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revision 75 by nigel, Sat Feb 24 21:40:37 2007 UTC revision 96 by nigel, Fri Mar 2 13:10:43 2007 UTC
# Line 6  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    
 PCRE(3)                                                                PCRE(3)  
9    
10    PCRE(3)                                                                PCRE(3)
11    
12    
13  NAME  NAME
14         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
15    
16    
17  INTRODUCTION  INTRODUCTION
18    
19         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
20         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
21         just  a  few  differences.  The current implementation of PCRE (release         just  a  few differences. (Certain features that appeared in Python and
22         5.x) corresponds approximately with Perl  5.8,  including  support  for         PCRE before they appeared in Perl are also available using  the  Python
23         UTF-8 encoded strings and Unicode general category properties. However,         syntax.)
24         this support has to be explicitly enabled; it is not the default.  
25           The  current  implementation of PCRE (release 7.x) corresponds approxi-
26         PCRE is written in C and released as a C library. A  number  of  people         mately with Perl 5.10, including support for UTF-8 encoded strings  and
27         have  written  wrappers and interfaces of various kinds. A C++ class is         Unicode general category properties. However, UTF-8 and Unicode support
28         included in these contributions, which can  be  found  in  the  Contrib         has to be explicitly enabled; it is not the default. The Unicode tables
29         directory at the primary FTP site, which is:         correspond to Unicode release 5.0.0.
30    
31           In  addition to the Perl-compatible matching function, PCRE contains an
32           alternative matching function that matches the same  compiled  patterns
33           in  a different way. In certain circumstances, the alternative function
34           has some advantages. For a discussion of the two  matching  algorithms,
35           see the pcrematching page.
36    
37           PCRE  is  written  in C and released as a C library. A number of people
38           have written wrappers and interfaces of various kinds.  In  particular,
39           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
40           included as part of the PCRE distribution. The pcrecpp page has details
41           of  this  interface.  Other  people's contributions can be found in the
42           Contrib directory at the primary FTP site, which is:
43    
44         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
45    
46         Details  of  exactly which Perl regular expression features are and are         Details of exactly which Perl regular expression features are  and  are
47         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
48         tern and pcrecompat pages.         tern and pcrecompat pages.
49    
50         Some  features  of  PCRE can be included, excluded, or changed when the         Some features of PCRE can be included, excluded, or  changed  when  the
51         library is built. The pcre_config() function makes it  possible  for  a         library  is  built.  The pcre_config() function makes it possible for a
52         client  to  discover  which  features are available. The features them-         client to discover which features are  available.  The  features  them-
53         selves are described in the pcrebuild page. Documentation about  build-         selves  are described in the pcrebuild page. Documentation about build-
54         ing  PCRE for various operating systems can be found in the README file         ing PCRE for various operating systems can be found in the README  file
55         in the source distribution.         in the source distribution.
56    
57           The  library  contains  a number of undocumented internal functions and
58           data tables that are used by more than one  of  the  exported  external
59           functions,  but  which  are  not  intended for use by external callers.
60           Their names all begin with "_pcre_", which hopefully will  not  provoke
61           any name clashes. In some environments, it is possible to control which
62           external symbols are exported when a shared library is  built,  and  in
63           these cases the undocumented symbols are not exported.
64    
65    
66  USER DOCUMENTATION  USER DOCUMENTATION
67    
68         The user documentation for PCRE comprises a number  of  different  sec-         The  user  documentation  for PCRE comprises a number of different sec-
69         tions.  In the "man" format, each of these is a separate "man page". In         tions. In the "man" format, each of these is a separate "man page".  In
70         the HTML format, each is a separate page, linked from the  index  page.         the  HTML  format, each is a separate page, linked from the index page.
71         In  the  plain text format, all the sections are concatenated, for ease         In the plain text format, all the sections are concatenated,  for  ease
72         of searching. The sections are as follows:         of searching. The sections are as follows:
73    
74           pcre              this document           pcre              this document
75           pcreapi           details of PCRE's native API           pcreapi           details of PCRE's native C API
76           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
77           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
78           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
79             pcrecpp           details of the C++ wrapper
80           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
81             pcrematching      discussion of the two matching algorithms
82           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
83           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
84                               regular expressions                               regular expressions
85           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
86           pcreposix         the POSIX-compatible API           pcreposix         the POSIX-compatible C API
87           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
88           pcresample        discussion of the sample program           pcresample        discussion of the sample program
89             pcrestack         discussion of stack usage
90           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
91    
92         In  addition,  in the "man" and HTML formats, there is a short page for         In addition, in the "man" and HTML formats, there is a short  page  for
93         each library function, listing its arguments and results.         each C library function, listing its arguments and results.
94    
95    
96  LIMITATIONS  LIMITATIONS
97    
98         There are some size limitations in PCRE but it is hoped that they  will         There  are some size limitations in PCRE but it is hoped that they will
99         never in practice be relevant.         never in practice be relevant.
100    
101         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE         The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE
102         is compiled with the default internal linkage size of 2. If you want to         is compiled with the default internal linkage size of 2. If you want to
103         process  regular  expressions  that are truly enormous, you can compile         process regular expressions that are truly enormous,  you  can  compile
104         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in         PCRE  with  an  internal linkage size of 3 or 4 (see the README file in
105         the  source  distribution and the pcrebuild documentation for details).         the source distribution and the pcrebuild documentation  for  details).
106         In these cases the limit is substantially larger.  However,  the  speed         In  these  cases the limit is substantially larger.  However, the speed
107         of execution will be slower.         of execution is slower.
108    
109         All values in repeating quantifiers must be less than 65536.  The maxi-         All values in repeating quantifiers must be less than 65536. The  maxi-
110         mum number of capturing subpatterns is 65535.         mum  compiled  length  of  subpattern  with an explicit repeat count is
111           30000 bytes. The maximum number of capturing subpatterns is 65535.
112         There is no limit to the number of non-capturing subpatterns,  but  the  
113         maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,         There is no limit to the number of parenthesized subpatterns, but there
114         including capturing subpatterns, assertions, and other types of subpat-         can be no more than 65535 capturing subpatterns.
115         tern, is 200.  
116           The maximum length of name for a named subpattern is 32 characters, and
117         The  maximum  length of a subject string is the largest positive number         the maximum number of named subpatterns is 10000.
118         that an integer variable can hold. However, PCRE uses recursion to han-  
119         dle  subpatterns  and indefinite repetition. This means that the avail-         The maximum length of a subject string is the largest  positive  number
120         able stack space may limit the size of a subject  string  that  can  be         that  an integer variable can hold. However, when using the traditional
121         processed by certain patterns.         matching function, PCRE uses recursion to handle subpatterns and indef-
122           inite  repetition.  This means that the available stack space may limit
123           the size of a subject string that can be processed by certain patterns.
124           For a discussion of stack issues, see the pcrestack documentation.
125    
126    
127  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
# Line 111  UTF-8 AND UNICODE PROPERTY SUPPORT Line 139  UTF-8 AND UNICODE PROPERTY SUPPORT
139    
140         If you compile PCRE with UTF-8 support, but do not use it at run  time,         If you compile PCRE with UTF-8 support, but do not use it at run  time,
141         the  library will be a bit bigger, but the additional run time overhead         the  library will be a bit bigger, but the additional run time overhead
142         is limited to testing the PCRE_UTF8 flag in several places,  so  should         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
143         not be very large.         very big.
144    
145         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
146         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
147         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
148         general category properties such as Lu for an upper case letter  or  Nd         general category properties such as Lu for an upper case letter  or  Nd
149         for  a decimal number. A full list is given in the pcrepattern documen-         for  a  decimal number, the Unicode script names such as Arabic or Han,
150         tation. The PCRE library is increased in size by about 90K when Unicode         and the derived properties Any and L&. A full  list  is  given  in  the
151         property support is included.         pcrepattern documentation. Only the short names for properties are sup-
152           ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
153           ter},  is  not  supported.   Furthermore,  in Perl, many properties may
154           optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
155           does not support this.
156    
157         The following comments apply when PCRE is running in UTF-8 mode:         The following comments apply when PCRE is running in UTF-8 mode:
158    
# Line 136  UTF-8 AND UNICODE PROPERTY SUPPORT Line 168  UTF-8 AND UNICODE PROPERTY SUPPORT
168         PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may         PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may
169         crash.         crash.
170    
171         2. In a pattern, the escape sequence \x{...}, where the contents of the         2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
172         braces is a string of hexadecimal digits, is  interpreted  as  a  UTF-8         two-byte UTF-8 character if the value is greater than 127.
        character  whose code number is the given hexadecimal number, for exam-  
        ple: \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.  
173    
174         3. The original hexadecimal escape sequence, \xhh, matches  a  two-byte         3. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
175         UTF-8 character if the value is greater than 127.         characters for values greater than \177.
176    
177         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
178         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
# Line 153  UTF-8 AND UNICODE PROPERTY SUPPORT Line 181  UTF-8 AND UNICODE PROPERTY SUPPORT
181         gle byte.         gle byte.
182    
183         6.  The  escape sequence \C can be used to match a single byte in UTF-8         6.  The  escape sequence \C can be used to match a single byte in UTF-8
184         mode, but its use can lead to some strange effects.         mode, but its use can lead to some strange effects.  This  facility  is
185           not available in the alternative matching function, pcre_dfa_exec().
186    
187         7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly         7.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
188         test  characters of any code value, but the characters that PCRE recog-         test characters of any code value, but the characters that PCRE  recog-
189         nizes as digits, spaces, or word characters  remain  the  same  set  as         nizes  as  digits,  spaces,  or  word characters remain the same set as
190         before, all with values less than 256. This remains true even when PCRE         before, all with values less than 256. This remains true even when PCRE
191         includes Unicode property support, because to do otherwise  would  slow         includes  Unicode  property support, because to do otherwise would slow
192         down  PCRE in many common cases. If you really want to test for a wider         down PCRE in many common cases. If you really want to test for a  wider
193         sense of, say, "digit", you must use Unicode  property  tests  such  as         sense  of,  say,  "digit",  you must use Unicode property tests such as
194         \p{Nd}.         \p{Nd}.
195    
196         8.  Similarly,  characters that match the POSIX named character classes         8. Similarly, characters that match the POSIX named  character  classes
197         are all low-valued characters.         are all low-valued characters.
198    
199         9. Case-insensitive matching applies only to  characters  whose  values         9.  Case-insensitive  matching  applies only to characters whose values
200         are  less than 128, unless PCRE is built with Unicode property support.         are less than 128, unless PCRE is built with Unicode property  support.
201         Even when Unicode property support is available, PCRE  still  uses  its         Even  when  Unicode  property support is available, PCRE still uses its
202         own  character  tables when checking the case of low-valued characters,         own character tables when checking the case of  low-valued  characters,
203         so as not to degrade performance.  The Unicode property information  is         so  as not to degrade performance.  The Unicode property information is
204         used only for characters with higher values.         used only for characters with higher values. Even when Unicode property
205           support is available, PCRE supports case-insensitive matching only when
206           there is a one-to-one mapping between a letter's  cases.  There  are  a
207           small  number  of  many-to-one  mappings in Unicode; these are not sup-
208           ported by PCRE.
209    
210    
211  AUTHOR  AUTHOR
212    
213         Philip Hazel <ph10@cam.ac.uk>         Philip Hazel
214         University Computing Service,         University Computing Service,
215         Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
        Phone: +44 1223 334714  
216    
217  Last updated: 09 September 2004         Putting an actual email address here seems to have been a spam  magnet,
218  Copyright (c) 1997-2004 University of Cambridge.         so I've taken it away. If you want to email me, use my initial and sur-
219  -----------------------------------------------------------------------------         name, separated by a dot, at the domain ucs.cam.ac.uk.
220    
221    Last updated: 23 November 2006
222    Copyright (c) 1997-2006 University of Cambridge.
223    ------------------------------------------------------------------------------
224    
 PCRE(3)                                                                PCRE(3)  
225    
226    PCREBUILD(3)                                                      PCREBUILD(3)
227    
228    
229  NAME  NAME
230         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
231    
232    
233  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
234    
235         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
# Line 212  PCRE BUILD-TIME OPTIONS Line 249  PCRE BUILD-TIME OPTIONS
249         not described.         not described.
250    
251    
252    C++ SUPPORT
253    
254           By default, the configure script will search for a C++ compiler and C++
255           header files. If it finds them, it automatically builds the C++ wrapper
256           library for PCRE. You can disable this by adding
257    
258             --disable-cpp
259    
260           to the configure command.
261    
262    
263  UTF-8 SUPPORT  UTF-8 SUPPORT
264    
265         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 character strings, add
# Line 245  UNICODE CHARACTER PROPERTY SUPPORT Line 293  UNICODE CHARACTER PROPERTY SUPPORT
293    
294  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
295    
296         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating
297         ter. This is the normal newline character on Unix-like systems. You can         the  end  of  a line. This is the normal newline character on Unix-like
298         compile PCRE to use character 13 (carriage return) instead by adding         systems. You can compile PCRE to use character 13 (carriage return, CR)
299           instead, by adding
300    
301           --enable-newline-is-cr           --enable-newline-is-cr
302    
303         to the configure command. For completeness there is  also  a  --enable-         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
304         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
305         line character.  
306           Alternatively, you can specify that line endings are to be indicated by
307           the two character sequence CRLF. If you want this, add
308    
309             --enable-newline-is-crlf
310    
311           to the configure command. There is a fourth option, specified by
312    
313             --enable-newline-is-any
314    
315           which causes PCRE to recognize any Unicode newline sequence.
316    
317           Whatever  line  ending convention is selected when PCRE is built can be
318           overridden when the library functions are called. At build time  it  is
319           conventional to use the standard for your operating system.
320    
321    
322  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
323    
324         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
325         Unix  libraries by default. You can suppress one of these by adding one         Unix libraries by default. You can suppress one of these by adding  one
326         of         of
327    
328           --disable-shared           --disable-shared
# Line 271  BUILDING SHARED AND STATIC LIBRARIES Line 334  BUILDING SHARED AND STATIC LIBRARIES
334  POSIX MALLOC USAGE  POSIX MALLOC USAGE
335    
336         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
337         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
338         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
339         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
340         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
341         on the stack, because this is faster than using malloc() for each call.         on the stack, because this is faster than using malloc() for each call.
342         The default threshold above which the stack is no longer used is 10; it         The default threshold above which the stack is no longer used is 10; it
# Line 284  POSIX MALLOC USAGE Line 347  POSIX MALLOC USAGE
347         to the configure command.         to the configure command.
348    
349    
 LIMITING PCRE RESOURCE USAGE  
   
        Internally,  PCRE has a function called match(), which it calls repeat-  
        edly (possibly recursively) when matching a pattern. By controlling the  
        maximum  number  of  times  this function may be called during a single  
        matching operation, a limit can be placed on the resources  used  by  a  
        single  call  to  pcre_exec(). The limit can be changed at run time, as  
        described in the pcreapi documentation. The default is 10 million,  but  
        this can be changed by adding a setting such as  
   
          --with-match-limit=500000  
   
        to the configure command.  
   
   
350  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
351    
352         Within  a  compiled  pattern,  offset values are used to point from one         Within a compiled pattern, offset values are used  to  point  from  one
353         part to another (for example, from an opening parenthesis to an  alter-         part  to another (for example, from an opening parenthesis to an alter-
354         nation  metacharacter).  By default, two-byte values are used for these         nation metacharacter). By default, two-byte values are used  for  these
355         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets,  leading  to  a  maximum size for a compiled pattern of around
356         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
357         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless,  some  people do want to process enormous patterns, so it
358         is  possible  to compile PCRE to use three-byte or four-byte offsets by         is possible to compile PCRE to use three-byte or four-byte  offsets  by
359         adding a setting such as         adding a setting such as
360    
361           --with-link-size=3           --with-link-size=3
362    
363         to the configure command. The value given must be 2,  3,  or  4.  Using         to  the  configure  command.  The value given must be 2, 3, or 4. Using
364         longer  offsets slows down the operation of PCRE because it has to load         longer offsets slows down the operation of PCRE because it has to  load
365         additional bytes when handling them.         additional bytes when handling them.
366    
367         If you build PCRE with an increased link size, test 2 (and  test  5  if         If  you  build  PCRE with an increased link size, test 2 (and test 5 if
368         you  are using UTF-8) will fail. Part of the output of these tests is a         you are using UTF-8) will fail. Part of the output of these tests is  a
369         representation of the compiled pattern, and this changes with the  link         representation  of the compiled pattern, and this changes with the link
370         size.         size.
371    
372    
373  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
374    
375         PCRE  implements  backtracking while matching by making recursive calls         When matching with the pcre_exec() function, PCRE implements backtrack-
376         to an internal function called match(). In environments where the  size         ing  by  making recursive calls to an internal function called match().
377         of the stack is limited, this can severely limit PCRE's operation. (The         In environments where the size of the stack is limited,  this  can  se-
378         Unix environment does not usually suffer from this problem.) An  alter-         verely  limit  PCRE's operation. (The Unix environment does not usually
379         native  approach  that  uses  memory  from  the  heap to remember data,         suffer from this problem, but it may sometimes be necessary to increase
380         instead of using recursive function calls, has been implemented to work         the  maximum  stack size.  There is a discussion in the pcrestack docu-
381         round  this  problem. If you want to build a version of PCRE that works         mentation.) An alternative approach to recursion that uses memory  from
382         this way, add         the  heap  to remember data, instead of using recursive function calls,
383           has been implemented to work round the problem of limited  stack  size.
384           If you want to build a version of PCRE that works this way, add
385    
386           --disable-stack-for-recursion           --disable-stack-for-recursion
387    
388         to the configure command. With this configuration, PCRE  will  use  the         to  the  configure  command. With this configuration, PCRE will use the
389         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
390         ment functions. Separate functions are provided because  the  usage  is         ment  functions.  Separate  functions are provided because the usage is
391         very  predictable:  the  block sizes requested are always the same, and         very predictable: the block sizes requested are always  the  same,  and
392         the blocks are always freed in reverse order. A calling  program  might         the  blocks  are always freed in reverse order. A calling program might
393         be  able  to implement optimized functions that perform better than the         be able to implement optimized functions that perform better  than  the
394         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more
395         slowly when built in this way.         slowly when built in this way. This option affects only the pcre_exec()
396           function; it is not relevant for the the pcre_dfa_exec() function.
397    
398    
399    LIMITING PCRE RESOURCE USAGE
400    
401           Internally,  PCRE has a function called match(), which it calls repeat-
402           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
403           pcre_exec()  function.  By controlling the maximum number of times this
404           function may be called during a single matching operation, a limit  can
405           be  placed  on  the resources used by a single call to pcre_exec(). The
406           limit can be changed at run time, as described in the pcreapi  documen-
407           tation.  The default is 10 million, but this can be changed by adding a
408           setting such as
409    
410             --with-match-limit=500000
411    
412           to  the  configure  command.  This  setting  has  no  effect   on   the
413           pcre_dfa_exec() matching function.
414    
415           In  some  environments  it is desirable to limit the depth of recursive
416           calls of match() more strictly than the total number of calls, in order
417           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
418           for-recursion is specified) that is used. A second limit controls this;
419           it  defaults  to  the  value  that is set for --with-match-limit, which
420           imposes no additional constraints. However, you can set a  lower  limit
421           by adding, for example,
422    
423             --with-match-limit-recursion=10000
424    
425           to  the  configure  command.  This  value can also be overridden at run
426           time.
427    
428    
429  USING EBCDIC CODE  USING EBCDIC CODE
430    
431         PCRE  assumes  by  default that it will run in an environment where the         PCRE assumes by default that it will run in an  environment  where  the
432         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
433         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by
434         adding         adding
435    
436           --enable-ebcdic           --enable-ebcdic
437    
438         to the configure command.         to the configure command.
439    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
440    
441  PCRE(3)                                                                PCRE(3)  SEE ALSO
442    
443           pcreapi(3), pcre_config(3).
444    
445    Last updated: 30 November 2006
446    Copyright (c) 1997-2006 University of Cambridge.
447    ------------------------------------------------------------------------------
448    
449    
450    PCREMATCHING(3)                                                PCREMATCHING(3)
451    
452    
453  NAME  NAME
454         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
455    
456    
457    PCRE MATCHING ALGORITHMS
458    
459           This document describes the two different algorithms that are available
460           in PCRE for matching a compiled regular expression against a given sub-
461           ject  string.  The  "standard"  algorithm  is  the  one provided by the
462           pcre_exec() function.  This works in the same was  as  Perl's  matching
463           function, and provides a Perl-compatible matching operation.
464    
465           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
466           this operates in a different way, and is not  Perl-compatible.  It  has
467           advantages  and disadvantages compared with the standard algorithm, and
468           these are described below.
469    
470           When there is only one possible way in which a given subject string can
471           match  a pattern, the two algorithms give the same answer. A difference
472           arises, however, when there are multiple possibilities. For example, if
473           the pattern
474    
475             ^<.*>
476    
477           is matched against the string
478    
479             <something> <something else> <something further>
480    
481           there are three possible answers. The standard algorithm finds only one
482           of them, whereas the alternative algorithm finds all three.
483    
484    
485    REGULAR EXPRESSIONS AS TREES
486    
487           The set of strings that are matched by a regular expression can be rep-
488           resented  as  a  tree structure. An unlimited repetition in the pattern
489           makes the tree of infinite size, but it is still a tree.  Matching  the
490           pattern  to a given subject string (from a given starting point) can be
491           thought of as a search of the tree.  There are two  ways  to  search  a
492           tree:  depth-first  and  breadth-first, and these correspond to the two
493           matching algorithms provided by PCRE.
494    
495    
496    THE STANDARD MATCHING ALGORITHM
497    
498           In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-
499           sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a
500           depth-first search of the pattern tree. That is, it  proceeds  along  a
501           single path through the tree, checking that the subject matches what is
502           required. When there is a mismatch, the algorithm  tries  any  alterna-
503           tives  at  the  current point, and if they all fail, it backs up to the
504           previous branch point in the  tree,  and  tries  the  next  alternative
505           branch  at  that  level.  This often involves backing up (moving to the
506           left) in the subject string as well.  The  order  in  which  repetition
507           branches  are  tried  is controlled by the greedy or ungreedy nature of
508           the quantifier.
509    
510           If a leaf node is reached, a matching string has  been  found,  and  at
511           that  point the algorithm stops. Thus, if there is more than one possi-
512           ble match, this algorithm returns the first one that it finds.  Whether
513           this  is the shortest, the longest, or some intermediate length depends
514           on the way the greedy and ungreedy repetition quantifiers are specified
515           in the pattern.
516    
517           Because  it  ends  up  with a single path through the tree, it is rela-
518           tively straightforward for this algorithm to keep  track  of  the  sub-
519           strings  that  are  matched  by portions of the pattern in parentheses.
520           This provides support for capturing parentheses and back references.
521    
522    
523    THE ALTERNATIVE MATCHING ALGORITHM
524    
525           This algorithm conducts a breadth-first search of  the  tree.  Starting
526           from  the  first  matching  point  in the subject, it scans the subject
527           string from left to right, once, character by character, and as it does
528           this,  it remembers all the paths through the tree that represent valid
529           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
530           though  it is not implemented as a traditional finite state machine (it
531           keeps multiple states active simultaneously).
532    
533           The scan continues until either the end of the subject is  reached,  or
534           there  are  no more unterminated paths. At this point, terminated paths
535           represent the different matching possibilities (if there are none,  the
536           match  has  failed).   Thus,  if there is more than one possible match,
537           this algorithm finds all of them, and in particular, it finds the long-
538           est.  In PCRE, there is an option to stop the algorithm after the first
539           match (which is necessarily the shortest) has been found.
540    
541           Note that all the matches that are found start at the same point in the
542           subject. If the pattern
543    
544             cat(er(pillar)?)
545    
546           is  matched  against the string "the caterpillar catchment", the result
547           will be the three strings "cat", "cater", and "caterpillar" that  start
548           at the fourth character of the subject. The algorithm does not automat-
549           ically move on to find matches that start at later positions.
550    
551           There are a number of features of PCRE regular expressions that are not
552           supported by the alternative matching algorithm. They are as follows:
553    
554           1.  Because  the  algorithm  finds  all possible matches, the greedy or
555           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
556           ungreedy quantifiers are treated in exactly the same way. However, pos-
557           sessive quantifiers can make a difference when what follows could  also
558           match what is quantified, for example in a pattern like this:
559    
560             ^a++\w!
561    
562           This  pattern matches "aaab!" but not "aaa!", which would be matched by
563           a non-possessive quantifier. Similarly, if an atomic group is  present,
564           it  is matched as if it were a standalone pattern at the current point,
565           and the longest match is then "locked in" for the rest of  the  overall
566           pattern.
567    
568           2. When dealing with multiple paths through the tree simultaneously, it
569           is not straightforward to keep track of  captured  substrings  for  the
570           different  matching  possibilities,  and  PCRE's implementation of this
571           algorithm does not attempt to do this. This means that no captured sub-
572           strings are available.
573    
574           3.  Because no substrings are captured, back references within the pat-
575           tern are not supported, and cause errors if encountered.
576    
577           4. For the same reason, conditional expressions that use  a  backrefer-
578           ence  as  the  condition or test for a specific group recursion are not
579           supported.
580    
581           5. Callouts are supported, but the value of the  capture_top  field  is
582           always 1, and the value of the capture_last field is always -1.
583    
584           6.  The \C escape sequence, which (in the standard algorithm) matches a
585           single byte, even in UTF-8 mode, is not supported because the  alterna-
586           tive  algorithm  moves  through  the  subject string one character at a
587           time, for all active paths through the tree.
588    
589    
590    ADVANTAGES OF THE ALTERNATIVE ALGORITHM
591    
592           Using the alternative matching algorithm provides the following  advan-
593           tages:
594    
595           1. All possible matches (at a single point in the subject) are automat-
596           ically found, and in particular, the longest match is  found.  To  find
597           more than one match using the standard algorithm, you have to do kludgy
598           things with callouts.
599    
600           2. There is much better support for partial matching. The  restrictions
601           on  the content of the pattern that apply when using the standard algo-
602           rithm for partial matching do not apply to the  alternative  algorithm.
603           For  non-anchored patterns, the starting position of a partial match is
604           available.
605    
606           3. Because the alternative algorithm  scans  the  subject  string  just
607           once,  and  never  needs to backtrack, it is possible to pass very long
608           subject strings to the matching function in  several  pieces,  checking
609           for partial matching each time.
610    
611    
612    DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
613    
614           The alternative algorithm suffers from a number of disadvantages:
615    
616           1.  It  is  substantially  slower  than the standard algorithm. This is
617           partly because it has to search for all possible matches, but  is  also
618           because it is less susceptible to optimization.
619    
620           2. Capturing parentheses and back references are not supported.
621    
622           3. Although atomic groups are supported, their use does not provide the
623           performance advantage that it does for the standard algorithm.
624    
625    Last updated: 24 November 2006
626    Copyright (c) 1997-2006 University of Cambridge.
627    ------------------------------------------------------------------------------
628    
629    
630    PCREAPI(3)                                                          PCREAPI(3)
631    
632    
633    NAME
634           PCRE - Perl-compatible regular expressions
635    
636    
637  PCRE NATIVE API  PCRE NATIVE API
638    
639         #include <pcre.h>         #include <pcre.h>
# Line 375  PCRE NATIVE API Line 642  PCRE NATIVE API
642              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
643              const unsigned char *tableptr);              const unsigned char *tableptr);
644    
645           pcre *pcre_compile2(const char *pattern, int options,
646                int *errorcodeptr,
647                const char **errptr, int *erroffset,
648                const unsigned char *tableptr);
649    
650         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options,
651              const char **errptr);              const char **errptr);
652    
# Line 382  PCRE NATIVE API Line 654  PCRE NATIVE API
654              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
655              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
656    
657           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
658                const char *subject, int length, int startoffset,
659                int options, int *ovector, int ovecsize,
660                int *workspace, int wscount);
661    
662         int pcre_copy_named_substring(const pcre *code,         int pcre_copy_named_substring(const pcre *code,
663              const char *subject, int *ovector,              const char *subject, int *ovector,
664              int stringcount, const char *stringname,              int stringcount, const char *stringname,
# Line 399  PCRE NATIVE API Line 676  PCRE NATIVE API
676         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
677              const char *name);              const char *name);
678    
679           int pcre_get_stringtable_entries(const pcre *code,
680                const char *name, char **first, char **last);
681    
682         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
683              int stringcount, int stringnumber,              int stringcount, int stringnumber,
684              const char **stringptr);              const char **stringptr);
# Line 417  PCRE NATIVE API Line 697  PCRE NATIVE API
697    
698         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
699    
700           int pcre_refcount(pcre *code, int adjust);
701    
702         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
703    
704         char *pcre_version(void);         char *pcre_version(void);
# Line 435  PCRE NATIVE API Line 717  PCRE NATIVE API
717  PCRE API OVERVIEW  PCRE API OVERVIEW
718    
719         PCRE has its own native API, which is described in this document. There         PCRE has its own native API, which is described in this document. There
720         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
721         expression API.  These are described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
722           Both of these APIs define a set of C function calls. A C++  wrapper  is
723           distributed with PCRE. It is documented in the pcrecpp page.
724    
725         The  native  API  function  prototypes  are  defined in the header file         The  native  API  C  function prototypes are defined in the header file
726         pcre.h, and on Unix systems the library itself is  called  libpcre.  It         pcre.h, and on Unix systems the library itself is called  libpcre.   It
727         can normally be accessed by adding -lpcre to the command for linking an         can normally be accessed by adding -lpcre to the command for linking an
728         application  that  uses  PCRE.  The  header  file  defines  the  macros         application  that  uses  PCRE.  The  header  file  defines  the  macros
729         PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-         PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
730         bers for the library.  Applications can use these  to  include  support         bers for the library.  Applications can use these  to  include  support
731         for different releases of PCRE.         for different releases of PCRE.
732    
733         The  functions  pcre_compile(),  pcre_study(), and pcre_exec() are used         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
734         for compiling and matching regular expressions. A sample  program  that         pcre_exec() are used for compiling and matching regular expressions  in
735         demonstrates  the  simplest  way  of using them is provided in the file         a  Perl-compatible  manner. A sample program that demonstrates the sim-
736         called pcredemo.c in the source distribution. The pcresample documenta-         plest way of using them is provided in the file  called  pcredemo.c  in
737         tion describes how to run it.         the  source distribution. The pcresample documentation describes how to
738           run it.
739         In  addition  to  the  main compiling and matching functions, there are  
740         convenience functions for extracting captured substrings from a matched         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
741         subject string.  They are:         ble,  is  also provided. This uses a different algorithm for the match-
742           ing. The alternative algorithm finds all possible matches (at  a  given
743           point  in  the subject), and scans the subject just once. However, this
744           algorithm does not return captured substrings. A description of the two
745           matching  algorithms and their advantages and disadvantages is given in
746           the pcrematching documentation.
747    
748           In addition to the main compiling and  matching  functions,  there  are
749           convenience functions for extracting captured substrings from a subject
750           string that is matched by pcre_exec(). They are:
751    
752           pcre_copy_substring()           pcre_copy_substring()
753           pcre_copy_named_substring()           pcre_copy_named_substring()
# Line 462  PCRE API OVERVIEW Line 755  PCRE API OVERVIEW
755           pcre_get_named_substring()           pcre_get_named_substring()
756           pcre_get_substring_list()           pcre_get_substring_list()
757           pcre_get_stringnumber()           pcre_get_stringnumber()
758             pcre_get_stringtable_entries()
759    
760         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
761         to free the memory used for extracted strings.         to free the memory used for extracted strings.
762    
763         The function pcre_maketables() is used to  build  a  set  of  character         The  function  pcre_maketables()  is  used  to build a set of character
764         tables   in  the  current  locale  for  passing  to  pcre_compile()  or         tables  in  the  current  locale   for   passing   to   pcre_compile(),
765         pcre_exec().  This is an optional facility that is  provided  for  spe-         pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
766         cialist use. Most commonly, no special tables are passed, in which case         provided for specialist use.  Most  commonly,  no  special  tables  are
767         internal tables that are generated when PCRE is built are used.         passed,  in  which case internal tables that are generated when PCRE is
768           built are used.
769    
770         The function pcre_fullinfo() is used to find out  information  about  a         The function pcre_fullinfo() is used to find out  information  about  a
771         compiled  pattern; pcre_info() is an obsolete version that returns only         compiled  pattern; pcre_info() is an obsolete version that returns only
# Line 478  PCRE API OVERVIEW Line 773  PCRE API OVERVIEW
773         patibility.   The function pcre_version() returns a pointer to a string         patibility.   The function pcre_version() returns a pointer to a string
774         containing the version of PCRE and its date of release.         containing the version of PCRE and its date of release.
775    
776           The function pcre_refcount() maintains a  reference  count  in  a  data
777           block  containing  a compiled pattern. This is provided for the benefit
778           of object-oriented applications.
779    
780         The global variables pcre_malloc and pcre_free  initially  contain  the         The global variables pcre_malloc and pcre_free  initially  contain  the
781         entry  points  of  the  standard malloc() and free() functions, respec-         entry  points  of  the  standard malloc() and free() functions, respec-
782         tively. PCRE calls the memory management functions via these variables,         tively. PCRE calls the memory management functions via these variables,
# Line 487  PCRE API OVERVIEW Line 786  PCRE API OVERVIEW
786         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
787         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
788         are used only when PCRE is compiled to use  the  heap  for  remembering         are used only when PCRE is compiled to use  the  heap  for  remembering
789         data,  instead  of recursive function calls. This is a non-standard way         data, instead of recursive function calls, when running the pcre_exec()
790         of building PCRE, for use in environments  that  have  limited  stacks.         function. See the pcrebuild documentation for  details  of  how  to  do
791         Because  of  the greater use of memory management, it runs more slowly.         this.  It  is  a non-standard way of building PCRE, for use in environ-
792         Separate functions are provided so that special-purpose  external  code         ments that have limited stacks. Because of the greater  use  of  memory
793         can be used for this case. When used, these functions are always called         management,  it  runs  more  slowly. Separate functions are provided so
794         in a stack-like manner (last obtained, first  freed),  and  always  for         that special-purpose external code can be  used  for  this  case.  When
795         memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
796           obtained, first freed), and always for memory blocks of the same  size.
797           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
798           mentation.
799    
800         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
801         by the caller to a "callout" function, which PCRE  will  then  call  at         by  the  caller  to  a "callout" function, which PCRE will then call at
802         specified  points during a matching operation. Details are given in the         specified points during a matching operation. Details are given in  the
803         pcrecallout documentation.         pcrecallout documentation.
804    
805    
806    NEWLINES
807    
808           PCRE  supports four different conventions for indicating line breaks in
809           strings: a single CR (carriage return) character, a  single  LF  (line-
810           feed)  character,  the two-character sequence CRLF, or any Unicode new-
811           line sequence.  The Unicode newline sequences are the three  just  men-
812           tioned, plus the single characters VT (vertical tab, U+000B), FF (form-
813           feed, U+000C), NEL (next line, U+0085), LS  (line  separator,  U+2028),
814           and PS (paragraph separator, U+2029).
815    
816           Each  of  the first three conventions is used by at least one operating
817           system as its standard newline sequence. When PCRE is built, a  default
818           can  be  specified.  The default default is LF, which is the Unix stan-
819           dard. When PCRE is run, the default can be overridden,  either  when  a
820           pattern is compiled, or when it is matched.
821    
822           In the PCRE documentation the word "newline" is used to mean "the char-
823           acter or pair of characters that indicate a line break". The choice  of
824           newline  convention  affects  the  handling of the dot, circumflex, and
825           dollar metacharacters, the handling of #-comments in /x mode, and, when
826           CRLF  is a recognized line ending sequence, the match position advance-
827           ment for a non-anchored pattern. The choice of newline convention  does
828           not affect the interpretation of the \n or \r escape sequences.
829    
830    
831  MULTITHREADING  MULTITHREADING
832    
833         The PCRE functions can be used in  multi-threading  applications,  with         The  PCRE  functions  can be used in multi-threading applications, with
834         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
835         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
836         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
837    
838         The compiled form of a regular expression is not altered during  match-         The  compiled form of a regular expression is not altered during match-
839         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
840         at once.         at once.
841    
# Line 516  MULTITHREADING Line 843  MULTITHREADING
843  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
844    
845         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
846         later  time,  possibly by a different program, and even on a host other         later time, possibly by a different program, and even on a  host  other
847         than the one on which  it  was  compiled.  Details  are  given  in  the         than  the  one  on  which  it  was  compiled.  Details are given in the
848         pcreprecompile documentation.         pcreprecompile documentation.
849    
850    
# Line 525  CHECKING BUILD-TIME OPTIONS Line 852  CHECKING BUILD-TIME OPTIONS
852    
853         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
854    
855         The  function pcre_config() makes it possible for a PCRE client to dis-         The function pcre_config() makes it possible for a PCRE client to  dis-
856         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
857         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
858         tures.         tures.
859    
860         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
861         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
862         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
863         available:         available:
864    
865           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
866    
867         The  output is an integer that is set to one if UTF-8 support is avail-         The output is an integer that is set to one if UTF-8 support is  avail-
868         able; otherwise it is set to zero.         able; otherwise it is set to zero.
869    
870           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
871    
872         The output is an integer that is set to  one  if  support  for  Unicode         The  output  is  an  integer  that is set to one if support for Unicode
873         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
874    
875           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
876    
877         The  output  is an integer that is set to the value of the code that is         The output is an integer whose value specifies  the  default  character
878         used for the newline character. It is either linefeed (10) or  carriage         sequence  that is recognized as meaning "newline". The four values that
879         return  (13),  and  should  normally be the standard character for your         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, and -1 for ANY.
880         operating system.         The default should normally be the standard sequence for your operating
881           system.
882    
883           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
884    
# Line 573  CHECKING BUILD-TIME OPTIONS Line 901  CHECKING BUILD-TIME OPTIONS
901         internal matching function calls in a  pcre_exec()  execution.  Further         internal matching function calls in a  pcre_exec()  execution.  Further
902         details are given with pcre_exec() below.         details are given with pcre_exec() below.
903    
904             PCRE_CONFIG_MATCH_LIMIT_RECURSION
905    
906           The  output is an integer that gives the default limit for the depth of
907           recursion when calling the internal matching function in a  pcre_exec()
908           execution. Further details are given with pcre_exec() below.
909    
910           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
911    
912         The  output  is  an integer that is set to one if internal recursion is         The  output is an integer that is set to one if internal recursion when
913         implemented by recursive function calls that use the stack to  remember         running pcre_exec() is implemented by recursive function calls that use
914         their state. This is the usual way that PCRE is compiled. The output is         the  stack  to remember their state. This is the usual way that PCRE is
915         zero if PCRE was compiled to use blocks of data on the heap instead  of         compiled. The output is zero if PCRE was compiled to use blocks of data
916         recursive   function   calls.   In  this  case,  pcre_stack_malloc  and         on  the  heap  instead  of  recursive  function  calls.  In  this case,
917         pcre_stack_free are called to manage memory blocks on  the  heap,  thus         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
918         avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
919    
920    
921  COMPILING A PATTERN  COMPILING A PATTERN
# Line 590  COMPILING A PATTERN Line 924  COMPILING A PATTERN
924              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
925              const unsigned char *tableptr);              const unsigned char *tableptr);
926    
927         The  function  pcre_compile()  is  called  to compile a pattern into an         pcre *pcre_compile2(const char *pattern, int options,
928         internal form. The pattern is a C string terminated by a  binary  zero,              int *errorcodeptr,
929         and  is  passed in the pattern argument. A pointer to a single block of              const char **errptr, int *erroffset,
930         memory that is obtained via pcre_malloc is returned. This contains  the              const unsigned char *tableptr);
931         compiled  code  and  related  data.  The  pcre  type is defined for the  
932         returned block; this is a typedef for a structure  whose  contents  are         Either of the functions pcre_compile() or pcre_compile2() can be called
933         not  externally defined. It is up to the caller to free the memory when         to compile a pattern into an internal form. The only difference between
934         it is no longer required.         the  two interfaces is that pcre_compile2() has an additional argument,
935           errorcodeptr, via which a numerical error code can be returned.
936    
937           The pattern is a C string terminated by a binary zero, and is passed in
938           the  pattern  argument.  A  pointer to a single block of memory that is
939           obtained via pcre_malloc is returned. This contains the  compiled  code
940           and related data. The pcre type is defined for the returned block; this
941           is a typedef for a structure whose contents are not externally defined.
942           It is up to the caller to free the memory (via pcre_free) when it is no
943           longer required.
944    
945         Although the compiled code of a PCRE regex is relocatable, that is,  it         Although the compiled code of a PCRE regex is relocatable, that is,  it
946         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
947         fully relocatable, because it may contain a copy of the tableptr  argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
948         ment, which is an address (see below).         ment, which is an address (see below).
949    
950         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
951         tion. It should be zero if  no  options  are  required.  The  available         pilation. It should be zero if no options are required.  The  available
952         options  are  described  below. Some of them, in particular, those that         options  are  described  below. Some of them, in particular, those that
953         are compatible with Perl, can also be set and  unset  from  within  the         are compatible with Perl, can also be set and  unset  from  within  the
954         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern  (see  the  detailed  description in the pcrepattern documenta-
955         tion). For these options, the contents of the options  argument  speci-         tion). For these options, the contents of the options  argument  speci-
956         fies  their initial settings at the start of compilation and execution.         fies  their initial settings at the start of compilation and execution.
957         The PCRE_ANCHORED option can be set at the time of matching as well  as         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time
958         at compile time.         of matching as well as at compile time.
959    
960         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
961         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
962         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
963         sage. The offset from the start of the pattern to the  character  where         sage. This is a static string that is part of the library. You must not
964         the  error  was  discovered  is  placed  in  the variable pointed to by         try to free it. The offset from the start of the pattern to the charac-
965         erroffset, which must not be NULL. If it  is,  an  immediate  error  is         ter where the error was discovered is placed in the variable pointed to
966           by  erroffset,  which must not be NULL. If it is, an immediate error is
967         given.         given.
968    
969           If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
970           codeptr  argument is not NULL, a non-zero error code number is returned
971           via this argument in the event of an error. This is in addition to  the
972           textual error message. Error codes and messages are listed below.
973    
974         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of
975         character tables that are  built  when  PCRE  is  compiled,  using  the         character tables that are  built  when  PCRE  is  compiled,  using  the
976         default  C  locale.  Otherwise, tableptr must be an address that is the         default  C  locale.  Otherwise, tableptr must be an address that is the
# Line 664  COMPILING A PATTERN Line 1013  COMPILING A PATTERN
1013    
1014         If  this  bit is set, letters in the pattern match both upper and lower         If  this  bit is set, letters in the pattern match both upper and lower
1015         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be
1016         changed  within  a  pattern  by  a (?i) option setting. When running in         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
1017         UTF-8 mode, case support for high-valued characters is  available  only         always understands the concept of case for characters whose values  are
1018         when PCRE is built with Unicode character property support.         less  than 128, so caseless matching is always possible. For characters
1019           with higher values, the concept of case is supported if  PCRE  is  com-
1020           piled  with Unicode property support, but not otherwise. If you want to
1021           use caseless matching for characters 128 and  above,  you  must  ensure
1022           that  PCRE  is  compiled  with Unicode property support as well as with
1023           UTF-8 support.
1024    
1025           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1026    
1027         If  this bit is set, a dollar metacharacter in the pattern matches only         If this bit is set, a dollar metacharacter in the pattern matches  only
1028         at the end of the subject string. Without this option,  a  dollar  also         at  the  end  of the subject string. Without this option, a dollar also
1029         matches  immediately before the final character if it is a newline (but         matches immediately before a newline at the end of the string (but  not
1030         not before any  other  newlines).  The  PCRE_DOLLAR_ENDONLY  option  is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1031         ignored if PCRE_MULTILINE is set. There is no equivalent to this option         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in
1032         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1033    
1034           PCRE_DOTALL           PCRE_DOTALL
1035    
1036         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharater in the pattern matches all char-
1037         acters,  including  newlines.  Without  it, newlines are excluded. This         acters, including those that indicate newline. Without it, a  dot  does
1038         option is equivalent to Perl's /s option, and it can be changed  within         not  match  when  the  current position is at a newline. This option is
1039         a  pattern  by  a  (?s)  option  setting. A negative class such as [^a]         equivalent to Perl's /s option, and it can be changed within a  pattern
1040         always matches a newline character, independent of the setting of  this         by  a (?s) option setting. A negative class such as [^a] always matches
1041         option.         newline characters, independent of the setting of this option.
1042    
1043             PCRE_DUPNAMES
1044    
1045           If this bit is set, names used to identify capturing  subpatterns  need
1046           not be unique. This can be helpful for certain types of pattern when it
1047           is known that only one instance of the named  subpattern  can  ever  be
1048           matched.  There  are  more details of named subpatterns below; see also
1049           the pcrepattern documentation.
1050    
1051           PCRE_EXTENDED           PCRE_EXTENDED
1052    
1053         If  this  bit  is  set,  whitespace  data characters in the pattern are         If this bit is set, whitespace  data  characters  in  the  pattern  are
1054         totally ignored except  when  escaped  or  inside  a  character  class.         totally ignored except when escaped or inside a character class. White-
1055         Whitespace  does  not  include the VT character (code 11). In addition,         space does not include the VT character (code 11). In addition, charac-
1056         characters between an unescaped # outside a  character  class  and  the         ters between an unescaped # outside a character class and the next new-
1057         next newline character, inclusive, are also ignored. This is equivalent         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1058         to Perl's /x option, and it can be changed within a pattern by  a  (?x)         option,  and  it  can be changed within a pattern by a (?x) option set-
1059         option setting.         ting.
1060    
1061         This  option  makes  it possible to include comments inside complicated         This option makes it possible to include  comments  inside  complicated
1062         patterns.  Note, however, that this applies only  to  data  characters.         patterns.   Note,  however,  that this applies only to data characters.
1063         Whitespace   characters  may  never  appear  within  special  character         Whitespace  characters  may  never  appear  within  special   character
1064         sequences in a pattern, for  example  within  the  sequence  (?(  which         sequences  in  a  pattern,  for  example  within the sequence (?( which
1065         introduces a conditional subpattern.         introduces a conditional subpattern.
1066    
1067           PCRE_EXTRA           PCRE_EXTRA
1068    
1069         This  option  was invented in order to turn on additional functionality         This option was invented in order to turn on  additional  functionality
1070         of PCRE that is incompatible with Perl, but it  is  currently  of  very         of  PCRE  that  is  incompatible with Perl, but it is currently of very
1071         little  use. When set, any backslash in a pattern that is followed by a         little use. When set, any backslash in a pattern that is followed by  a
1072         letter that has no special meaning  causes  an  error,  thus  reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1073         these  combinations  for  future  expansion.  By default, as in Perl, a         these combinations for future expansion. By  default,  as  in  Perl,  a
1074         backslash followed by a letter with no special meaning is treated as  a         backslash  followed by a letter with no special meaning is treated as a
1075         literal.  There  are  at  present  no other features controlled by this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1076         option. It can also be set by a (?X) option setting within a pattern.         There  are  at  present no other features controlled by this option. It
1077           can also be set by a (?X) option setting within a pattern.
1078    
1079             PCRE_FIRSTLINE
1080    
1081           If this option is set, an  unanchored  pattern  is  required  to  match
1082           before  or  at  the  first  newline  in  the subject string, though the
1083           matched text may continue over the newline.
1084    
1085           PCRE_MULTILINE           PCRE_MULTILINE
1086    
# Line 723  COMPILING A PATTERN Line 1092  COMPILING A PATTERN
1092         is set). This is the same as Perl.         is set). This is the same as Perl.
1093    
1094         When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"         When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1095         constructs match immediately following or immediately before  any  new-         constructs match immediately following or immediately  before  internal
1096         line  in the subject string, respectively, as well as at the very start         newlines  in  the  subject string, respectively, as well as at the very
1097         and end. This is equivalent to Perl's /m option, and it can be  changed         start and end. This is equivalent to Perl's /m option, and  it  can  be
1098         within a pattern by a (?m) option setting. If there are no "\n" charac-         changed within a pattern by a (?m) option setting. If there are no new-
1099         ters in a subject string, or no occurrences of ^ or  $  in  a  pattern,         lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1100         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1101    
1102             PCRE_NEWLINE_CR
1103             PCRE_NEWLINE_LF
1104             PCRE_NEWLINE_CRLF
1105             PCRE_NEWLINE_ANY
1106    
1107           These  options  override the default newline definition that was chosen
1108           when PCRE was built. Setting the first or the second specifies  that  a
1109           newline  is  indicated  by a single character (CR or LF, respectively).
1110           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1111           two-character  CRLF  sequence.  Setting PCRE_NEWLINE_ANY specifies that
1112           any Unicode newline sequence should be recognized. The Unicode  newline
1113           sequences  are  the three just mentioned, plus the single characters VT
1114           (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085),
1115           LS  (line separator, U+2028), and PS (paragraph separator, U+2029). The
1116           last two are recognized only in UTF-8 mode.
1117    
1118           The newline setting in the  options  word  uses  three  bits  that  are
1119           treated  as  a  number, giving eight possibilities. Currently only five
1120           are used (default plus the four values above). This means that  if  you
1121           set  more  than  one  newline option, the combination may or may not be
1122           sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is  equiva-
1123           lent  to PCRE_NEWLINE_CRLF, but other combinations yield unused numbers
1124           and cause an error.
1125    
1126           The only time that a line break is specially recognized when  compiling
1127           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1128           character class is encountered. This indicates  a  comment  that  lasts
1129           until  after the next line break sequence. In other circumstances, line
1130           break  sequences  are  treated  as  literal  data,   except   that   in
1131           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1132           and are therefore ignored.
1133    
1134           The newline option that is set at compile time becomes the default that
1135           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1136    
1137           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1138    
1139         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
1140         theses in the pattern. Any opening parenthesis that is not followed  by         theses  in the pattern. Any opening parenthesis that is not followed by
1141         ?  behaves as if it were followed by ?: but named parentheses can still         ? behaves as if it were followed by ?: but named parentheses can  still
1142         be used for capturing (and they acquire  numbers  in  the  usual  way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1143         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1144    
1145           PCRE_UNGREEDY           PCRE_UNGREEDY
1146    
1147         This  option  inverts  the "greediness" of the quantifiers so that they         This option inverts the "greediness" of the quantifiers  so  that  they
1148         are not greedy by default, but become greedy if followed by "?". It  is         are  not greedy by default, but become greedy if followed by "?". It is
1149         not  compatible  with Perl. It can also be set by a (?U) option setting         not compatible with Perl. It can also be set by a (?U)  option  setting
1150         within the pattern.         within the pattern.
1151    
1152           PCRE_UTF8           PCRE_UTF8
1153    
1154         This option causes PCRE to regard both the pattern and the  subject  as         This  option  causes PCRE to regard both the pattern and the subject as
1155         strings  of  UTF-8 characters instead of single-byte character strings.         strings of UTF-8 characters instead of single-byte  character  strings.
1156         However, it is available only when PCRE is built to include UTF-8  sup-         However,  it is available only when PCRE is built to include UTF-8 sup-
1157         port.  If not, the use of this option provokes an error. Details of how         port. If not, the use of this option provokes an error. Details of  how
1158         this option changes the behaviour of PCRE are given in the  section  on         this  option  changes the behaviour of PCRE are given in the section on
1159         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1160    
1161           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1162    
1163         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1164         automatically checked. If an invalid UTF-8 sequence of bytes is  found,         automatically  checked. If an invalid UTF-8 sequence of bytes is found,
1165         pcre_compile()  returns an error. If you already know that your pattern         pcre_compile() returns an error. If you already know that your  pattern
1166         is valid, and you want to skip this check for performance reasons,  you         is  valid, and you want to skip this check for performance reasons, you
1167         can  set  the  PCRE_NO_UTF8_CHECK option. When it is set, the effect of         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of
1168         passing an invalid UTF-8 string as a pattern is undefined. It may cause         passing an invalid UTF-8 string as a pattern is undefined. It may cause
1169         your  program  to  crash.   Note that this option can also be passed to         your program to crash.  Note that this option can  also  be  passed  to
1170         pcre_exec(),  to  suppress  the  UTF-8  validity  checking  of  subject         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1171         strings.         ing of subject strings.
1172    
1173    
1174    COMPILATION ERROR CODES
1175    
1176           The following table lists the error  codes  than  may  be  returned  by
1177           pcre_compile2(),  along with the error messages that may be returned by
1178           both compiling functions. As PCRE has developed, some error codes  have
1179           fallen out of use. To avoid confusion, they have not been re-used.
1180    
1181              0  no error
1182              1  \ at end of pattern
1183              2  \c at end of pattern
1184              3  unrecognized character follows \
1185              4  numbers out of order in {} quantifier
1186              5  number too big in {} quantifier
1187              6  missing terminating ] for character class
1188              7  invalid escape sequence in character class
1189              8  range out of order in character class
1190              9  nothing to repeat
1191             10  [this code is not in use]
1192             11  internal error: unexpected repeat
1193             12  unrecognized character after (?
1194             13  POSIX named classes are supported only within a class
1195             14  missing )
1196             15  reference to non-existent subpattern
1197             16  erroffset passed as NULL
1198             17  unknown option bit(s) set
1199             18  missing ) after comment
1200             19  [this code is not in use]
1201             20  regular expression too large
1202             21  failed to get memory
1203             22  unmatched parentheses
1204             23  internal error: code overflow
1205             24  unrecognized character after (?<
1206             25  lookbehind assertion is not fixed length
1207             26  malformed number or name after (?(
1208             27  conditional group contains more than two branches
1209             28  assertion expected after (?(
1210             29  (?R or (?digits must be followed by )
1211             30  unknown POSIX class name
1212             31  POSIX collating elements are not supported
1213             32  this version of PCRE is not compiled with PCRE_UTF8 support
1214             33  [this code is not in use]
1215             34  character value in \x{...} sequence is too large
1216             35  invalid condition (?(0)
1217             36  \C not allowed in lookbehind assertion
1218             37  PCRE does not support \L, \l, \N, \U, or \u
1219             38  number after (?C is > 255
1220             39  closing ) for (?C expected
1221             40  recursive call could loop indefinitely
1222             41  unrecognized character after (?P
1223             42  syntax error in subpattern name (missing terminator)
1224             43  two named subpatterns have the same name
1225             44  invalid UTF-8 string
1226             45  support for \P, \p, and \X has not been compiled
1227             46  malformed \P or \p sequence
1228             47  unknown property name after \P or \p
1229             48  subpattern name is too long (maximum 32 characters)
1230             49  too many named subpatterns (maximum 10,000)
1231             50  repeated subpattern is too long
1232             51  octal value is greater than \377 (not in UTF-8 mode)
1233             52  internal error: overran compiling workspace
1234             53   internal  error:  previously-checked  referenced  subpattern not
1235           found
1236             54  DEFINE group contains more than one branch
1237             55  repeating a DEFINE group is not allowed
1238             56  inconsistent NEWLINE options"
1239    
1240    
1241  STUDYING A PATTERN  STUDYING A PATTERN
1242    
1243         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1244              const char **errptr);              const char **errptr);
1245    
1246         If  a  compiled  pattern is going to be used several times, it is worth         If a compiled pattern is going to be used several times,  it  is  worth
1247         spending more time analyzing it in order to speed up the time taken for         spending more time analyzing it in order to speed up the time taken for
1248         matching.  The function pcre_study() takes a pointer to a compiled pat-         matching. The function pcre_study() takes a pointer to a compiled  pat-
1249         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1250         information  that  will  help speed up matching, pcre_study() returns a         information that will help speed up matching,  pcre_study()  returns  a
1251         pointer to a pcre_extra block, in which the study_data field points  to         pointer  to a pcre_extra block, in which the study_data field points to
1252         the results of the study.         the results of the study.
1253    
1254         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1255         pcre_exec(). However, a pcre_extra block  also  contains  other  fields         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1256         that  can  be  set  by the caller before the block is passed; these are         that can be set by the caller before the block  is  passed;  these  are
1257         described below in the section on matching a pattern.         described below in the section on matching a pattern.
1258    
1259         If studying the pattern does not produce  any  additional  information,         If  studying  the  pattern  does not produce any additional information
1260         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1261         wants to pass any of the other fields to pcre_exec(), it  must  set  up         wants  to  pass  any of the other fields to pcre_exec(), it must set up
1262         its own pcre_extra block.         its own pcre_extra block.
1263    
1264         The  second  argument of pcre_study() contains option bits. At present,         The second argument of pcre_study() contains option bits.  At  present,
1265         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1266    
1267         The third argument for pcre_study() is a pointer for an error  message.         The  third argument for pcre_study() is a pointer for an error message.
1268         If  studying  succeeds  (even  if no data is returned), the variable it         If studying succeeds (even if no data is  returned),  the  variable  it
1269         points to is set to NULL. Otherwise it points to a textual  error  mes-         points  to  is  set  to NULL. Otherwise it is set to point to a textual
1270         sage.  You should therefore test the error pointer for NULL after call-         error message. This is a static string that is part of the library. You
1271         ing pcre_study(), to be sure that it has run successfully.         must  not  try  to  free it. You should test the error pointer for NULL
1272           after calling pcre_study(), to be sure that it has run successfully.
1273    
1274         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1275    
# Line 815  STUDYING A PATTERN Line 1287  STUDYING A PATTERN
1287  LOCALE SUPPORT  LOCALE SUPPORT
1288    
1289         PCRE handles caseless matching, and determines whether  characters  are         PCRE handles caseless matching, and determines whether  characters  are
1290         letters,  digits, or whatever, by reference to a set of tables, indexed         letters  digits,  or whatever, by reference to a set of tables, indexed
1291         by character value. (When running in UTF-8 mode, this applies  only  to         by character value. When running in UTF-8 mode, this  applies  only  to
1292         characters  with  codes  less than 128. Higher-valued codes never match         characters  with  codes  less than 128. Higher-valued codes never match
1293         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
1294         with Unicode character property support.)         with  Unicode  character property support. The use of locales with Uni-
1295           code is discouraged.
1296    
1297         An  internal set of tables is created in the default C locale when PCRE         An internal set of tables is created in the default C locale when  PCRE
1298         is built. This is used when the final  argument  of  pcre_compile()  is         is  built.  This  is  used when the final argument of pcre_compile() is
1299         NULL,  and  is  sufficient for many applications. An alternative set of         NULL, and is sufficient for many applications. An  alternative  set  of
1300         tables can, however, be supplied. These may be created in  a  different         tables  can,  however, be supplied. These may be created in a different
1301         locale  from the default. As more and more applications change to using         locale from the default. As more and more applications change to  using
1302         Unicode, the need for this locale support is expected to die away.         Unicode, the need for this locale support is expected to die away.
1303    
1304         External tables are built by calling  the  pcre_maketables()  function,         External  tables  are  built by calling the pcre_maketables() function,
1305         which  has no arguments, in the relevant locale. The result can then be         which has no arguments, in the relevant locale. The result can then  be
1306         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
1307         example,  to  build  and use tables that are appropriate for the French         example, to build and use tables that are appropriate  for  the  French
1308         locale (where accented characters with  values  greater  than  128  are         locale  (where  accented  characters  with  values greater than 128 are
1309         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1310    
1311           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1312           tables = pcre_maketables();           tables = pcre_maketables();
1313           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1314    
1315         When  pcre_maketables()  runs,  the  tables are built in memory that is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1316         obtained via pcre_malloc. It is the caller's responsibility  to  ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1317         that  the memory containing the tables remains available for as long as         that the memory containing the tables remains available for as long  as
1318         it is needed.         it is needed.
1319    
1320         The pointer that is passed to pcre_compile() is saved with the compiled         The pointer that is passed to pcre_compile() is saved with the compiled
1321         pattern,  and the same tables are used via this pointer by pcre_study()         pattern, and the same tables are used via this pointer by  pcre_study()
1322         and normally also by pcre_exec(). Thus, by default, for any single pat-         and normally also by pcre_exec(). Thus, by default, for any single pat-
1323         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1324         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1325    
1326         It is possible to pass a table pointer or NULL (indicating the  use  of         It  is  possible to pass a table pointer or NULL (indicating the use of
1327         the  internal  tables)  to  pcre_exec(). Although not intended for this         the internal tables) to pcre_exec(). Although  not  intended  for  this
1328         purpose, this facility could be used to match a pattern in a  different         purpose,  this facility could be used to match a pattern in a different
1329         locale from the one in which it was compiled. Passing table pointers at         locale from the one in which it was compiled. Passing table pointers at
1330         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1331    
# Line 862  INFORMATION ABOUT A PATTERN Line 1335  INFORMATION ABOUT A PATTERN
1335         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1336              int what, void *where);              int what, void *where);
1337    
1338         The pcre_fullinfo() function returns information about a compiled  pat-         The  pcre_fullinfo() function returns information about a compiled pat-
1339         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1340         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1341    
1342         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1343         pattern.  The second argument is the result of pcre_study(), or NULL if         pattern. The second argument is the result of pcre_study(), or NULL  if
1344         the pattern was not studied. The third argument specifies  which  piece         the  pattern  was not studied. The third argument specifies which piece
1345         of  information  is required, and the fourth argument is a pointer to a         of information is required, and the fourth argument is a pointer  to  a
1346         variable to receive the data. The yield of the  function  is  zero  for         variable  to  receive  the  data. The yield of the function is zero for
1347         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1348    
1349           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 878  INFORMATION ABOUT A PATTERN Line 1351  INFORMATION ABOUT A PATTERN
1351           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1352           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1353    
1354         The  "magic  number" is placed at the start of each compiled pattern as         The "magic number" is placed at the start of each compiled  pattern  as
1355         an simple check against passing an arbitrary memory pointer. Here is  a         an  simple check against passing an arbitrary memory pointer. Here is a
1356         typical  call  of pcre_fullinfo(), to obtain the length of the compiled         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1357         pattern:         pattern:
1358    
1359           int rc;           int rc;
1360           unsigned long int length;           size_t length;
1361           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1362             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1363             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1364             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1365             &length);         /* where to put the data */             &length);         /* where to put the data */
1366    
1367         The possible values for the third argument are defined in  pcre.h,  and         The  possible  values for the third argument are defined in pcre.h, and
1368         are as follows:         are as follows:
1369    
1370           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1371    
1372         Return  the  number  of  the highest back reference in the pattern. The         Return the number of the highest back reference  in  the  pattern.  The
1373         fourth argument should point to an int variable. Zero  is  returned  if         fourth  argument  should  point to an int variable. Zero is returned if
1374         there are no back references.         there are no back references.
1375    
1376           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1377    
1378         Return  the  number of capturing subpatterns in the pattern. The fourth         Return the number of capturing subpatterns in the pattern.  The  fourth
1379         argument should point to an int variable.         argument should point to an int variable.
1380    
1381           PCRE_INFO_DEFAULTTABLES           PCRE_INFO_DEFAULT_TABLES
1382    
1383         Return a pointer to the internal default character tables within  PCRE.         Return  a pointer to the internal default character tables within PCRE.
1384         The  fourth  argument should point to an unsigned char * variable. This         The fourth argument should point to an unsigned char *  variable.  This
1385         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1386         tion.  External  callers  can  cause PCRE to use its internal tables by         tion. External callers can cause PCRE to use  its  internal  tables  by
1387         passing a NULL table pointer.         passing a NULL table pointer.
1388    
1389           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1390    
1391         Return information about the first byte of any matched  string,  for  a         Return  information  about  the first byte of any matched string, for a
1392         non-anchored    pattern.    (This    option    used    to   be   called         non-anchored pattern. The fourth argument should point to an int  vari-
1393         PCRE_INFO_FIRSTCHAR; the old name is  still  recognized  for  backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1394         compatibility.)         is still recognized for backwards compatibility.)
1395    
1396         If  there  is  a  fixed first byte, for example, from a pattern such as         If there is a fixed first byte, for example, from  a  pattern  such  as
1397         (cat|cow|coyote), it is returned in the integer pointed  to  by  where.         (cat|cow|coyote), its value is returned. Otherwise, if either
        Otherwise, if either  
1398    
1399         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1400         branch starts with "^", or         branch starts with "^", or
# Line 958  INFORMATION ABOUT A PATTERN Line 1430  INFORMATION ABOUT A PATTERN
1430    
1431         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1432         ses. The names are just an additional way of identifying the  parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1433         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1434         pcre_get_named_substring() is provided  for  extracting  an  individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1435         captured  substring  by  name.  It is also possible to extract the data         strings  by  name. It is also possible to extract the data directly, by
1436         directly, by first converting the name to a number in order  to  access         first converting the name to a number in order to  access  the  correct
1437         the  correct  pointers in the output vector (described with pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1438         below). To do the conversion, you need to use the  name-to-number  map,         the conversion, you need  to  use  the  name-to-number  map,  which  is
1439         which is described by these three values.         described by these three values.
1440    
1441         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1442         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
# Line 974  INFORMATION ABOUT A PATTERN Line 1446  INFORMATION ABOUT A PATTERN
1446         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1447         sis,  most  significant byte first. The rest of the entry is the corre-         sis,  most  significant byte first. The rest of the entry is the corre-
1448         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1449         For  example,  consider  the following pattern (assume PCRE_EXTENDED is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1450         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1451           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1452           ignored):
1453    
1454           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1455           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1456    
1457         There are four named subpatterns, so the table has  four  entries,  and         There are four named subpatterns, so the table has  four  entries,  and
1458         each  entry  in the table is eight bytes long. The table is as follows,         each  entry  in the table is eight bytes long. The table is as follows,
# Line 991  INFORMATION ABOUT A PATTERN Line 1465  INFORMATION ABOUT A PATTERN
1465           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1466    
1467         When  writing  code  to  extract  data from named subpatterns using the         When  writing  code  to  extract  data from named subpatterns using the
1468         name-to-number map, remember that the length of each entry is likely to         name-to-number map, remember that the length of the entries  is  likely
1469         be different for each compiled pattern.         to be different for each compiled pattern.
1470    
1471           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1472    
# Line 1051  OBSOLETE INFO FUNCTION Line 1525  OBSOLETE INFO FUNCTION
1525         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1526    
1527    
1528  MATCHING A PATTERN  REFERENCE COUNTS
1529    
1530           int pcre_refcount(pcre *code, int adjust);
1531    
1532           The  pcre_refcount()  function is used to maintain a reference count in
1533           the data block that contains a compiled pattern. It is provided for the
1534           benefit  of  applications  that  operate  in an object-oriented manner,
1535           where different parts of the application may be using the same compiled
1536           pattern, but you want to free the block when they are all done.
1537    
1538           When a pattern is compiled, the reference count field is initialized to
1539           zero.  It is changed only by calling this function, whose action is  to
1540           add  the  adjust  value  (which may be positive or negative) to it. The
1541           yield of the function is the new value. However, the value of the count
1542           is  constrained to lie between 0 and 65535, inclusive. If the new value
1543           is outside these limits, it is forced to the appropriate limit value.
1544    
1545           Except when it is zero, the reference count is not correctly  preserved
1546           if  a  pattern  is  compiled on one host and then transferred to a host
1547           whose byte-order is different. (This seems a highly unlikely scenario.)
1548    
1549    
1550    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1551    
1552         int pcre_exec(const pcre *code, const pcre_extra *extra,         int pcre_exec(const pcre *code, const pcre_extra *extra,
1553              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
# Line 1060  MATCHING A PATTERN Line 1556  MATCHING A PATTERN
1556         The  function pcre_exec() is called to match a subject string against a         The  function pcre_exec() is called to match a subject string against a
1557         compiled pattern, which is passed in the code argument. If the  pattern         compiled pattern, which is passed in the code argument. If the  pattern
1558         has been studied, the result of the study should be passed in the extra         has been studied, the result of the study should be passed in the extra
1559         argument.         argument. This function is the main matching facility of  the  library,
1560           and it operates in a Perl-like manner. For specialist use there is also
1561           an alternative matching function, which is described below in the  sec-
1562           tion about the pcre_dfa_exec() function.
1563    
1564         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1565         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1566         is possible to save compiled patterns and study data, and then use them         is possible to save compiled patterns and study data, and then use them
1567         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1568         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1569    
1570         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1080  MATCHING A PATTERN Line 1579  MATCHING A PATTERN
1579             0,              /* start at offset 0 in the subject */             0,              /* start at offset 0 in the subject */
1580             0,              /* default options */             0,              /* default options */
1581             ovector,        /* vector of integers for substring information */             ovector,        /* vector of integers for substring information */
1582             30);            /* number of elements in the vector  (NOT  size  in             30);            /* number of elements (NOT size in bytes) */
        bytes) */  
1583    
1584     Extra data for pcre_exec()     Extra data for pcre_exec()
1585    
1586         If  the  extra argument is not NULL, it must point to a pcre_extra data         If  the  extra argument is not NULL, it must point to a pcre_extra data
1587         block. The pcre_study() function returns such a block (when it  doesn't         block. The pcre_study() function returns such a block (when it  doesn't
1588         return  NULL), but you can also create one for yourself, and pass addi-         return  NULL), but you can also create one for yourself, and pass addi-
1589         tional information in it. The fields in a pcre_extra block are as  fol-         tional information in it. The pcre_extra block contains  the  following
1590         lows:         fields (not necessarily in this order):
1591    
1592           unsigned long int flags;           unsigned long int flags;
1593           void *study_data;           void *study_data;
1594           unsigned long int match_limit;           unsigned long int match_limit;
1595             unsigned long int match_limit_recursion;
1596           void *callout_data;           void *callout_data;
1597           const unsigned char *tables;           const unsigned char *tables;
1598    
# Line 1102  MATCHING A PATTERN Line 1601  MATCHING A PATTERN
1601    
1602           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1603           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1604             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1605           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1606           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1607    
# Line 1118  MATCHING A PATTERN Line 1618  MATCHING A PATTERN
1618         repeats.         repeats.
1619    
1620         Internally, PCRE uses a function called match() which it calls  repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1621         edly  (sometimes  recursively).  The  limit is imposed on the number of         edly  (sometimes  recursively). The limit set by match_limit is imposed
1622         times this function is called during a match, which has the  effect  of         on the number of times this function is called during  a  match,  which
1623         limiting  the amount of recursion and backtracking that can take place.         has  the  effect  of  limiting the amount of backtracking that can take
1624         For patterns that are not anchored, the count starts from zero for each         place. For patterns that are not anchored, the count restarts from zero
1625         position in the subject string.         for each position in the subject string.
1626    
1627         The  default  limit  for the library can be set when PCRE is built; the         The  default  value  for  the  limit can be set when PCRE is built; the
1628         default default is 10 million, which handles all but the  most  extreme         default default is 10 million, which handles all but the  most  extreme
1629         cases.  You  can  reduce  the  default  by  suppling pcre_exec() with a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1630         pcre_extra block in which match_limit is set to a  smaller  value,  and         pcre_extra    block    in    which    match_limit    is    set,     and
1631         PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is         PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1632         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1633    
1634           The match_limit_recursion field is similar to match_limit, but  instead
1635           of limiting the total number of times that match() is called, it limits
1636           the depth of recursion. The recursion depth is a  smaller  number  than
1637           the  total number of calls, because not all calls to match() are recur-
1638           sive.  This limit is of use only if it is set smaller than match_limit.
1639    
1640           Limiting  the  recursion  depth  limits the amount of stack that can be
1641           used, or, when PCRE has been compiled to use memory on the heap instead
1642           of the stack, the amount of heap memory that can be used.
1643    
1644           The  default  value  for  match_limit_recursion can be set when PCRE is
1645           built; the default default  is  the  same  value  as  the  default  for
1646           match_limit.  You can override the default by suppling pcre_exec() with
1647           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1648           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1649           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1650    
1651         The pcre_callout field is used in conjunction with the  "callout"  fea-         The pcre_callout field is used in conjunction with the  "callout"  fea-
1652         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1653    
# Line 1148  MATCHING A PATTERN Line 1665  MATCHING A PATTERN
1665     Option bits for pcre_exec()     Option bits for pcre_exec()
1666    
1667         The unused bits of the options argument for pcre_exec() must  be  zero.         The unused bits of the options argument for pcre_exec() must  be  zero.
1668         The   only  bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NOTBOL,         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1669         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1670           PCRE_PARTIAL.
1671    
1672           PCRE_ANCHORED           PCRE_ANCHORED
1673    
1674         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1675         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1676         turned out to be anchored by virtue of its contents, it cannot be  made         turned  out to be anchored by virtue of its contents, it cannot be made
1677         unachored at matching time.         unachored at matching time.
1678    
1679             PCRE_NEWLINE_CR
1680             PCRE_NEWLINE_LF
1681             PCRE_NEWLINE_CRLF
1682             PCRE_NEWLINE_ANY
1683    
1684           These options override  the  newline  definition  that  was  chosen  or
1685           defaulted  when the pattern was compiled. For details, see the descrip-
1686           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1687           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1688           ters. It may also alter the way the match position is advanced after  a
1689           match  failure  for  an  unanchored  pattern. When PCRE_NEWLINE_CRLF or
1690           PCRE_NEWLINE_ANY is set, and a match attempt  fails  when  the  current
1691           position  is  at a CRLF sequence, the match position is advanced by two
1692           characters instead of one, in other words, to after the CRLF.
1693    
1694           PCRE_NOTBOL           PCRE_NOTBOL
1695    
1696         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1697         the beginning of a line, so the  circumflex  metacharacter  should  not         the  beginning  of  a  line, so the circumflex metacharacter should not
1698         match  before it. Setting this without PCRE_MULTILINE (at compile time)         match before it. Setting this without PCRE_MULTILINE (at compile  time)
1699         causes  circumflex  never  to  match.  This  option  affects  only  the         causes  circumflex  never to match. This option affects only the behav-
1700         behaviour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1701    
1702           PCRE_NOTEOL           PCRE_NOTEOL
1703    
1704         This option specifies that the end of the subject string is not the end         This option specifies that the end of the subject string is not the end
1705         of a line, so the dollar metacharacter should not match it nor  (except         of  a line, so the dollar metacharacter should not match it nor (except
1706         in  multiline mode) a newline immediately before it. Setting this with-         in multiline mode) a newline immediately before it. Setting this  with-
1707         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1708         option  affects only the behaviour of the dollar metacharacter. It does         option affects only the behaviour of the dollar metacharacter. It  does
1709         not affect \Z or \z.         not affect \Z or \z.
1710    
1711           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1712    
1713         An empty string is not considered to be a valid match if this option is         An empty string is not considered to be a valid match if this option is
1714         set.  If  there are alternatives in the pattern, they are tried. If all         set. If there are alternatives in the pattern, they are tried.  If  all
1715         the alternatives match the empty string, the entire  match  fails.  For         the  alternatives  match  the empty string, the entire match fails. For
1716         example, if the pattern         example, if the pattern
1717    
1718           a?b?           a?b?
1719    
1720         is  applied  to  a string not beginning with "a" or "b", it matches the         is applied to a string not beginning with "a" or "b",  it  matches  the
1721         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this         empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
1722         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
1723         rences of "a" or "b".         rences of "a" or "b".
1724    
1725         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1726         cial  case  of  a  pattern match of the empty string within its split()         cial case of a pattern match of the empty  string  within  its  split()
1727         function, and when using the /g modifier. It  is  possible  to  emulate         function,  and  when  using  the /g modifier. It is possible to emulate
1728         Perl's behaviour after matching a null string by first trying the match         Perl's behaviour after matching a null string by first trying the match
1729         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1730         if  that  fails by advancing the starting offset (see below) and trying         if that fails by advancing the starting offset (see below)  and  trying
1731         an ordinary match again. There is some code that demonstrates how to do         an ordinary match again. There is some code that demonstrates how to do
1732         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
1733    
1734           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1735    
1736         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
1737         UTF-8 string is automatically checked when pcre_exec() is  subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
1738         called.   The  value  of  startoffset is also checked to ensure that it         called.  The value of startoffset is also checked  to  ensure  that  it
1739         points to the start of a UTF-8 character. If an invalid UTF-8  sequence         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence
1740         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1741         startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is
1742         returned.         returned.
1743    
1744         If  you  already  know that your subject is valid, and you want to skip         If you already know that your subject is valid, and you  want  to  skip
1745         these   checks   for   performance   reasons,   you   can    set    the         these    checks    for   performance   reasons,   you   can   set   the
1746         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
1747         do this for the second and subsequent calls to pcre_exec() if  you  are         do  this  for the second and subsequent calls to pcre_exec() if you are
1748         making  repeated  calls  to  find  all  the matches in a single subject         making repeated calls to find all  the  matches  in  a  single  subject
1749         string. However, you should be  sure  that  the  value  of  startoffset         string.  However,  you  should  be  sure  that the value of startoffset
1750         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
1751         set, the effect of passing an invalid UTF-8 string as a subject,  or  a         set,  the  effect of passing an invalid UTF-8 string as a subject, or a
1752         value  of startoffset that does not point to the start of a UTF-8 char-         value of startoffset that does not point to the start of a UTF-8  char-
1753         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1754    
1755           PCRE_PARTIAL           PCRE_PARTIAL
1756    
1757         This option turns on the  partial  matching  feature.  If  the  subject         This  option  turns  on  the  partial  matching feature. If the subject
1758         string  fails to match the pattern, but at some point during the match-         string fails to match the pattern, but at some point during the  match-
1759         ing process the end of the subject was reached (that  is,  the  subject         ing  process  the  end of the subject was reached (that is, the subject
1760         partially  matches  the  pattern and the failure to match occurred only         partially matches the pattern and the failure to  match  occurred  only
1761         because there were not enough subject characters), pcre_exec()  returns         because  there were not enough subject characters), pcre_exec() returns
1762         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1763         used, there are restrictions on what may appear in the  pattern.  These         used,  there  are restrictions on what may appear in the pattern. These
1764         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1765    
1766     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1767    
1768         The  subject string is passed to pcre_exec() as a pointer in subject, a         The subject string is passed to pcre_exec() as a pointer in subject,  a
1769         length in length, and a starting byte offset in startoffset.  In  UTF-8         length  in  length, and a starting byte offset in startoffset. In UTF-8
1770         mode,  the  byte  offset  must point to the start of a UTF-8 character.         mode, the byte offset must point to the start  of  a  UTF-8  character.
1771         Unlike the pattern string, the subject may contain binary  zero  bytes.         Unlike  the  pattern string, the subject may contain binary zero bytes.
1772         When  the starting offset is zero, the search for a match starts at the         When the starting offset is zero, the search for a match starts at  the
1773         beginning of the subject, and this is by far the most common case.         beginning of the subject, and this is by far the most common case.
1774    
1775         A non-zero starting offset is useful when searching for  another  match         A  non-zero  starting offset is useful when searching for another match
1776         in  the same subject by calling pcre_exec() again after a previous suc-         in the same subject by calling pcre_exec() again after a previous  suc-
1777         cess.  Setting startoffset differs from just passing over  a  shortened         cess.   Setting  startoffset differs from just passing over a shortened
1778         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
1779         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1780    
1781           \Biss\B           \Biss\B
1782    
1783         which finds occurrences of "iss" in the middle of  words.  (\B  matches         which  finds  occurrences  of "iss" in the middle of words. (\B matches
1784         only  if  the  current position in the subject is not a word boundary.)         only if the current position in the subject is not  a  word  boundary.)
1785         When applied to the string "Mississipi" the first call  to  pcre_exec()         When  applied  to the string "Mississipi" the first call to pcre_exec()
1786         finds  the  first  occurrence. If pcre_exec() is called again with just         finds the first occurrence. If pcre_exec() is called  again  with  just
1787         the remainder of the subject,  namely  "issipi",  it  does  not  match,         the  remainder  of  the  subject,  namely  "issipi", it does not match,
1788         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
1789         to be a word boundary. However, if pcre_exec()  is  passed  the  entire         to  be  a  word  boundary. However, if pcre_exec() is passed the entire
1790         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
1791         rence of "iss" because it is able to look behind the starting point  to         rence  of "iss" because it is able to look behind the starting point to
1792         discover that it is preceded by a letter.         discover that it is preceded by a letter.
1793    
1794         If  a  non-zero starting offset is passed when the pattern is anchored,         If a non-zero starting offset is passed when the pattern  is  anchored,
1795         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
1796         if  the  pattern  does  not require the match to be at the start of the         if the pattern does not require the match to be at  the  start  of  the
1797         subject.         subject.
1798    
1799     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
1800    
1801         In general, a pattern matches a certain portion of the subject, and  in         In  general, a pattern matches a certain portion of the subject, and in
1802         addition,  further  substrings  from  the  subject may be picked out by         addition, further substrings from the subject  may  be  picked  out  by
1803         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,
1804         this  is  called "capturing" in what follows, and the phrase "capturing         this is called "capturing" in what follows, and the  phrase  "capturing
1805         subpattern" is used for a fragment of a pattern that picks out  a  sub-         subpattern"  is  used for a fragment of a pattern that picks out a sub-
1806         string.  PCRE  supports several other kinds of parenthesized subpattern         string. PCRE supports several other kinds of  parenthesized  subpattern
1807         that do not cause substrings to be captured.         that do not cause substrings to be captured.
1808    
1809         Captured substrings are returned to the caller via a vector of  integer         Captured  substrings are returned to the caller via a vector of integer
1810         offsets  whose  address is passed in ovector. The number of elements in         offsets whose address is passed in ovector. The number of  elements  in
1811         the vector is passed in ovecsize, which must be a non-negative  number.         the  vector is passed in ovecsize, which must be a non-negative number.
1812         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
1813    
1814         The  first  two-thirds of the vector is used to pass back captured sub-         The first two-thirds of the vector is used to pass back  captured  sub-
1815         strings, each substring using a pair of integers. The  remaining  third         strings,  each  substring using a pair of integers. The remaining third
1816         of  the  vector is used as workspace by pcre_exec() while matching cap-         of the vector is used as workspace by pcre_exec() while  matching  cap-
1817         turing subpatterns, and is not available for passing back  information.         turing  subpatterns, and is not available for passing back information.
1818         The  length passed in ovecsize should always be a multiple of three. If         The length passed in ovecsize should always be a multiple of three.  If
1819         it is not, it is rounded down.         it is not, it is rounded down.
1820    
1821         When a match is successful, information about  captured  substrings  is         When  a  match  is successful, information about captured substrings is
1822         returned  in  pairs  of integers, starting at the beginning of ovector,         returned in pairs of integers, starting at the  beginning  of  ovector,
1823         and continuing up to two-thirds of its length at the  most.  The  first         and  continuing  up  to two-thirds of its length at the most. The first
1824         element of a pair is set to the offset of the first character in a sub-         element of a pair is set to the offset of the first character in a sub-
1825         string, and the second is set to the  offset  of  the  first  character         string,  and  the  second  is  set to the offset of the first character
1826         after  the  end  of  a  substring. The first pair, ovector[0] and ovec-         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-
1827         tor[1], identify the portion of  the  subject  string  matched  by  the         tor[1],  identify  the  portion  of  the  subject string matched by the
1828         entire  pattern.  The next pair is used for the first capturing subpat-         entire pattern. The next pair is used for the first  capturing  subpat-
1829         tern, and so on. The value returned by pcre_exec()  is  the  number  of         tern, and so on. The value returned by pcre_exec() is one more than the
1830         pairs  that  have  been set. If there are no capturing subpatterns, the         highest numbered pair that has been set. For example, if two substrings
1831         return value from a successful match is 1,  indicating  that  just  the         have  been captured, the returned value is 3. If there are no capturing
1832         first pair of offsets has been set.         subpatterns, the return value from a successful match is 1,  indicating
1833           that just the first pair of offsets has been set.
        Some  convenience  functions  are  provided for extracting the captured  
        substrings as separate strings. These are described  in  the  following  
        section.  
   
        It  is  possible  for  an capturing subpattern number n+1 to match some  
        part of the subject when subpattern n has not been  used  at  all.  For  
        example, if the string "abc" is matched against the pattern (a|(z))(bc)  
        subpatterns 1 and 3 are matched, but 2 is not. When this happens,  both  
        offset values corresponding to the unused subpattern are set to -1.  
1834    
1835         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1836         of the string that it matched that is returned.         of the string that it matched that is returned.
# Line 1320  MATCHING A PATTERN Line 1844  MATCHING A PATTERN
1844         substrings, PCRE has to get additional memory for use during  matching.         substrings, PCRE has to get additional memory for use during  matching.
1845         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1846    
1847         Note  that  pcre_info() can be used to find out how many capturing sub-         The  pcre_info()  function  can  be used to find out how many capturing
1848         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
1849         that  will  allow for n captured substrings, in addition to the offsets         ovector  that  will allow for n captured substrings, in addition to the
1850         of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
1851    
1852           It is possible for capturing subpattern number n+1 to match  some  part
1853           of the subject when subpattern n has not been used at all. For example,
1854           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1855           return from the function is 4, and subpatterns 1 and 3 are matched, but
1856           2 is not. When this happens, both values in  the  offset  pairs  corre-
1857           sponding to unused subpatterns are set to -1.
1858    
1859           Offset  values  that correspond to unused subpatterns at the end of the
1860           expression are also set to -1. For example,  if  the  string  "abc"  is
1861           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1862           matched. The return from the function is 2, because  the  highest  used
1863           capturing subpattern number is 1. However, you can refer to the offsets
1864           for the second and third capturing subpatterns if  you  wish  (assuming
1865           the vector is large enough, of course).
1866    
1867           Some  convenience  functions  are  provided for extracting the captured
1868           substrings as separate strings. These are described below.
1869    
1870     Return values from pcre_exec()     Error return values from pcre_exec()
1871    
1872         If pcre_exec() fails, it returns a negative number. The  following  are         If pcre_exec() fails, it returns a negative number. The  following  are
1873         defined in the header file:         defined in the header file:
# Line 1351  MATCHING A PATTERN Line 1893  MATCHING A PATTERN
1893         an  environment  with the other endianness. This is the error that PCRE         an  environment  with the other endianness. This is the error that PCRE
1894         gives when the magic number is not present.         gives when the magic number is not present.
1895    
1896           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1897    
1898         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1899         compiled  pattern.  This  error  could be caused by a bug in PCRE or by         compiled  pattern.  This  error  could be caused by a bug in PCRE or by
# Line 1373  MATCHING A PATTERN Line 1915  MATCHING A PATTERN
1915    
1916           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
1917    
1918         The recursion and backtracking limit, as specified by  the  match_limit         The backtracking limit, as specified by  the  match_limit  field  in  a
1919         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         pcre_extra  structure  (or  defaulted) was reached. See the description
1920         description above.         above.
1921    
1922           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
1923    
# Line 1394  MATCHING A PATTERN Line 1936  MATCHING A PATTERN
1936         value of startoffset did not point to the beginning of a UTF-8  charac-         value of startoffset did not point to the beginning of a UTF-8  charac-
1937         ter.         ter.
1938    
1939           PCRE_ERROR_PARTIAL (-12)           PCRE_ERROR_PARTIAL        (-12)
1940    
1941         The  subject  string did not match, but it did match partially. See the         The  subject  string did not match, but it did match partially. See the
1942         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
1943    
1944           PCRE_ERROR_BAD_PARTIAL (-13)           PCRE_ERROR_BADPARTIAL     (-13)
1945    
1946         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
1947         items  that are not supported for partial matching. See the pcrepartial         items  that are not supported for partial matching. See the pcrepartial
1948         documentation for details of partial matching.         documentation for details of partial matching.
1949    
1950           PCRE_ERROR_INTERNAL (-14)           PCRE_ERROR_INTERNAL       (-14)
1951    
1952         An unexpected internal error has occurred. This error could  be  caused         An unexpected internal error has occurred. This error could  be  caused
1953         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
1954    
1955           PCRE_ERROR_BADCOUNT (-15)           PCRE_ERROR_BADCOUNT       (-15)
1956    
1957         This  error is given if the value of the ovecsize argument is negative.         This  error is given if the value of the ovecsize argument is negative.
1958    
1959             PCRE_ERROR_RECURSIONLIMIT (-21)
1960    
1961           The internal recursion limit, as specified by the match_limit_recursion
1962           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
1963           description above.
1964    
1965             PCRE_ERROR_NULLWSLIMIT    (-22)
1966    
1967           When a group that can match an empty  substring  is  repeated  with  an
1968           unbounded  upper  limit, the subject position at the start of the group
1969           must be remembered, so that a test for an empty string can be made when
1970           the  end  of the group is reached. Some workspace is required for this;
1971           if it runs out, this error is given.
1972    
1973             PCRE_ERROR_BADNEWLINE     (-23)
1974    
1975           An invalid combination of PCRE_NEWLINE_xxx options was given.
1976    
1977           Error numbers -16 to -20 are not used by pcre_exec().
1978    
1979    
1980  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
1981    
# Line 1434  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 1996  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
1996         string_list()  are  provided for extracting captured substrings as new,         string_list()  are  provided for extracting captured substrings as new,
1997         separate, zero-terminated strings. These functions identify  substrings         separate, zero-terminated strings. These functions identify  substrings
1998         by  number.  The  next section describes functions for extracting named         by  number.  The  next section describes functions for extracting named
1999         substrings. A substring  that  contains  a  binary  zero  is  correctly         substrings.
2000         extracted  and  has  a further zero added on the end, but the result is  
2001         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2002           a  further zero added on the end, but the result is not, of course, a C
2003           string.  However, you can process such a string  by  referring  to  the
2004           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2005           string().  Unfortunately, the interface to pcre_get_substring_list() is
2006           not  adequate for handling strings containing binary zeros, because the
2007           end of the final string is not independently indicated.
2008    
2009         The first three arguments are the same for all  three  of  these  func-         The first three arguments are the same for all  three  of  these  func-
2010         tions:  subject  is  the subject string that has just been successfully         tions:  subject  is  the subject string that has just been successfully
# Line 1456  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2024  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2024         buffersize,  while  for  pcre_get_substring()  a new block of memory is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2025         obtained via pcre_malloc, and its address is  returned  via  stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2026         The  yield  of  the function is the length of the string, not including         The  yield  of  the function is the length of the string, not including
2027         the terminating zero, or one of         the terminating zero, or one of these error codes:
2028    
2029           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2030    
# Line 1472  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2040  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2040         single block of memory that is obtained via pcre_malloc. The address of         single block of memory that is obtained via pcre_malloc. The address of
2041         the memory block is returned via listptr, which is also  the  start  of         the memory block is returned via listptr, which is also  the  start  of
2042         the  list  of  string pointers. The end of the list is marked by a NULL         the  list  of  string pointers. The end of the list is marked by a NULL
2043         pointer. The yield of the function is zero if all went well, or         pointer. The yield of the function is zero if all  went  well,  or  the
2044           error code
2045    
2046           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2047    
2048         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2049    
2050         When any of these functions encounter a substring that is unset,  which         When  any of these functions encounter a substring that is unset, which
2051         can  happen  when  capturing subpattern number n+1 matches some part of         can happen when capturing subpattern number n+1 matches  some  part  of
2052         the subject, but subpattern n has not been used at all, they return  an         the  subject, but subpattern n has not been used at all, they return an
2053         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2054         string by inspecting the appropriate offset in ovector, which is  nega-         string  by inspecting the appropriate offset in ovector, which is nega-
2055         tive for unset substrings.         tive for unset substrings.
2056    
2057         The  two convenience functions pcre_free_substring() and pcre_free_sub-         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2058         string_list() can be used to free the memory  returned  by  a  previous         string_list()  can  be  used  to free the memory returned by a previous
2059         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2060         tively. They do nothing more than  call  the  function  pointed  to  by         tively.  They  do  nothing  more  than  call the function pointed to by
2061         pcre_free,  which  of course could be called directly from a C program.         pcre_free, which of course could be called directly from a  C  program.
2062         However, PCRE is used in some situations where it is linked via a  spe-         However,  PCRE is used in some situations where it is linked via a spe-
2063         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2064         pcre_free directly; it is  for  these  cases  that  the  functions  are         pcre_free  directly;  it is for these cases that the functions are pro-
2065         provided.         vided.
2066    
2067    
2068  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
# Line 1511  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2080  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2080              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2081              const char **stringptr);              const char **stringptr);
2082    
2083         To  extract a substring by name, you first have to find associated num-         To extract a substring by name, you first have to find associated  num-
2084         ber.  For example, for this pattern         ber.  For example, for this pattern
2085    
2086           (a+)b(?<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2087    
2088         the number of the subpattern called "xxx" is 2. You can find the number         the number of the subpattern called "xxx" is 2. If the name is known to
2089         from the name by calling pcre_get_stringnumber(). The first argument is         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2090         the compiled pattern, and the second is the  name.  The  yield  of  the         name by calling pcre_get_stringnumber(). The first argument is the com-
2091         function  is  the  subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if         piled pattern, and the second is the name. The yield of the function is
2092         there is no subpattern of that name.         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2093           subpattern of that name.
2094    
2095         Given the number, you can extract the substring directly, or use one of         Given the number, you can extract the substring directly, or use one of
2096         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
# Line 1541  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2111  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2111         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2112         ate.         ate.
2113    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
2114    
2115  PCRE(3)                                                                PCRE(3)  DUPLICATE SUBPATTERN NAMES
2116    
2117           int pcre_get_stringtable_entries(const pcre *code,
2118                const char *name, char **first, char **last);
2119    
2120           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2121           subpatterns are not required to  be  unique.  Normally,  patterns  with
2122           duplicate  names  are such that in any one match, only one of the named
2123           subpatterns participates. An example is shown in the pcrepattern  docu-
2124           mentation. When duplicates are present, pcre_copy_named_substring() and
2125           pcre_get_named_substring() return the first substring corresponding  to
2126           the  given  name  that  is  set.  If  none  are set, an empty string is
2127           returned.  The pcre_get_stringnumber() function returns one of the num-
2128           bers  that are associated with the name, but it is not defined which it
2129           is.
2130    
2131           If you want to get full details of all captured substrings for a  given
2132           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2133           first argument is the compiled pattern, and the second is the name. The
2134           third  and  fourth  are  pointers to variables which are updated by the
2135           function. After it has run, they point to the first and last entries in
2136           the  name-to-number  table  for  the  given  name.  The function itself
2137           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2138           there  are none. The format of the table is described above in the sec-
2139           tion entitled Information about a  pattern.   Given  all  the  relevant
2140           entries  for the name, you can extract each of their numbers, and hence
2141           the captured data, if any.
2142    
2143    
2144    FINDING ALL POSSIBLE MATCHES
2145    
2146           The traditional matching function uses a  similar  algorithm  to  Perl,
2147           which stops when it finds the first match, starting at a given point in
2148           the subject. If you want to find all possible matches, or  the  longest
2149           possible  match,  consider using the alternative matching function (see
2150           below) instead. If you cannot use the alternative function,  but  still
2151           need  to  find all possible matches, you can kludge it up by making use
2152           of the callout facility, which is described in the pcrecallout documen-
2153           tation.
2154    
2155           What you have to do is to insert a callout right at the end of the pat-
2156           tern.  When your callout function is called, extract and save the  cur-
2157           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2158           backtrack and try other alternatives. Ultimately, when it runs  out  of
2159           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2160    
2161    
2162    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2163    
2164           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2165                const char *subject, int length, int startoffset,
2166                int options, int *ovector, int ovecsize,
2167                int *workspace, int wscount);
2168    
2169           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2170           against a compiled pattern, using a matching algorithm that  scans  the
2171           subject  string  just  once, and does not backtrack. This has different
2172           characteristics to the normal algorithm, and  is  not  compatible  with
2173           Perl.  Some  of the features of PCRE patterns are not supported. Never-
2174           theless, there are times when this kind of matching can be useful.  For
2175           a discussion of the two matching algorithms, see the pcrematching docu-
2176           mentation.
2177    
2178           The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2179           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2180           ent way, and this is described below. The other  common  arguments  are
2181           used  in  the  same way as for pcre_exec(), so their description is not
2182           repeated here.
2183    
2184           The two additional arguments provide workspace for  the  function.  The
2185           workspace  vector  should  contain at least 20 elements. It is used for
2186           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2187           workspace  will  be  needed for patterns and subjects where there are a
2188           lot of potential matches.
2189    
2190           Here is an example of a simple call to pcre_dfa_exec():
2191    
2192             int rc;
2193             int ovector[10];
2194             int wspace[20];
2195             rc = pcre_dfa_exec(
2196               re,             /* result of pcre_compile() */
2197               NULL,           /* we didn't study the pattern */
2198               "some string",  /* the subject string */
2199               11,             /* the length of the subject string */
2200               0,              /* start at offset 0 in the subject */
2201               0,              /* default options */
2202               ovector,        /* vector of integers for substring information */
2203               10,             /* number of elements (NOT size in bytes) */
2204               wspace,         /* working space vector */
2205               20);            /* number of elements (NOT size in bytes) */
2206    
2207       Option bits for pcre_dfa_exec()
2208    
2209           The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2210           zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2211           LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2212           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2213           three of these are the same as for pcre_exec(), so their description is
2214           not repeated here.
2215    
2216             PCRE_PARTIAL
2217    
2218           This  has  the  same general effect as it does for pcre_exec(), but the
2219           details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2220           pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2221           PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2222           been no complete matches, but there is still at least one matching pos-
2223           sibility. The portion of the string that provided the partial match  is
2224           set as the first matching string.
2225    
2226             PCRE_DFA_SHORTEST
2227    
2228           Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2229           stop as soon as it has found one match. Because of the way the alterna-
2230           tive  algorithm  works, this is necessarily the shortest possible match
2231           at the first possible matching point in the subject string.
2232    
2233             PCRE_DFA_RESTART
2234    
2235           When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2236           returns  a  partial  match, it is possible to call it again, with addi-
2237           tional subject characters, and have it continue with  the  same  match.
2238           The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2239           workspace and wscount options must reference the same vector as  before
2240           because  data  about  the  match so far is left in them after a partial
2241           match. There is more discussion of this  facility  in  the  pcrepartial
2242           documentation.
2243    
2244       Successful returns from pcre_dfa_exec()
2245    
2246           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2247           string in the subject. Note, however, that all the matches from one run
2248           of  the  function  start  at the same point in the subject. The shorter
2249           matches are all initial substrings of the longer matches. For  example,
2250           if the pattern
2251    
2252             <.*>
2253    
2254           is matched against the string
2255    
2256             This is <something> <something else> <something further> no more
2257    
2258           the three matched strings are
2259    
2260             <something>
2261             <something> <something else>
2262             <something> <something else> <something further>
2263    
2264           On  success,  the  yield of the function is a number greater than zero,
2265           which is the number of matched substrings.  The  substrings  themselves
2266           are  returned  in  ovector. Each string uses two elements; the first is
2267           the offset to the start, and the second is the offset to  the  end.  In
2268           fact,  all  the  strings  have the same start offset. (Space could have
2269           been saved by giving this only once, but it was decided to retain  some
2270           compatibility  with  the  way pcre_exec() returns data, even though the
2271           meaning of the strings is different.)
2272    
2273           The strings are returned in reverse order of length; that is, the long-
2274           est  matching  string is given first. If there were too many matches to
2275           fit into ovector, the yield of the function is zero, and the vector  is
2276           filled with the longest matches.
2277    
2278       Error returns from pcre_dfa_exec()
2279    
2280           The  pcre_dfa_exec()  function returns a negative number when it fails.
2281           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2282           described  above.   There are in addition the following errors that are
2283           specific to pcre_dfa_exec():
2284    
2285             PCRE_ERROR_DFA_UITEM      (-16)
2286    
2287           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2288           tern  that  it  does not support, for instance, the use of \C or a back
2289           reference.
2290    
2291             PCRE_ERROR_DFA_UCOND      (-17)
2292    
2293           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2294           that  uses  a back reference for the condition, or a test for recursion
2295           in a specific group. These are not supported.
2296    
2297             PCRE_ERROR_DFA_UMLIMIT    (-18)
2298    
2299           This return is given if pcre_dfa_exec() is called with an  extra  block
2300           that contains a setting of the match_limit field. This is not supported
2301           (it is meaningless).
2302    
2303             PCRE_ERROR_DFA_WSSIZE     (-19)
2304    
2305           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2306           workspace vector.
2307    
2308             PCRE_ERROR_DFA_RECURSE    (-20)
2309    
2310           When  a  recursive subpattern is processed, the matching function calls
2311           itself recursively, using private vectors for  ovector  and  workspace.
2312           This  error  is  given  if  the output vector is not large enough. This
2313           should be extremely rare, as a vector of size 1000 is used.
2314    
2315    
2316    SEE ALSO
2317    
2318           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2319           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2320    
2321    Last updated: 30 November 2006
2322    Copyright (c) 1997-2006 University of Cambridge.
2323    ------------------------------------------------------------------------------
2324    
2325    
2326    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2327    
2328    
2329  NAME  NAME
2330         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2331    
2332    
2333  PCRE CALLOUTS  PCRE CALLOUTS
2334    
2335         int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
# Line 1606  MISSING CALLOUTS Line 2384  MISSING CALLOUTS
2384  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2385    
2386         During matching, when PCRE reaches a callout point, the external  func-         During matching, when PCRE reaches a callout point, the external  func-
2387         tion  defined  by pcre_callout is called (if it is set). The only argu-         tion  defined by pcre_callout is called (if it is set). This applies to
2388         ment is a pointer to a pcre_callout block. This structure contains  the         both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2389         following fields:         only  argument  to  the callout function is a pointer to a pcre_callout
2390           block. This structure contains the following fields:
2391    
2392           int          version;           int          version;
2393           int          callout_number;           int          callout_number;
# Line 1623  THE CALLOUT INTERFACE Line 2402  THE CALLOUT INTERFACE
2402           int          pattern_position;           int          pattern_position;
2403           int          next_item_length;           int          next_item_length;
2404    
2405         The  version  field  is an integer containing the version number of the         The version field is an integer containing the version  number  of  the
2406         block format. The initial version was 0; the current version is 1.  The         block  format. The initial version was 0; the current version is 1. The
2407         version  number  will  change  again in future if additional fields are         version number will change again in future  if  additional  fields  are
2408         added, but the intention is never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2409    
2410         The  callout_number  field  contains the number of the callout, as com-         The callout_number field contains the number of the  callout,  as  com-
2411         piled into the pattern (that is, the number after ?C for  manual  call-         piled  into  the pattern (that is, the number after ?C for manual call-
2412         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2413    
2414         The  offset_vector field is a pointer to the vector of offsets that was         The offset_vector field is a pointer to the vector of offsets that  was
2415         passed by the caller to pcre_exec(). The contents can be  inspected  in         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2416         order  to extract substrings that have been matched so far, in the same         pcre_exec() is used, the contents can be inspected in order to  extract
2417         way as for extracting substrings after a match has completed.         substrings  that  have  been  matched  so  far,  in the same way as for
2418           extracting substrings after a match has completed. For  pcre_dfa_exec()
2419           this field is not useful.
2420    
2421         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2422         were passed to pcre_exec().         were passed to pcre_exec().
2423    
2424         The  start_match  field contains the offset within the subject at which         The start_match field contains the offset within the subject  at  which
2425         the current match attempt started. If the pattern is not anchored,  the         the  current match attempt started. If the pattern is not anchored, the
2426         callout function may be called several times from the same point in the         callout function may be called several times from the same point in the
2427         pattern for different starting points in the subject.         pattern for different starting points in the subject.
2428    
2429         The current_position field contains the offset within  the  subject  of         The  current_position  field  contains the offset within the subject of
2430         the current match pointer.         the current match pointer.
2431    
2432         The  capture_top field contains one more than the number of the highest         When the pcre_exec() function is used, the capture_top  field  contains
2433         numbered captured substring so far. If no  substrings  have  been  cap-         one  more than the number of the highest numbered captured substring so
2434         tured, the value of capture_top is one.         far. If no substrings have been captured, the value of  capture_top  is
2435           one.  This  is always the case when pcre_dfa_exec() is used, because it
2436         The  capture_last  field  contains the number of the most recently cap-         does not support captured substrings.
2437         tured substring. If no substrings have been captured, its value is  -1.  
2438           The capture_last field contains the number of the  most  recently  cap-
2439         The  callout_data  field contains a value that is passed to pcre_exec()         tured  substring. If no substrings have been captured, its value is -1.
2440         by the caller specifically so that it can be passed back  in  callouts.         This is always the case when pcre_dfa_exec() is used.
2441         It  is  passed  in the pcre_callout field of the pcre_extra data struc-  
2442         ture. If no such data was  passed,  the  value  of  callout_data  in  a         The callout_data field contains a value that is passed  to  pcre_exec()
2443         pcre_callout  block  is  NULL. There is a description of the pcre_extra         or  pcre_dfa_exec() specifically so that it can be passed back in call-
2444           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2445           structure.  If  no such data was passed, the value of callout_data in a
2446           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2447         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2448    
2449         The pattern_position field is present from version 1 of the  pcre_call-         The  pattern_position field is present from version 1 of the pcre_call-
2450         out structure. It contains the offset to the next item to be matched in         out structure. It contains the offset to the next item to be matched in
2451         the pattern string.         the pattern string.
2452    
2453         The next_item_length field is present from version 1 of the  pcre_call-         The  next_item_length field is present from version 1 of the pcre_call-
2454         out structure. It contains the length of the next item to be matched in         out structure. It contains the length of the next item to be matched in
2455         the pattern string. When the callout immediately precedes  an  alterna-         the  pattern  string. When the callout immediately precedes an alterna-
2456         tion  bar, a closing parenthesis, or the end of the pattern, the length         tion bar, a closing parenthesis, or the end of the pattern, the  length
2457         is zero. When the callout precedes an opening parenthesis,  the  length         is  zero.  When the callout precedes an opening parenthesis, the length
2458         is that of the entire subpattern.         is that of the entire subpattern.
2459    
2460         The  pattern_position  and next_item_length fields are intended to help         The pattern_position and next_item_length fields are intended  to  help
2461         in distinguishing between different automatic callouts, which all  have         in  distinguishing between different automatic callouts, which all have
2462         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
2463    
2464    
2465  RETURN VALUES  RETURN VALUES
2466    
2467         The  external callout function returns an integer to PCRE. If the value         The external callout function returns an integer to PCRE. If the  value
2468         is zero, matching proceeds as normal. If  the  value  is  greater  than         is  zero,  matching  proceeds  as  normal. If the value is greater than
2469         zero,  matching  fails  at  the current point, but backtracking to test         zero, matching fails at the current point, but  the  testing  of  other
2470         other matching possibilities goes ahead, just as if a lookahead  asser-         matching possibilities goes ahead, just as if a lookahead assertion had
2471         tion  had  failed.  If  the value is less than zero, the match is aban-         failed. If the value is less than zero, the  match  is  abandoned,  and
2472         doned, and pcre_exec() returns the negative value.         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2473    
2474         Negative  values  should  normally  be   chosen   from   the   set   of         Negative   values   should   normally   be   chosen  from  the  set  of
2475         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2476         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2477         reserved  for  use  by callout functions; it will never be used by PCRE         reserved for use by callout functions; it will never be  used  by  PCRE
2478         itself.         itself.
2479    
2480  Last updated: 09 September 2004  Last updated: 28 February 2005
2481  Copyright (c) 1997-2004 University of Cambridge.  Copyright (c) 1997-2005 University of Cambridge.
2482  -----------------------------------------------------------------------------  ------------------------------------------------------------------------------
2483    
 PCRE(3)                                                                PCRE(3)  
2484    
2485    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2486    
2487    
2488  NAME  NAME
2489         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2490    
2491    
2492  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2493    
2494         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2495         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2496         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2497           tures that are expected to be in the forthcoming Perl 5.10.
2498         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2499         are given in the section on UTF-8 support in the main pcre page.         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2500           of  what  it does have are given in the section on UTF-8 support in the
2501           main pcre page.
2502    
2503         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2504         permits  them,  but they do not mean what you might think. For example,         permits  them,  but they do not mean what you might think. For example,
# Line 1738  DIFFERENCES BETWEEN PCRE AND PERL Line 2525  DIFFERENCES BETWEEN PCRE AND PERL
2525         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2526         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2527         can be tested with \p and \P are limited to the general category  prop-         can be tested with \p and \P are limited to the general category  prop-
2528         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2529           derived properties Any and L&.
2530    
2531         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2532         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2533         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2534         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2535         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2536    
2537             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 1753  DIFFERENCES BETWEEN PCRE AND PERL Line 2541  DIFFERENCES BETWEEN PCRE AND PERL
2541             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2542             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2543    
2544         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2545         classes.         classes.
2546    
2547         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2548         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2549         the non-Perl items (?R),  (?number),  and  (?P>name).  Also,  the  PCRE         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2550         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2551         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2552    
2553         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2554         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2555         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2556    
2557           10.  There are some differences that are concerned with the settings of
2558           captured strings when part of  a  pattern  is  repeated.  For  example,
2559           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2560         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2561    
2562         10. PCRE provides some extensions to the Perl regular expression facil-         11. PCRE provides some extensions to the Perl regular expression facil-
2563         ities:         ities.   Perl  5.10  will  include new features that are not in earlier
2564           versions, some of which (such as named parentheses) have been  in  PCRE
2565           for some time. This list is with respect to Perl 5.10:
2566    
2567         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2568         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2569         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2570    
2571         (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
2572         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2573    
2574         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2575         cial meaning is faulted.         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2576           ignored. (Perl can be made to issue a warning.)
2577    
2578         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2579         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
# Line 1790  DIFFERENCES BETWEEN PCRE AND PERL Line 2585  DIFFERENCES BETWEEN PCRE AND PERL
2585         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2586         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2587    
2588         (g) The (?R), (?number), and (?P>name) constructs allows for  recursive         (g) The callout facility is PCRE-specific.
        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.  
   
        (j) The (R) condition, for testing recursion, is a PCRE extension.  
2589    
2590         (k) The callout facility is PCRE-specific.         (h) The partial matching facility is PCRE-specific.
2591    
2592         (l) The partial matching facility is PCRE-specific.         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
   
        (m) Patterns compiled by PCRE can be saved and re-used at a later time,  
2593         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2594    
2595  Last updated: 09 September 2004         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2596  Copyright (c) 1997-2004 University of Cambridge.         different way and is not Perl-compatible.
2597  -----------------------------------------------------------------------------  
2598    Last updated: 28 November 2006
2599    Copyright (c) 1997-2006 University of Cambridge.
2600    ------------------------------------------------------------------------------
2601    
 PCRE(3)                                                                PCRE(3)  
2602    
2603    PCREPATTERN(3)                                                  PCREPATTERN(3)
2604    
2605    
2606  NAME  NAME
2607         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2608    
2609    
2610  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2611    
2612         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax  and semantics of the regular expressions supported by PCRE
# Line 1836  PCRE REGULAR EXPRESSION DETAILS Line 2624  PCRE REGULAR EXPRESSION DETAILS
2624         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
2625         page.         page.
2626    
2627           The remainder of this document discusses the  patterns  that  are  sup-
2628           ported  by  PCRE when its main matching function, pcre_exec(), is used.
2629           From  release  6.0,   PCRE   offers   a   second   matching   function,
2630           pcre_dfa_exec(),  which matches using a different algorithm that is not
2631           Perl-compatible. The advantages and disadvantages  of  the  alternative
2632           function, and how it differs from the normal function, are discussed in
2633           the pcrematching page.
2634    
2635    
2636    CHARACTERS AND METACHARACTERS
2637    
2638         A regular expression is a pattern that is  matched  against  a  subject         A regular expression is a pattern that is  matched  against  a  subject
2639         string  from  left  to right. Most characters stand for themselves in a         string  from  left  to right. Most characters stand for themselves in a
2640         pattern, and match the corresponding characters in the  subject.  As  a         pattern, and match the corresponding characters in the  subject.  As  a
# Line 1843  PCRE REGULAR EXPRESSION DETAILS Line 2642  PCRE REGULAR EXPRESSION DETAILS
2642    
2643           The quick brown fox           The quick brown fox
2644    
2645         matches  a portion of a subject string that is identical to itself. The         matches a portion of a subject string that is identical to itself. When
2646         power of regular expressions comes from the ability to include alterna-         caseless matching is specified (the PCRE_CASELESS option), letters  are
2647         tives  and repetitions in the pattern. These are encoded in the pattern         matched  independently  of case. In UTF-8 mode, PCRE always understands
2648         by the use of metacharacters, which do not  stand  for  themselves  but         the concept of case for characters whose values are less than  128,  so
2649         instead are interpreted in some special way.         caseless  matching  is always possible. For characters with higher val-
2650           ues, the concept of case is supported if PCRE is compiled with  Unicode
2651         There  are  two different sets of metacharacters: those that are recog-         property  support,  but  not  otherwise.   If  you want to use caseless
2652         nized anywhere in the pattern except within square brackets, and  those         matching for characters 128 and above, you must  ensure  that  PCRE  is
2653         that  are  recognized  in square brackets. Outside square brackets, the         compiled with Unicode property support as well as with UTF-8 support.
2654         metacharacters are as follows:  
2655           The  power  of  regular  expressions  comes from the ability to include
2656           alternatives and repetitions in the pattern. These are encoded  in  the
2657           pattern by the use of metacharacters, which do not stand for themselves
2658           but instead are interpreted in some special way.
2659    
2660           There are two different sets of metacharacters: those that  are  recog-
2661           nized  anywhere in the pattern except within square brackets, and those
2662           that are recognized within square brackets.  Outside  square  brackets,
2663           the metacharacters are as follows:
2664    
2665           \      general escape character with several uses           \      general escape character with several uses
2666           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 1870  PCRE REGULAR EXPRESSION DETAILS Line 2678  PCRE REGULAR EXPRESSION DETAILS
2678                  also "possessive quantifier"                  also "possessive quantifier"
2679           {      start min/max quantifier           {      start min/max quantifier
2680    
2681         Part of a pattern that is in square brackets  is  called  a  "character         Part  of  a  pattern  that is in square brackets is called a "character
2682         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
2683    
2684           \      general escape character           \      general escape character
# Line 1880  PCRE REGULAR EXPRESSION DETAILS Line 2688  PCRE REGULAR EXPRESSION DETAILS
2688                    syntax)                    syntax)
2689           ]      terminates the character class           ]      terminates the character class
2690    
2691         The  following sections describe the use of each of the metacharacters.         The following sections describe the use of each of the  metacharacters.
2692    
2693    
2694  BACKSLASH  BACKSLASH
2695    
2696         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
2697         a  non-alphanumeric  character,  it takes away any special meaning that         a non-alphanumeric character, it takes away any  special  meaning  that
2698         character may have. This  use  of  backslash  as  an  escape  character         character  may  have.  This  use  of  backslash  as an escape character
2699         applies both inside and outside character classes.         applies both inside and outside character classes.
2700    
2701         For  example,  if  you want to match a * character, you write \* in the         For example, if you want to match a * character, you write  \*  in  the
2702         pattern.  This escaping action applies whether  or  not  the  following         pattern.   This  escaping  action  applies whether or not the following
2703         character  would  otherwise be interpreted as a metacharacter, so it is         character would otherwise be interpreted as a metacharacter, so  it  is
2704         always safe to precede a non-alphanumeric  with  backslash  to  specify         always  safe  to  precede  a non-alphanumeric with backslash to specify
2705         that  it stands for itself. In particular, if you want to match a back-         that it stands for itself. In particular, if you want to match a  back-
2706         slash, you write \\.         slash, you write \\.
2707    
2708         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2709         the  pattern (other than in a character class) and characters between a         the pattern (other than in a character class) and characters between  a
2710         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2711         An  escaping backslash can be used to include a whitespace or # charac-         ing backslash can be used to include a whitespace  or  #  character  as
2712         ter as part of the pattern.         part of the pattern.
2713    
2714         If you want to remove the special meaning from a  sequence  of  charac-         If  you  want  to remove the special meaning from a sequence of charac-
2715         ters,  you can do so by putting them between \Q and \E. This is differ-         ters, you can do so by putting them between \Q and \E. This is  differ-
2716         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E
2717         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
2718         tion. Note the following examples:         tion. Note the following examples:
2719    
2720           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 1916  BACKSLASH Line 2724  BACKSLASH
2724           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
2725           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
2726    
2727         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
2728         classes.         classes.
2729    
2730     Non-printing characters     Non-printing characters
2731    
2732         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
2733         acters in patterns in a visible manner. There is no restriction on  the         acters  in patterns in a visible manner. There is no restriction on the
2734         appearance  of non-printing characters, apart from the binary zero that         appearance of non-printing characters, apart from the binary zero  that
2735         terminates a pattern, but when a pattern  is  being  prepared  by  text         terminates  a  pattern,  but  when  a pattern is being prepared by text
2736         editing,  it  is  usually  easier  to  use  one of the following escape         editing, it is usually easier  to  use  one  of  the  following  escape
2737         sequences than the binary character it represents:         sequences than the binary character it represents:
2738    
2739           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
# Line 1937  BACKSLASH Line 2745  BACKSLASH
2745           \t        tab (hex 09)           \t        tab (hex 09)
2746           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
2747           \xhh      character with hex code hh           \xhh      character with hex code hh
2748           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
2749    
2750         The precise effect of \cx is as follows: if x is a lower  case  letter,         The  precise  effect of \cx is as follows: if x is a lower case letter,
2751         it  is converted to upper case. Then bit 6 of the character (hex 40) is         it is converted to upper case. Then bit 6 of the character (hex 40)  is
2752         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;
2753         becomes hex 7B.         becomes hex 7B.
2754    
2755         After  \x, from zero to two hexadecimal digits are read (letters can be         After \x, from zero to two hexadecimal digits are read (letters can  be
2756         in upper or lower case). In UTF-8 mode, any number of hexadecimal  dig-         in  upper  or  lower case). Any number of hexadecimal digits may appear
2757         its  may  appear between \x{ and }, but the value of the character code         between \x{ and }, but the value of the character  code  must  be  less
2758         must be less than 2**31 (that is,  the  maximum  hexadecimal  value  is         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode (that is,
2759         7FFFFFFF).  If  characters other than hexadecimal digits appear between         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than
2760         \x{ and }, or if there is no terminating }, this form of escape is  not         hexadecimal  digits  appear between \x{ and }, or if there is no termi-
2761         recognized. Instead, the initial \x will be interpreted as a basic hex-         nating }, this form of escape is not recognized.  Instead, the  initial
2762         adecimal escape, with no following digits,  giving  a  character  whose         \x will be interpreted as a basic hexadecimal escape, with no following
2763         value is zero.         digits, giving a character whose value is zero.
2764    
2765         Characters whose value is less than 256 can be defined by either of the         Characters whose value is less than 256 can be defined by either of the
2766         two syntaxes for \x when PCRE is in UTF-8 mode. There is no  difference         two  syntaxes  for  \x. There is no difference in the way they are han-
2767         in  the  way they are handled. For example, \xdc is exactly the same as         dled. For example, \xdc is exactly the same as \x{dc}.
2768         \x{dc}.  
2769           After \0 up to two further octal digits are read. If  there  are  fewer
2770         After \0 up to two further octal digits are read.  In  both  cases,  if         than  two  digits,  just  those  that  are  present  are used. Thus the
2771         there  are fewer than two digits, just those that are present are used.         sequence \0\x\07 specifies two binary zeros followed by a BEL character
2772         Thus the sequence \0\x\07 specifies two binary zeros followed by a  BEL         (code  value 7). Make sure you supply two digits after the initial zero
2773         character  (code  value  7).  Make sure you supply two digits after the         if the pattern character that follows is itself an octal digit.
        initial zero if the pattern character that follows is itself  an  octal  
        digit.  
2774    
2775         The handling of a backslash followed by a digit other than 0 is compli-         The handling of a backslash followed by a digit other than 0 is compli-
2776         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
2777         its  as  a  decimal  number. If the number is less than 10, or if there         its as a decimal number. If the number is less than  10,  or  if  there
2778         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
2779         expression,  the  entire  sequence  is  taken  as  a  back reference. A         expression, the entire  sequence  is  taken  as  a  back  reference.  A
2780         description of how this works is given later, following the  discussion         description  of how this works is given later, following the discussion
2781         of parenthesized subpatterns.         of parenthesized subpatterns.
2782    
2783         Inside  a  character  class, or if the decimal number is greater than 9         Inside a character class, or if the decimal number is  greater  than  9
2784         and there have not been that many capturing subpatterns, PCRE  re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
2785         up  to three octal digits following the backslash, and generates a sin-         up to three octal digits following the backslash, and uses them to gen-
2786         gle byte from the least significant 8 bits of the value. Any subsequent         erate  a data character. Any subsequent digits stand for themselves. In
2787         digits stand for themselves.  For example:         non-UTF-8 mode, the value of a character specified  in  octal  must  be
2788           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
2789           example:
2790    
2791           \040   is another way of writing a space           \040   is another way of writing a space
2792           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 1995  BACKSLASH Line 2803  BACKSLASH
2803           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
2804                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
2805    
2806         Note  that  octal  values of 100 or greater must not be introduced by a         Note that octal values of 100 or greater must not be  introduced  by  a
2807         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2808    
2809         All the sequences that define a single byte value  or  a  single  UTF-8         All the sequences that define a single character value can be used both
2810         character (in UTF-8 mode) can be used both inside and outside character         inside and outside character classes. In addition, inside  a  character
2811         classes. In addition, inside a character  class,  the  sequence  \b  is         class,  the  sequence \b is interpreted as the backspace character (hex
2812         interpreted as the backspace character (hex 08), and the sequence \X is         08), and the sequences \R and \X are interpreted as the characters  "R"
2813         interpreted as the character "X".  Outside  a  character  class,  these         and  "X", respectively. Outside a character class, these sequences have
2814         sequences have different meanings (see below).         different meanings (see below).
2815    
2816       Absolute and relative back references
2817    
2818           The sequence \g followed by a positive or negative  number,  optionally
2819           enclosed  in  braces,  is  an absolute or relative back reference. Back
2820           references are discussed later, following the discussion  of  parenthe-
2821           sized subpatterns.
2822    
2823     Generic character types     Generic character types
2824    
2825         The  third  use of backslash is for specifying generic character types.         Another use of backslash is for specifying generic character types. The
2826         The following are always recognized:         following are always recognized:
2827    
2828           \d     any decimal digit           \d     any decimal digit
2829           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 2028  BACKSLASH Line 2843  BACKSLASH
2843    
2844         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
2845         11).  This makes it different from the the POSIX "space" class. The  \s         11).  This makes it different from the the POSIX "space" class. The  \s
2846         characters are HT (9), LF (10), FF (12), CR (13), and space (32).         characters  are  HT (9), LF (10), FF (12), CR (13), and space (32). (If
2847           "use locale;" is included in a Perl script, \s may match the VT charac-
2848           ter. In PCRE, it never does.)
2849    
2850         A "word" character is an underscore or any character less than 256 that         A "word" character is an underscore or any character less than 256 that
2851         is a letter or digit. The definition of  letters  and  digits  is  con-         is a letter or digit. The definition of  letters  and  digits  is  con-
# Line 2040  BACKSLASH Line 2857  BACKSLASH
2857    
2858         In  UTF-8 mode, characters with values greater than 128 never match \d,         In  UTF-8 mode, characters with values greater than 128 never match \d,
2859         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
2860         code character property support is available.         code  character  property support is available. The use of locales with
2861           Unicode is discouraged.
2862    
2863       Newline sequences
2864    
2865           Outside a character class, the escape sequence \R matches  any  Unicode
2866           newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2867           equivalent to the following:
2868    
2869             (?>\r\n|\n|\x0b|\f|\r|\x85)
2870    
2871           This is an example of an "atomic group", details  of  which  are  given
2872           below.  This particular group matches either the two-character sequence
2873           CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
2874           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2875           return, U+000D), or NEL (next line, U+0085). The two-character sequence
2876           is treated as a single unit that cannot be split.
2877    
2878           In  UTF-8  mode, two additional characters whose codepoints are greater
2879           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2880           rator,  U+2029).   Unicode character property support is not needed for
2881           these characters to be recognized.
2882    
2883           Inside a character class, \R matches the letter "R".
2884    
2885     Unicode character properties     Unicode character properties
2886    
2887         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
2888         tional escape sequences to match generic character types are  available         tional  escape  sequences  to  match character properties are available
2889         when UTF-8 mode is selected. They are:         when UTF-8 mode is selected. They are:
2890    
2891          \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
2892          \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
2893          \X       an extended Unicode sequence           \X       an extended Unicode sequence
2894    
2895         The  property  names represented by xx above are limited to the Unicode         The property names represented by xx above are limited to  the  Unicode
2896         general category properties. Each character has exactly one such  prop-         script names, the general category properties, and "Any", which matches
2897         erty,  specified  by  a two-letter abbreviation. For compatibility with         any character (including newline). Other properties such as "InMusical-
2898         Perl, negation can be specified by including a circumflex  between  the         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
2899         opening  brace  and the property name. For example, \p{^Lu} is the same         not match any characters, so always causes a match failure.
2900         as \P{Lu}.  
2901           Sets of Unicode characters are defined as belonging to certain scripts.
2902         If only one letter is specified with \p or  \P,  it  includes  all  the         A  character from one of these sets can be matched using a script name.
2903         properties that start with that letter. In this case, in the absence of         For example:
2904         negation, the curly brackets in the escape sequence are optional; these  
2905         two examples have the same effect:           \p{Greek}
2906             \P{Han}
2907    
2908           Those that are not part of an identified script are lumped together  as
2909           "Common". The current list of scripts is:
2910    
2911           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
2912           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
2913           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
2914           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
2915           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
2916           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
2917           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
2918           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
2919           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
2920    
2921           Each  character has exactly one general category property, specified by
2922           a two-letter abbreviation. For compatibility with Perl, negation can be
2923           specified  by  including a circumflex between the opening brace and the
2924           property name. For example, \p{^Lu} is the same as \P{Lu}.
2925    
2926           If only one letter is specified with \p or \P, it includes all the gen-
2927           eral  category properties that start with that letter. In this case, in
2928           the absence of negation, the curly brackets in the escape sequence  are
2929           optional; these two examples have the same effect:
2930    
2931           \p{L}           \p{L}
2932           \pL           \pL
2933    
2934         The following property codes are supported:         The following general category property codes are supported:
2935    
2936           C     Other           C     Other
2937           Cc    Control           Cc    Control
# Line 2113  BACKSLASH Line 2977  BACKSLASH
2977           Zp    Paragraph separator           Zp    Paragraph separator
2978           Zs    Space separator           Zs    Space separator
2979    
2980         Extended  properties such as "Greek" or "InMusicalSymbols" are not sup-         The  special property L& is also supported: it matches a character that
2981         ported by PCRE.         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
2982           classified as a modifier or "other".
2983    
2984           The  long  synonyms  for  these  properties that Perl supports (such as
2985           \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
2986           any of these properties with "Is".
2987    
2988           No character that is in the Unicode table has the Cn (unassigned) prop-
2989           erty.  Instead, this property is assumed for any code point that is not
2990           in the Unicode table.
2991    
2992         Specifying caseless matching does not affect  these  escape  sequences.         Specifying  caseless  matching  does not affect these escape sequences.
2993         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
2994    
2995         The  \X  escape  matches  any number of Unicode characters that form an         The \X escape matches any number of Unicode  characters  that  form  an
2996         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
2997    
2998           (?>\PM\pM*)           (?>\PM\pM*)
2999    
3000         That is, it matches a character without the "mark"  property,  followed         That  is,  it matches a character without the "mark" property, followed
3001         by  zero  or  more  characters with the "mark" property, and treats the         by zero or more characters with the "mark"  property,  and  treats  the
3002         sequence as an atomic group (see below).  Characters  with  the  "mark"         sequence  as  an  atomic group (see below).  Characters with the "mark"
3003         property are typically accents that affect the preceding character.         property are typically accents that affect the preceding character.
3004    
3005         Matching  characters  by Unicode property is not fast, because PCRE has         Matching characters by Unicode property is not fast, because  PCRE  has
3006         to search a structure that contains  data  for  over  fifteen  thousand         to  search  a  structure  that  contains data for over fifteen thousand
3007         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3008         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3009    
3010     Simple assertions     Simple assertions
3011    
3012         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3013         tion  specifies a condition that has to be met at a particular point in         tion specifies a condition that has to be met at a particular point  in
3014         a match, without consuming any characters from the subject string.  The         a  match, without consuming any characters from the subject string. The
3015         use  of subpatterns for more complicated assertions is described below.         use of subpatterns for more complicated assertions is described  below.
3016         The backslashed assertions are:         The backslashed assertions are:
3017    
3018           \b     matches at a word boundary           \b     matches at a word boundary
3019           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3020           \A     matches at start of subject           \A     matches at the start of the subject
3021           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3022           \z     matches at end of subject                   also matches before a newline at the end of the subject
3023           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3024             \G     matches at the first matching position in the subject
3025    
3026         These assertions may not appear in character classes (but note that  \b         These  assertions may not appear in character classes (but note that \b
3027         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3028         acter class).         acter class).
3029    
3030         A word boundary is a position in the subject string where  the  current         A  word  boundary is a position in the subject string where the current
3031         character  and  the previous character do not both match \w or \W (i.e.         character and the previous character do not both match \w or  \W  (i.e.
3032         one matches \w and the other matches \W), or the start or  end  of  the         one  matches  \w  and the other matches \W), or the start or end of the
3033         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
3034    
3035         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The \A, \Z, and \z assertions differ from  the  traditional  circumflex
3036         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
3037         at  the  very start and end of the subject string, whatever options are         at the very start and end of the subject string, whatever  options  are
3038         set. Thus, they are independent of multiline mode. These  three  asser-         set.  Thus,  they are independent of multiline mode. These three asser-
3039         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3040         affect only the behaviour of the circumflex and dollar  metacharacters.         affect  only the behaviour of the circumflex and dollar metacharacters.
3041         However,  if the startoffset argument of pcre_exec() is non-zero, indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3042         cating that matching is to start at a point other than the beginning of         cating that matching is to start at a point other than the beginning of
3043         the  subject,  \A  can never match. The difference between \Z and \z is         the subject, \A can never match. The difference between \Z  and  \z  is
3044         that \Z matches before a newline that is  the  last  character  of  the         that \Z matches before a newline at the end of the string as well as at
3045         string  as well as at the end of the string, whereas \z matches only at         the very end, whereas \z matches only at the end.
        the end.  
3046    
3047         The \G assertion is true only when the current matching position is  at         The \G assertion is true only when the current matching position is  at
3048         the  start point of the match, as specified by the startoffset argument         the  start point of the match, as specified by the startoffset argument
# Line 2208  CIRCUMFLEX AND DOLLAR Line 3081  CIRCUMFLEX AND DOLLAR
3081    
3082         A dollar character is an assertion that is true  only  if  the  current         A dollar character is an assertion that is true  only  if  the  current
3083         matching  point  is  at  the  end of the subject string, or immediately         matching  point  is  at  the  end of the subject string, or immediately
3084         before a newline character that is the last character in the string (by         before a newline at the end of the string (by default). Dollar need not
3085         default).  Dollar  need  not  be the last character of the pattern if a         be  the  last  character of the pattern if a number of alternatives are
3086         number of alternatives are involved, but it should be the last item  in         involved, but it should be the last item in  any  branch  in  which  it
3087         any  branch  in  which  it appears.  Dollar has no special meaning in a         appears. Dollar has no special meaning in a character class.
        character class.  
3088    
3089         The meaning of dollar can be changed so that it  matches  only  at  the         The  meaning  of  dollar  can be changed so that it matches only at the
3090         very  end  of  the string, by setting the PCRE_DOLLAR_ENDONLY option at         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at
3091         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3092    
3093         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3094         PCRE_MULTILINE option is set. When this is the case, they match immedi-         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex
3095         ately after and  immediately  before  an  internal  newline  character,         matches  immediately after internal newlines as well as at the start of
3096         respectively,  in addition to matching at the start and end of the sub-         the subject string. It does not match after a  newline  that  ends  the
3097         ject string. For example,  the  pattern  /^abc$/  matches  the  subject         string.  A dollar matches before any newlines in the string, as well as
3098         string  "def\nabc"  (where \n represents a newline character) in multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3099         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3100         in  single line mode because all branches start with ^ are not anchored         not indicate newlines.
3101         in multiline mode, and a match for  circumflex  is  possible  when  the  
3102         startoffset   argument   of  pcre_exec()  is  non-zero.  The  PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3103         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3104           Consequently, patterns that are anchored in single  line  mode  because
3105           all  branches  start  with  ^ are not anchored in multiline mode, and a
3106           match for circumflex is  possible  when  the  startoffset  argument  of
3107           pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
3108           PCRE_MULTILINE is set.
3109    
3110         Note that the sequences \A, \Z, and \z can be used to match  the  start         Note that the sequences \A, \Z, and \z can be used to match  the  start
3111         and  end of the subject in both modes, and if all branches of a pattern         and  end of the subject in both modes, and if all branches of a pattern
3112         start with \A it is always anchored, whether PCRE_MULTILINE is  set  or         start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3113         not.         set.
3114    
3115    
3116  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3117    
3118         Outside a character class, a dot in the pattern matches any one charac-         Outside a character class, a dot in the pattern matches any one charac-
3119         ter in the subject, including a non-printing  character,  but  not  (by         ter in the subject string except (by default) a character  that  signi-
3120         default)  newline.   In  UTF-8 mode, a dot matches any UTF-8 character,         fies  the  end  of  a line. In UTF-8 mode, the matched character may be
3121         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3122         the  PCRE_DOTALL  option  is set, dots match newlines as well. The han-  
3123         dling of dot is entirely independent of the handling of circumflex  and         When a line ending is defined as a single character, dot never  matches
3124         dollar,  the  only  relationship  being  that they both involve newline         that  character; when the two-character sequence CRLF is used, dot does
3125         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3126           matches  all characters (including isolated CRs and LFs). When any Uni-
3127           code line endings are being recognized, dot does not match CR or LF  or
3128           any of the other line ending characters.
3129    
3130           The  behaviour  of  dot  with regard to newlines can be changed. If the
3131           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3132           exception. If the two-character sequence CRLF is present in the subject
3133           string, it takes two dots to match it.
3134    
3135           The handling of dot is entirely independent of the handling of  circum-
3136           flex  and  dollar,  the  only relationship being that they both involve
3137           newlines. Dot has no special meaning in a character class.
3138    
3139    
3140  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3141    
3142         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3143         both  in  and  out of UTF-8 mode. Unlike a dot, it can match a newline.         both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any
3144         The feature is provided in Perl in order to match individual  bytes  in         line-ending characters. The feature is provided in  Perl  in  order  to
3145         UTF-8  mode.  Because  it  breaks  up  UTF-8 characters into individual         match  individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-
3146         bytes, what remains in the string may be a malformed UTF-8 string.  For         acters into individual bytes, what remains in the string may be a  mal-
3147         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3148           avoided.
3149    
3150         PCRE  does  not  allow \C to appear in lookbehind assertions (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3151         below), because in UTF-8 mode this would make it impossible  to  calcu-         below),  because  in UTF-8 mode this would make it impossible to calcu-
3152         late the length of the lookbehind.         late the length of the lookbehind.
3153    
3154    
# Line 2267  SQUARE BRACKETS AND CHARACTER CLASSES Line 3157  SQUARE BRACKETS AND CHARACTER CLASSES
3157         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3158         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3159         cial. If a closing square bracket is required as a member of the class,         cial. If a closing square bracket is required as a member of the class,
3160         it should be the first data character in the class  (after  an  initial         it  should  be  the first data character in the class (after an initial
3161         circumflex, if present) or escaped with a backslash.         circumflex, if present) or escaped with a backslash.
3162    
3163         A  character  class matches a single character in the subject. In UTF-8         A character class matches a single character in the subject.  In  UTF-8
3164         mode, the character may occupy more than one byte. A matched  character         mode,  the character may occupy more than one byte. A matched character
3165         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3166         character in the class definition is a circumflex, in  which  case  the         character  in  the  class definition is a circumflex, in which case the
3167         subject  character  must  not  be in the set defined by the class. If a         subject character must not be in the set defined by  the  class.  If  a
3168         circumflex is actually required as a member of the class, ensure it  is         circumflex  is actually required as a member of the class, ensure it is
3169         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3170    
3171         For  example, the character class [aeiou] matches any lower case vowel,         For example, the character class [aeiou] matches any lower case  vowel,
3172         while [^aeiou] matches any character that is not a  lower  case  vowel.         while  [^aeiou]  matches  any character that is not a lower case vowel.
3173         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3174         characters that are in the class by enumerating those that are  not.  A         characters  that  are in the class by enumerating those that are not. A
3175         class  that starts with a circumflex is not an assertion: it still con-         class that starts with a circumflex is not an assertion: it still  con-
3176         sumes a character from the subject string, and therefore  it  fails  if         sumes  a  character  from the subject string, and therefore it fails if
3177         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3178    
3179         In  UTF-8 mode, characters with values greater than 255 can be included         In UTF-8 mode, characters with values greater than 255 can be  included
3180         in a class as a literal string of bytes, or by using the  \x{  escaping         in  a  class as a literal string of bytes, or by using the \x{ escaping
3181         mechanism.         mechanism.
3182    
3183         When  caseless  matching  is set, any letters in a class represent both         When caseless matching is set, any letters in a  class  represent  both
3184         their upper case and lower case versions, so for  example,  a  caseless         their  upper  case  and lower case versions, so for example, a caseless
3185         [aeiou]  matches  "A"  as well as "a", and a caseless [^aeiou] does not         [aeiou] matches "A" as well as "a", and a caseless  [^aeiou]  does  not
3186         match "A", whereas a caseful version would. When running in UTF-8 mode,         match  "A", whereas a caseful version would. In UTF-8 mode, PCRE always
3187         PCRE  supports  the  concept of case for characters with values greater         understands the concept of case for characters whose  values  are  less
3188         than 128 only when it is compiled with Unicode property support.         than  128, so caseless matching is always possible. For characters with
3189           higher values, the concept of case is supported  if  PCRE  is  compiled
3190         The newline character is never treated in any special way in  character         with  Unicode  property support, but not otherwise.  If you want to use
3191         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         caseless matching for characters 128 and above, you  must  ensure  that
3192         options is. A class such as [^a] will always match a newline.         PCRE  is  compiled  with Unicode property support as well as with UTF-8
3193           support.
3194    
3195           Characters that might indicate line breaks are  never  treated  in  any
3196           special  way  when  matching  character  classes,  whatever line-ending
3197           sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3198           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3199           of these characters.
3200    
3201         The minus (hyphen) character can be used to specify a range of  charac-         The minus (hyphen) character can be used to specify a range of  charac-
3202         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters  in  a  character  class.  For  example,  [d-m] matches any letter
# Line 2400  VERTICAL BAR Line 3297  VERTICAL BAR
3297    
3298         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3299         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3300         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3301         left to right, and the first one that succeeds is used. If the alterna-         to right, and the first one that succeeds is used. If the  alternatives
3302         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3303         ing the rest of the main pattern as well as the alternative in the sub-         rest of the main pattern as well as the alternative in the  subpattern.
        pattern.  
3304    
3305    
3306  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 2432  INTERNAL OPTION SETTING Line 3328  INTERNAL OPTION SETTING
3328         PCRE extracts it into the global options (and it will therefore show up         PCRE extracts it into the global options (and it will therefore show up
3329         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3330    
3331         An option change within a subpattern affects only that part of the cur-         An  option  change  within a subpattern (see below for a description of
3332         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3333           it, so
3334    
3335           (a(?i)b)c           (a(?i)b)c
3336    
3337         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
3338         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3339         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3340         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3341         example,         example,
3342    
3343           (a(?i)b|c)           (a(?i)b|c)
3344    
3345         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3346         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3347         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3348         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3349    
3350         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3351         in the same way as the Perl-compatible options by using the  characters         can  be changed in the same way as the Perl-compatible options by using
3352         U  and X respectively. The (?X) flag setting is special in that it must         the characters J, U and X respectively.
        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 to put it at the  
        start.  
3353    
3354    
3355  SUBPATTERNS  SUBPATTERNS
# Line 2468  SUBPATTERNS Line 3362  SUBPATTERNS
3362           cat(aract|erpillar|)           cat(aract|erpillar|)
3363    
3364         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3365         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3366         string.         string.
3367    
3368         2.  It  sets  up  the  subpattern as a capturing subpattern. This means         2.  It  sets  up  the  subpattern as a capturing subpattern. This means
# Line 2497  SUBPATTERNS Line 3391  SUBPATTERNS
3391           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3392    
3393         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3394         1  and 2. The maximum number of capturing subpatterns is 65535, and the         1 and 2. The maximum number of capturing subpatterns is 65535.
        maximum depth of nesting of all subpatterns, both  capturing  and  non-  
        capturing, is 200.  
3395    
3396         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3397         start of a non-capturing subpattern,  the  option  letters  may  appear         start of a non-capturing subpattern,  the  option  letters  may  appear
# Line 2521  NAMED SUBPATTERNS Line 3413  NAMED SUBPATTERNS
3413         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3414         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3415         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3416         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3417         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3418         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3419           tax.
3420    
3421           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3422           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3423           to capturing parentheses from other parts of the pattern, such as back-
3424           references,  recursion,  and conditions, can be made by name as well as
3425           by number.
3426    
3427           Names consist of up to  32  alphanumeric  characters  and  underscores.
3428         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3429         names. The PCRE API provides function calls for extracting the name-to-         names, exactly as if the names were not present. The PCRE API  provides
3430         number  translation table from a compiled pattern. There is also a con-         function calls for extracting the name-to-number translation table from
3431         venience function for extracting a captured substring by name. For fur-         a compiled pattern. There is also a convenience function for extracting
3432         ther details see the pcreapi documentation.         a captured substring by name.
3433    
3434           By  default, a name must be unique within a pattern, but it is possible
3435           to relax this constraint by setting the PCRE_DUPNAMES option at compile
3436           time.  This  can  be useful for patterns where only one instance of the
3437           named parentheses can match. Suppose you want to match the  name  of  a
3438           weekday,  either as a 3-letter abbreviation or as the full name, and in
3439           both cases you want to extract the abbreviation. This pattern (ignoring
3440           the line breaks) does the job:
3441    
3442             (?<DN>Mon|Fri|Sun)(?:day)?|
3443             (?<DN>Tue)(?:sday)?|
3444             (?<DN>Wed)(?:nesday)?|
3445             (?<DN>Thu)(?:rsday)?|
3446             (?<DN>Sat)(?:urday)?
3447    
3448           There  are  five capturing substrings, but only one is ever set after a
3449           match.  The convenience  function  for  extracting  the  data  by  name
3450           returns  the  substring  for  the first (and in this example, the only)
3451           subpattern of that name that matched.  This  saves  searching  to  find
3452           which  numbered  subpattern  it  was. If you make a reference to a non-
3453           unique named subpattern from elsewhere in the  pattern,  the  one  that
3454           corresponds  to  the  lowest number is used. For further details of the
3455           interfaces for handling named subpatterns, see the  pcreapi  documenta-
3456           tion.
3457    
3458    
3459  REPETITION  REPETITION
# Line 2538  REPETITION Line 3462  REPETITION
3462         following items:         following items:
3463    
3464           a literal data character           a literal data character
3465           the . metacharacter           the dot metacharacter
3466           the \C escape sequence           the \C escape sequence
3467           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3468             the \R escape sequence
3469           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3470           a character class           a character class
3471           a back reference (see next section)           a back reference (see next section)
# Line 2580  REPETITION Line 3505  REPETITION
3505         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3506         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3507    
3508         For  convenience  (and  historical compatibility) the three most common         For  convenience, the three most common quantifiers have single-charac-
3509         quantifiers have single-character abbreviations:         ter abbreviations:
3510    
3511           *    is equivalent to {0,}           *    is equivalent to {0,}
3512           +    is equivalent to {1,}           +    is equivalent to {1,}
# Line 2633  REPETITION Line 3558  REPETITION
3558         which matches one digit by preference, but can match two if that is the         which matches one digit by preference, but can match two if that is the
3559         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3560    
3561         If the PCRE_UNGREEDY option is set (an option which is not available in         If the PCRE_UNGREEDY option is set (an option that is not available  in
3562         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3563         can be made greedy by following them with a  question  mark.  In  other         can be made greedy by following them with a  question  mark.  In  other
3564         words, it inverts the default behaviour.         words, it inverts the default behaviour.
# Line 2644  REPETITION Line 3569  REPETITION
3569         minimum or maximum.         minimum or maximum.
3570    
3571         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
3572         alent  to Perl's /s) is set, thus allowing the . to match newlines, the         alent  to  Perl's  /s) is set, thus allowing the dot to match newlines,
3573         pattern is implicitly anchored, because whatever follows will be  tried         the pattern is implicitly anchored, because whatever  follows  will  be
3574         against  every character position in the subject string, so there is no         tried  against every character position in the subject string, so there
3575         point in retrying the overall match at any position  after  the  first.         is no point in retrying the overall match at  any  position  after  the
3576         PCRE normally treats such a pattern as though it were preceded by \A.         first.  PCRE  normally treats such a pattern as though it were preceded
3577           by \A.
3578    
3579         In  cases  where  it  is known that the subject string contains no new-         In cases where it is known that the subject  string  contains  no  new-
3580         lines, it is worth setting PCRE_DOTALL in order to  obtain  this  opti-         lines,  it  is  worth setting PCRE_DOTALL in order to obtain this opti-
3581         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3582    
3583         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3584         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3585         backreference  elsewhere in the pattern, a match at the start may fail,         backreference elsewhere in the pattern, a match at the start  may  fail
3586         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3587    
3588           (.*)abc\1           (.*)abc\1
3589    
3590         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3591         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3592    
3593         When a capturing subpattern is repeated, the value captured is the sub-         When a capturing subpattern is repeated, the value captured is the sub-
# Line 2670  REPETITION Line 3596  REPETITION
3596           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
3597    
3598         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
3599         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
3600         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
3601         tions. For example, after         tions. For example, after
3602    
3603           /(a|(b))+/           /(a|(b))+/
# Line 2681  REPETITION Line 3607  REPETITION
3607    
3608  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
3609    
3610         With both maximizing and minimizing repetition, failure of what follows         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
3611         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition,  failure  of what follows normally causes the repeated item
3612         ferent number of repeats allows the rest of the pattern to match. Some-         to be re-evaluated to see if a different number of repeats  allows  the
3613         times it is useful to prevent this, either to change the nature of  the         rest  of  the pattern to match. Sometimes it is useful to prevent this,
3614         match,  or  to  cause it fail earlier than it otherwise might, when the         either to change the nature of the match, or to cause it  fail  earlier
3615         author of the pattern knows there is no point in carrying on.         than  it otherwise might, when the author of the pattern knows there is
3616           no point in carrying on.
3617    
3618         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider, for example, the pattern \d+foo when applied to  the  subject
3619         line         line
# Line 2700  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3627  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3627         the  means for specifying that once a subpattern has matched, it is not         the  means for specifying that once a subpattern has matched, it is not
3628         to be re-evaluated in this way.         to be re-evaluated in this way.
3629    
3630         If we use atomic grouping for the previous example, the  matcher  would         If we use atomic grouping for the previous example, the  matcher  gives
3631         give up immediately on failing to match "foo" the first time. The nota-         up  immediately  on failing to match "foo" the first time. The notation
3632         tion is a kind of special parenthesis, starting with  (?>  as  in  this         is a kind of special parenthesis, starting with (?> as in this example:
        example:  
3633    
3634           (?>\d+)foo           (?>\d+)foo
3635    
# Line 2735  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3661  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3661         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
3662         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
3663         simpler forms of atomic group. However, there is no difference  in  the         simpler forms of atomic group. However, there is no difference  in  the
3664         meaning  or  processing  of  a possessive quantifier and the equivalent         meaning  of  a  possessive  quantifier and the equivalent atomic group,
3665         atomic group.         though there may be a performance  difference;  possessive  quantifiers
3666           should be slightly faster.
3667         The possessive quantifier syntax is an extension to the Perl syntax. It  
3668         originates in Sun's Java package.         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
3669           tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first