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revision 83 by nigel, Sat Feb 24 21:41:06 2007 UTC revision 142 by ph10, Fri Mar 30 15:55:18 2007 UTC
# Line 18  INTRODUCTION Line 18  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         6.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         In addition to the Perl-compatible matching function,  PCRE  also  con-         mately with Perl 5.10, including support for UTF-8 encoded strings  and
27         tains  an  alternative matching function that matches the same compiled         Unicode general category properties. However, UTF-8 and Unicode support
28         patterns in a different way. In certain circumstances, the  alternative         has to be explicitly enabled; it is not the default. The Unicode tables
29         function  has  some  advantages.  For  a discussion of the two matching         correspond to Unicode release 5.0.0.
30         algorithms, see the pcrematching page.  
31           In  addition to the Perl-compatible matching function, PCRE contains an
32         PCRE is written in C and released as a C library. A  number  of  people         alternative matching function that matches the same  compiled  patterns
33         have  written  wrappers and interfaces of various kinds. In particular,         in  a different way. In certain circumstances, the alternative function
34         Google Inc.  have provided a comprehensive C++  wrapper.  This  is  now         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         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         of  this  interface.  Other  people's contributions can be found in the
42         Contrib directory at the primary FTP site, which is:         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         The  library  contains  a number of undocumented internal functions and
58         data  tables  that  are  used by more than one of the exported external         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.         functions,  but  which  are  not  intended for use by external callers.
60         Their  names  all begin with "_pcre_", which hopefully will not provoke         Their names all begin with "_pcre_", which hopefully will  not  provoke
61         any name clashes. In some environments, it is possible to control which         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         external symbols are exported when a shared library is  built,  and  in
63         these cases the undocumented symbols are not exported.         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
# Line 81  USER DOCUMENTATION Line 86  USER DOCUMENTATION
86           pcreposix         the POSIX-compatible C 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 C 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.
        There is no limit to the number of non-capturing subpatterns,  but  the  
        maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,  
        including capturing subpatterns, assertions, and other types of subpat-  
        tern, is 200.  
112    
113         The  maximum  length of a subject string is the largest positive number         There is no limit to the number of parenthesized subpatterns, but there
114         that an integer variable can hold. However, when using the  traditional         can be no more than 65535 capturing subpatterns.
115    
116           The maximum length of name for a named subpattern is 32 characters, and
117           the maximum number of named subpatterns is 10000.
118    
119           The maximum length of a subject string is the largest  positive  number
120           that  an integer variable can hold. However, when using the traditional
121         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
122         inite repetition.  This means that the available stack space may  limit         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.         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
128    
129         From release 3.3, PCRE has  had  some  support  for  character  strings         From  release  3.3,  PCRE  has  had  some support for character strings
130         encoded  in the UTF-8 format. For release 4.0 this was greatly extended         encoded in the UTF-8 format. For release 4.0 this was greatly  extended
131         to cover most common requirements, and in release 5.0  additional  sup-         to  cover  most common requirements, and in release 5.0 additional sup-
132         port for Unicode general category properties was added.         port for Unicode general category properties was added.
133    
134         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         In order process UTF-8 strings, you must build PCRE  to  include  UTF-8
135         support in the code, and, in addition,  you  must  call  pcre_compile()         support  in  the  code,  and, in addition, you must call pcre_compile()
136         with  the PCRE_UTF8 option flag. When you do this, both the pattern and         with the PCRE_UTF8 option flag. When you do this, both the pattern  and
137         any subject strings that are matched against it are  treated  as  UTF-8         any  subject  strings  that are matched against it are treated as UTF-8
138         strings instead of just strings of bytes.         strings instead of just strings of bytes.
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    
159         1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and         1.  When you set the PCRE_UTF8 flag, the strings passed as patterns and
160         subjects  are  checked for validity on entry to the relevant functions.         subjects are checked for validity on entry to the  relevant  functions.
161         If an invalid UTF-8 string is passed, an error return is given. In some         If an invalid UTF-8 string is passed, an error return is given. In some
162         situations,  you  may  already  know  that  your strings are valid, and         situations, you may already know  that  your  strings  are  valid,  and
163         therefore want to skip these checks in order to improve performance. If         therefore want to skip these checks in order to improve performance. If
164         you  set  the  PCRE_NO_UTF8_CHECK  flag at compile time or at run time,         you set the PCRE_NO_UTF8_CHECK flag at compile time  or  at  run  time,
165         PCRE assumes that the pattern or subject  it  is  given  (respectively)         PCRE  assumes  that  the  pattern or subject it is given (respectively)
166         contains  only valid UTF-8 codes. In this case, it does not diagnose an         contains only valid UTF-8 codes. In this case, it does not diagnose  an
167         invalid UTF-8 string. If you pass an invalid UTF-8 string to PCRE  when         invalid  UTF-8 string. If you pass an invalid UTF-8 string to PCRE when
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}.
179    
180         5.  The dot metacharacter matches one UTF-8 character instead of a sin-         5. The dot metacharacter matches one UTF-8 character instead of a  sin-
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. This facility is         mode, but its use can lead to some strange effects.  This  facility  is
185         not available in the alternative matching function, pcre_dfa_exec().         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         Philip Hazel
214         University Computing Service,         University Computing Service
215         Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
216    
217         Putting  an actual email address here seems to have been a spam magnet,         Putting an actual email address here seems to have been a spam  magnet,
218         so I've taken it away. If you want to email me, use my initial and sur-         so I've taken it away. If you want to email me, use my initial and sur-
219         name, separated by a dot, at the domain ucs.cam.ac.uk.         name, separated by a dot, at the domain ucs.cam.ac.uk.
220    
221  Last updated: 07 March 2005  
222  Copyright (c) 1997-2005 University of Cambridge.  REVISION
223    
224           Last updated: 06 March 2007
225           Copyright (c) 1997-2007 University of Cambridge.
226  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
227    
228    
# Line 228  PCRE BUILD-TIME OPTIONS Line 244  PCRE BUILD-TIME OPTIONS
244    
245           ./configure --help           ./configure --help
246    
247         The following sections describe certain options whose names begin  with         The following sections include  descriptions  of  options  whose  names
248         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
249         for the configure command. Because of the  way  that  configure  works,         defaults for the configure command. Because of the way  that  configure
250         --enable  and  --disable  always  come  in  pairs, so the complementary         works,  --enable  and --disable always come in pairs, so the complemen-
251         option always exists as well, but as it specifies the  default,  it  is         tary option always exists as well, but as it specifies the default,  it
252         not described.         is not described.
253    
254    
255  C++ SUPPORT  C++ SUPPORT
# Line 272  UNICODE CHARACTER PROPERTY SUPPORT Line 288  UNICODE CHARACTER PROPERTY SUPPORT
288         to the configure command. This implies UTF-8 support, even if you  have         to the configure command. This implies UTF-8 support, even if you  have
289         not explicitly requested it.         not explicitly requested it.
290    
291         Including  Unicode  property  support  adds around 90K of tables to the         Including  Unicode  property  support  adds around 30K of tables to the
292         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE library. Only the general category properties such as  Lu  and  Nd
293         gory  properties  such as Lu and Nd are supported. Details are given in         are supported. Details are given in the pcrepattern documentation.
        the pcrepattern documentation.  
294    
295    
296  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
297    
298         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating
299         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
300         compile PCRE to use character 13 (carriage return) instead by adding         systems. You can compile PCRE to use character 13 (carriage return, CR)
301           instead, by adding
302    
303           --enable-newline-is-cr           --enable-newline-is-cr
304    
305         to the configure command. For completeness there is  also  a  --enable-         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
306         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
307         line character.  
308           Alternatively, you can specify that line endings are to be indicated by
309           the two character sequence CRLF. If you want this, add
310    
311             --enable-newline-is-crlf
312    
313           to the configure command. There is a fourth option, specified by
314    
315             --enable-newline-is-any
316    
317           which causes PCRE to recognize any Unicode newline sequence.
318    
319           Whatever line ending convention is selected when PCRE is built  can  be
320           overridden  when  the library functions are called. At build time it is
321           conventional to use the standard for your operating system.
322    
323    
324  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
# Line 319  POSIX MALLOC USAGE Line 349  POSIX MALLOC USAGE
349         to the configure command.         to the configure command.
350    
351    
 LIMITING PCRE RESOURCE USAGE  
   
        Internally,  PCRE has a function called match(), which it calls repeat-  
        edly  (possibly  recursively)  when  matching  a   pattern   with   the  
        pcre_exec()  function.  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  documen-  
        tation.  The default is 10 million, but this can be changed by adding a  
        setting such as  
   
          --with-match-limit=500000  
   
        to  the  configure  command.  This  setting  has  no  effect   on   the  
        pcre_dfa_exec() matching function.  
   
   
352  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
353    
354         Within  a  compiled  pattern,  offset values are used to point from one         Within  a  compiled  pattern,  offset values are used to point from one
# Line 353  HANDLING VERY LARGE PATTERNS Line 366  HANDLING VERY LARGE PATTERNS
366         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
367         additional bytes when handling them.         additional bytes when handling them.
368    
        If you build PCRE with an increased link size, test 2 (and  test  5  if  
        you  are using UTF-8) will fail. Part of the output of these tests is a  
        representation of the compiled pattern, and this changes with the  link  
        size.  
   
369    
370  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
371    
372         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
373         ing by making recursive calls to an internal function  called  match().         ing  by  making recursive calls to an internal function called match().
374         In  environments  where  the size of the stack is limited, this can se-         In environments where the size of the stack is limited,  this  can  se-
375         verely limit PCRE's operation. (The Unix environment does  not  usually         verely  limit  PCRE's operation. (The Unix environment does not usually
376         suffer  from  this  problem.)  An alternative approach that uses memory         suffer from this problem, but it may sometimes be necessary to increase
377         from the heap to remember data, instead  of  using  recursive  function         the  maximum  stack size.  There is a discussion in the pcrestack docu-
378         calls,  has been implemented to work round this problem. If you want to         mentation.) An alternative approach to recursion that uses memory  from
379         build a version of PCRE that works this way, add         the  heap  to remember data, instead of using recursive function calls,
380           has been implemented to work round the problem of limited  stack  size.
381           If you want to build a version of PCRE that works this way, add
382    
383           --disable-stack-for-recursion           --disable-stack-for-recursion
384    
385         to the configure command. With this configuration, PCRE  will  use  the         to  the  configure  command. With this configuration, PCRE will use the
386         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
387         ment functions. Separate functions are provided because  the  usage  is         ment  functions.  Separate  functions are provided because the usage is
388         very  predictable:  the  block sizes requested are always the same, and         very predictable: the block sizes requested are always  the  same,  and
389         the blocks are always freed in reverse order. A calling  program  might         the  blocks  are always freed in reverse order. A calling program might
390         be  able  to implement optimized functions that perform better than the         be able to implement optimized functions that perform better  than  the
391         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more
392         slowly when built in this way. This option affects only the pcre_exec()         slowly when built in this way. This option affects only the pcre_exec()
393         function; it is not relevant for the the pcre_dfa_exec() function.         function; it is not relevant for the the pcre_dfa_exec() function.
394    
395    
396    LIMITING PCRE RESOURCE USAGE
397    
398           Internally,  PCRE has a function called match(), which it calls repeat-
399           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
400           pcre_exec()  function.  By controlling the maximum number of times this
401           function may be called during a single matching operation, a limit  can
402           be  placed  on  the resources used by a single call to pcre_exec(). The
403           limit can be changed at run time, as described in the pcreapi  documen-
404           tation.  The default is 10 million, but this can be changed by adding a
405           setting such as
406    
407             --with-match-limit=500000
408    
409           to  the  configure  command.  This  setting  has  no  effect   on   the
410           pcre_dfa_exec() matching function.
411    
412           In  some  environments  it is desirable to limit the depth of recursive
413           calls of match() more strictly than the total number of calls, in order
414           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
415           for-recursion is specified) that is used. A second limit controls this;
416           it  defaults  to  the  value  that is set for --with-match-limit, which
417           imposes no additional constraints. However, you can set a  lower  limit
418           by adding, for example,
419    
420             --with-match-limit-recursion=10000
421    
422           to  the  configure  command.  This  value can also be overridden at run
423           time.
424    
425    
426    CREATING CHARACTER TABLES AT BUILD TIME
427    
428           PCRE uses fixed tables for processing characters whose code values  are
429           less  than 256. By default, PCRE is built with a set of tables that are
430           distributed in the file pcre_chartables.c.dist. These  tables  are  for
431           ASCII codes only. If you add
432    
433             --enable-rebuild-chartables
434    
435           to  the  configure  command, the distributed tables are no longer used.
436           Instead, a program called dftables is compiled and  run.  This  outputs
437           the source for new set of tables, created in the default locale of your
438           C runtime system. (This method of replacing the tables does not work if
439           you  are cross compiling, because dftables is run on the local host. If
440           you need to create alternative tables when cross  compiling,  you  will
441           have to do so "by hand".)
442    
443    
444  USING EBCDIC CODE  USING EBCDIC CODE
445    
446         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
447         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
448         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by
449         adding         adding
450    
451           --enable-ebcdic           --enable-ebcdic
452    
453         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
454           bles.
455    
456    
457    SEE ALSO
458    
459           pcreapi(3), pcre_config(3).
460    
461  Last updated: 15 August 2005  
462  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
463    
464           Philip Hazel
465           University Computing Service
466           Cambridge CB2 3QH, England.
467    
468    
469    REVISION
470    
471           Last updated: 20 March 2007
472           Copyright (c) 1997-2007 University of Cambridge.
473  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
474    
475    
# Line 431  PCRE MATCHING ALGORITHMS Line 505  PCRE MATCHING ALGORITHMS
505           <something> <something else> <something further>           <something> <something else> <something further>
506    
507         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
508         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
509    
510    
511  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 440  REGULAR EXPRESSIONS AS TREES Line 514  REGULAR EXPRESSIONS AS TREES
514         resented  as  a  tree structure. An unlimited repetition in the pattern         resented  as  a  tree structure. An unlimited repetition in the pattern
515         makes the tree of infinite size, but it is still a tree.  Matching  the         makes the tree of infinite size, but it is still a tree.  Matching  the
516         pattern  to a given subject string (from a given starting point) can be         pattern  to a given subject string (from a given starting point) can be
517         thought of as a search of the tree.  There are  two  standard  ways  to         thought of as a search of the tree.  There are two  ways  to  search  a
518         search  a  tree: depth-first and breadth-first, and these correspond to         tree:  depth-first  and  breadth-first, and these correspond to the two
519         the two matching algorithms provided by PCRE.         matching algorithms provided by PCRE.
520    
521    
522  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
# Line 472  THE STANDARD MATCHING ALGORITHM Line 546  THE STANDARD MATCHING ALGORITHM
546         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
547    
548    
549  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
550    
551         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
552         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
553         first search of the tree. Starting from the first matching point in the         string from left to right, once, character by character, and as it does
554         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
555         ter by character, and as it does  this,  it  remembers  all  the  paths         matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
556         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
557           keeps multiple states active simultaneously).
558         The  scan  continues until either the end of the subject is reached, or  
559         there are no more unterminated paths. At this point,  terminated  paths         The scan continues until either the end of the subject is  reached,  or
560         represent  the different matching possibilities (if there are none, the         there  are  no more unterminated paths. At this point, terminated paths
561         match has failed).  Thus, if there is more  than  one  possible  match,         represent the different matching possibilities (if there are none,  the
562           match  has  failed).   Thus,  if there is more than one possible match,
563         this algorithm finds all of them, and in particular, it finds the long-         this algorithm finds all of them, and in particular, it finds the long-
564         est. In PCRE, there is an option to stop the algorithm after the  first         est.  In PCRE, there is an option to stop the algorithm after the first
565         match (which is necessarily the shortest) has been found.         match (which is necessarily the shortest) has been found.
566    
567         Note that all the matches that are found start at the same point in the         Note that all the matches that are found start at the same point in the
# Line 494  THE DFA MATCHING ALGORITHM Line 569  THE DFA MATCHING ALGORITHM
569    
570           cat(er(pillar)?)           cat(er(pillar)?)
571    
572         is matched against the string "the caterpillar catchment",  the  result         is  matched  against the string "the caterpillar catchment", the result
573         will  be the three strings "cat", "cater", and "caterpillar" that start         will be the three strings "cat", "cater", and "caterpillar" that  start
574         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
575         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
576    
577         There are a number of features of PCRE regular expressions that are not         There are a number of features of PCRE regular expressions that are not
578         supported by the DFA matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
579    
580         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1.  Because  the  algorithm  finds  all possible matches, the greedy or
581         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
582         ungreedy quantifiers are treated in exactly the same way.         ungreedy quantifiers are treated in exactly the same way. However, pos-
583           sessive quantifiers can make a difference when what follows could  also
584           match what is quantified, for example in a pattern like this:
585    
586             ^a++\w!
587    
588           This  pattern matches "aaab!" but not "aaa!", which would be matched by
589           a non-possessive quantifier. Similarly, if an atomic group is  present,
590           it  is matched as if it were a standalone pattern at the current point,
591           and the longest match is then "locked in" for the rest of  the  overall
592           pattern.
593    
594         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
595         is  not  straightforward  to  keep track of captured substrings for the         is not straightforward to keep track of  captured  substrings  for  the
596         different matching possibilities, and  PCRE's  implementation  of  this         different  matching  possibilities,  and  PCRE's implementation of this
597         algorithm does not attempt to do this. This means that no captured sub-         algorithm does not attempt to do this. This means that no captured sub-
598         strings are available.         strings are available.
599    
600         3. Because no substrings are captured, back references within the  pat-         3.  Because no substrings are captured, back references within the pat-
601         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
602    
603         4.  For  the same reason, conditional expressions that use a backrefer-         4. For the same reason, conditional expressions that use  a  backrefer-
604         ence as the condition are not supported.         ence  as  the  condition or test for a specific group recursion are not
605           supported.
606    
607         5. Callouts are supported, but the value of the  capture_top  field  is         5. Callouts are supported, but the value of the  capture_top  field  is
608         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
609    
610         6.  The \C escape sequence, which (in the standard algorithm) matches a         6.  The \C escape sequence, which (in the standard algorithm) matches a
611         single byte, even in UTF-8 mode, is not supported because the DFA algo-         single byte, even in UTF-8 mode, is not supported because the  alterna-
612         rithm moves through the subject string one character at a time, for all         tive  algorithm  moves  through  the  subject string one character at a
613         active paths through the tree.         time, for all active paths through the tree.
614    
615    
616  ADVANTAGES OF THE DFA ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
617    
618         Using the DFA matching algorithm provides the following advantages:         Using the alternative matching algorithm provides the following  advan-
619           tages:
620    
621         1. All possible matches (at a single point in the subject) are automat-         1. All possible matches (at a single point in the subject) are automat-
622         ically  found,  and  in particular, the longest match is found. To find         ically found, and in particular, the longest match is  found.  To  find
623         more than one match using the standard algorithm, you have to do kludgy         more than one match using the standard algorithm, you have to do kludgy
624         things with callouts.         things with callouts.
625    
626         2.  There is much better support for partial matching. The restrictions         2. There is much better support for partial matching. The  restrictions
627         on the content of the pattern that apply when using the standard  algo-         on  the content of the pattern that apply when using the standard algo-
628         rithm  for partial matching do not apply to the DFA algorithm. For non-         rithm for partial matching do not apply to the  alternative  algorithm.
629         anchored patterns, the starting position of a partial match  is  avail-         For  non-anchored patterns, the starting position of a partial match is
630         able.         available.
631    
632         3.  Because  the  DFA algorithm scans the subject string just once, and         3. Because the alternative algorithm  scans  the  subject  string  just
633         never needs to backtrack, it is possible  to  pass  very  long  subject         once,  and  never  needs to backtrack, it is possible to pass very long
634         strings  to  the matching function in several pieces, checking for par-         subject strings to the matching function in  several  pieces,  checking
635         tial matching each time.         for partial matching each time.
636    
637    
638  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
639    
640         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
641    
642         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
643         partly  because  it has to search for all possible matches, but is also         partly because it has to search for all possible matches, but  is  also
644         because it is less susceptible to optimization.         because it is less susceptible to optimization.
645    
646         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
647    
648         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
649         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
650         rithm.  
651    
652  Last updated: 28 February 2005  AUTHOR
653  Copyright (c) 1997-2005 University of Cambridge.  
654           Philip Hazel
655           University Computing Service
656           Cambridge CB2 3QH, England.
657    
658    
659    REVISION
660    
661           Last updated: 06 March 2007
662           Copyright (c) 1997-2007 University of Cambridge.
663  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
664    
665    
# Line 616  PCRE NATIVE API Line 712  PCRE NATIVE API
712         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
713              const char *name);              const char *name);
714    
715           int pcre_get_stringtable_entries(const pcre *code,
716                const char *name, char **first, char **last);
717    
718         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
719              int stringcount, int stringnumber,              int stringcount, int stringnumber,
720              const char **stringptr);              const char **stringptr);
# Line 654  PCRE NATIVE API Line 753  PCRE NATIVE API
753  PCRE API OVERVIEW  PCRE API OVERVIEW
754    
755         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
756         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
757         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
758         Both of these APIs define a set of C function calls. A C++  wrapper  is         Both of these APIs define a set of C function calls. A C++  wrapper  is
759         distributed with PCRE. It is documented in the pcrecpp page.         distributed with PCRE. It is documented in the pcrecpp page.
# Line 676  PCRE API OVERVIEW Line 775  PCRE API OVERVIEW
775    
776         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
777         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
778         ing. This allows it to find all possible matches (at a given  point  in         ing. The alternative algorithm finds all possible matches (at  a  given
779         the  subject),  not  just  one. However, this algorithm does not return         point  in  the subject), and scans the subject just once. However, this
780         captured substrings. A description of the two matching  algorithms  and         algorithm does not return captured substrings. A description of the two
781         their  advantages  and disadvantages is given in the pcrematching docu-         matching  algorithms and their advantages and disadvantages is given in
782         mentation.         the pcrematching documentation.
783    
784         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
785         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 692  PCRE API OVERVIEW Line 791  PCRE API OVERVIEW
791           pcre_get_named_substring()           pcre_get_named_substring()
792           pcre_get_substring_list()           pcre_get_substring_list()
793           pcre_get_stringnumber()           pcre_get_stringnumber()
794             pcre_get_stringtable_entries()
795    
796         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
797         to free the memory used for extracted strings.         to free the memory used for extracted strings.
# Line 723  PCRE API OVERVIEW Line 823  PCRE API OVERVIEW
823         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
824         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
825         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
826         function. This is a non-standard way of building PCRE, for use in envi-         function. See the pcrebuild documentation for  details  of  how  to  do
827         ronments that have limited stacks. Because of the greater use of memory         this.  It  is  a non-standard way of building PCRE, for use in environ-
828         management, it runs more slowly.  Separate functions  are  provided  so         ments that have limited stacks. Because of the greater  use  of  memory
829         that  special-purpose  external  code  can  be used for this case. When         management,  it  runs  more  slowly. Separate functions are provided so
830         used, these functions are always called in a  stack-like  manner  (last         that special-purpose external code can be  used  for  this  case.  When
831         obtained,  first freed), and always for memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
832           obtained, first freed), and always for memory blocks of the same  size.
833           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
834           mentation.
835    
836         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
837         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
# Line 736  PCRE API OVERVIEW Line 839  PCRE API OVERVIEW
839         pcrecallout documentation.         pcrecallout documentation.
840    
841    
842    NEWLINES
843    
844           PCRE  supports four different conventions for indicating line breaks in
845           strings: a single CR (carriage return) character, a  single  LF  (line-
846           feed)  character,  the two-character sequence CRLF, or any Unicode new-
847           line sequence.  The Unicode newline sequences are the three  just  men-
848           tioned, plus the single characters VT (vertical tab, U+000B), FF (form-
849           feed, U+000C), NEL (next line, U+0085), LS  (line  separator,  U+2028),
850           and PS (paragraph separator, U+2029).
851    
852           Each  of  the first three conventions is used by at least one operating
853           system as its standard newline sequence. When PCRE is built, a  default
854           can  be  specified.  The default default is LF, which is the Unix stan-
855           dard. When PCRE is run, the default can be overridden,  either  when  a
856           pattern is compiled, or when it is matched.
857    
858           In the PCRE documentation the word "newline" is used to mean "the char-
859           acter or pair of characters that indicate a line break". The choice  of
860           newline  convention  affects  the  handling of the dot, circumflex, and
861           dollar metacharacters, the handling of #-comments in /x mode, and, when
862           CRLF  is a recognized line ending sequence, the match position advance-
863           ment for a non-anchored pattern. The choice of newline convention  does
864           not affect the interpretation of the \n or \r escape sequences.
865    
866    
867  MULTITHREADING  MULTITHREADING
868    
869         The  PCRE  functions  can be used in multi-threading applications, with         The  PCRE  functions  can be used in multi-threading applications, with
# Line 782  CHECKING BUILD-TIME OPTIONS Line 910  CHECKING BUILD-TIME OPTIONS
910    
911           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
912    
913         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
914         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
915         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.
916         operating system.         The default should normally be the standard sequence for your operating
917           system.
918    
919           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
920    
921         The  output  is  an  integer that contains the number of bytes used for         The output is an integer that contains the number  of  bytes  used  for
922         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
923         4.  Larger  values  allow larger regular expressions to be compiled, at         4. Larger values allow larger regular expressions to  be  compiled,  at
924         the expense of slower matching. The default value of  2  is  sufficient         the  expense  of  slower matching. The default value of 2 is sufficient
925         for  all  but  the  most massive patterns, since it allows the compiled         for all but the most massive patterns, since  it  allows  the  compiled
926         pattern to be up to 64K in size.         pattern to be up to 64K in size.
927    
928           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
929    
930         The output is an integer that contains the threshold  above  which  the         The  output  is  an integer that contains the threshold above which the
931         POSIX  interface  uses malloc() for output vectors. Further details are         POSIX interface uses malloc() for output vectors. Further  details  are
932         given in the pcreposix documentation.         given in the pcreposix documentation.
933    
934           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
935    
936         The output is an integer that gives the default limit for the number of         The output is an integer that gives the default limit for the number of
937         internal  matching  function  calls in a pcre_exec() execution. Further         internal matching function calls in a  pcre_exec()  execution.  Further
938         details are given with pcre_exec() below.         details are given with pcre_exec() below.
939    
940             PCRE_CONFIG_MATCH_LIMIT_RECURSION
941    
942           The  output is an integer that gives the default limit for the depth of
943           recursion when calling the internal matching function in a  pcre_exec()
944           execution. Further details are given with pcre_exec() below.
945    
946           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
947    
948         The output is an integer that is set to one if internal recursion  when         The  output is an integer that is set to one if internal recursion when
949         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
950         the stack to remember their state. This is the usual way that  PCRE  is         the  stack  to remember their state. This is the usual way that PCRE is
951         compiled. The output is zero if PCRE was compiled to use blocks of data         compiled. The output is zero if PCRE was compiled to use blocks of data
952         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
953         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
954         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
955    
956    
# Line 832  COMPILING A PATTERN Line 967  COMPILING A PATTERN
967    
968         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
969         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
970         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
971         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
972    
973         The pattern is a C string terminated by a binary zero, and is passed in         The pattern is a C string terminated by a binary zero, and is passed in
974         the pattern argument. A pointer to a single block  of  memory  that  is         the  pattern  argument.  A  pointer to a single block of memory that is
975         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
976         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
977         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
978         It is up to the caller  to  free  the  memory  when  it  is  no  longer         It is up to the caller to free the memory (via pcre_free) when it is no
979         required.         longer required.
980    
981         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
982         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
983         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
984         ment, which is an address (see below).         ment, which is an address (see below).
985    
986         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
987         tion.  It  should  be  zero  if  no options are required. The available         pilation. It should be zero if no options are required.  The  available
988         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them, in particular, those that
989         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
990         pattern (see the detailed description  in  the  pcrepattern  documenta-         pattern  (see  the  detailed  description in the pcrepattern documenta-
991         tion).  For  these options, the contents of the options argument speci-         tion). For these options, the contents of the options  argument  speci-
992         fies their initial settings at the start of compilation and  execution.         fies  their initial settings at the start of compilation and execution.
993         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
994         at compile time.         of matching as well as at compile time.
995    
996         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
997         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
998         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-
999         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
1000         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-
1001         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
1002           by  erroffset,  which must not be NULL. If it is, an immediate error is
1003         given.         given.
1004    
1005         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
# Line 926  COMPILING A PATTERN Line 1062  COMPILING A PATTERN
1062    
1063         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
1064         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
1065         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
1066         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1067         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
1068         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1069    
1070           PCRE_DOTALL           PCRE_DOTALL
1071    
1072         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-
1073         acters, including newlines. Without it,  newlines  are  excluded.  This         acters, including those that indicate newline. Without it, a  dot  does
1074         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
1075         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
1076         always  matches a newline character, independent of the setting of this         by  a (?s) option setting. A negative class such as [^a] always matches
1077         option.         newline characters, independent of the setting of this option.
1078    
1079             PCRE_DUPNAMES
1080    
1081           If this bit is set, names used to identify capturing  subpatterns  need
1082           not be unique. This can be helpful for certain types of pattern when it
1083           is known that only one instance of the named  subpattern  can  ever  be
1084           matched.  There  are  more details of named subpatterns below; see also
1085           the pcrepattern documentation.
1086    
1087           PCRE_EXTENDED           PCRE_EXTENDED
1088    
# Line 946  COMPILING A PATTERN Line 1090  COMPILING A PATTERN
1090         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1091         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1092         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1093         line character, inclusive, are also  ignored.  This  is  equivalent  to         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1094         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-
1095         option setting.         ting.
1096    
1097         This option makes it possible to include  comments  inside  complicated         This option makes it possible to include  comments  inside  complicated
1098         patterns.   Note,  however,  that this applies only to data characters.         patterns.   Note,  however,  that this applies only to data characters.
# Line 964  COMPILING A PATTERN Line 1108  COMPILING A PATTERN
1108         letter  that  has  no  special  meaning causes an error, thus reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1109         these combinations for future expansion. By  default,  as  in  Perl,  a         these combinations for future expansion. By  default,  as  in  Perl,  a
1110         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
1111         literal. There are at present no  other  features  controlled  by  this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1112         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
1113           can also be set by a (?X) option setting within a pattern.
1114    
1115           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1116    
1117         If  this  option  is  set,  an  unanchored pattern is required to match         If this option is set, an  unanchored  pattern  is  required  to  match
1118         before or at the first newline character in the subject string,  though         before  or  at  the  first  newline  in  the subject string, though the
1119         the matched text may continue over the newline.         matched text may continue over the newline.
1120    
1121           PCRE_MULTILINE           PCRE_MULTILINE
1122    
1123         By  default,  PCRE  treats the subject string as consisting of a single         By default, PCRE treats the subject string as consisting  of  a  single
1124         line of characters (even if it actually contains newlines). The  "start         line  of characters (even if it actually contains newlines). The "start
1125         of  line"  metacharacter  (^)  matches only at the start of the string,         of line" metacharacter (^) matches only at the  start  of  the  string,
1126         while the "end of line" metacharacter ($) matches only at  the  end  of         while  the  "end  of line" metacharacter ($) matches only at the end of
1127         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1128         is set). This is the same as Perl.         is set). This is the same as Perl.
1129    
1130         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"
1131         constructs  match  immediately following or immediately before any new-         constructs match immediately following or immediately  before  internal
1132         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
1133         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
1134         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-
1135         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,
1136         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1137    
1138             PCRE_NEWLINE_CR
1139             PCRE_NEWLINE_LF
1140             PCRE_NEWLINE_CRLF
1141             PCRE_NEWLINE_ANY
1142    
1143           These  options  override the default newline definition that was chosen
1144           when PCRE was built. Setting the first or the second specifies  that  a
1145           newline  is  indicated  by a single character (CR or LF, respectively).
1146           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1147           two-character  CRLF  sequence.  Setting PCRE_NEWLINE_ANY specifies that
1148           any Unicode newline sequence should be recognized. The Unicode  newline
1149           sequences  are  the three just mentioned, plus the single characters VT
1150           (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085),
1151           LS  (line separator, U+2028), and PS (paragraph separator, U+2029). The
1152           last two are recognized only in UTF-8 mode.
1153    
1154           The newline setting in the  options  word  uses  three  bits  that  are
1155           treated  as  a  number, giving eight possibilities. Currently only five
1156           are used (default plus the four values above). This means that  if  you
1157           set  more  than  one  newline option, the combination may or may not be
1158           sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is  equiva-
1159           lent  to PCRE_NEWLINE_CRLF, but other combinations yield unused numbers
1160           and cause an error.
1161    
1162           The only time that a line break is specially recognized when  compiling
1163           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1164           character class is encountered. This indicates  a  comment  that  lasts
1165           until  after the next line break sequence. In other circumstances, line
1166           break  sequences  are  treated  as  literal  data,   except   that   in
1167           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1168           and are therefore ignored.
1169    
1170           The newline option that is set at compile time becomes the default that
1171           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1172    
1173           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1174    
1175         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-
# Line 1031  COMPILATION ERROR CODES Line 1211  COMPILATION ERROR CODES
1211    
1212         The following table lists the error  codes  than  may  be  returned  by         The following table lists the error  codes  than  may  be  returned  by
1213         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(),  along with the error messages that may be returned by
1214         both compiling functions.         both compiling functions. As PCRE has developed, some error codes  have
1215           fallen out of use. To avoid confusion, they have not been re-used.
1216    
1217            0  no error            0  no error
1218            1  \ at end of pattern            1  \ at end of pattern
# Line 1043  COMPILATION ERROR CODES Line 1224  COMPILATION ERROR CODES
1224            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1225            8  range out of order in character class            8  range out of order in character class
1226            9  nothing to repeat            9  nothing to repeat
1227           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1228           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1229           12  unrecognized character after (?           12  unrecognized character after (?
1230           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
# Line 1052  COMPILATION ERROR CODES Line 1233  COMPILATION ERROR CODES
1233           16  erroffset passed as NULL           16  erroffset passed as NULL
1234           17  unknown option bit(s) set           17  unknown option bit(s) set
1235           18  missing ) after comment           18  missing ) after comment
1236           19  parentheses nested too deeply           19  [this code is not in use]
1237           20  regular expression too large           20  regular expression too large
1238           21  failed to get memory           21  failed to get memory
1239           22  unmatched parentheses           22  unmatched parentheses
1240           23  internal error: code overflow           23  internal error: code overflow
1241           24  unrecognized character after (?<           24  unrecognized character after (?<
1242           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1243           26  malformed number after (?(           26  malformed number or name after (?(
1244           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1245           28  assertion expected after (?(           28  assertion expected after (?(
1246           29  (?R or (?digits must be followed by )           29  (?R or (?digits must be followed by )
1247           30  unknown POSIX class name           30  unknown POSIX class name
1248           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1249           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1250           33  spare error           33  [this code is not in use]
1251           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1252           35  invalid condition (?(0)           35  invalid condition (?(0)
1253           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1075  COMPILATION ERROR CODES Line 1256  COMPILATION ERROR CODES
1256           39  closing ) for (?C expected           39  closing ) for (?C expected
1257           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1258           41  unrecognized character after (?P           41  unrecognized character after (?P
1259           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1260           43  two named groups have the same name           43  two named subpatterns have the same name
1261           44  invalid UTF-8 string           44  invalid UTF-8 string
1262           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1263           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1264           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1265             48  subpattern name is too long (maximum 32 characters)
1266             49  too many named subpatterns (maximum 10,000)
1267             50  repeated subpattern is too long
1268             51  octal value is greater than \377 (not in UTF-8 mode)
1269             52  internal error: overran compiling workspace
1270             53   internal  error:  previously-checked  referenced  subpattern not
1271           found
1272             54  DEFINE group contains more than one branch
1273             55  repeating a DEFINE group is not allowed
1274             56  inconsistent NEWLINE options"
1275    
1276    
1277  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1111  STUDYING A PATTERN Line 1302  STUDYING A PATTERN
1302    
1303         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.
1304         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1305         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
1306         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
1307         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
1308           after calling pcre_study(), to be sure that it has run successfully.
1309    
1310         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1311    
# Line 1124  STUDYING A PATTERN Line 1316  STUDYING A PATTERN
1316             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1317    
1318         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1319         that do not have a single fixed starting character. A bitmap of  possi-         that  do not have a single fixed starting character. A bitmap of possi-
1320         ble starting bytes is created.         ble starting bytes is created.
1321    
1322    
1323  LOCALE SUPPORT  LOCALE SUPPORT
1324    
1325         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1326         letters digits, or whatever, by reference to a set of  tables,  indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1327         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
1328         characters with codes less than 128. Higher-valued  codes  never  match         characters  with  codes  less than 128. Higher-valued codes never match
1329         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
1330         with Unicode character property support.         with  Unicode  character property support. The use of locales with Uni-
1331           code is discouraged. If you are handling characters with codes  greater
1332         An internal set of tables is created in the default C locale when  PCRE         than  128, you should either use UTF-8 and Unicode, or use locales, but
1333         is  built.  This  is  used when the final argument of pcre_compile() is         not try to mix the two.
1334         NULL, and is sufficient for many applications. An  alternative  set  of  
1335         tables  can,  however, be supplied. These may be created in a different         PCRE contains an internal set of tables that are used  when  the  final
1336         locale from the default. As more and more applications change to  using         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1337         Unicode, the need for this locale support is expected to die away.         applications.  Normally, the internal tables recognize only ASCII char-
1338           acters. However, when PCRE is built, it is possible to cause the inter-
1339         External  tables  are  built by calling the pcre_maketables() function,         nal tables to be rebuilt in the default "C" locale of the local system,
1340         which has no arguments, in the relevant locale. The result can then  be         which may cause them to be different.
1341         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For  
1342         example, to build and use tables that are appropriate  for  the  French         The  internal tables can always be overridden by tables supplied by the
1343         locale  (where  accented  characters  with  values greater than 128 are         application that calls PCRE. These may be created in a different locale
1344           from  the  default.  As more and more applications change to using Uni-
1345           code, the need for this locale support is expected to die away.
1346    
1347           External tables are built by calling  the  pcre_maketables()  function,
1348           which  has no arguments, in the relevant locale. The result can then be
1349           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1350           example,  to  build  and use tables that are appropriate for the French
1351           locale (where accented characters with  values  greater  than  128  are
1352         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1353    
1354           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1355           tables = pcre_maketables();           tables = pcre_maketables();
1356           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1357    
1358           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1359           if you are using Windows, the name for the French locale is "french".
1360    
1361         When pcre_maketables() runs, the tables are built  in  memory  that  is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1362         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1363         that the memory containing the tables remains available for as long  as         that the memory containing the tables remains available for as long  as
# Line 1200  INFORMATION ABOUT A PATTERN Line 1403  INFORMATION ABOUT A PATTERN
1403         pattern:         pattern:
1404    
1405           int rc;           int rc;
1406           unsigned long int length;           size_t length;
1407           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1408             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1409             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
# Line 1232  INFORMATION ABOUT A PATTERN Line 1435  INFORMATION ABOUT A PATTERN
1435           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1436    
1437         Return  information  about  the first byte of any matched string, for a         Return  information  about  the first byte of any matched string, for a
1438         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored pattern. The fourth argument should point to an int  vari-
1439         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1440         compatibility.)         is still recognized for backwards compatibility.)
1441    
1442         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
1443         (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  
1444    
1445         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1446         branch starts with "^", or         branch starts with "^", or
1447    
1448         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1449         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1450    
1451         -1 is returned, indicating that the pattern matches only at  the  start         -1  is  returned, indicating that the pattern matches only at the start
1452         of  a  subject string or after any newline within the string. Otherwise         of a subject string or after any newline within the  string.  Otherwise
1453         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1454    
1455           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1456    
1457         If the pattern was studied, and this resulted in the construction of  a         If  the pattern was studied, and this resulted in the construction of a
1458         256-bit table indicating a fixed set of bytes for the first byte in any         256-bit table indicating a fixed set of bytes for the first byte in any
1459         matching string, a pointer to the table is returned. Otherwise NULL  is         matching  string, a pointer to the table is returned. Otherwise NULL is
1460         returned.  The fourth argument should point to an unsigned char * vari-         returned. The fourth argument should point to an unsigned char *  vari-
1461         able.         able.
1462    
1463           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1464    
1465         Return the value of the rightmost literal byte that must exist  in  any         Return  the  value of the rightmost literal byte that must exist in any
1466         matched  string,  other  than  at  its  start,  if such a byte has been         matched string, other than at its  start,  if  such  a  byte  has  been
1467         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1468         is  no such byte, -1 is returned. For anchored patterns, a last literal         is no such byte, -1 is returned. For anchored patterns, a last  literal
1469         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1470         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1471         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1472    
# Line 1272  INFORMATION ABOUT A PATTERN Line 1474  INFORMATION ABOUT A PATTERN
1474           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1475           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1476    
1477         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1478         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1479         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1480         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1481         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
1482         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
1483         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1484         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
1485         which is described by these three values.         described by these three values.
1486    
1487         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
1488         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1489         of each entry; both of these  return  an  int  value.  The  entry  size         of  each  entry;  both  of  these  return  an int value. The entry size
1490         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1491         a pointer to the first entry of the table  (a  pointer  to  char).  The         a  pointer  to  the  first  entry of the table (a pointer to char). The
1492         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-
1493         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-
1494         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1495         For example, consider the following pattern  (assume  PCRE_EXTENDED  is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1496         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1497           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1498           ignored):
1499    
1500           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1501           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1502    
1503         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1504         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,
1505         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1506         as ??:         as ??:
1507    
# Line 1306  INFORMATION ABOUT A PATTERN Line 1510  INFORMATION ABOUT A PATTERN
1510           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1511           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1512    
1513         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1514         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
1515         be different for each compiled pattern.         to be different for each compiled pattern.
1516    
1517           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1518    
1519         Return a copy of the options with which the pattern was  compiled.  The         Return  a  copy of the options with which the pattern was compiled. The
1520         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1521         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1522         by any top-level option settings within the pattern itself.         by any top-level option settings within the pattern itself.
1523    
1524         A  pattern  is  automatically  anchored by PCRE if all of its top-level         A pattern is automatically anchored by PCRE if  all  of  its  top-level
1525         alternatives begin with one of the following:         alternatives begin with one of the following:
1526    
1527           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1331  INFORMATION ABOUT A PATTERN Line 1535  INFORMATION ABOUT A PATTERN
1535    
1536           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1537    
1538         Return  the  size  of the compiled pattern, that is, the value that was         Return the size of the compiled pattern, that is, the  value  that  was
1539         passed as the argument to pcre_malloc() when PCRE was getting memory in         passed as the argument to pcre_malloc() when PCRE was getting memory in
1540         which to place the compiled data. The fourth argument should point to a         which to place the compiled data. The fourth argument should point to a
1541         size_t variable.         size_t variable.
# Line 1339  INFORMATION ABOUT A PATTERN Line 1543  INFORMATION ABOUT A PATTERN
1543           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1544    
1545         Return the size of the data block pointed to by the study_data field in         Return the size of the data block pointed to by the study_data field in
1546         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to         a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1547         pcre_malloc() when PCRE was getting memory into which to place the data         pcre_malloc() when PCRE was getting memory into which to place the data
1548         created  by  pcre_study(). The fourth argument should point to a size_t         created by pcre_study(). The fourth argument should point to  a  size_t
1549         variable.         variable.
1550    
1551    
# Line 1349  OBSOLETE INFO FUNCTION Line 1553  OBSOLETE INFO FUNCTION
1553    
1554         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1555    
1556         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1557         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1558         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1559         pcre_info()  is the number of capturing subpatterns, or one of the fol-         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1560         lowing negative numbers:         lowing negative numbers:
1561    
1562           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1563           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1564    
1565         If the optptr argument is not NULL, a copy of the  options  with  which         If  the  optptr  argument is not NULL, a copy of the options with which
1566         the  pattern  was  compiled  is placed in the integer it points to (see         the pattern was compiled is placed in the integer  it  points  to  (see
1567         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1568    
1569         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1570         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1571         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1572    
1573    
# Line 1371  REFERENCE COUNTS Line 1575  REFERENCE COUNTS
1575    
1576         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1577    
1578         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1579         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1580         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1581         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1582         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1583    
1584         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1585         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1586         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1587         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1588         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1589         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1590    
1591         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1592         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1593         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1594    
1595    
# Line 1395  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1599  MATCHING A PATTERN: THE TRADITIONAL FUNC
1599              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1600              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1601    
1602         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
1603         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1604         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
1605         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1606         and it operates in a Perl-like manner. For specialist use there is also         and it operates in a Perl-like manner. For specialist use there is also
1607         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1608         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1609    
1610         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1611         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1612         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
1613         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1614         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1615    
1616         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1425  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1629  MATCHING A PATTERN: THE TRADITIONAL FUNC
1629    
1630     Extra data for pcre_exec()     Extra data for pcre_exec()
1631    
1632         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
1633         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
1634         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-
1635         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
1636         lows:         fields (not necessarily in this order):
1637    
1638           unsigned long int flags;           unsigned long int flags;
1639           void *study_data;           void *study_data;
1640           unsigned long int match_limit;           unsigned long int match_limit;
1641             unsigned long int match_limit_recursion;
1642           void *callout_data;           void *callout_data;
1643           const unsigned char *tables;           const unsigned char *tables;
1644    
1645         The flags field is a bitmap that specifies which of  the  other  fields         The  flags  field  is a bitmap that specifies which of the other fields
1646         are set. The flag bits are:         are set. The flag bits are:
1647    
1648           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1649           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1650             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1651           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1652           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1653    
1654         Other  flag  bits should be set to zero. The study_data field is set in         Other flag bits should be set to zero. The study_data field is  set  in
1655         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1656         the appropriate flag bit. You should not set this yourself, but you may         the appropriate flag bit. You should not set this yourself, but you may
1657         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1658         flag bits.         flag bits.
1659    
1660         The match_limit field provides a means of preventing PCRE from using up         The match_limit field provides a means of preventing PCRE from using up
1661         a vast amount of resources when running patterns that are not going  to         a  vast amount of resources when running patterns that are not going to
1662         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1663         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1664         repeats.         repeats.
1665    
1666         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1667         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly  (sometimes  recursively). The limit set by match_limit is imposed
1668         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
1669         limiting the amount of recursion and backtracking that can take  place.         has  the  effect  of  limiting the amount of backtracking that can take
1670         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
1671         position in the subject string.         for each position in the subject string.
1672    
1673         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
1674         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1675         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1676         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra    block    in    which    match_limit    is    set,     and
1677         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
1678         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1679    
1680         The  pcre_callout  field is used in conjunction with the "callout" fea-         The match_limit_recursion field is similar to match_limit, but  instead
1681           of limiting the total number of times that match() is called, it limits
1682           the depth of recursion. The recursion depth is a  smaller  number  than
1683           the  total number of calls, because not all calls to match() are recur-
1684           sive.  This limit is of use only if it is set smaller than match_limit.
1685    
1686           Limiting  the  recursion  depth  limits the amount of stack that can be
1687           used, or, when PCRE has been compiled to use memory on the heap instead
1688           of the stack, the amount of heap memory that can be used.
1689    
1690           The  default  value  for  match_limit_recursion can be set when PCRE is
1691           built; the default default  is  the  same  value  as  the  default  for
1692           match_limit.  You can override the default by suppling pcre_exec() with
1693           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1694           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1695           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1696    
1697           The pcre_callout field is used in conjunction with the  "callout"  fea-
1698         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1699    
1700         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1701         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
1702         pattern. A non-NULL value is stored with the compiled pattern  only  if         pattern.  A  non-NULL value is stored with the compiled pattern only if
1703         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1704         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1705         PCRE's  internal  tables  to be used. This facility is helpful when re-         PCRE's internal tables to be used. This facility is  helpful  when  re-
1706         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
1707         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
1708         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1709         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1710    
1711     Option bits for pcre_exec()     Option bits for pcre_exec()
1712    
1713         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.
1714         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,
1715         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1716           PCRE_PARTIAL.
1717    
1718           PCRE_ANCHORED           PCRE_ANCHORED
1719    
# Line 1498  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1722  MATCHING A PATTERN: THE TRADITIONAL FUNC
1722         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
1723         unachored at matching time.         unachored at matching time.
1724    
1725             PCRE_NEWLINE_CR
1726             PCRE_NEWLINE_LF
1727             PCRE_NEWLINE_CRLF
1728             PCRE_NEWLINE_ANY
1729    
1730           These options override  the  newline  definition  that  was  chosen  or
1731           defaulted  when the pattern was compiled. For details, see the descrip-
1732           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1733           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1734           ters. It may also alter the way the match position is advanced after  a
1735           match  failure  for  an  unanchored  pattern. When PCRE_NEWLINE_CRLF or
1736           PCRE_NEWLINE_ANY is set, and a match attempt  fails  when  the  current
1737           position  is  at a CRLF sequence, the match position is advanced by two
1738           characters instead of one, in other words, to after the CRLF.
1739    
1740           PCRE_NOTBOL           PCRE_NOTBOL
1741    
1742         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
# Line 1633  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1872  MATCHING A PATTERN: THE TRADITIONAL FUNC
1872         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-
1873         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1],  identify  the  portion  of  the  subject string matched by the
1874         entire pattern. The next pair is used for the first  capturing  subpat-         entire pattern. The next pair is used for the first  capturing  subpat-
1875         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
1876         pairs that have been set. If there are no  capturing  subpatterns,  the         highest numbered pair that has been set. For example, if two substrings
1877         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
1878         first pair of offsets has been set.         subpatterns, the return value from a successful match is 1,  indicating
1879           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.  
1880    
1881         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1882         of the string that it matched that is returned.         of the string that it matched that is returned.
1883    
1884         If  the vector is too small to hold all the captured substring offsets,         If the vector is too small to hold all the captured substring  offsets,
1885         it is used as far as possible (up to two-thirds of its length), and the         it is used as far as possible (up to two-thirds of its length), and the
1886         function  returns a value of zero. In particular, if the substring off-         function returns a value of zero. In particular, if the substring  off-
1887         sets are not of interest, pcre_exec() may be called with ovector passed         sets are not of interest, pcre_exec() may be called with ovector passed
1888         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         as NULL and ovecsize as zero. However, if  the  pattern  contains  back
1889         references and the ovector is not big enough to  remember  the  related         references  and  the  ovector is not big enough to remember the related
1890         substrings,  PCRE has to get additional memory for use during matching.         substrings, PCRE has to get additional memory for use during  matching.
1891         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1892    
1893         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
1894         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
1895         that will allow for n captured substrings, in addition to  the  offsets         ovector  that  will allow for n captured substrings, in addition to the
1896         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.
1897    
1898           It is possible for capturing subpattern number n+1 to match  some  part
1899           of the subject when subpattern n has not been used at all. For example,
1900           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1901           return from the function is 4, and subpatterns 1 and 3 are matched, but
1902           2 is not. When this happens, both values in  the  offset  pairs  corre-
1903           sponding to unused subpatterns are set to -1.
1904    
1905           Offset  values  that correspond to unused subpatterns at the end of the
1906           expression are also set to -1. For example,  if  the  string  "abc"  is
1907           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1908           matched. The return from the function is 2, because  the  highest  used
1909           capturing subpattern number is 1. However, you can refer to the offsets
1910           for the second and third capturing subpatterns if  you  wish  (assuming
1911           the vector is large enough, of course).
1912    
1913           Some  convenience  functions  are  provided for extracting the captured
1914           substrings as separate strings. These are described below.
1915    
1916     Return values from pcre_exec()     Error return values from pcre_exec()
1917    
1918         If  pcre_exec()  fails, it returns a negative number. The following are         If pcre_exec() fails, it returns a negative number. The  following  are
1919         defined in the header file:         defined in the header file:
1920    
1921           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1676  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1924  MATCHING A PATTERN: THE TRADITIONAL FUNC
1924    
1925           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
1926    
1927         Either code or subject was passed as NULL,  or  ovector  was  NULL  and         Either  code  or  subject  was  passed as NULL, or ovector was NULL and
1928         ovecsize was not zero.         ovecsize was not zero.
1929    
1930           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1685  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1933  MATCHING A PATTERN: THE TRADITIONAL FUNC
1933    
1934           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
1935    
1936         PCRE  stores a 4-byte "magic number" at the start of the compiled code,         PCRE stores a 4-byte "magic number" at the start of the compiled  code,
1937         to catch the case when it is passed a junk pointer and to detect when a         to catch the case when it is passed a junk pointer and to detect when a
1938         pattern that was compiled in an environment of one endianness is run in         pattern that was compiled in an environment of one endianness is run in
1939         an environment with the other endianness. This is the error  that  PCRE         an  environment  with the other endianness. This is the error that PCRE
1940         gives when the magic number is not present.         gives when the magic number is not present.
1941    
1942           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1943    
1944         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1945         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
1946         overwriting of the compiled pattern.         overwriting of the compiled pattern.
1947    
1948           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
1949    
1950         If  a  pattern contains back references, but the ovector that is passed         If a pattern contains back references, but the ovector that  is  passed
1951         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
1952         PCRE  gets  a  block of memory at the start of matching to use for this         PCRE gets a block of memory at the start of matching to  use  for  this
1953         purpose. If the call via pcre_malloc() fails, this error is given.  The         purpose.  If the call via pcre_malloc() fails, this error is given. The
1954         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
1955    
1956           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
1957    
1958         This  error is used by the pcre_copy_substring(), pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
1959         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
1960         returned by pcre_exec().         returned by pcre_exec().
1961    
1962           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
1963    
1964         The  recursion  and backtracking limit, as specified by the match_limit         The backtracking limit, as specified by  the  match_limit  field  in  a
1965         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra  structure  (or  defaulted) was reached. See the description
1966         description above.         above.
1967    
1968           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
1969    
1970         This error is never generated by pcre_exec() itself. It is provided for         This error is never generated by pcre_exec() itself. It is provided for
1971         use by callout functions that want to yield a distinctive  error  code.         use  by  callout functions that want to yield a distinctive error code.
1972         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
1973    
1974           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
1975    
1976         A  string  that contains an invalid UTF-8 byte sequence was passed as a         A string that contains an invalid UTF-8 byte sequence was passed  as  a
1977         subject.         subject.
1978    
1979           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
1980    
1981         The UTF-8 byte sequence that was passed as a subject was valid, but the         The UTF-8 byte sequence that was passed as a subject was valid, but the
1982         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-
1983         ter.         ter.
1984    
1985           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
1986    
1987         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
1988         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
1989    
1990           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
1991    
1992         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
1993         items that are not supported for partial matching. See the  pcrepartial         items  that are not supported for partial matching. See the pcrepartial
1994         documentation for details of partial matching.         documentation for details of partial matching.
1995    
1996           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
1997    
1998         An  unexpected  internal error has occurred. This error could be caused         An unexpected internal error has occurred. This error could  be  caused
1999         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2000    
2001           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2002    
2003         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.
2004    
2005             PCRE_ERROR_RECURSIONLIMIT (-21)
2006    
2007           The internal recursion limit, as specified by the match_limit_recursion
2008           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2009           description above.
2010    
2011             PCRE_ERROR_NULLWSLIMIT    (-22)
2012    
2013           When a group that can match an empty  substring  is  repeated  with  an
2014           unbounded  upper  limit, the subject position at the start of the group
2015           must be remembered, so that a test for an empty string can be made when
2016           the  end  of the group is reached. Some workspace is required for this;
2017           if it runs out, this error is given.
2018    
2019             PCRE_ERROR_BADNEWLINE     (-23)
2020    
2021           An invalid combination of PCRE_NEWLINE_xxx options was given.
2022    
2023           Error numbers -16 to -20 are not used by pcre_exec().
2024    
2025    
2026  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 1768  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2036  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2036         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2037              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2038    
2039         Captured  substrings  can  be  accessed  directly  by using the offsets         Captured substrings can be  accessed  directly  by  using  the  offsets
2040         returned by pcre_exec() in  ovector.  For  convenience,  the  functions         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2041         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2042         string_list() are provided for extracting captured substrings  as  new,         string_list()  are  provided for extracting captured substrings as new,
2043         separate,  zero-terminated strings. These functions identify substrings         separate, zero-terminated strings. These functions identify  substrings
2044         by number. The next section describes functions  for  extracting  named         by  number.  The  next section describes functions for extracting named
2045         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2046         extracted and has a further zero added on the end, but  the  result  is  
2047         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2048           a  further zero added on the end, but the result is not, of course, a C
2049           string.  However, you can process such a string  by  referring  to  the
2050           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2051           string().  Unfortunately, the interface to pcre_get_substring_list() is
2052           not  adequate for handling strings containing binary zeros, because the
2053           end of the final string is not independently indicated.
2054    
2055         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-
2056         tions: subject is the subject string that has  just  been  successfully         tions:  subject  is  the subject string that has just been successfully
2057         matched, ovector is a pointer to the vector of integer offsets that was         matched, ovector is a pointer to the vector of integer offsets that was
2058         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2059         were  captured  by  the match, including the substring that matched the         were captured by the match, including the substring  that  matched  the
2060         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2061         it  is greater than zero. If pcre_exec() returned zero, indicating that         it is greater than zero. If pcre_exec() returned zero, indicating  that
2062         it ran out of space in ovector, the value passed as stringcount  should         it  ran out of space in ovector, the value passed as stringcount should
2063         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2064    
2065         The  functions pcre_copy_substring() and pcre_get_substring() extract a         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2066         single substring, whose number is given as  stringnumber.  A  value  of         single  substring,  whose  number  is given as stringnumber. A value of
2067         zero  extracts  the  substring that matched the entire pattern, whereas         zero extracts the substring that matched the  entire  pattern,  whereas
2068         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2069         string(),  the  string  is  placed  in buffer, whose length is given by         string(), the string is placed in buffer,  whose  length  is  given  by
2070         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2071         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2072         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
2073         the terminating zero, or one of         the terminating zero, or one of these error codes:
2074    
2075           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2076    
2077         The  buffer  was too small for pcre_copy_substring(), or the attempt to         The buffer was too small for pcre_copy_substring(), or the  attempt  to
2078         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2079    
2080           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2081    
2082         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2083    
2084         The pcre_get_substring_list()  function  extracts  all  available  sub-         The  pcre_get_substring_list()  function  extracts  all  available sub-
2085         strings  and  builds  a list of pointers to them. All this is done in a         strings and builds a list of pointers to them. All this is  done  in  a
2086         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
2087         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
2088         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
2089         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
2090           error code
2091    
2092           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2093    
# Line 1831  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2106  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2106         tively.  They  do  nothing  more  than  call the function pointed to by         tively.  They  do  nothing  more  than  call the function pointed to by
2107         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.
2108         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-
2109         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2110         pcre_free  directly;  it is for these cases that the functions are pro-         pcre_free  directly;  it is for these cases that the functions are pro-
2111         vided.         vided.
2112    
# Line 1854  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2129  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2129         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-
2130         ber.  For example, for this pattern         ber.  For example, for this pattern
2131    
2132           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2133    
2134         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
2135         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
2136         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-
2137         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
2138         there is no subpattern of that name.         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2139           subpattern of that name.
2140    
2141         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
2142         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2143         are also two functions that do the whole job.         are also two functions that do the whole job.
2144    
2145         Most    of    the    arguments   of   pcre_copy_named_substring()   and         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2146         pcre_get_named_substring() are the same  as  those  for  the  similarly         pcre_get_named_substring()  are  the  same  as  those for the similarly
2147         named  functions  that extract by number. As these are described in the         named functions that extract by number. As these are described  in  the
2148         previous section, they are not re-described here. There  are  just  two         previous  section,  they  are not re-described here. There are just two
2149         differences:         differences:
2150    
2151         First,  instead  of a substring number, a substring name is given. Sec-         First, instead of a substring number, a substring name is  given.  Sec-
2152         ond, there is an extra argument, given at the start, which is a pointer         ond, there is an extra argument, given at the start, which is a pointer
2153         to  the compiled pattern. This is needed in order to gain access to the         to the compiled pattern. This is needed in order to gain access to  the
2154         name-to-number translation table.         name-to-number translation table.
2155    
2156         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2157         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2158         ate.         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2159           behaviour may not be what you want (see the next section).
2160    
2161    
2162    DUPLICATE SUBPATTERN NAMES
2163    
2164           int pcre_get_stringtable_entries(const pcre *code,
2165                const char *name, char **first, char **last);
2166    
2167           When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2168           subpatterns  are  not  required  to  be unique. Normally, patterns with
2169           duplicate names are such that in any one match, only one of  the  named
2170           subpatterns  participates. An example is shown in the pcrepattern docu-
2171           mentation. When duplicates are present, pcre_copy_named_substring() and
2172           pcre_get_named_substring()  return the first substring corresponding to
2173           the given name that is set.  If  none  are  set,  an  empty  string  is
2174           returned.  The pcre_get_stringnumber() function returns one of the num-
2175           bers that are associated with the name, but it is not defined which  it
2176           is.
2177    
2178           If  you want to get full details of all captured substrings for a given
2179           name, you must use  the  pcre_get_stringtable_entries()  function.  The
2180           first argument is the compiled pattern, and the second is the name. The
2181           third and fourth are pointers to variables which  are  updated  by  the
2182           function. After it has run, they point to the first and last entries in
2183           the name-to-number table  for  the  given  name.  The  function  itself
2184           returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2185           there are none. The format of the table is described above in the  sec-
2186           tion  entitled  Information  about  a  pattern.  Given all the relevant
2187           entries for the name, you can extract each of their numbers, and  hence
2188           the captured data, if any.
2189    
2190    
2191  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2192    
2193         The traditional matching function uses a  similar  algorithm  to  Perl,         The  traditional  matching  function  uses a similar algorithm to Perl,
2194         which stops when it finds the first match, starting at a given point in         which stops when it finds the first match, starting at a given point in
2195         the subject. If you want to find all possible matches, or  the  longest         the  subject.  If you want to find all possible matches, or the longest
2196         possible  match,  consider using the alternative matching function (see         possible match, consider using the alternative matching  function  (see
2197         below) instead. If you cannot use the alternative function,  but  still         below)  instead.  If you cannot use the alternative function, but still
2198         need  to  find all possible matches, you can kludge it up by making use         need to find all possible matches, you can kludge it up by  making  use
2199         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2200         tation.         tation.
2201    
2202         What you have to do is to insert a callout right at the end of the pat-         What you have to do is to insert a callout right at the end of the pat-
2203         tern.  When your callout function is called, extract and save the  cur-         tern.   When your callout function is called, extract and save the cur-
2204         rent  matched  substring.  Then  return  1, which forces pcre_exec() to         rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2205         backtrack and try other alternatives. Ultimately, when it runs  out  of         backtrack  and  try other alternatives. Ultimately, when it runs out of
2206         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2207    
2208    
# Line 1907  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2213  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2213              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2214              int *workspace, int wscount);              int *workspace, int wscount);
2215    
2216         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2217         against a compiled pattern, using a "DFA" matching algorithm. This  has         against  a  compiled pattern, using a matching algorithm that scans the
2218         different  characteristics to the normal algorithm, and is not compati-         subject string just once, and does not backtrack.  This  has  different
2219         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics  to  the  normal  algorithm, and is not compatible with
2220         Nevertheless, there are times when this kind of matching can be useful.         Perl. Some of the features of PCRE patterns are not  supported.  Never-
2221         For a discussion of the two matching algorithms, see  the  pcrematching         theless,  there are times when this kind of matching can be useful. For
2222         documentation.         a discussion of the two matching algorithms, see the pcrematching docu-
2223           mentation.
2224    
2225         The  arguments  for  the  pcre_dfa_exec()  function are the same as for         The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2226         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
# Line 1925  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2232  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2232         workspace vector should contain at least 20 elements. It  is  used  for         workspace vector should contain at least 20 elements. It  is  used  for
2233         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2234         workspace will be needed for patterns and subjects where  there  are  a         workspace will be needed for patterns and subjects where  there  are  a
2235         lot of possible matches.         lot of potential matches.
2236    
2237         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2238    
2239           int rc;           int rc;
2240           int ovector[10];           int ovector[10];
2241           int wspace[20];           int wspace[20];
2242           rc = pcre_exec(           rc = pcre_dfa_exec(
2243             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2244             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2245             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1947  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2254  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2254     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2255    
2256         The  unused  bits  of  the options argument for pcre_dfa_exec() must be         The  unused  bits  of  the options argument for pcre_dfa_exec() must be
2257         zero. The only bits that may be  set  are  PCRE_ANCHORED,  PCRE_NOTBOL,         zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2258         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
2259         PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last  three  of         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2260         these  are  the  same  as  for pcre_exec(), so their description is not         three of these are the same as for pcre_exec(), so their description is
2261         repeated here.         not repeated here.
2262    
2263           PCRE_PARTIAL           PCRE_PARTIAL
2264    
# Line 1966  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2273  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2273           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2274    
2275         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2276         stop  as  soon  as  it  has found one match. Because of the way the DFA         stop as soon as it has found one match. Because of the way the alterna-
2277         algorithm works, this is necessarily the shortest possible match at the         tive algorithm works, this is necessarily the shortest  possible  match
2278         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2279    
2280           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2281    
# Line 2004  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2311  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2311         On success, the yield of the function is a number  greater  than  zero,         On success, the yield of the function is a number  greater  than  zero,
2312         which  is  the  number of matched substrings. The substrings themselves         which  is  the  number of matched substrings. The substrings themselves
2313         are returned in ovector. Each string uses two elements;  the  first  is         are returned in ovector. Each string uses two elements;  the  first  is
2314         the  offset  to the start, and the second is the offset to the end. All         the  offset  to  the start, and the second is the offset to the end. In
2315         the strings have the same start offset. (Space could have been saved by         fact, all the strings have the same start  offset.  (Space  could  have
2316         giving  this only once, but it was decided to retain some compatibility         been  saved by giving this only once, but it was decided to retain some
2317         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility with the way pcre_exec() returns data,  even  though  the
2318         strings is different.)         meaning of the strings is different.)
2319    
2320         The strings are returned in reverse order of length; that is, the long-         The strings are returned in reverse order of length; that is, the long-
2321         est matching string is given first. If there were too many  matches  to         est matching string is given first. If there were too many  matches  to
# Line 2030  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2337  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2337    
2338           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2339    
2340         This  return is given if pcre_dfa_exec() encounters a condition item in         This  return  is  given  if pcre_dfa_exec() encounters a condition item
2341         a pattern that uses a back reference for the  condition.  This  is  not         that uses a back reference for the condition, or a test  for  recursion
2342         supported.         in a specific group. These are not supported.
2343    
2344           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2345    
# Line 2052  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2359  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2359         This error is given if the output vector  is  not  large  enough.  This         This error is given if the output vector  is  not  large  enough.  This
2360         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2361    
2362  Last updated: 16 May 2005  
2363  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2364    
2365           pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2366           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
2367    
2368    
2369    AUTHOR
2370    
2371           Philip Hazel
2372           University Computing Service
2373           Cambridge CB2 3QH, England.
2374    
2375    
2376    REVISION
2377    
2378           Last updated: 06 March 2007
2379           Copyright (c) 1997-2007 University of Cambridge.
2380  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2381    
2382    
# Line 2211  RETURN VALUES Line 2534  RETURN VALUES
2534         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
2535         itself.         itself.
2536    
2537  Last updated: 28 February 2005  
2538  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2539    
2540           Philip Hazel
2541           University Computing Service
2542           Cambridge CB2 3QH, England.
2543    
2544    
2545    REVISION
2546    
2547           Last updated: 06 March 2007
2548           Copyright (c) 1997-2007 University of Cambridge.
2549  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2550    
2551    
# Line 2226  NAME Line 2559  NAME
2559  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2560    
2561         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2562         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2563         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2564           tures that are expected to be in the forthcoming Perl 5.10.
2565         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2566         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
2567           of  what  it does have are given in the section on UTF-8 support in the
2568           main pcre page.
2569    
2570         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2571         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 2257  DIFFERENCES BETWEEN PCRE AND PERL Line 2592  DIFFERENCES BETWEEN PCRE AND PERL
2592         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
2593         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2594         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-
2595         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2596           derived properties Any and L&.
2597    
2598         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2599         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2600         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2601         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2602         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2603    
2604             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2272  DIFFERENCES BETWEEN PCRE AND PERL Line 2608  DIFFERENCES BETWEEN PCRE AND PERL
2608             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2609             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2610    
2611         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2612         classes.         classes.
2613    
2614         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2615         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2616         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
2617         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2618         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2619    
2620         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2621         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2622         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2623    
2624           10.  There are some differences that are concerned with the settings of
2625           captured strings when part of  a  pattern  is  repeated.  For  example,
2626           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2627         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2628    
2629         10. PCRE provides some extensions to the Perl regular expression facil-         11. PCRE provides some extensions to the Perl regular expression facil-
2630         ities:         ities.   Perl  5.10  will  include new features that are not in earlier
2631           versions, some of which (such as named parentheses) have been  in  PCRE
2632           for some time. This list is with respect to Perl 5.10:
2633    
2634         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2635         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2636         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2637    
2638         (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 $
2639         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2640    
2641         (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-
2642         cial meaning is faulted.         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2643           ignored. (Perl can be made to issue a warning.)
2644    
2645         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2646         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 2309  DIFFERENCES BETWEEN PCRE AND PERL Line 2652  DIFFERENCES BETWEEN PCRE AND PERL
2652         (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-
2653         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2654    
2655         (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.)  
2656    
2657         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The partial matching facility is PCRE-specific.
2658    
2659         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2660         Sun's Java package.         even on different hosts that have the other endianness.
2661    
2662         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2663           different way and is not Perl-compatible.
2664    
        (k) The callout facility is PCRE-specific.  
2665    
2666         (l) The partial matching facility is PCRE-specific.  AUTHOR
2667    
2668         (m) Patterns compiled by PCRE can be saved and re-used at a later time,         Philip Hazel
2669         even on different hosts that have the other endianness.         University Computing Service
2670           Cambridge CB2 3QH, England.
2671    
        (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  
        different way and is not Perl-compatible.  
2672    
2673  Last updated: 28 February 2005  REVISION
2674  Copyright (c) 1997-2005 University of Cambridge.  
2675           Last updated: 06 March 2007
2676           Copyright (c) 1997-2007 University of Cambridge.
2677  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2678    
2679    
# Line 2367  PCRE REGULAR EXPRESSION DETAILS Line 2709  PCRE REGULAR EXPRESSION DETAILS
2709         function, and how it differs from the normal function, are discussed in         function, and how it differs from the normal function, are discussed in
2710         the pcrematching page.         the pcrematching page.
2711    
2712    
2713    CHARACTERS AND METACHARACTERS
2714    
2715         A regular expression is a pattern that is  matched  against  a  subject         A regular expression is a pattern that is  matched  against  a  subject
2716         string  from  left  to right. Most characters stand for themselves in a         string  from  left  to right. Most characters stand for themselves in a
2717         pattern, and match the corresponding characters in the  subject.  As  a         pattern, and match the corresponding characters in the  subject.  As  a
# Line 2391  PCRE REGULAR EXPRESSION DETAILS Line 2736  PCRE REGULAR EXPRESSION DETAILS
2736    
2737         There are two different sets of metacharacters: those that  are  recog-         There are two different sets of metacharacters: those that  are  recog-
2738         nized  anywhere in the pattern except within square brackets, and those         nized  anywhere in the pattern except within square brackets, and those
2739         that are recognized in square brackets. Outside  square  brackets,  the         that are recognized within square brackets.  Outside  square  brackets,
2740         metacharacters are as follows:         the metacharacters are as follows:
2741    
2742           \      general escape character with several uses           \      general escape character with several uses
2743           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2439  BACKSLASH Line 2784  BACKSLASH
2784    
2785         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2786         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
2787         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2788         An escaping backslash can be used to include a whitespace or #  charac-         ing backslash can be used to include a whitespace  or  #  character  as
2789         ter as part of the pattern.         part of the pattern.
2790    
2791         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-
2792         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-
# Line 2477  BACKSLASH Line 2822  BACKSLASH
2822           \t        tab (hex 09)           \t        tab (hex 09)
2823           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
2824           \xhh      character with hex code hh           \xhh      character with hex code hh
2825           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
2826    
2827         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,
2828         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
# Line 2485  BACKSLASH Line 2830  BACKSLASH
2830         becomes hex 7B.         becomes hex 7B.
2831    
2832         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
2833         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
2834         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
2835         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,
2836         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than
2837         \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-
2838         recognized. Instead, the initial \x will  be  interpreted  as  a  basic         nating }, this form of escape is not recognized.  Instead, the  initial
2839         hexadecimal  escape, with no following digits, giving a character whose         \x will be interpreted as a basic hexadecimal escape, with no following
2840         value is zero.         digits, giving a character whose value is zero.
2841    
2842         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
2843         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-
2844         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}.
2845         \x{dc}.  
2846           After \0 up to two further octal digits are read. If  there  are  fewer
2847         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
2848         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
2849         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
2850         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.  
2851    
2852         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-
2853         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
# Line 2516  BACKSLASH Line 2859  BACKSLASH
2859    
2860         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
2861         and  there have not been that many capturing subpatterns, PCRE re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
2862         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-
2863         gle byte from the least significant 8 bits of the value. Any subsequent         erate  a data character. Any subsequent digits stand for themselves. In
2864         digits stand for themselves.  For example:         non-UTF-8 mode, the value of a character specified  in  octal  must  be
2865           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
2866           example:
2867    
2868           \040   is another way of writing a space           \040   is another way of writing a space
2869           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2538  BACKSLASH Line 2883  BACKSLASH
2883         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
2884         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2885    
2886         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
2887         character (in UTF-8 mode) can be used both inside and outside character         inside and outside character classes. In addition, inside  a  character
2888         classes.  In  addition,  inside  a  character class, the sequence \b is         class,  the  sequence \b is interpreted as the backspace character (hex
2889         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"
2890         interpreted  as  the  character  "X".  Outside a character class, these         and  "X", respectively. Outside a character class, these sequences have
2891         sequences have different meanings (see below).         different meanings (see below).
2892    
2893       Absolute and relative back references
2894    
2895           The sequence \g followed by a positive or negative  number,  optionally
2896           enclosed  in  braces,  is  an absolute or relative back reference. Back
2897           references are discussed later, following the discussion  of  parenthe-
2898           sized subpatterns.
2899    
2900     Generic character types     Generic character types
2901    
2902         The third use of backslash is for specifying generic  character  types.         Another use of backslash is for specifying generic character types. The
2903         The following are always recognized:         following are always recognized:
2904    
2905           \d     any decimal digit           \d     any decimal digit
2906           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 2558  BACKSLASH Line 2910  BACKSLASH
2910           \W     any "non-word" character           \W     any "non-word" character
2911    
2912         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
2913         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
2914         of each pair.         of each pair.
2915    
2916         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
2917         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
2918         If  the current matching point is at the end of the subject string, all         If the current matching point is at the end of the subject string,  all
2919         of them fail, since there is no character to match.         of them fail, since there is no character to match.
2920    
2921         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
2922         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
2923         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
2924           "use locale;" is included in a Perl script, \s may match the VT charac-
2925           ter. In PCRE, it never does.)
2926    
2927         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
2928         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-
2929         trolled by PCRE's low-valued character tables, and may vary if  locale-         trolled  by PCRE's low-valued character tables, and may vary if locale-
2930         specific  matching is taking place (see "Locale support" in the pcreapi         specific matching is taking place (see "Locale support" in the  pcreapi
2931         page). For example, in the  "fr_FR"  (French)  locale,  some  character         page).  For  example,  in  a French locale such as "fr_FR" in Unix-like
2932         codes  greater  than  128  are used for accented letters, and these are         systems, or "french" in Windows, some character codes greater than  128
2933         matched by \w.         are used for accented letters, and these are matched by \w.
2934    
2935         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,
2936         \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-
2937         code character property support is available.         code  character  property support is available. The use of locales with
2938           Unicode is discouraged.
2939    
2940       Newline sequences
2941    
2942           Outside a character class, the escape sequence \R matches  any  Unicode
2943           newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2944           equivalent to the following:
2945    
2946             (?>\r\n|\n|\x0b|\f|\r|\x85)
2947    
2948           This is an example of an "atomic group", details  of  which  are  given
2949           below.  This particular group matches either the two-character sequence
2950           CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
2951           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2952           return, U+000D), or NEL (next line, U+0085). The two-character sequence
2953           is treated as a single unit that cannot be split.
2954    
2955           In  UTF-8  mode, two additional characters whose codepoints are greater
2956           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2957           rator,  U+2029).   Unicode character property support is not needed for
2958           these characters to be recognized.
2959    
2960           Inside a character class, \R matches the letter "R".
2961    
2962     Unicode character properties     Unicode character properties
2963    
2964         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
2965         tional  escape sequences to match generic character types are available         tional  escape  sequences  to  match character properties are available
2966         when UTF-8 mode is selected. They are:         when UTF-8 mode is selected. They are:
2967    
2968          \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
2969          \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
2970          \X       an extended Unicode sequence           \X       an extended Unicode sequence
2971    
2972         The property names represented by xx above are limited to  the  Unicode         The property names represented by xx above are limited to  the  Unicode
2973         general  category properties. Each character has exactly one such prop-         script names, the general category properties, and "Any", which matches
2974         erty, specified by a two-letter abbreviation.  For  compatibility  with         any character (including newline). Other properties such as "InMusical-
2975         Perl,  negation  can be specified by including a circumflex between the         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
2976         opening brace and the property name. For example, \p{^Lu} is  the  same         not match any characters, so always causes a match failure.
2977         as \P{Lu}.  
2978           Sets of Unicode characters are defined as belonging to certain scripts.
2979         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.
2980         properties that start with that letter. In this case, in the absence of         For example:
2981         negation, the curly brackets in the escape sequence are optional; these  
2982         two examples have the same effect:           \p{Greek}
2983             \P{Han}
2984    
2985           Those that are not part of an identified script are lumped together  as
2986           "Common". The current list of scripts is:
2987    
2988           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
2989           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
2990           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
2991           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
2992           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
2993           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
2994           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
2995           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
2996           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
2997    
2998           Each  character has exactly one general category property, specified by
2999           a two-letter abbreviation. For compatibility with Perl, negation can be
3000           specified  by  including a circumflex between the opening brace and the
3001           property name. For example, \p{^Lu} is the same as \P{Lu}.
3002    
3003           If only one letter is specified with \p or \P, it includes all the gen-
3004           eral  category properties that start with that letter. In this case, in
3005           the absence of negation, the curly brackets in the escape sequence  are
3006           optional; these two examples have the same effect:
3007    
3008           \p{L}           \p{L}
3009           \pL           \pL
3010    
3011         The following property codes are supported:         The following general category property codes are supported:
3012    
3013           C     Other           C     Other
3014           Cc    Control           Cc    Control
# Line 2653  BACKSLASH Line 3054  BACKSLASH
3054           Zp    Paragraph separator           Zp    Paragraph separator
3055           Zs    Space separator           Zs    Space separator
3056    
3057         Extended properties such as "Greek" or "InMusicalSymbols" are not  sup-         The  special property L& is also supported: it matches a character that
3058         ported by PCRE.         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
3059           classified as a modifier or "other".
3060    
3061           The  long  synonyms  for  these  properties that Perl supports (such as
3062           \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3063           any of these properties with "Is".
3064    
3065           No character that is in the Unicode table has the Cn (unassigned) prop-
3066           erty.  Instead, this property is assumed for any code point that is not
3067           in the Unicode table.
3068    
3069         Specifying  caseless  matching  does not affect these escape sequences.         Specifying  caseless  matching  does not affect these escape sequences.
3070         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
# Line 2676  BACKSLASH Line 3086  BACKSLASH
3086    
3087     Simple assertions     Simple assertions
3088    
3089         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3090         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
3091         a  match, without consuming any characters from the subject string. The         a  match, without consuming any characters from the subject string. The
3092         use of subpatterns for more complicated assertions is described  below.         use of subpatterns for more complicated assertions is described  below.
# Line 2684  BACKSLASH Line 3094  BACKSLASH
3094    
3095           \b     matches at a word boundary           \b     matches at a word boundary
3096           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3097           \A     matches at start of subject           \A     matches at the start of the subject
3098           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3099           \z     matches at end of subject                   also matches before a newline at the end of the subject
3100           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3101             \G     matches at the first matching position in the subject
3102    
3103         These  assertions may not appear in character classes (but note that \b         These  assertions may not appear in character classes (but note that \b
3104         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
# Line 2707  BACKSLASH Line 3118  BACKSLASH
3118         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3119         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
3120         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
3121         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
3122         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.
3123         the end.  
3124           The \G assertion is true only when the current matching position is  at
3125         The  \G assertion is true only when the current matching position is at         the  start point of the match, as specified by the startoffset argument
3126         the start point of the match, as specified by the startoffset  argument         of pcre_exec(). It differs from \A when the  value  of  startoffset  is
3127         of  pcre_exec().  It  differs  from \A when the value of startoffset is         non-zero.  By calling pcre_exec() multiple times with appropriate argu-
        non-zero. By calling pcre_exec() multiple times with appropriate  argu-  
3128         ments, you can mimic Perl's /g option, and it is in this kind of imple-         ments, you can mimic Perl's /g option, and it is in this kind of imple-
3129         mentation where \G can be useful.         mentation where \G can be useful.
3130    
3131         Note, however, that PCRE's interpretation of \G, as the  start  of  the         Note,  however,  that  PCRE's interpretation of \G, as the start of the
3132         current match, is subtly different from Perl's, which defines it as the         current match, is subtly different from Perl's, which defines it as the
3133         end of the previous match. In Perl, these can  be  different  when  the         end  of  the  previous  match. In Perl, these can be different when the
3134         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3135         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3136    
3137         If all the alternatives of a pattern begin with \G, the  expression  is         If  all  the alternatives of a pattern begin with \G, the expression is
3138         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3139         in the compiled regular expression.         in the compiled regular expression.
3140    
# Line 2732  BACKSLASH Line 3142  BACKSLASH
3142  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3143    
3144         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3145         character  is  an  assertion  that is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3146         point is at the start of the subject string. If the  startoffset  argu-         point  is  at the start of the subject string. If the startoffset argu-
3147         ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the         ment of pcre_exec() is non-zero, circumflex  can  never  match  if  the
3148         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3149         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3150    
3151         Circumflex  need  not be the first character of the pattern if a number         Circumflex need not be the first character of the pattern if  a  number
3152         of alternatives are involved, but it should be the first thing in  each         of  alternatives are involved, but it should be the first thing in each
3153         alternative  in  which  it appears if the pattern is ever to match that         alternative in which it appears if the pattern is ever  to  match  that
3154         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3155         if  the  pattern  is constrained to match only at the start of the sub-         if the pattern is constrained to match only at the start  of  the  sub-
3156         ject, it is said to be an "anchored" pattern.  (There  are  also  other         ject,  it  is  said  to be an "anchored" pattern. (There are also other
3157         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3158    
3159         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
3160         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3161         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
3162         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
3163         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
3164         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.  
3165    
3166         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
3167         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
3168         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3169    
3170         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3171         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
3172         ately  after  and  immediately  before  an  internal newline character,         matches  immediately after internal newlines as well as at the start of
3173         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
3174         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         string.  A dollar matches before any newlines in the string, as well as
3175         string "def\nabc" (where \n represents a newline character)  in  multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3176         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3177         in single line mode because all branches start with ^ are not  anchored         not indicate newlines.
3178         in  multiline  mode,  and  a  match for circumflex is possible when the  
3179         startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3180         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3181           Consequently, patterns that are anchored in single  line  mode  because
3182         Note  that  the sequences \A, \Z, and \z can be used to match the start         all  branches  start  with  ^ are not anchored in multiline mode, and a
3183         and end of the subject in both modes, and if all branches of a  pattern         match for circumflex is  possible  when  the  startoffset  argument  of
3184         start  with  \A it is always anchored, whether PCRE_MULTILINE is set or         pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
3185         not.         PCRE_MULTILINE is set.
3186    
3187           Note that the sequences \A, \Z, and \z can be used to match  the  start
3188           and  end of the subject in both modes, and if all branches of a pattern
3189           start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3190           set.
3191    
3192    
3193  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3194    
3195         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-
3196         ter  in  the  subject,  including a non-printing character, but not (by         ter in the subject string except (by default) a character  that  signi-
3197         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
3198         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3199         the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-  
3200         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
3201         dollar, the only relationship being  that  they  both  involve  newline         that  character; when the two-character sequence CRLF is used, dot does
3202         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3203           matches  all characters (including isolated CRs and LFs). When any Uni-
3204           code line endings are being recognized, dot does not match CR or LF  or
3205           any of the other line ending characters.
3206    
3207           The  behaviour  of  dot  with regard to newlines can be changed. If the
3208           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3209           exception. If the two-character sequence CRLF is present in the subject
3210           string, it takes two dots to match it.
3211    
3212           The handling of dot is entirely independent of the handling of  circum-
3213           flex  and  dollar,  the  only relationship being that they both involve
3214           newlines. Dot has no special meaning in a character class.
3215    
3216    
3217  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3218    
3219         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3220         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
3221         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
3222         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-
3223         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-
3224         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3225           avoided.
3226    
3227         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3228         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-
# Line 2842  SQUARE BRACKETS AND CHARACTER CLASSES Line 3269  SQUARE BRACKETS AND CHARACTER CLASSES
3269         PCRE  is  compiled  with Unicode property support as well as with UTF-8         PCRE  is  compiled  with Unicode property support as well as with UTF-8
3270         support.         support.
3271    
3272         The newline character is never treated in any special way in  character         Characters that might indicate line breaks are  never  treated  in  any
3273         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         special  way  when  matching  character  classes,  whatever line-ending
3274         options is. A class such as [^a] will always match a newline.         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3275           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3276           of these characters.
3277    
3278         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-
3279         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 2870  SQUARE BRACKETS AND CHARACTER CLASSES Line 3299  SQUARE BRACKETS AND CHARACTER CLASSES
3299         If a range that includes letters is used when caseless matching is set,         If a range that includes letters is used when caseless matching is set,
3300         it matches the letters in either case. For example, [W-c] is equivalent         it matches the letters in either case. For example, [W-c] is equivalent
3301         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3302         character tables for the "fr_FR" locale are in use, [\xc8-\xcb] matches         character tables for a French locale are in  use,  [\xc8-\xcb]  matches
3303         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the
3304         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3305         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 2945  VERTICAL BAR Line 3374  VERTICAL BAR
3374    
3375         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3376         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3377         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3378         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
3379         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3380         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.  
3381    
3382    
3383  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 2977  INTERNAL OPTION SETTING Line 3405  INTERNAL OPTION SETTING
3405         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
3406         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3407    
3408         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
3409         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3410           it, so
3411    
3412           (a(?i)b)c           (a(?i)b)c
3413    
3414         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
3415         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3416         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3417         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3418         example,         example,
3419    
3420           (a(?i)b|c)           (a(?i)b|c)
3421    
3422         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3423         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3424         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3425         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3426    
3427         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3428         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
3429         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.  
3430    
3431    
3432  SUBPATTERNS  SUBPATTERNS
# Line 3013  SUBPATTERNS Line 3439  SUBPATTERNS
3439           cat(aract|erpillar|)           cat(aract|erpillar|)
3440    
3441         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3442         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3443         string.         string.
3444    
3445         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 3042  SUBPATTERNS Line 3468  SUBPATTERNS
3468           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3469    
3470         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3471         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.  
3472    
3473         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3474         start of a non-capturing subpattern,  the  option  letters  may  appear         start of a non-capturing subpattern,  the  option  letters  may  appear
# Line 3066  NAMED SUBPATTERNS Line 3490  NAMED SUBPATTERNS
3490         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3491         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3492         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3493         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3494         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3495         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3496           tax.
3497    
3498           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3499           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3500           to capturing parentheses from other parts of the pattern, such as back-
3501           references,  recursion,  and conditions, can be made by name as well as
3502           by number.
3503    
3504           Names consist of up to  32  alphanumeric  characters  and  underscores.
3505         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3506         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
3507         number  translation table from a compiled pattern. There is also a con-         function calls for extracting the name-to-number translation table from
3508         venience function for extracting a captured substring by name. For fur-         a compiled pattern. There is also a convenience function for extracting
3509         ther details see the pcreapi documentation.         a captured substring by name.
3510    
3511           By  default, a name must be unique within a pattern, but it is possible
3512           to relax this constraint by setting the PCRE_DUPNAMES option at compile
3513           time.  This  can  be useful for patterns where only one instance of the
3514           named parentheses can match. Suppose you want to match the  name  of  a
3515           weekday,  either as a 3-letter abbreviation or as the full name, and in
3516           both cases you want to extract the abbreviation. This pattern (ignoring
3517           the line breaks) does the job:
3518    
3519             (?<DN>Mon|Fri|Sun)(?:day)?|
3520             (?<DN>Tue)(?:sday)?|
3521             (?<DN>Wed)(?:nesday)?|
3522             (?<DN>Thu)(?:rsday)?|
3523             (?<DN>Sat)(?:urday)?
3524    
3525           There  are  five capturing substrings, but only one is ever set after a
3526           match.  The convenience  function  for  extracting  the  data  by  name
3527           returns  the  substring  for  the first (and in this example, the only)
3528           subpattern of that name that matched.  This  saves  searching  to  find
3529           which  numbered  subpattern  it  was. If you make a reference to a non-
3530           unique named subpattern from elsewhere in the  pattern,  the  one  that
3531           corresponds  to  the  lowest number is used. For further details of the
3532           interfaces for handling named subpatterns, see the  pcreapi  documenta-
3533           tion.
3534    
3535    
3536  REPETITION  REPETITION
# Line 3083  REPETITION Line 3539  REPETITION
3539         following items:         following items:
3540    
3541           a literal data character           a literal data character
3542           the . metacharacter           the dot metacharacter
3543           the \C escape sequence           the \C escape sequence
3544           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3545             the \R escape sequence
3546           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3547           a character class           a character class
3548           a back reference (see next section)           a back reference (see next section)
# Line 3125  REPETITION Line 3582  REPETITION
3582         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3583         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3584    
3585         For  convenience  (and  historical compatibility) the three most common         For  convenience, the three most common quantifiers have single-charac-
3586         quantifiers have single-character abbreviations:         ter abbreviations:
3587    
3588           *    is equivalent to {0,}           *    is equivalent to {0,}
3589           +    is equivalent to {1,}           +    is equivalent to {1,}
# Line 3178  REPETITION Line 3635  REPETITION
3635         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
3636         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3637    
3638         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
3639         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3640         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
3641         words, it inverts the default behaviour.         words, it inverts the default behaviour.
# Line 3189  REPETITION Line 3646  REPETITION
3646         minimum or maximum.         minimum or maximum.
3647    
3648         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-
3649         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,
3650         pattern is implicitly anchored, because whatever follows will be  tried         the pattern is implicitly anchored, because whatever  follows  will  be
3651         against  every character position in the subject string, so there is no         tried  against every character position in the subject string, so there
3652         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
3653         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
3654           by \A.
3655    
3656         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-
3657         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-
3658         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3659    
3660         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3661         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3662         backreference  elsewhere in the pattern, a match at the start may fail,         backreference elsewhere in the pattern, a match at the start  may  fail
3663         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3664    
3665           (.*)abc\1           (.*)abc\1
3666    
3667         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3668         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3669    
3670         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 3215  REPETITION Line 3673  REPETITION
3673           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
3674    
3675         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
3676         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
3677         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
3678         tions. For example, after         tions. For example, after
3679    
3680           /(a|(b))+/           /(a|(b))+/
# Line 3226  REPETITION Line 3684  REPETITION
3684    
3685  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
3686    
3687         With both maximizing and minimizing repetition, failure of what follows         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
3688         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition,  failure  of what follows normally causes the repeated item
3689         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
3690         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,
3691         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
3692         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
3693           no point in carrying on.
3694    
3695         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider, for example, the pattern \d+foo when applied to  the  subject
3696         line         line
# Line 3245  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3704  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3704         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
3705         to be re-evaluated in this way.         to be re-evaluated in this way.
3706    
3707         If we use atomic grouping for the previous example, the  matcher  would         If we use atomic grouping for the previous example, the  matcher  gives
3708         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
3709         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:  
3710    
3711           (?>\d+)foo           (?>\d+)foo
3712    
# Line 3280  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3738  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3738         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
3739         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
3740         simpler forms of atomic group. However, there is no difference  in  the         simpler forms of atomic group. However, there is no difference  in  the
3741         meaning  or  processing  of  a possessive quantifier and the equivalent         meaning  of  a  possessive  quantifier and the equivalent atomic group,
3742         atomic group.         though there may be a performance  difference;  possessive  quantifiers
3743           should be slightly faster.
3744         The possessive quantifier syntax is an extension to the Perl syntax. It  
3745         originates in Sun's Java package.         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
3746           tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first
3747         When  a  pattern  contains an unlimited repeat inside a subpattern that         edition of his book. Mike McCloskey liked it, so implemented it when he
3748         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
3749         atomic  group  is  the  only way to avoid some failing matches taking a         found its way into Perl at release 5.10.
3750    
3751           PCRE has an optimization that automatically "possessifies" certain sim-
3752           ple pattern constructs. For example, the sequence  A+B  is  treated  as
3753           A++B  because  there is no point in backtracking into a sequence of A's
3754           when B must follow.
3755    
3756           When a pattern contains an unlimited repeat inside  a  subpattern  that
3757           can  itself  be  repeated  an  unlimited number of times, the use of an
3758           atomic group is the only way to avoid some  failing  matches  taking  a
3759         very long time indeed. The pattern         very long time indeed. The pattern
3760    
3761           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
3762    
3763         matches an unlimited number of substrings that either consist  of  non-         matches  an  unlimited number of substrings that either consist of non-
3764         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it
3765         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
3766    
3767           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
3768    
3769         it takes a long time before reporting  failure.  This  is  because  the         it  takes  a  long  time  before reporting failure. This is because the
3770         string  can be divided between the internal \D+ repeat and the external         string can be divided between the internal \D+ repeat and the  external
3771         * 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
3772         example  uses  [!?]  rather than a single character at the end, because         example uses [!?] rather than a single character at  the  end,  because
3773         both PCRE and Perl have an optimization that allows  for  fast  failure         both  PCRE  and  Perl have an optimization that allows for fast failure
3774         when  a single character is used. They remember the last single charac-         when a single character is used. They remember the last single  charac-
3775         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
3776         in  the  string.)  If  the pattern is changed so that it uses an atomic         in the string.) If the pattern is changed so that  it  uses  an  atomic
3777         group, like this:         group, like this:
3778    
3779           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
3780    
3781         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences  of non-digits cannot be broken, and failure happens quickly.
3782    
3783    
3784  BACK REFERENCES  BACK REFERENCES
3785    
3786         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
3787         0 (and possibly further digits) is a back reference to a capturing sub-         0 (and possibly further digits) is a back reference to a capturing sub-
3788         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
3789         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
3790    
3791         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
3792         it  is  always  taken  as a back reference, and causes an error only if         it is always taken as a back reference, and causes  an  error  only  if
3793         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
3794         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
3795         to the left of the reference for numbers less than 10. See the  subsec-         to  the left of the reference for numbers less than 10. A "forward back
3796         tion  entitled  "Non-printing  characters" above for further details of         reference" of this type can make sense when a  repetition  is  involved
3797         the handling of digits following a backslash.         and  the  subpattern to the right has participated in an earlier itera-
3798           tion.
3799    
3800           It is not possible to have a numerical "forward back  reference"  to  a
3801           subpattern  whose  number  is  10  or  more using this syntax because a
3802           sequence such as \50 is interpreted as a character  defined  in  octal.
3803           See the subsection entitled "Non-printing characters" above for further
3804           details of the handling of digits following a backslash.  There  is  no
3805           such  problem  when named parentheses are used. A back reference to any
3806           subpattern is possible using named parentheses (see below).
3807    
3808           Another way of avoiding the ambiguity inherent in  the  use  of  digits
3809           following a backslash is to use the \g escape sequence, which is a fea-
3810           ture introduced in Perl 5.10. This escape must be followed by  a  posi-
3811           tive  or  a negative number, optionally enclosed in braces. These exam-
3812           ples are all identical:
3813    
3814             (ring), \1
3815             (ring), \g1
3816             (ring), \g{1}
3817    
3818           A positive number specifies an absolute reference without the ambiguity
3819           that  is  present  in  the older syntax. It is also useful when literal
3820           digits follow the reference. A negative number is a relative reference.
3821           Consider this example:
3822    
3823             (abc(def)ghi)\g{-1}
3824    
3825           The sequence \g{-1} is a reference to the most recently started captur-
3826           ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,
3827           \g{-2} would be equivalent to \1. The use of relative references can be
3828           helpful in long patterns, and also in  patterns  that  are  created  by
3829           joining together fragments that contain references within themselves.
3830    
3831         A back reference matches whatever actually matched the  capturing  sub-         A  back  reference matches whatever actually matched the capturing sub-
3832         pattern  in  the  current subject string, rather than anything matching         pattern in the current subject string, rather  than  anything  matching
3833         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
3834         of doing that). So the pattern         of doing that). So the pattern
3835    
3836           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
3837    
3838         matches  "sense and sensibility" and "response and responsibility", but         matches "sense and sensibility" and "response and responsibility",  but
3839         not "sense and responsibility". If caseful matching is in force at  the         not  "sense and responsibility". If caseful matching is in force at the
3840         time  of the back reference, the case of letters is relevant. For exam-         time of the back reference, the case of letters is relevant. For  exam-
3841         ple,         ple,
3842    
3843           ((?i)rah)\s+\1           ((?i)rah)\s+\1
3844    
3845         matches "rah rah" and "RAH RAH", but not "RAH  rah",  even  though  the         matches  "rah  rah"  and  "RAH RAH", but not "RAH rah", even though the
3846         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
3847    
3848         Back  references  to named subpatterns use the Python syntax (?P=name).         Back references to named subpatterns use the Perl  syntax  \k<name>  or
3849         We could rewrite the above example as follows:         \k'name'  or  the  Python  syntax (?P=name). We could rewrite the above
3850           example in either of the following ways:
3851    
3852             (?<p1>(?i)rah)\s+\k<p1>
3853             (?P<p1>(?i)rah)\s+(?P=p1)
3854    
3855           (?<p1>(?i)rah)\s+(?P=p1)         A subpattern that is referenced by  name  may  appear  in  the  pattern
3856           before or after the reference.
3857    
3858         There may be more than one back reference to the same subpattern. If  a         There  may be more than one back reference to the same subpattern. If a
3859         subpattern  has  not actually been used in a particular match, any back         subpattern has not actually been used in a particular match,  any  back
3860         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
3861    
3862           (a|(bc))\2           (a|(bc))\2
3863    
3864         always fails if it starts to match "a" rather than "bc". Because  there         always  fails if it starts to match "a" rather than "bc". Because there
3865         may  be  many  capturing parentheses in a pattern, all digits following         may be many capturing parentheses in a pattern,  all  digits  following
3866         the backslash are taken as part of a potential back  reference  number.         the  backslash  are taken as part of a potential back reference number.
3867         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
3868         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         used  to  terminate  the back reference. If the PCRE_EXTENDED option is
3869         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-
3870         ments" below) can be used.         ments" below) can be used.
3871    
3872         A back reference that occurs inside the parentheses to which it  refers         A  back reference that occurs inside the parentheses to which it refers
3873         fails  when  the subpattern is first used, so, for example, (a\1) never         fails when the subpattern is first used, so, for example,  (a\1)  never
3874         matches.  However, such references can be useful inside  repeated  sub-         matches.   However,  such references can be useful inside repeated sub-
3875         patterns. For example, the pattern         patterns. For example, the pattern
3876    
3877           (a|b\1)+           (a|b\1)+
3878    
3879         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-
3880         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
3881         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
3882         work, the pattern must be such that the first iteration does  not  need         work,  the  pattern must be such that the first iteration does not need
3883         to  match the back reference. This can be done using alternation, as in         to match the back reference. This can be done using alternation, as  in
3884         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
3885    
3886    
3887  ASSERTIONS  ASSERTIONS
3888    
3889         An assertion is a test on the characters  following  or  preceding  the         An  assertion  is  a  test on the characters following or preceding the
3890         current  matching  point that does not actually consume any characters.         current matching point that does not actually consume  any  characters.
3891         The simple assertions coded as \b, \B, \A, \G, \Z,  \z,  ^  and  $  are         The  simple  assertions  coded  as  \b, \B, \A, \G, \Z, \z, ^ and $ are
3892         described above.         described above.
3893    
3894         More  complicated  assertions  are  coded as subpatterns. There are two         More complicated assertions are coded as  subpatterns.  There  are  two
3895         kinds: those that look ahead of the current  position  in  the  subject         kinds:  those  that  look  ahead of the current position in the subject
3896         string,  and  those  that  look  behind  it. An assertion subpattern is         string, and those that look  behind  it.  An  assertion  subpattern  is
3897         matched in the normal way, except that it does not  cause  the  current         matched  in  the  normal way, except that it does not cause the current
3898         matching position to be changed.         matching position to be changed.
3899    
3900         Assertion  subpatterns  are  not  capturing subpatterns, and may not be         Assertion subpatterns are not capturing subpatterns,  and  may  not  be
3901         repeated, because it makes no sense to assert the  same  thing  several         repeated,  because  it  makes no sense to assert the same thing several
3902         times.  If  any kind of assertion contains capturing subpatterns within         times. If any kind of assertion contains capturing  subpatterns  within
3903         it, these are counted for the purposes of numbering the capturing  sub-         it,  these are counted for the purposes of numbering the capturing sub-
3904         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
3905         out only for positive assertions, because it does not  make  sense  for         out  only  for  positive assertions, because it does not make sense for
3906         negative assertions.         negative assertions.
3907    
3908     Lookahead assertions     Lookahead assertions
# Line 3408  ASSERTIONS Line 3912  ASSERTIONS
3912    
3913           \w+(?=;)           \w+(?=;)
3914    
3915         matches a word followed by a semicolon, but does not include the  semi-         matches  a word followed by a semicolon, but does not include the semi-
3916         colon in the match, and         colon in the match, and
3917    
3918           foo(?!bar)           foo(?!bar)
3919    
3920         matches  any  occurrence  of  "foo" that is not followed by "bar". Note         matches any occurrence of "foo" that is not  followed  by  "bar".  Note
3921         that the apparently similar pattern         that the apparently similar pattern
3922    
3923           (?!foo)bar           (?!foo)bar
3924    
3925         does not find an occurrence of "bar"  that  is  preceded  by  something         does  not  find  an  occurrence  of "bar" that is preceded by something
3926         other  than "foo"; it finds any occurrence of "bar" whatsoever, because         other than "foo"; it finds any occurrence of "bar" whatsoever,  because
3927         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
3928         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
3929    
3930         If you want to force a matching failure at some point in a pattern, the         If you want to force a matching failure at some point in a pattern, the
3931         most convenient way to do it is  with  (?!)  because  an  empty  string         most  convenient  way  to  do  it  is with (?!) because an empty string
3932         always  matches, so an assertion that requires there not to be an empty         always matches, so an assertion that requires there not to be an  empty
3933         string must always fail.         string must always fail.
3934    
3935     Lookbehind assertions     Lookbehind assertions
3936    
3937         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
3938         for negative assertions. For example,         for negative assertions. For example,
3939    
3940           (?<!foo)bar           (?<!foo)bar
3941    
3942         does  find  an  occurrence  of "bar" that is not preceded by "foo". The         does find an occurrence of "bar" that is not  preceded  by  "foo".  The
3943         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
3944         strings it matches must have a fixed length. However, if there are sev-         strings it matches must have a fixed length. However, if there are sev-
3945         eral alternatives, they do not all have to have the same fixed  length.         eral  top-level  alternatives,  they  do  not all have to have the same
3946         Thus         fixed length. Thus
3947    
3948           (?<=bullock|donkey)           (?<=bullock|donkey)
3949    
# Line 3447  ASSERTIONS Line 3951  ASSERTIONS
3951    
3952           (?<!dogs?|cats?)           (?<!dogs?|cats?)
3953    
3954         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
3955         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
3956         This  is  an  extension  compared  with  Perl (at least for 5.8), which         This is an extension compared with  Perl  (at  least  for  5.8),  which
3957         requires all branches to match the same length of string. An  assertion         requires  all branches to match the same length of string. An assertion
3958         such as         such as
3959    
3960           (?<=ab(c|de))           (?<=ab(c|de))
3961    
3962         is  not  permitted,  because  its single top-level branch can match two         is not permitted, because its single top-level  branch  can  match  two
3963         different lengths, but it is acceptable if rewritten to  use  two  top-         different  lengths,  but  it is acceptable if rewritten to use two top-
3964         level branches:         level branches:
3965    
3966           (?<=abc|abde)           (?<=abc|abde)
3967    
3968         The  implementation  of lookbehind assertions is, for each alternative,         The implementation of lookbehind assertions is, for  each  alternative,
3969         to temporarily move the current position back by the  fixed  width  and         to  temporarily  move the current position back by the fixed length and
3970         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
3971         rent position, the match is deemed to fail.         rent position, the assertion fails.
3972    
3973         PCRE does not allow the \C escape (which matches a single byte in UTF-8         PCRE does not allow the \C escape (which matches a single byte in UTF-8
3974         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode) to appear in lookbehind assertions, because it makes it  impossi-
3975         ble to calculate the length of the lookbehind. The \X escape, which can         ble  to  calculate the length of the lookbehind. The \X and \R escapes,
3976         match different numbers of bytes, is also not permitted.         which can match different numbers of bytes, are also not permitted.
3977    
3978         Atomic  groups can be used in conjunction with lookbehind assertions to         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind
3979         specify efficient matching at the end of the subject string. Consider a         assertions  to  specify  efficient  matching  at the end of the subject
3980         simple pattern such as         string. Consider a simple pattern such as
3981    
3982           abcd$           abcd$
3983    
3984         when  applied  to  a  long string that does not match. Because matching         when applied to a long string that does  not  match.  Because  matching
3985         proceeds from left to right, PCRE will look for each "a" in the subject         proceeds from left to right, PCRE will look for each "a" in the subject
3986         and  then  see  if what follows matches the rest of the pattern. If the         and then see if what follows matches the rest of the  pattern.  If  the
3987         pattern is specified as         pattern is specified as
3988    
3989           ^.*abcd$           ^.*abcd$
3990    
3991         the initial .* matches the entire string at first, but when this  fails         the  initial .* matches the entire string at first, but when this fails
3992         (because there is no following "a"), it backtracks to match all but the         (because there is no following "a"), it backtracks to match all but the
3993         last character, then all but the last two characters, and so  on.  Once         last  character,  then all but the last two characters, and so on. Once
3994         again  the search for "a" covers the entire string, from right to left,         again the search for "a" covers the entire string, from right to  left,
3995         so we are no better off. However, if the pattern is written as         so we are no better off. However, if the pattern is written as
3996    
          ^(?>.*)(?<=abcd)  
   
        or, equivalently, using the possessive quantifier syntax,  
   
3997           ^.*+(?<=abcd)           ^.*+(?<=abcd)
3998    
3999         there can be no backtracking for the .* item; it  can  match  only  the         there  can  be  no backtracking for the .*+ item; it can match only the
4000         entire  string.  The subsequent lookbehind assertion does a single test         entire string. The subsequent lookbehind assertion does a  single  test
4001         on the last four characters. If it fails, the match fails  immediately.         on  the last four characters. If it fails, the match fails immediately.
4002         For  long  strings, this approach makes a significant difference to the         For long strings, this approach makes a significant difference  to  the
4003         processing time.         processing time.
4004    
4005     Using multiple assertions     Using multiple assertions
# Line 3508  ASSERTIONS Line 4008  ASSERTIONS
4008    
4009           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4010    
4011         matches "foo" preceded by three digits that are not "999". Notice  that         matches  "foo" preceded by three digits that are not "999". Notice that
4012         each  of  the  assertions is applied independently at the same point in         each of the assertions is applied independently at the  same  point  in
4013         the subject string. First there is a  check  that  the  previous  three         the  subject  string.  First  there  is a check that the previous three
4014         characters  are  all  digits,  and  then there is a check that the same         characters are all digits, and then there is  a  check  that  the  same
4015         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4016         ceded  by  six  characters,  the first of which are digits and the last         ceded by six characters, the first of which are  digits  and  the  last
4017         three of which are not "999". For example, it  doesn't  match  "123abc-         three  of  which  are not "999". For example, it doesn't match "123abc-
4018         foo". A pattern to do that is         foo". A pattern to do that is
4019    
4020           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4021    
4022         This  time  the  first assertion looks at the preceding six characters,         This time the first assertion looks at the  preceding  six  characters,
4023         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4024         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4025    
# Line 3527  ASSERTIONS Line 4027  ASSERTIONS
4027    
4028           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4029    
4030         matches  an occurrence of "baz" that is preceded by "bar" which in turn         matches an occurrence of "baz" that is preceded by "bar" which in  turn
4031         is not preceded by "foo", while         is not preceded by "foo", while
4032    
4033           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4034    
4035         is another pattern that matches "foo" preceded by three digits and  any         is  another pattern that matches "foo" preceded by three digits and any
4036         three characters that are not "999".         three characters that are not "999".
4037    
4038    
4039  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4040    
4041         It  is possible to cause the matching process to obey a subpattern con-         It is possible to cause the matching process to obey a subpattern  con-
4042         ditionally or to choose between two alternative subpatterns,  depending         ditionally  or to choose between two alternative subpatterns, depending
4043         on  the result of an assertion, or whether a previous capturing subpat-         on the result of an assertion, or whether a previous capturing  subpat-
4044         tern matched or not. The two possible forms of  conditional  subpattern         tern  matched  or not. The two possible forms of conditional subpattern
4045         are         are
4046    
4047           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4048           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4049    
4050         If  the  condition is satisfied, the yes-pattern is used; otherwise the         If the condition is satisfied, the yes-pattern is used;  otherwise  the
4051         no-pattern (if present) is used. If there are more  than  two  alterna-         no-pattern  (if  present)  is used. If there are more than two alterna-
4052         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4053    
4054         There are three kinds of condition. If the text between the parentheses         There are four kinds of condition: references  to  subpatterns,  refer-
4055         consists of a sequence of digits, the condition  is  satisfied  if  the         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4056         capturing  subpattern of that number has previously matched. The number  
4057         must be greater than zero. Consider the following pattern,  which  con-     Checking for a used subpattern by number
4058         tains  non-significant white space to make it more readable (assume the  
4059         PCRE_EXTENDED option) and to divide it into three  parts  for  ease  of         If  the  text between the parentheses consists of a sequence of digits,
4060         discussion:         the condition is true if the capturing subpattern of  that  number  has
4061           previously matched.
4062    
4063           Consider  the  following  pattern, which contains non-significant white
4064           space to make it more readable (assume the PCRE_EXTENDED option) and to
4065           divide it into three parts for ease of discussion:
4066    
4067           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4068    
# Line 3572  CONDITIONAL SUBPATTERNS Line 4077  CONDITIONAL SUBPATTERNS
4077         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other  words,  this  pattern  matches  a  sequence  of non-parentheses,
4078         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4079    
4080         If the condition is the string (R), it is satisfied if a recursive call     Checking for a used subpattern by name
4081         to  the pattern or subpattern has been made. At "top level", the condi-  
4082         tion is false.  This  is  a  PCRE  extension.  Recursive  patterns  are         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a
4083         described in the next section.         used  subpattern  by  name.  For compatibility with earlier versions of
4084           PCRE, which had this facility before Perl, the syntax  (?(name)...)  is
4085           also  recognized. However, there is a possible ambiguity with this syn-
4086           tax, because subpattern names may  consist  entirely  of  digits.  PCRE
4087           looks  first for a named subpattern; if it cannot find one and the name
4088           consists entirely of digits, PCRE looks for a subpattern of  that  num-
4089           ber,  which must be greater than zero. Using subpattern names that con-
4090           sist entirely of digits is not recommended.
4091    
4092           Rewriting the above example to use a named subpattern gives this:
4093    
4094             (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
4095    
4096    
4097       Checking for pattern recursion
4098    
4099           If the condition is the string (R), and there is no subpattern with the
4100           name  R, the condition is true if a recursive call to the whole pattern
4101           or any subpattern has been made. If digits or a name preceded by amper-
4102           sand follow the letter R, for example:
4103    
4104             (?(R3)...) or (?(R&name)...)
4105    
4106         If  the  condition  is  not  a sequence of digits or (R), it must be an         the  condition is true if the most recent recursion is into the subpat-
4107           tern whose number or name is given. This condition does not  check  the
4108           entire recursion stack.
4109    
4110           At  "top  level", all these recursion test conditions are false. Recur-
4111           sive patterns are described below.
4112    
4113       Defining subpatterns for use by reference only
4114    
4115           If the condition is the string (DEFINE), and  there  is  no  subpattern
4116           with  the  name  DEFINE,  the  condition is always false. In this case,
4117           there may be only one alternative  in  the  subpattern.  It  is  always
4118           skipped  if  control  reaches  this  point  in the pattern; the idea of
4119           DEFINE is that it can be used to define "subroutines" that can be  ref-
4120           erenced  from elsewhere. (The use of "subroutines" is described below.)
4121           For example, a pattern to match an IPv4 address could be  written  like
4122           this (ignore whitespace and line breaks):
4123    
4124             (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
4125             \b (?&byte) (\.(?&byte)){3} \b
4126    
4127           The  first part of the pattern is a DEFINE group inside which a another
4128           group named "byte" is defined. This matches an individual component  of
4129           an  IPv4  address  (a number less than 256). When matching takes place,
4130           this part of the pattern is skipped because DEFINE acts  like  a  false
4131           condition.
4132    
4133           The rest of the pattern uses references to the named group to match the
4134           four dot-separated components of an IPv4 address, insisting on  a  word
4135           boundary at each end.
4136    
4137       Assertion conditions
4138    
4139           If  the  condition  is  not  in any of the above formats, it must be an
4140         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.  This may be a positive or negative lookahead or  lookbehind
4141         assertion.  Consider  this  pattern,  again  containing non-significant         assertion.  Consider  this  pattern,  again  containing non-significant
4142         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
# Line 3602  COMMENTS Line 4161  COMMENTS
4161         at all.         at all.
4162    
4163         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If  the PCRE_EXTENDED option is set, an unescaped # character outside a
4164         character class introduces a comment that continues up to the next new-         character class introduces a  comment  that  continues  to  immediately
4165         line character in the pattern.         after the next newline in the pattern.
4166    
4167    
4168  RECURSIVE PATTERNS  RECURSIVE PATTERNS
# Line 3612  RECURSIVE PATTERNS Line 4171  RECURSIVE PATTERNS
4171         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited nested parentheses. Without the use of  recursion,  the  best
4172         that  can  be  done  is  to use a pattern that matches up to some fixed         that  can  be  done  is  to use a pattern that matches up to some fixed
4173         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth of nesting. It is not possible to  handle  an  arbitrary  nesting
4174         depth.  Perl  provides  a  facility  that allows regular expressions to         depth.
4175         recurse (amongst other things). It does this by interpolating Perl code  
4176         in the expression at run time, and the code can refer to the expression         For some time, Perl has provided a facility that allows regular expres-
4177         itself. A Perl pattern to solve the parentheses problem can be  created         sions to recurse (amongst other things). It does this by  interpolating
4178         like this:         Perl  code in the expression at run time, and the code can refer to the
4179           expression itself. A Perl pattern using code interpolation to solve the
4180           parentheses problem can be created like this:
4181    
4182           $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x;           $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x;
4183    
4184         The (?p{...}) item interpolates Perl code at run time, and in this case         The (?p{...}) item interpolates Perl code at run time, and in this case
4185         refers recursively to the pattern in which it appears. Obviously,  PCRE         refers recursively to the pattern in which it appears.
4186         cannot  support  the  interpolation  of Perl code. Instead, it supports  
4187         some special syntax for recursion of the entire pattern, and  also  for         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4188         individual subpattern recursion.         it  supports  special  syntax  for recursion of the entire pattern, and
4189           also for individual subpattern recursion.  After  its  introduction  in
4190           PCRE  and  Python,  this  kind of recursion was introduced into Perl at
4191           release 5.10.
4192    
4193         The  special item that consists of (? followed by a number greater than         A special item that consists of (? followed by a  number  greater  than
4194         zero and a closing parenthesis is a recursive call of the subpattern of         zero and a closing parenthesis is a recursive call of the subpattern of
4195         the  given  number, provided that it occurs inside that subpattern. (If         the given number, provided that it occurs inside that  subpattern.  (If
4196         not, it is a "subroutine" call, which is described  in  the  next  sec-         not,  it  is  a  "subroutine" call, which is described in the next sec-
4197         tion.)  The special item (?R) is a recursive call of the entire regular         tion.) The special item (?R) or (?0) is a recursive call of the  entire
4198         expression.         regular expression.
4199    
4200           In  PCRE (like Python, but unlike Perl), a recursive subpattern call is
4201           always treated as an atomic group. That is, once it has matched some of
4202           the subject string, it is never re-entered, even if it contains untried
4203           alternatives and there is a subsequent matching failure.
4204    
4205         For example, this PCRE pattern solves the  nested  parentheses  problem         This PCRE pattern solves the nested  parentheses  problem  (assume  the
4206         (assume  the  PCRE_EXTENDED  option  is  set  so  that  white  space is         PCRE_EXTENDED option is set so that white space is ignored):
        ignored):  
4207    
4208           \( ( (?>[^()]+) | (?R) )* \)           \( ( (?>[^()]+) | (?R) )* \)
4209    
4210         First it matches an opening parenthesis. Then it matches any number  of         First  it matches an opening parenthesis. Then it matches any number of
4211         substrings  which  can  either  be  a sequence of non-parentheses, or a         substrings which can either be a  sequence  of  non-parentheses,  or  a
4212         recursive match of the pattern itself (that is  a  correctly  parenthe-         recursive  match  of the pattern itself (that is, a correctly parenthe-
4213         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis.
4214    
4215         If  this  were  part of a larger pattern, you would not want to recurse         If this were part of a larger pattern, you would not  want  to  recurse
4216         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4217    
4218           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( (?>[^()]+) | (?1) )* \) )
4219    
4220         We have put the pattern into parentheses, and caused the  recursion  to         We  have  put the pattern into parentheses, and caused the recursion to
4221         refer  to them instead of the whole pattern. In a larger pattern, keep-         refer to them instead of the whole pattern. In a larger pattern,  keep-
4222         ing track of parenthesis numbers can be tricky. It may be  more  conve-         ing  track  of parenthesis numbers can be tricky. It may be more conve-
4223         nient  to use named parentheses instead. For this, PCRE uses (?P>name),         nient to use named parentheses instead. The Perl  syntax  for  this  is
4224         which is an extension to the Python syntax that  PCRE  uses  for  named         (?&name);  PCRE's  earlier syntax (?P>name) is also supported. We could
4225         parentheses (Perl does not provide named parentheses). We could rewrite         rewrite the above example as follows:
4226         the above example as follows:  
4227             (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
4228           (?P<pn> \( ( (?>[^()]+) | (?P>pn) )* \) )  
4229           If there is more than one subpattern with the same name,  the  earliest
4230         This particular example pattern contains nested unlimited repeats,  and         one  is used. This particular example pattern contains nested unlimited
4231         so  the  use of atomic grouping for matching strings of non-parentheses         repeats, and so the use of atomic grouping for matching strings of non-
4232         is important when applying the pattern to strings that  do  not  match.         parentheses  is  important when applying the pattern to strings that do
4233         For example, when this pattern is applied to         not match. For example, when this pattern is applied to
4234    
4235           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
4236    
4237         it  yields "no match" quickly. However, if atomic grouping is not used,         it yields "no match" quickly. However, if atomic grouping is not  used,
4238         the match runs for a very long time indeed because there  are  so  many         the  match  runs  for a very long time indeed because there are so many
4239         different  ways  the  + and * repeats can carve up the subject, and all         different ways the + and * repeats can carve up the  subject,  and  all
4240         have to be tested before failure can be reported.         have to be tested before failure can be reported.
4241    
4242         At the end of a match, the values set for any capturing subpatterns are         At the end of a match, the values set for any capturing subpatterns are
4243         those from the outermost level of the recursion at which the subpattern         those from the outermost level of the recursion at which the subpattern
4244         value is set.  If you want to obtain  intermediate  values,  a  callout         value  is  set.   If  you want to obtain intermediate values, a callout
4245         function can be used (see the next section and the pcrecallout documen-         function can be used (see below and the pcrecallout documentation).  If
4246         tation). If the pattern above is matched against         the pattern above is matched against
4247    
4248           (ab(cd)ef)           (ab(cd)ef)
4249    
4250         the value for the capturing parentheses is  "ef",  which  is  the  last         the  value  for  the  capturing  parentheses is "ef", which is the last
4251         value  taken  on at the top level. If additional parentheses are added,         value taken on at the top level. If additional parentheses  are  added,
4252         giving         giving
4253    
4254           \( ( ( (?>[^()]+) | (?R) )* ) \)           \( ( ( (?>[^()]+) | (?R) )* ) \)
4255              ^                        ^