilly,  covers them in great detail. The description here         tion of PCRE's regular expressions is intended as reference material.
1830       is intended as reference documentation.  
1831           The original operation of PCRE was on strings of  one-byte  characters.
1832       The basic operation of PCRE is on strings of bytes. However,         However,  there is now also support for UTF-8 character strings. To use
1833       there  is  also  support for UTF-8 character strings. To use         this, you must build PCRE to  include  UTF-8  support,  and  then  call
1834       this support you must build PCRE to include  UTF-8  support,         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern
1835       and  then call pcre_compile() with the PCRE_UTF8 option. How         matching is mentioned in several places below. There is also a  summary
1836       this affects the pattern matching is  mentioned  in  several         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
1837       places  below.  There is also a summary of UTF-8 features in         page.
1838       the section on UTF-8 support in the main pcre page.  
1839           A regular expression is a pattern that is  matched  against  a  subject
1840       A regular expression is a pattern that is matched against  a         string  from  left  to right. Most characters stand for themselves in a
1841       subject string from left to right. Most characters stand for         pattern, and match the corresponding characters in the  subject.  As  a
1842       themselves in a pattern, and match the corresponding charac-         trivial example, the pattern
1843       ters in the subject. As a trivial example, the pattern  
1844             The quick brown fox
1845         The quick brown fox  
1846           matches  a portion of a subject string that is identical to itself. The
1847       matches a portion of a subject string that is  identical  to         power of regular expressions comes from the ability to include alterna-
1848       itself.  The  power  of  regular  expressions comes from the         tives  and repetitions in the pattern. These are encoded in the pattern
1849       ability to include alternatives and repetitions in the  pat-         by the use of metacharacters, which do not  stand  for  themselves  but
1850       tern.  These  are encoded in the pattern by the use of meta-         instead are interpreted in some special way.
1851       characters, which do not stand for  themselves  but  instead  
1852       are interpreted in some special way.         There  are  two different sets of metacharacters: those that are recog-
1853           nized anywhere in the pattern except within square brackets, and  those
1854       There are two different sets of meta-characters: those  that         that  are  recognized  in square brackets. Outside square brackets, the
1855       are  recognized anywhere in the pattern except within square         metacharacters are as follows:
1856       brackets, and those that are recognized in square  brackets.  
1857       Outside square brackets, the meta-characters are as follows:           \      general escape character with several uses
1858             ^      assert start of string (or line, in multiline mode)
1859         \      general escape character with several uses           $      assert end of string (or line, in multiline mode)
1860         ^      assert start of string (or line, in multiline mode)           .      match any character except newline (by default)
1861         $      assert end of string (or line, in multiline mode)           [      start character class definition
1862         .      match any character except newline (by default)           |      start of alternative branch
1863         [      start character class definition           (      start subpattern
1864         |      start of alternative branch           )      end subpattern
1865         (      start subpattern           ?      extends the meaning of (
1866         )      end subpattern                  also 0 or 1 quantifier
1867         ?      extends the meaning of (                  also quantifier minimizer
1868                also 0 or 1 quantifier           *      0 or more quantifier
1869                also quantifier minimizer           +      1 or more quantifier
1870         *      0 or more quantifier                  also "possessive quantifier"
1871         +      1 or more quantifier           {      start min/max quantifier
1872                also "possessive quantifier"  
1873         {      start min/max quantifier         Part of a pattern that is in square brackets  is  called  a  "character
1874           class". In a character class the only metacharacters are:
1875       Part of a pattern that is in square  brackets  is  called  a  
1876       "character  class".  In  a  character  class  the only meta-           \      general escape character
1877       characters are:           ^      negate the class, but only if the first character
1878             -      indicates character range
1879         \      general escape character           [      POSIX character class (only if followed by POSIX
1880         ^      negate the class, but only if the first character                    syntax)
1881         -      indicates character range           ]      terminates the character class
        [      POSIX character class (only if followed by POSIX  
                 syntax)  
        ]      terminates the character class  
1882    
1883       The following sections describe  the  use  of  each  of  the         The  following sections describe the use of each of the metacharacters.
      meta-characters.  
1884    
1885    
1886  BACKSLASH  BACKSLASH
1887    
1888       The backslash character has several uses. Firstly, if it  is         The backslash character has several uses. Firstly, if it is followed by
1889       followed  by  a  non-alphameric character, it takes away any         a  non-alphanumeric  character,  it takes away any special meaning that
1890       special  meaning  that  character  may  have.  This  use  of         character may have. This  use  of  backslash  as  an  escape  character
1891       backslash  as  an  escape  character applies both inside and         applies both inside and outside character classes.
1892       outside character classes.  
1893           For  example,  if  you want to match a * character, you write \* in the
1894       For example, if you want to match a * character,  you  write         pattern.  This escaping action applies whether  or  not  the  following
1895       \*  in the pattern.  This escaping action applies whether or         character  would  otherwise be interpreted as a metacharacter, so it is
1896       not the following character would otherwise  be  interpreted         always safe to precede a non-alphanumeric  with  backslash  to  specify
1897       as  a meta-character, so it is always safe to precede a non-         that  it stands for itself. In particular, if you want to match a back-
1898       alphameric with backslash to  specify  that  it  stands  for         slash, you write \\.
1899       itself. In particular, if you want to match a backslash, you  
1900       write \\.         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
1901           the  pattern (other than in a character class) and characters between a
1902       If a pattern is compiled with the PCRE_EXTENDED option, whi-         # outside a character class and the next newline character are ignored.
1903       tespace in the pattern (other than in a character class) and         An  escaping backslash can be used to include a whitespace or # charac-
1904       characters between a # outside a  character  class  and  the         ter as part of the pattern.
1905       next  newline  character  are ignored. An escaping backslash  
1906       can be used to include a whitespace or # character  as  part         If you want to remove the special meaning from a  sequence  of  charac-
1907       of the pattern.         ters,  you can do so by putting them between \Q and \E. This is differ-
1908           ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E
1909       If you want to remove the special meaning from a sequence of         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
1910       characters, you can do so by putting them between \Q and \E.         tion. Note the following examples:
1911       This is different from Perl in that $ and @ are  handled  as  
1912       literals  in  \Q...\E  sequences in PCRE, whereas in Perl, $           Pattern            PCRE matches   Perl matches
1913       and @ cause variable interpolation. Note the following exam-  
1914       ples:           \Qabc$xyz\E        abc$xyz        abc followed by the
1915                                                 contents of $xyz
1916         Pattern            PCRE matches   Perl matches           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
1917             \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
1918         \Qabc$xyz\E        abc$xyz        abc followed by the  
1919           The \Q...\E sequence is recognized both inside  and  outside  character
1920                                             contents of $xyz         classes.
1921         \Qabc\$xyz\E       abc\$xyz       abc\$xyz  
1922         \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz     Non-printing characters
1923    
1924       The \Q...\E sequence is recognized both inside  and  outside         A second use of backslash provides a way of encoding non-printing char-
1925       character classes.         acters in patterns in a visible manner. There is no restriction on  the
1926           appearance  of non-printing characters, apart from the binary zero that
1927       A second use of backslash provides a way  of  encoding  non-         terminates a pattern, but when a pattern  is  being  prepared  by  text
1928       printing  characters  in patterns in a visible manner. There         editing,  it  is  usually  easier  to  use  one of the following escape
1929       is no restriction on the appearance of non-printing  charac-         sequences than the binary character it represents:
1930       ters,  apart from the binary zero that terminates a pattern,  
1931       but when a pattern is being prepared by text editing, it  is           \a        alarm, that is, the BEL character (hex 07)
1932       usually  easier to use one of the following escape sequences           \cx       "control-x", where x is any character
1933       than the binary character it represents:           \e        escape (hex 1B)
1934             \f        formfeed (hex 0C)
1935         \a        alarm, that is, the BEL character (hex 07)           \n        newline (hex 0A)
1936         \cx       "control-x", where x is any character           \r        carriage return (hex 0D)
1937         \e        escape (hex 1B)           \t        tab (hex 09)
1938         \f        formfeed (hex 0C)           \ddd      character with octal code ddd, or backreference
1939         \n        newline (hex 0A)           \xhh      character with hex code hh
1940         \r        carriage return (hex 0D)           \x{hhh..} character with hex code hhh... (UTF-8 mode only)
1941         \t        tab (hex 09)  
1942         \ddd      character with octal code ddd, or backreference         The precise effect of \cx is as follows: if x is a lower  case  letter,
1943         \xhh      character with hex code hh         it  is converted to upper case. Then bit 6 of the character (hex 40) is
1944         \x{hhh..} character with hex code hhh... (UTF-8 mode only)         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;
1945           becomes hex 7B.
1946       The precise effect of \cx is as follows: if  x  is  a  lower  
1947       case  letter,  it  is converted to upper case. Then bit 6 of         After  \x, from zero to two hexadecimal digits are read (letters can be
1948       the character (hex 40) is inverted.  Thus  \cz  becomes  hex         in upper or lower case). In UTF-8 mode, any number of hexadecimal  dig-
1949       1A, but \c{ becomes hex 3B, while \c; becomes hex 7B.         its  may  appear between \x{ and }, but the value of the character code
1950           must be less than 2**31 (that is,  the  maximum  hexadecimal  value  is
1951       After \x, from zero  to  two  hexadecimal  digits  are  read         7FFFFFFF).  If  characters other than hexadecimal digits appear between
1952       (letters  can be in upper or lower case). In UTF-8 mode, any         \x{ and }, or if there is no terminating }, this form of escape is  not
1953       number of hexadecimal digits may appear between \x{  and  },         recognized. Instead, the initial \x will be interpreted as a basic hex-
1954       but  the value of the character code must be less than 2**31         adecimal escape, with no following digits,  giving  a  character  whose
1955       (that is, the maximum hexadecimal  value  is  7FFFFFFF).  If         value is zero.
1956       characters  other than hexadecimal digits appear between \x{  
1957       and }, or if there is no terminating }, this form of  escape         Characters whose value is less than 256 can be defined by either of the
1958       is  not  recognized.  Instead, the initial \x will be inter-         two syntaxes for \x when PCRE is in UTF-8 mode. There is no  difference
1959       preted as a basic  hexadecimal  escape,  with  no  following         in  the  way they are handled. For example, \xdc is exactly the same as
1960       digits, giving a byte whose value is zero.         \x{dc}.
1961    
1962       Characters whose value is less than 256 can  be  defined  by         After \0 up to two further octal digits are read.  In  both  cases,  if
1963       either  of  the  two  syntaxes  for \x when PCRE is in UTF-8         there  are fewer than two digits, just those that are present are used.
1964       mode. There is no difference in the way  they  are  handled.         Thus the sequence \0\x\07 specifies two binary zeros followed by a  BEL
1965       For example, \xdc is exactly the same as \x{dc}.         character  (code  value  7).  Make sure you supply two digits after the
1966           initial zero if the pattern character that follows is itself  an  octal
1967       After \0 up to two further octal digits are  read.  In  both         digit.
1968       cases,  if  there are fewer than two digits, just those that  
1969       are present are used. Thus the  sequence  \0\x\07  specifies         The handling of a backslash followed by a digit other than 0 is compli-
1970       two binary zeros followed by a BEL character (code value 7).         cated.  Outside a character class, PCRE reads it and any following dig-
1971       Make sure you supply two digits after the  initial  zero  if         its  as  a  decimal  number. If the number is less than 10, or if there
1972       the character that follows is itself an octal digit.         have been at least that many previous capturing left parentheses in the
1973           expression,  the  entire  sequence  is  taken  as  a  back reference. A
1974       The handling of a backslash followed by a digit other than 0         description of how this works is given later, following the  discussion
1975       is  complicated.   Outside  a character class, PCRE reads it         of parenthesized subpatterns.
1976       and any following digits as a decimal number. If the  number  
1977       is  less  than  10, or if there have been at least that many         Inside  a  character  class, or if the decimal number is greater than 9
1978       previous capturing left parentheses in the  expression,  the         and there have not been that many capturing subpatterns, PCRE  re-reads
1979       entire  sequence is taken as a back reference. A description         up  to three octal digits following the backslash, and generates a sin-
1980       of how this works is given later, following  the  discussion         gle byte from the least significant 8 bits of the value. Any subsequent
1981       of parenthesized subpatterns.         digits stand for themselves.  For example:
1982    
1983       Inside a character  class,  or  if  the  decimal  number  is           \040   is another way of writing a space
1984       greater  than  9 and there have not been that many capturing           \40    is the same, provided there are fewer than 40
1985       subpatterns, PCRE re-reads up to three octal digits  follow-                     previous capturing subpatterns
1986       ing  the  backslash,  and  generates  a single byte from the           \7     is always a back reference
1987       least significant 8 bits of the value. Any subsequent digits           \11    might be a back reference, or another way of
1988       stand for themselves.  For example:                     writing a tab
1989             \011   is always a tab
1990         \040   is another way of writing a space           \0113  is a tab followed by the character "3"
1991         \40    is the same, provided there are fewer than 40           \113   might be a back reference, otherwise the
1992                   previous capturing subpatterns                     character with octal code 113
1993         \7     is always a back reference           \377   might be a back reference, otherwise
1994         \11    might be a back reference, or another way of                     the byte consisting entirely of 1 bits
1995                   writing a tab           \81    is either a back reference, or a binary zero
1996         \011   is always a tab                     followed by the two characters "8" and "1"
1997         \0113  is a tab followed by the character "3"  
1998         \113   might be a back reference, otherwise the         Note  that  octal  values of 100 or greater must not be introduced by a
1999                   character with octal code 113         leading zero, because no more than three octal digits are ever read.
2000         \377   might be a back reference, otherwise  
2001                   the byte consisting entirely of 1 bits         All the sequences that define a single byte value  or  a  single  UTF-8
2002         \81    is either a back reference, or a binary zero         character (in UTF-8 mode) can be used both inside and outside character
2003                   followed by the two characters "8" and "1"         classes. In addition, inside a character  class,  the  sequence  \b  is
2004           interpreted as the backspace character (hex 08), and the sequence \X is
2005       Note that octal values of 100 or greater must not be  intro-         interpreted as the character "X".  Outside  a  character  class,  these
2006       duced  by  a  leading zero, because no more than three octal         sequences have different meanings (see below).
2007       digits are ever read.  
2008       Generic character types
2009       All the sequences that define a single byte value or a  sin-  
2010       gle  UTF-8 character (in UTF-8 mode) can be used both inside         The  third  use of backslash is for specifying generic character types.
2011       and outside character classes. In addition, inside a charac-         The following are always recognized:
2012       ter  class,  the sequence \b is interpreted as the backspace  
2013       character (hex 08). Outside a character class it has a  dif-           \d     any decimal digit
2014       ferent meaning (see below).           \D     any character that is not a decimal digit
2015             \s     any whitespace character
2016       The third use of backslash is for specifying generic charac-           \S     any character that is not a whitespace character
2017       ter types:           \w     any "word" character
2018             \W     any "non-word" character
2019         \d     any decimal digit  
2020         \D     any character that is not a decimal digit         Each pair of escape sequences partitions the complete set of characters
2021         \s     any whitespace character         into  two disjoint sets. Any given character matches one, and only one,
2022         \S     any character that is not a whitespace character         of each pair.
2023         \w     any "word" character  
2024         W     any "non-word" character         These character type sequences can appear both inside and outside char-
2025           acter  classes.  They each match one character of the appropriate type.
2026       Each pair of escape sequences partitions the complete set of         If the current matching point is at the end of the subject string,  all
2027       characters  into  two  disjoint  sets.  Any  given character         of them fail, since there is no character to match.
2028       matches one, and only one, of each pair.  
2029           For  compatibility  with Perl, \s does not match the VT character (code
2030       In UTF-8 mode, characters with values greater than 255 never         11).  This makes it different from the the POSIX "space" class. The  \s
2031       match \d, \s, or \w, and always match \D, \S, and \W.         characters are HT (9), LF (10), FF (12), CR (13), and space (32).
2032    
2033       For compatibility with Perl, \s does not match the VT  char-         A "word" character is an underscore or any character less than 256 that
2034       acter (code 11).  This makes it different from the the POSIX         is a letter or digit. The definition of  letters  and  digits  is  con-
2035       "space" class. The \s characters are HT  (9),  LF  (10),  FF         trolled  by PCRE's low-valued character tables, and may vary if locale-
2036       (12), CR (13), and space (32).         specific matching is taking place (see "Locale support" in the  pcreapi
2037           page).  For  example,  in  the  "fr_FR" (French) locale, some character
2038       A "word" character is any letter or digit or the  underscore         codes greater than 128 are used for accented  letters,  and  these  are
2039       character,  that  is,  any  character which can be part of a         matched by \w.
2040       Perl "word". The definition of letters and  digits  is  con-  
2041       trolled  by PCRE's character tables, and may vary if locale-         In  UTF-8 mode, characters with values greater than 128 never match \d,
2042       specific matching is taking place (see "Locale  support"  in         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
2043       the pcreapi page). For example, in the "fr" (French) locale,         code character property support is available.
2044       some character codes greater than 128 are used for  accented  
2045       letters, and these are matched by \w.     Unicode character properties
2046    
2047       These character type sequences can appear  both  inside  and         When PCRE is built with Unicode character property support, three addi-
2048       outside  character classes. They each match one character of         tional escape sequences to match generic character types are  available
2049       the appropriate type. If the current matching  point  is  at         when UTF-8 mode is selected. They are:
2050       the end of the subject string, all of them fail, since there  
2051       is no character to match.          \p{xx}   a character with the xx property
2052            \P{xx}   a character without the xx property
2053       The fourth use of backslash is  for  certain  simple  asser-          \X       an extended Unicode sequence
2054       tions. An assertion specifies a condition that has to be met  
2055       at a particular point in  a  match,  without  consuming  any         The  property  names represented by xx above are limited to the Unicode
2056       characters  from  the subject string. The use of subpatterns         general category properties. Each character has exactly one such  prop-
2057       for more complicated  assertions  is  described  below.  The         erty,  specified  by  a two-letter abbreviation. For compatibility with
2058       backslashed assertions are         Perl, negation can be specified by including a circumflex  between  the
2059           opening  brace  and the property name. For example, \p{^Lu} is the same
2060         \b     matches at a word boundary         as \P{Lu}.
2061         \B     matches when not at a word boundary  
2062         \A     matches at start of subject         If only one letter is specified with \p or  \P,  it  includes  all  the
2063         \Z     matches at end of subject or before newline at end         properties that start with that letter. In this case, in the absence of
2064         \z     matches at end of subject         negation, the curly brackets in the escape sequence are optional; these
2065         \G     matches at first matching position in subject         two examples have the same effect:
2066    
2067       These assertions may not appear in  character  classes  (but           \p{L}
2068       note  that  \b has a different meaning, namely the backspace           \pL
2069       character, inside a character class).  
2070           The following property codes are supported:
2071       A word boundary is a position in the  subject  string  where  
2072       the current character and the previous character do not both           C     Other
2073       match \w or \W (i.e. one matches \w and  the  other  matches           Cc    Control
2074       \W),  or the start or end of the string if the first or last           Cf    Format
2075       character matches \w, respectively.           Cn    Unassigned
2076       The \A, \Z, and \z assertions differ  from  the  traditional           Co    Private use
2077       circumflex  and  dollar  (described below) in that they only           Cs    Surrogate
2078       ever match at the very start and end of the subject  string,  
2079       whatever options are set. Thus, they are independent of mul-           L     Letter
2080       tiline mode.           Ll    Lower case letter
2081             Lm    Modifier letter
2082       They are not affected  by  the  PCRE_NOTBOL  or  PCRE_NOTEOL           Lo    Other letter
2083       options.  If the startoffset argument of pcre_exec() is non-           Lt    Title case letter
2084       zero, indicating that matching is to start at a point  other           Lu    Upper case letter
2085       than  the  beginning of the subject, \A can never match. The  
2086       difference between \Z and \z is that  \Z  matches  before  a           M     Mark
2087       newline  that is the last character of the string as well as           Mc    Spacing mark
2088       at the end of the string, whereas \z  matches  only  at  the           Me    Enclosing mark
2089       end.           Mn    Non-spacing mark
2090    
2091       The \G assertion is true  only  when  the  current  matching           N     Number
2092       position is at the start point of the match, as specified by           Nd    Decimal number
2093       the startoffset argument of pcre_exec(). It differs from  \A           Nl    Letter number
2094       when  the  value  of  startoffset  is  non-zero.  By calling           No    Other number
2095       pcre_exec() multiple times with appropriate  arguments,  you  
2096       can mimic Perl's /g option, and it is in this kind of imple-           P     Punctuation
2097       mentation where \G can be useful.           Pc    Connector punctuation
2098             Pd    Dash punctuation
2099       Note, however, that PCRE's  interpretation  of  \G,  as  the           Pe    Close punctuation
2100       start of the current match, is subtly different from Perl's,           Pf    Final punctuation
2101       which defines it as the end of the previous match. In  Perl,           Pi    Initial punctuation
2102       these  can  be  different when the previously matched string           Po    Other punctuation
2103       was empty. Because PCRE does just one match at  a  time,  it           Ps    Open punctuation
2104       cannot reproduce this behaviour.  
2105             S     Symbol
2106       If all the alternatives of a  pattern  begin  with  \G,  the           Sc    Currency symbol
2107       expression  is  anchored to the starting match position, and           Sk    Modifier symbol
2108       the "anchored" flag is set in the compiled  regular  expres-           Sm    Mathematical symbol
2109       sion.           So    Other symbol
2110    
2111             Z     Separator
2112             Zl    Line separator
2113             Zp    Paragraph separator
2114             Zs    Space separator
2115    
2116           Extended  properties such as "Greek" or "InMusicalSymbols" are not sup-
2117           ported by PCRE.
2118    
2119           Specifying caseless matching does not affect  these  escape  sequences.
2120           For example, \p{Lu} always matches only upper case letters.
2121    
2122           The  \X  escape  matches  any number of Unicode characters that form an
2123           extended Unicode sequence. \X is equivalent to
2124    
2125             (?>\PM\pM*)
2126    
2127           That is, it matches a character without the "mark"  property,  followed
2128           by  zero  or  more  characters with the "mark" property, and treats the
2129           sequence as an atomic group (see below).  Characters  with  the  "mark"
2130           property are typically accents that affect the preceding character.
2131    
2132           Matching  characters  by Unicode property is not fast, because PCRE has
2133           to search a structure that contains  data  for  over  fifteen  thousand
2134           characters. That is why the traditional escape sequences such as \d and
2135           \w do not use Unicode properties in PCRE.
2136    
2137       Simple assertions
2138    
2139           The fourth use of backslash is for certain simple assertions. An asser-
2140           tion  specifies a condition that has to be met at a particular point in
2141           a match, without consuming any characters from the subject string.  The
2142           use  of subpatterns for more complicated assertions is described below.
2143           The backslashed assertions are:
2144    
2145             \b     matches at a word boundary
2146             \B     matches when not at a word boundary
2147             \A     matches at start of subject
2148             \Z     matches at end of subject or before newline at end
2149             \z     matches at end of subject
2150             \G     matches at first matching position in subject
2151    
2152           These assertions may not appear in character classes (but note that  \b
2153           has a different meaning, namely the backspace character, inside a char-
2154           acter class).
2155    
2156           A word boundary is a position in the subject string where  the  current
2157           character  and  the previous character do not both match \w or \W (i.e.
2158           one matches \w and the other matches \W), or the start or  end  of  the
2159           string if the first or last character matches \w, respectively.
2160    
2161           The  \A,  \Z,  and \z assertions differ from the traditional circumflex
2162           and dollar (described in the next section) in that they only ever match
2163           at  the  very start and end of the subject string, whatever options are
2164           set. Thus, they are independent of multiline mode. These  three  asser-
2165           tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
2166           affect only the behaviour of the circumflex and dollar  metacharacters.
2167           However,  if the startoffset argument of pcre_exec() is non-zero, indi-
2168           cating that matching is to start at a point other than the beginning of
2169           the  subject,  \A  can never match. The difference between \Z and \z is
2170           that \Z matches before a newline that is  the  last  character  of  the
2171           string  as well as at the end of the string, whereas \z matches only at
2172           the end.
2173    
2174           The \G assertion is true only when the current matching position is  at
2175           the  start point of the match, as specified by the startoffset argument
2176           of pcre_exec(). It differs from \A when the  value  of  startoffset  is
2177           non-zero.  By calling pcre_exec() multiple times with appropriate argu-
2178           ments, you can mimic Perl's /g option, and it is in this kind of imple-
2179           mentation where \G can be useful.
2180    
2181           Note,  however,  that  PCRE's interpretation of \G, as the start of the
2182           current match, is subtly different from Perl's, which defines it as the
2183           end  of  the  previous  match. In Perl, these can be different when the
2184           previously matched string was empty. Because PCRE does just  one  match
2185           at a time, it cannot reproduce this behaviour.
2186    
2187           If  all  the alternatives of a pattern begin with \G, the expression is
2188           anchored to the starting match position, and the "anchored" flag is set
2189           in the compiled regular expression.
2190    
2191    
2192  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
2193    
2194       Outside a character class, in the default matching mode, the         Outside a character class, in the default matching mode, the circumflex
2195       circumflex  character  is an assertion which is true only if         character is an assertion that is true only  if  the  current  matching
2196       the current matching point is at the start  of  the  subject         point  is  at the start of the subject string. If the startoffset argu-
2197       string.  If  the startoffset argument of pcre_exec() is non-         ment of pcre_exec() is non-zero, circumflex  can  never  match  if  the
2198       zero, circumflex  can  never  match  if  the  PCRE_MULTILINE         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
2199       option is unset. Inside a character class, circumflex has an         has an entirely different meaning (see below).
2200       entirely different meaning (see below).  
2201           Circumflex need not be the first character of the pattern if  a  number
2202       Circumflex need not be the first character of the pattern if         of  alternatives are involved, but it should be the first thing in each
2203       a  number of alternatives are involved, but it should be the         alternative in which it appears if the pattern is ever  to  match  that
2204       first thing in each alternative in which it appears  if  the         branch.  If all possible alternatives start with a circumflex, that is,
2205       pattern is ever to match that branch. If all possible alter-         if the pattern is constrained to match only at the start  of  the  sub-
2206       natives start with a circumflex, that is, if the pattern  is         ject,  it  is  said  to be an "anchored" pattern. (There are also other
2207       constrained to match only at the start of the subject, it is         constructs that can cause a pattern to be anchored.)
2208       said to be an "anchored" pattern. (There are also other con-  
2209       structs that can cause a pattern to be anchored.)         A dollar character is an assertion that is true  only  if  the  current
2210           matching  point  is  at  the  end of the subject string, or immediately
2211       A dollar character is an assertion which is true only if the         before a newline character that is the last character in the string (by
2212       current  matching point is at the end of the subject string,         default).  Dollar  need  not  be the last character of the pattern if a
2213       or immediately before a newline character that is  the  last         number of alternatives are involved, but it should be the last item  in
2214       character in the string (by default). Dollar need not be the         any  branch  in  which  it appears.  Dollar has no special meaning in a
2215       last character of the pattern if a  number  of  alternatives         character class.
2216       are  involved,  but it should be the last item in any branch  
2217       in which it appears.  Dollar has no  special  meaning  in  a         The meaning of dollar can be changed so that it  matches  only  at  the
2218       character class.         very  end  of  the string, by setting the PCRE_DOLLAR_ENDONLY option at
2219           compile time. This does not affect the \Z assertion.
2220       The meaning of dollar can be changed so that it matches only  
2221       at   the   very   end   of   the   string,  by  setting  the         The meanings of the circumflex and dollar characters are changed if the
2222       PCRE_DOLLAR_ENDONLY option at compile time.  This  does  not         PCRE_MULTILINE option is set. When this is the case, they match immedi-
2223       affect the \Z assertion.         ately after and  immediately  before  an  internal  newline  character,
2224           respectively,  in addition to matching at the start and end of the sub-
2225       The meanings of the circumflex  and  dollar  characters  are         ject string. For example,  the  pattern  /^abc$/  matches  the  subject
2226       changed  if  the  PCRE_MULTILINE option is set. When this is         string  "def\nabc"  (where \n represents a newline character) in multi-
2227       the case,  they  match  immediately  after  and  immediately         line mode, but not otherwise.  Consequently, patterns that are anchored
2228       before an internal newline character, respectively, in addi-         in  single line mode because all branches start with ^ are not anchored
2229       tion to matching at the start and end of the subject string.         in multiline mode, and a match for  circumflex  is  possible  when  the
2230       For  example, the pattern /^abc$/ matches the subject string         startoffset   argument   of  pcre_exec()  is  non-zero.  The  PCRE_DOL-
2231       "def\nabc" in multiline  mode,  but  not  otherwise.  Conse-         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
2232       quently,  patterns  that  are  anchored  in single line mode  
2233       because all branches start with ^ are not anchored in multi-         Note that the sequences \A, \Z, and \z can be used to match  the  start
2234       line  mode,  and a match for circumflex is possible when the         and  end of the subject in both modes, and if all branches of a pattern
2235       startoffset  argument  of  pcre_exec()  is   non-zero.   The         start with \A it is always anchored, whether PCRE_MULTILINE is  set  or
2236       PCRE_DOLLAR_ENDONLY  option  is ignored if PCRE_MULTILINE is         not.
      set.  
   
      Note that the sequences \A, \Z, and \z can be used to  match  
      the  start  and end of the subject in both modes, and if all  
      branches of a pattern start with \A it is  always  anchored,  
      whether PCRE_MULTILINE is set or not.  
2237    
2238    
2239  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
2240    
2241       Outside a character class, a dot in the pattern matches  any         Outside a character class, a dot in the pattern matches any one charac-
2242       one character in the subject, including a non-printing char-         ter in the subject, including a non-printing  character,  but  not  (by
2243       acter, but not (by default) newline.  In UTF-8 mode,  a  dot         default)  newline.   In  UTF-8 mode, a dot matches any UTF-8 character,
2244       matches  any  UTF-8  character, which might be more than one         which might be more than one byte long, except (by default) newline. If
2245       byte  long,  except  (by  default)  for  newline.   If   the         the  PCRE_DOTALL  option  is set, dots match newlines as well. The han-
2246       PCRE_DOTALL  option is set, dots match newlines as well. The         dling of dot is entirely independent of the handling of circumflex  and
2247       handling of dot is entirely independent of the  handling  of         dollar,  the  only  relationship  being  that they both involve newline
2248       circumflex and dollar, the only relationship being that they         characters. Dot has no special meaning in a character class.
      both involve newline characters. Dot has no special  meaning  
      in a character class.  
   
2249    
2250    
2251  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
2252    
2253       Outside a character class, the escape  sequence  \C  matches         Outside a character class, the escape sequence \C matches any one byte,
2254       any  one  byte, both in and out of UTF-8 mode. Unlike a dot,         both  in  and  out of UTF-8 mode. Unlike a dot, it can match a newline.
2255       it always matches a newline. The feature is provided in Perl         The feature is provided in Perl in order to match individual  bytes  in
2256       in  order  to match individual bytes in UTF-8 mode.  Because         UTF-8  mode.  Because  it  breaks  up  UTF-8 characters into individual
2257       it breaks up UTF-8 characters into  individual  bytes,  what         bytes, what remains in the string may be a malformed UTF-8 string.  For
2258       remains  in  the string may be a malformed UTF-8 string. For         this reason, the \C escape sequence is best avoided.
2259       this reason it is best avoided.  
2260           PCRE  does  not  allow \C to appear in lookbehind assertions (described
2261       PCRE does not allow \C to appear  in  lookbehind  assertions         below), because in UTF-8 mode this would make it impossible  to  calcu-
2262       (see below), because in UTF-8 mode it makes it impossible to         late the length of the lookbehind.
2263       calculate the length of the lookbehind.  
2264    
2265    SQUARE BRACKETS AND CHARACTER CLASSES
2266  SQUARE BRACKETS  
2267           An opening square bracket introduces a character class, terminated by a
2268       An opening square bracket introduces a character class, ter-         closing square bracket. A closing square bracket on its own is not spe-
2269       minated  by  a  closing  square  bracket.  A  closing square         cial. If a closing square bracket is required as a member of the class,
2270       bracket on its own is  not  special.  If  a  closing  square         it should be the first data character in the class  (after  an  initial
2271       bracket  is  required as a member of the class, it should be         circumflex, if present) or escaped with a backslash.
2272       the first data character in the class (after an initial cir-  
2273       cumflex, if present) or escaped with a backslash.         A  character  class matches a single character in the subject. In UTF-8
2274           mode, the character may occupy more than one byte. A matched  character
2275       A character class matches a single character in the subject.         must be in the set of characters defined by the class, unless the first
2276       In  UTF-8 mode, the character may occupy more than one byte.         character in the class definition is a circumflex, in  which  case  the
2277       A matched character must be in the set of characters defined         subject  character  must  not  be in the set defined by the class. If a
2278       by the class, unless the first character in the class defin-         circumflex is actually required as a member of the class, ensure it  is
2279       ition is a circumflex, in which case the  subject  character         not the first character, or escape it with a backslash.
2280       must not be in the set defined by the class. If a circumflex  
2281       is actually required as a member of the class, ensure it  is         For  example, the character class [aeiou] matches any lower case vowel,
2282       not the first character, or escape it with a backslash.         while [^aeiou] matches any character that is not a  lower  case  vowel.
2283           Note that a circumflex is just a convenient notation for specifying the
2284       For example, the character class [aeiou] matches  any  lower         characters that are in the class by enumerating those that are  not.  A
2285       case vowel, while [^aeiou] matches any character that is not         class  that starts with a circumflex is not an assertion: it still con-
2286       a lower case vowel. Note that a circumflex is  just  a  con-         sumes a character from the subject string, and therefore  it  fails  if
2287       venient  notation for specifying the characters which are in         the current pointer is at the end of the string.
2288       the class by enumerating those that are not. It  is  not  an  
2289       assertion:  it  still  consumes a character from the subject         In  UTF-8 mode, characters with values greater than 255 can be included
2290       string, and fails if the current pointer is at  the  end  of         in a class as a literal string of bytes, or by using the  \x{  escaping
2291       the string.         mechanism.
2292    
2293       In UTF-8 mode, characters with values greater than  255  can         When  caseless  matching  is set, any letters in a class represent both
2294       be  included  in a class as a literal string of bytes, or by         their upper case and lower case versions, so for  example,  a  caseless
2295       using the \x{ escaping mechanism.         [aeiou]  matches  "A"  as well as "a", and a caseless [^aeiou] does not
2296           match "A", whereas a caseful version would. When running in UTF-8 mode,
2297       When caseless matching  is  set,  any  letters  in  a  class         PCRE  supports  the  concept of case for characters with values greater
2298       represent  both their upper case and lower case versions, so         than 128 only when it is compiled with Unicode property support.
2299       for example, a caseless [aeiou] matches "A" as well as  "a",  
2300       and  a caseless [^aeiou] does not match "A", whereas a case-         The newline character is never treated in any special way in  character
2301       ful version would. PCRE does not support the concept of case         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE
2302       for characters with values greater than 255.         options is. A class such as [^a] will always match a newline.
2303       The newline character is never treated in any special way in  
2304       character  classes,  whatever the setting of the PCRE_DOTALL         The minus (hyphen) character can be used to specify a range of  charac-
2305       or PCRE_MULTILINE options is. A  class  such  as  [^a]  will         ters  in  a  character  class.  For  example,  [d-m] matches any letter
2306       always match a newline.         between d and m, inclusive. If a  minus  character  is  required  in  a
2307           class,  it  must  be  escaped  with a backslash or appear in a position
2308       The minus (hyphen) character can be used to specify a  range         where it cannot be interpreted as indicating a range, typically as  the
2309       of  characters  in  a  character  class.  For example, [d-m]         first or last character in the class.
2310       matches any letter between d and m, inclusive.  If  a  minus  
2311       character  is required in a class, it must be escaped with a         It is not possible to have the literal character "]" as the end charac-
2312       backslash or appear in a position where it cannot be  inter-         ter of a range. A pattern such as [W-]46] is interpreted as a class  of
2313       preted as indicating a range, typically as the first or last         two  characters ("W" and "-") followed by a literal string "46]", so it
2314       character in the class.         would match "W46]" or "-46]". However, if the "]"  is  escaped  with  a
2315           backslash  it is interpreted as the end of range, so [W-\]46] is inter-
2316       It is not possible to have the literal character "]" as  the         preted as a class containing a range followed by two other  characters.
2317       end  character  of  a  range.  A  pattern such as [W-]46] is         The  octal or hexadecimal representation of "]" can also be used to end
2318       interpreted as a class of two characters ("W" and "-")  fol-         a range.
2319       lowed by a literal string "46]", so it would match "W46]" or  
2320       "-46]". However, if the "]" is escaped with a  backslash  it         Ranges operate in the collating sequence of character values. They  can
2321       is  interpreted  as  the end of range, so [W-\]46] is inter-         also   be  used  for  characters  specified  numerically,  for  example
2322       preted as a single class containing a range followed by  two         [\000-\037]. In UTF-8 mode, ranges can include characters whose  values
2323       separate characters. The octal or hexadecimal representation         are greater than 255, for example [\x{100}-\x{2ff}].
2324       of "]" can also be used to end a range.  
2325           If a range that includes letters is used when caseless matching is set,
2326       Ranges  operate  in  the  collating  sequence  of  character         it matches the letters in either case. For example, [W-c] is equivalent
2327       values.  They  can  also  be  used  for characters specified         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
2328       numerically, for example [\000-\037]. In UTF-8 mode,  ranges         character tables for the "fr_FR" locale are in use, [\xc8-\xcb] matches
2329       can  include  characters  whose values are greater than 255,         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the
2330       for example [\x{100}-\x{2ff}].         concept of case for characters with values greater than 128  only  when
2331           it is compiled with Unicode property support.
2332       If a range that  includes  letters  is  used  when  caseless  
2333       matching  is set, it matches the letters in either case. For         The  character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear
2334       example, [W-c] is  equivalent  to  [][\^_`wxyzabc],  matched         in a character class, and add the characters that  they  match  to  the
2335       caselessly,  and if character tables for the "fr" locale are         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
2336       in use, [\xc8-\xcb] matches accented E  characters  in  both         flex can conveniently be used with the upper case  character  types  to
2337       cases.         specify  a  more  restricted  set of characters than the matching lower
2338           case type. For example, the class [^\W_] matches any letter  or  digit,
2339       The character types \d, \D, \s, \S,  \w,  and  \W  may  also         but not underscore.
2340       appear  in  a  character  class, and add the characters that  
2341       they match to the class. For example, [\dABCDEF] matches any         The  only  metacharacters  that are recognized in character classes are
2342       hexadecimal  digit.  A  circumflex  can conveniently be used         backslash, hyphen (only where it can be  interpreted  as  specifying  a
2343       with the upper case character types to specify a  more  res-         range),  circumflex  (only  at the start), opening square bracket (only
2344       tricted set of characters than the matching lower case type.         when it can be interpreted as introducing a POSIX class name - see  the
2345       For example, the class [^\W_] matches any letter  or  digit,         next  section),  and  the  terminating closing square bracket. However,
2346       but not underscore.         escaping other non-alphanumeric characters does no harm.
   
      All non-alphameric characters other than \,  -,  ^  (at  the  
      start)  and  the  terminating ] are non-special in character  
      classes, but it does no harm if they are escaped.  
2347    
2348    
2349  POSIX CHARACTER CLASSES  POSIX CHARACTER CLASSES
2350    
2351       Perl supports the  POSIX  notation  for  character  classes,         Perl supports the POSIX notation for character classes. This uses names
2352       which  uses names enclosed by [: and :] within the enclosing         enclosed  by  [: and :] within the enclosing square brackets. PCRE also
2353       square brackets. PCRE also supports this notation. For exam-         supports this notation. For example,
2354       ple,  
2355             [01[:alpha:]%]
2356         [01[:alpha:]%]  
2357           matches "0", "1", any alphabetic character, or "%". The supported class
2358       matches "0", "1", any alphabetic character, or "%". The sup-         names are
2359       ported class names are  
2360             alnum    letters and digits
2361         alnum    letters and digits           alpha    letters
2362         alpha    letters           ascii    character codes 0 - 127
2363         ascii    character codes 0 - 127           blank    space or tab only
2364         blank    space or tab only           cntrl    control characters
2365         cntrl    control characters           digit    decimal digits (same as \d)
2366         digit    decimal digits (same as \d)           graph    printing characters, excluding space
2367         graph    printing characters, excluding space           lower    lower case letters
2368         lower    lower case letters           print    printing characters, including space
2369         print    printing characters, including space           punct    printing characters, excluding letters and digits
2370         punct    printing characters, excluding letters and digits           space    white space (not quite the same as \s)
2371         space    white space (not quite the same as \s)           upper    upper case letters
2372         upper    upper case letters           word     "word" characters (same as \w)
2373         word     "word" characters (same as \w)           xdigit   hexadecimal digits
2374         xdigit   hexadecimal digits  
2375           The  "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),
2376       The "space" characters are HT (9),  LF  (10),  VT  (11),  FF         and space (32). Notice that this list includes the VT  character  (code
2377       (12),  CR  (13),  and  space  (32).  Notice  that  this list         11). This makes "space" different to \s, which does not include VT (for
2378       includes the VT character (code 11). This makes "space" dif-         Perl compatibility).
2379       ferent  to  \s, which does not include VT (for Perl compati-  
2380       bility).         The name "word" is a Perl extension, and "blank"  is  a  GNU  extension
2381           from  Perl  5.8. Another Perl extension is negation, which is indicated
2382       The name "word" is a Perl extension, and "blank"  is  a  GNU         by a ^ character after the colon. For example,
2383       extension from Perl 5.8. Another Perl extension is negation,  
2384       which is indicated by a ^ character  after  the  colon.  For           [12[:^digit:]]
2385       example,  
2386           matches "1", "2", or any non-digit. PCRE (and Perl) also recognize  the
2387         [12[:^digit:]]         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
2388           these are not supported, and an error is given if they are encountered.
      matches "1", "2", or any non-digit.  PCRE  (and  Perl)  also  
      recognize the POSIX syntax [.ch.] and [=ch=] where "ch" is a  
      "collating element", but these are  not  supported,  and  an  
      error is given if they are encountered.  
2389    
2390       In UTF-8 mode, characters with values greater  than  255  do         In UTF-8 mode, characters with values greater than 128 do not match any
2391       not match any of the POSIX character classes.         of the POSIX character classes.
2392    
2393    
2394  VERTICAL BAR  VERTICAL BAR
2395    
2396       Vertical bar characters are  used  to  separate  alternative         Vertical bar characters are used to separate alternative patterns.  For
2397       patterns. For example, the pattern         example, the pattern
2398    
2399         gilbert|sullivan           gilbert|sullivan
2400    
2401       matches either "gilbert" or "sullivan". Any number of alter-         matches  either "gilbert" or "sullivan". Any number of alternatives may
2402       natives  may  appear,  and an empty alternative is permitted         appear, and an empty  alternative  is  permitted  (matching  the  empty
2403       (matching the empty string).   The  matching  process  tries         string).   The  matching  process  tries each alternative in turn, from
2404       each  alternative in turn, from left to right, and the first         left to right, and the first one that succeeds is used. If the alterna-
2405       one that succeeds is used. If the alternatives are within  a         tives  are within a subpattern (defined below), "succeeds" means match-
2406       subpattern  (defined  below),  "succeeds" means matching the         ing the rest of the main pattern as well as the alternative in the sub-
2407       rest of the main pattern as well as the alternative  in  the         pattern.
      subpattern.  
2408    
2409    
2410  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
2411    
2412       The   settings   of   the   PCRE_CASELESS,   PCRE_MULTILINE,         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
2413       PCRE_DOTALL,  and  PCRE_EXTENDED options can be changed from         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a
2414       within the pattern by a  sequence  of  Perl  option  letters         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The
2415       enclosed between "(?" and ")". The option letters are         option letters are
2416    
2417         i  for PCRE_CASELESS           i  for PCRE_CASELESS
2418         m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
2419         s  for PCRE_DOTALL           s  for PCRE_DOTALL
2420         x  for PCRE_EXTENDED           x  for PCRE_EXTENDED
2421    
2422       For example, (?im) sets caseless, multiline matching. It  is         For example, (?im) sets caseless, multiline matching. It is also possi-
2423       also possible to unset these options by preceding the letter         ble to unset these options by preceding the letter with a hyphen, and a
2424       with a hyphen, and a combined setting and unsetting such  as         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-
2425       (?im-sx),  which sets PCRE_CASELESS and PCRE_MULTILINE while         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
2426       unsetting PCRE_DOTALL and PCRE_EXTENDED, is also  permitted.         is also permitted. If a  letter  appears  both  before  and  after  the
2427       If  a  letter  appears both before and after the hyphen, the         hyphen, the option is unset.
2428       option is unset.  
2429           When  an option change occurs at top level (that is, not inside subpat-
2430       When an option change occurs at  top  level  (that  is,  not         tern parentheses), the change applies to the remainder of  the  pattern
2431       inside  subpattern  parentheses),  the change applies to the         that follows.  If the change is placed right at the start of a pattern,
2432       remainder of the pattern that follows.   If  the  change  is         PCRE extracts it into the global options (and it will therefore show up
2433       placed  right  at  the  start of a pattern, PCRE extracts it         in data extracted by the pcre_fullinfo() function).
2434       into the global options (and it will therefore  show  up  in  
2435       data extracted by the pcre_fullinfo() function).         An option change within a subpattern affects only that part of the cur-
2436           rent pattern that follows it, so
2437       An option change within a subpattern affects only that  part  
2438       of the current pattern that follows it, so           (a(?i)b)c
2439    
2440         (a(?i)b)c         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
2441           used).   By  this means, options can be made to have different settings
2442       matches  abc  and  aBc  and  no  other   strings   (assuming         in different parts of the pattern. Any changes made in one  alternative
2443       PCRE_CASELESS  is  not used).  By this means, options can be         do  carry  on  into subsequent branches within the same subpattern. For
2444       made to have different settings in different  parts  of  the         example,
2445       pattern.  Any  changes  made  in one alternative do carry on  
2446       into subsequent branches within  the  same  subpattern.  For           (a(?i)b|c)
2447       example,  
2448           matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the
2449         (a(?i)b|c)         first  branch  is  abandoned before the option setting. This is because
2450           the effects of option settings happen at compile time. There  would  be
2451       matches "ab", "aB", "c", and "C", even though when  matching         some very weird behaviour otherwise.
2452       "C" the first branch is abandoned before the option setting.  
2453       This is because the effects of  option  settings  happen  at         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed
2454       compile  time. There would be some very weird behaviour oth-         in the same way as the Perl-compatible options by using the  characters
2455       erwise.         U  and X respectively. The (?X) flag setting is special in that it must
2456           always occur earlier in the pattern than any of the additional features
2457       The PCRE-specific options PCRE_UNGREEDY and  PCRE_EXTRA  can         it  turns on, even when it is at top level. It is best to put it at the
2458       be changed in the same way as the Perl-compatible options by         start.
      using the characters U and X  respectively.  The  (?X)  flag  
      setting  is  special in that it must always occur earlier in  
      the pattern than any of the additional features it turns on,  
      even when it is at top level. It is best put at the start.  
2459    
2460    
2461  SUBPATTERNS  SUBPATTERNS
2462    
2463       Subpatterns are delimited by parentheses  (round  brackets),         Subpatterns are delimited by parentheses (round brackets), which can be
2464       which can be nested.  Marking part of a pattern as a subpat-         nested.  Turning part of a pattern into a subpattern does two things:
2465       tern does two things:  
2466           1. It localizes a set of alternatives. For example, the pattern
2467       1. It localizes a set of alternatives. For example, the pat-  
2468       tern           cat(aract|erpillar|)
2469    
2470         cat(aract|erpillar|)         matches  one  of the words "cat", "cataract", or "caterpillar". Without
2471           the parentheses, it would match "cataract",  "erpillar"  or  the  empty
2472       matches one of the words "cat",  "cataract",  or  "caterpil-         string.
2473       lar".  Without  the  parentheses, it would match "cataract",  
2474       "erpillar" or the empty string.         2.  It  sets  up  the  subpattern as a capturing subpattern. This means
2475           that, when the whole pattern  matches,  that  portion  of  the  subject
2476       2. It sets up the subpattern as a capturing  subpattern  (as         string that matched the subpattern is passed back to the caller via the
2477       defined  above).   When the whole pattern matches, that por-         ovector argument of pcre_exec(). Opening parentheses are  counted  from
2478       tion of the subject string that matched  the  subpattern  is         left  to  right  (starting  from 1) to obtain numbers for the capturing
2479       passed  back  to  the  caller  via  the  ovector argument of         subpatterns.
2480       pcre_exec(). Opening parentheses are counted  from  left  to  
2481       right (starting from 1) to obtain the numbers of the captur-         For example, if the string "the red king" is matched against  the  pat-
2482       ing subpatterns.         tern
2483    
2484       For example, if the string "the red king" is matched against           the ((red|white) (king|queen))
2485       the pattern  
2486           the captured substrings are "red king", "red", and "king", and are num-
2487         the ((red|white) (king|queen))         bered 1, 2, and 3, respectively.
2488    
2489       the captured substrings are "red king", "red",  and  "king",         The fact that plain parentheses fulfil  two  functions  is  not  always
2490       and are numbered 1, 2, and 3, respectively.         helpful.   There are often times when a grouping subpattern is required
2491           without a capturing requirement. If an opening parenthesis is  followed
2492       The fact that plain parentheses fulfil two functions is  not         by  a question mark and a colon, the subpattern does not do any captur-
2493       always  helpful.  There are often times when a grouping sub-         ing, and is not counted when computing the  number  of  any  subsequent
2494       pattern is required without a capturing requirement.  If  an         capturing  subpatterns. For example, if the string "the white queen" is
2495       opening  parenthesis  is  followed  by a question mark and a         matched against the pattern
2496       colon, the subpattern does not do any capturing, and is  not  
2497       counted  when computing the number of any subsequent captur-           the ((?:red|white) (king|queen))
2498       ing subpatterns. For  example,  if  the  string  "the  white  
2499       queen" is matched against the pattern         the captured substrings are "white queen" and "queen", and are numbered
2500           1  and 2. The maximum number of capturing subpatterns is 65535, and the
2501         the ((?:red|white) (king|queen))         maximum depth of nesting of all subpatterns, both  capturing  and  non-
2502           capturing, is 200.
2503       the captured substrings are "white queen" and  "queen",  and  
2504       are  numbered  1 and 2. The maximum number of capturing sub-         As  a  convenient shorthand, if any option settings are required at the
2505       patterns is 65535, and the maximum depth of nesting  of  all         start of a non-capturing subpattern,  the  option  letters  may  appear
2506       subpatterns, both capturing and non-capturing, is 200.         between the "?" and the ":". Thus the two patterns
2507    
2508       As a  convenient  shorthand,  if  any  option  settings  are           (?i:saturday|sunday)
2509       required  at  the  start  of a non-capturing subpattern, the           (?:(?i)saturday|sunday)
2510       option letters may appear between the "?" and the ":".  Thus  
2511       the two patterns         match exactly the same set of strings. Because alternative branches are
2512           tried from left to right, and options are not reset until  the  end  of
2513         (?i:saturday|sunday)         the  subpattern is reached, an option setting in one branch does affect
2514         (?:(?i)saturday|sunday)         subsequent branches, so the above patterns match "SUNDAY"  as  well  as
2515           "Saturday".
      match exactly the same set of strings.  Because  alternative  
      branches  are  tried from left to right, and options are not  
      reset until the end of the subpattern is reached, an  option  
      setting  in  one  branch does affect subsequent branches, so  
      the above patterns match "SUNDAY" as well as "Saturday".  
2516    
2517    
2518  NAMED SUBPATTERNS  NAMED SUBPATTERNS
2519    
2520       Identifying capturing parentheses by number is  simple,  but         Identifying  capturing  parentheses  by number is simple, but it can be
2521       it  can be very hard to keep track of the numbers in compli-         very hard to keep track of the numbers in complicated  regular  expres-
2522       cated regular expressions. Furthermore, if an expression  is         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
2523       modified,  the  numbers  may change. To help with the diffi-         change. To help with this difficulty, PCRE supports the naming of  sub-
2524       culty, PCRE supports the naming  of  subpatterns,  something         patterns,  something  that  Perl  does  not  provide. The Python syntax
2525       that  Perl does not provide. The Python syntax (?P<name>...)         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and
2526       is used. Names consist of alphanumeric characters and under-         underscores, and must be unique within a pattern.
2527       scores, and must be unique within a pattern.  
2528           Named  capturing  parentheses  are  still  allocated numbers as well as
2529       Named capturing parentheses are still allocated  numbers  as         names. The PCRE API provides function calls for extracting the name-to-
2530       well  as  names.  The  PCRE  API provides function calls for         number  translation table from a compiled pattern. There is also a con-
2531       extracting the name-to-number translation table from a  com-         venience function for extracting a captured substring by name. For fur-
2532       piled  pattern. For further details see the pcreapi documen-         ther details see the pcreapi documentation.
      tation.  
2533    
2534    
2535  REPETITION  REPETITION
2536    
2537       Repetition is specified by quantifiers, which can follow any         Repetition  is  specified  by  quantifiers, which can follow any of the
2538       of the following items:         following items:
2539    
2540             a literal data character
2541             the . metacharacter
2542             the \C escape sequence
2543             the \X escape sequence (in UTF-8 mode with Unicode properties)
2544             an escape such as \d that matches a single character
2545             a character class
2546             a back reference (see next section)
2547             a parenthesized subpattern (unless it is an assertion)
2548    
2549           The general repetition quantifier specifies a minimum and maximum  num-
2550           ber  of  permitted matches, by giving the two numbers in curly brackets
2551           (braces), separated by a comma. The numbers must be  less  than  65536,
2552           and the first must be less than or equal to the second. For example:
2553    
2554             z{2,4}
2555    
2556           matches  "zz",  "zzz",  or  "zzzz". A closing brace on its own is not a
2557           special character. If the second number is omitted, but  the  comma  is
2558           present,  there  is  no upper limit; if the second number and the comma
2559           are both omitted, the quantifier specifies an exact number of  required
2560           matches. Thus
2561    
2562             [aeiou]{3,}
2563    
2564           matches at least 3 successive vowels, but may match many more, while
2565    
2566             \d{8}
2567    
2568           matches  exactly  8  digits. An opening curly bracket that appears in a
2569           position where a quantifier is not allowed, or one that does not  match
2570           the  syntax of a quantifier, is taken as a literal character. For exam-
2571           ple, {,6} is not a quantifier, but a literal string of four characters.
2572    
2573           In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to
2574           individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-
2575           acters, each of which is represented by a two-byte sequence. Similarly,
2576           when Unicode property support is available, \X{3} matches three Unicode
2577           extended  sequences,  each of which may be several bytes long (and they
2578           may be of different lengths).
2579    
2580           The quantifier {0} is permitted, causing the expression to behave as if
2581           the previous item and the quantifier were not present.
2582    
2583         a literal data character         For  convenience  (and  historical compatibility) the three most common
2584         the . metacharacter         quantifiers have single-character abbreviations:
        the \C escape sequence  
        escapes such as \d that match single characters  
        a character class  
        a back reference (see next section)  
        a parenthesized subpattern (unless it is an assertion)  
   
      The general repetition quantifier specifies  a  minimum  and  
      maximum  number  of  permitted  matches,  by  giving the two  
      numbers in curly brackets (braces), separated  by  a  comma.  
      The  numbers  must be less than 65536, and the first must be  
      less than or equal to the second. For example:  
   
        z{2,4}  
   
      matches "zz", "zzz", or "zzzz". A closing brace on  its  own  
      is not a special character. If the second number is omitted,  
      but the comma is present, there is no upper  limit;  if  the  
      second number and the comma are both omitted, the quantifier  
      specifies an exact number of required matches. Thus  
   
        [aeiou]{3,}  
   
      matches at least 3 successive vowels,  but  may  match  many  
      more, while  
   
        \d{8}  
   
      matches exactly 8 digits.  An  opening  curly  bracket  that  
      appears  in a position where a quantifier is not allowed, or  
      one that does not match the syntax of a quantifier, is taken  
      as  a literal character. For example, {,6} is not a quantif-  
      ier, but a literal string of four characters.  
   
      In UTF-8 mode, quantifiers apply to UTF-8 characters  rather  
      than  to  individual  bytes.  Thus,  for example, \x{100}{2}  
      matches two UTF-8 characters, each of which  is  represented  
      by a two-byte sequence.  
   
      The quantifier {0} is permitted, causing the  expression  to  
      behave  as  if the previous item and the quantifier were not  
      present.  
   
      For convenience (and  historical  compatibility)  the  three  
      most common quantifiers have single-character abbreviations:  
   
        *    is equivalent to {0,}  
        +    is equivalent to {1,}  
        ?    is equivalent to {0,1}  
   
      It is possible to construct infinite loops  by  following  a  
      subpattern  that  can  match no characters with a quantifier  
      that has no upper limit, for example:  
   
        (a?)*  
   
      Earlier versions of Perl and PCRE used to give an  error  at  
      compile  time  for such patterns. However, because there are  
      cases where this  can  be  useful,  such  patterns  are  now  
      accepted,  but  if  any repetition of the subpattern does in  
      fact match no characters, the loop is forcibly broken.  
   
      By default, the quantifiers  are  "greedy",  that  is,  they  
      match  as much as possible (up to the maximum number of per-  
      mitted times), without causing the rest of  the  pattern  to  
      fail. The classic example of where this gives problems is in  
      trying to match comments in C programs. These appear between  
      the  sequences /* and */ and within the sequence, individual  
      * and / characters may appear. An attempt to  match  C  com-  
      ments by applying the pattern  
   
        /\*.*\*/  
   
      to the string  
   
        /* first command */  not comment  /* second comment */  
   
      fails, because it matches the entire  string  owing  to  the  
      greediness of the .*  item.  
   
      However, if a quantifier is followed by a question mark,  it  
      ceases  to be greedy, and instead matches the minimum number  
      of times possible, so the pattern  
   
        /\*.*?\*/  
   
      does the right thing with the C comments. The meaning of the  
      various  quantifiers is not otherwise changed, just the pre-  
      ferred number of matches.  Do not confuse this use of  ques-  
      tion  mark  with  its  use as a quantifier in its own right.  
      Because it has two uses, it can sometimes appear doubled, as  
      in  
   
        \d??\d  
   
      which matches one digit by preference, but can match two  if  
      that is the only way the rest of the pattern matches.  
   
      If the PCRE_UNGREEDY option is set (an option which  is  not  
      available  in  Perl),  the  quantifiers  are  not  greedy by  
      default, but individual ones can be made greedy by following  
      them  with  a  question mark. In other words, it inverts the  
      default behaviour.  
   
      When a parenthesized subpattern is quantified with a minimum  
      repeat  count  that is greater than 1 or with a limited max-  
      imum, more store is required for the  compiled  pattern,  in  
      proportion to the size of the minimum or maximum.  
      If a pattern starts with .* or  .{0,}  and  the  PCRE_DOTALL  
      option (equivalent to Perl's /s) is set, thus allowing the .  
      to match  newlines,  the  pattern  is  implicitly  anchored,  
      because whatever follows will be tried against every charac-  
      ter position in the subject string, so there is no point  in  
      retrying  the overall match at any position after the first.  
      PCRE normally treats such a pattern as though it  were  pre-  
      ceded by \A.  
   
      In cases where it is known that the subject string  contains  
      no  newlines,  it  is  worth setting PCRE_DOTALL in order to  
      obtain this optimization, or alternatively using ^ to  indi-  
      cate anchoring explicitly.  
   
      However, there is one situation where the optimization  can-  
      not  be  used. When .*  is inside capturing parentheses that  
      are the subject of a backreference elsewhere in the pattern,  
      a match at the start may fail, and a later one succeed. Con-  
      sider, for example:  
   
        (.*)abc\1  
   
      If the subject is "xyz123abc123"  the  match  point  is  the  
      fourth  character.  For  this  reason, such a pattern is not  
      implicitly anchored.  
   
      When a capturing subpattern is repeated, the value  captured  
      is the substring that matched the final iteration. For exam-  
      ple, after  
   
        (tweedle[dume]{3}\s*)+  
   
      has matched "tweedledum tweedledee" the value  of  the  cap-  
      tured  substring  is  "tweedledee".  However,  if  there are  
      nested capturing  subpatterns,  the  corresponding  captured  
      values  may  have been set in previous iterations. For exam-  
      ple, after  
2585    
2586         /(a|(b))+/           *    is equivalent to {0,}
2587             +    is equivalent to {1,}
2588             ?    is equivalent to {0,1}
2589    
2590       matches "aba" the value of the second captured substring  is         It is possible to construct infinite loops by  following  a  subpattern
2591       "b".         that can match no characters with a quantifier that has no upper limit,
2592           for example:
2593    
2594             (a?)*
2595    
2596           Earlier versions of Perl and PCRE used to give an error at compile time
2597           for  such  patterns. However, because there are cases where this can be
2598           useful, such patterns are now accepted, but if any  repetition  of  the
2599           subpattern  does in fact match no characters, the loop is forcibly bro-
2600           ken.
2601    
2602           By default, the quantifiers are "greedy", that is, they match  as  much
2603           as  possible  (up  to  the  maximum number of permitted times), without
2604           causing the rest of the pattern to fail. The classic example  of  where
2605           this gives problems is in trying to match comments in C programs. These
2606           appear between /* and */ and within the comment,  individual  *  and  /
2607           characters  may  appear. An attempt to match C comments by applying the
2608           pattern
2609    
2610             /\*.*\*/
2611    
2612           to the string
2613    
2614             /* first comment */  not comment  /* second comment */
2615    
2616           fails, because it matches the entire string owing to the greediness  of
2617           the .*  item.
2618    
2619           However,  if  a quantifier is followed by a question mark, it ceases to
2620           be greedy, and instead matches the minimum number of times possible, so
2621           the pattern
2622    
2623             /\*.*?\*/
2624    
2625           does  the  right  thing with the C comments. The meaning of the various
2626           quantifiers is not otherwise changed,  just  the  preferred  number  of
2627           matches.   Do  not  confuse this use of question mark with its use as a
2628           quantifier in its own right. Because it has two uses, it can  sometimes
2629           appear doubled, as in
2630    
2631             \d??\d
2632    
2633           which matches one digit by preference, but can match two if that is the
2634           only way the rest of the pattern matches.
2635    
2636           If the PCRE_UNGREEDY option is set (an option which is not available in
2637           Perl),  the  quantifiers are not greedy by default, but individual ones
2638           can be made greedy by following them with a  question  mark.  In  other
2639           words, it inverts the default behaviour.
2640    
2641           When  a  parenthesized  subpattern  is quantified with a minimum repeat
2642           count that is greater than 1 or with a limited maximum, more memory  is
2643           required  for  the  compiled  pattern, in proportion to the size of the
2644           minimum or maximum.
2645    
2646           If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
2647           alent  to Perl's /s) is set, thus allowing the . to match newlines, the
2648           pattern is implicitly anchored, because whatever follows will be  tried
2649           against  every character position in the subject string, so there is no
2650           point in retrying the overall match at any position  after  the  first.
2651           PCRE normally treats such a pattern as though it were preceded by \A.
2652    
2653           In  cases  where  it  is known that the subject string contains no new-
2654           lines, it is worth setting PCRE_DOTALL in order to  obtain  this  opti-
2655           mization, or alternatively using ^ to indicate anchoring explicitly.
2656    
2657           However,  there is one situation where the optimization cannot be used.
2658           When .*  is inside capturing parentheses that  are  the  subject  of  a
2659           backreference  elsewhere in the pattern, a match at the start may fail,
2660           and a later one succeed. Consider, for example:
2661    
2662             (.*)abc\1
2663    
2664           If the subject is "xyz123abc123" the match point is the fourth  charac-
2665           ter. For this reason, such a pattern is not implicitly anchored.
2666    
2667           When a capturing subpattern is repeated, the value captured is the sub-
2668           string that matched the final iteration. For example, after
2669    
2670             (tweedle[dume]{3}\s*)+
2671    
2672           has matched "tweedledum tweedledee" the value of the captured substring
2673           is  "tweedledee".  However,  if there are nested capturing subpatterns,
2674           the corresponding captured values may have been set in previous  itera-
2675           tions. For example, after
2676    
2677             /(a|(b))+/
2678    
2679         &n