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revision 75 by nigel, Sat Feb 24 21:40:37 2007 UTC revision 99 by ph10, Tue Mar 6 12:27:42 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.
216         Phone: +44 1223 334714  
217           Putting an actual email address here seems to have been a spam  magnet,
218  Last updated: 09 September 2004         so I've taken it away. If you want to email me, use my initial and sur-
219  Copyright (c) 1997-2004 University of Cambridge.         name, separated by a dot, at the domain ucs.cam.ac.uk.
220  -----------------------------------------------------------------------------  
221    
222  PCRE(3)                                                                PCRE(3)  REVISION
223    
224           Last updated: 06 March 2007
225           Copyright (c) 1997-2007 University of Cambridge.
226    ------------------------------------------------------------------------------
227    
228    
229    PCREBUILD(3)                                                      PCREBUILD(3)
230    
231    
232  NAME  NAME
233         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
234    
235    
236  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
237    
238         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 252  PCRE BUILD-TIME OPTIONS
252         not described.         not described.
253    
254    
255    C++ SUPPORT
256    
257           By default, the configure script will search for a C++ compiler and C++
258           header files. If it finds them, it automatically builds the C++ wrapper
259           library for PCRE. You can disable this by adding
260    
261             --disable-cpp
262    
263           to the configure command.
264    
265    
266  UTF-8 SUPPORT  UTF-8 SUPPORT
267    
268         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 296  UNICODE CHARACTER PROPERTY SUPPORT
296    
297  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
298    
299         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating
300         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
301         compile PCRE to use character 13 (carriage return) instead by adding         systems. You can compile PCRE to use character 13 (carriage return, CR)
302           instead, by adding
303    
304           --enable-newline-is-cr           --enable-newline-is-cr
305    
306         to the configure command. For completeness there is  also  a  --enable-         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
307         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
308         line character.  
309           Alternatively, you can specify that line endings are to be indicated by
310           the two character sequence CRLF. If you want this, add
311    
312             --enable-newline-is-crlf
313    
314           to the configure command. There is a fourth option, specified by
315    
316             --enable-newline-is-any
317    
318           which causes PCRE to recognize any Unicode newline sequence.
319    
320           Whatever  line  ending convention is selected when PCRE is built can be
321           overridden when the library functions are called. At build time  it  is
322           conventional to use the standard for your operating system.
323    
324    
325  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
326    
327         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
328         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
329         of         of
330    
331           --disable-shared           --disable-shared
# Line 271  BUILDING SHARED AND STATIC LIBRARIES Line 337  BUILDING SHARED AND STATIC LIBRARIES
337  POSIX MALLOC USAGE  POSIX MALLOC USAGE
338    
339         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
340         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
341         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
342         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
343         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
344         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.
345         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 350  POSIX MALLOC USAGE
350         to the configure command.         to the configure command.
351    
352    
 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.  
   
   
353  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
354    
355         Within  a  compiled  pattern,  offset values are used to point from one         Within a compiled pattern, offset values are used  to  point  from  one
356         part to another (for example, from an opening parenthesis to an  alter-         part  to another (for example, from an opening parenthesis to an alter-
357         nation  metacharacter).  By default, two-byte values are used for these         nation metacharacter). By default, two-byte values are used  for  these
358         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets,  leading  to  a  maximum size for a compiled pattern of around
359         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
360         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless,  some  people do want to process enormous patterns, so it
361         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
362         adding a setting such as         adding a setting such as
363    
364           --with-link-size=3           --with-link-size=3
365    
366         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
367         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
368         additional bytes when handling them.         additional bytes when handling them.
369    
370         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
371         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
372         representation of the compiled pattern, and this changes with the  link         representation  of the compiled pattern, and this changes with the link
373         size.         size.
374    
375    
376  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
377    
378         PCRE  implements  backtracking while matching by making recursive calls         When matching with the pcre_exec() function, PCRE implements backtrack-
379         to an internal function called match(). In environments where the  size         ing  by  making recursive calls to an internal function called match().
380         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-
381         Unix environment does not usually suffer from this problem.) An  alter-         verely  limit  PCRE's operation. (The Unix environment does not usually
382         native  approach  that  uses  memory  from  the  heap to remember data,         suffer from this problem, but it may sometimes be necessary to increase
383         instead of using recursive function calls, has been implemented to work         the  maximum  stack size.  There is a discussion in the pcrestack docu-
384         round  this  problem. If you want to build a version of PCRE that works         mentation.) An alternative approach to recursion that uses memory  from
385         this way, add         the  heap  to remember data, instead of using recursive function calls,
386           has been implemented to work round the problem of limited  stack  size.
387           If you want to build a version of PCRE that works this way, add
388    
389           --disable-stack-for-recursion           --disable-stack-for-recursion
390    
391         to the configure command. With this configuration, PCRE  will  use  the         to  the  configure  command. With this configuration, PCRE will use the
392         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
393         ment functions. Separate functions are provided because  the  usage  is         ment  functions.  Separate  functions are provided because the usage is
394         very  predictable:  the  block sizes requested are always the same, and         very predictable: the block sizes requested are always  the  same,  and
395         the blocks are always freed in reverse order. A calling  program  might         the  blocks  are always freed in reverse order. A calling program might
396         be  able  to implement optimized functions that perform better than the         be able to implement optimized functions that perform better  than  the
397         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more
398         slowly when built in this way.         slowly when built in this way. This option affects only the pcre_exec()
399           function; it is not relevant for the the pcre_dfa_exec() function.
400    
401    
402    LIMITING PCRE RESOURCE USAGE
403    
404           Internally,  PCRE has a function called match(), which it calls repeat-
405           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
406           pcre_exec()  function.  By controlling the maximum number of times this
407           function may be called during a single matching operation, a limit  can
408           be  placed  on  the resources used by a single call to pcre_exec(). The
409           limit can be changed at run time, as described in the pcreapi  documen-
410           tation.  The default is 10 million, but this can be changed by adding a
411           setting such as
412    
413             --with-match-limit=500000
414    
415           to  the  configure  command.  This  setting  has  no  effect   on   the
416           pcre_dfa_exec() matching function.
417    
418           In  some  environments  it is desirable to limit the depth of recursive
419           calls of match() more strictly than the total number of calls, in order
420           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
421           for-recursion is specified) that is used. A second limit controls this;
422           it  defaults  to  the  value  that is set for --with-match-limit, which
423           imposes no additional constraints. However, you can set a  lower  limit
424           by adding, for example,
425    
426             --with-match-limit-recursion=10000
427    
428           to  the  configure  command.  This  value can also be overridden at run
429           time.
430    
431    
432  USING EBCDIC CODE  USING EBCDIC CODE
433    
434         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
435         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
436         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by
437         adding         adding
438    
439           --enable-ebcdic           --enable-ebcdic
440    
441         to the configure command.         to the configure command.
442    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
443    
444  PCRE(3)                                                                PCRE(3)  SEE ALSO
445    
446           pcreapi(3), pcre_config(3).
447    
448    
449    AUTHOR
450    
451           Philip Hazel
452           University Computing Service
453           Cambridge CB2 3QH, England.
454    
455    
456    REVISION
457    
458           Last updated: 06 March 2007
459           Copyright (c) 1997-2007 University of Cambridge.
460    ------------------------------------------------------------------------------
461    
462    
463    PCREMATCHING(3)                                                PCREMATCHING(3)
464    
465    
466    NAME
467           PCRE - Perl-compatible regular expressions
468    
469    
470    PCRE MATCHING ALGORITHMS
471    
472           This document describes the two different algorithms that are available
473           in PCRE for matching a compiled regular expression against a given sub-
474           ject  string.  The  "standard"  algorithm  is  the  one provided by the
475           pcre_exec() function.  This works in the same was  as  Perl's  matching
476           function, and provides a Perl-compatible matching operation.
477    
478           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
479           this operates in a different way, and is not  Perl-compatible.  It  has
480           advantages  and disadvantages compared with the standard algorithm, and
481           these are described below.
482    
483           When there is only one possible way in which a given subject string can
484           match  a pattern, the two algorithms give the same answer. A difference
485           arises, however, when there are multiple possibilities. For example, if
486           the pattern
487    
488             ^<.*>
489    
490           is matched against the string
491    
492             <something> <something else> <something further>
493    
494           there are three possible answers. The standard algorithm finds only one
495           of them, whereas the alternative algorithm finds all three.
496    
497    
498    REGULAR EXPRESSIONS AS TREES
499    
500           The set of strings that are matched by a regular expression can be rep-
501           resented  as  a  tree structure. An unlimited repetition in the pattern
502           makes the tree of infinite size, but it is still a tree.  Matching  the
503           pattern  to a given subject string (from a given starting point) can be
504           thought of as a search of the tree.  There are two  ways  to  search  a
505           tree:  depth-first  and  breadth-first, and these correspond to the two
506           matching algorithms provided by PCRE.
507    
508    
509    THE STANDARD MATCHING ALGORITHM
510    
511           In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-
512           sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a
513           depth-first search of the pattern tree. That is, it  proceeds  along  a
514           single path through the tree, checking that the subject matches what is
515           required. When there is a mismatch, the algorithm  tries  any  alterna-
516           tives  at  the  current point, and if they all fail, it backs up to the
517           previous branch point in the  tree,  and  tries  the  next  alternative
518           branch  at  that  level.  This often involves backing up (moving to the
519           left) in the subject string as well.  The  order  in  which  repetition
520           branches  are  tried  is controlled by the greedy or ungreedy nature of
521           the quantifier.
522    
523           If a leaf node is reached, a matching string has  been  found,  and  at
524           that  point the algorithm stops. Thus, if there is more than one possi-
525           ble match, this algorithm returns the first one that it finds.  Whether
526           this  is the shortest, the longest, or some intermediate length depends
527           on the way the greedy and ungreedy repetition quantifiers are specified
528           in the pattern.
529    
530           Because  it  ends  up  with a single path through the tree, it is rela-
531           tively straightforward for this algorithm to keep  track  of  the  sub-
532           strings  that  are  matched  by portions of the pattern in parentheses.
533           This provides support for capturing parentheses and back references.
534    
535    
536    THE ALTERNATIVE MATCHING ALGORITHM
537    
538           This algorithm conducts a breadth-first search of  the  tree.  Starting
539           from  the  first  matching  point  in the subject, it scans the subject
540           string from left to right, once, character by character, and as it does
541           this,  it remembers all the paths through the tree that represent valid
542           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
543           though  it is not implemented as a traditional finite state machine (it
544           keeps multiple states active simultaneously).
545    
546           The scan continues until either the end of the subject is  reached,  or
547           there  are  no more unterminated paths. At this point, terminated paths
548           represent the different matching possibilities (if there are none,  the
549           match  has  failed).   Thus,  if there is more than one possible match,
550           this algorithm finds all of them, and in particular, it finds the long-
551           est.  In PCRE, there is an option to stop the algorithm after the first
552           match (which is necessarily the shortest) has been found.
553    
554           Note that all the matches that are found start at the same point in the
555           subject. If the pattern
556    
557             cat(er(pillar)?)
558    
559           is  matched  against the string "the caterpillar catchment", the result
560           will be the three strings "cat", "cater", and "caterpillar" that  start
561           at the fourth character of the subject. The algorithm does not automat-
562           ically move on to find matches that start at later positions.
563    
564           There are a number of features of PCRE regular expressions that are not
565           supported by the alternative matching algorithm. They are as follows:
566    
567           1.  Because  the  algorithm  finds  all possible matches, the greedy or
568           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
569           ungreedy quantifiers are treated in exactly the same way. However, pos-
570           sessive quantifiers can make a difference when what follows could  also
571           match what is quantified, for example in a pattern like this:
572    
573             ^a++\w!
574    
575           This  pattern matches "aaab!" but not "aaa!", which would be matched by
576           a non-possessive quantifier. Similarly, if an atomic group is  present,
577           it  is matched as if it were a standalone pattern at the current point,
578           and the longest match is then "locked in" for the rest of  the  overall
579           pattern.
580    
581           2. When dealing with multiple paths through the tree simultaneously, it
582           is not straightforward to keep track of  captured  substrings  for  the
583           different  matching  possibilities,  and  PCRE's implementation of this
584           algorithm does not attempt to do this. This means that no captured sub-
585           strings are available.
586    
587           3.  Because no substrings are captured, back references within the pat-
588           tern are not supported, and cause errors if encountered.
589    
590           4. For the same reason, conditional expressions that use  a  backrefer-
591           ence  as  the  condition or test for a specific group recursion are not
592           supported.
593    
594           5. Callouts are supported, but the value of the  capture_top  field  is
595           always 1, and the value of the capture_last field is always -1.
596    
597           6.  The \C escape sequence, which (in the standard algorithm) matches a
598           single byte, even in UTF-8 mode, is not supported because the  alterna-
599           tive  algorithm  moves  through  the  subject string one character at a
600           time, for all active paths through the tree.
601    
602    
603    ADVANTAGES OF THE ALTERNATIVE ALGORITHM
604    
605           Using the alternative matching algorithm provides the following  advan-
606           tages:
607    
608           1. All possible matches (at a single point in the subject) are automat-
609           ically found, and in particular, the longest match is  found.  To  find
610           more than one match using the standard algorithm, you have to do kludgy
611           things with callouts.
612    
613           2. There is much better support for partial matching. The  restrictions
614           on  the content of the pattern that apply when using the standard algo-
615           rithm for partial matching do not apply to the  alternative  algorithm.
616           For  non-anchored patterns, the starting position of a partial match is
617           available.
618    
619           3. Because the alternative algorithm  scans  the  subject  string  just
620           once,  and  never  needs to backtrack, it is possible to pass very long
621           subject strings to the matching function in  several  pieces,  checking
622           for partial matching each time.
623    
624    
625    DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
626    
627           The alternative algorithm suffers from a number of disadvantages:
628    
629           1.  It  is  substantially  slower  than the standard algorithm. This is
630           partly because it has to search for all possible matches, but  is  also
631           because it is less susceptible to optimization.
632    
633           2. Capturing parentheses and back references are not supported.
634    
635           3. Although atomic groups are supported, their use does not provide the
636           performance advantage that it does for the standard algorithm.
637    
638    
639    AUTHOR
640    
641           Philip Hazel
642           University Computing Service
643           Cambridge CB2 3QH, England.
644    
645    
646    REVISION
647    
648           Last updated: 06 March 2007
649           Copyright (c) 1997-2007 University of Cambridge.
650    ------------------------------------------------------------------------------
651    
652    
653    PCREAPI(3)                                                          PCREAPI(3)
654    
655    
656  NAME  NAME
657         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
658    
659    
660  PCRE NATIVE API  PCRE NATIVE API
661    
662         #include <pcre.h>         #include <pcre.h>
# Line 375  PCRE NATIVE API Line 665  PCRE NATIVE API
665              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
666              const unsigned char *tableptr);              const unsigned char *tableptr);
667    
668           pcre *pcre_compile2(const char *pattern, int options,
669                int *errorcodeptr,
670                const char **errptr, int *erroffset,
671                const unsigned char *tableptr);
672    
673         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options,
674              const char **errptr);              const char **errptr);
675    
# Line 382  PCRE NATIVE API Line 677  PCRE NATIVE API
677              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
678              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
679    
680           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
681                const char *subject, int length, int startoffset,
682                int options, int *ovector, int ovecsize,
683                int *workspace, int wscount);
684    
685         int pcre_copy_named_substring(const pcre *code,         int pcre_copy_named_substring(const pcre *code,
686              const char *subject, int *ovector,              const char *subject, int *ovector,
687              int stringcount, const char *stringname,              int stringcount, const char *stringname,
# Line 399  PCRE NATIVE API Line 699  PCRE NATIVE API
699         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
700              const char *name);              const char *name);
701    
702           int pcre_get_stringtable_entries(const pcre *code,
703                const char *name, char **first, char **last);
704    
705         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
706              int stringcount, int stringnumber,              int stringcount, int stringnumber,
707              const char **stringptr);              const char **stringptr);
# Line 417  PCRE NATIVE API Line 720  PCRE NATIVE API
720    
721         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
722    
723           int pcre_refcount(pcre *code, int adjust);
724    
725         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
726    
727         char *pcre_version(void);         char *pcre_version(void);
# Line 435  PCRE NATIVE API Line 740  PCRE NATIVE API
740  PCRE API OVERVIEW  PCRE API OVERVIEW
741    
742         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
743         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
744         expression API.  These are described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
745           Both of these APIs define a set of C function calls. A C++  wrapper  is
746           distributed with PCRE. It is documented in the pcrecpp page.
747    
748         The  native  API  function  prototypes  are  defined in the header file         The  native  API  C  function prototypes are defined in the header file
749         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
750         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
751         application  that  uses  PCRE.  The  header  file  defines  the  macros         application  that  uses  PCRE.  The  header  file  defines  the  macros
752         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-
753         bers for the library.  Applications can use these  to  include  support         bers for the library.  Applications can use these  to  include  support
754         for different releases of PCRE.         for different releases of PCRE.
755    
756         The  functions  pcre_compile(),  pcre_study(), and pcre_exec() are used         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
757         for compiling and matching regular expressions. A sample  program  that         pcre_exec() are used for compiling and matching regular expressions  in
758         demonstrates  the  simplest  way  of using them is provided in the file         a  Perl-compatible  manner. A sample program that demonstrates the sim-
759         called pcredemo.c in the source distribution. The pcresample documenta-         plest way of using them is provided in the file  called  pcredemo.c  in
760         tion describes how to run it.         the  source distribution. The pcresample documentation describes how to
761           run it.
762         In  addition  to  the  main compiling and matching functions, there are  
763         convenience functions for extracting captured substrings from a matched         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
764         subject string.  They are:         ble,  is  also provided. This uses a different algorithm for the match-
765           ing. The alternative algorithm finds all possible matches (at  a  given
766           point  in  the subject), and scans the subject just once. However, this
767           algorithm does not return captured substrings. A description of the two
768           matching  algorithms and their advantages and disadvantages is given in
769           the pcrematching documentation.
770    
771           In addition to the main compiling and  matching  functions,  there  are
772           convenience functions for extracting captured substrings from a subject
773           string that is matched by pcre_exec(). They are:
774    
775           pcre_copy_substring()           pcre_copy_substring()
776           pcre_copy_named_substring()           pcre_copy_named_substring()
# Line 462  PCRE API OVERVIEW Line 778  PCRE API OVERVIEW
778           pcre_get_named_substring()           pcre_get_named_substring()
779           pcre_get_substring_list()           pcre_get_substring_list()
780           pcre_get_stringnumber()           pcre_get_stringnumber()
781             pcre_get_stringtable_entries()
782    
783         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
784         to free the memory used for extracted strings.         to free the memory used for extracted strings.
785    
786         The function pcre_maketables() is used to  build  a  set  of  character         The  function  pcre_maketables()  is  used  to build a set of character
787         tables   in  the  current  locale  for  passing  to  pcre_compile()  or         tables  in  the  current  locale   for   passing   to   pcre_compile(),
788         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
789         cialist use. Most commonly, no special tables are passed, in which case         provided for specialist use.  Most  commonly,  no  special  tables  are
790         internal tables that are generated when PCRE is built are used.         passed,  in  which case internal tables that are generated when PCRE is
791           built are used.
792    
793         The function pcre_fullinfo() is used to find out  information  about  a         The function pcre_fullinfo() is used to find out  information  about  a
794         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 796  PCRE API OVERVIEW
796         patibility.   The function pcre_version() returns a pointer to a string         patibility.   The function pcre_version() returns a pointer to a string
797         containing the version of PCRE and its date of release.         containing the version of PCRE and its date of release.
798    
799           The function pcre_refcount() maintains a  reference  count  in  a  data
800           block  containing  a compiled pattern. This is provided for the benefit
801           of object-oriented applications.
802    
803         The global variables pcre_malloc and pcre_free  initially  contain  the         The global variables pcre_malloc and pcre_free  initially  contain  the
804         entry  points  of  the  standard malloc() and free() functions, respec-         entry  points  of  the  standard malloc() and free() functions, respec-
805         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 809  PCRE API OVERVIEW
809         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
810         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
811         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
812         data,  instead  of recursive function calls. This is a non-standard way         data, instead of recursive function calls, when running the pcre_exec()
813         of building PCRE, for use in environments  that  have  limited  stacks.         function. See the pcrebuild documentation for  details  of  how  to  do
814         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-
815         Separate functions are provided so that special-purpose  external  code         ments that have limited stacks. Because of the greater  use  of  memory
816         can be used for this case. When used, these functions are always called         management,  it  runs  more  slowly. Separate functions are provided so
817         in a stack-like manner (last obtained, first  freed),  and  always  for         that special-purpose external code can be  used  for  this  case.  When
818         memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
819           obtained, first freed), and always for memory blocks of the same  size.
820           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
821           mentation.
822    
823         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
824         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
825         specified  points during a matching operation. Details are given in the         specified points during a matching operation. Details are given in  the
826         pcrecallout documentation.         pcrecallout documentation.
827    
828    
829    NEWLINES
830    
831           PCRE  supports four different conventions for indicating line breaks in
832           strings: a single CR (carriage return) character, a  single  LF  (line-
833           feed)  character,  the two-character sequence CRLF, or any Unicode new-
834           line sequence.  The Unicode newline sequences are the three  just  men-
835           tioned, plus the single characters VT (vertical tab, U+000B), FF (form-
836           feed, U+000C), NEL (next line, U+0085), LS  (line  separator,  U+2028),
837           and PS (paragraph separator, U+2029).
838    
839           Each  of  the first three conventions is used by at least one operating
840           system as its standard newline sequence. When PCRE is built, a  default
841           can  be  specified.  The default default is LF, which is the Unix stan-
842           dard. When PCRE is run, the default can be overridden,  either  when  a
843           pattern is compiled, or when it is matched.
844    
845           In the PCRE documentation the word "newline" is used to mean "the char-
846           acter or pair of characters that indicate a line break". The choice  of
847           newline  convention  affects  the  handling of the dot, circumflex, and
848           dollar metacharacters, the handling of #-comments in /x mode, and, when
849           CRLF  is a recognized line ending sequence, the match position advance-
850           ment for a non-anchored pattern. The choice of newline convention  does
851           not affect the interpretation of the \n or \r escape sequences.
852    
853    
854  MULTITHREADING  MULTITHREADING
855    
856         The PCRE functions can be used in  multi-threading  applications,  with         The  PCRE  functions  can be used in multi-threading applications, with
857         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
858         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
859         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
860    
861         The compiled form of a regular expression is not altered during  match-         The  compiled form of a regular expression is not altered during match-
862         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
863         at once.         at once.
864    
# Line 516  MULTITHREADING Line 866  MULTITHREADING
866  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
867    
868         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
869         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
870         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
871         pcreprecompile documentation.         pcreprecompile documentation.
872    
873    
# Line 525  CHECKING BUILD-TIME OPTIONS Line 875  CHECKING BUILD-TIME OPTIONS
875    
876         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
877    
878         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-
879         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
880         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
881         tures.         tures.
882    
883         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
884         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
885         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
886         available:         available:
887    
888           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
889    
890         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-
891         able; otherwise it is set to zero.         able; otherwise it is set to zero.
892    
893           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
894    
895         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
896         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
897    
898           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
899    
900         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
901         used for the newline character. It is either linefeed (10) or  carriage         sequence  that is recognized as meaning "newline". The four values that
902         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.
903         operating system.         The default should normally be the standard sequence for your operating
904           system.
905    
906           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
907    
# Line 573  CHECKING BUILD-TIME OPTIONS Line 924  CHECKING BUILD-TIME OPTIONS
924         internal matching function calls in a  pcre_exec()  execution.  Further         internal matching function calls in a  pcre_exec()  execution.  Further
925         details are given with pcre_exec() below.         details are given with pcre_exec() below.
926    
927             PCRE_CONFIG_MATCH_LIMIT_RECURSION
928    
929           The  output is an integer that gives the default limit for the depth of
930           recursion when calling the internal matching function in a  pcre_exec()
931           execution. Further details are given with pcre_exec() below.
932    
933           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
934    
935         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
936         implemented by recursive function calls that use the stack to  remember         running pcre_exec() is implemented by recursive function calls that use
937         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
938         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
939         recursive   function   calls.   In  this  case,  pcre_stack_malloc  and         on  the  heap  instead  of  recursive  function  calls.  In  this case,
940         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
941         avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
942    
943    
944  COMPILING A PATTERN  COMPILING A PATTERN
# Line 590  COMPILING A PATTERN Line 947  COMPILING A PATTERN
947              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
948              const unsigned char *tableptr);              const unsigned char *tableptr);
949    
950         The  function  pcre_compile()  is  called  to compile a pattern into an         pcre *pcre_compile2(const char *pattern, int options,
951         internal form. The pattern is a C string terminated by a  binary  zero,              int *errorcodeptr,
952         and  is  passed in the pattern argument. A pointer to a single block of              const char **errptr, int *erroffset,
953         memory that is obtained via pcre_malloc is returned. This contains  the              const unsigned char *tableptr);
954         compiled  code  and  related  data.  The  pcre  type is defined for the  
955         returned block; this is a typedef for a structure  whose  contents  are         Either of the functions pcre_compile() or pcre_compile2() can be called
956         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
957         it is no longer required.         the  two interfaces is that pcre_compile2() has an additional argument,
958           errorcodeptr, via which a numerical error code can be returned.
959    
960           The pattern is a C string terminated by a binary zero, and is passed in
961           the  pattern  argument.  A  pointer to a single block of memory that is
962           obtained via pcre_malloc is returned. This contains the  compiled  code
963           and related data. The pcre type is defined for the returned block; this
964           is a typedef for a structure whose contents are not externally defined.
965           It is up to the caller to free the memory (via pcre_free) when it is no
966           longer required.
967    
968         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
969         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
970         fully relocatable, because it may contain a copy of the tableptr  argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
971         ment, which is an address (see below).         ment, which is an address (see below).
972    
973         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
974         tion. It should be zero if  no  options  are  required.  The  available         pilation. It should be zero if no options are required.  The  available
975         options  are  described  below. Some of them, in particular, those that         options  are  described  below. Some of them, in particular, those that
976         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
977         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern  (see  the  detailed  description in the pcrepattern documenta-
978         tion). For these options, the contents of the options  argument  speci-         tion). For these options, the contents of the options  argument  speci-
979         fies  their initial settings at the start of compilation and execution.         fies  their initial settings at the start of compilation and execution.
980         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
981         at compile time.         of matching as well as at compile time.
982    
983         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
984         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
985         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-
986         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
987         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-
988         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
989           by  erroffset,  which must not be NULL. If it is, an immediate error is
990         given.         given.
991    
992           If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
993           codeptr  argument is not NULL, a non-zero error code number is returned
994           via this argument in the event of an error. This is in addition to  the
995           textual error message. Error codes and messages are listed below.
996    
997         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
998         character tables that are  built  when  PCRE  is  compiled,  using  the         character tables that are  built  when  PCRE  is  compiled,  using  the
999         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 1036  COMPILING A PATTERN
1036    
1037         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
1038         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
1039         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
1040         UTF-8 mode, case support for high-valued characters is  available  only         always understands the concept of case for characters whose values  are
1041         when PCRE is built with Unicode character property support.         less  than 128, so caseless matching is always possible. For characters
1042           with higher values, the concept of case is supported if  PCRE  is  com-
1043           piled  with Unicode property support, but not otherwise. If you want to
1044           use caseless matching for characters 128 and  above,  you  must  ensure
1045           that  PCRE  is  compiled  with Unicode property support as well as with
1046           UTF-8 support.
1047    
1048           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1049    
1050         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
1051         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
1052         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
1053         not before any  other  newlines).  The  PCRE_DOLLAR_ENDONLY  option  is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1054         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
1055         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1056    
1057           PCRE_DOTALL           PCRE_DOTALL
1058    
1059         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-
1060         acters,  including  newlines.  Without  it, newlines are excluded. This         acters, including those that indicate newline. Without it, a  dot  does
1061         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
1062         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
1063         always matches a newline character, independent of the setting of  this         by  a (?s) option setting. A negative class such as [^a] always matches
1064         option.         newline characters, independent of the setting of this option.
1065    
1066             PCRE_DUPNAMES
1067    
1068           If this bit is set, names used to identify capturing  subpatterns  need
1069           not be unique. This can be helpful for certain types of pattern when it
1070           is known that only one instance of the named  subpattern  can  ever  be
1071           matched.  There  are  more details of named subpatterns below; see also
1072           the pcrepattern documentation.
1073    
1074           PCRE_EXTENDED           PCRE_EXTENDED
1075    
1076         If  this  bit  is  set,  whitespace  data characters in the pattern are         If this bit is set, whitespace  data  characters  in  the  pattern  are
1077         totally ignored except  when  escaped  or  inside  a  character  class.         totally ignored except when escaped or inside a character class. White-
1078         Whitespace  does  not  include the VT character (code 11). In addition,         space does not include the VT character (code 11). In addition, charac-
1079         characters between an unescaped # outside a  character  class  and  the         ters between an unescaped # outside a character class and the next new-
1080         next newline character, inclusive, are also ignored. This is equivalent         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1081         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-
1082         option setting.         ting.
1083    
1084         This  option  makes  it possible to include comments inside complicated         This option makes it possible to include  comments  inside  complicated
1085         patterns.  Note, however, that this applies only  to  data  characters.         patterns.   Note,  however,  that this applies only to data characters.
1086         Whitespace   characters  may  never  appear  within  special  character         Whitespace  characters  may  never  appear  within  special   character
1087         sequences in a pattern, for  example  within  the  sequence  (?(  which         sequences  in  a  pattern,  for  example  within the sequence (?( which
1088         introduces a conditional subpattern.         introduces a conditional subpattern.
1089    
1090           PCRE_EXTRA           PCRE_EXTRA
1091    
1092         This  option  was invented in order to turn on additional functionality         This option was invented in order to turn on  additional  functionality
1093         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
1094         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
1095         letter that has no special meaning  causes  an  error,  thus  reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1096         these  combinations  for  future  expansion.  By default, as in Perl, a         these combinations for future expansion. By  default,  as  in  Perl,  a
1097         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
1098         literal.  There  are  at  present  no other features controlled by this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1099         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
1100           can also be set by a (?X) option setting within a pattern.
1101    
1102             PCRE_FIRSTLINE
1103    
1104           If this option is set, an  unanchored  pattern  is  required  to  match
1105           before  or  at  the  first  newline  in  the subject string, though the
1106           matched text may continue over the newline.
1107    
1108           PCRE_MULTILINE           PCRE_MULTILINE
1109    
# Line 723  COMPILING A PATTERN Line 1115  COMPILING A PATTERN
1115         is set). This is the same as Perl.         is set). This is the same as Perl.
1116    
1117         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"
1118         constructs match immediately following or immediately before  any  new-         constructs match immediately following or immediately  before  internal
1119         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
1120         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
1121         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-
1122         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,
1123         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1124    
1125             PCRE_NEWLINE_CR
1126             PCRE_NEWLINE_LF
1127             PCRE_NEWLINE_CRLF
1128             PCRE_NEWLINE_ANY
1129    
1130           These  options  override the default newline definition that was chosen
1131           when PCRE was built. Setting the first or the second specifies  that  a
1132           newline  is  indicated  by a single character (CR or LF, respectively).
1133           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1134           two-character  CRLF  sequence.  Setting PCRE_NEWLINE_ANY specifies that
1135           any Unicode newline sequence should be recognized. The Unicode  newline
1136           sequences  are  the three just mentioned, plus the single characters VT
1137           (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085),
1138           LS  (line separator, U+2028), and PS (paragraph separator, U+2029). The
1139           last two are recognized only in UTF-8 mode.
1140    
1141           The newline setting in the  options  word  uses  three  bits  that  are
1142           treated  as  a  number, giving eight possibilities. Currently only five
1143           are used (default plus the four values above). This means that  if  you
1144           set  more  than  one  newline option, the combination may or may not be
1145           sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is  equiva-
1146           lent  to PCRE_NEWLINE_CRLF, but other combinations yield unused numbers
1147           and cause an error.
1148    
1149           The only time that a line break is specially recognized when  compiling
1150           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1151           character class is encountered. This indicates  a  comment  that  lasts
1152           until  after the next line break sequence. In other circumstances, line
1153           break  sequences  are  treated  as  literal  data,   except   that   in
1154           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1155           and are therefore ignored.
1156    
1157           The newline option that is set at compile time becomes the default that
1158           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1159    
1160           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1161    
1162         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-
1163         theses in the pattern. Any opening parenthesis that is not followed  by         theses  in the pattern. Any opening parenthesis that is not followed by
1164         ?  behaves as if it were followed by ?: but named parentheses can still         ? behaves as if it were followed by ?: but named parentheses can  still
1165         be used for capturing (and they acquire  numbers  in  the  usual  way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1166         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1167    
1168           PCRE_UNGREEDY           PCRE_UNGREEDY
1169    
1170         This  option  inverts  the "greediness" of the quantifiers so that they         This option inverts the "greediness" of the quantifiers  so  that  they
1171         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
1172         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
1173         within the pattern.         within the pattern.
1174    
1175           PCRE_UTF8           PCRE_UTF8
1176    
1177         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
1178         strings  of  UTF-8 characters instead of single-byte character strings.         strings of UTF-8 characters instead of single-byte  character  strings.
1179         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-
1180         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
1181         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
1182         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1183    
1184           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1185    
1186         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
1187         automatically checked. If an invalid UTF-8 sequence of bytes is  found,         automatically  checked. If an invalid UTF-8 sequence of bytes is found,
1188         pcre_compile()  returns an error. If you already know that your pattern         pcre_compile() returns an error. If you already know that your  pattern
1189         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
1190         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
1191         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
1192         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
1193         pcre_exec(),  to  suppress  the  UTF-8  validity  checking  of  subject         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1194         strings.         ing of subject strings.
1195    
1196    
1197    COMPILATION ERROR CODES
1198    
1199           The following table lists the error  codes  than  may  be  returned  by
1200           pcre_compile2(),  along with the error messages that may be returned by
1201           both compiling functions. As PCRE has developed, some error codes  have
1202           fallen out of use. To avoid confusion, they have not been re-used.
1203    
1204              0  no error
1205              1  \ at end of pattern
1206              2  \c at end of pattern
1207              3  unrecognized character follows \
1208              4  numbers out of order in {} quantifier
1209              5  number too big in {} quantifier
1210              6  missing terminating ] for character class
1211              7  invalid escape sequence in character class
1212              8  range out of order in character class
1213              9  nothing to repeat
1214             10  [this code is not in use]
1215             11  internal error: unexpected repeat
1216             12  unrecognized character after (?
1217             13  POSIX named classes are supported only within a class
1218             14  missing )
1219             15  reference to non-existent subpattern
1220             16  erroffset passed as NULL
1221             17  unknown option bit(s) set
1222             18  missing ) after comment
1223             19  [this code is not in use]
1224             20  regular expression too large
1225             21  failed to get memory
1226             22  unmatched parentheses
1227             23  internal error: code overflow
1228             24  unrecognized character after (?<
1229             25  lookbehind assertion is not fixed length
1230             26  malformed number or name after (?(
1231             27  conditional group contains more than two branches
1232             28  assertion expected after (?(
1233             29  (?R or (?digits must be followed by )
1234             30  unknown POSIX class name
1235             31  POSIX collating elements are not supported
1236             32  this version of PCRE is not compiled with PCRE_UTF8 support
1237             33  [this code is not in use]
1238             34  character value in \x{...} sequence is too large
1239             35  invalid condition (?(0)
1240             36  \C not allowed in lookbehind assertion
1241             37  PCRE does not support \L, \l, \N, \U, or \u
1242             38  number after (?C is > 255
1243             39  closing ) for (?C expected
1244             40  recursive call could loop indefinitely
1245             41  unrecognized character after (?P
1246             42  syntax error in subpattern name (missing terminator)
1247             43  two named subpatterns have the same name
1248             44  invalid UTF-8 string
1249             45  support for \P, \p, and \X has not been compiled
1250             46  malformed \P or \p sequence
1251             47  unknown property name after \P or \p
1252             48  subpattern name is too long (maximum 32 characters)
1253             49  too many named subpatterns (maximum 10,000)
1254             50  repeated subpattern is too long
1255             51  octal value is greater than \377 (not in UTF-8 mode)
1256             52  internal error: overran compiling workspace
1257             53   internal  error:  previously-checked  referenced  subpattern not
1258           found
1259             54  DEFINE group contains more than one branch
1260             55  repeating a DEFINE group is not allowed
1261             56  inconsistent NEWLINE options"
1262    
1263    
1264  STUDYING A PATTERN  STUDYING A PATTERN
1265    
1266         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1267              const char **errptr);              const char **errptr);
1268    
1269         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
1270         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
1271         matching.  The function pcre_study() takes a pointer to a compiled pat-         matching. The function pcre_study() takes a pointer to a compiled  pat-
1272         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1273         information  that  will  help speed up matching, pcre_study() returns a         information that will help speed up matching,  pcre_study()  returns  a
1274         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
1275         the results of the study.         the results of the study.
1276    
1277         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1278         pcre_exec(). However, a pcre_extra block  also  contains  other  fields         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1279         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
1280         described below in the section on matching a pattern.         described below in the section on matching a pattern.
1281    
1282         If studying the pattern does not produce  any  additional  information,         If  studying  the  pattern  does not produce any additional information
1283         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1284         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
1285         its own pcre_extra block.         its own pcre_extra block.
1286    
1287         The  second  argument of pcre_study() contains option bits. At present,         The second argument of pcre_study() contains option bits.  At  present,
1288         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1289    
1290         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.
1291         If  studying  succeeds  (even  if no data is returned), the variable it         If studying succeeds (even if no data is  returned),  the  variable  it
1292         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
1293         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
1294         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
1295           after calling pcre_study(), to be sure that it has run successfully.
1296    
1297         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1298    
# Line 815  STUDYING A PATTERN Line 1310  STUDYING A PATTERN
1310  LOCALE SUPPORT  LOCALE SUPPORT
1311    
1312         PCRE handles caseless matching, and determines whether  characters  are         PCRE handles caseless matching, and determines whether  characters  are
1313         letters,  digits, or whatever, by reference to a set of tables, indexed         letters  digits,  or whatever, by reference to a set of tables, indexed
1314         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
1315         characters  with  codes  less than 128. Higher-valued codes never match         characters  with  codes  less than 128. Higher-valued codes never match
1316         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
1317         with Unicode character property support.)         with  Unicode  character property support. The use of locales with Uni-
1318           code is discouraged.
1319    
1320         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
1321         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
1322         NULL,  and  is  sufficient for many applications. An alternative set of         NULL, and is sufficient for many applications. An  alternative  set  of
1323         tables can, however, be supplied. These may be created in  a  different         tables  can,  however, be supplied. These may be created in a different
1324         locale  from the default. As more and more applications change to using         locale from the default. As more and more applications change to  using
1325         Unicode, the need for this locale support is expected to die away.         Unicode, the need for this locale support is expected to die away.
1326    
1327         External tables are built by calling  the  pcre_maketables()  function,         External  tables  are  built by calling the pcre_maketables() function,
1328         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
1329         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
1330         example,  to  build  and use tables that are appropriate for the French         example, to build and use tables that are appropriate  for  the  French
1331         locale (where accented characters with  values  greater  than  128  are         locale  (where  accented  characters  with  values greater than 128 are
1332         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1333    
1334           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1335           tables = pcre_maketables();           tables = pcre_maketables();
1336           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1337    
1338         When  pcre_maketables()  runs,  the  tables are built in memory that is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1339         obtained via pcre_malloc. It is the caller's responsibility  to  ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1340         that  the memory containing the tables remains available for as long as         that the memory containing the tables remains available for as long  as
1341         it is needed.         it is needed.
1342    
1343         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
1344         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()
1345         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-
1346         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1347         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1348    
1349         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
1350         the  internal  tables)  to  pcre_exec(). Although not intended for this         the internal tables) to pcre_exec(). Although  not  intended  for  this
1351         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
1352         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
1353         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1354    
# Line 862  INFORMATION ABOUT A PATTERN Line 1358  INFORMATION ABOUT A PATTERN
1358         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1359              int what, void *where);              int what, void *where);
1360    
1361         The pcre_fullinfo() function returns information about a compiled  pat-         The  pcre_fullinfo() function returns information about a compiled pat-
1362         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1363         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1364    
1365         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1366         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
1367         the pattern was not studied. The third argument specifies  which  piece         the  pattern  was not studied. The third argument specifies which piece
1368         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
1369         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
1370         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1371    
1372           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 878  INFORMATION ABOUT A PATTERN Line 1374  INFORMATION ABOUT A PATTERN
1374           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1375           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1376    
1377         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
1378         an simple check against passing an arbitrary memory pointer. Here is  a         an  simple check against passing an arbitrary memory pointer. Here is a
1379         typical  call  of pcre_fullinfo(), to obtain the length of the compiled         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1380         pattern:         pattern:
1381    
1382           int rc;           int rc;
1383           unsigned long int length;           size_t length;
1384           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1385             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1386             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1387             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1388             &length);         /* where to put the data */             &length);         /* where to put the data */
1389    
1390         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
1391         are as follows:         are as follows:
1392    
1393           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1394    
1395         Return  the  number  of  the highest back reference in the pattern. The         Return the number of the highest back reference  in  the  pattern.  The
1396         fourth argument should point to an int variable. Zero  is  returned  if         fourth  argument  should  point to an int variable. Zero is returned if
1397         there are no back references.         there are no back references.
1398    
1399           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1400    
1401         Return  the  number of capturing subpatterns in the pattern. The fourth         Return the number of capturing subpatterns in the pattern.  The  fourth
1402         argument should point to an int variable.         argument should point to an int variable.
1403    
1404           PCRE_INFO_DEFAULTTABLES           PCRE_INFO_DEFAULT_TABLES
1405    
1406         Return a pointer to the internal default character tables within  PCRE.         Return  a pointer to the internal default character tables within PCRE.
1407         The  fourth  argument should point to an unsigned char * variable. This         The fourth argument should point to an unsigned char *  variable.  This
1408         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1409         tion.  External  callers  can  cause PCRE to use its internal tables by         tion. External callers can cause PCRE to use  its  internal  tables  by
1410         passing a NULL table pointer.         passing a NULL table pointer.
1411    
1412           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1413    
1414         Return information about the first byte of any matched  string,  for  a         Return  information  about  the first byte of any matched string, for a
1415         non-anchored    pattern.    (This    option    used    to   be   called         non-anchored pattern. The fourth argument should point to an int  vari-
1416         PCRE_INFO_FIRSTCHAR; the old name is  still  recognized  for  backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1417         compatibility.)         is still recognized for backwards compatibility.)
1418    
1419         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
1420         (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  
1421    
1422         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1423         branch starts with "^", or         branch starts with "^", or
# Line 958  INFORMATION ABOUT A PATTERN Line 1453  INFORMATION ABOUT A PATTERN
1453    
1454         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1455         ses. The names are just an additional way of identifying the  parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1456         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1457         pcre_get_named_substring() is provided  for  extracting  an  individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1458         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
1459         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
1460         the  correct  pointers in the output vector (described with pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1461         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
1462         which is described by these three values.         described by these three values.
1463    
1464         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
1465         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 1469  INFORMATION ABOUT A PATTERN
1469         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-
1470         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-
1471         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1472         For  example,  consider  the following pattern (assume PCRE_EXTENDED is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1473         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1474           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1475           ignored):
1476    
1477           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1478           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1479    
1480         There are four named subpatterns, so the table has  four  entries,  and         There are four named subpatterns, so the table has  four  entries,  and
1481         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 1488  INFORMATION ABOUT A PATTERN
1488           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1489    
1490         When  writing  code  to  extract  data from named subpatterns using the         When  writing  code  to  extract  data from named subpatterns using the
1491         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
1492         be different for each compiled pattern.         to be different for each compiled pattern.
1493    
1494           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1495    
# Line 1051  OBSOLETE INFO FUNCTION Line 1548  OBSOLETE INFO FUNCTION
1548         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1549    
1550    
1551  MATCHING A PATTERN  REFERENCE COUNTS
1552    
1553           int pcre_refcount(pcre *code, int adjust);
1554    
1555           The  pcre_refcount()  function is used to maintain a reference count in
1556           the data block that contains a compiled pattern. It is provided for the
1557           benefit  of  applications  that  operate  in an object-oriented manner,
1558           where different parts of the application may be using the same compiled
1559           pattern, but you want to free the block when they are all done.
1560    
1561           When a pattern is compiled, the reference count field is initialized to
1562           zero.  It is changed only by calling this function, whose action is  to
1563           add  the  adjust  value  (which may be positive or negative) to it. The
1564           yield of the function is the new value. However, the value of the count
1565           is  constrained to lie between 0 and 65535, inclusive. If the new value
1566           is outside these limits, it is forced to the appropriate limit value.
1567    
1568           Except when it is zero, the reference count is not correctly  preserved
1569           if  a  pattern  is  compiled on one host and then transferred to a host
1570           whose byte-order is different. (This seems a highly unlikely scenario.)
1571    
1572    
1573    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1574    
1575         int pcre_exec(const pcre *code, const pcre_extra *extra,         int pcre_exec(const pcre *code, const pcre_extra *extra,
1576              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
# Line 1060  MATCHING A PATTERN Line 1579  MATCHING A PATTERN
1579         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
1580         compiled pattern, which is passed in the code argument. If the  pattern         compiled pattern, which is passed in the code argument. If the  pattern
1581         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
1582         argument.         argument. This function is the main matching facility of  the  library,
1583           and it operates in a Perl-like manner. For specialist use there is also
1584           an alternative matching function, which is described below in the  sec-
1585           tion about the pcre_dfa_exec() function.
1586    
1587         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1588         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1589         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
1590         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1591         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1592    
1593         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 1602  MATCHING A PATTERN
1602             0,              /* start at offset 0 in the subject */             0,              /* start at offset 0 in the subject */
1603             0,              /* default options */             0,              /* default options */
1604             ovector,        /* vector of integers for substring information */             ovector,        /* vector of integers for substring information */
1605             30);            /* number of elements in the vector  (NOT  size  in             30);            /* number of elements (NOT size in bytes) */
        bytes) */  
1606    
1607     Extra data for pcre_exec()     Extra data for pcre_exec()
1608    
1609         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
1610         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
1611         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-
1612         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
1613         lows:         fields (not necessarily in this order):
1614    
1615           unsigned long int flags;           unsigned long int flags;
1616           void *study_data;           void *study_data;
1617           unsigned long int match_limit;           unsigned long int match_limit;
1618             unsigned long int match_limit_recursion;
1619           void *callout_data;           void *callout_data;
1620           const unsigned char *tables;           const unsigned char *tables;
1621    
# Line 1102  MATCHING A PATTERN Line 1624  MATCHING A PATTERN
1624    
1625           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1626           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1627             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1628           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1629           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1630    
# Line 1118  MATCHING A PATTERN Line 1641  MATCHING A PATTERN
1641         repeats.         repeats.
1642    
1643         Internally, PCRE uses a function called match() which it calls  repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1644         edly  (sometimes  recursively).  The  limit is imposed on the number of         edly  (sometimes  recursively). The limit set by match_limit is imposed
1645         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
1646         limiting  the amount of recursion and backtracking that can take place.         has  the  effect  of  limiting the amount of backtracking that can take
1647         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
1648         position in the subject string.         for each position in the subject string.
1649    
1650         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
1651         default default is 10 million, which handles all but the  most  extreme         default default is 10 million, which handles all but the  most  extreme
1652         cases.  You  can  reduce  the  default  by  suppling pcre_exec() with a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1653         pcre_extra block in which match_limit is set to a  smaller  value,  and         pcre_extra    block    in    which    match_limit    is    set,     and
1654         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
1655         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1656    
1657           The match_limit_recursion field is similar to match_limit, but  instead
1658           of limiting the total number of times that match() is called, it limits
1659           the depth of recursion. The recursion depth is a  smaller  number  than
1660           the  total number of calls, because not all calls to match() are recur-
1661           sive.  This limit is of use only if it is set smaller than match_limit.
1662    
1663           Limiting  the  recursion  depth  limits the amount of stack that can be
1664           used, or, when PCRE has been compiled to use memory on the heap instead
1665           of the stack, the amount of heap memory that can be used.
1666    
1667           The  default  value  for  match_limit_recursion can be set when PCRE is
1668           built; the default default  is  the  same  value  as  the  default  for
1669           match_limit.  You can override the default by suppling pcre_exec() with
1670           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1671           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1672           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1673    
1674         The pcre_callout field is used in conjunction with the  "callout"  fea-         The pcre_callout field is used in conjunction with the  "callout"  fea-
1675         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1676    
# Line 1148  MATCHING A PATTERN Line 1688  MATCHING A PATTERN
1688     Option bits for pcre_exec()     Option bits for pcre_exec()
1689    
1690         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.
1691         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,
1692         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1693           PCRE_PARTIAL.
1694    
1695           PCRE_ANCHORED           PCRE_ANCHORED
1696    
1697         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1698         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1699         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
1700         unachored at matching time.         unachored at matching time.
1701    
1702             PCRE_NEWLINE_CR
1703             PCRE_NEWLINE_LF
1704             PCRE_NEWLINE_CRLF
1705             PCRE_NEWLINE_ANY
1706    
1707           These options override  the  newline  definition  that  was  chosen  or
1708           defaulted  when the pattern was compiled. For details, see the descrip-
1709           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1710           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1711           ters. It may also alter the way the match position is advanced after  a
1712           match  failure  for  an  unanchored  pattern. When PCRE_NEWLINE_CRLF or
1713           PCRE_NEWLINE_ANY is set, and a match attempt  fails  when  the  current
1714           position  is  at a CRLF sequence, the match position is advanced by two
1715           characters instead of one, in other words, to after the CRLF.
1716    
1717           PCRE_NOTBOL           PCRE_NOTBOL
1718    
1719         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1720         the beginning of a line, so the  circumflex  metacharacter  should  not         the  beginning  of  a  line, so the circumflex metacharacter should not
1721         match  before it. Setting this without PCRE_MULTILINE (at compile time)         match before it. Setting this without PCRE_MULTILINE (at compile  time)
1722         causes  circumflex  never  to  match.  This  option  affects  only  the         causes  circumflex  never to match. This option affects only the behav-
1723         behaviour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1724    
1725           PCRE_NOTEOL           PCRE_NOTEOL
1726    
1727         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
1728         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
1729         in  multiline mode) a newline immediately before it. Setting this with-         in multiline mode) a newline immediately before it. Setting this  with-
1730         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1731         option  affects only the behaviour of the dollar metacharacter. It does         option affects only the behaviour of the dollar metacharacter. It  does
1732         not affect \Z or \z.         not affect \Z or \z.
1733    
1734           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1735    
1736         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
1737         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
1738         the alternatives match the empty string, the entire  match  fails.  For         the  alternatives  match  the empty string, the entire match fails. For
1739         example, if the pattern         example, if the pattern
1740    
1741           a?b?           a?b?
1742    
1743         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
1744         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
1745         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-
1746         rences of "a" or "b".         rences of "a" or "b".
1747    
1748         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-
1749         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()
1750         function, and when using the /g modifier. It  is  possible  to  emulate         function,  and  when  using  the /g modifier. It is possible to emulate
1751         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
1752         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
1753         if  that  fails by advancing the starting offset (see below) and trying         if that fails by advancing the starting offset (see below)  and  trying
1754         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
1755         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
1756    
1757           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1758    
1759         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
1760         UTF-8 string is automatically checked when pcre_exec() is  subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
1761         called.   The  value  of  startoffset is also checked to ensure that it         called.  The value of startoffset is also checked  to  ensure  that  it
1762         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
1763         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
1764         startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is
1765         returned.         returned.
1766    
1767         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
1768         these   checks   for   performance   reasons,   you   can    set    the         these    checks    for   performance   reasons,   you   can   set   the
1769         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
1770         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
1771         making  repeated  calls  to  find  all  the matches in a single subject         making repeated calls to find all  the  matches  in  a  single  subject
1772         string. However, you should be  sure  that  the  value  of  startoffset         string.  However,  you  should  be  sure  that the value of startoffset
1773         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
1774         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
1775         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-
1776         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1777    
1778           PCRE_PARTIAL           PCRE_PARTIAL
1779    
1780         This option turns on the  partial  matching  feature.  If  the  subject         This  option  turns  on  the  partial  matching feature. If the subject
1781         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-
1782         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
1783         partially  matches  the  pattern and the failure to match occurred only         partially matches the pattern and the failure to  match  occurred  only
1784         because there were not enough subject characters), pcre_exec()  returns         because  there were not enough subject characters), pcre_exec() returns
1785         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1786         used, there are restrictions on what may appear in the  pattern.  These         used,  there  are restrictions on what may appear in the pattern. These
1787         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1788    
1789     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1790    
1791         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
1792         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
1793         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.
1794         Unlike the pattern string, the subject may contain binary  zero  bytes.         Unlike  the  pattern string, the subject may contain binary zero bytes.
1795         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
1796         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.
1797    
1798         A non-zero starting offset is useful when searching for  another  match         A  non-zero  starting offset is useful when searching for another match
1799         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-
1800         cess.  Setting startoffset differs from just passing over  a  shortened         cess.   Setting  startoffset differs from just passing over a shortened
1801         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
1802         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1803    
1804           \Biss\B           \Biss\B
1805    
1806         which finds occurrences of "iss" in the middle of  words.  (\B  matches         which  finds  occurrences  of "iss" in the middle of words. (\B matches
1807         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.)
1808         When applied to the string "Mississipi" the first call  to  pcre_exec()         When  applied  to the string "Mississipi" the first call to pcre_exec()
1809         finds  the  first  occurrence. If pcre_exec() is called again with just         finds the first occurrence. If pcre_exec() is called  again  with  just
1810         the remainder of the subject,  namely  "issipi",  it  does  not  match,         the  remainder  of  the  subject,  namely  "issipi", it does not match,
1811         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
1812         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
1813         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-
1814         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
1815         discover that it is preceded by a letter.         discover that it is preceded by a letter.
1816    
1817         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,
1818         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
1819         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
1820         subject.         subject.
1821    
1822     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
1823    
1824         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
1825         addition,  further  substrings  from  the  subject may be picked out by         addition, further substrings from the subject  may  be  picked  out  by
1826         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,
1827         this  is  called "capturing" in what follows, and the phrase "capturing         this is called "capturing" in what follows, and the  phrase  "capturing
1828         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-
1829         string.  PCRE  supports several other kinds of parenthesized subpattern         string. PCRE supports several other kinds of  parenthesized  subpattern
1830         that do not cause substrings to be captured.         that do not cause substrings to be captured.
1831    
1832         Captured substrings are returned to the caller via a vector of  integer         Captured  substrings are returned to the caller via a vector of integer
1833         offsets  whose  address is passed in ovector. The number of elements in         offsets whose address is passed in ovector. The number of  elements  in
1834         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.
1835         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
1836    
1837         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-
1838         strings, each substring using a pair of integers. The  remaining  third         strings,  each  substring using a pair of integers. The remaining third
1839         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-
1840         turing subpatterns, and is not available for passing back  information.         turing  subpatterns, and is not available for passing back information.
1841         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
1842         it is not, it is rounded down.         it is not, it is rounded down.
1843    
1844         When a match is successful, information about  captured  substrings  is         When  a  match  is successful, information about captured substrings is
1845         returned  in  pairs  of integers, starting at the beginning of ovector,         returned in pairs of integers, starting at the  beginning  of  ovector,
1846         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
1847         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-
1848         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
1849         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-
1850         tor[1], identify the portion of  the  subject  string  matched  by  the         tor[1],  identify  the  portion  of  the  subject string matched by the
1851         entire  pattern.  The next pair is used for the first capturing subpat-         entire pattern. The next pair is used for the first  capturing  subpat-
1852         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
1853         pairs  that  have  been set. If there are no capturing subpatterns, the         highest numbered pair that has been set. For example, if two substrings
1854         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
1855         first pair of offsets has been set.         subpatterns, the return value from a successful match is 1,  indicating
1856           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.  
1857    
1858         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1859         of the string that it matched that is returned.         of the string that it matched that is returned.
# Line 1320  MATCHING A PATTERN Line 1867  MATCHING A PATTERN
1867         substrings, PCRE has to get additional memory for use during  matching.         substrings, PCRE has to get additional memory for use during  matching.
1868         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1869    
1870         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
1871         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
1872         that  will  allow for n captured substrings, in addition to the offsets         ovector  that  will allow for n captured substrings, in addition to the
1873         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.
1874    
1875           It is possible for capturing subpattern number n+1 to match  some  part
1876           of the subject when subpattern n has not been used at all. For example,
1877           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1878           return from the function is 4, and subpatterns 1 and 3 are matched, but
1879           2 is not. When this happens, both values in  the  offset  pairs  corre-
1880           sponding to unused subpatterns are set to -1.
1881    
1882           Offset  values  that correspond to unused subpatterns at the end of the
1883           expression are also set to -1. For example,  if  the  string  "abc"  is
1884           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1885           matched. The return from the function is 2, because  the  highest  used
1886           capturing subpattern number is 1. However, you can refer to the offsets
1887           for the second and third capturing subpatterns if  you  wish  (assuming
1888           the vector is large enough, of course).
1889    
1890           Some  convenience  functions  are  provided for extracting the captured
1891           substrings as separate strings. These are described below.
1892    
1893     Return values from pcre_exec()     Error return values from pcre_exec()
1894    
1895         If pcre_exec() fails, it returns a negative number. The  following  are         If pcre_exec() fails, it returns a negative number. The  following  are
1896         defined in the header file:         defined in the header file:
# Line 1351  MATCHING A PATTERN Line 1916  MATCHING A PATTERN
1916         an  environment  with the other endianness. This is the error that PCRE         an  environment  with the other endianness. This is the error that PCRE
1917         gives when the magic number is not present.         gives when the magic number is not present.
1918    
1919           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1920    
1921         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1922         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 1938  MATCHING A PATTERN
1938    
1939           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
1940    
1941         The recursion and backtracking limit, as specified by  the  match_limit         The backtracking limit, as specified by  the  match_limit  field  in  a
1942         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         pcre_extra  structure  (or  defaulted) was reached. See the description
1943         description above.         above.
1944    
1945           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
1946    
# Line 1394  MATCHING A PATTERN Line 1959  MATCHING A PATTERN
1959         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-
1960         ter.         ter.
1961    
1962           PCRE_ERROR_PARTIAL (-12)           PCRE_ERROR_PARTIAL        (-12)
1963    
1964         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
1965         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
1966    
1967           PCRE_ERROR_BAD_PARTIAL (-13)           PCRE_ERROR_BADPARTIAL     (-13)
1968    
1969         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
1970         items  that are not supported for partial matching. See the pcrepartial         items  that are not supported for partial matching. See the pcrepartial
1971         documentation for details of partial matching.         documentation for details of partial matching.
1972    
1973           PCRE_ERROR_INTERNAL (-14)           PCRE_ERROR_INTERNAL       (-14)
1974    
1975         An unexpected internal error has occurred. This error could  be  caused         An unexpected internal error has occurred. This error could  be  caused
1976         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
1977    
1978           PCRE_ERROR_BADCOUNT (-15)           PCRE_ERROR_BADCOUNT       (-15)
1979    
1980         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.
1981    
1982             PCRE_ERROR_RECURSIONLIMIT (-21)
1983    
1984           The internal recursion limit, as specified by the match_limit_recursion
1985           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
1986           description above.
1987    
1988             PCRE_ERROR_NULLWSLIMIT    (-22)
1989    
1990           When a group that can match an empty  substring  is  repeated  with  an
1991           unbounded  upper  limit, the subject position at the start of the group
1992           must be remembered, so that a test for an empty string can be made when
1993           the  end  of the group is reached. Some workspace is required for this;
1994           if it runs out, this error is given.
1995    
1996             PCRE_ERROR_BADNEWLINE     (-23)
1997    
1998           An invalid combination of PCRE_NEWLINE_xxx options was given.
1999    
2000           Error numbers -16 to -20 are not used by pcre_exec().
2001    
2002    
2003  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2004    
# Line 1434  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2019  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2019         string_list()  are  provided for extracting captured substrings as new,         string_list()  are  provided for extracting captured substrings as new,
2020         separate, zero-terminated strings. These functions identify  substrings         separate, zero-terminated strings. These functions identify  substrings
2021         by  number.  The  next section describes functions for extracting named         by  number.  The  next section describes functions for extracting named
2022         substrings. A substring  that  contains  a  binary  zero  is  correctly         substrings.
2023         extracted  and  has  a further zero added on the end, but the result is  
2024         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2025           a  further zero added on the end, but the result is not, of course, a C
2026           string.  However, you can process such a string  by  referring  to  the
2027           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2028           string().  Unfortunately, the interface to pcre_get_substring_list() is
2029           not  adequate for handling strings containing binary zeros, because the
2030           end of the final string is not independently indicated.
2031    
2032         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-
2033         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 2047  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2047         buffersize,  while  for  pcre_get_substring()  a new block of memory is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2048         obtained via pcre_malloc, and its address is  returned  via  stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2049         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
2050         the terminating zero, or one of         the terminating zero, or one of these error codes:
2051    
2052           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2053    
# Line 1472  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2063  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2063         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
2064         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
2065         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
2066         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
2067           error code
2068    
2069           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2070    
2071         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2072    
2073         When any of these functions encounter a substring that is unset,  which         When  any of these functions encounter a substring that is unset, which
2074         can  happen  when  capturing subpattern number n+1 matches some part of         can happen when capturing subpattern number n+1 matches  some  part  of
2075         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
2076         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2077         string by inspecting the appropriate offset in ovector, which is  nega-         string  by inspecting the appropriate offset in ovector, which is nega-
2078         tive for unset substrings.         tive for unset substrings.
2079    
2080         The  two convenience functions pcre_free_substring() and pcre_free_sub-         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2081         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
2082         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2083         tively. They do nothing more than  call  the  function  pointed  to  by         tively.  They  do  nothing  more  than  call the function pointed to by
2084         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.
2085         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-
2086         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2087         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-
2088         provided.         vided.
2089    
2090    
2091  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
# Line 1511  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2103  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2103              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2104              const char **stringptr);              const char **stringptr);
2105    
2106         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-
2107         ber.  For example, for this pattern         ber.  For example, for this pattern
2108    
2109           (a+)b(?<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2110    
2111         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
2112         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
2113         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-
2114         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
2115         there is no subpattern of that name.         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2116           subpattern of that name.
2117    
2118         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
2119         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 2134  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2134         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2135         ate.         ate.
2136    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
2137    
2138  PCRE(3)                                                                PCRE(3)  DUPLICATE SUBPATTERN NAMES
2139    
2140           int pcre_get_stringtable_entries(const pcre *code,
2141                const char *name, char **first, char **last);
2142    
2143           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2144           subpatterns are not required to  be  unique.  Normally,  patterns  with
2145           duplicate  names  are such that in any one match, only one of the named
2146           subpatterns participates. An example is shown in the pcrepattern  docu-
2147           mentation. When duplicates are present, pcre_copy_named_substring() and
2148           pcre_get_named_substring() return the first substring corresponding  to
2149           the  given  name  that  is  set.  If  none  are set, an empty string is
2150           returned.  The pcre_get_stringnumber() function returns one of the num-
2151           bers  that are associated with the name, but it is not defined which it
2152           is.
2153    
2154           If you want to get full details of all captured substrings for a  given
2155           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2156           first argument is the compiled pattern, and the second is the name. The
2157           third  and  fourth  are  pointers to variables which are updated by the
2158           function. After it has run, they point to the first and last entries in
2159           the  name-to-number  table  for  the  given  name.  The function itself
2160           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2161           there  are none. The format of the table is described above in the sec-
2162           tion entitled Information about a  pattern.   Given  all  the  relevant
2163           entries  for the name, you can extract each of their numbers, and hence
2164           the captured data, if any.
2165    
2166    
2167    FINDING ALL POSSIBLE MATCHES
2168    
2169           The traditional matching function uses a  similar  algorithm  to  Perl,
2170           which stops when it finds the first match, starting at a given point in
2171           the subject. If you want to find all possible matches, or  the  longest
2172           possible  match,  consider using the alternative matching function (see
2173           below) instead. If you cannot use the alternative function,  but  still
2174           need  to  find all possible matches, you can kludge it up by making use
2175           of the callout facility, which is described in the pcrecallout documen-
2176           tation.
2177    
2178           What you have to do is to insert a callout right at the end of the pat-
2179           tern.  When your callout function is called, extract and save the  cur-
2180           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2181           backtrack and try other alternatives. Ultimately, when it runs  out  of
2182           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2183    
2184    
2185    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2186    
2187           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2188                const char *subject, int length, int startoffset,
2189                int options, int *ovector, int ovecsize,
2190                int *workspace, int wscount);
2191    
2192           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2193           against a compiled pattern, using a matching algorithm that  scans  the
2194           subject  string  just  once, and does not backtrack. This has different
2195           characteristics to the normal algorithm, and  is  not  compatible  with
2196           Perl.  Some  of the features of PCRE patterns are not supported. Never-
2197           theless, there are times when this kind of matching can be useful.  For
2198           a discussion of the two matching algorithms, see the pcrematching docu-
2199           mentation.
2200    
2201           The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2202           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2203           ent way, and this is described below. The other  common  arguments  are
2204           used  in  the  same way as for pcre_exec(), so their description is not
2205           repeated here.
2206    
2207           The two additional arguments provide workspace for  the  function.  The
2208           workspace  vector  should  contain at least 20 elements. It is used for
2209           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2210           workspace  will  be  needed for patterns and subjects where there are a
2211           lot of potential matches.
2212    
2213           Here is an example of a simple call to pcre_dfa_exec():
2214    
2215             int rc;
2216             int ovector[10];
2217             int wspace[20];
2218             rc = pcre_dfa_exec(
2219               re,             /* result of pcre_compile() */
2220               NULL,           /* we didn't study the pattern */
2221               "some string",  /* the subject string */
2222               11,             /* the length of the subject string */
2223               0,              /* start at offset 0 in the subject */
2224               0,              /* default options */
2225               ovector,        /* vector of integers for substring information */
2226               10,             /* number of elements (NOT size in bytes) */
2227               wspace,         /* working space vector */
2228               20);            /* number of elements (NOT size in bytes) */
2229    
2230       Option bits for pcre_dfa_exec()
2231    
2232           The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2233           zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2234           LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2235           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2236           three of these are the same as for pcre_exec(), so their description is
2237           not repeated here.
2238    
2239             PCRE_PARTIAL
2240    
2241           This  has  the  same general effect as it does for pcre_exec(), but the
2242           details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2243           pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2244           PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2245           been no complete matches, but there is still at least one matching pos-
2246           sibility. The portion of the string that provided the partial match  is
2247           set as the first matching string.
2248    
2249             PCRE_DFA_SHORTEST
2250    
2251           Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2252           stop as soon as it has found one match. Because of the way the alterna-
2253           tive  algorithm  works, this is necessarily the shortest possible match
2254           at the first possible matching point in the subject string.
2255    
2256             PCRE_DFA_RESTART
2257    
2258           When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2259           returns  a  partial  match, it is possible to call it again, with addi-
2260           tional subject characters, and have it continue with  the  same  match.
2261           The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2262           workspace and wscount options must reference the same vector as  before
2263           because  data  about  the  match so far is left in them after a partial
2264           match. There is more discussion of this  facility  in  the  pcrepartial
2265           documentation.
2266    
2267       Successful returns from pcre_dfa_exec()
2268    
2269           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2270           string in the subject. Note, however, that all the matches from one run
2271           of  the  function  start  at the same point in the subject. The shorter
2272           matches are all initial substrings of the longer matches. For  example,
2273           if the pattern
2274    
2275             <.*>
2276    
2277           is matched against the string
2278    
2279             This is <something> <something else> <something further> no more
2280    
2281           the three matched strings are
2282    
2283             <something>
2284             <something> <something else>
2285             <something> <something else> <something further>
2286    
2287           On  success,  the  yield of the function is a number greater than zero,
2288           which is the number of matched substrings.  The  substrings  themselves
2289           are  returned  in  ovector. Each string uses two elements; the first is
2290           the offset to the start, and the second is the offset to  the  end.  In
2291           fact,  all  the  strings  have the same start offset. (Space could have
2292           been saved by giving this only once, but it was decided to retain  some
2293           compatibility  with  the  way pcre_exec() returns data, even though the
2294           meaning of the strings is different.)
2295    
2296           The strings are returned in reverse order of length; that is, the long-
2297           est  matching  string is given first. If there were too many matches to
2298           fit into ovector, the yield of the function is zero, and the vector  is
2299           filled with the longest matches.
2300    
2301       Error returns from pcre_dfa_exec()
2302    
2303           The  pcre_dfa_exec()  function returns a negative number when it fails.
2304           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2305           described  above.   There are in addition the following errors that are
2306           specific to pcre_dfa_exec():
2307    
2308             PCRE_ERROR_DFA_UITEM      (-16)
2309    
2310           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2311           tern  that  it  does not support, for instance, the use of \C or a back
2312           reference.
2313    
2314             PCRE_ERROR_DFA_UCOND      (-17)
2315    
2316           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2317           that  uses  a back reference for the condition, or a test for recursion
2318           in a specific group. These are not supported.
2319    
2320             PCRE_ERROR_DFA_UMLIMIT    (-18)
2321    
2322           This return is given if pcre_dfa_exec() is called with an  extra  block
2323           that contains a setting of the match_limit field. This is not supported
2324           (it is meaningless).
2325    
2326             PCRE_ERROR_DFA_WSSIZE     (-19)
2327    
2328           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2329           workspace vector.
2330    
2331             PCRE_ERROR_DFA_RECURSE    (-20)
2332    
2333           When  a  recursive subpattern is processed, the matching function calls
2334           itself recursively, using private vectors for  ovector  and  workspace.
2335           This  error  is  given  if  the output vector is not large enough. This
2336           should be extremely rare, as a vector of size 1000 is used.
2337    
2338    
2339    SEE ALSO
2340    
2341           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2342           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2343    
2344    
2345    AUTHOR
2346    
2347           Philip Hazel
2348           University Computing Service
2349           Cambridge CB2 3QH, England.
2350    
2351    
2352    REVISION
2353    
2354           Last updated: 06 March 2007
2355           Copyright (c) 1997-2007 University of Cambridge.
2356    ------------------------------------------------------------------------------
2357    
2358    
2359    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2360    
2361    
2362  NAME  NAME
2363         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2364    
2365    
2366  PCRE CALLOUTS  PCRE CALLOUTS
2367    
2368         int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
# Line 1606  MISSING CALLOUTS Line 2417  MISSING CALLOUTS
2417  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2418    
2419         During matching, when PCRE reaches a callout point, the external  func-         During matching, when PCRE reaches a callout point, the external  func-
2420         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
2421         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
2422         following fields:         only  argument  to  the callout function is a pointer to a pcre_callout
2423           block. This structure contains the following fields:
2424    
2425           int          version;           int          version;
2426           int          callout_number;           int          callout_number;
# Line 1623  THE CALLOUT INTERFACE Line 2435  THE CALLOUT INTERFACE
2435           int          pattern_position;           int          pattern_position;
2436           int          next_item_length;           int          next_item_length;
2437    
2438         The  version  field  is an integer containing the version number of the         The version field is an integer containing the version  number  of  the
2439         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
2440         version  number  will  change  again in future if additional fields are         version number will change again in future  if  additional  fields  are
2441         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.
2442    
2443         The  callout_number  field  contains the number of the callout, as com-         The callout_number field contains the number of the  callout,  as  com-
2444         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-
2445         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2446    
2447         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
2448         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
2449         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
2450         way as for extracting substrings after a match has completed.         substrings  that  have  been  matched  so  far,  in the same way as for
2451           extracting substrings after a match has completed. For  pcre_dfa_exec()
2452           this field is not useful.
2453    
2454         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2455         were passed to pcre_exec().         were passed to pcre_exec().
2456    
2457         The  start_match  field contains the offset within the subject at which         The start_match field contains the offset within the subject  at  which
2458         the current match attempt started. If the pattern is not anchored,  the         the  current match attempt started. If the pattern is not anchored, the
2459         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
2460         pattern for different starting points in the subject.         pattern for different starting points in the subject.
2461    
2462         The current_position field contains the offset within  the  subject  of         The  current_position  field  contains the offset within the subject of
2463         the current match pointer.         the current match pointer.
2464    
2465         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
2466         numbered captured substring so far. If no  substrings  have  been  cap-         one  more than the number of the highest numbered captured substring so
2467         tured, the value of capture_top is one.         far. If no substrings have been captured, the value of  capture_top  is
2468           one.  This  is always the case when pcre_dfa_exec() is used, because it
2469         The  capture_last  field  contains the number of the most recently cap-         does not support captured substrings.
2470         tured substring. If no substrings have been captured, its value is  -1.  
2471           The capture_last field contains the number of the  most  recently  cap-
2472         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.
2473         by the caller specifically so that it can be passed back  in  callouts.         This is always the case when pcre_dfa_exec() is used.
2474         It  is  passed  in the pcre_callout field of the pcre_extra data struc-  
2475         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()
2476         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-
2477           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2478           structure.  If  no such data was passed, the value of callout_data in a
2479           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2480         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2481    
2482         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-
2483         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
2484         the pattern string.         the pattern string.
2485    
2486         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-
2487         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
2488         the pattern string. When the callout immediately precedes  an  alterna-         the  pattern  string. When the callout immediately precedes an alterna-
2489         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
2490         is zero. When the callout precedes an opening parenthesis,  the  length         is  zero.  When the callout precedes an opening parenthesis, the length
2491         is that of the entire subpattern.         is that of the entire subpattern.
2492    
2493         The  pattern_position  and next_item_length fields are intended to help         The pattern_position and next_item_length fields are intended  to  help
2494         in distinguishing between different automatic callouts, which all  have         in  distinguishing between different automatic callouts, which all have
2495         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
2496    
2497    
2498  RETURN VALUES  RETURN VALUES
2499    
2500         The  external callout function returns an integer to PCRE. If the value         The external callout function returns an integer to PCRE. If the  value
2501         is zero, matching proceeds as normal. If  the  value  is  greater  than         is  zero,  matching  proceeds  as  normal. If the value is greater than
2502         zero,  matching  fails  at  the current point, but backtracking to test         zero, matching fails at the current point, but  the  testing  of  other
2503         other matching possibilities goes ahead, just as if a lookahead  asser-         matching possibilities goes ahead, just as if a lookahead assertion had
2504         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
2505         doned, and pcre_exec() returns the negative value.         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2506    
2507         Negative  values  should  normally  be   chosen   from   the   set   of         Negative   values   should   normally   be   chosen  from  the  set  of
2508         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2509         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2510         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
2511         itself.         itself.
2512    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
2513    
2514  PCRE(3)                                                                PCRE(3)  AUTHOR
2515    
2516           Philip Hazel
2517           University Computing Service
2518           Cambridge CB2 3QH, England.
2519    
2520    
2521    REVISION
2522    
2523           Last updated: 06 March 2007
2524           Copyright (c) 1997-2007 University of Cambridge.
2525    ------------------------------------------------------------------------------
2526    
2527    
2528    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2529    
2530    
2531  NAME  NAME
2532         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2533    
2534    
2535  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2536    
2537         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2538         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2539         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2540           tures that are expected to be in the forthcoming Perl 5.10.
2541         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2542         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
2543           of  what  it does have are given in the section on UTF-8 support in the
2544           main pcre page.
2545    
2546         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2547         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 2568  DIFFERENCES BETWEEN PCRE AND PERL
2568         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
2569         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2570         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-
2571         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2572           derived properties Any and L&.
2573    
2574         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2575         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2576         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2577         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2578         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2579    
2580             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 1753  DIFFERENCES BETWEEN PCRE AND PERL Line 2584  DIFFERENCES BETWEEN PCRE AND PERL
2584             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2585             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2586    
2587         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2588         classes.         classes.
2589    
2590         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2591         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2592         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
2593         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2594         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2595    
2596         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2597         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2598         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2599    
2600           10.  There are some differences that are concerned with the settings of
2601           captured strings when part of  a  pattern  is  repeated.  For  example,
2602           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2603         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2604    
2605         10. PCRE provides some extensions to the Perl regular expression facil-         11. PCRE provides some extensions to the Perl regular expression facil-
2606         ities:         ities.   Perl  5.10  will  include new features that are not in earlier
2607           versions, some of which (such as named parentheses) have been  in  PCRE
2608           for some time. This list is with respect to Perl 5.10:
2609    
2610         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2611         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2612         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2613    
2614         (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 $
2615         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2616    
2617         (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-
2618         cial meaning is faulted.         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2619           ignored. (Perl can be made to issue a warning.)
2620    
2621         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2622         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 2628  DIFFERENCES BETWEEN PCRE AND PERL
2628         (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-
2629         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2630    
2631         (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.  
2632    
2633         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (h) The partial matching facility is PCRE-specific.
        Sun's Java package.  
2634    
2635         (j) The (R) condition, for testing recursion, is a PCRE extension.         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2636           even on different hosts that have the other endianness.
2637    
2638         (k) The callout facility is PCRE-specific.         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2639           different way and is not Perl-compatible.
2640    
        (l) The partial matching facility is PCRE-specific.  
2641    
2642         (m) Patterns compiled by PCRE can be saved and re-used at a later time,  AUTHOR
        even on different hosts that have the other endianness.  
2643    
2644  Last updated: 09 September 2004         Philip Hazel
2645  Copyright (c) 1997-2004 University of Cambridge.         University Computing Service
2646  -----------------------------------------------------------------------------         Cambridge CB2 3QH, England.
2647    
 PCRE(3)                                                                PCRE(3)  
2648    
2649    REVISION
2650    
2651           Last updated: 06 March 2007
2652           Copyright (c) 1997-2007 University of Cambridge.
2653    ------------------------------------------------------------------------------
2654    
2655    
2656    PCREPATTERN(3)                                                  PCREPATTERN(3)
2657    
2658    
2659  NAME  NAME
2660         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2661    
2662    
2663  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2664    
2665         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 2677  PCRE REGULAR EXPRESSION DETAILS
2677         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
2678         page.         page.
2679    
2680           The remainder of this document discusses the  patterns  that  are  sup-
2681           ported  by  PCRE when its main matching function, pcre_exec(), is used.
2682           From  release  6.0,   PCRE   offers   a   second   matching   function,
2683           pcre_dfa_exec(),  which matches using a different algorithm that is not
2684           Perl-compatible. The advantages and disadvantages  of  the  alternative
2685           function, and how it differs from the normal function, are discussed in
2686           the pcrematching page.
2687    
2688    
2689    CHARACTERS AND METACHARACTERS
2690    
2691         A regular expression is a pattern that is  matched  against  a  subject         A regular expression is a pattern that is  matched  against  a  subject
2692         string  from  left  to right. Most characters stand for themselves in a         string  from  left  to right. Most characters stand for themselves in a
2693         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 2695  PCRE REGULAR EXPRESSION DETAILS
2695    
2696           The quick brown fox           The quick brown fox
2697    
2698         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
2699         power of regular expressions comes from the ability to include alterna-         caseless matching is specified (the PCRE_CASELESS option), letters  are
2700         tives  and repetitions in the pattern. These are encoded in the pattern         matched  independently  of case. In UTF-8 mode, PCRE always understands
2701         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
2702         instead are interpreted in some special way.         caseless  matching  is always possible. For characters with higher val-
2703           ues, the concept of case is supported if PCRE is compiled with  Unicode
2704         There  are  two different sets of metacharacters: those that are recog-         property  support,  but  not  otherwise.   If  you want to use caseless
2705         nized anywhere in the pattern except within square brackets, and  those         matching for characters 128 and above, you must  ensure  that  PCRE  is
2706         that  are  recognized  in square brackets. Outside square brackets, the         compiled with Unicode property support as well as with UTF-8 support.
2707         metacharacters are as follows:  
2708           The  power  of  regular  expressions  comes from the ability to include
2709           alternatives and repetitions in the pattern. These are encoded  in  the
2710           pattern by the use of metacharacters, which do not stand for themselves
2711           but instead are interpreted in some special way.
2712    
2713           There are two different sets of metacharacters: those that  are  recog-
2714           nized  anywhere in the pattern except within square brackets, and those
2715           that are recognized within square brackets.  Outside  square  brackets,
2716           the metacharacters are as follows:
2717    
2718           \      general escape character with several uses           \      general escape character with several uses
2719           ^      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 2731  PCRE REGULAR EXPRESSION DETAILS
2731                  also "possessive quantifier"                  also "possessive quantifier"
2732           {      start min/max quantifier           {      start min/max quantifier
2733    
2734         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
2735         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
2736    
2737           \      general escape character           \      general escape character
# Line 1880  PCRE REGULAR EXPRESSION DETAILS Line 2741  PCRE REGULAR EXPRESSION DETAILS
2741                    syntax)                    syntax)
2742           ]      terminates the character class           ]      terminates the character class
2743    
2744         The  following sections describe the use of each of the metacharacters.         The following sections describe the use of each of the  metacharacters.
2745    
2746    
2747  BACKSLASH  BACKSLASH
2748    
2749         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
2750         a  non-alphanumeric  character,  it takes away any special meaning that         a non-alphanumeric character, it takes away any  special  meaning  that
2751         character may have. This  use  of  backslash  as  an  escape  character         character  may  have.  This  use  of  backslash  as an escape character
2752         applies both inside and outside character classes.         applies both inside and outside character classes.
2753    
2754         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
2755         pattern.  This escaping action applies whether  or  not  the  following         pattern.   This  escaping  action  applies whether or not the following
2756         character  would  otherwise be interpreted as a metacharacter, so it is         character would otherwise be interpreted as a metacharacter, so  it  is
2757         always safe to precede a non-alphanumeric  with  backslash  to  specify         always  safe  to  precede  a non-alphanumeric with backslash to specify
2758         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-
2759         slash, you write \\.         slash, you write \\.
2760    
2761         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2762         the  pattern (other than in a character class) and characters between a         the pattern (other than in a character class) and characters between  a
2763         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2764         An  escaping backslash can be used to include a whitespace or # charac-         ing backslash can be used to include a whitespace  or  #  character  as
2765         ter as part of the pattern.         part of the pattern.
2766    
2767         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-
2768         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-
2769         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
2770         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
2771         tion. Note the following examples:         tion. Note the following examples:
2772    
2773           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 1916  BACKSLASH Line 2777  BACKSLASH
2777           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
2778           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
2779    
2780         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
2781         classes.         classes.
2782    
2783     Non-printing characters     Non-printing characters
2784    
2785         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-
2786         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
2787         appearance  of non-printing characters, apart from the binary zero that         appearance of non-printing characters, apart from the binary zero  that
2788         terminates a pattern, but when a pattern  is  being  prepared  by  text         terminates  a  pattern,  but  when  a pattern is being prepared by text
2789         editing,  it  is  usually  easier  to  use  one of the following escape         editing, it is usually easier  to  use  one  of  the  following  escape
2790         sequences than the binary character it represents:         sequences than the binary character it represents:
2791    
2792           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
# Line 1937  BACKSLASH Line 2798  BACKSLASH
2798           \t        tab (hex 09)           \t        tab (hex 09)
2799           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
2800           \xhh      character with hex code hh           \xhh      character with hex code hh
2801           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
2802    
2803         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,
2804         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
2805         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;
2806         becomes hex 7B.         becomes hex 7B.
2807    
2808         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
2809         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
2810         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
2811         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,
2812         7FFFFFFF).  If  characters other than hexadecimal digits appear between         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than
2813         \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-
2814         recognized. Instead, the initial \x will be interpreted as a basic hex-         nating }, this form of escape is not recognized.  Instead, the  initial
2815         adecimal escape, with no following digits,  giving  a  character  whose         \x will be interpreted as a basic hexadecimal escape, with no following
2816         value is zero.         digits, giving a character whose value is zero.
2817    
2818         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
2819         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-
2820         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}.
2821         \x{dc}.  
2822           After \0 up to two further octal digits are read. If  there  are  fewer
2823         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
2824         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
2825         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
2826         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.  
2827    
2828         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-
2829         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
2830         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
2831         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
2832         expression,  the  entire  sequence  is  taken  as  a  back reference. A         expression, the entire  sequence  is  taken  as  a  back  reference.  A
2833         description of how this works is given later, following the  discussion         description  of how this works is given later, following the discussion
2834         of parenthesized subpatterns.         of parenthesized subpatterns.
2835    
2836         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
2837         and there have not been that many capturing subpatterns, PCRE  re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
2838         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-
2839         gle byte from the least significant 8 bits of the value. Any subsequent         erate  a data character. Any subsequent digits stand for themselves. In
2840         digits stand for themselves.  For example:         non-UTF-8 mode, the value of a character specified  in  octal  must  be
2841           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
2842           example:
2843    
2844           \040   is another way of writing a space           \040   is another way of writing a space
2845           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 1995  BACKSLASH Line 2856  BACKSLASH
2856           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
2857                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
2858    
2859         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
2860         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2861    
2862         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
2863         character (in UTF-8 mode) can be used both inside and outside character         inside and outside character classes. In addition, inside  a  character
2864         classes. In addition, inside a character  class,  the  sequence  \b  is         class,  the  sequence \b is interpreted as the backspace character (hex
2865         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"
2866         interpreted as the character "X".  Outside  a  character  class,  these         and  "X", respectively. Outside a character class, these sequences have
2867         sequences have different meanings (see below).         different meanings (see below).
2868    
2869       Absolute and relative back references
2870    
2871           The sequence \g followed by a positive or negative  number,  optionally
2872           enclosed  in  braces,  is  an absolute or relative back reference. Back
2873           references are discussed later, following the discussion  of  parenthe-
2874           sized subpatterns.
2875    
2876     Generic character types     Generic character types
2877    
2878         The  third  use of backslash is for specifying generic character types.         Another use of backslash is for specifying generic character types. The
2879         The following are always recognized:         following are always recognized:
2880    
2881           \d     any decimal digit           \d     any decimal digit
2882           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 2028  BACKSLASH Line 2896  BACKSLASH
2896    
2897         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
2898         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
2899         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
2900           "use locale;" is included in a Perl script, \s may match the VT charac-
2901           ter. In PCRE, it never does.)
2902    
2903         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
2904         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 2910  BACKSLASH
2910    
2911         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,
2912         \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-
2913         code character property support is available.         code  character  property support is available. The use of locales with
2914           Unicode is discouraged.
2915    
2916       Newline sequences
2917    
2918           Outside a character class, the escape sequence \R matches  any  Unicode
2919           newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2920           equivalent to the following:
2921    
2922             (?>\r\n|\n|\x0b|\f|\r|\x85)
2923    
2924           This is an example of an "atomic group", details  of  which  are  given
2925           below.  This particular group matches either the two-character sequence
2926           CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
2927           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2928           return, U+000D), or NEL (next line, U+0085). The two-character sequence
2929           is treated as a single unit that cannot be split.
2930    
2931           In  UTF-8  mode, two additional characters whose codepoints are greater
2932           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2933           rator,  U+2029).   Unicode character property support is not needed for
2934           these characters to be recognized.
2935    
2936           Inside a character class, \R matches the letter "R".
2937    
2938     Unicode character properties     Unicode character properties
2939    
2940         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
2941         tional escape sequences to match generic character types are  available         tional  escape  sequences  to  match character properties are available
2942         when UTF-8 mode is selected. They are:         when UTF-8 mode is selected. They are:
2943    
2944          \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
2945          \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
2946          \X       an extended Unicode sequence           \X       an extended Unicode sequence
2947    
2948         The  property  names represented by xx above are limited to the Unicode         The property names represented by xx above are limited to  the  Unicode
2949         general category properties. Each character has exactly one such  prop-         script names, the general category properties, and "Any", which matches
2950         erty,  specified  by  a two-letter abbreviation. For compatibility with         any character (including newline). Other properties such as "InMusical-
2951         Perl, negation can be specified by including a circumflex  between  the         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
2952         opening  brace  and the property name. For example, \p{^Lu} is the same         not match any characters, so always causes a match failure.
2953         as \P{Lu}.  
2954           Sets of Unicode characters are defined as belonging to certain scripts.
2955         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.
2956         properties that start with that letter. In this case, in the absence of         For example:
2957         negation, the curly brackets in the escape sequence are optional; these  
2958         two examples have the same effect:           \p{Greek}
2959             \P{Han}
2960    
2961           Those that are not part of an identified script are lumped together  as
2962           "Common". The current list of scripts is:
2963    
2964           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
2965           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
2966           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
2967           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
2968           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
2969           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
2970           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
2971           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
2972           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
2973    
2974           Each  character has exactly one general category property, specified by
2975           a two-letter abbreviation. For compatibility with Perl, negation can be
2976           specified  by  including a circumflex between the opening brace and the
2977           property name. For example, \p{^Lu} is the same as \P{Lu}.
2978    
2979           If only one letter is specified with \p or \P, it includes all the gen-
2980           eral  category properties that start with that letter. In this case, in
2981           the absence of negation, the curly brackets in the escape sequence  are
2982           optional; these two examples have the same effect:
2983    
2984           \p{L}           \p{L}
2985           \pL           \pL
2986    
2987         The following property codes are supported:         The following general category property codes are supported:
2988    
2989           C     Other           C     Other
2990           Cc    Control           Cc    Control
# Line 2113  BACKSLASH Line 3030  BACKSLASH
3030           Zp    Paragraph separator           Zp    Paragraph separator
3031           Zs    Space separator           Zs    Space separator
3032    
3033         Extended  properties such as "Greek" or "InMusicalSymbols" are not sup-         The  special property L& is also supported: it matches a character that
3034         ported by PCRE.         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
3035           classified as a modifier or "other".
3036    
3037           The  long  synonyms  for  these  properties that Perl supports (such as
3038           \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3039           any of these properties with "Is".
3040    
3041           No character that is in the Unicode table has the Cn (unassigned) prop-
3042           erty.  Instead, this property is assumed for any code point that is not
3043           in the Unicode table.
3044    
3045         Specifying caseless matching does not affect  these  escape  sequences.         Specifying  caseless  matching  does not affect these escape sequences.
3046         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3047    
3048         The  \X  escape  matches  any number of Unicode characters that form an         The \X escape matches any number of Unicode  characters  that  form  an
3049         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3050    
3051           (?>\PM\pM*)           (?>\PM\pM*)
3052    
3053         That is, it matches a character without the "mark"  property,  followed         That  is,  it matches a character without the "mark" property, followed
3054         by  zero  or  more  characters with the "mark" property, and treats the         by zero or more characters with the "mark"  property,  and  treats  the
3055         sequence as an atomic group (see below).  Characters  with  the  "mark"         sequence  as  an  atomic group (see below).  Characters with the "mark"
3056         property are typically accents that affect the preceding character.         property are typically accents that affect the preceding character.
3057    
3058         Matching  characters  by Unicode property is not fast, because PCRE has         Matching characters by Unicode property is not fast, because  PCRE  has
3059         to search a structure that contains  data  for  over  fifteen  thousand         to  search  a  structure  that  contains data for over fifteen thousand
3060         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3061         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3062    
3063     Simple assertions     Simple assertions
3064    
3065         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3066         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
3067         a match, without consuming any characters from the subject string.  The         a  match, without consuming any characters from the subject string. The
3068         use  of subpatterns for more complicated assertions is described below.         use of subpatterns for more complicated assertions is described  below.
3069         The backslashed assertions are:         The backslashed assertions are:
3070    
3071           \b     matches at a word boundary           \b     matches at a word boundary
3072           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3073           \A     matches at start of subject           \A     matches at the start of the subject
3074           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3075           \z     matches at end of subject                   also matches before a newline at the end of the subject
3076           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3077             \G     matches at the first matching position in the subject
3078    
3079         These assertions may not appear in character classes (but note that  \b         These  assertions may not appear in character classes (but note that \b
3080         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3081         acter class).         acter class).
3082    
3083         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
3084         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.
3085         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
3086         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
3087    
3088         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The \A, \Z, and \z assertions differ from  the  traditional  circumflex
3089         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
3090         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
3091         set. Thus, they are independent of multiline mode. These  three  asser-         set.  Thus,  they are independent of multiline mode. These three asser-
3092         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
3093         affect only the behaviour of the circumflex and dollar  metacharacters.         affect  only the behaviour of the circumflex and dollar metacharacters.
3094         However,  if the startoffset argument of pcre_exec() is non-zero, indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3095         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
3096         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
3097         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
3098         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.  
3099    
3100         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
3101         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 3134  CIRCUMFLEX AND DOLLAR
3134    
3135         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
3136         matching  point  is  at  the  end of the subject string, or immediately         matching  point  is  at  the  end of the subject string, or immediately
3137         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
3138         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
3139         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
3140         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.  
3141    
3142         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
3143         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
3144         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3145    
3146         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3147         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
3148         ately after and  immediately  before  an  internal  newline  character,         matches  immediately after internal newlines as well as at the start of
3149         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
3150         ject string. For example,  the  pattern  /^abc$/  matches  the  subject         string.  A dollar matches before any newlines in the string, as well as
3151         string  "def\nabc"  (where \n represents a newline character) in multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3152         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3153         in  single line mode because all branches start with ^ are not anchored         not indicate newlines.
3154         in multiline mode, and a match for  circumflex  is  possible  when  the  
3155         startoffset   argument   of  pcre_exec()  is  non-zero.  The  PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3156         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3157           Consequently, patterns that are anchored in single  line  mode  because
3158           all  branches  start  with  ^ are not anchored in multiline mode, and a
3159           match for circumflex is  possible  when  the  startoffset  argument  of
3160           pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
3161           PCRE_MULTILINE is set.
3162    
3163         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
3164         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
3165         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
3166         not.         set.
3167    
3168    
3169  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3170    
3171         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-
3172         ter in the subject, including a non-printing  character,  but  not  (by         ter in the subject string except (by default) a character  that  signi-
3173         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
3174         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3175         the  PCRE_DOTALL  option  is set, dots match newlines as well. The han-  
3176         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
3177         dollar,  the  only  relationship  being  that they both involve newline         that  character; when the two-character sequence CRLF is used, dot does
3178         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3179           matches  all characters (including isolated CRs and LFs). When any Uni-
3180           code line endings are being recognized, dot does not match CR or LF  or
3181           any of the other line ending characters.
3182    
3183           The  behaviour  of  dot  with regard to newlines can be changed. If the
3184           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3185           exception. If the two-character sequence CRLF is present in the subject
3186           string, it takes two dots to match it.
3187    
3188           The handling of dot is entirely independent of the handling of  circum-
3189           flex  and  dollar,  the  only relationship being that they both involve
3190           newlines. Dot has no special meaning in a character class.
3191    
3192    
3193  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3194    
3195         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3196         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
3197         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
3198         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-
3199         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-
3200         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3201           avoided.
3202    
3203         PCRE  does  not  allow \C to appear in lookbehind assertions (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3204         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-
3205         late the length of the lookbehind.         late the length of the lookbehind.
3206    
3207    
# Line 2267  SQUARE BRACKETS AND CHARACTER CLASSES Line 3210  SQUARE BRACKETS AND CHARACTER CLASSES
3210         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3211         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-
3212         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,
3213         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
3214         circumflex, if present) or escaped with a backslash.         circumflex, if present) or escaped with a backslash.
3215    
3216         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
3217         mode, the character may occupy more than one byte. A matched  character         mode,  the character may occupy more than one byte. A matched character
3218         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
3219         character in the class definition is a circumflex, in  which  case  the         character  in  the  class definition is a circumflex, in which case the
3220         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
3221         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
3222         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3223    
3224         For  example, the character class [aeiou] matches any lower case vowel,         For example, the character class [aeiou] matches any lower case  vowel,
3225         while [^aeiou] matches any character that is not a  lower  case  vowel.         while  [^aeiou]  matches  any character that is not a lower case vowel.
3226         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3227         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
3228         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-
3229         sumes a character from the subject string, and therefore  it  fails  if         sumes  a  character  from the subject string, and therefore it fails if
3230         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3231    
3232         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
3233         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
3234         mechanism.         mechanism.
3235    
3236         When  caseless  matching  is set, any letters in a class represent both         When caseless matching is set, any letters in a  class  represent  both
3237         their upper case and lower case versions, so for  example,  a  caseless         their  upper  case  and lower case versions, so for example, a caseless
3238         [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
3239         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
3240         PCRE  supports  the  concept of case for characters with values greater         understands the concept of case for characters whose  values  are  less
3241         than 128 only when it is compiled with Unicode property support.         than  128, so caseless matching is always possible. For characters with
3242           higher values, the concept of case is supported  if  PCRE  is  compiled
3243         The newline character is never treated in any special way in  character         with  Unicode  property support, but not otherwise.  If you want to use
3244         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         caseless matching for characters 128 and above, you  must  ensure  that
3245         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
3246           support.
3247    
3248           Characters that might indicate line breaks are  never  treated  in  any
3249           special  way  when  matching  character  classes,  whatever line-ending
3250           sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3251           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3252           of these characters.
3253    
3254         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-
3255         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 3350  VERTICAL BAR
3350    
3351         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3352         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3353         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3354         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
3355         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3356         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.  
3357    
3358    
3359  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 2432  INTERNAL OPTION SETTING Line 3381  INTERNAL OPTION SETTING
3381         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
3382         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3383    
3384         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
3385         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3386           it, so
3387    
3388           (a(?i)b)c           (a(?i)b)c
3389    
3390         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
3391         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3392         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3393         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3394         example,         example,
3395    
3396           (a(?i)b|c)           (a(?i)b|c)
3397    
3398         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3399         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3400         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3401         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3402    
3403         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3404         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
3405         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.  
3406    
3407    
3408  SUBPATTERNS  SUBPATTERNS
# Line 2468  SUBPATTERNS Line 3415  SUBPATTERNS
3415           cat(aract|erpillar|)           cat(aract|erpillar|)
3416    
3417         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3418         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3419         string.         string.
3420    
3421         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 3444  SUBPATTERNS
3444           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3445    
3446         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3447         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.  
3448    
3449         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3450         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 3466  NAMED SUBPATTERNS
3466         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3467         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3468         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3469         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3470         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3471         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3472           tax.
3473    
3474           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3475           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3476           to capturing parentheses from other parts of the pattern, such as back-
3477           references,  recursion,  and conditions, can be made by name as well as
3478           by number.
3479    
3480           Names consist of up to  32  alphanumeric  characters  and  underscores.
3481         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3482         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
3483         number  translation table from a compiled pattern. There is also a con-         function calls for extracting the name-to-number translation table from
3484         venience function for extracting a captured substring by name. For fur-         a compiled pattern. There is also a convenience function for extracting
3485         ther details see the pcreapi documentation.         a captured substring by name.
3486    
3487           By  default, a name must be unique within a pattern, but it is possible
3488           to relax this constraint by setting the PCRE_DUPNAMES option at compile
3489           time.  This  can  be useful for patterns where only one instance of the
3490           named parentheses can match. Suppose you want to match the  name  of  a
3491           weekday,  either as a 3-letter abbreviation or as the full name, and in
3492           both cases you want to extract the abbreviation. This pattern (ignoring
3493           the line breaks) does the job:
3494    
3495             (?<DN>Mon|Fri|Sun)(?:day)?|
3496             (?<DN>Tue)(?:sday)?|
3497             (?<DN>Wed)(?:nesday)?|
3498             (?<DN>Thu)(?:rsday)?|
3499             (?<DN>Sat)(?:urday)?
3500    
3501           There  are  five capturing substrings, but only one is ever set after a
3502           match.  The convenience  function  for  extracting  the  data  by  name
3503           returns  the  substring  for  the first (and in this example, the only)
3504           subpattern of that name that matched.  This  saves  searching  to  find
3505           which  numbered  subpattern  it  was. If you make a reference to a non-
3506           unique named subpattern from elsewhere in the  pattern,  the  one  that
3507           corresponds  to  the  lowest number is used. For further details of the
3508           interfaces for handling named subpatterns, see the  pcreapi  documenta-
3509           tion.
3510    
3511    
3512  REPETITION  REPETITION
# Line 2538  REPETITION Line 3515  REPETITION
3515         following items:         following items:
3516    
3517           a literal data character           a literal data character
3518           the . metacharacter           the dot metacharacter
3519           the \C escape sequence           the \C escape sequence
3520           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3521             the \R escape sequence
3522           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3523           a character class           a character class
3524           a back reference (see next section)           a back reference (see next section)
# Line 2580  REPETITION Line 3558  REPETITION
3558         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3559         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3560    
3561         For  convenience  (and  historical compatibility) the three most common         For  convenience, the three most common quantifiers have single-charac-
3562         quantifiers have single-character abbreviations:         ter abbreviations:
3563    
3564           *    is equivalent to {0,}           *    is equivalent to {0,}
3565           +    is equivalent to {1,}           +    is equivalent to {1,}
# Line 2633  REPETITION Line 3611  REPETITION
3611         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
3612         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3613    
3614         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
3615         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3616         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
3617         words, it inverts the default behaviour.         words, it inverts the default behaviour.
# Line 2644  REPETITION Line 3622  REPETITION
3622         minimum or maximum.         minimum or maximum.
3623    
3624         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-
3625         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,
3626         pattern is implicitly anchored, because whatever follows will be  tried         the pattern is implicitly anchored, because whatever  follows  will  be
3627         against  every character position in the subject string, so there is no         tried  against every character position in the subject string, so there
3628         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
3629         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
3630           by \A.
3631    
3632         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-
3633         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-
3634         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3635    
3636         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3637         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3638         backreference  elsewhere in the pattern, a match at the start may fail,         backreference elsewhere in the pattern, a match at the start  may  fail
3639         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3640    
3641           (.*)abc\1           (.*)abc\1
3642    
3643         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3644         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3645    
3646         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 3649  REPETITION
3649           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
3650    
3651         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
3652         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
3653         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
3654         tions. For example, after         tions. For example, after
3655    
3656           /(a|(b))+/           /(a|(b))+/
# Line 2681  REPETITION Line 3660  REPETITION
3660    
3661  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
3662    
3663         With both maximizing and minimizing repetition, failure of what follows         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
3664         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition,  failure  of what follows normally causes the repeated item
3665         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
3666         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,
3667         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
3668         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
3669           no point in carrying on.
3670    
3671         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider, for example, the pattern \d+foo when applied to  the  subject
3672         line         line
# Line 2700  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3680  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3680         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
3681         to be re-evaluated in this way.         to be re-evaluated in this way.
3682    
3683         If we use atomic grouping for the previous example, the  matcher  would         If we use atomic grouping for the previous example, the  matcher  gives
3684         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
3685         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:  
3686    
3687           (?>\d+)foo           (?>\d+)foo
3688    
# Line 2735  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3714  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3714         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
3715         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
3716         simpler forms of atomic group. However, there is no difference  in  the         simpler forms of atomic group. However, there is no difference  in  the
3717         meaning  or  processing  of  a possessive quantifier and the equivalent         meaning  of  a  possessive  quantifier and the equivalent atomic group,
3718         atomic group.         though there may be a performance  difference;  possessive  quantifiers
3719           should be slightly faster.
3720         The possessive quantifier syntax is an extension to the Perl syntax. It  
3721         originates in Sun's Java package.         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
3722           tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first
3723         When  a  pattern  contains an unlimited repeat inside a subpattern that         edition of his book. Mike McCloskey liked it, so implemented it when he
3724         can itself be repeated an unlimited number of  times,  the  use  of  an         built Sun's Java package, and PCRE copied it from there. It  ultimately
3725         atomic  group  is  the  only way to avoid some failing matches taking a         found its way into Perl at release 5.10.
3726    
3727           PCRE has an optimization that automatically "possessifies" certain sim-
3728           ple pattern constructs. For example, the sequence  A+B  is  treated  as
3729           A++B  because  there is no point in backtracking into a sequence of A's
3730           when B must follow.
3731    
3732           When a pattern contains an unlimited repeat inside  a  subpattern  that
3733           can  itself  be  repeated  an  unlimited number of times, the use of an
3734           atomic group is the only way to avoid some  failing  matches  taking  a
3735         very long time indeed. The pattern         very long time indeed. The pattern
3736    
3737           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
3738    
3739         matches an unlimited number of substrings that either consist  of  non-         matches  an  unlimited number of substrings that either consist of non-
3740         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it
3741         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
3742    
3743           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
3744    
3745         it takes a long time before reporting  failure.  This  is  because  the         it  takes  a  long  time  before reporting failure. This is because the
3746         string  can be divided between the internal \D+ repeat and the external         string can be divided between the internal \D+ repeat and the  external
3747         * repeat in a large number of ways, and all  have  to  be  tried.  (The         *  repeat  in  a  large  number of ways, and all have to be tried. (The
3748         example  uses  [!?]  rather than a single character at the end, because         example uses [!?] rather than a single character at  the  end,  because
3749         both PCRE and Perl have an optimization that allows  for  fast  failure         both  PCRE  and  Perl have an optimization that allows for fast failure
3750         when  a single character is used. They remember the last single charac-         when a single character is used. They remember the last single  charac-
3751         ter that is required for a match, and fail early if it is  not  present         ter  that  is required for a match, and fail early if it is not present
3752         in  the  string.)  If  the pattern is