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# 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-anycrlf
316    
317           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
318           CRLF as indicating a line ending. Finally, a fifth option, specified by
319    
320             --enable-newline-is-any
321    
322           causes PCRE to recognize any Unicode newline sequence.
323    
324           Whatever line ending convention is selected when PCRE is built  can  be
325           overridden  when  the library functions are called. At build time it is
326           conventional to use the standard for your operating system.
327    
328    
329  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
# Line 319  POSIX MALLOC USAGE Line 354  POSIX MALLOC USAGE
354         to the configure command.         to the configure command.
355    
356    
 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.  
   
   
357  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
358    
359         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 371  HANDLING VERY LARGE PATTERNS
371         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
372         additional bytes when handling them.         additional bytes when handling them.
373    
        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.  
   
374    
375  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
376    
377         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
378         ing by making recursive calls to an internal function  called  match().         ing  by  making recursive calls to an internal function called match().
379         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-
380         verely limit PCRE's operation. (The Unix environment does  not  usually         verely  limit  PCRE's operation. (The Unix environment does not usually
381         suffer  from  this  problem.)  An alternative approach that uses memory         suffer from this problem, but it may sometimes be necessary to increase
382         from the heap to remember data, instead  of  using  recursive  function         the  maximum  stack size.  There is a discussion in the pcrestack docu-
383         calls,  has been implemented to work round this problem. If you want to         mentation.) An alternative approach to recursion that uses memory  from
384         build a version of PCRE that works this way, add         the  heap  to remember data, instead of using recursive function calls,
385           has been implemented to work round the problem of limited  stack  size.
386           If you want to build a version of PCRE that works this way, add
387    
388           --disable-stack-for-recursion           --disable-stack-for-recursion
389    
390         to the configure command. With this configuration, PCRE  will  use  the         to  the  configure  command. With this configuration, PCRE will use the
391         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
392         ment functions. Separate functions are provided because  the  usage  is         ment  functions.  Separate  functions are provided because the usage is
393         very  predictable:  the  block sizes requested are always the same, and         very predictable: the block sizes requested are always  the  same,  and
394         the blocks are always freed in reverse order. A calling  program  might         the  blocks  are always freed in reverse order. A calling program might
395         be  able  to implement optimized functions that perform better than the         be able to implement optimized functions that perform better  than  the
396         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more
397         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()
398         function; it is not relevant for the the pcre_dfa_exec() function.         function; it is not relevant for the the pcre_dfa_exec() function.
399    
400    
401    LIMITING PCRE RESOURCE USAGE
402    
403           Internally,  PCRE has a function called match(), which it calls repeat-
404           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
405           pcre_exec()  function.  By controlling the maximum number of times this
406           function may be called during a single matching operation, a limit  can
407           be  placed  on  the resources used by a single call to pcre_exec(). The
408           limit can be changed at run time, as described in the pcreapi  documen-
409           tation.  The default is 10 million, but this can be changed by adding a
410           setting such as
411    
412             --with-match-limit=500000
413    
414           to  the  configure  command.  This  setting  has  no  effect   on   the
415           pcre_dfa_exec() matching function.
416    
417           In  some  environments  it is desirable to limit the depth of recursive
418           calls of match() more strictly than the total number of calls, in order
419           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
420           for-recursion is specified) that is used. A second limit controls this;
421           it  defaults  to  the  value  that is set for --with-match-limit, which
422           imposes no additional constraints. However, you can set a  lower  limit
423           by adding, for example,
424    
425             --with-match-limit-recursion=10000
426    
427           to  the  configure  command.  This  value can also be overridden at run
428           time.
429    
430    
431    CREATING CHARACTER TABLES AT BUILD TIME
432    
433           PCRE uses fixed tables for processing characters whose code values  are
434           less  than 256. By default, PCRE is built with a set of tables that are
435           distributed in the file pcre_chartables.c.dist. These  tables  are  for
436           ASCII codes only. If you add
437    
438             --enable-rebuild-chartables
439    
440           to  the  configure  command, the distributed tables are no longer used.
441           Instead, a program called dftables is compiled and  run.  This  outputs
442           the source for new set of tables, created in the default locale of your
443           C runtime system. (This method of replacing the tables does not work if
444           you  are cross compiling, because dftables is run on the local host. If
445           you need to create alternative tables when cross  compiling,  you  will
446           have to do so "by hand".)
447    
448    
449  USING EBCDIC CODE  USING EBCDIC CODE
450    
451         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
452         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
453         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by
454         adding         adding
455    
456           --enable-ebcdic           --enable-ebcdic
457    
458         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
459           bles.
460    
461  Last updated: 15 August 2005  
462  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
463    
464           pcreapi(3), pcre_config(3).
465    
466    
467    AUTHOR
468    
469           Philip Hazel
470           University Computing Service
471           Cambridge CB2 3QH, England.
472    
473    
474    REVISION
475    
476           Last updated: 16 April 2007
477           Copyright (c) 1997-2007 University of Cambridge.
478  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
479    
480    
# Line 431  PCRE MATCHING ALGORITHMS Line 510  PCRE MATCHING ALGORITHMS
510           <something> <something else> <something further>           <something> <something else> <something further>
511    
512         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
513         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
514    
515    
516  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 440  REGULAR EXPRESSIONS AS TREES Line 519  REGULAR EXPRESSIONS AS TREES
519         resented  as  a  tree structure. An unlimited repetition in the pattern         resented  as  a  tree structure. An unlimited repetition in the pattern
520         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
521         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
522         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
523         search  a  tree: depth-first and breadth-first, and these correspond to         tree:  depth-first  and  breadth-first, and these correspond to the two
524         the two matching algorithms provided by PCRE.         matching algorithms provided by PCRE.
525    
526    
527  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
528    
529         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
530         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
531         depth-first search of the pattern tree. That is, it  proceeds  along  a         depth-first search of the pattern tree. That is, it  proceeds  along  a
532         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
533         required. When there is a mismatch, the algorithm  tries  any  alterna-         required. When there is a mismatch, the algorithm  tries  any  alterna-
# Line 472  THE STANDARD MATCHING ALGORITHM Line 551  THE STANDARD MATCHING ALGORITHM
551         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
552    
553    
554  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
555    
556         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
557         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
558         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
559         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
560         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",
561         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
562           keeps multiple states active simultaneously).
563         The  scan  continues until either the end of the subject is reached, or  
564         there are no more unterminated paths. At this point,  terminated  paths         The scan continues until either the end of the subject is  reached,  or
565         represent  the different matching possibilities (if there are none, the         there  are  no more unterminated paths. At this point, terminated paths
566         match has failed).  Thus, if there is more  than  one  possible  match,         represent the different matching possibilities (if there are none,  the
567           match  has  failed).   Thus,  if there is more than one possible match,
568         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-
569         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
570         match (which is necessarily the shortest) has been found.         match (which is necessarily the shortest) has been found.
571    
572         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 574  THE DFA MATCHING ALGORITHM
574    
575           cat(er(pillar)?)           cat(er(pillar)?)
576    
577         is matched against the string "the caterpillar catchment",  the  result         is  matched  against the string "the caterpillar catchment", the result
578         will  be the three strings "cat", "cater", and "caterpillar" that start         will be the three strings "cat", "cater", and "caterpillar" that  start
579         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
580         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
581    
582         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
583         supported by the DFA matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
584    
585         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1.  Because  the  algorithm  finds  all possible matches, the greedy or
586         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
587         ungreedy quantifiers are treated in exactly the same way.         ungreedy quantifiers are treated in exactly the same way. However, pos-
588           sessive quantifiers can make a difference when what follows could  also
589           match what is quantified, for example in a pattern like this:
590    
591             ^a++\w!
592    
593           This  pattern matches "aaab!" but not "aaa!", which would be matched by
594           a non-possessive quantifier. Similarly, if an atomic group is  present,
595           it  is matched as if it were a standalone pattern at the current point,
596           and the longest match is then "locked in" for the rest of  the  overall
597           pattern.
598    
599         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
600         is  not  straightforward  to  keep track of captured substrings for the         is not straightforward to keep track of  captured  substrings  for  the
601         different matching possibilities, and  PCRE's  implementation  of  this         different  matching  possibilities,  and  PCRE's implementation of this
602         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-
603         strings are available.         strings are available.
604    
605         3. Because no substrings are captured, back references within the  pat-         3.  Because no substrings are captured, back references within the pat-
606         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
607    
608         4.  For  the same reason, conditional expressions that use a backrefer-         4. For the same reason, conditional expressions that use  a  backrefer-
609         ence as the condition are not supported.         ence  as  the  condition or test for a specific group recursion are not
610           supported.
611    
612         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
613         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.
614    
615         6.  The \C escape sequence, which (in the standard algorithm) matches a         6.  The \C escape sequence, which (in the standard algorithm) matches a
616         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-
617         rithm moves through the subject string one character at a time, for all         tive  algorithm  moves  through  the  subject string one character at a
618         active paths through the tree.         time, for all active paths through the tree.
619    
620    
621  ADVANTAGES OF THE DFA ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
622    
623         Using the DFA matching algorithm provides the following advantages:         Using the alternative matching algorithm provides the following  advan-
624           tages:
625    
626         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-
627         ically  found,  and  in particular, the longest match is found. To find         ically found, and in particular, the longest match is  found.  To  find
628         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
629         things with callouts.         things with callouts.
630    
631         2.  There is much better support for partial matching. The restrictions         2. There is much better support for partial matching. The  restrictions
632         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-
633         rithm  for partial matching do not apply to the DFA algorithm. For non-         rithm for partial matching do not apply to the  alternative  algorithm.
634         anchored patterns, the starting position of a partial match  is  avail-         For  non-anchored patterns, the starting position of a partial match is
635         able.         available.
636    
637         3.  Because  the  DFA algorithm scans the subject string just once, and         3. Because the alternative algorithm  scans  the  subject  string  just
638         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
639         strings  to  the matching function in several pieces, checking for par-         subject strings to the matching function in  several  pieces,  checking
640         tial matching each time.         for partial matching each time.
641    
642    
643  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
644    
645         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
646    
647         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
648         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
649         because it is less susceptible to optimization.         because it is less susceptible to optimization.
650    
651         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
652    
653         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
654         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
655         rithm.  
656    
657    AUTHOR
658    
659  Last updated: 28 February 2005         Philip Hazel
660  Copyright (c) 1997-2005 University of Cambridge.         University Computing Service
661           Cambridge CB2 3QH, England.
662    
663    
664    REVISION
665    
666           Last updated: 06 March 2007
667           Copyright (c) 1997-2007 University of Cambridge.
668  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
669    
670    
# Line 616  PCRE NATIVE API Line 717  PCRE NATIVE API
717         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
718              const char *name);              const char *name);
719    
720           int pcre_get_stringtable_entries(const pcre *code,
721                const char *name, char **first, char **last);
722    
723         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
724              int stringcount, int stringnumber,              int stringcount, int stringnumber,
725              const char **stringptr);              const char **stringptr);
# Line 654  PCRE NATIVE API Line 758  PCRE NATIVE API
758  PCRE API OVERVIEW  PCRE API OVERVIEW
759    
760         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
761         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
762         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
763         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
764         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 780  PCRE API OVERVIEW
780    
781         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
782         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
783         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
784         the  subject),  not  just  one. However, this algorithm does not return         point  in  the subject), and scans the subject just once. However, this
785         captured substrings. A description of the two matching  algorithms  and         algorithm does not return captured substrings. A description of the two
786         their  advantages  and disadvantages is given in the pcrematching docu-         matching  algorithms and their advantages and disadvantages is given in
787         mentation.         the pcrematching documentation.
788    
789         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
790         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 692  PCRE API OVERVIEW Line 796  PCRE API OVERVIEW
796           pcre_get_named_substring()           pcre_get_named_substring()
797           pcre_get_substring_list()           pcre_get_substring_list()
798           pcre_get_stringnumber()           pcre_get_stringnumber()
799             pcre_get_stringtable_entries()
800    
801         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
802         to free the memory used for extracted strings.         to free the memory used for extracted strings.
# Line 723  PCRE API OVERVIEW Line 828  PCRE API OVERVIEW
828         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
829         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
830         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
831         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
832         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-
833         management, it runs more slowly.  Separate functions  are  provided  so         ments that have limited stacks. Because of the greater  use  of  memory
834         that  special-purpose  external  code  can  be used for this case. When         management,  it  runs  more  slowly. Separate functions are provided so
835         used, these functions are always called in a  stack-like  manner  (last         that special-purpose external code can be  used  for  this  case.  When
836         obtained,  first freed), and always for memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
837           obtained, first freed), and always for memory blocks of the same  size.
838           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
839           mentation.
840    
841         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
842         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 844  PCRE API OVERVIEW
844         pcrecallout documentation.         pcrecallout documentation.
845    
846    
847    NEWLINES
848    
849           PCRE  supports five different conventions for indicating line breaks in
850           strings: a single CR (carriage return) character, a  single  LF  (line-
851           feed) character, the two-character sequence CRLF, any of the three pre-
852           ceding, or any Unicode newline sequence. The Unicode newline  sequences
853           are  the  three just mentioned, plus the single characters VT (vertical
854           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
855           separator, U+2028), and PS (paragraph separator, U+2029).
856    
857           Each  of  the first three conventions is used by at least one operating
858           system as its standard newline sequence. When PCRE is built, a  default
859           can  be  specified.  The default default is LF, which is the Unix stan-
860           dard. When PCRE is run, the default can be overridden,  either  when  a
861           pattern is compiled, or when it is matched.
862    
863           In the PCRE documentation the word "newline" is used to mean "the char-
864           acter or pair of characters that indicate a line break". The choice  of
865           newline  convention  affects  the  handling of the dot, circumflex, and
866           dollar metacharacters, the handling of #-comments in /x mode, and, when
867           CRLF  is a recognized line ending sequence, the match position advance-
868           ment for a non-anchored pattern. The choice of newline convention  does
869           not affect the interpretation of the \n or \r escape sequences.
870    
871    
872  MULTITHREADING  MULTITHREADING
873    
874         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 915  CHECKING BUILD-TIME OPTIONS
915    
916           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
917    
918         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
919         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
920         return (13), and should normally be the  standard  character  for  your         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
921         operating system.         and  -1  for  ANY. The default should normally be the standard sequence
922           for your operating system.
923    
924           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
925    
926         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
927         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
928         4.  Larger  values  allow larger regular expressions to be compiled, at         4. Larger values allow larger regular expressions to  be  compiled,  at
929         the expense of slower matching. The default value of  2  is  sufficient         the  expense  of  slower matching. The default value of 2 is sufficient
930         for  all  but  the  most massive patterns, since it allows the compiled         for all but the most massive patterns, since  it  allows  the  compiled
931         pattern to be up to 64K in size.         pattern to be up to 64K in size.
932    
933           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
934    
935         The output is an integer that contains the threshold  above  which  the         The  output  is  an integer that contains the threshold above which the
936         POSIX  interface  uses malloc() for output vectors. Further details are         POSIX interface uses malloc() for output vectors. Further  details  are
937         given in the pcreposix documentation.         given in the pcreposix documentation.
938    
939           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
940    
941         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
942         internal  matching  function  calls in a pcre_exec() execution. Further         internal matching function calls in a  pcre_exec()  execution.  Further
943         details are given with pcre_exec() below.         details are given with pcre_exec() below.
944    
945             PCRE_CONFIG_MATCH_LIMIT_RECURSION
946    
947           The  output is an integer that gives the default limit for the depth of
948           recursion when calling the internal matching function in a  pcre_exec()
949           execution. Further details are given with pcre_exec() below.
950    
951           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
952    
953         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
954         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
955         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
956         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
957         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
958         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
959         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
960    
961    
# Line 832  COMPILING A PATTERN Line 972  COMPILING A PATTERN
972    
973         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
974         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
975         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
976         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
977    
978         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
979         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
980         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
981         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
982         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
983         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
984         required.         longer required.
985    
986         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
987         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
988         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
989         ment, which is an address (see below).         ment, which is an address (see below).
990    
991         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
992         tion.  It  should  be  zero  if  no options are required. The available         pilation. It should be zero if no options are required.  The  available
993         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them, in particular, those that
994         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
995         pattern (see the detailed description  in  the  pcrepattern  documenta-         pattern  (see  the  detailed  description in the pcrepattern documenta-
996         tion).  For  these options, the contents of the options argument speci-         tion). For these options, the contents of the options  argument  speci-
997         fies their initial settings at the start of compilation and  execution.         fies  their initial settings at the start of compilation and execution.
998         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
999         at compile time.         of matching as well as at compile time.
1000    
1001         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1002         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1003         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-
1004         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
1005         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-
1006         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
1007           by  erroffset,  which must not be NULL. If it is, an immediate error is
1008         given.         given.
1009    
1010         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 1067  COMPILING A PATTERN
1067    
1068         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
1069         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
1070         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
1071         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1072         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
1073         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1074    
1075           PCRE_DOTALL           PCRE_DOTALL
1076    
1077         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-
1078         acters, including newlines. Without it,  newlines  are  excluded.  This         acters, including those that indicate newline. Without it, a  dot  does
1079         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
1080         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
1081         always  matches a newline character, independent of the setting of this         by  a (?s) option setting. A negative class such as [^a] always matches
1082         option.         newline characters, independent of the setting of this option.
1083    
1084             PCRE_DUPNAMES
1085    
1086           If this bit is set, names used to identify capturing  subpatterns  need
1087           not be unique. This can be helpful for certain types of pattern when it
1088           is known that only one instance of the named  subpattern  can  ever  be
1089           matched.  There  are  more details of named subpatterns below; see also
1090           the pcrepattern documentation.
1091    
1092           PCRE_EXTENDED           PCRE_EXTENDED
1093    
# Line 946  COMPILING A PATTERN Line 1095  COMPILING A PATTERN
1095         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1096         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1097         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1098         line character, inclusive, are also  ignored.  This  is  equivalent  to         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1099         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-
1100         option setting.         ting.
1101    
1102         This option makes it possible to include  comments  inside  complicated         This option makes it possible to include  comments  inside  complicated
1103         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 1113  COMPILING A PATTERN
1113         letter  that  has  no  special  meaning causes an error, thus reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1114         these combinations for future expansion. By  default,  as  in  Perl,  a         these combinations for future expansion. By  default,  as  in  Perl,  a
1115         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
1116         literal. There are at present no  other  features  controlled  by  this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1117         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
1118           can also be set by a (?X) option setting within a pattern.
1119    
1120           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1121    
1122         If  this  option  is  set,  an  unanchored pattern is required to match         If this option is set, an  unanchored  pattern  is  required  to  match
1123         before or at the first newline character in the subject string,  though         before  or  at  the  first  newline  in  the subject string, though the
1124         the matched text may continue over the newline.         matched text may continue over the newline.
1125    
1126           PCRE_MULTILINE           PCRE_MULTILINE
1127    
1128         By  default,  PCRE  treats the subject string as consisting of a single         By default, PCRE treats the subject string as consisting  of  a  single
1129         line of characters (even if it actually contains newlines). The  "start         line  of characters (even if it actually contains newlines). The "start
1130         of  line"  metacharacter  (^)  matches only at the start of the string,         of line" metacharacter (^) matches only at the  start  of  the  string,
1131         while the "end of line" metacharacter ($) matches only at  the  end  of         while  the  "end  of line" metacharacter ($) matches only at the end of
1132         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1133         is set). This is the same as Perl.         is set). This is the same as Perl.
1134    
1135         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"
1136         constructs  match  immediately following or immediately before any new-         constructs match immediately following or immediately  before  internal
1137         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
1138         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
1139         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-
1140         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,
1141         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1142    
1143             PCRE_NEWLINE_CR
1144             PCRE_NEWLINE_LF
1145             PCRE_NEWLINE_CRLF
1146             PCRE_NEWLINE_ANYCRLF
1147             PCRE_NEWLINE_ANY
1148    
1149           These  options  override the default newline definition that was chosen
1150           when PCRE was built. Setting the first or the second specifies  that  a
1151           newline  is  indicated  by a single character (CR or LF, respectively).
1152           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1153           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1154           that any of the three preceding sequences should be recognized. Setting
1155           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1156           recognized. The Unicode newline sequences are the three just mentioned,
1157           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1158           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1159           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1160           UTF-8 mode.
1161    
1162           The newline setting in the  options  word  uses  three  bits  that  are
1163           treated as a number, giving eight possibilities. Currently only six are
1164           used (default plus the five values above). This means that if  you  set
1165           more  than one newline option, the combination may or may not be sensi-
1166           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1167           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1168           cause an error.
1169    
1170           The only time that a line break is specially recognized when  compiling
1171           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1172           character class is encountered. This indicates  a  comment  that  lasts
1173           until  after the next line break sequence. In other circumstances, line
1174           break  sequences  are  treated  as  literal  data,   except   that   in
1175           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1176           and are therefore ignored.
1177    
1178           The newline option that is set at compile time becomes the default that
1179           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1180    
1181           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1182    
1183         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 1219  COMPILATION ERROR CODES
1219    
1220         The following table lists the error  codes  than  may  be  returned  by         The following table lists the error  codes  than  may  be  returned  by
1221         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(),  along with the error messages that may be returned by
1222         both compiling functions.         both compiling functions. As PCRE has developed, some error codes  have
1223           fallen out of use. To avoid confusion, they have not been re-used.
1224    
1225            0  no error            0  no error
1226            1  \ at end of pattern            1  \ at end of pattern
# Line 1043  COMPILATION ERROR CODES Line 1232  COMPILATION ERROR CODES
1232            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1233            8  range out of order in character class            8  range out of order in character class
1234            9  nothing to repeat            9  nothing to repeat
1235           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1236           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1237           12  unrecognized character after (?           12  unrecognized character after (?
1238           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 1241  COMPILATION ERROR CODES
1241           16  erroffset passed as NULL           16  erroffset passed as NULL
1242           17  unknown option bit(s) set           17  unknown option bit(s) set
1243           18  missing ) after comment           18  missing ) after comment
1244           19  parentheses nested too deeply           19  [this code is not in use]
1245           20  regular expression too large           20  regular expression too large
1246           21  failed to get memory           21  failed to get memory
1247           22  unmatched parentheses           22  unmatched parentheses
1248           23  internal error: code overflow           23  internal error: code overflow
1249           24  unrecognized character after (?<           24  unrecognized character after (?<
1250           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1251           26  malformed number after (?(           26  malformed number or name after (?(
1252           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1253           28  assertion expected after (?(           28  assertion expected after (?(
1254           29  (?R or (?digits must be followed by )           29  (?R or (?digits must be followed by )
1255           30  unknown POSIX class name           30  unknown POSIX class name
1256           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1257           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1258           33  spare error           33  [this code is not in use]
1259           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1260           35  invalid condition (?(0)           35  invalid condition (?(0)
1261           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1075  COMPILATION ERROR CODES Line 1264  COMPILATION ERROR CODES
1264           39  closing ) for (?C expected           39  closing ) for (?C expected
1265           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1266           41  unrecognized character after (?P           41  unrecognized character after (?P
1267           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1268           43  two named groups have the same name           43  two named subpatterns have the same name
1269           44  invalid UTF-8 string           44  invalid UTF-8 string
1270           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1271           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1272           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1273             48  subpattern name is too long (maximum 32 characters)
1274             49  too many named subpatterns (maximum 10,000)
1275             50  repeated subpattern is too long
1276             51  octal value is greater than \377 (not in UTF-8 mode)
1277             52  internal error: overran compiling workspace
1278             53   internal  error:  previously-checked  referenced  subpattern not
1279           found
1280             54  DEFINE group contains more than one branch
1281             55  repeating a DEFINE group is not allowed
1282             56  inconsistent NEWLINE options"
1283    
1284    
1285  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1111  STUDYING A PATTERN Line 1310  STUDYING A PATTERN
1310    
1311         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.
1312         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1313         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
1314         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
1315         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
1316           after calling pcre_study(), to be sure that it has run successfully.
1317    
1318         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1319    
# Line 1124  STUDYING A PATTERN Line 1324  STUDYING A PATTERN
1324             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1325    
1326         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1327         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-
1328         ble starting bytes is created.         ble starting bytes is created.
1329    
1330    
1331  LOCALE SUPPORT  LOCALE SUPPORT
1332    
1333         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1334         letters digits, or whatever, by reference to a set of  tables,  indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1335         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
1336         characters with codes less than 128. Higher-valued  codes  never  match         characters  with  codes  less than 128. Higher-valued codes never match
1337         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
1338         with Unicode character property support.         with  Unicode  character property support. The use of locales with Uni-
1339           code is discouraged. If you are handling characters with codes  greater
1340         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
1341         is  built.  This  is  used when the final argument of pcre_compile() is         not try to mix the two.
1342         NULL, and is sufficient for many applications. An  alternative  set  of  
1343         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
1344         locale from the default. As more and more applications change to  using         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1345         Unicode, the need for this locale support is expected to die away.         applications.  Normally, the internal tables recognize only ASCII char-
1346           acters. However, when PCRE is built, it is possible to cause the inter-
1347         External  tables  are  built by calling the pcre_maketables() function,         nal tables to be rebuilt in the default "C" locale of the local system,
1348         which has no arguments, in the relevant locale. The result can then  be         which may cause them to be different.
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         The  internal tables can always be overridden by tables supplied by the
1351         locale  (where  accented  characters  with  values greater than 128 are         application that calls PCRE. These may be created in a different locale
1352           from  the  default.  As more and more applications change to using Uni-
1353           code, the need for this locale support is expected to die away.
1354    
1355           External tables are built by calling  the  pcre_maketables()  function,
1356           which  has no arguments, in the relevant locale. The result can then be
1357           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1358           example,  to  build  and use tables that are appropriate for the French
1359           locale (where accented characters with  values  greater  than  128  are
1360         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1361    
1362           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1363           tables = pcre_maketables();           tables = pcre_maketables();
1364           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1365    
1366           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1367           if you are using Windows, the name for the French locale is "french".
1368    
1369         When pcre_maketables() runs, the tables are built  in  memory  that  is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1370         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1371         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 1411  INFORMATION ABOUT A PATTERN
1411         pattern:         pattern:
1412    
1413           int rc;           int rc;
1414           unsigned long int length;           size_t length;
1415           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1416             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1417             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
# Line 1232  INFORMATION ABOUT A PATTERN Line 1443  INFORMATION ABOUT A PATTERN
1443           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1444    
1445         Return  information  about  the first byte of any matched string, for a         Return  information  about  the first byte of any matched string, for a
1446         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored pattern. The fourth argument should point to an int  vari-
1447         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1448         compatibility.)         is still recognized for backwards compatibility.)
1449    
1450         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
1451         (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  
1452    
1453         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1454         branch starts with "^", or         branch starts with "^", or
1455    
1456         (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
1457         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1458    
1459         -1 is returned, indicating that the pattern matches only at  the  start         -1  is  returned, indicating that the pattern matches only at the start
1460         of  a  subject string or after any newline within the string. Otherwise         of a subject string or after any newline within the  string.  Otherwise
1461         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1462    
1463           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1464    
1465         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
1466         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
1467         matching string, a pointer to the table is returned. Otherwise NULL  is         matching  string, a pointer to the table is returned. Otherwise NULL is
1468         returned.  The fourth argument should point to an unsigned char * vari-         returned. The fourth argument should point to an unsigned char *  vari-
1469         able.         able.
1470    
1471           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1472    
1473         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
1474         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
1475         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1476         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
1477         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1478         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
1479         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1480    
# Line 1272  INFORMATION ABOUT A PATTERN Line 1482  INFORMATION ABOUT A PATTERN
1482           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1483           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1484    
1485         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1486         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1487         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1488         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1489         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
1490         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
1491         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1492         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
1493         which is described by these three values.         described by these three values.
1494    
1495         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
1496         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1497         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
1498         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1499         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
1500         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-
1501         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-
1502         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1503         For example, consider the following pattern  (assume  PCRE_EXTENDED  is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1504         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1505           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1506           ignored):
1507    
1508           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1509           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1510    
1511         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1512         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,
1513         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1514         as ??:         as ??:
1515    
# Line 1306  INFORMATION ABOUT A PATTERN Line 1518  INFORMATION ABOUT A PATTERN
1518           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1519           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1520    
1521         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1522         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
1523         be different for each compiled pattern.         to be different for each compiled pattern.
1524    
1525           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1526    
1527         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
1528         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1529         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1530         by any top-level option settings within the pattern itself.         by any top-level option settings within the pattern itself.
1531    
1532         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
1533         alternatives begin with one of the following:         alternatives begin with one of the following:
1534    
1535           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1331  INFORMATION ABOUT A PATTERN Line 1543  INFORMATION ABOUT A PATTERN
1543    
1544           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1545    
1546         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
1547         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
1548         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
1549         size_t variable.         size_t variable.
# Line 1339  INFORMATION ABOUT A PATTERN Line 1551  INFORMATION ABOUT A PATTERN
1551           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1552    
1553         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
1554         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
1555         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
1556         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
1557         variable.         variable.
1558    
1559    
# Line 1349  OBSOLETE INFO FUNCTION Line 1561  OBSOLETE INFO FUNCTION
1561    
1562         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1563    
1564         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1565         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1566         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1567         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-
1568         lowing negative numbers:         lowing negative numbers:
1569    
1570           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1571           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1572    
1573         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
1574         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
1575         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1576    
1577         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1578         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
1579         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1580    
1581    
# Line 1371  REFERENCE COUNTS Line 1583  REFERENCE COUNTS
1583    
1584         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1585    
1586         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1587         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
1588         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1589         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1590         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.
1591    
1592         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1593         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
1594         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
1595         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
1596         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
1597         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1598    
1599         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1600         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
1601         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1602    
1603    
# Line 1395  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1607  MATCHING A PATTERN: THE TRADITIONAL FUNC
1607              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1608              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1609    
1610         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
1611         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1612         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
1613         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1614         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
1615         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1616         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1617    
1618         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1619         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1620         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
1621         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1622         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1623    
1624         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 1637  MATCHING A PATTERN: THE TRADITIONAL FUNC
1637    
1638     Extra data for pcre_exec()     Extra data for pcre_exec()
1639    
1640         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
1641         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
1642         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-
1643         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
1644         lows:         fields (not necessarily in this order):
1645    
1646           unsigned long int flags;           unsigned long int flags;
1647           void *study_data;           void *study_data;
1648           unsigned long int match_limit;           unsigned long int match_limit;
1649             unsigned long int match_limit_recursion;
1650           void *callout_data;           void *callout_data;
1651           const unsigned char *tables;           const unsigned char *tables;
1652    
1653         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
1654         are set. The flag bits are:         are set. The flag bits are:
1655    
1656           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1657           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1658             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1659           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1660           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1661    
1662         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
1663         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1664         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
1665         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1666         flag bits.         flag bits.
1667    
1668         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
1669         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
1670         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1671         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1672         repeats.         repeats.
1673    
1674         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1675         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly  (sometimes  recursively). The limit set by match_limit is imposed
1676         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
1677         limiting the amount of recursion and backtracking that can take  place.         has  the  effect  of  limiting the amount of backtracking that can take
1678         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
1679         position in the subject string.         for each position in the subject string.
1680    
1681         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
1682         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1683         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1684         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra    block    in    which    match_limit    is    set,     and
1685         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
1686         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1687    
1688         The  pcre_callout  field is used in conjunction with the "callout" fea-         The match_limit_recursion field is similar to match_limit, but  instead
1689           of limiting the total number of times that match() is called, it limits
1690           the depth of recursion. The recursion depth is a  smaller  number  than
1691           the  total number of calls, because not all calls to match() are recur-
1692           sive.  This limit is of use only if it is set smaller than match_limit.
1693    
1694           Limiting  the  recursion  depth  limits the amount of stack that can be
1695           used, or, when PCRE has been compiled to use memory on the heap instead
1696           of the stack, the amount of heap memory that can be used.
1697    
1698           The  default  value  for  match_limit_recursion can be set when PCRE is
1699           built; the default default  is  the  same  value  as  the  default  for
1700           match_limit.  You can override the default by suppling pcre_exec() with
1701           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1702           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1703           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1704    
1705           The pcre_callout field is used in conjunction with the  "callout"  fea-
1706         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1707    
1708         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1709         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
1710         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
1711         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1712         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
1713         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-
1714         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
1715         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
1716         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1717         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1718    
1719     Option bits for pcre_exec()     Option bits for pcre_exec()
1720    
1721         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.
1722         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,
1723         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1724           PCRE_PARTIAL.
1725    
1726           PCRE_ANCHORED           PCRE_ANCHORED
1727    
# Line 1498  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1730  MATCHING A PATTERN: THE TRADITIONAL FUNC
1730         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
1731         unachored at matching time.         unachored at matching time.
1732    
1733             PCRE_NEWLINE_CR
1734             PCRE_NEWLINE_LF
1735             PCRE_NEWLINE_CRLF
1736             PCRE_NEWLINE_ANYCRLF
1737             PCRE_NEWLINE_ANY
1738    
1739           These options override  the  newline  definition  that  was  chosen  or
1740           defaulted  when the pattern was compiled. For details, see the descrip-
1741           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1742           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1743           ters. It may also alter the way the match position is advanced after  a
1744           match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,
1745           PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a  match  attempt
1746           fails  when the current position is at a CRLF sequence, the match posi-
1747           tion is advanced by two characters instead of one, in other  words,  to
1748           after the CRLF.
1749    
1750           PCRE_NOTBOL           PCRE_NOTBOL
1751    
1752         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1753         the  beginning  of  a  line, so the circumflex metacharacter should not         the beginning of a line, so the  circumflex  metacharacter  should  not
1754         match before it. Setting this without PCRE_MULTILINE (at compile  time)         match  before it. Setting this without PCRE_MULTILINE (at compile time)
1755         causes  circumflex  never to match. This option affects only the behav-         causes circumflex never to match. This option affects only  the  behav-
1756         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1757    
1758           PCRE_NOTEOL           PCRE_NOTEOL
1759    
1760         This option specifies that the end of the subject string is not the end         This option specifies that the end of the subject string is not the end
1761         of  a line, so the dollar metacharacter should not match it nor (except         of a line, so the dollar metacharacter should not match it nor  (except
1762         in multiline mode) a newline immediately before it. Setting this  with-         in  multiline mode) a newline immediately before it. Setting this with-
1763         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1764         option affects only the behaviour of the dollar metacharacter. It  does         option  affects only the behaviour of the dollar metacharacter. It does
1765         not affect \Z or \z.         not affect \Z or \z.
1766    
1767           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1768    
1769         An empty string is not considered to be a valid match if this option is         An empty string is not considered to be a valid match if this option is
1770         set. If there are alternatives in the pattern, they are tried.  If  all         set.  If  there are alternatives in the pattern, they are tried. If all
1771         the  alternatives  match  the empty string, the entire match fails. For         the alternatives match the empty string, the entire  match  fails.  For
1772         example, if the pattern         example, if the pattern
1773    
1774           a?b?           a?b?
1775    
1776         is applied to a string not beginning with "a" or "b",  it  matches  the         is  applied  to  a string not beginning with "a" or "b", it matches the
1777         empty  string at the start of the subject. With PCRE_NOTEMPTY set, this         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
1778         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
1779         rences of "a" or "b".         rences of "a" or "b".
1780    
1781         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1782         cial case of a pattern match of the empty  string  within  its  split()         cial  case  of  a  pattern match of the empty string within its split()
1783         function,  and  when  using  the /g modifier. It is possible to emulate         function, and when using the /g modifier. It  is  possible  to  emulate
1784         Perl's behaviour after matching a null string by first trying the match         Perl's behaviour after matching a null string by first trying the match
1785         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1786         if that fails by advancing the starting offset (see below)  and  trying         if  that  fails by advancing the starting offset (see below) and trying
1787         an ordinary match again. There is some code that demonstrates how to do         an ordinary match again. There is some code that demonstrates how to do
1788         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
1789    
1790           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1791    
1792         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
1793         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8 string is automatically checked when pcre_exec() is  subsequently
1794         called.  The value of startoffset is also checked  to  ensure  that  it         called.   The  value  of  startoffset is also checked to ensure that it
1795         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence         points to the start of a UTF-8 character. If an invalid UTF-8  sequence
1796         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1797         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is
1798         returned.         returned.
1799    
1800         If you already know that your subject is valid, and you  want  to  skip         If  you  already  know that your subject is valid, and you want to skip
1801         these    checks    for   performance   reasons,   you   can   set   the         these   checks   for   performance   reasons,   you   can    set    the
1802         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
1803         do  this  for the second and subsequent calls to pcre_exec() if you are         do this for the second and subsequent calls to pcre_exec() if  you  are
1804         making repeated calls to find all  the  matches  in  a  single  subject         making  repeated  calls  to  find  all  the matches in a single subject
1805         string.  However,  you  should  be  sure  that the value of startoffset         string. However, you should be  sure  that  the  value  of  startoffset
1806         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
1807         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         set, the effect of passing an invalid UTF-8 string as a subject,  or  a
1808         value of startoffset that does not point to the start of a UTF-8  char-         value  of startoffset that does not point to the start of a UTF-8 char-
1809         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1810    
1811           PCRE_PARTIAL           PCRE_PARTIAL
1812    
1813         This  option  turns  on  the  partial  matching feature. If the subject         This option turns on the  partial  matching  feature.  If  the  subject
1814         string fails to match the pattern, but at some point during the  match-         string  fails to match the pattern, but at some point during the match-
1815         ing  process  the  end of the subject was reached (that is, the subject         ing process the end of the subject was reached (that  is,  the  subject
1816         partially matches the pattern and the failure to  match  occurred  only         partially  matches  the  pattern and the failure to match occurred only
1817         because  there were not enough subject characters), pcre_exec() returns         because there were not enough subject characters), pcre_exec()  returns
1818         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1819         used,  there  are restrictions on what may appear in the pattern. These         used, there are restrictions on what may appear in the  pattern.  These
1820         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1821    
1822     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1823    
1824         The subject string is passed to pcre_exec() as a pointer in subject,  a         The  subject string is passed to pcre_exec() as a pointer in subject, a
1825         length  in  length, and a starting byte offset in startoffset. In UTF-8         length in length, and a starting byte offset in startoffset.  In  UTF-8
1826         mode, the byte offset must point to the start  of  a  UTF-8  character.         mode,  the  byte  offset  must point to the start of a UTF-8 character.
1827         Unlike  the  pattern string, the subject may contain binary zero bytes.         Unlike the pattern string, the subject may contain binary  zero  bytes.
1828         When the starting offset is zero, the search for a match starts at  the         When  the starting offset is zero, the search for a match starts at the
1829         beginning of the subject, and this is by far the most common case.         beginning of the subject, and this is by far the most common case.
1830    
1831         A  non-zero  starting offset is useful when searching for another match         A non-zero starting offset is useful when searching for  another  match
1832         in the same subject by calling pcre_exec() again after a previous  suc-         in  the same subject by calling pcre_exec() again after a previous suc-
1833         cess.   Setting  startoffset differs from just passing over a shortened         cess.  Setting startoffset differs from just passing over  a  shortened
1834         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
1835         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1836    
1837           \Biss\B           \Biss\B
1838    
1839         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
1840         only if the current position in the subject is not  a  word  boundary.)         only  if  the  current position in the subject is not a word boundary.)
1841         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
1842         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
1843         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
1844         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
1845         to  be  a  word  boundary. However, if pcre_exec() is passed the entire         to be a word boundary. However, if pcre_exec()  is  passed  the  entire
1846         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
1847         rence  of "iss" because it is able to look behind the starting point to         rence of "iss" because it is able to look behind the starting point  to
1848         discover that it is preceded by a letter.         discover that it is preceded by a letter.
1849    
1850         If a non-zero starting offset is passed when the pattern  is  anchored,         If  a  non-zero starting offset is passed when the pattern is anchored,
1851         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
1852         if the pattern does not require the match to be at  the  start  of  the         if  the  pattern  does  not require the match to be at the start of the
1853         subject.         subject.
1854    
1855     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
1856    
1857         In  general, a pattern matches a certain portion of the subject, and in         In general, a pattern matches a certain portion of the subject, and  in
1858         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
1859         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
1860         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
1861         subpattern"  is  used for a fragment of a pattern that picks out a sub-         subpattern" is used for a fragment of a pattern that picks out  a  sub-
1862         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
1863         that do not cause substrings to be captured.         that do not cause substrings to be captured.
1864    
1865         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of  integer
1866         offsets whose address is passed in ovector. The number of  elements  in         offsets  whose  address is passed in ovector. The number of elements in
1867         the  vector is passed in ovecsize, which must be a non-negative number.         the vector is passed in ovecsize, which must be a non-negative  number.
1868         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
1869    
1870         The first two-thirds of the vector is used to pass back  captured  sub-         The  first  two-thirds of the vector is used to pass back captured sub-
1871         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
1872         of the vector is used as workspace by pcre_exec() while  matching  cap-         of  the  vector is used as workspace by pcre_exec() while matching cap-
1873         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
1874         The length passed in ovecsize should always be a multiple of three.  If         The  length passed in ovecsize should always be a multiple of three. If
1875         it is not, it is rounded down.         it is not, it is rounded down.
1876    
1877         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
1878         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
1879         and  continuing  up  to two-thirds of its length at the most. The first         and continuing up to two-thirds of its length at the  most.  The  first
1880         element of a pair is set to the offset of the first character in a sub-         element of a pair is set to the offset of the first character in a sub-
1881         string,  and  the  second  is  set to the offset of the first character         string, and the second is set to the  offset  of  the  first  character
1882         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-
1883         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1], identify the portion of  the  subject  string  matched  by  the
1884         entire pattern. The next pair is used for the first  capturing  subpat-         entire  pattern.  The next pair is used for the first capturing subpat-
1885         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
1886         pairs that have been set. If there are no  capturing  subpatterns,  the         highest numbered pair that has been set. For example, if two substrings
1887         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
1888         first pair of offsets has been set.         subpatterns,  the return value from a successful match is 1, indicating
1889           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.  
1890    
1891         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1892         of the string that it matched that is returned.         of the string that it matched that is returned.
# Line 1660  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1900  MATCHING A PATTERN: THE TRADITIONAL FUNC
1900         substrings,  PCRE has to get additional memory for use during matching.         substrings,  PCRE has to get additional memory for use during matching.
1901         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1902    
1903         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
1904         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns  there  are  in  a  compiled pattern. The smallest size for
1905         that will allow for n captured substrings, in addition to  the  offsets         ovector that will allow for n captured substrings, in addition  to  the
1906         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.
1907    
1908           It  is  possible for capturing subpattern number n+1 to match some part
1909           of the subject when subpattern n has not been used at all. For example,
1910           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
1911           return from the function is 4, and subpatterns 1 and 3 are matched, but
1912           2  is  not.  When  this happens, both values in the offset pairs corre-
1913           sponding to unused subpatterns are set to -1.
1914    
1915           Offset values that correspond to unused subpatterns at the end  of  the
1916           expression  are  also  set  to  -1. For example, if the string "abc" is
1917           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
1918           matched.  The  return  from the function is 2, because the highest used
1919           capturing subpattern number is 1. However, you can refer to the offsets
1920           for  the  second  and third capturing subpatterns if you wish (assuming
1921           the vector is large enough, of course).
1922    
1923           Some convenience functions are provided  for  extracting  the  captured
1924           substrings as separate strings. These are described below.
1925    
1926     Return values from pcre_exec()     Error return values from pcre_exec()
1927    
1928         If  pcre_exec()  fails, it returns a negative number. The following are         If  pcre_exec()  fails, it returns a negative number. The following are
1929         defined in the header file:         defined in the header file:
# Line 1691  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1949  MATCHING A PATTERN: THE TRADITIONAL FUNC
1949         an environment with the other endianness. This is the error  that  PCRE         an environment with the other endianness. This is the error  that  PCRE
1950         gives when the magic number is not present.         gives when the magic number is not present.
1951    
1952           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1953    
1954         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1955         compiled pattern. This error could be caused by a bug  in  PCRE  or  by         compiled pattern. This error could be caused by a bug  in  PCRE  or  by
# Line 1713  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1971  MATCHING A PATTERN: THE TRADITIONAL FUNC
1971    
1972           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
1973    
1974         The  recursion  and backtracking limit, as specified by the match_limit         The  backtracking  limit,  as  specified  by the match_limit field in a
1975         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra structure (or defaulted) was reached.  See  the  description
1976         description above.         above.
1977    
1978           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
1979    
# Line 1754  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2012  MATCHING A PATTERN: THE TRADITIONAL FUNC
2012    
2013         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.
2014    
2015             PCRE_ERROR_RECURSIONLIMIT (-21)
2016    
2017           The internal recursion limit, as specified by the match_limit_recursion
2018           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2019           description above.
2020    
2021             PCRE_ERROR_NULLWSLIMIT    (-22)
2022    
2023           When  a  group  that  can  match an empty substring is repeated with an
2024           unbounded upper limit, the subject position at the start of  the  group
2025           must be remembered, so that a test for an empty string can be made when
2026           the end of the group is reached. Some workspace is required  for  this;
2027           if it runs out, this error is given.
2028    
2029             PCRE_ERROR_BADNEWLINE     (-23)
2030    
2031           An invalid combination of PCRE_NEWLINE_xxx options was given.
2032    
2033           Error numbers -16 to -20 are not used by pcre_exec().
2034    
2035    
2036  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2037    
# Line 1774  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2052  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2052         string_list() are provided for extracting captured substrings  as  new,         string_list() are provided for extracting captured substrings  as  new,
2053         separate,  zero-terminated strings. These functions identify substrings         separate,  zero-terminated strings. These functions identify substrings
2054         by number. The next section describes functions  for  extracting  named         by number. The next section describes functions  for  extracting  named
2055         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2056         extracted and has a further zero added on the end, but  the  result  is  
2057         not, of course, a C string.         A  substring that contains a binary zero is correctly extracted and has
2058           a further zero added on the end, but the result is not, of course, a  C
2059           string.   However,  you  can  process such a string by referring to the
2060           length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2061           string().  Unfortunately, the interface to pcre_get_substring_list() is
2062           not adequate for handling strings containing binary zeros, because  the
2063           end of the final string is not independently indicated.
2064    
2065         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-
2066         tions: subject is the subject string that has  just  been  successfully         tions: subject is the subject string that has  just  been  successfully
# Line 1796  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2080  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2080         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2081         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2082         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
2083         the terminating zero, or one of         the terminating zero, or one of these error codes:
2084    
2085           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2086    
# Line 1812  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2096  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2096         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
2097         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
2098         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
2099         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
2100           error code
2101    
2102           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2103    
2104         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2105    
2106         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2107         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2108         the  subject, but subpattern n has not been used at all, they return an         the subject, but subpattern n has not been used at all, they return  an
2109         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2110         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2111         tive for unset substrings.         tive for unset substrings.
2112    
2113         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2114         string_list()  can  be  used  to free the memory returned by a previous         string_list() can be used to free the memory  returned  by  a  previous
2115         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2116         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2117         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.
2118         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-
2119         cial  interface  to  another  programming  language  which  cannot  use         cial   interface  to  another  programming  language  that  cannot  use
2120         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-
2121         vided.         vided.
2122    
2123    
# Line 1851  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2136  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2136              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2137              const char **stringptr);              const char **stringptr);
2138    
2139         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-
2140         ber.  For example, for this pattern         ber.  For example, for this pattern
2141    
2142           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2143    
2144         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
2145         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
2146         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-
2147         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
2148         there is no subpattern of that name.         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2149           subpattern of that name.
2150    
2151         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
2152         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
# Line 1879  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2165  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2165    
2166         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2167         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2168         ate.         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2169           behaviour may not be what you want (see the next section).
2170    
2171    
2172    DUPLICATE SUBPATTERN NAMES
2173    
2174           int pcre_get_stringtable_entries(const pcre *code,
2175                const char *name, char **first, char **last);
2176    
2177           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2178           subpatterns are not required to  be  unique.  Normally,  patterns  with
2179           duplicate  names  are such that in any one match, only one of the named
2180           subpatterns participates. An example is shown in the pcrepattern  docu-
2181           mentation. When duplicates are present, pcre_copy_named_substring() and
2182           pcre_get_named_substring() return the first substring corresponding  to
2183           the  given  name  that  is  set.  If  none  are set, an empty string is
2184           returned.  The pcre_get_stringnumber() function returns one of the num-
2185           bers  that are associated with the name, but it is not defined which it
2186           is.
2187    
2188           If you want to get full details of all captured substrings for a  given
2189           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2190           first argument is the compiled pattern, and the second is the name. The
2191           third  and  fourth  are  pointers to variables which are updated by the
2192           function. After it has run, they point to the first and last entries in
2193           the  name-to-number  table  for  the  given  name.  The function itself
2194           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2195           there  are none. The format of the table is described above in the sec-
2196           tion entitled Information about a  pattern.   Given  all  the  relevant
2197           entries  for the name, you can extract each of their numbers, and hence
2198           the captured data, if any.
2199    
2200    
2201  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
# Line 1908  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2224  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2224              int *workspace, int wscount);              int *workspace, int wscount);
2225    
2226         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2227         against a compiled pattern, using a "DFA" matching algorithm. This  has         against a compiled pattern, using a matching algorithm that  scans  the
2228         different  characteristics to the normal algorithm, and is not compati-         subject  string  just  once, and does not backtrack. This has different
2229         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics to the normal algorithm, and  is  not  compatible  with
2230         Nevertheless, there are times when this kind of matching can be useful.         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2231         For a discussion of the two matching algorithms, see  the  pcrematching         theless, there are times when this kind of matching can be useful.  For
2232         documentation.         a discussion of the two matching algorithms, see the pcrematching docu-
2233           mentation.
2234    
2235         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
2236         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-
2237         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2238         used in the same way as for pcre_exec(), so their  description  is  not         used  in  the  same way as for pcre_exec(), so their description is not
2239         repeated here.         repeated here.
2240    
2241         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2242         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2243         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2244         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2245         lot of possible matches.         lot of potential matches.
2246    
2247         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2248    
2249           int rc;           int rc;
2250           int ovector[10];           int ovector[10];
2251           int wspace[20];           int wspace[20];
2252           rc = pcre_exec(           rc = pcre_dfa_exec(
2253             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2254             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2255             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1946  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2263  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2263    
2264     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2265    
2266         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
2267         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-
2268         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2269         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
2270         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
2271         repeated here.         not repeated here.
2272    
2273           PCRE_PARTIAL           PCRE_PARTIAL
2274    
2275         This has the same general effect as it does for  pcre_exec(),  but  the         This  has  the  same general effect as it does for pcre_exec(), but the
2276         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2277         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2278         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have         PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2279         been no complete matches, but there is still at least one matching pos-         been no complete matches, but there is still at least one matching pos-
2280         sibility.  The portion of the string that provided the partial match is         sibility. The portion of the string that provided the partial match  is
2281         set as the first matching string.         set as the first matching string.
2282    
2283           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2284    
2285         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2286         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-
2287         algorithm works, this is necessarily the shortest possible match at the         tive  algorithm  works, this is necessarily the shortest possible match
2288         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2289    
2290           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2291    
2292         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2293         returns a partial match, it is possible to call it  again,  with  addi-         returns  a  partial  match, it is possible to call it again, with addi-
2294         tional  subject  characters,  and have it continue with the same match.         tional subject characters, and have it continue with  the  same  match.
2295         The PCRE_DFA_RESTART option requests this action; when it is  set,  the         The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2296         workspace  and wscount options must reference the same vector as before         workspace and wscount options must reference the same vector as  before
2297         because data about the match so far is left in  them  after  a  partial         because  data  about  the  match so far is left in them after a partial
2298         match.  There  is  more  discussion of this facility in the pcrepartial         match. There is more discussion of this  facility  in  the  pcrepartial
2299         documentation.         documentation.
2300    
2301     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2302    
2303         When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-         When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2304         string in the subject. Note, however, that all the matches from one run         string in the subject. Note, however, that all the matches from one run
2305         of the function start at the same point in  the  subject.  The  shorter         of  the  function  start  at the same point in the subject. The shorter
2306         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2307         if the pattern         if the pattern
2308    
2309           <.*>           <.*>
# Line 2001  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2318  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2318           <something> <something else>           <something> <something else>
2319           <something> <something else> <something further>           <something> <something else> <something further>
2320    
2321         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,
2322         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2323         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2324         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
2325         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
2326         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
2327         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility  with  the  way pcre_exec() returns data, even though the
2328         strings is different.)         meaning of the strings is different.)
2329    
2330         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-
2331         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
2332         fit  into ovector, the yield of the function is zero, and the vector is         fit into ovector, the yield of the function is zero, and the vector  is
2333         filled with the longest matches.         filled with the longest matches.
2334    
2335     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2336    
2337         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2338         Many  of  the  errors  are  the  same as for pcre_exec(), and these are         Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2339         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2340         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2341    
2342           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2343    
2344         This  return is given if pcre_dfa_exec() encounters an item in the pat-         This return is given if pcre_dfa_exec() encounters an item in the  pat-
2345         tern that it does not support, for instance, the use of \C  or  a  back         tern  that  it  does not support, for instance, the use of \C or a back
2346         reference.         reference.
2347    
2348           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2349    
2350         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
2351         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
2352         supported.         in a specific group. These are not supported.
2353    
2354           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2355    
2356         This  return  is given if pcre_dfa_exec() is called with an extra block         This return is given if pcre_dfa_exec() is called with an  extra  block
2357         that contains a setting of the match_limit field. This is not supported         that contains a setting of the match_limit field. This is not supported
2358         (it is meaningless).         (it is meaningless).
2359    
2360           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2361    
2362         This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the         This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2363         workspace vector.         workspace vector.
2364    
2365           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2366    
2367         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2368         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2369         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
2370         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2371    
2372  Last updated: 16 May 2005  
2373  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2374    
2375           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2376           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2377    
2378    
2379    AUTHOR
2380    
2381           Philip Hazel
2382           University Computing Service
2383           Cambridge CB2 3QH, England.
2384    
2385    
2386    REVISION
2387    
2388           Last updated: 16 April 2007
2389           Copyright (c) 1997-2007 University of Cambridge.
2390  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2391    
2392    
# Line 2211  RETURN VALUES Line 2544  RETURN VALUES
2544         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
2545         itself.         itself.
2546    
2547  Last updated: 28 February 2005  
2548  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2549    
2550           Philip Hazel
2551           University Computing Service
2552           Cambridge CB2 3QH, England.
2553    
2554    
2555    REVISION
2556    
2557           Last updated: 06 March 2007
2558           Copyright (c) 1997-2007 University of Cambridge.
2559  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2560    
2561    
# Line 2226  NAME Line 2569  NAME
2569  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2570    
2571         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2572         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2573         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2574           tures that are expected to be in the forthcoming Perl 5.10.
2575         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2576         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
2577           of  what  it does have are given in the section on UTF-8 support in the
2578           main pcre page.
2579    
2580         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2581         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 2602  DIFFERENCES BETWEEN PCRE AND PERL
2602         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
2603         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2604         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-
2605         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2606           derived properties Any and L&.
2607    
2608         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2609         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2610         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2611         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2612         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2613    
2614             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2272  DIFFERENCES BETWEEN PCRE AND PERL Line 2618  DIFFERENCES BETWEEN PCRE AND PERL
2618             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2619             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2620    
2621         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2622         classes.         classes.
2623    
2624         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2625         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2626         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
2627         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2628         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2629    
2630         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2631         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2632         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2633    
2634           10.  There are some differences that are concerned with the settings of
2635           captured strings when part of  a  pattern  is  repeated.  For  example,
2636           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2637         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2638    
2639         10. PCRE provides some extensions to the Perl regular expression facil-         11. PCRE provides some extensions to the Perl regular expression facil-
2640         ities:         ities.   Perl  5.10  will  include new features that are not in earlier
2641           versions, some of which (such as named parentheses) have been  in  PCRE
2642           for some time. This list is with respect to Perl 5.10:
2643    
2644         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2645         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2646         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2647    
2648         (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 $
2649         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2650    
2651         (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-
2652         cial meaning is faulted.         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2653           ignored. (Perl can be made to issue a warning.)
2654    
2655         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2656         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 2662  DIFFERENCES BETWEEN PCRE AND PERL
2662         (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-
2663         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2664    
2665         (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.)  
2666    
2667         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The partial matching facility is PCRE-specific.
2668    
2669         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2670         Sun's Java package.         even on different hosts that have the other endianness.
2671    
2672         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2673           different way and is not Perl-compatible.
2674    
        (k) The callout facility is PCRE-specific.  
2675    
2676         (l) The partial matching facility is PCRE-specific.  AUTHOR
2677    
2678         (m) Patterns compiled by PCRE can be saved and re-used at a later time,         Philip Hazel
2679         even on different hosts that have the other endianness.         University Computing Service
2680           Cambridge CB2 3QH, England.
2681    
        (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  
        different way and is not Perl-compatible.  
2682    
2683  Last updated: 28 February 2005  REVISION
2684  Copyright (c) 1997-2005 University of Cambridge.  
2685           Last updated: 06 March 2007
2686           Copyright (c) 1997-2007 University of Cambridge.
2687  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2688    
2689    
# Line 2367  PCRE REGULAR EXPRESSION DETAILS Line 2719  PCRE REGULAR EXPRESSION DETAILS
2719         function, and how it differs from the normal function, are discussed in         function, and how it differs from the normal function, are discussed in
2720         the pcrematching page.         the pcrematching page.
2721    
2722    
2723    CHARACTERS AND METACHARACTERS
2724    
2725         A regular expression is a pattern that is  matched  against  a  subject         A regular expression is a pattern that is  matched  against  a  subject
2726         string  from  left  to right. Most characters stand for themselves in a         string  from  left  to right. Most characters stand for themselves in a
2727         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 2746  PCRE REGULAR EXPRESSION DETAILS
2746    
2747         There are two different sets of metacharacters: those that  are  recog-         There are two different sets of metacharacters: those that  are  recog-
2748         nized  anywhere in the pattern except within square brackets, and those         nized  anywhere in the pattern except within square brackets, and those
2749         that are recognized in square brackets. Outside  square  brackets,  the         that are recognized within square brackets.  Outside  square  brackets,
2750         metacharacters are as follows:         the metacharacters are as follows:
2751    
2752           \      general escape character with several uses           \      general escape character with several uses
2753           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2439  BACKSLASH Line 2794  BACKSLASH
2794    
2795         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2796         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
2797         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2798         An escaping backslash can be used to include a whitespace or #  charac-         ing backslash can be used to include a whitespace  or  #  character  as
2799         ter as part of the pattern.         part of the pattern.
2800    
2801         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-
2802         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 2832  BACKSLASH
2832           \t        tab (hex 09)           \t        tab (hex 09)
2833           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
2834           \xhh      character with hex code hh           \xhh      character with hex code hh
2835           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
2836    
2837         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,
2838         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 2840  BACKSLASH
2840         becomes hex 7B.         becomes hex 7B.
2841    
2842         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
2843         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
2844         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
2845         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,
2846         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than
2847         \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-
2848         recognized. Instead, the initial \x will  be  interpreted  as  a  basic         nating }, this form of escape is not recognized.  Instead, the  initial
2849         hexadecimal  escape, with no following digits, giving a character whose         \x will be interpreted as a basic hexadecimal escape, with no following
2850         value is zero.         digits, giving a character whose value is zero.
2851    
2852         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
2853         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-
2854         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}.
2855         \x{dc}.  
2856           After \0 up to two further octal digits are read. If  there  are  fewer
2857         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
2858         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
2859         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
2860         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.  
2861    
2862         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-
2863         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 2869  BACKSLASH
2869    
2870         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
2871         and  there have not been that many capturing subpatterns, PCRE re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
2872         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-
2873         gle byte from the least significant 8 bits of the value. Any subsequent         erate  a data character. Any subsequent digits stand for themselves. In
2874         digits stand for themselves.  For example:         non-UTF-8 mode, the value of a character specified  in  octal  must  be
2875           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
2876           example:
2877    
2878           \040   is another way of writing a space           \040   is another way of writing a space
2879           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2538  BACKSLASH Line 2893  BACKSLASH
2893         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
2894         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2895    
2896         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
2897         character (in UTF-8 mode) can be used both inside and outside character         inside and outside character classes. In addition, inside  a  character
2898         classes.  In  addition,  inside  a  character class, the sequence \b is         class,  the  sequence \b is interpreted as the backspace character (hex
2899         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"
2900         interpreted  as  the  character  "X".  Outside a character class, these         and  "X", respectively. Outside a character class, these sequences have
2901         sequences have different meanings (see below).         different meanings (see below).
2902    
2903       Absolute and relative back references
2904    
2905           The sequence \g followed by a positive or negative  number,  optionally
2906           enclosed  in  braces,  is  an absolute or relative back reference. Back
2907           references are discussed later, following the discussion  of  parenthe-
2908           sized subpatterns.
2909    
2910     Generic character types     Generic character types
2911    
2912         The third use of backslash is for specifying generic  character  types.         Another use of backslash is for specifying generic character types. The
2913         The following are always recognized:         following are always recognized:
2914    
2915           \d     any decimal digit           \d     any decimal digit
2916           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 2558  BACKSLASH Line 2920  BACKSLASH
2920           \W     any "non-word" character           \W     any "non-word" character
2921    
2922         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
2923         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
2924         of each pair.         of each pair.
2925    
2926         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
2927         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
2928         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
2929         of them fail, since there is no character to match.         of them fail, since there is no character to match.
2930    
2931         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
2932         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
2933         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
2934           "use locale;" is included in a Perl script, \s may match the VT charac-
2935           ter. In PCRE, it never does.)
2936    
2937         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
2938         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-
2939         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-
2940         specific  matching is taking place (see "Locale support" in the pcreapi         specific matching is taking place (see "Locale support" in the  pcreapi
2941         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
2942         codes  greater  than  128  are used for accented letters, and these are         systems, or "french" in Windows, some character codes greater than  128
2943         matched by \w.         are used for accented letters, and these are matched by \w.
2944    
2945         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,
2946         \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-
2947         code character property support is available.         code  character  property support is available. The use of locales with
2948           Unicode is discouraged.
2949    
2950       Newline sequences
2951    
2952           Outside a character class, the escape sequence \R matches  any  Unicode
2953           newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2954           equivalent to the following:
2955    
2956             (?>\r\n|\n|\x0b|\f|\r|\x85)
2957    
2958           This is an example of an "atomic group", details  of  which  are  given
2959           below.  This particular group matches either the two-character sequence
2960           CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
2961           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2962           return, U+000D), or NEL (next line, U+0085). The two-character sequence
2963           is treated as a single unit that cannot be split.
2964    
2965           In  UTF-8  mode, two additional characters whose codepoints are greater
2966           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2967           rator,  U+2029).   Unicode character property support is not needed for
2968           these characters to be recognized.
2969    
2970           Inside a character class, \R matches the letter "R".
2971    
2972     Unicode character properties     Unicode character properties
2973    
2974         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
2975         tional  escape sequences to match generic character types are available         tional  escape  sequences  to  match character properties are available
2976         when UTF-8 mode is selected. They are:         when UTF-8 mode is selected. They are:
2977    
2978          \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
2979          \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
2980          \X       an extended Unicode sequence           \X       an extended Unicode sequence
2981    
2982         The property names represented by xx above are limited to  the  Unicode         The property names represented by xx above are limited to  the  Unicode
2983         general  category properties. Each character has exactly one such prop-         script names, the general category properties, and "Any", which matches
2984         erty, specified by a two-letter abbreviation.  For  compatibility  with         any character (including newline). Other properties such as "InMusical-
2985         Perl,  negation  can be specified by including a circumflex between the         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
2986         opening brace and the property name. For example, \p{^Lu} is  the  same         not match any characters, so always causes a match failure.
2987         as \P{Lu}.  
2988           Sets of Unicode characters are defined as belonging to certain scripts.
2989         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.
2990         properties that start with that letter. In this case, in the absence of         For example:
2991         negation, the curly brackets in the escape sequence are optional; these  
2992         two examples have the same effect:           \p{Greek}
2993             \P{Han}
2994    
2995           Those that are not part of an identified script are lumped together  as
2996           "Common". The current list of scripts is:
2997    
2998           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
2999           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
3000           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3001           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
3002           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
3003           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3004           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
3005           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3006           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3007    
3008           Each  character has exactly one general category property, specified by
3009           a two-letter abbreviation. For compatibility with Perl, negation can be
3010           specified  by  including a circumflex between the opening brace and the
3011           property name. For example, \p{^Lu} is the same as \P{Lu}.
3012    
3013           If only one letter is specified with \p or \P, it includes all the gen-
3014           eral  category properties that start with that letter. In this case, in
3015           the absence of negation, the curly brackets in the escape sequence  are
3016           optional; these two examples have the same effect:
3017    
3018           \p{L}           \p{L}
3019           \pL           \pL
3020    
3021         The following property codes are supported:         The following general category property codes are supported:
3022    
3023           C     Other           C     Other
3024           Cc    Control           Cc    Control
# Line 2653  BACKSLASH Line 3064  BACKSLASH
3064           Zp    Paragraph separator           Zp    Paragraph separator
3065           Zs    Space separator           Zs    Space separator
3066    
3067         Extended properties such as "Greek" or "InMusicalSymbols" are not  sup-         The  special property L& is also supported: it matches a character that
3068         ported by PCRE.         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
3069           classified as a modifier or "other".
3070    
3071           The  long  synonyms  for  these  properties that Perl supports (such as
3072           \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3073           any of these properties with "Is".
3074    
3075           No character that is in the Unicode table has the Cn (unassigned) prop-
3076           erty.  Instead, this property is assumed for any code point that is not
3077           in the Unicode table.
3078    
3079         Specifying  caseless  matching  does not affect these escape sequences.         Specifying  caseless  matching  does not affect these escape sequences.
3080         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
# Line 2676  BACKSLASH Line 3096  BACKSLASH
3096    
3097     Simple assertions     Simple assertions
3098    
3099         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3100         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
3101         a  match, without consuming any characters from the subject string. The         a  match, without consuming any characters from the subject string. The
3102         use of subpatterns for more complicated assertions is described  below.         use of subpatterns for more complicated assertions is described  below.
# Line 2684  BACKSLASH Line 3104  BACKSLASH
3104    
3105           \b     matches at a word boundary           \b     matches at a word boundary
3106           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3107           \A     matches at start of subject           \A     matches at the start of the subject
3108           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3109           \z     matches at end of subject                   also matches before a newline at the end of the subject
3110           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3111             \G     matches at the first matching position in the subject
3112    
3113         These  assertions may not appear in character classes (but note that \b         These  assertions may not appear in character classes (but note that \b
3114         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 3128  BACKSLASH
3128         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3129         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
3130         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
3131         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
3132         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.
3133         the end.  
3134           The \G assertion is true only when the current matching position is  at
3135         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
3136         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
3137         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-  
3138         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-
3139         mentation where \G can be useful.         mentation where \G can be useful.
3140    
3141         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
3142         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
3143         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
3144         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3145         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3146    
3147         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
3148         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3149         in the compiled regular expression.         in the compiled regular expression.
3150    
# Line 2732  BACKSLASH Line 3152  BACKSLASH
3152  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3153    
3154         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3155         character  is  an  assertion  that is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3156         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-
3157         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
3158         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3159         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3160    
3161         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
3162         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
3163         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
3164         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3165         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-
3166         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
3167         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3168    
3169         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
3170         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3171         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
3172         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
3173         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
3174         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.  
3175    
3176         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
3177         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
3178         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3179    
3180         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3181         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
3182         ately  after  and  immediately  before  an  internal newline character,         matches  immediately after internal newlines as well as at the start of
3183         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
3184         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         string.  A dollar matches before any newlines in the string, as well as
3185         string "def\nabc" (where \n represents a newline character)  in  multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3186         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3187         in single line mode because all branches start with ^ are not  anchored         not indicate newlines.
3188         in  multiline  mode,  and  a  match for circumflex is possible when the  
3189         startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3190         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3191           Consequently, patterns that are anchored in single  line  mode  because
3192         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
3193         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
3194         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
3195         not.         PCRE_MULTILINE is set.
3196    
3197           Note that the sequences \A, \Z, and \z can be used to match  the  start
3198           and  end of the subject in both modes, and if all branches of a pattern
3199           start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3200           set.
3201    
3202    
3203  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3204    
3205         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-
3206         ter  in  the  subject,  including a non-printing character, but not (by         ter in the subject string except (by default) a character  that  signi-
3207         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
3208         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3209         the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-  
3210         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
3211         dollar, the only relationship being  that  they  both  involve  newline         that  character; when the two-character sequence CRLF is used, dot does
3212         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3213           matches  all characters (including isolated CRs and LFs). When any Uni-
3214           code line endings are being recognized, dot does not match CR or LF  or
3215           any of the other line ending characters.
3216    
3217           The  behaviour  of  dot  with regard to newlines can be changed. If the
3218           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3219           exception. If the two-character sequence CRLF is present in the subject
3220           string, it takes two dots to match it.
3221    
3222           The handling of dot is entirely independent of the handling of  circum-
3223           flex  and  dollar,  the  only relationship being that they both involve
3224           newlines. Dot has no special meaning in a character class.
3225    
3226    
3227  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3228    
3229         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3230         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
3231         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
3232         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-
3233         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-
3234         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3235           avoided.
3236    
3237         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3238         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 3279  SQUARE BRACKETS AND CHARACTER CLASSES
3279         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
3280         support.         support.
3281    
3282         The newline character is never treated in any special way in  character         Characters that might indicate line breaks are  never  treated  in  any
3283         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         special  way  when  matching  character  classes,  whatever line-ending
3284         options is. A class such as [^a] will always match a newline.         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3285           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3286           of these characters.
3287    
3288         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-
3289         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 3309  SQUARE BRACKETS AND CHARACTER CLASSES
3309         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,
3310         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
3311         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3312         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
3313         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
3314         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3315         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 2945  VERTICAL BAR Line 3384  VERTICAL BAR
3384    
3385         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3386         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3387         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3388         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
3389         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3390         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.  
3391    
3392    
3393  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 2977  INTERNAL OPTION SETTING Line 3415  INTERNAL OPTION SETTING
3415         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
3416         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3417    
3418         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
3419         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3420           it, so
3421    
3422           (a(?i)b)c           (a(?i)b)c
3423    
3424         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
3425         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3426         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3427         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3428         example,         example,
3429    
3430           (a(?i)b|c)           (a(?i)b|c)
3431    
3432         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3433         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3434         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3435         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3436    
3437         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3438         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
3439         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.  
3440    
3441    
3442  SUBPATTERNS  SUBPATTERNS
# Line 3013  SUBPATTERNS Line 3449  SUBPATTERNS
3449           cat(aract|erpillar|)           cat(aract|erpillar|)
3450    
3451         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3452         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3453         string.         string.
3454    
3455         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 3478  SUBPATTERNS
3478           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3479    
3480         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3481         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.  
3482    
3483         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3484         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 3500  NAMED SUBPATTERNS
3500         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3501         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3502         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3503         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3504         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3505         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3506           tax.
3507    
3508           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3509           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3510           to capturing parentheses from other parts of the pattern, such as back-
3511           references,  recursion,  and conditions, can be made by name as well as
3512           by number.
3513    
3514           Names consist of up to  32  alphanumeric  characters  and  underscores.
3515         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3516         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
3517         number  translation table from a compiled pattern. There is also a con-         function calls for extracting the name-to-number translation table from
3518         venience function for extracting a captured substring by name. For fur-         a compiled pattern. There is also a convenience function for extracting
3519         ther details see the pcreapi documentation.         a captured substring by name.
3520    
3521           By  default, a name must be unique within a pattern, but it is possible
3522           to relax this constraint by setting the PCRE_DUPNAMES option at compile
3523           time.  This  can  be useful for patterns where only one instance of the
3524           named parentheses can match. Suppose you want to match the  name  of  a
3525           weekday,  either as a 3-letter abbreviation or as the full name, and in
3526           both cases you want to extract the abbreviation. This pattern (ignoring
3527           the line breaks) does the job:
3528    
3529             (?<DN>Mon|Fri|Sun)(?:day)?|
3530             (?<DN>Tue)(?:sday)?|
3531             (?<DN>Wed)(?:nesday)?|
3532             (?<DN>Thu)(?:rsday)?|
3533             (?<DN>Sat)(?:urday)?
3534    
3535           There  are  five capturing substrings, but only one is ever set after a
3536           match.  The convenience  function  for  extracting  the  data  by  name
3537           returns  the  substring  for  the first (and in this example, the only)
3538           subpattern of that name that matched.  This  saves  searching  to  find
3539           which  numbered  subpattern  it  was. If you make a reference to a non-
3540           unique named subpattern from elsewhere in the  pattern,  the  one  that
3541           corresponds  to  the  lowest number is used. For further details of the
3542           interfaces for handling named subpatterns, see the  pcreapi  documenta-
3543           tion.
3544    
3545    
3546  REPETITION  REPETITION
# Line 3083  REPETITION Line 3549  REPETITION
3549         following items:         following items:
3550    
3551           a literal data character           a literal data character
3552           the . metacharacter           the dot metacharacter
3553           the \C escape sequence           the \C escape sequence
3554           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3555             the \R escape sequence
3556           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3557           a character class           a character class
3558           a back reference (see next section)           a back reference (see next section)
# Line 3125  REPETITION Line 3592  REPETITION
3592         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3593         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3594    
3595         For  convenience  (and  historical compatibility) the three most common         For  convenience, the three most common quantifiers have single-charac-
3596         quantifiers have single-character abbreviations:         ter abbreviations:
3597    
3598           *    is equivalent to {0,}           *    is equivalent to {0,}
3599           +    is equivalent to {1,}           +    is equivalent to {1,}
# Line 3178  REPETITION Line 3645  REPETITION
3645         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
3646         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3647    
3648         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
3649         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3650         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
3651         words, it inverts the default behaviour.         words, it inverts the default behaviour.
# Line 3189  REPETITION Line 3656  REPETITION
3656         minimum or maximum.         minimum or maximum.
3657    
3658         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-
3659         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,
3660         pattern is implicitly anchored, because whatever follows will be  tried         the pattern is implicitly anchored, because whatever  follows  will  be
3661         against  every character position in the subject string, so there is no         tried  against every character position in the subject string, so there
3662         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
3663         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
3664           by \A.
3665    
3666         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-
3667         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-
3668         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3669    
3670         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3671         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3672         backreference  elsewhere in the pattern, a match at the start may fail,         backreference elsewhere in the pattern, a match at the start  may  fail
3673         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3674    
3675           (.*)abc\1           (.*)abc\1
3676    
3677         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3678         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3679    
3680         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 3683  REPETITION
3683           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
3684    
3685         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
3686         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
3687         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
3688         tions. For example, after         tions. For example, after
3689    
3690           /(a|(b))+/           /(a|(b))+/
# Line 3226  REPETITION Line 3694  REPETITION
3694    
3695  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
3696    
3697         With both maximizing and minimizing repetition, failure of what follows         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
3698         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition,  failure  of what follows normally causes the repeated item
3699         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
3700         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,
3701         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
3702         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
3703           no point in carrying on.
3704    
3705         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider, for example, the pattern \d+foo when applied to  the  subject
3706         line         line
# Line 3245  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3714  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3714         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
3715         to be re-evaluated in this way.         to be re-evaluated in this way.
3716    
3717         If we use atomic grouping for the previous example, the  matcher  would         If we use atomic grouping for the previous example, the  matcher  gives
3718         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
3719         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:  
3720    
3721           (?>\d+)foo           (?>\d+)foo
3722    
# Line 3280  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3748  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3748         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
3749         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
3750         simpler forms of atomic group. However, there is no difference  in  the         simpler forms of atomic group. However, there is no difference  in  the
3751         meaning  or  processing  of  a possessive quantifier and the equivalent         meaning  of  a  possessive  quantifier and the equivalent atomic group,
3752         atomic group.         though there may be a performance  difference;  possessive  quantifiers
3753           should be slightly faster.
3754         The possessive quantifier syntax is an extension to the Perl syntax. It  
3755         originates in Sun's Java package.         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
3756           tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first
3757         When  a  pattern  contains an unlimited repeat inside a subpattern that         edition of his book. Mike McCloskey liked it, so implemented it when he
3758         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
3759         atomic  group  is  the  only way to avoid some failing matches taking a         found its way into Perl at release 5.10.
3760    
3761           PCRE has an optimization that automatically "possessifies" certain sim-
3762           ple pattern constructs. For example, the sequence  A+B  is  treated  as
3763           A++B  because  there is no point in backtracking into a sequence of A's
3764           when B must follow.
3765    
3766           When a pattern contains an unlimited repeat inside  a  subpattern  that
3767           can  itself  be  repeated  an  unlimited number of times, the use of an
3768           atomic group is the only way to avoid some  failing  matches  taking  a
3769         very long time indeed. The pattern         very long time indeed. The pattern
3770    
3771           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
3772    
3773         matches an unlimited number of substrings that either consist  of  non-         matches  an  unlimited number of substrings that either consist of non-
3774         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it
3775         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
3776    
3777           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
3778    
3779         it takes a long time before reporting  failure.  This  is  because  the         it  takes  a  long  time  before reporting failure. This is because the
3780         string  can be divided between the internal \D+ repeat and the external         string can be divided between the internal \D+ repeat and the  external
3781         * 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
3782         example  uses  [!?]  rather than a single character at the end, because         example uses [!?] rather than a single character at  the  end,  because
3783         both PCRE and Perl have an optimization that allows  for  fast  failure         both  PCRE  and  Perl have an optimization that allows for fast failure
3784         when  a single character is used. They remember the last single charac-         when a single character is used. They remember the last single  charac-
3785         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
3786         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
3787         group, like this:         group, like this:
3788    
3789           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
3790    
3791         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences  of non-digits cannot be broken, and failure happens quickly.
3792    
3793    
3794  BACK REFERENCES  BACK REFERENCES
3795    
3796         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
3797         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-
3798         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
3799         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
3800    
3801         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
3802         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
3803         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
3804         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
3805         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
3806         tion  entitled  "Non-printing  characters" above for further details of         reference" of this type can make sense when a  repetition  is  involved
3807         the handling of digits following a backslash.         and  the  subpattern to the right has participated in an earlier itera-
3808           tion.
3809    
3810         A back reference matches whatever actually matched the  capturing  sub-         It is not possible to have a numerical "forward back  reference"  to  a
3811         pattern  in  the  current subject string, rather than anything matching         subpattern  whose  number  is  10  or  more using this syntax because a
3812           sequence such as \50 is interpreted as a character  defined  in  octal.
3813           See the subsection entitled "Non-printing characters" above for further
3814           details of the handling of digits following a backslash.  There  is  no
3815           such  problem  when named parentheses are used. A back reference to any
3816           subpattern is possible using named parentheses (see below).
3817    
3818           Another way of avoiding the ambiguity inherent in  the  use  of  digits
3819           following a backslash is to use the \g escape sequence, which is a fea-
3820           ture introduced in Perl 5.10. This escape must be followed by  a  posi-
3821           tive  or  a negative number, optionally enclosed in braces. These exam-
3822           ples are all identical:
3823    
3824             (ring), \1
3825             (ring), \g1
3826             (ring), \g{1}
3827    
3828           A positive number specifies an absolute reference without the ambiguity
3829           that  is  present  in  the older syntax. It is also useful when literal
3830           digits follow the reference. A negative number is a relative reference.
3831           Consider this example:
3832    
3833             (abc(def)ghi)\g{-1}
3834    
3835           The sequence \g{-1} is a reference to the most recently started captur-
3836           ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,
3837           \g{-2} would be equivalent to \1. The use of relative references can be
3838           helpful in long patterns, and also in  patterns  that  are  created  by
3839           joining together fragments that contain references within themselves.
3840    
3841           A  back  reference matches whatever actually matched the capturing sub-
3842           pattern in the current subject string, rather  than  anything  matching
3843         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
3844         of doing that). So the pattern         of doing that). So the pattern
3845    
3846           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
3847    
3848         matches  "sense and sensibility" and "response and responsibility", but         matches "sense and sensibility" and "response and responsibility",  but
3849         not "sense and responsibility". If caseful matching is in force at  the         not  "sense and responsibility". If caseful matching is in force at the
3850         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-
3851         ple,         ple,
3852    
3853           ((?i)rah)\s+\1           ((?i)rah)\s+\1
3854    
3855         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
3856         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
3857    
3858         Back  references  to named subpatterns use the Python syntax (?P=name).         Back references to named subpatterns use the Perl  syntax  \k<name>  or
3859         We could rewrite the above example as follows:         \k'name'  or  the  Python  syntax (?P=name). We could rewrite the above
3860           example in either of the following ways:
3861    
3862           (?<p1>(?i)rah)\s+(?P=p1)           (?<p1>(?i)rah)\s+\k<p1>
3863             (?P<p1>(?i)rah)\s+(?P=p1)
3864    
3865         There may be more than one back reference to the same subpattern. If  a         A subpattern that is referenced by  name  may  appear  in  the  pattern
3866         subpattern  has  not actually been used in a particular match, any back         before or after the reference.
3867    
3868           There  may be more than one back reference to the same subpattern. If a
3869           subpattern has not actually been used in a particular match,  any  back
3870         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
3871    
3872           (a|(bc))\2           (a|(bc))\2
3873    
3874         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
3875         may  be  many  capturing parentheses in a pattern, all digits following         may be many capturing parentheses in a pattern,  all  digits  following
3876         the backslash are taken as part of a potential back  reference  number.         the  backslash  are taken as part of a potential back reference number.
3877         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
3878         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         used  to  terminate  the back reference. If the PCRE_EXTENDED option is
3879         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-
3880         ments" below) can be used.         ments" below) can be used.
3881    
3882         A back reference that occurs inside the parentheses to which it  refers         A  back reference that occurs inside the parentheses to which it refers
3883         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
3884         matches.  However, such references can be useful inside  repeated  sub-         matches.   However,  such references can be useful inside repeated sub-
3885         patterns. For example, the pattern         patterns. For example, the pattern
3886    
3887           (a|b\1)+           (a|b\1)+
3888    
3889         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-
3890         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
3891         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
3892         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
3893         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
3894         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
3895    
3896    
3897  ASSERTIONS  ASSERTIONS
3898    
3899         An assertion is a test on the characters  following  or  preceding  the         An  assertion  is  a  test on the characters following or preceding the
3900         current  matching  point that does not actually consume any characters.         current matching point that does not actually consume  any  characters.
3901         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
3902         described above.         described above.
3903    
3904         More  complicated  assertions  are  coded as subpatterns. There are two         More complicated assertions are coded as  subpatterns.  There  are  two
3905         kinds: those that look ahead of the current  position  in  the  subject         kinds:  those  that  look  ahead of the current position in the subject
3906         string,  and  those  that  look  behind  it. An assertion subpattern is         string, and those that look  behind  it.  An  assertion  subpattern  is
3907         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
3908         matching position to be changed.         matching position to be changed.
3909    
3910         Assertion  subpatterns  are  not  capturing subpatterns, and may not be         Assertion subpatterns are not capturing subpatterns,  and  may  not  be
3911         repeated, because it makes no sense to assert the  same  thing  several         repeated,  because  it  makes no sense to assert the same thing several
3912         times.  If  any kind of assertion contains capturing subpatterns within         times. If any kind of assertion contains capturing  subpatterns  within
3913         it, these are counted for the purposes of numbering the capturing  sub-         it,  these are counted for the purposes of numbering the capturing sub-
3914         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
3915         out only for positive assertions, because it does not  make  sense  for         out  only  for  positive assertions, because it does not make sense for
3916         negative assertions.         negative assertions.
3917    
3918     Lookahead assertions     Lookahead assertions
# Line 3408  ASSERTIONS Line 3922  ASSERTIONS
3922    
3923           \w+(?=;)           \w+(?=;)
3924    
3925         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-
3926         colon in the match, and         colon in the match, and
3927    
3928           foo(?!bar)           foo(?!bar)
3929    
3930         matches  any  occurrence  of  "foo" that is not followed by "bar". Note         matches any occurrence of "foo" that is not  followed  by  "bar".  Note
3931         that the apparently similar pattern         that the apparently similar pattern
3932    
3933           (?!foo)bar           (?!foo)bar
3934    
3935         does not find an occurrence of "bar"  that  is  preceded  by  something         does  not  find  an  occurrence  of "bar" that is preceded by something
3936         other  than "foo"; it finds any occurrence of "bar" whatsoever, because         other than "foo"; it finds any occurrence of "bar" whatsoever,  because
3937         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
3938         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
3939    
3940         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
3941         most convenient way to do it is  with  (?!)  because  an  empty  string         most  convenient  way  to  do  it  is with (?!) because an empty string
3942         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
3943         string must always fail.         string must always fail.
3944    
3945     Lookbehind assertions     Lookbehind assertions
3946    
3947         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
3948         for negative assertions. For example,         for negative assertions. For example,
3949    
3950           (?<!foo)bar           (?<!foo)bar
3951    
3952         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
3953         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
3954         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-
3955         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
3956         Thus         fixed length. Thus
3957    
3958           (?<=bullock|donkey)           (?<=bullock|donkey)
3959    
# Line 3447  ASSERTIONS Line 3961  ASSERTIONS
3961    
3962           (?<!dogs?|cats?)           (?<!dogs?|cats?)
3963    
3964         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
3965         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
3966         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
3967         requires all branches to match the same length of string. An  assertion         requires  all branches to match the same length of string. An assertion
3968         such as         such as
3969    
3970           (?<=ab(c|de))           (?<=ab(c|de))
3971    
3972         is  not  permitted,  because  its single top-level branch can match two         is not permitted, because its single top-level  branch  can  match  two
3973         different lengths, but it is acceptable if rewritten to  use  two  top-         different  lengths,  but  it is acceptable if rewritten to use two top-
3974         level branches:         level branches:
3975    
3976           (?<=abc|abde)           (?<=abc|abde)
3977    
3978         The  implementation  of lookbehind assertions is, for each alternative,         The implementation of lookbehind assertions is, for  each  alternative,
3979         to temporarily move the current position back by the  fixed  width  and         to  temporarily  move the current position back by the fixed length and
3980         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
3981         rent position, the match is deemed to fail.         rent position, the assertion fails.
3982    
3983         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
3984         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode) to appear in lookbehind assertions, because it makes it  impossi-
3985         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,
3986         match different numbers of bytes, is also not permitted.         which can match different numbers of bytes, are also not permitted.
3987    
3988         Atomic  groups can be used in conjunction with lookbehind assertions to         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind
3989         specify efficient matching at the end of the subject string. Consider a         assertions  to  specify  efficient  matching  at the end of the subject
3990         simple pattern such as         string. Consider a simple pattern such as
3991    
3992           abcd$           abcd$
3993    
3994         when  applied  to  a  long string that does not match. Because matching         when applied to a long string that does  not  match.  Because  matching
3995         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
3996         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
3997         pattern is specified as         pattern is specified as
3998    
3999           ^.*abcd$           ^.*abcd$
4000    
4001         the initial .* matches the entire string at first, but when this  fails         the  initial .* matches the entire string at first, but when this fails
4002         (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
4003         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
4004         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,
4005         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
4006    
          ^(?>.*)(?<=abcd)  
   
        or, equivalently, using the possessive quantifier syntax,  
   
4007           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4008    
4009         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
4010         entire  string.  The subsequent lookbehind assertion does a single test         entire string. The subsequent lookbehind assertion does a  single  test
4011         on the last four characters. If it fails, the match fails  immediately.         on  the last four characters. If it fails, the match fails immediately.
4012         For  long  strings, this approach makes a significant difference to the         For long strings, this approach makes a significant difference  to  the
4013         processing time.         processing time.
4014    
4015     Using multiple assertions     Using multiple assertions
# Line 3508  ASSERTIONS Line 4018  ASSERTIONS
4018    
4019           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4020    
4021         matches "foo" preceded by three digits that are not "999". Notice  that         matches  "foo" preceded by three digits that are not "999". Notice that
4022         each  of  the  assertions is applied independently at the same point in         each of the assertions is applied independently at the  same  point  in
4023         the subject string. First there is a  check  that  the  previous  three         the  subject  string.  First  there  is a check that the previous three
4024         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
4025         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4026         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
4027         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-
4028         foo". A pattern to do that is         foo". A pattern to do that is
4029    
4030           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4031    
4032         This  time  the  first assertion looks at the preceding six characters,         This time the first assertion looks at the  preceding  six  characters,
4033         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4034         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4035    
# Line 3527  ASSERTIONS Line 4037  ASSERTIONS
4037    
4038           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4039    
4040         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
4041         is not preceded by "foo", while         is not preceded by "foo", while
4042    
4043           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4044    
4045         is another pattern that matches "foo" preceded by three digits and  any         is  another pattern that matches "foo" preceded by three digits and any
4046         three characters that are not "999".         three characters that are not "999".
4047    
4048    
4049  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4050    
4051         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-
4052         ditionally or to choose between two alternative subpatterns,  depending         ditionally  or to choose between two alternative subpatterns, depending
4053         on  the result of an assertion, or whether a previous capturing subpat-         on the result of an assertion, or whether a previous capturing  subpat-
4054         tern matched or not. The two possible forms of  conditional  subpattern         tern  matched  or not. The two possible forms of conditional subpattern
4055         are         are
4056    
4057           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4058           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4059    
4060         If  the  condition is satisfied, the yes-pattern is used; otherwise the         If the condition is satisfied, the yes-pattern is used;  otherwise  the
4061         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-
4062         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4063    
4064         There are three kinds of condition. If the text between the parentheses         There are four kinds of condition: references  to  subpatterns,  refer-
4065         consists of a sequence of digits, the condition  is  satisfied  if  the         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4066         capturing  subpattern of that number has previously matched. The number  
4067         must be greater than zero. Consider the following pattern,  which  con-     Checking for a used subpattern by number
4068         tains  non-significant white space to make it more readable (assume the  
4069         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,
4070         discussion:         the condition is true if the capturing subpattern of  that  number  has
4071           previously matched.
4072    
4073           Consider  the  following  pattern, which contains non-significant white
4074           space to make it more readable (assume the PCRE_EXTENDED option) and to
4075           divide it into three parts for ease of discussion:
4076    
4077           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4078    
# Line 3572  CONDITIONAL SUBPATTERNS Line 4087  CONDITIONAL SUBPATTERNS
4087         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other  words,  this  pattern  matches  a  sequence  of non-parentheses,
4088         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4089    
4090         If the condition is the string (R), it is satisfied if a recursive call     Checking for a used subpattern by name
4091         to  the pattern or subpattern has been made. At "top level", the condi-  
4092         tion is false.  This  is  a  PCRE  extension.  Recursive  patterns  are         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a
4093         described in the next section.         used  subpattern  by  name.  For compatibility with earlier versions of
4094           PCRE, which had this facility before Perl, the syntax  (?(name)...)  is
4095           also  recognized. However, there is a possible ambiguity with this syn-
4096           tax, because subpattern names may  consist  entirely  of  digits.  PCRE
4097           looks  first for a named subpattern; if it cannot find one and the name
4098           consists entirely of digits, PCRE looks for a subpattern of  that  num-
4099           ber,  which must be greater than zero. Using subpattern names that con-
4100           sist entirely of digits is not recommended.
4101    
4102           Rewriting the above example to use a named subpattern gives this:
4103    
4104             (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
4105    
4106         If  the  condition  is  not  a sequence of digits or (R), it must be an  
4107       Checking for pattern recursion
4108    
4109           If the condition is the string (R), and there is no subpattern with the
4110           name  R, the condition is true if a recursive call to the whole pattern
4111           or any subpattern has been made. If digits or a name preceded by amper-
4112           sand follow the letter R, for example:
4113    
4114             (?(R3)...) or (?(R&name)...)
4115    
4116           the  condition is true if the most recent recursion is into the subpat-
4117           tern whose number or name is given. This condition does not  check  the
4118           entire recursion stack.
4119    
4120           At  "top  level", all these recursion test conditions are false. Recur-
4121           sive patterns are described below.
4122    
4123       Defining subpatterns for use by reference only
4124    
4125           If the condition is the string (DEFINE), and  there  is  no  subpattern
4126           with  the  name  DEFINE,  the  condition is always false. In this case,
4127           there may be only one alternative  in  the  subpattern.  It  is  always
4128           skipped  if  control  reaches  this  point  in the pattern; the idea of
4129           DEFINE is that it can be used to define "subroutines" that can be  ref-
4130           erenced  from elsewhere. (The use of "subroutines" is described below.)
4131           For example, a pattern to match an IPv4 address could be  written  like
4132           this (ignore whitespace and line breaks):
4133    
4134             (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
4135             \b (?&byte) (\.(?&byte)){3} \b
4136    
4137           The  first part of the pattern is a DEFINE group inside which a another
4138           group named "byte" is defined. This matches an individual component  of
4139           an  IPv4  address  (a number less than 256). When matching takes place,
4140           this part of the pattern is skipped because DEFINE acts  like  a  false
4141           condition.
4142    
4143           The rest of the pattern uses references to the named group to match the
4144           four dot-separated components of an IPv4 address, insisting on  a  word