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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, the Unicode script names such as Arabic  or  Han,         for  a  decimal number, the Unicode script names such as Arabic or Han,
150         and  the  derived  properties  Any  and L&. A full list is given in the         and the derived properties Any and L&. A full  list  is  given  in  the
151         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
152         ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-         ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
153         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may         ter},  is  not  supported.   Furthermore,  in Perl, many properties may
154         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
155         does not support this.         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. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a         2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
172         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
173    
174         3.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-         3. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
175           characters for values greater than \177.
176    
177           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         4. 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         5.  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         6.  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
# Line 181  UTF-8 AND UNICODE PROPERTY SUPPORT Line 193  UTF-8 AND UNICODE PROPERTY SUPPORT
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         7. 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         8.  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,
# Line 199  UTF-8 AND UNICODE PROPERTY SUPPORT Line 211  UTF-8 AND UNICODE PROPERTY SUPPORT
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: 24 January 2006  
222  Copyright (c) 1997-2006 University of Cambridge.  REVISION
223    
224           Last updated: 06 March 2007
225           Copyright (c) 1997-2007 University of Cambridge.
226  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
227    
228    
# Line 281  UNICODE CHARACTER PROPERTY SUPPORT Line 296  UNICODE CHARACTER PROPERTY SUPPORT
296    
297  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
298    
299         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating
300         ter. This is the normal newline character on Unix-like systems. You can         the  end  of  a line. This is the normal newline character on Unix-like
301         compile PCRE to use character 13 (carriage return) instead by adding         systems. You can compile PCRE to use character 13 (carriage return, CR)
302           instead, by adding
303    
304           --enable-newline-is-cr           --enable-newline-is-cr
305    
306         to the configure command. For completeness there is  also  a  --enable-         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
307         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
308         line character.  
309           Alternatively, you can specify that line endings are to be indicated by
310           the two character sequence CRLF. If you want this, add
311    
312             --enable-newline-is-crlf
313    
314           to the configure command. There is a fourth option, specified by
315    
316             --enable-newline-is-any
317    
318           which causes PCRE to recognize any Unicode newline sequence.
319    
320           Whatever  line  ending convention is selected when PCRE is built can be
321           overridden when the library functions are called. At build time  it  is
322           conventional to use the standard for your operating system.
323    
324    
325  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
326    
327         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
328         Unix  libraries by default. You can suppress one of these by adding one         Unix libraries by default. You can suppress one of these by adding  one
329         of         of
330    
331           --disable-shared           --disable-shared
# Line 307  BUILDING SHARED AND STATIC LIBRARIES Line 337  BUILDING SHARED AND STATIC LIBRARIES
337  POSIX MALLOC USAGE  POSIX MALLOC USAGE
338    
339         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
340         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
341         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
342         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
343         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
344         on the stack, because this is faster than using malloc() for each call.         on the stack, because this is faster than using malloc() for each call.
345         The default threshold above which the stack is no longer used is 10; it         The default threshold above which the stack is no longer used is 10; it
# Line 320  POSIX MALLOC USAGE Line 350  POSIX MALLOC USAGE
350         to the configure command.         to the configure command.
351    
352    
 LIMITING PCRE RESOURCE USAGE  
   
        Internally,  PCRE has a function called match(), which it calls repeat-  
        edly  (possibly  recursively)  when  matching  a   pattern   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.  
   
   
353  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
354    
355         Within  a  compiled  pattern,  offset values are used to point from one         Within a compiled pattern, offset values are used  to  point  from  one
356         part to another (for example, from an opening parenthesis to an  alter-         part  to another (for example, from an opening parenthesis to an alter-
357         nation  metacharacter).  By default, two-byte values are used for these         nation metacharacter). By default, two-byte values are used  for  these
358         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets,  leading  to  a  maximum size for a compiled pattern of around
359         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
360         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless,  some  people do want to process enormous patterns, so it
361         is  possible  to compile PCRE to use three-byte or four-byte offsets by         is possible to compile PCRE to use three-byte or four-byte  offsets  by
362         adding a setting such as         adding a setting such as
363    
364           --with-link-size=3           --with-link-size=3
365    
366         to the configure command. The value given must be 2,  3,  or  4.  Using         to  the  configure  command.  The value given must be 2, 3, or 4. Using
367         longer  offsets slows down the operation of PCRE because it has to load         longer offsets slows down the operation of PCRE because it has to  load
368         additional bytes when handling them.         additional bytes when handling them.
369    
370         If you build PCRE with an increased link size, test 2 (and  test  5  if         If  you  build  PCRE with an increased link size, test 2 (and test 5 if
371         you  are using UTF-8) will fail. Part of the output of these tests is a         you are using UTF-8) will fail. Part of the output of these tests is  a
372         representation of the compiled pattern, and this changes with the  link         representation  of the compiled pattern, and this changes with the link
373         size.         size.
374    
375    
376  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
377    
378         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
379         ing by making recursive calls to an internal function  called  match().         ing  by  making recursive calls to an internal function called match().
380         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-
381         verely limit PCRE's operation. (The Unix environment does  not  usually         verely  limit  PCRE's operation. (The Unix environment does not usually
382         suffer  from  this  problem.)  An alternative approach that uses memory         suffer from this problem, but it may sometimes be necessary to increase
383         from the heap to remember data, instead  of  using  recursive  function         the  maximum  stack size.  There is a discussion in the pcrestack docu-
384         calls,  has been implemented to work round this problem. If you want to         mentation.) An alternative approach to recursion that uses memory  from
385         build a version of PCRE that works this way, add         the  heap  to remember data, instead of using recursive function calls,
386           has been implemented to work round the problem of limited  stack  size.
387           If you want to build a version of PCRE that works this way, add
388    
389           --disable-stack-for-recursion           --disable-stack-for-recursion
390    
391         to the configure command. With this configuration, PCRE  will  use  the         to  the  configure  command. With this configuration, PCRE will use the
392         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
393         ment functions. Separate functions are provided because  the  usage  is         ment  functions.  Separate  functions are provided because the usage is
394         very  predictable:  the  block sizes requested are always the same, and         very predictable: the block sizes requested are always  the  same,  and
395         the blocks are always freed in reverse order. A calling  program  might         the  blocks  are always freed in reverse order. A calling program might
396         be  able  to implement optimized functions that perform better than the         be able to implement optimized functions that perform better  than  the
397         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more
398         slowly when built in this way. This option affects only the pcre_exec()         slowly when built in this way. This option affects only the pcre_exec()
399         function; it is not relevant for the the pcre_dfa_exec() function.         function; it is not relevant for the the pcre_dfa_exec() function.
400    
401    
402    LIMITING PCRE RESOURCE USAGE
403    
404           Internally,  PCRE has a function called match(), which it calls repeat-
405           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
406           pcre_exec()  function.  By controlling the maximum number of times this
407           function may be called during a single matching operation, a limit  can
408           be  placed  on  the resources used by a single call to pcre_exec(). The
409           limit can be changed at run time, as described in the pcreapi  documen-
410           tation.  The default is 10 million, but this can be changed by adding a
411           setting such as
412    
413             --with-match-limit=500000
414    
415           to  the  configure  command.  This  setting  has  no  effect   on   the
416           pcre_dfa_exec() matching function.
417    
418           In  some  environments  it is desirable to limit the depth of recursive
419           calls of match() more strictly than the total number of calls, in order
420           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
421           for-recursion is specified) that is used. A second limit controls this;
422           it  defaults  to  the  value  that is set for --with-match-limit, which
423           imposes no additional constraints. However, you can set a  lower  limit
424           by adding, for example,
425    
426             --with-match-limit-recursion=10000
427    
428           to  the  configure  command.  This  value can also be overridden at run
429           time.
430    
431    
432  USING EBCDIC CODE  USING EBCDIC CODE
433    
434         PCRE assumes by default that it will run in an  environment  where  the         PCRE assumes by default that it will run in an  environment  where  the
# Line 395  USING EBCDIC CODE Line 440  USING EBCDIC CODE
440    
441         to the configure command.         to the configure command.
442    
443  Last updated: 15 August 2005  
444  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
445    
446           pcreapi(3), pcre_config(3).
447    
448    
449    AUTHOR
450    
451           Philip Hazel
452           University Computing Service
453           Cambridge CB2 3QH, England.
454    
455    
456    REVISION
457    
458           Last updated: 06 March 2007
459           Copyright (c) 1997-2007 University of Cambridge.
460  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
461    
462    
# Line 432  PCRE MATCHING ALGORITHMS Line 492  PCRE MATCHING ALGORITHMS
492           <something> <something else> <something further>           <something> <something else> <something further>
493    
494         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
495         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
496    
497    
498  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 441  REGULAR EXPRESSIONS AS TREES Line 501  REGULAR EXPRESSIONS AS TREES
501         resented  as  a  tree structure. An unlimited repetition in the pattern         resented  as  a  tree structure. An unlimited repetition in the pattern
502         makes the tree of infinite size, but it is still a tree.  Matching  the         makes the tree of infinite size, but it is still a tree.  Matching  the
503         pattern  to a given subject string (from a given starting point) can be         pattern  to a given subject string (from a given starting point) can be
504         thought of as a search of the tree.  There are  two  standard  ways  to         thought of as a search of the tree.  There are two  ways  to  search  a
505         search  a  tree: depth-first and breadth-first, and these correspond to         tree:  depth-first  and  breadth-first, and these correspond to the two
506         the two matching algorithms provided by PCRE.         matching algorithms provided by PCRE.
507    
508    
509  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
# Line 473  THE STANDARD MATCHING ALGORITHM Line 533  THE STANDARD MATCHING ALGORITHM
533         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
534    
535    
536  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
537    
538         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
539         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
540         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
541         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
542         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",
543         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
544           keeps multiple states active simultaneously).
545         The  scan  continues until either the end of the subject is reached, or  
546         there are no more unterminated paths. At this point,  terminated  paths         The scan continues until either the end of the subject is  reached,  or
547         represent  the different matching possibilities (if there are none, the         there  are  no more unterminated paths. At this point, terminated paths
548         match has failed).  Thus, if there is more  than  one  possible  match,         represent the different matching possibilities (if there are none,  the
549           match  has  failed).   Thus,  if there is more than one possible match,
550         this algorithm finds all of them, and in particular, it finds the long-         this algorithm finds all of them, and in particular, it finds the long-
551         est. In PCRE, there is an option to stop the algorithm after the  first         est.  In PCRE, there is an option to stop the algorithm after the first
552         match (which is necessarily the shortest) has been found.         match (which is necessarily the shortest) has been found.
553    
554         Note that all the matches that are found start at the same point in the         Note that all the matches that are found start at the same point in the
# Line 495  THE DFA MATCHING ALGORITHM Line 556  THE DFA MATCHING ALGORITHM
556    
557           cat(er(pillar)?)           cat(er(pillar)?)
558    
559         is matched against the string "the caterpillar catchment",  the  result         is  matched  against the string "the caterpillar catchment", the result
560         will  be the three strings "cat", "cater", and "caterpillar" that start         will be the three strings "cat", "cater", and "caterpillar" that  start
561         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
562         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
563    
564         There are a number of features of PCRE regular expressions that are not         There are a number of features of PCRE regular expressions that are not
565         supported by the DFA matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
566    
567         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1.  Because  the  algorithm  finds  all possible matches, the greedy or
568         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
569         ungreedy quantifiers are treated in exactly the same way.         ungreedy quantifiers are treated in exactly the same way. However, pos-
570           sessive quantifiers can make a difference when what follows could  also
571           match what is quantified, for example in a pattern like this:
572    
573             ^a++\w!
574    
575           This  pattern matches "aaab!" but not "aaa!", which would be matched by
576           a non-possessive quantifier. Similarly, if an atomic group is  present,
577           it  is matched as if it were a standalone pattern at the current point,
578           and the longest match is then "locked in" for the rest of  the  overall
579           pattern.
580    
581         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
582         is  not  straightforward  to  keep track of captured substrings for the         is not straightforward to keep track of  captured  substrings  for  the
583         different matching possibilities, and  PCRE's  implementation  of  this         different  matching  possibilities,  and  PCRE's implementation of this
584         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-
585         strings are available.         strings are available.
586    
587         3. Because no substrings are captured, back references within the  pat-         3.  Because no substrings are captured, back references within the pat-
588         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
589    
590         4.  For  the same reason, conditional expressions that use a backrefer-         4. For the same reason, conditional expressions that use  a  backrefer-
591         ence as the condition are not supported.         ence  as  the  condition or test for a specific group recursion are not
592           supported.
593    
594         5. Callouts are supported, but the value of the  capture_top  field  is         5. Callouts are supported, but the value of the  capture_top  field  is
595         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
596    
597         6.  The \C escape sequence, which (in the standard algorithm) matches a         6.  The \C escape sequence, which (in the standard algorithm) matches a
598         single byte, even in UTF-8 mode, is not supported because the DFA algo-         single byte, even in UTF-8 mode, is not supported because the  alterna-
599         rithm moves through the subject string one character at a time, for all         tive  algorithm  moves  through  the  subject string one character at a
600         active paths through the tree.         time, for all active paths through the tree.
601    
602    
603  ADVANTAGES OF THE DFA ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
604    
605         Using the DFA matching algorithm provides the following advantages:         Using the alternative matching algorithm provides the following  advan-
606           tages:
607    
608         1. All possible matches (at a single point in the subject) are automat-         1. All possible matches (at a single point in the subject) are automat-
609         ically  found,  and  in particular, the longest match is found. To find         ically found, and in particular, the longest match is  found.  To  find
610         more than one match using the standard algorithm, you have to do kludgy         more than one match using the standard algorithm, you have to do kludgy
611         things with callouts.         things with callouts.
612    
613         2.  There is much better support for partial matching. The restrictions         2. There is much better support for partial matching. The  restrictions
614         on the content of the pattern that apply when using the standard  algo-         on  the content of the pattern that apply when using the standard algo-
615         rithm  for partial matching do not apply to the DFA algorithm. For non-         rithm for partial matching do not apply to the  alternative  algorithm.
616         anchored patterns, the starting position of a partial match  is  avail-         For  non-anchored patterns, the starting position of a partial match is
617         able.         available.
618    
619         3.  Because  the  DFA algorithm scans the subject string just once, and         3. Because the alternative algorithm  scans  the  subject  string  just
620         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
621         strings  to  the matching function in several pieces, checking for par-         subject strings to the matching function in  several  pieces,  checking
622         tial matching each time.         for partial matching each time.
623    
624    
625  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
626    
627         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
628    
629         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
630         partly  because  it has to search for all possible matches, but is also         partly because it has to search for all possible matches, but  is  also
631         because it is less susceptible to optimization.         because it is less susceptible to optimization.
632    
633         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
634    
635         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
636         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
637         rithm.  
638    
639    AUTHOR
640    
641           Philip Hazel
642           University Computing Service
643           Cambridge CB2 3QH, England.
644    
645    
646    REVISION
647    
648  Last updated: 28 February 2005         Last updated: 06 March 2007
649  Copyright (c) 1997-2005 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
650  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
651    
652    
# Line 617  PCRE NATIVE API Line 699  PCRE NATIVE API
699         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
700              const char *name);              const char *name);
701    
702           int pcre_get_stringtable_entries(const pcre *code,
703                const char *name, char **first, char **last);
704    
705         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
706              int stringcount, int stringnumber,              int stringcount, int stringnumber,
707              const char **stringptr);              const char **stringptr);
# Line 655  PCRE NATIVE API Line 740  PCRE NATIVE API
740  PCRE API OVERVIEW  PCRE API OVERVIEW
741    
742         PCRE has its own native API, which is described in this document. There         PCRE has its own native API, which is described in this document. There
743         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
744         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
745         Both of these APIs define a set of C function calls. A C++  wrapper  is         Both of these APIs define a set of C function calls. A C++  wrapper  is
746         distributed with PCRE. It is documented in the pcrecpp page.         distributed with PCRE. It is documented in the pcrecpp page.
# Line 677  PCRE API OVERVIEW Line 762  PCRE API OVERVIEW
762    
763         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
764         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
765         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
766         the  subject),  not  just  one. However, this algorithm does not return         point  in  the subject), and scans the subject just once. However, this
767         captured substrings. A description of the two matching  algorithms  and         algorithm does not return captured substrings. A description of the two
768         their  advantages  and disadvantages is given in the pcrematching docu-         matching  algorithms and their advantages and disadvantages is given in
769         mentation.         the pcrematching documentation.
770    
771         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
772         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 693  PCRE API OVERVIEW Line 778  PCRE API OVERVIEW
778           pcre_get_named_substring()           pcre_get_named_substring()
779           pcre_get_substring_list()           pcre_get_substring_list()
780           pcre_get_stringnumber()           pcre_get_stringnumber()
781             pcre_get_stringtable_entries()
782    
783         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
784         to free the memory used for extracted strings.         to free the memory used for extracted strings.
# Line 724  PCRE API OVERVIEW Line 810  PCRE API OVERVIEW
810         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
811         are used only when PCRE is compiled to use  the  heap  for  remembering         are used only when PCRE is compiled to use  the  heap  for  remembering
812         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
813         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
814         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-
815         management, it runs more slowly.  Separate functions  are  provided  so         ments that have limited stacks. Because of the greater  use  of  memory
816         that  special-purpose  external  code  can  be used for this case. When         management,  it  runs  more  slowly. Separate functions are provided so
817         used, these functions are always called in a  stack-like  manner  (last         that special-purpose external code can be  used  for  this  case.  When
818         obtained,  first freed), and always for memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
819           obtained, first freed), and always for memory blocks of the same  size.
820           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
821           mentation.
822    
823         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
824         by  the  caller  to  a "callout" function, which PCRE will then call at         by  the  caller  to  a "callout" function, which PCRE will then call at
# Line 737  PCRE API OVERVIEW Line 826  PCRE API OVERVIEW
826         pcrecallout documentation.         pcrecallout documentation.
827    
828    
829    NEWLINES
830    
831           PCRE  supports four different conventions for indicating line breaks in
832           strings: a single CR (carriage return) character, a  single  LF  (line-
833           feed)  character,  the two-character sequence CRLF, or any Unicode new-
834           line sequence.  The Unicode newline sequences are the three  just  men-
835           tioned, plus the single characters VT (vertical tab, U+000B), FF (form-
836           feed, U+000C), NEL (next line, U+0085), LS  (line  separator,  U+2028),
837           and PS (paragraph separator, U+2029).
838    
839           Each  of  the first three conventions is used by at least one operating
840           system as its standard newline sequence. When PCRE is built, a  default
841           can  be  specified.  The default default is LF, which is the Unix stan-
842           dard. When PCRE is run, the default can be overridden,  either  when  a
843           pattern is compiled, or when it is matched.
844    
845           In the PCRE documentation the word "newline" is used to mean "the char-
846           acter or pair of characters that indicate a line break". The choice  of
847           newline  convention  affects  the  handling of the dot, circumflex, and
848           dollar metacharacters, the handling of #-comments in /x mode, and, when
849           CRLF  is a recognized line ending sequence, the match position advance-
850           ment for a non-anchored pattern. The choice of newline convention  does
851           not affect the interpretation of the \n or \r escape sequences.
852    
853    
854  MULTITHREADING  MULTITHREADING
855    
856         The  PCRE  functions  can be used in multi-threading applications, with         The  PCRE  functions  can be used in multi-threading applications, with
# Line 783  CHECKING BUILD-TIME OPTIONS Line 897  CHECKING BUILD-TIME OPTIONS
897    
898           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
899    
900         The output is an integer that is set to the value of the code  that  is         The output is an integer whose value specifies  the  default  character
901         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
902         return (13), and should normally be the  standard  character  for  your         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, and -1 for ANY.
903         operating system.         The default should normally be the standard sequence for your operating
904           system.
905    
906           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
907    
908         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
909         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
910         4.  Larger  values  allow larger regular expressions to be compiled, at         4. Larger values allow larger regular expressions to  be  compiled,  at
911         the expense of slower matching. The default value of  2  is  sufficient         the  expense  of  slower matching. The default value of 2 is sufficient
912         for  all  but  the  most massive patterns, since it allows the compiled         for all but the most massive patterns, since  it  allows  the  compiled
913         pattern to be up to 64K in size.         pattern to be up to 64K in size.
914    
915           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
916    
917         The output is an integer that contains the threshold  above  which  the         The  output  is  an integer that contains the threshold above which the
918         POSIX  interface  uses malloc() for output vectors. Further details are         POSIX interface uses malloc() for output vectors. Further  details  are
919         given in the pcreposix documentation.         given in the pcreposix documentation.
920    
921           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
922    
923         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
924         internal  matching  function  calls in a pcre_exec() execution. Further         internal matching function calls in a  pcre_exec()  execution.  Further
925         details are given with pcre_exec() below.         details are given with pcre_exec() below.
926    
927           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
928    
929         The output is an integer that gives the default limit for the depth  of         The  output is an integer that gives the default limit for the depth of
930         recursion  when calling the internal matching function in a pcre_exec()         recursion when calling the internal matching function in a  pcre_exec()
931         execution. Further details are given with pcre_exec() below.         execution. Further details are given with pcre_exec() below.
932    
933           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
934    
935         The output is an integer that is set to one if internal recursion  when         The  output is an integer that is set to one if internal recursion when
936         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
937         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
938         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
939         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
940         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
941         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
942    
943    
# Line 839  COMPILING A PATTERN Line 954  COMPILING A PATTERN
954    
955         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
956         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
957         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
958         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
959    
960         The pattern is a C string terminated by a binary zero, and is passed in         The pattern is a C string terminated by a binary zero, and is passed in
961         the pattern argument. A pointer to a single block  of  memory  that  is         the  pattern  argument.  A  pointer to a single block of memory that is
962         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
963         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
964         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
965         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
966         required.         longer required.
967    
968         Although  the compiled code of a PCRE regex is relocatable, that is, it         Although the compiled code of a PCRE regex is relocatable, that is,  it
969         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
970         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
971         ment, which is an address (see below).         ment, which is an address (see below).
972    
973         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
974         tion.  It  should  be  zero  if  no options are required. The available         pilation. It should be zero if no options are required.  The  available
975         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them, in particular, those that
976         are  compatible  with  Perl,  can also be set and unset from within the         are compatible with Perl, can also be set and  unset  from  within  the
977         pattern (see the detailed description  in  the  pcrepattern  documenta-         pattern  (see  the  detailed  description in the pcrepattern documenta-
978         tion).  For  these options, the contents of the options argument speci-         tion). For these options, the contents of the options  argument  speci-
979         fies their initial settings at the start of compilation and  execution.         fies  their initial settings at the start of compilation and execution.
980         The  PCRE_ANCHORED option can be set at the time of matching as well as         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time
981         at compile time.         of matching as well as at compile time.
982    
983         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
984         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
985         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
986         sage. This is a static string that is part of the library. You must not         sage. This is a static string that is part of the library. You must not
987         try to free it. The offset from the start of the pattern to the charac-         try to free it. The offset from the start of the pattern to the charac-
988         ter where the error was discovered is placed in the variable pointed to         ter where the error was discovered is placed in the variable pointed to
989         by erroffset, which must not be NULL. If it is, an immediate  error  is         by  erroffset,  which must not be NULL. If it is, an immediate error is
990         given.         given.
991    
992         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
993         codeptr argument is not NULL, a non-zero error code number is  returned         codeptr  argument is not NULL, a non-zero error code number is returned
994         via  this argument in the event of an error. This is in addition to the         via this argument in the event of an error. This is in addition to  the
995         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
996    
997         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of
998         character  tables  that  are  built  when  PCRE  is compiled, using the         character tables that are  built  when  PCRE  is  compiled,  using  the
999         default C locale. Otherwise, tableptr must be an address  that  is  the         default  C  locale.  Otherwise, tableptr must be an address that is the
1000         result  of  a  call to pcre_maketables(). This value is stored with the         result of a call to pcre_maketables(). This value is  stored  with  the
1001         compiled pattern, and used again by pcre_exec(), unless  another  table         compiled  pattern,  and used again by pcre_exec(), unless another table
1002         pointer is passed to it. For more discussion, see the section on locale         pointer is passed to it. For more discussion, see the section on locale
1003         support below.         support below.
1004    
1005         This code fragment shows a typical straightforward  call  to  pcre_com-         This  code  fragment  shows a typical straightforward call to pcre_com-
1006         pile():         pile():
1007    
1008           pcre *re;           pcre *re;
# Line 900  COMPILING A PATTERN Line 1015  COMPILING A PATTERN
1015             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1016             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1017    
1018         The  following  names  for option bits are defined in the pcre.h header         The following names for option bits are defined in  the  pcre.h  header
1019         file:         file:
1020    
1021           PCRE_ANCHORED           PCRE_ANCHORED
1022    
1023         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
1024         is  constrained to match only at the first matching point in the string         is constrained to match only at the first matching point in the  string
1025         that is being searched (the "subject string"). This effect can also  be         that  is being searched (the "subject string"). This effect can also be
1026         achieved  by appropriate constructs in the pattern itself, which is the         achieved by appropriate constructs in the pattern itself, which is  the
1027         only way to do it in Perl.         only way to do it in Perl.
1028    
1029           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1030    
1031         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1032         all  with  number  255, before each pattern item. For discussion of the         all with number 255, before each pattern item. For  discussion  of  the
1033         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1034    
1035           PCRE_CASELESS           PCRE_CASELESS
1036    
1037         If this bit is set, letters in the pattern match both upper  and  lower         If  this  bit is set, letters in the pattern match both upper and lower
1038         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be
1039         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
1040         always  understands the concept of case for characters whose values are         always understands the concept of case for characters whose values  are
1041         less than 128, so caseless matching is always possible. For  characters         less  than 128, so caseless matching is always possible. For characters
1042         with  higher  values,  the concept of case is supported if PCRE is com-         with higher values, the concept of case is supported if  PCRE  is  com-
1043         piled with Unicode property support, but not otherwise. If you want  to         piled  with Unicode property support, but not otherwise. If you want to
1044         use  caseless  matching  for  characters 128 and above, you must ensure         use caseless matching for characters 128 and  above,  you  must  ensure
1045         that PCRE is compiled with Unicode property support  as  well  as  with         that  PCRE  is  compiled  with Unicode property support as well as with
1046         UTF-8 support.         UTF-8 support.
1047    
1048           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1049    
1050         If  this bit is set, a dollar metacharacter in the pattern matches only         If this bit is set, a dollar metacharacter in the pattern matches  only
1051         at the end of the subject string. Without this option,  a  dollar  also         at  the  end  of the subject string. Without this option, a dollar also
1052         matches  immediately before the final character if it is a newline (but         matches immediately before a newline at the end of the string (but  not
1053         not before any  other  newlines).  The  PCRE_DOLLAR_ENDONLY  option  is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1054         ignored if PCRE_MULTILINE is set. There is no equivalent to this option         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in
1055         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1056    
1057           PCRE_DOTALL           PCRE_DOTALL
1058    
1059         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharater in the pattern matches all char-
1060         acters,  including  newlines.  Without  it, newlines are excluded. This         acters, including those that indicate newline. Without it, a  dot  does
1061         option is equivalent to Perl's /s option, and it can be changed  within         not  match  when  the  current position is at a newline. This option is
1062         a  pattern  by  a  (?s)  option  setting. A negative class such as [^a]         equivalent to Perl's /s option, and it can be changed within a  pattern
1063         always matches a newline character, independent of the setting of  this         by  a (?s) option setting. A negative class such as [^a] always matches
1064         option.         newline characters, independent of the setting of this option.
1065    
1066             PCRE_DUPNAMES
1067    
1068           If this bit is set, names used to identify capturing  subpatterns  need
1069           not be unique. This can be helpful for certain types of pattern when it
1070           is known that only one instance of the named  subpattern  can  ever  be
1071           matched.  There  are  more details of named subpatterns below; see also
1072           the pcrepattern documentation.
1073    
1074           PCRE_EXTENDED           PCRE_EXTENDED
1075    
1076         If  this  bit  is  set,  whitespace  data characters in the pattern are         If this bit is set, whitespace  data  characters  in  the  pattern  are
1077         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1078         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1079         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1080         line  character,  inclusive,  are  also  ignored. This is equivalent to         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1081         Perl's /x option, and it can be changed within  a  pattern  by  a  (?x)         option,  and  it  can be changed within a pattern by a (?x) option set-
1082         option setting.         ting.
1083    
1084         This  option  makes  it possible to include comments inside complicated         This option makes it possible to include  comments  inside  complicated
1085         patterns.  Note, however, that this applies only  to  data  characters.         patterns.   Note,  however,  that this applies only to data characters.
1086         Whitespace   characters  may  never  appear  within  special  character         Whitespace  characters  may  never  appear  within  special   character
1087         sequences in a pattern, for  example  within  the  sequence  (?(  which         sequences  in  a  pattern,  for  example  within the sequence (?( which
1088         introduces a conditional subpattern.         introduces a conditional subpattern.
1089    
1090           PCRE_EXTRA           PCRE_EXTRA
1091    
1092         This  option  was invented in order to turn on additional functionality         This option was invented in order to turn on  additional  functionality
1093         of PCRE that is incompatible with Perl, but it  is  currently  of  very         of  PCRE  that  is  incompatible with Perl, but it is currently of very
1094         little  use. When set, any backslash in a pattern that is followed by a         little use. When set, any backslash in a pattern that is followed by  a
1095         letter that has no special meaning  causes  an  error,  thus  reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1096         these  combinations  for  future  expansion.  By default, as in Perl, a         these combinations for future expansion. By  default,  as  in  Perl,  a
1097         backslash followed by a letter with no special meaning is treated as  a         backslash  followed by a letter with no special meaning is treated as a
1098         literal.  There  are  at  present  no other features controlled by this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1099         option. It can also be set by a (?X) option setting within a pattern.         There  are  at  present no other features controlled by this option. It
1100           can also be set by a (?X) option setting within a pattern.
1101    
1102           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1103    
1104         If this option is set, an  unanchored  pattern  is  required  to  match         If this option is set, an  unanchored  pattern  is  required  to  match
1105         before  or at the first newline character in the subject string, though         before  or  at  the  first  newline  in  the subject string, though the
1106         the matched text may continue over the newline.         matched text may continue over the newline.
1107    
1108           PCRE_MULTILINE           PCRE_MULTILINE
1109    
# Line 991  COMPILING A PATTERN Line 1115  COMPILING A PATTERN
1115         is set). This is the same as Perl.         is set). This is the same as Perl.
1116    
1117         When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"         When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1118         constructs match immediately following or immediately before  any  new-         constructs match immediately following or immediately  before  internal
1119         line  in the subject string, respectively, as well as at the very start         newlines  in  the  subject string, respectively, as well as at the very
1120         and end. This is equivalent to Perl's /m option, and it can be  changed         start and end. This is equivalent to Perl's /m option, and  it  can  be
1121         within a pattern by a (?m) option setting. If there are no "\n" charac-         changed within a pattern by a (?m) option setting. If there are no new-
1122         ters in a subject string, or no occurrences of ^ or  $  in  a  pattern,         lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1123         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1124    
1125             PCRE_NEWLINE_CR
1126             PCRE_NEWLINE_LF
1127             PCRE_NEWLINE_CRLF
1128             PCRE_NEWLINE_ANY
1129    
1130           These  options  override the default newline definition that was chosen
1131           when PCRE was built. Setting the first or the second specifies  that  a
1132           newline  is  indicated  by a single character (CR or LF, respectively).
1133           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1134           two-character  CRLF  sequence.  Setting PCRE_NEWLINE_ANY specifies that
1135           any Unicode newline sequence should be recognized. The Unicode  newline
1136           sequences  are  the three just mentioned, plus the single characters VT
1137           (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085),
1138           LS  (line separator, U+2028), and PS (paragraph separator, U+2029). The
1139           last two are recognized only in UTF-8 mode.
1140    
1141           The newline setting in the  options  word  uses  three  bits  that  are
1142           treated  as  a  number, giving eight possibilities. Currently only five
1143           are used (default plus the four values above). This means that  if  you
1144           set  more  than  one  newline option, the combination may or may not be
1145           sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is  equiva-
1146           lent  to PCRE_NEWLINE_CRLF, but other combinations yield unused numbers
1147           and cause an error.
1148    
1149           The only time that a line break is specially recognized when  compiling
1150           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1151           character class is encountered. This indicates  a  comment  that  lasts
1152           until  after the next line break sequence. In other circumstances, line
1153           break  sequences  are  treated  as  literal  data,   except   that   in
1154           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1155           and are therefore ignored.
1156    
1157           The newline option that is set at compile time becomes the default that
1158           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1159    
1160           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1161    
1162         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
1163         theses in the pattern. Any opening parenthesis that is not followed  by         theses  in the pattern. Any opening parenthesis that is not followed by
1164         ?  behaves as if it were followed by ?: but named parentheses can still         ? behaves as if it were followed by ?: but named parentheses can  still
1165         be used for capturing (and they acquire  numbers  in  the  usual  way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1166         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1167    
1168           PCRE_UNGREEDY           PCRE_UNGREEDY
1169    
1170         This  option  inverts  the "greediness" of the quantifiers so that they         This option inverts the "greediness" of the quantifiers  so  that  they
1171         are not greedy by default, but become greedy if followed by "?". It  is         are  not greedy by default, but become greedy if followed by "?". It is
1172         not  compatible  with Perl. It can also be set by a (?U) option setting         not compatible with Perl. It can also be set by a (?U)  option  setting
1173         within the pattern.         within the pattern.
1174    
1175           PCRE_UTF8           PCRE_UTF8
1176    
1177         This option causes PCRE to regard both the pattern and the  subject  as         This  option  causes PCRE to regard both the pattern and the subject as
1178         strings  of  UTF-8 characters instead of single-byte character strings.         strings of UTF-8 characters instead of single-byte  character  strings.
1179         However, it is available only when PCRE is built to include UTF-8  sup-         However,  it is available only when PCRE is built to include UTF-8 sup-
1180         port.  If not, the use of this option provokes an error. Details of how         port. If not, the use of this option provokes an error. Details of  how
1181         this option changes the behaviour of PCRE are given in the  section  on         this  option  changes the behaviour of PCRE are given in the section on
1182         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1183    
1184           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1185    
1186         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1187         automatically checked. If an invalid UTF-8 sequence of bytes is  found,         automatically  checked. If an invalid UTF-8 sequence of bytes is found,
1188         pcre_compile()  returns an error. If you already know that your pattern         pcre_compile() returns an error. If you already know that your  pattern
1189         is valid, and you want to skip this check for performance reasons,  you         is  valid, and you want to skip this check for performance reasons, you
1190         can  set  the  PCRE_NO_UTF8_CHECK option. When it is set, the effect of         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of
1191         passing an invalid UTF-8 string as a pattern is undefined. It may cause         passing an invalid UTF-8 string as a pattern is undefined. It may cause
1192         your  program  to  crash.   Note that this option can also be passed to         your program to crash.  Note that this option can  also  be  passed  to
1193         pcre_exec() and pcre_dfa_exec(), to suppress the UTF-8 validity  check-         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1194         ing of subject strings.         ing of subject strings.
1195    
1196    
1197  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1198    
1199         The  following  table  lists  the  error  codes than may be returned by         The following table lists the error  codes  than  may  be  returned  by
1200         pcre_compile2(), along with the error messages that may be returned  by         pcre_compile2(),  along with the error messages that may be returned by
1201         both compiling functions.         both compiling functions. As PCRE has developed, some error codes  have
1202           fallen out of use. To avoid confusion, they have not been re-used.
1203    
1204            0  no error            0  no error
1205            1  \ at end of pattern            1  \ at end of pattern
# Line 1051  COMPILATION ERROR CODES Line 1211  COMPILATION ERROR CODES
1211            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1212            8  range out of order in character class            8  range out of order in character class
1213            9  nothing to repeat            9  nothing to repeat
1214           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1215           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1216           12  unrecognized character after (?           12  unrecognized character after (?
1217           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
# Line 1060  COMPILATION ERROR CODES Line 1220  COMPILATION ERROR CODES
1220           16  erroffset passed as NULL           16  erroffset passed as NULL
1221           17  unknown option bit(s) set           17  unknown option bit(s) set
1222           18  missing ) after comment           18  missing ) after comment
1223           19  parentheses nested too deeply           19  [this code is not in use]
1224           20  regular expression too large           20  regular expression too large
1225           21  failed to get memory           21  failed to get memory
1226           22  unmatched parentheses           22  unmatched parentheses
1227           23  internal error: code overflow           23  internal error: code overflow
1228           24  unrecognized character after (?<           24  unrecognized character after (?<
1229           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1230           26  malformed number after (?(           26  malformed number or name after (?(
1231           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1232           28  assertion expected after (?(           28  assertion expected after (?(
1233           29  (?R or (?digits must be followed by )           29  (?R or (?digits must be followed by )
1234           30  unknown POSIX class name           30  unknown POSIX class name
1235           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1236           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1237           33  spare error           33  [this code is not in use]
1238           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1239           35  invalid condition (?(0)           35  invalid condition (?(0)
1240           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1083  COMPILATION ERROR CODES Line 1243  COMPILATION ERROR CODES
1243           39  closing ) for (?C expected           39  closing ) for (?C expected
1244           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1245           41  unrecognized character after (?P           41  unrecognized character after (?P
1246           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1247           43  two named groups have the same name           43  two named subpatterns have the same name
1248           44  invalid UTF-8 string           44  invalid UTF-8 string
1249           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1250           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1251           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1252             48  subpattern name is too long (maximum 32 characters)
1253             49  too many named subpatterns (maximum 10,000)
1254             50  repeated subpattern is too long
1255             51  octal value is greater than \377 (not in UTF-8 mode)
1256             52  internal error: overran compiling workspace
1257             53   internal  error:  previously-checked  referenced  subpattern not
1258           found
1259             54  DEFINE group contains more than one branch
1260             55  repeating a DEFINE group is not allowed
1261             56  inconsistent NEWLINE options"
1262    
1263    
1264  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1096  STUDYING A PATTERN Line 1266  STUDYING A PATTERN
1266         pcre_extra *pcre_study(const pcre *code, int options         pcre_extra *pcre_study(const pcre *code, int options
1267              const char **errptr);              const char **errptr);
1268    
1269         If  a  compiled  pattern is going to be used several times, it is worth         If a compiled pattern is going to be used several times,  it  is  worth
1270         spending more time analyzing it in order to speed up the time taken for         spending more time analyzing it in order to speed up the time taken for
1271         matching.  The function pcre_study() takes a pointer to a compiled pat-         matching. The function pcre_study() takes a pointer to a compiled  pat-
1272         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1273         information  that  will  help speed up matching, pcre_study() returns a         information that will help speed up matching,  pcre_study()  returns  a
1274         pointer to a pcre_extra block, in which the study_data field points  to         pointer  to a pcre_extra block, in which the study_data field points to
1275         the results of the study.         the results of the study.
1276    
1277         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1278         pcre_exec(). However, a pcre_extra block  also  contains  other  fields         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1279         that  can  be  set  by the caller before the block is passed; these are         that can be set by the caller before the block  is  passed;  these  are
1280         described below in the section on matching a pattern.         described below in the section on matching a pattern.
1281    
1282         If studying the pattern does not  produce  any  additional  information         If  studying  the  pattern  does not produce any additional information
1283         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1284         wants to pass any of the other fields to pcre_exec(), it  must  set  up         wants  to  pass  any of the other fields to pcre_exec(), it must set up
1285         its own pcre_extra block.         its own pcre_extra block.
1286    
1287         The  second  argument of pcre_study() contains option bits. At present,         The second argument of pcre_study() contains option bits.  At  present,
1288         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1289    
1290         The third argument for pcre_study() is a pointer for an error  message.         The  third argument for pcre_study() is a pointer for an error message.
1291         If  studying  succeeds  (even  if no data is returned), the variable it         If studying succeeds (even if no data is  returned),  the  variable  it
1292         points to is set to NULL. Otherwise it is set to  point  to  a  textual         points  to  is  set  to NULL. Otherwise it is set to point to a textual
1293         error message. This is a static string that is part of the library. You         error message. This is a static string that is part of the library. You
1294         must not try to free it. You should test the  error  pointer  for  NULL         must  not  try  to  free it. You should test the error pointer for NULL
1295         after calling pcre_study(), to be sure that it has run successfully.         after calling pcre_study(), to be sure that it has run successfully.
1296    
1297         This is a typical call to pcre_study():         This is a typical call to pcre_study():
# Line 1133  STUDYING A PATTERN Line 1303  STUDYING A PATTERN
1303             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1304    
1305         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1306         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-
1307         ble starting bytes is created.         ble starting bytes is created.
1308    
1309    
1310  LOCALE SUPPORT  LOCALE SUPPORT
1311    
1312         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1313         letters digits, or whatever, by reference to a set of  tables,  indexed         letters  digits,  or whatever, by reference to a set of tables, indexed
1314         by  character  value.  When running in UTF-8 mode, this applies only to         by character value. When running in UTF-8 mode, this  applies  only  to
1315         characters with codes less than 128. Higher-valued  codes  never  match         characters  with  codes  less than 128. Higher-valued codes never match
1316         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
1317         with Unicode character property support. The use of locales  with  Uni-         with  Unicode  character property support. The use of locales with Uni-
1318         code is discouraged.         code is discouraged.
1319    
1320         An  internal set of tables is created in the default C locale when PCRE         An internal set of tables is created in the default C locale when  PCRE
1321         is built. This is used when the final  argument  of  pcre_compile()  is         is  built.  This  is  used when the final argument of pcre_compile() is
1322         NULL,  and  is  sufficient for many applications. An alternative set of         NULL, and is sufficient for many applications. An  alternative  set  of
1323         tables can, however, be supplied. These may be created in  a  different         tables  can,  however, be supplied. These may be created in a different
1324         locale  from the default. As more and more applications change to using         locale from the default. As more and more applications change to  using
1325         Unicode, the need for this locale support is expected to die away.         Unicode, the need for this locale support is expected to die away.
1326    
1327         External tables are built by calling  the  pcre_maketables()  function,         External  tables  are  built by calling the pcre_maketables() function,
1328         which  has no arguments, in the relevant locale. The result can then be         which has no arguments, in the relevant locale. The result can then  be
1329         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
1330         example,  to  build  and use tables that are appropriate for the French         example, to build and use tables that are appropriate  for  the  French
1331         locale (where accented characters with  values  greater  than  128  are         locale  (where  accented  characters  with  values greater than 128 are
1332         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1333    
1334           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1335           tables = pcre_maketables();           tables = pcre_maketables();
1336           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1337    
1338         When  pcre_maketables()  runs,  the  tables are built in memory that is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1339         obtained via pcre_malloc. It is the caller's responsibility  to  ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1340         that  the memory containing the tables remains available for as long as         that the memory containing the tables remains available for as long  as
1341         it is needed.         it is needed.
1342    
1343         The pointer that is passed to pcre_compile() is saved with the compiled         The pointer that is passed to pcre_compile() is saved with the compiled
1344         pattern,  and the same tables are used via this pointer by pcre_study()         pattern, and the same tables are used via this pointer by  pcre_study()
1345         and normally also by pcre_exec(). Thus, by default, for any single pat-         and normally also by pcre_exec(). Thus, by default, for any single pat-
1346         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1347         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1348    
1349         It is possible to pass a table pointer or NULL (indicating the  use  of         It  is  possible to pass a table pointer or NULL (indicating the use of
1350         the  internal  tables)  to  pcre_exec(). Although not intended for this         the internal tables) to pcre_exec(). Although  not  intended  for  this
1351         purpose, this facility could be used to match a pattern in a  different         purpose,  this facility could be used to match a pattern in a different
1352         locale from the one in which it was compiled. Passing table pointers at         locale from the one in which it was compiled. Passing table pointers at
1353         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1354    
# Line 1188  INFORMATION ABOUT A PATTERN Line 1358  INFORMATION ABOUT A PATTERN
1358         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1359              int what, void *where);              int what, void *where);
1360    
1361         The pcre_fullinfo() function returns information about a compiled  pat-         The  pcre_fullinfo() function returns information about a compiled pat-
1362         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1363         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1364    
1365         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1366         pattern.  The second argument is the result of pcre_study(), or NULL if         pattern. The second argument is the result of pcre_study(), or NULL  if
1367         the pattern was not studied. The third argument specifies  which  piece         the  pattern  was not studied. The third argument specifies which piece
1368         of  information  is required, and the fourth argument is a pointer to a         of information is required, and the fourth argument is a pointer  to  a
1369         variable to receive the data. The yield of the  function  is  zero  for         variable  to  receive  the  data. The yield of the function is zero for
1370         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1371    
1372           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 1204  INFORMATION ABOUT A PATTERN Line 1374  INFORMATION ABOUT A PATTERN
1374           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1375           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1376    
1377         The  "magic  number" is placed at the start of each compiled pattern as         The "magic number" is placed at the start of each compiled  pattern  as
1378         an simple check against passing an arbitrary memory pointer. Here is  a         an  simple check against passing an arbitrary memory pointer. Here is a
1379         typical  call  of pcre_fullinfo(), to obtain the length of the compiled         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1380         pattern:         pattern:
1381    
1382           int rc;           int rc;
1383           unsigned long int length;           size_t length;
1384           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1385             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1386             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1387             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1388             &length);         /* where to put the data */             &length);         /* where to put the data */
1389    
1390         The possible values for the third argument are defined in  pcre.h,  and         The  possible  values for the third argument are defined in pcre.h, and
1391         are as follows:         are as follows:
1392    
1393           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1394    
1395         Return  the  number  of  the highest back reference in the pattern. The         Return the number of the highest back reference  in  the  pattern.  The
1396         fourth argument should point to an int variable. Zero  is  returned  if         fourth  argument  should  point to an int variable. Zero is returned if
1397         there are no back references.         there are no back references.
1398    
1399           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1400    
1401         Return  the  number of capturing subpatterns in the pattern. The fourth         Return the number of capturing subpatterns in the pattern.  The  fourth
1402         argument should point to an int variable.         argument should point to an int variable.
1403    
1404           PCRE_INFO_DEFAULT_TABLES           PCRE_INFO_DEFAULT_TABLES
1405    
1406         Return a pointer to the internal default character tables within  PCRE.         Return  a pointer to the internal default character tables within PCRE.
1407         The  fourth  argument should point to an unsigned char * variable. This         The fourth argument should point to an unsigned char *  variable.  This
1408         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1409         tion.  External  callers  can  cause PCRE to use its internal tables by         tion. External callers can cause PCRE to use  its  internal  tables  by
1410         passing a NULL table pointer.         passing a NULL table pointer.
1411    
1412           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1413    
1414         Return information about the first byte of any matched  string,  for  a         Return  information  about  the first byte of any matched string, for a
1415         non-anchored    pattern.    (This    option    used    to   be   called         non-anchored pattern. The fourth argument should point to an int  vari-
1416         PCRE_INFO_FIRSTCHAR; the old name is  still  recognized  for  backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1417         compatibility.)         is still recognized for backwards compatibility.)
1418    
1419         If  there  is  a  fixed first byte, for example, from a pattern such as         If there is a fixed first byte, for example, from  a  pattern  such  as
1420         (cat|cow|coyote), it is returned in the integer pointed  to  by  where.         (cat|cow|coyote), its value is returned. Otherwise, if either
        Otherwise, if either  
1421    
1422         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1423         branch starts with "^", or         branch starts with "^", or
# Line 1284  INFORMATION ABOUT A PATTERN Line 1453  INFORMATION ABOUT A PATTERN
1453    
1454         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1455         ses. The names are just an additional way of identifying the  parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1456         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1457         pcre_get_named_substring() is provided  for  extracting  an  individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1458         captured  substring  by  name.  It is also possible to extract the data         strings  by  name. It is also possible to extract the data directly, by
1459         directly, by first converting the name to a number in order  to  access         first converting the name to a number in order to  access  the  correct
1460         the  correct  pointers in the output vector (described with pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1461         below). To do the conversion, you need to use the  name-to-number  map,         the conversion, you need  to  use  the  name-to-number  map,  which  is
1462         which is described by these three values.         described by these three values.
1463    
1464         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1465         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
# Line 1300  INFORMATION ABOUT A PATTERN Line 1469  INFORMATION ABOUT A PATTERN
1469         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1470         sis,  most  significant byte first. The rest of the entry is the corre-         sis,  most  significant byte first. The rest of the entry is the corre-
1471         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1472         For  example,  consider  the following pattern (assume PCRE_EXTENDED is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1473         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1474           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1475           ignored):
1476    
1477           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1478           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1479    
1480         There are four named subpatterns, so the table has  four  entries,  and         There are four named subpatterns, so the table has  four  entries,  and
1481         each  entry  in the table is eight bytes long. The table is as follows,         each  entry  in the table is eight bytes long. The table is as follows,
# Line 1317  INFORMATION ABOUT A PATTERN Line 1488  INFORMATION ABOUT A PATTERN
1488           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1489    
1490         When  writing  code  to  extract  data from named subpatterns using the         When  writing  code  to  extract  data from named subpatterns using the
1491         name-to-number map, remember that the length of each entry is likely to         name-to-number map, remember that the length of the entries  is  likely
1492         be different for each compiled pattern.         to be different for each compiled pattern.
1493    
1494           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1495    
# Line 1517  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1688  MATCHING A PATTERN: THE TRADITIONAL FUNC
1688     Option bits for pcre_exec()     Option bits for pcre_exec()
1689    
1690         The unused bits of the options argument for pcre_exec() must  be  zero.         The unused bits of the options argument for pcre_exec() must  be  zero.
1691         The   only  bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NOTBOL,         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1692         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1693           PCRE_PARTIAL.
1694    
1695           PCRE_ANCHORED           PCRE_ANCHORED
1696    
1697         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1698         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1699         turned out to be anchored by virtue of its contents, it cannot be  made         turned  out to be anchored by virtue of its contents, it cannot be made
1700         unachored at matching time.         unachored at matching time.
1701    
1702             PCRE_NEWLINE_CR
1703             PCRE_NEWLINE_LF
1704             PCRE_NEWLINE_CRLF
1705             PCRE_NEWLINE_ANY
1706    
1707           These options override  the  newline  definition  that  was  chosen  or
1708           defaulted  when the pattern was compiled. For details, see the descrip-
1709           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1710           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1711           ters. It may also alter the way the match position is advanced after  a
1712           match  failure  for  an  unanchored  pattern. When PCRE_NEWLINE_CRLF or
1713           PCRE_NEWLINE_ANY is set, and a match attempt  fails  when  the  current
1714           position  is  at a CRLF sequence, the match position is advanced by two
1715           characters instead of one, in other words, to after the CRLF.
1716    
1717           PCRE_NOTBOL           PCRE_NOTBOL
1718    
1719         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1720         the beginning of a line, so the  circumflex  metacharacter  should  not         the  beginning  of  a  line, so the circumflex metacharacter should not
1721         match  before it. Setting this without PCRE_MULTILINE (at compile time)         match before it. Setting this without PCRE_MULTILINE (at compile  time)
1722         causes circumflex never to match. This option affects only  the  behav-         causes  circumflex  never to match. This option affects only the behav-
1723         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1724    
1725           PCRE_NOTEOL           PCRE_NOTEOL
1726    
1727         This option specifies that the end of the subject string is not the end         This option specifies that the end of the subject string is not the end
1728         of a line, so the dollar metacharacter should not match it nor  (except         of  a line, so the dollar metacharacter should not match it nor (except
1729         in  multiline mode) a newline immediately before it. Setting this with-         in multiline mode) a newline immediately before it. Setting this  with-
1730         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1731         option  affects only the behaviour of the dollar metacharacter. It does         option affects only the behaviour of the dollar metacharacter. It  does
1732         not affect \Z or \z.         not affect \Z or \z.
1733    
1734           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1735    
1736         An empty string is not considered to be a valid match if this option is         An empty string is not considered to be a valid match if this option is
1737         set.  If  there are alternatives in the pattern, they are tried. If all         set. If there are alternatives in the pattern, they are tried.  If  all
1738         the alternatives match the empty string, the entire  match  fails.  For         the  alternatives  match  the empty string, the entire match fails. For
1739         example, if the pattern         example, if the pattern
1740    
1741           a?b?           a?b?
1742    
1743         is  applied  to  a string not beginning with "a" or "b", it matches the         is applied to a string not beginning with "a" or "b",  it  matches  the
1744         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this         empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
1745         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
1746         rences of "a" or "b".         rences of "a" or "b".
1747    
1748         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1749         cial  case  of  a  pattern match of the empty string within its split()         cial case of a pattern match of the empty  string  within  its  split()
1750         function, and when using the /g modifier. It  is  possible  to  emulate         function,  and  when  using  the /g modifier. It is possible to emulate
1751         Perl's behaviour after matching a null string by first trying the match         Perl's behaviour after matching a null string by first trying the match
1752         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1753         if  that  fails by advancing the starting offset (see below) and trying         if that fails by advancing the starting offset (see below)  and  trying
1754         an ordinary match again. There is some code that demonstrates how to do         an ordinary match again. There is some code that demonstrates how to do
1755         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
1756    
1757           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1758    
1759         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
1760         UTF-8 string is automatically checked when pcre_exec() is  subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
1761         called.   The  value  of  startoffset is also checked to ensure that it         called.  The value of startoffset is also checked  to  ensure  that  it
1762         points to the start of a UTF-8 character. If an invalid UTF-8  sequence         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence
1763         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1764         startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is
1765         returned.         returned.
1766    
1767         If  you  already  know that your subject is valid, and you want to skip         If you already know that your subject is valid, and you  want  to  skip
1768         these   checks   for   performance   reasons,   you   can    set    the         these    checks    for   performance   reasons,   you   can   set   the
1769         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
1770         do this for the second and subsequent calls to pcre_exec() if  you  are         do  this  for the second and subsequent calls to pcre_exec() if you are
1771         making  repeated  calls  to  find  all  the matches in a single subject         making repeated calls to find all  the  matches  in  a  single  subject
1772         string. However, you should be  sure  that  the  value  of  startoffset         string.  However,  you  should  be  sure  that the value of startoffset
1773         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
1774         set, the effect of passing an invalid UTF-8 string as a subject,  or  a         set,  the  effect of passing an invalid UTF-8 string as a subject, or a
1775         value  of startoffset that does not point to the start of a UTF-8 char-         value of startoffset that does not point to the start of a UTF-8  char-
1776         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1777    
1778           PCRE_PARTIAL           PCRE_PARTIAL
1779    
1780         This option turns on the  partial  matching  feature.  If  the  subject         This  option  turns  on  the  partial  matching feature. If the subject
1781         string  fails to match the pattern, but at some point during the match-         string fails to match the pattern, but at some point during the  match-
1782         ing process the end of the subject was reached (that  is,  the  subject         ing  process  the  end of the subject was reached (that is, the subject
1783         partially  matches  the  pattern and the failure to match occurred only         partially matches the pattern and the failure to  match  occurred  only
1784         because there were not enough subject characters), pcre_exec()  returns         because  there were not enough subject characters), pcre_exec() returns
1785         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1786         used, there are restrictions on what may appear in the  pattern.  These         used,  there  are restrictions on what may appear in the pattern. These
1787         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1788    
1789     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1790    
1791         The  subject string is passed to pcre_exec() as a pointer in subject, a         The subject string is passed to pcre_exec() as a pointer in subject,  a
1792         length in length, and a starting byte offset in startoffset.  In  UTF-8         length  in  length, and a starting byte offset in startoffset. In UTF-8
1793         mode,  the  byte  offset  must point to the start of a UTF-8 character.         mode, the byte offset must point to the start  of  a  UTF-8  character.
1794         Unlike the pattern string, the subject may contain binary  zero  bytes.         Unlike  the  pattern string, the subject may contain binary zero bytes.
1795         When  the starting offset is zero, the search for a match starts at the         When the starting offset is zero, the search for a match starts at  the
1796         beginning of the subject, and this is by far the most common case.         beginning of the subject, and this is by far the most common case.
1797    
1798         A non-zero starting offset is useful when searching for  another  match         A  non-zero  starting offset is useful when searching for another match
1799         in  the same subject by calling pcre_exec() again after a previous suc-         in the same subject by calling pcre_exec() again after a previous  suc-
1800         cess.  Setting startoffset differs from just passing over  a  shortened         cess.   Setting  startoffset differs from just passing over a shortened
1801         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
1802         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1803    
1804           \Biss\B           \Biss\B
1805    
1806         which finds occurrences of "iss" in the middle of  words.  (\B  matches         which  finds  occurrences  of "iss" in the middle of words. (\B matches
1807         only  if  the  current position in the subject is not a word boundary.)         only if the current position in the subject is not  a  word  boundary.)
1808         When applied to the string "Mississipi" the first call  to  pcre_exec()         When  applied  to the string "Mississipi" the first call to pcre_exec()
1809         finds  the  first  occurrence. If pcre_exec() is called again with just         finds the first occurrence. If pcre_exec() is called  again  with  just
1810         the remainder of the subject,  namely  "issipi",  it  does  not  match,         the  remainder  of  the  subject,  namely  "issipi", it does not match,
1811         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
1812         to be a word boundary. However, if pcre_exec()  is  passed  the  entire         to  be  a  word  boundary. However, if pcre_exec() is passed the entire
1813         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
1814         rence of "iss" because it is able to look behind the starting point  to         rence  of "iss" because it is able to look behind the starting point to
1815         discover that it is preceded by a letter.         discover that it is preceded by a letter.
1816    
1817         If  a  non-zero starting offset is passed when the pattern is anchored,         If a non-zero starting offset is passed when the pattern  is  anchored,
1818         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
1819         if  the  pattern  does  not require the match to be at the start of the         if the pattern does not require the match to be at  the  start  of  the
1820         subject.         subject.
1821    
1822     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
1823    
1824         In general, a pattern matches a certain portion of the subject, and  in         In  general, a pattern matches a certain portion of the subject, and in
1825         addition,  further  substrings  from  the  subject may be picked out by         addition, further substrings from the subject  may  be  picked  out  by
1826         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,
1827         this  is  called "capturing" in what follows, and the phrase "capturing         this is called "capturing" in what follows, and the  phrase  "capturing
1828         subpattern" is used for a fragment of a pattern that picks out  a  sub-         subpattern"  is  used for a fragment of a pattern that picks out a sub-
1829         string.  PCRE  supports several other kinds of parenthesized subpattern         string. PCRE supports several other kinds of  parenthesized  subpattern
1830         that do not cause substrings to be captured.         that do not cause substrings to be captured.
1831    
1832         Captured substrings are returned to the caller via a vector of  integer         Captured  substrings are returned to the caller via a vector of integer
1833         offsets  whose  address is passed in ovector. The number of elements in         offsets whose address is passed in ovector. The number of  elements  in
1834         the vector is passed in ovecsize, which must be a non-negative  number.         the  vector is passed in ovecsize, which must be a non-negative number.
1835         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
1836    
1837         The  first  two-thirds of the vector is used to pass back captured sub-         The first two-thirds of the vector is used to pass back  captured  sub-
1838         strings, each substring using a pair of integers. The  remaining  third         strings,  each  substring using a pair of integers. The remaining third
1839         of  the  vector is used as workspace by pcre_exec() while matching cap-         of the vector is used as workspace by pcre_exec() while  matching  cap-
1840         turing subpatterns, and is not available for passing back  information.         turing  subpatterns, and is not available for passing back information.
1841         The  length passed in ovecsize should always be a multiple of three. If         The length passed in ovecsize should always be a multiple of three.  If
1842         it is not, it is rounded down.         it is not, it is rounded down.
1843    
1844         When a match is successful, information about  captured  substrings  is         When  a  match  is successful, information about captured substrings is
1845         returned  in  pairs  of integers, starting at the beginning of ovector,         returned in pairs of integers, starting at the  beginning  of  ovector,
1846         and continuing up to two-thirds of its length at the  most.  The  first         and  continuing  up  to two-thirds of its length at the most. The first
1847         element of a pair is set to the offset of the first character in a sub-         element of a pair is set to the offset of the first character in a sub-
1848         string, and the second is set to the  offset  of  the  first  character         string,  and  the  second  is  set to the offset of the first character
1849         after  the  end  of  a  substring. The first pair, ovector[0] and ovec-         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-
1850         tor[1], identify the portion of  the  subject  string  matched  by  the         tor[1],  identify  the  portion  of  the  subject string matched by the
1851         entire  pattern.  The next pair is used for the first capturing subpat-         entire pattern. The next pair is used for the first  capturing  subpat-
1852         tern, and so on. The value returned by pcre_exec()  is  the  number  of         tern, and so on. The value returned by pcre_exec() is one more than the
1853         pairs  that  have  been set. If there are no capturing subpatterns, the         highest numbered pair that has been set. For example, if two substrings
1854         return value from a successful match is 1,  indicating  that  just  the         have  been captured, the returned value is 3. If there are no capturing
1855         first pair of offsets has been set.         subpatterns, the return value from a successful match is 1,  indicating
1856           that just the first pair of offsets has been set.
        Some  convenience  functions  are  provided for extracting the captured  
        substrings as separate strings. These are described  in  the  following  
        section.  
   
        It  is  possible  for  an capturing subpattern number n+1 to match some  
        part of the subject when subpattern n has not been  used  at  all.  For  
        example, if the string "abc" is matched against the pattern (a|(z))(bc)  
        subpatterns 1 and 3 are matched, but 2 is not. When this happens,  both  
        offset values corresponding to the unused subpattern are set to -1.  
1857    
1858         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1859         of the string that it matched that is returned.         of the string that it matched that is returned.
# Line 1689  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1867  MATCHING A PATTERN: THE TRADITIONAL FUNC
1867         substrings, PCRE has to get additional memory for use during  matching.         substrings, PCRE has to get additional memory for use during  matching.
1868         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1869    
1870         Note  that  pcre_info() can be used to find out how many capturing sub-         The  pcre_info()  function  can  be used to find out how many capturing
1871         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
1872         that  will  allow for n captured substrings, in addition to the offsets         ovector  that  will allow for n captured substrings, in addition to the
1873         of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
1874    
1875           It is possible for capturing subpattern number n+1 to match  some  part
1876           of the subject when subpattern n has not been used at all. For example,
1877           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1878           return from the function is 4, and subpatterns 1 and 3 are matched, but
1879           2 is not. When this happens, both values in  the  offset  pairs  corre-
1880           sponding to unused subpatterns are set to -1.
1881    
1882           Offset  values  that correspond to unused subpatterns at the end of the
1883           expression are also set to -1. For example,  if  the  string  "abc"  is
1884           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1885           matched. The return from the function is 2, because  the  highest  used
1886           capturing subpattern number is 1. However, you can refer to the offsets
1887           for the second and third capturing subpatterns if  you  wish  (assuming
1888           the vector is large enough, of course).
1889    
1890           Some  convenience  functions  are  provided for extracting the captured
1891           substrings as separate strings. These are described below.
1892    
1893     Return values from pcre_exec()     Error return values from pcre_exec()
1894    
1895         If pcre_exec() fails, it returns a negative number. The  following  are         If pcre_exec() fails, it returns a negative number. The  following  are
1896         defined in the header file:         defined in the header file:
# Line 1720  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1916  MATCHING A PATTERN: THE TRADITIONAL FUNC
1916         an  environment  with the other endianness. This is the error that PCRE         an  environment  with the other endianness. This is the error that PCRE
1917         gives when the magic number is not present.         gives when the magic number is not present.
1918    
1919           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1920    
1921         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1922         compiled  pattern.  This  error  could be caused by a bug in PCRE or by         compiled  pattern.  This  error  could be caused by a bug in PCRE or by
# Line 1746  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1942  MATCHING A PATTERN: THE TRADITIONAL FUNC
1942         pcre_extra  structure  (or  defaulted) was reached. See the description         pcre_extra  structure  (or  defaulted) was reached. See the description
1943         above.         above.
1944    
          PCRE_ERROR_RECURSIONLIMIT (-21)  
   
        The internal recursion limit, as specified by the match_limit_recursion  
        field  in  a  pcre_extra  structure (or defaulted) was reached. See the  
        description above.  
   
1945           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
1946    
1947         This error is never generated by pcre_exec() itself. It is provided for         This error is never generated by pcre_exec() itself. It is provided for
# Line 1789  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1979  MATCHING A PATTERN: THE TRADITIONAL FUNC
1979    
1980         This  error is given if the value of the ovecsize argument is negative.         This  error is given if the value of the ovecsize argument is negative.
1981    
1982             PCRE_ERROR_RECURSIONLIMIT (-21)
1983    
1984           The internal recursion limit, as specified by the match_limit_recursion
1985           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
1986           description above.
1987    
1988             PCRE_ERROR_NULLWSLIMIT    (-22)
1989    
1990           When a group that can match an empty  substring  is  repeated  with  an
1991           unbounded  upper  limit, the subject position at the start of the group
1992           must be remembered, so that a test for an empty string can be made when
1993           the  end  of the group is reached. Some workspace is required for this;
1994           if it runs out, this error is given.
1995    
1996             PCRE_ERROR_BADNEWLINE     (-23)
1997    
1998           An invalid combination of PCRE_NEWLINE_xxx options was given.
1999    
2000           Error numbers -16 to -20 are not used by pcre_exec().
2001    
2002    
2003  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2004    
# Line 1809  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2019  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2019         string_list()  are  provided for extracting captured substrings as new,         string_list()  are  provided for extracting captured substrings as new,
2020         separate, zero-terminated strings. These functions identify  substrings         separate, zero-terminated strings. These functions identify  substrings
2021         by  number.  The  next section describes functions for extracting named         by  number.  The  next section describes functions for extracting named
2022         substrings. A substring  that  contains  a  binary  zero  is  correctly         substrings.
2023         extracted  and  has  a further zero added on the end, but the result is  
2024         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2025           a  further zero added on the end, but the result is not, of course, a C
2026           string.  However, you can process such a string  by  referring  to  the
2027           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2028           string().  Unfortunately, the interface to pcre_get_substring_list() is
2029           not  adequate for handling strings containing binary zeros, because the
2030           end of the final string is not independently indicated.
2031    
2032         The first three arguments are the same for all  three  of  these  func-         The first three arguments are the same for all  three  of  these  func-
2033         tions:  subject  is  the subject string that has just been successfully         tions:  subject  is  the subject string that has just been successfully
# Line 1831  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2047  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2047         buffersize,  while  for  pcre_get_substring()  a new block of memory is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2048         obtained via pcre_malloc, and its address is  returned  via  stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2049         The  yield  of  the function is the length of the string, not including         The  yield  of  the function is the length of the string, not including
2050         the terminating zero, or one of         the terminating zero, or one of these error codes:
2051    
2052           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2053    
# Line 1847  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2063  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2063         single block of memory that is obtained via pcre_malloc. The address of         single block of memory that is obtained via pcre_malloc. The address of
2064         the memory block is returned via listptr, which is also  the  start  of         the memory block is returned via listptr, which is also  the  start  of
2065         the  list  of  string pointers. The end of the list is marked by a NULL         the  list  of  string pointers. The end of the list is marked by a NULL
2066         pointer. The yield of the function is zero if all went well, or         pointer. The yield of the function is zero if all  went  well,  or  the
2067           error code
2068    
2069           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2070    
2071         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2072    
2073         When any of these functions encounter a substring that is unset,  which         When  any of these functions encounter a substring that is unset, which
2074         can  happen  when  capturing subpattern number n+1 matches some part of         can happen when capturing subpattern number n+1 matches  some  part  of
2075         the subject, but subpattern n has not been used at all, they return  an         the  subject, but subpattern n has not been used at all, they return an
2076         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2077         string by inspecting the appropriate offset in ovector, which is  nega-         string  by inspecting the appropriate offset in ovector, which is nega-
2078         tive for unset substrings.         tive for unset substrings.
2079    
2080         The  two convenience functions pcre_free_substring() and pcre_free_sub-         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2081         string_list() can be used to free the memory  returned  by  a  previous         string_list()  can  be  used  to free the memory returned by a previous
2082         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2083         tively. They do nothing more than  call  the  function  pointed  to  by         tively.  They  do  nothing  more  than  call the function pointed to by
2084         pcre_free,  which  of course could be called directly from a C program.         pcre_free, which of course could be called directly from a  C  program.
2085         However, PCRE is used in some situations where it is linked via a  spe-         However,  PCRE is used in some situations where it is linked via a spe-
2086         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2087         pcre_free directly; it is for these cases that the functions  are  pro-         pcre_free  directly;  it is for these cases that the functions are pro-
2088         vided.         vided.
2089    
2090    
# Line 1886  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2103  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2103              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2104              const char **stringptr);              const char **stringptr);
2105    
2106         To  extract a substring by name, you first have to find associated num-         To extract a substring by name, you first have to find associated  num-
2107         ber.  For example, for this pattern         ber.  For example, for this pattern
2108    
2109           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2110    
2111         the number of the subpattern called "xxx" is 2. You can find the number         the number of the subpattern called "xxx" is 2. If the name is known to
2112         from the name by calling pcre_get_stringnumber(). The first argument is         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2113         the compiled pattern, and the second is the  name.  The  yield  of  the         name by calling pcre_get_stringnumber(). The first argument is the com-
2114         function  is  the  subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if         piled pattern, and the second is the name. The yield of the function is
2115         there is no subpattern of that name.         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2116           subpattern of that name.
2117    
2118         Given the number, you can extract the substring directly, or use one of         Given the number, you can extract the substring directly, or use one of
2119         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
# Line 1917  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2135  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2135         ate.         ate.
2136    
2137    
2138    DUPLICATE SUBPATTERN NAMES
2139    
2140           int pcre_get_stringtable_entries(const pcre *code,
2141                const char *name, char **first, char **last);
2142    
2143           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2144           subpatterns are not required to  be  unique.  Normally,  patterns  with
2145           duplicate  names  are such that in any one match, only one of the named
2146           subpatterns participates. An example is shown in the pcrepattern  docu-
2147           mentation. When duplicates are present, pcre_copy_named_substring() and
2148           pcre_get_named_substring() return the first substring corresponding  to
2149           the  given  name  that  is  set.  If  none  are set, an empty string is
2150           returned.  The pcre_get_stringnumber() function returns one of the num-
2151           bers  that are associated with the name, but it is not defined which it
2152           is.
2153    
2154           If you want to get full details of all captured substrings for a  given
2155           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2156           first argument is the compiled pattern, and the second is the name. The
2157           third  and  fourth  are  pointers to variables which are updated by the
2158           function. After it has run, they point to the first and last entries in
2159           the  name-to-number  table  for  the  given  name.  The function itself
2160           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2161           there  are none. The format of the table is described above in the sec-
2162           tion entitled Information about a  pattern.   Given  all  the  relevant
2163           entries  for the name, you can extract each of their numbers, and hence
2164           the captured data, if any.
2165    
2166    
2167  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2168    
2169         The  traditional  matching  function  uses a similar algorithm to Perl,         The traditional matching function uses a  similar  algorithm  to  Perl,
2170         which stops when it finds the first match, starting at a given point in         which stops when it finds the first match, starting at a given point in
2171         the  subject.  If you want to find all possible matches, or the longest         the subject. If you want to find all possible matches, or  the  longest
2172         possible match, consider using the alternative matching  function  (see         possible  match,  consider using the alternative matching function (see
2173         below)  instead.  If you cannot use the alternative function, but still         below) instead. If you cannot use the alternative function,  but  still
2174         need to find all possible matches, you can kludge it up by  making  use         need  to  find all possible matches, you can kludge it up by making use
2175         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2176         tation.         tation.
2177    
2178         What you have to do is to insert a callout right at the end of the pat-         What you have to do is to insert a callout right at the end of the pat-
2179         tern.   When your callout function is called, extract and save the cur-         tern.  When your callout function is called, extract and save the  cur-
2180         rent matched substring. Then return  1,  which  forces  pcre_exec()  to         rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2181         backtrack  and  try other alternatives. Ultimately, when it runs out of         backtrack and try other alternatives. Ultimately, when it runs  out  of
2182         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2183    
2184    
# Line 1942  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2189  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2189              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2190              int *workspace, int wscount);              int *workspace, int wscount);
2191    
2192         The function pcre_dfa_exec()  is  called  to  match  a  subject  string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2193         against  a compiled pattern, using a "DFA" matching algorithm. This has         against a compiled pattern, using a matching algorithm that  scans  the
2194         different characteristics to the normal algorithm, and is not  compati-         subject  string  just  once, and does not backtrack. This has different
2195         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics to the normal algorithm, and  is  not  compatible  with
2196         Nevertheless, there are times when this kind of matching can be useful.         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2197         For  a  discussion of the two matching algorithms, see the pcrematching         theless, there are times when this kind of matching can be useful.  For
2198         documentation.         a discussion of the two matching algorithms, see the pcrematching docu-
2199           mentation.
2200    
2201         The arguments for the pcre_dfa_exec() function  are  the  same  as  for         The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2202         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
# Line 1960  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2208  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2208         workspace  vector  should  contain at least 20 elements. It is used for         workspace  vector  should  contain at least 20 elements. It is used for
2209         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2210         workspace  will  be  needed for patterns and subjects where there are a         workspace  will  be  needed for patterns and subjects where there are a
2211         lot of possible matches.         lot of potential matches.
2212    
2213         Here is an example of a simple call to pcre_dfa_exec():         Here is an example of a simple call to pcre_dfa_exec():
2214    
# Line 1982  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2230  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2230     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2231    
2232         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
2233         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-
2234         PCRE_NOTEOL,    PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,     PCRE_PARTIAL,         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2235         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
2236         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
2237         repeated here.         not repeated here.
2238    
2239           PCRE_PARTIAL           PCRE_PARTIAL
2240    
# Line 2001  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2249  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2249           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2250    
2251         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2252         stop as soon as it has found one match. Because  of  the  way  the  DFA         stop as soon as it has found one match. Because of the way the alterna-
2253         algorithm works, this is necessarily the shortest possible match at the         tive  algorithm  works, this is necessarily the shortest possible match
2254         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2255    
2256           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2257    
# Line 2039  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2287  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2287         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,
2288         which is the number of matched substrings.  The  substrings  themselves         which is the number of matched substrings.  The  substrings  themselves
2289         are  returned  in  ovector. Each string uses two elements; the first is         are  returned  in  ovector. Each string uses two elements; the first is
2290         the offset to the start, and the second is the offset to the  end.  All         the offset to the start, and the second is the offset to  the  end.  In
2291         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
2292         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
2293         with  the  way pcre_exec() returns data, even though the meaning of the         compatibility  with  the  way pcre_exec() returns data, even though the
2294         strings is different.)         meaning of the strings is different.)
2295    
2296         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-
2297         est  matching  string is given first. If there were too many matches to         est  matching  string is given first. If there were too many matches to
# Line 2065  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2313  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2313    
2314           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2315    
2316         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
2317         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
2318         supported.         in a specific group. These are not supported.
2319    
2320           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2321    
# Line 2087  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2335  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2335         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
2336         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2337    
2338  Last updated: 18 January 2006  
2339  Copyright (c) 1997-2006 University of Cambridge.  SEE ALSO
2340    
2341           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2342           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2343    
2344    
2345    AUTHOR
2346    
2347           Philip Hazel
2348           University Computing Service
2349           Cambridge CB2 3QH, England.
2350    
2351    
2352    REVISION
2353    
2354           Last updated: 06 March 2007
2355           Copyright (c) 1997-2007 University of Cambridge.
2356  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2357    
2358    
# Line 2246  RETURN VALUES Line 2510  RETURN VALUES
2510         reserved for use by callout functions; it will never be  used  by  PCRE         reserved for use by callout functions; it will never be  used  by  PCRE
2511         itself.         itself.
2512    
2513  Last updated: 28 February 2005  
2514  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2515    
2516           Philip Hazel
2517           University Computing Service
2518           Cambridge CB2 3QH, England.
2519    
2520    
2521    REVISION
2522    
2523           Last updated: 06 March 2007
2524           Copyright (c) 1997-2007 University of Cambridge.
2525  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2526    
2527    
# Line 2261  NAME Line 2535  NAME
2535  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2536    
2537         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2538         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2539         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2540           tures that are expected to be in the forthcoming Perl 5.10.
2541    
2542         1.  PCRE has only a subset of Perl's UTF-8 and Unicode support. Details         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2543         of what it does have are given in the section on UTF-8 support  in  the         of  what  it does have are given in the section on UTF-8 support in the
2544         main pcre page.         main pcre page.
2545    
2546         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2547         permits them, but they do not mean what you might think.  For  example,         permits  them,  but they do not mean what you might think. For example,
2548         (?!a){3} does not assert that the next three characters are not "a". It         (?!a){3} does not assert that the next three characters are not "a". It
2549         just asserts that the next character is not "a" three times.         just asserts that the next character is not "a" three times.
2550    
2551         3. Capturing subpatterns that occur inside  negative  lookahead  asser-         3.  Capturing  subpatterns  that occur inside negative lookahead asser-
2552         tions  are  counted,  but their entries in the offsets vector are never         tions are counted, but their entries in the offsets  vector  are  never
2553         set. Perl sets its numerical variables from any such patterns that  are         set.  Perl sets its numerical variables from any such patterns that are
2554         matched before the assertion fails to match something (thereby succeed-         matched before the assertion fails to match something (thereby succeed-
2555         ing), but only if the negative lookahead assertion  contains  just  one         ing),  but  only  if the negative lookahead assertion contains just one
2556         branch.         branch.
2557    
2558         4.  Though  binary zero characters are supported in the subject string,         4. Though binary zero characters are supported in the  subject  string,
2559         they are not allowed in a pattern string because it is passed as a nor-         they are not allowed in a pattern string because it is passed as a nor-
2560         mal C string, terminated by zero. The escape sequence \0 can be used in         mal C string, terminated by zero. The escape sequence \0 can be used in
2561         the pattern to represent a binary zero.         the pattern to represent a binary zero.
2562    
2563         5. The following Perl escape sequences are not supported: \l,  \u,  \L,         5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2564         \U, and \N. In fact these are implemented by Perl's general string-han-         \U, and \N. In fact these are implemented by Perl's general string-han-
2565         dling and are not part of its pattern matching engine. If any of  these         dling  and are not part of its pattern matching engine. If any of these
2566         are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
2567    
2568         6.  The Perl escape sequences \p, \P, and \X are supported only if PCRE         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2569         is built with Unicode character property support. The  properties  that         is  built  with Unicode character property support. The properties that
2570         can  be tested with \p and \P are limited to the general category prop-         can be tested with \p and \P are limited to the general category  prop-
2571         erties such as Lu and Nd, script names such as Greek or  Han,  and  the         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2572         derived properties Any and L&.         derived properties Any and L&.
2573    
2574         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2575         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2576         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2577         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2578         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2579    
2580             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2309  DIFFERENCES BETWEEN PCRE AND PERL Line 2584  DIFFERENCES BETWEEN PCRE AND PERL
2584             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2585             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2586    
2587         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2588         classes.         classes.
2589    
2590         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2591         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2592         the non-Perl items (?R),  (?number),  and  (?P>name).  Also,  the  PCRE         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2593         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2594         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2595    
2596         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2597         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2598         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2599    
2600           10.  There are some differences that are concerned with the settings of
2601           captured strings when part of  a  pattern  is  repeated.  For  example,
2602           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2603         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2604    
2605         10. PCRE provides some extensions to the Perl regular expression facil-         11. PCRE provides some extensions to the Perl regular expression facil-
2606         ities:         ities.   Perl  5.10  will  include new features that are not in earlier
2607           versions, some of which (such as named parentheses) have been  in  PCRE
2608           for some time. This list is with respect to Perl 5.10:
2609    
2610         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2611         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2612         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2613    
2614         (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
2615         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2616    
2617         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2618         cial meaning is faulted.         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2619           ignored. (Perl can be made to issue a warning.)
2620    
2621         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2622         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
# Line 2346  DIFFERENCES BETWEEN PCRE AND PERL Line 2628  DIFFERENCES BETWEEN PCRE AND PERL
2628         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2629         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2630    
2631         (g) The (?R), (?number), and (?P>name) constructs allows for  recursive         (g) The callout facility is PCRE-specific.
        pattern  matching  (Perl  can  do  this using the (?p{code}) construct,  
        which PCRE cannot support.)  
2632    
2633         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The partial matching facility is PCRE-specific.
2634    
2635         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2636         Sun's Java package.         even on different hosts that have the other endianness.
2637    
2638         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2639           different way and is not Perl-compatible.
2640    
        (k) The callout facility is PCRE-specific.  
2641    
2642         (l) The partial matching facility is PCRE-specific.  AUTHOR
2643    
2644         (m) Patterns compiled by PCRE can be saved and re-used at a later time,         Philip Hazel
2645         even on different hosts that have the other endianness.         University Computing Service
2646           Cambridge CB2 3QH, England.
2647    
        (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  
        different way and is not Perl-compatible.  
2648    
2649  Last updated: 24 January 2006  REVISION
2650  Copyright (c) 1997-2006 University of Cambridge.  
2651           Last updated: 06 March 2007
2652           Copyright (c) 1997-2007 University of Cambridge.
2653  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2654    
2655    
# Line 2404  PCRE REGULAR EXPRESSION DETAILS Line 2685  PCRE REGULAR EXPRESSION DETAILS
2685         function, and how it differs from the normal function, are discussed in         function, and how it differs from the normal function, are discussed in
2686         the pcrematching page.         the pcrematching page.
2687    
2688    
2689    CHARACTERS AND METACHARACTERS
2690    
2691         A regular expression is a pattern that is  matched  against  a  subject         A regular expression is a pattern that is  matched  against  a  subject
2692         string  from  left  to right. Most characters stand for themselves in a         string  from  left  to right. Most characters stand for themselves in a
2693         pattern, and match the corresponding characters in the  subject.  As  a         pattern, and match the corresponding characters in the  subject.  As  a
# Line 2428  PCRE REGULAR EXPRESSION DETAILS Line 2712  PCRE REGULAR EXPRESSION DETAILS
2712    
2713         There are two different sets of metacharacters: those that  are  recog-         There are two different sets of metacharacters: those that  are  recog-
2714         nized  anywhere in the pattern except within square brackets, and those         nized  anywhere in the pattern except within square brackets, and those
2715         that are recognized in square brackets. Outside  square  brackets,  the         that are recognized within square brackets.  Outside  square  brackets,
2716         metacharacters are as follows:         the metacharacters are as follows:
2717    
2718           \      general escape character with several uses           \      general escape character with several uses
2719           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2476  BACKSLASH Line 2760  BACKSLASH
2760    
2761         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2762         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
2763         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2764         An escaping backslash can be used to include a whitespace or #  charac-         ing backslash can be used to include a whitespace  or  #  character  as
2765         ter as part of the pattern.         part of the pattern.
2766    
2767         If  you  want  to remove the special meaning from a sequence of charac-         If  you  want  to remove the special meaning from a sequence of charac-
2768         ters, you can do so by putting them between \Q and \E. This is  differ-         ters, you can do so by putting them between \Q and \E. This is  differ-
# Line 2535  BACKSLASH Line 2819  BACKSLASH
2819         two  syntaxes  for  \x. There is no difference in the way they are han-         two  syntaxes  for  \x. There is no difference in the way they are han-
2820         dled. For example, \xdc is exactly the same as \x{dc}.         dled. For example, \xdc is exactly the same as \x{dc}.
2821    
2822         After \0 up to two further octal digits are read.  In  both  cases,  if         After \0 up to two further octal digits are read. If  there  are  fewer
2823         there  are fewer than two digits, just those that are present are used.         than  two  digits,  just  those  that  are  present  are used. Thus the
2824         Thus the sequence \0\x\07 specifies two binary zeros followed by a  BEL         sequence \0\x\07 specifies two binary zeros followed by a BEL character
2825         character  (code  value  7).  Make sure you supply two digits after the         (code  value 7). Make sure you supply two digits after the initial zero
2826         initial zero if the pattern character that follows is itself  an  octal         if the pattern character that follows is itself an octal digit.
        digit.  
2827    
2828         The handling of a backslash followed by a digit other than 0 is compli-         The handling of a backslash followed by a digit other than 0 is compli-
2829         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
2830         its  as  a  decimal  number. If the number is less than 10, or if there         its as a decimal number. If the number is less than  10,  or  if  there
2831         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
2832         expression,  the  entire  sequence  is  taken  as  a  back reference. A         expression, the entire  sequence  is  taken  as  a  back  reference.  A
2833         description of how this works is given later, following the  discussion         description  of how this works is given later, following the discussion
2834         of parenthesized subpatterns.         of parenthesized subpatterns.
2835    
2836         Inside  a  character  class, or if the decimal number is greater than 9         Inside a character class, or if the decimal number is  greater  than  9
2837         and there have not been that many capturing subpatterns, PCRE  re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
2838         up  to three octal digits following the backslash, and generates a sin-         up to three octal digits following the backslash, and uses them to gen-
2839         gle byte from the least significant 8 bits of the value. Any subsequent         erate  a data character. Any subsequent digits stand for themselves. In
2840         digits stand for themselves.  For example:         non-UTF-8 mode, the value of a character specified  in  octal  must  be
2841           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
2842           example:
2843    
2844           \040   is another way of writing a space           \040   is another way of writing a space
2845           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2571  BACKSLASH Line 2856  BACKSLASH
2856           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
2857                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
2858    
2859         Note  that  octal  values of 100 or greater must not be introduced by a         Note that octal values of 100 or greater must not be  introduced  by  a
2860         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2861    
2862         All the sequences that define a single byte value  or  a  single  UTF-8         All the sequences that define a single character value can be used both
2863         character (in UTF-8 mode) can be used both inside and outside character         inside and outside character classes. In addition, inside  a  character
2864         classes. In addition, inside a character  class,  the  sequence  \b  is         class,  the  sequence \b is interpreted as the backspace character (hex
2865         interpreted as the backspace character (hex 08), and the sequence \X is         08), and the sequences \R and \X are interpreted as the characters  "R"
2866         interpreted as the character "X".  Outside  a  character  class,  these         and  "X", respectively. Outside a character class, these sequences have
2867         sequences have different meanings (see below).         different meanings (see below).
2868    
2869       Absolute and relative back references
2870    
2871           The sequence \g followed by a positive or negative  number,  optionally
2872           enclosed  in  braces,  is  an absolute or relative back reference. Back
2873           references are discussed later, following the discussion  of  parenthe-
2874           sized subpatterns.
2875    
2876     Generic character types     Generic character types
2877    
2878         The  third  use of backslash is for specifying generic character types.         Another use of backslash is for specifying generic character types. The
2879         The following are always recognized:         following are always recognized:
2880    
2881           \d     any decimal digit           \d     any decimal digit
2882           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 2604  BACKSLASH Line 2896  BACKSLASH
2896    
2897         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
2898         11).  This makes it different from the the POSIX "space" class. The  \s         11).  This makes it different from the the POSIX "space" class. The  \s
2899         characters are HT (9), LF (10), FF (12), CR (13), and space (32).         characters  are  HT (9), LF (10), FF (12), CR (13), and space (32). (If
2900           "use locale;" is included in a Perl script, \s may match the VT charac-
2901           ter. In PCRE, it never does.)
2902    
2903         A "word" character is an underscore or any character less than 256 that         A "word" character is an underscore or any character less than 256 that
2904         is a letter or digit. The definition of  letters  and  digits  is  con-         is a letter or digit. The definition of  letters  and  digits  is  con-
# Line 2619  BACKSLASH Line 2913  BACKSLASH
2913         code  character  property support is available. The use of locales with         code  character  property support is available. The use of locales with
2914         Unicode is discouraged.         Unicode is discouraged.
2915    
2916       Newline sequences
2917    
2918           Outside a character class, the escape sequence \R matches  any  Unicode
2919           newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2920           equivalent to the following:
2921    
2922             (?>\r\n|\n|\x0b|\f|\r|\x85)
2923    
2924           This is an example of an "atomic group", details  of  which  are  given
2925           below.  This particular group matches either the two-character sequence
2926           CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
2927           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2928           return, U+000D), or NEL (next line, U+0085). The two-character sequence
2929           is treated as a single unit that cannot be split.
2930    
2931           In  UTF-8  mode, two additional characters whose codepoints are greater
2932           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2933           rator,  U+2029).   Unicode character property support is not needed for
2934           these characters to be recognized.
2935    
2936           Inside a character class, \R matches the letter "R".
2937    
2938     Unicode character properties     Unicode character properties
2939    
2940         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
# Line 2645  BACKSLASH Line 2961  BACKSLASH
2961         Those that are not part of an identified script are lumped together  as         Those that are not part of an identified script are lumped together  as
2962         "Common". The current list of scripts is:         "Common". The current list of scripts is:
2963    
2964         Arabic,  Armenian,  Bengali,  Bopomofo, Braille, Buginese, Buhid, Cana-         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
2965         dian_Aboriginal, Cherokee, Common, Coptic, Cypriot, Cyrillic,  Deseret,         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
2966         Devanagari,  Ethiopic,  Georgian,  Glagolitic, Gothic, Greek, Gujarati,         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
2967         Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana,  Inherited,  Kannada,         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
2968         Katakana,  Kharoshthi,  Khmer,  Lao, Latin, Limbu, Linear_B, Malayalam,         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
2969         Mongolian, Myanmar, New_Tai_Lue, Ogham, Old_Italic, Old_Persian, Oriya,         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
2970         Osmanya,  Runic,  Shavian, Sinhala, Syloti_Nagri, Syriac, Tagalog, Tag-         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
2971         banwa,  Tai_Le,  Tamil,  Telugu,  Thaana,  Thai,   Tibetan,   Tifinagh,         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
2972         Ugaritic, Yi.         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
2973    
2974         Each  character has exactly one general category property, specified by         Each  character has exactly one general category property, specified by
2975         a two-letter abbreviation. For compatibility with Perl, negation can be         a two-letter abbreviation. For compatibility with Perl, negation can be
# Line 2719  BACKSLASH Line 3035  BACKSLASH
3035         classified as a modifier or "other".         classified as a modifier or "other".
3036    
3037         The  long  synonyms  for  these  properties that Perl supports (such as         The  long  synonyms  for  these  properties that Perl supports (such as
3038         \p{Letter}) are not supported by PCRE. Nor is is  permitted  to  prefix         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3039         any of these properties with "Is".         any of these properties with "Is".
3040    
3041         No character that is in the Unicode table has the Cn (unassigned) prop-         No character that is in the Unicode table has the Cn (unassigned) prop-
# Line 2746  BACKSLASH Line 3062  BACKSLASH
3062    
3063     Simple assertions     Simple assertions
3064    
3065         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3066         tion specifies a condition that has to be met at a particular point  in         tion specifies a condition that has to be met at a particular point  in
3067         a  match, without consuming any characters from the subject string. The         a  match, without consuming any characters from the subject string. The
3068         use of subpatterns for more complicated assertions is described  below.         use of subpatterns for more complicated assertions is described  below.
# Line 2754  BACKSLASH Line 3070  BACKSLASH
3070    
3071           \b     matches at a word boundary           \b     matches at a word boundary
3072           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3073           \A     matches at start of subject           \A     matches at the start of the subject
3074           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3075           \z     matches at end of subject                   also matches before a newline at the end of the subject
3076           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3077             \G     matches at the first matching position in the subject
3078    
3079         These  assertions may not appear in character classes (but note that \b         These  assertions may not appear in character classes (but note that \b
3080         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
# Line 2777  BACKSLASH Line 3094  BACKSLASH
3094         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3095         cating that matching is to start at a point other than the beginning of         cating that matching is to start at a point other than the beginning of
3096         the subject, \A can never match. The difference between \Z  and  \z  is         the subject, \A can never match. The difference between \Z  and  \z  is
3097         that  \Z  matches  before  a  newline that is the last character of the         that \Z matches before a newline at the end of the string as well as at
3098         string as well as at the end of the string, whereas \z matches only  at         the very end, whereas \z matches only at the end.
3099         the end.  
3100           The \G assertion is true only when the current matching position is  at
3101         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
3102         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
3103         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-  
3104         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-
3105         mentation where \G can be useful.         mentation where \G can be useful.
3106    
3107         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
3108         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
3109         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
3110         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3111         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3112    
3113         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
3114         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3115         in the compiled regular expression.         in the compiled regular expression.
3116    
# Line 2802  BACKSLASH Line 3118  BACKSLASH
3118  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3119    
3120         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3121         character  is  an  assertion  that is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3122         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-
3123         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
3124         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3125         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3126    
3127         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
3128         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
3129         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
3130         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3131         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-
3132         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
3133         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3134    
3135         A  dollar  character  is  an assertion that is true only if the current         A dollar character is an assertion that is true  only  if  the  current
3136         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3137         before a newline character that is the last character in the string (by         before a newline at the end of the string (by default). Dollar need not
3138         default). Dollar need not be the last character of  the  pattern  if  a         be  the  last  character of the pattern if a number of alternatives are
3139         number  of alternatives are involved, but it should be the last item in         involved, but it should be the last item in  any  branch  in  which  it
3140         any branch in which it appears.  Dollar has no  special  meaning  in  a         appears. Dollar has no special meaning in a character class.
        character class.  
3141    
3142         The  meaning  of  dollar  can be changed so that it matches only at the         The  meaning  of  dollar  can be changed so that it matches only at the
3143         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at
3144         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3145    
3146         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3147         PCRE_MULTILINE option is set. When this is the case, they match immedi-         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex
3148         ately  after  and  immediately  before  an  internal newline character,         matches  immediately after internal newlines as well as at the start of
3149         respectively, in addition to matching at the start and end of the  sub-         the subject string. It does not match after a  newline  that  ends  the
3150         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         string.  A dollar matches before any newlines in the string, as well as
3151         string "def\nabc" (where \n represents a newline character)  in  multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3152         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3153         in single line mode because all branches start with ^ are not  anchored         not indicate newlines.
3154         in  multiline  mode,  and  a  match for circumflex is possible when the  
3155         startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3156         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3157           Consequently, patterns that are anchored in single  line  mode  because
3158         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
3159         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
3160         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
3161         not.         PCRE_MULTILINE is set.
3162    
3163           Note that the sequences \A, \Z, and \z can be used to match  the  start
3164           and  end of the subject in both modes, and if all branches of a pattern
3165           start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3166           set.
3167    
3168    
3169  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3170    
3171         Outside a character class, a dot in the pattern matches any one charac-         Outside a character class, a dot in the pattern matches any one charac-
3172         ter  in  the  subject,  including a non-printing character, but not (by         ter in the subject string except (by default) a character  that  signi-
3173         default) newline.  In UTF-8 mode, a dot matches  any  UTF-8  character,         fies  the  end  of  a line. In UTF-8 mode, the matched character may be
3174         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3175         the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-  
3176         dling  of dot is entirely independent of the handling of circumflex and         When a line ending is defined as a single character, dot never  matches
3177         dollar, the only relationship being  that  they  both  involve  newline         that  character; when the two-character sequence CRLF is used, dot does
3178         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3179           matches  all characters (including isolated CRs and LFs). When any Uni-
3180           code line endings are being recognized, dot does not match CR or LF  or
3181           any of the other line ending characters.
3182    
3183           The  behaviour  of  dot  with regard to newlines can be changed. If the
3184           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3185           exception. If the two-character sequence CRLF is present in the subject
3186           string, it takes two dots to match it.
3187    
3188           The handling of dot is entirely independent of the handling of  circum-
3189           flex  and  dollar,  the  only relationship being that they both involve
3190           newlines. Dot has no special meaning in a character class.
3191    
3192    
3193  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3194    
3195         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3196         both in and out of UTF-8 mode. Unlike a dot, it can  match  a  newline.         both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any
3197         The  feature  is provided in Perl in order to match individual bytes in         line-ending characters. The feature is provided in  Perl  in  order  to
3198         UTF-8 mode. Because it  breaks  up  UTF-8  characters  into  individual         match  individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-
3199         bytes,  what remains in the string may be a malformed UTF-8 string. For         acters into individual bytes, what remains in the string may be a  mal-
3200         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3201           avoided.
3202    
3203         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3204         below),  because  in UTF-8 mode this would make it impossible to calcu-         below),  because  in UTF-8 mode this would make it impossible to calcu-
# Line 2912  SQUARE BRACKETS AND CHARACTER CLASSES Line 3245  SQUARE BRACKETS AND CHARACTER CLASSES
3245         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
3246         support.         support.
3247    
3248         The newline character is never treated in any special way in  character         Characters that might indicate line breaks are  never  treated  in  any
3249         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         special  way  when  matching  character  classes,  whatever line-ending
3250         options is. A class such as [^a] will always match a newline.         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3251           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3252           of these characters.
3253    
3254         The minus (hyphen) character can be used to specify a range of  charac-         The minus (hyphen) character can be used to specify a range of  charac-
3255         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters  in  a  character  class.  For  example,  [d-m] matches any letter
# Line 3015  VERTICAL BAR Line 3350  VERTICAL BAR
3350    
3351         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3352         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3353         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3354         left to right, and the first one that succeeds is used. If the alterna-         to right, and the first one that succeeds is used. If the  alternatives
3355         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3356         ing the rest of the main pattern as well as the alternative in the sub-         rest of the main pattern as well as the alternative in the  subpattern.
        pattern.  
3357    
3358    
3359  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 3047  INTERNAL OPTION SETTING Line 3381  INTERNAL OPTION SETTING
3381         PCRE extracts it into the global options (and it will therefore show up         PCRE extracts it into the global options (and it will therefore show up
3382         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3383    
3384         An option change within a subpattern affects only that part of the cur-         An  option  change  within a subpattern (see below for a description of
3385         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3386           it, so
3387    
3388           (a(?i)b)c           (a(?i)b)c
3389    
3390         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
3391         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3392         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3393         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3394         example,         example,
3395    
3396           (a(?i)b|c)           (a(?i)b|c)
3397    
3398         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3399         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3400         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3401         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3402    
3403         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3404         in the same way as the Perl-compatible options by using the  characters         can  be changed in the same way as the Perl-compatible options by using
3405         U  and X respectively. The (?X) flag setting is special in that it must         the characters J, U and X respectively.
        always occur earlier in the pattern than any of the additional features  
        it  turns on, even when it is at top level. It is best to put it at the  
        start.  
3406    
3407    
3408  SUBPATTERNS  SUBPATTERNS
# Line 3083  SUBPATTERNS Line 3415  SUBPATTERNS
3415           cat(aract|erpillar|)           cat(aract|erpillar|)
3416    
3417         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3418         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3419         string.         string.
3420    
3421         2.  It  sets  up  the  subpattern as a capturing subpattern. This means         2.  It  sets  up  the  subpattern as a capturing subpattern. This means
# Line 3112  SUBPATTERNS Line 3444  SUBPATTERNS
3444           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3445    
3446         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3447         1  and 2. The maximum number of capturing subpatterns is 65535, and the         1 and 2. The maximum number of capturing subpatterns is 65535.
        maximum depth of nesting of all subpatterns, both  capturing  and  non-  
        capturing, is 200.  
3448    
3449         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3450         start of a non-capturing subpattern,  the  option  letters  may  appear         start of a non-capturing subpattern,  the  option  letters  may  appear
# Line 3136  NAMED SUBPATTERNS Line 3466  NAMED SUBPATTERNS
3466         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3467         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3468         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3469         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3470         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3471         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3472           tax.
3473    
3474           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3475           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3476           to capturing parentheses from other parts of the pattern, such as back-
3477           references,  recursion,  and conditions, can be made by name as well as
3478           by number.
3479    
3480           Names consist of up to  32  alphanumeric  characters  and  underscores.
3481         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3482         names. The PCRE API provides function calls for extracting the name-to-         names, exactly as if the names were not present. The PCRE API  provides
3483         number  translation table from a compiled pattern. There is also a con-         function calls for extracting the name-to-number translation table from
3484         venience function for extracting a captured substring by name. For fur-         a compiled pattern. There is also a convenience function for extracting
3485         ther details see the pcreapi documentation.         a captured substring by name.
3486    
3487           By  default, a name must be unique within a pattern, but it is possible
3488           to relax this constraint by setting the PCRE_DUPNAMES option at compile
3489           time.  This  can  be useful for patterns where only one instance of the
3490           named parentheses can match. Suppose you want to match the  name  of  a
3491           weekday,  either as a 3-letter abbreviation or as the full name, and in
3492           both cases you want to extract the abbreviation. This pattern (ignoring
3493           the line breaks) does the job:
3494    
3495             (?<DN>Mon|Fri|Sun)(?:day)?|
3496             (?<DN>Tue)(?:sday)?|
3497             (?<DN>Wed)(?:nesday)?|
3498             (?<DN>Thu)(?:rsday)?|
3499             (?<DN>Sat)(?:urday)?
3500    
3501           There  are  five capturing substrings, but only one is ever set after a
3502           match.  The convenience  function  for  extracting  the  data  by  name
3503           returns  the  substring  for  the first (and in this example, the only)
3504           subpattern of that name that matched.  This  saves  searching  to  find
3505           which  numbered  subpattern  it  was. If you make a reference to a non-
3506           unique named subpattern from elsewhere in the  pattern,  the  one  that
3507           corresponds  to  the  lowest number is used. For further details of the
3508           interfaces for handling named subpatterns, see the  pcreapi  documenta-
3509           tion.
3510    
3511    
3512  REPETITION  REPETITION
# Line 3153  REPETITION Line 3515  REPETITION
3515         following items:         following items:
3516    
3517           a literal data character           a literal data character
3518           the . metacharacter           the dot metacharacter
3519           the \C escape sequence           the \C escape sequence
3520           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3521             the \R escape sequence
3522           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3523           a character class           a character class
3524           a back reference (see next section)           a back reference (see next section)
# Line 3195  REPETITION Line 3558  REPETITION
3558         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3559         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3560    
3561         For  convenience  (and  historical compatibility) the three most common         For  convenience, the three most common quantifiers have single-charac-
3562         quantifiers have single-character abbreviations:         ter abbreviations:
3563    
3564           *    is equivalent to {0,}           *    is equivalent to {0,}
3565           +    is equivalent to {1,}           +    is equivalent to {1,}
# Line 3248  REPETITION Line 3611  REPETITION
3611         which matches one digit by preference, but can match two if that is the         which matches one digit by preference, but can match two if that is the
3612         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3613    
3614         If the PCRE_UNGREEDY option is set (an option which is not available in         If the PCRE_UNGREEDY option is set (an option that is not available  in
3615         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3616         can be made greedy by following them with a  question  mark.  In  other         can be made greedy by following them with a  question  mark.  In  other
3617         words, it inverts the default behaviour.         words, it inverts the default behaviour.
# Line 3259  REPETITION Line 3622  REPETITION
3622         minimum or maximum.         minimum or maximum.
3623    
3624         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
3625         alent  to Perl's /s) is set, thus allowing the . to match newlines, the         alent  to  Perl's  /s) is set, thus allowing the dot to match newlines,
3626         pattern is implicitly anchored, because whatever follows will be  tried         the pattern is implicitly anchored, because whatever  follows  will  be
3627         against  every character position in the subject string, so there is no         tried  against every character position in the subject string, so there
3628         point in retrying the overall match at any position  after  the  first.         is no point in retrying the overall match at  any  position  after  the
3629         PCRE normally treats such a pattern as though it were preceded by \A.         first.  PCRE  normally treats such a pattern as though it were preceded
3630           by \A.
3631    
3632         In  cases  where  it  is known that the subject string contains no new-         In cases where it is known that the subject  string  contains  no  new-
3633         lines, it is worth setting PCRE_DOTALL in order to  obtain  this  opti-         lines,  it  is  worth setting PCRE_DOTALL in order to obtain this opti-
3634         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3635    
3636         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3637         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3638         backreference  elsewhere in the pattern, a match at the start may fail,         backreference elsewhere in the pattern, a match at the start  may  fail
3639         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3640    
3641           (.*)abc\1           (.*)abc\1
3642    
3643         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3644         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3645    
3646         When a capturing subpattern is repeated, the value captured is the sub-         When a capturing subpattern is repeated, the value captured is the sub-
# Line 3285  REPETITION Line 3649  REPETITION
3649           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
3650    
3651         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
3652         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
3653         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
3654         tions. For example, after         tions. For example, after
3655    
3656           /(a|(b))+/           /(a|(b))+/
# Line 3296  REPETITION Line 3660  REPETITION
3660    
3661  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
3662    
3663         With both maximizing and minimizing repetition, failure of what follows         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
3664         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition,  failure  of what follows normally causes the repeated item
3665         ferent number of repeats allows the rest of the pattern to match. Some-         to be re-evaluated to see if a different number of repeats  allows  the
3666         times it is useful to prevent this, either to change the nature of  the         rest  of  the pattern to match. Sometimes it is useful to prevent this,
3667         match,  or  to  cause it fail earlier than it otherwise might, when the         either to change the nature of the match, or to cause it  fail  earlier
3668         author of the pattern knows there is no point in carrying on.         than  it otherwise might, when the author of the pattern knows there is
3669           no point in carrying on.
3670    
3671         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider, for example, the pattern \d+foo when applied to  the  subject
3672         line         line
# Line 3315  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3680  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3680         the  means for specifying that once a subpattern has matched, it is not         the  means for specifying that once a subpattern has matched, it is not
3681         to be re-evaluated in this way.         to be re-evaluated in this way.
3682    
3683         If we use atomic grouping for the previous example, the  matcher  would         If we use atomic grouping for the previous example, the  matcher  gives
3684         give up immediately on failing to match "foo" the first time. The nota-         up  immediately  on failing to match "foo" the first time. The notation
3685         tion is a kind of special parenthesis, starting with  (?>  as  in  this         is a kind of special parenthesis, starting with (?> as in this example:
        example:  
3686    
3687           (?>\d+)foo           (?>\d+)foo
3688    
# Line 3350  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3714  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3714         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
3715         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
3716         simpler forms of atomic group. However, there is no difference  in  the         simpler forms of atomic group. However, there is no difference  in  the
3717         meaning  or  processing  of  a possessive quantifier and the equivalent         meaning  of  a  possessive  quantifier and the equivalent atomic group,
3718         atomic group.         though there may be a performance  difference;  possessive  quantifiers
3719           should be slightly faster.
3720         The possessive quantifier syntax is an extension to the Perl syntax. It  
3721         originates in Sun's Java package.         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
3722           tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first
3723         When  a  pattern  contains an unlimited repeat inside a subpattern that         edition of his book. Mike McCloskey liked it, so implemented it when he
3724         can itself be repeated an unlimited number of  times,  the  use  of  an         built Sun's Java package, and PCRE copied it from there. It  ultimately
3725         atomic  group  is  the  only way to avoid some failing matches taking a         found its way into Perl at release 5.10.
3726    
3727           PCRE has an optimization that automatically "possessifies" certain sim-
3728           ple pattern constructs. For example, the sequence  A+B  is  treated  as
3729           A++B  because  there is no point in backtracking into a sequence of A's
3730           when B must follow.
3731    
3732           When a pattern contains an unlimited repeat inside  a  subpattern  that
3733           can  itself  be  repeated  an  unlimited number of times, the use of an
3734           atomic group is the only way to avoid some  failing  matches  taking  a
3735         very long time indeed. The pattern         very long time indeed. The pattern
3736    
3737           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
3738    
3739         matches an unlimited number of substrings that either consist  of  non-         matches  an  unlimited number of substrings that either consist of non-
3740         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it
3741         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
3742    
3743           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
3744    
3745         it takes a long time before reporting  failure.  This  is  because  the         it  takes  a  long  time  before reporting failure. This is because the
3746         string  can be divided between the internal \D+ repeat and the external         string can be divided between the internal \D+ repeat and the  external
3747         * repeat in a large number of ways, and all  have  to  be  tried.  (The         *  repeat  in  a  large  number of ways, and all have to be tried. (The
3748         example  uses  [!?]  rather than a single character at the end, because         example uses [!?] rather than a single character at  the  end,  because
3749         both PCRE and Perl have an optimization that allows  for  fast  failure         both  PCRE  and  Perl have an optimization that allows for fast failure
3750         when  a single character is used. They remember the last single charac-         when a single character is used. They remember the last single  charac-
3751         ter that is required for a match, and fail early if it is  not  present         ter  that  is required for a match, and fail early if it is not present
3752         in  the  string.)  If  the pattern is changed so that it uses an atomic         in the string.) If the pattern is changed so that  it  uses  an  atomic
3753         group, like this:         group, like this:
3754    
3755           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
3756    
3757         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences  of non-digits cannot be broken, and failure happens quickly.
3758    
3759    
3760  BACK REFERENCES  BACK REFERENCES
3761    
3762         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
3763         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-
3764         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
3765         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
3766    
3767         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
3768         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
3769         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
3770         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
3771         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
3772         tion  entitled  "Non-printing  characters" above for further details of         reference" of this type can make sense when a  repetition  is  involved
3773         the handling of digits following a backslash.         and  the  subpattern to the right has participated in an earlier itera-
3774           tion.
3775    
3776         A back reference matches whatever actually matched the  capturing  sub-         It is not possible to have a numerical "forward back  reference"  to  a
3777         pattern  in  the  current subject string, rather than anything matching         subpattern  whose  number  is  10  or  more using this syntax because a
3778           sequence such as \50 is interpreted as a character  defined  in  octal.
3779           See the subsection entitled "Non-printing characters" above for further
3780           details of the handling of digits following a backslash.  There  is  no
3781           such  problem  when named parentheses are used. A back reference to any
3782           subpattern is possible using named parentheses (see below).
3783    
3784           Another way of avoiding the ambiguity inherent in  the  use  of  digits
3785           following a backslash is to use the \g escape sequence, which is a fea-
3786           ture introduced in Perl 5.10. This escape must be followed by  a  posi-
3787           tive  or  a negative number, optionally enclosed in braces. These exam-
3788           ples are all identical:
3789    
3790             (ring), \1
3791             (ring), \g1
3792             (ring), \g{1}
3793    
3794           A positive number specifies an absolute reference without the ambiguity
3795           that  is  present  in  the older syntax. It is also useful when literal
3796           digits follow the reference. A negative number is a relative reference.
3797           Consider this example:
3798    
3799             (abc(def)ghi)\g{-1}
3800    
3801           The sequence \g{-1} is a reference to the most recently started captur-
3802           ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,
3803           \g{-2} would be equivalent to \1. The use of relative references can be
3804           helpful in long patterns, and also in  patterns  that  are  created  by
3805           joining together fragments that contain references within themselves.
3806    
3807           A  back  reference matches whatever actually matched the capturing sub-
3808           pattern in the current subject string, rather  than  anything  matching
3809         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
3810         of doing that). So the pattern         of doing that). So the pattern
3811    
3812           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
3813    
3814         matches  "sense and sensibility" and "response and responsibility", but         matches "sense and sensibility" and "response and responsibility",  but
3815         not "sense and responsibility". If caseful matching is in force at  the         not  "sense and responsibility". If caseful matching is in force at the
3816         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-
3817         ple,         ple,
3818    
3819           ((?i)rah)\s+\1           ((?i)rah)\s+\1
3820    
3821         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
3822         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
3823    
3824         Back  references  to named subpatterns use the Python syntax (?P=name).         Back references to named subpatterns use the Perl  syntax  \k<name>  or
3825         We could rewrite the above example as follows:         \k'name'  or  the  Python  syntax (?P=name). We could rewrite the above
3826           example in either of the following ways:
3827    
3828           (?<p1>(?i)rah)\s+(?P=p1)           (?<p1>(?i)rah)\s+\k<p1>
3829             (?P<p1>(?i)rah)\s+(?P=p1)
3830    
3831         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
3832         subpattern  has  not actually been used in a particular match, any back         before or after the reference.
3833    
3834           There  may be more than one back reference to the same subpattern. If a
3835           subpattern has not actually been used in a particular match,  any  back
3836         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
3837    
3838           (a|(bc))\2           (a|(bc))\2
3839    
3840         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
3841         may  be  many  capturing parentheses in a pattern, all digits following         may be many capturing parentheses in a pattern,  all  digits  following
3842         the backslash are taken as part of a potential back  reference  number.         the  backslash  are taken as part of a potential back reference number.
3843         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
3844         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         used  to  terminate  the back reference. If the PCRE_EXTENDED option is
3845         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-
3846         ments" below) can be used.         ments" below) can be used.
3847    
3848         A back reference that occurs inside the parentheses to which it  refers         A  back reference that occurs inside the parentheses to which it refers
3849         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
3850         matches.  However, such references can be useful inside  repeated  sub-         matches.   However,  such references can be useful inside repeated sub-
3851         patterns. For example, the pattern         patterns. For example, the pattern
3852    
3853           (a|b\1)+           (a|b\1)+
3854    
3855         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-
3856         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
3857         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
3858         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
3859         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
3860         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
3861    
3862    
3863  ASSERTIONS  ASSERTIONS
3864    
3865         An assertion is a test on the characters  following  or  preceding  the         An  assertion  is  a  test on the characters following or preceding the
3866         current  matching  point that does not actually consume any characters.         current matching point that does not actually consume  any  characters.
3867         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
3868         described above.         described above.
3869    
3870         More  complicated  assertions  are  coded as subpatterns. There are two         More complicated assertions are coded as  subpatterns.  There  are  two
3871         kinds: those that look ahead of the current  position  in  the  subject         kinds:  those  that  look  ahead of the current position in the subject
3872         string,  and  those  that  look  behind  it. An assertion subpattern is         string, and those that look  behind  it.  An  assertion  subpattern  is
3873         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
3874         matching position to be changed.         matching position to be changed.
3875    
3876         Assertion  subpatterns  are  not  capturing subpatterns, and may not be         Assertion subpatterns are not capturing subpatterns,  and  may  not  be
3877         repeated, because it makes no sense to assert the  same  thing  several         repeated,  because  it  makes no sense to assert the same thing several
3878         times.  If  any kind of assertion contains capturing subpatterns within         times. If any kind of assertion contains capturing  subpatterns  within
3879         it, these are counted for the purposes of numbering the capturing  sub-         it,  these are counted for the purposes of numbering the capturing sub-
3880         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
3881         out only for positive assertions, because it does not  make  sense  for         out  only  for  positive assertions, because it does not make sense for
3882         negative assertions.         negative assertions.
3883    
3884     Lookahead assertions     Lookahead assertions
# Line 3478  ASSERTIONS Line 3888  ASSERTIONS
3888    
3889           \w+(?=;)           \w+(?=;)
3890    
3891         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-
3892         colon in the match, and         colon in the match, and
3893    
3894           foo(?!bar)           foo(?!bar)
3895    
3896         matches  any  occurrence  of  "foo" that is not followed by "bar". Note         matches any occurrence of "foo" that is not  followed  by  "bar".  Note
3897         that the apparently similar pattern         that the apparently similar pattern
3898    
3899           (?!foo)bar           (?!foo)bar
3900    
3901         does not find an occurrence of "bar"  that  is  preceded  by  something         does  not  find  an  occurrence  of "bar" that is preceded by something
3902         other  than "foo"; it finds any occurrence of "bar" whatsoever, because         other than "foo"; it finds any occurrence of "bar" whatsoever,  because
3903         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
3904         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
3905    
3906         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
3907         most convenient way to do it is  with  (?!)  because  an  empty  string         most  convenient  way  to  do  it  is with (?!) because an empty string
3908         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
3909         string must always fail.         string must always fail.
3910    
3911     Lookbehind assertions     Lookbehind assertions
3912    
3913         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
3914         for negative assertions. For example,         for negative assertions. For example,
3915    
3916           (?<!foo)bar           (?<!foo)bar
3917    
3918         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
3919         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
3920         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-
3921         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
3922         Thus         fixed length. Thus
3923    
3924           (?<=bullock|donkey)           (?<=bullock|donkey)
3925    
# Line 3517  ASSERTIONS Line 3927  ASSERTIONS
3927    
3928           (?<!dogs?|cats?)           (?<!dogs?|cats?)
3929    
3930         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
3931         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
3932         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
3933         requires all branches to match the same length of string. An  assertion         requires  all branches to match the same length of string. An assertion
3934         such as         such as
3935    
3936           (?<=ab(c|de))           (?<=ab(c|de))
3937    
3938         is  not  permitted,  because  its single top-level branch can match two         is not permitted, because its single top-level  branch  can  match  two
3939         different lengths, but it is acceptable if rewritten to  use  two  top-         different  lengths,  but  it is acceptable if rewritten to use two top-
3940         level branches:         level branches:
3941    
3942           (?<=abc|abde)           (?<=abc|abde)
3943    
3944         The  implementation  of lookbehind assertions is, for each alternative,         The implementation of lookbehind assertions is, for  each  alternative,
3945         to temporarily move the current position back by the  fixed  width  and         to  temporarily  move the current position back by the fixed length and
3946         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
3947         rent position, the match is deemed to fail.         rent position, the assertion fails.
3948    
3949         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
3950         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode) to appear in lookbehind assertions, because it makes it  impossi-
3951         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,
3952         match different numbers of bytes, is also not permitted.         which can match different numbers of bytes, are also not permitted.
3953    
3954         Atomic  groups can be used in conjunction with lookbehind assertions to         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind
3955         specify efficient matching at the end of the subject string. Consider a         assertions  to  specify  efficient  matching  at the end of the subject
3956         simple pattern such as         string. Consider a simple pattern such as
3957    
3958           abcd$           abcd$
3959    
3960         when  applied  to  a  long string that does not match. Because matching         when applied to a long string that does  not  match.  Because  matching
3961         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
3962         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
3963         pattern is specified as         pattern is specified as
3964    
3965           ^.*abcd$           ^.*abcd$
3966    
3967         the initial .* matches the entire string at first, but when this  fails         the  initial .* matches the entire string at first, but when this fails
3968         (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
3969         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
3970         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,
3971         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
3972    
          ^(?>.*)(?<=abcd)  
   
        or, equivalently, using the possessive quantifier syntax,  
   
3973           ^.*+(?<=abcd)           ^.*+(?<=abcd)
3974    
3975         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
3976         entire  string.  The subsequent lookbehind assertion does a single test         entire string. The subsequent lookbehind assertion does a  single  test
3977         on the last four characters. If it fails, the match fails  immediately.         on  the last four characters. If it fails, the match fails immediately.
3978         For  long  strings, this approach makes a significant difference to the         For long strings, this approach makes a significant difference  to  the
3979         processing time.         processing time.
3980    
3981     Using multiple assertions     Using multiple assertions
# Line 3578  ASSERTIONS Line 3984  ASSERTIONS
3984    
3985           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
3986    
3987         matches "foo" preceded by three digits that are not "999". Notice  that         matches  "foo" preceded by three digits that are not "999". Notice that
3988         each  of  the  assertions is applied independently at the same point in         each of the assertions is applied independently at the  same  point  in
3989         the subject string. First there is a  check  that  the  previous  three         the  subject  string.  First  there  is a check that the previous three
3990         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
3991         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
3992         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
3993         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-
3994         foo". A pattern to do that is         foo". A pattern to do that is
3995    
3996           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
3997    
3998         This  time  the  first assertion looks at the preceding six characters,         This time the first assertion looks at the  preceding  six  characters,
3999         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4000         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4001    
# Line 3597  ASSERTIONS Line 4003  ASSERTIONS
4003    
4004           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4005    
4006         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
4007         is not preceded by "foo", while         is not preceded by "foo", while
4008    
4009           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4010    
4011         is another pattern that matches "foo" preceded by three digits and  any         is  another pattern that matches "foo" preceded by three digits and any
4012         three characters that are not "999".         three characters that are not "999".
4013    
4014    
4015  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4016    
4017         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-
4018         ditionally or to choose between two alternative subpatterns,  depending         ditionally  or to choose between two alternative subpatterns, depending
4019         on  the result of an assertion, or whether a previous capturing subpat-         on the result of an assertion, or whether a previous capturing  subpat-
4020         tern matched or not. The two possible forms of  conditional  subpattern         tern  matched  or not. The two possible forms of conditional subpattern
4021         are         are
4022    
4023           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4024           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4025    
4026         If  the  condition is satisfied, the yes-pattern is used; otherwise the         If the condition is satisfied, the yes-pattern is used;  otherwise  the
4027         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-
4028         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4029    
4030         There are three kinds of condition. If the text between the parentheses         There are four kinds of condition: references  to  subpatterns,  refer-
4031         consists of a sequence of digits, the condition  is  satisfied  if  the         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4032         capturing  subpattern of that number has previously matched. The number  
4033         must be greater than zero. Consider the following pattern,  which  con-     Checking for a used subpattern by number
4034         tains  non-significant white space to make it more readable (assume the  
4035         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,
4036         discussion:         the condition is true if the capturing subpattern of  that  number  has
4037           previously matched.
4038    
4039           Consider  the  following  pattern, which contains non-significant white
4040           space to make it more readable (assume the PCRE_EXTENDED option) and to
4041           divide it into three parts for ease of discussion:
4042    
4043           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4044    
# Line 3642  CONDITIONAL SUBPATTERNS Line 4053  CONDITIONAL SUBPATTERNS
4053         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other  words,  this  pattern  matches  a  sequence  of non-parentheses,
4054         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4055    
4056         If the condition is the string (R), it is satisfied if a recursive call     Checking for a used subpattern by name
4057         to  the pattern or subpattern has been made. At "top level", the condi-  
4058         tion is false.  This  is  a  PCRE  extension.  Recursive  patterns  are         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a
4059         described in the next section.         used  subpattern  by  name.  For compatibility with earlier versions of
4060           PCRE, which had this facility before Perl, the syntax  (?(name)...)  is
4061           also  recognized. However, there is a possible ambiguity with this syn-
4062           tax, because subpattern names may  consist  entirely  of  digits.  PCRE
4063           looks  first for a named subpattern; if it cannot find one and the name
4064           consists entirely of digits, PCRE looks for a subpattern of  that  num-
4065           ber,  which must be greater than zero. Using subpattern names that con-
4066           sist entirely of digits is not recommended.
4067    
4068           Rewriting the above example to use a named subpattern gives this:
4069    
4070         If  the  condition  is  not  a sequence of digits or (R), it must be an           (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
4071    
4072    
4073       Checking for pattern recursion
4074    
4075           If the condition is the string (R), and there is no subpattern with the
4076           name  R, the condition is true if a recursive call to the whole pattern
4077           or any subpattern has been made. If digits or a name preceded by amper-
4078           sand follow the letter R, for example:
4079    
4080             (?(R3)...) or (?(R&name)...)
4081    
4082           the  condition is true if the most recent recursion is into the subpat-
4083           tern whose number or name is given. This condition does not  check  the
4084           entire recursion stack.
4085    
4086           At  "top  level", all these recursion test conditions are false. Recur-
4087           sive patterns are described below.
4088    
4089       Defining subpatterns for use by reference only
4090    
4091           If the condition is the string (DEFINE), and  there  is  no  subpattern
4092           with  the  name  DEFINE,  the  condition is always false. In this case,
4093           there may be only one alternative  in  the  subpattern.  It  is  always
4094           skipped  if  control  reaches  this  point  in the pattern; the idea of
4095           DEFINE is that it can be used to define "subroutines" that can be  ref-
4096           erenced  from elsewhere. (The use of "subroutines" is described below.)
4097           For example, a pattern to match an IPv4 address could be  written  like
4098           this (ignore whitespace and line breaks):
4099    
4100             (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
4101             \b (?&byte) (\.(?&byte)){3} \b
4102    
4103           The  first part of the pattern is a DEFINE group inside which a another
4104           group named "byte" is defined. This matches an individual component  of
4105           an  IPv4  address  (a number less than 256). When matching takes place,
4106           this part of the pattern is skipped because DEFINE acts  like  a  false
4107           condition.
4108    
4109           The rest of the pattern uses references to the named group to match the
4110           four dot-separated components of an IPv4 address, insisting on  a  word
4111           boundary at each end.
4112    
4113       Assertion conditions
4114    
4115           If  the  condition  is  not  in any of the above formats, it must be an
4116         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.  This may be a positive or negative lookahead or  lookbehind
4117         assertion.  Consider  this  pattern,  again  containing non-significant         assertion.  Consider  this  pattern,  again  containing non-significant
4118         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
# Line 3672  COMMENTS Line 4137  COMMENTS
4137         at all.         at all.
4138    
4139         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If  the PCRE_EXTENDED option is set, an unescaped # character outside a
4140         character class introduces a comment that continues up to the next new-         character class introduces a  comment  that  continues  to  immediately
4141         line character in the pattern.         after the next newline in the pattern.
4142    
4143    
4144  RECURSIVE PATTERNS  RECURSIVE PATTERNS
# Line 3682  RECURSIVE PATTERNS Line 4147  RECURSIVE PATTERNS
4147         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited nested parentheses. Without the use of  recursion,  the  best
4148         that  can  be  done  is  to use a pattern that matches up to some fixed         that  can  be  done  is  to use a pattern that matches up to some fixed
4149         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth of nesting. It is not possible to  handle  an  arbitrary  nesting
4150         depth.  Perl  provides  a  facility  that allows regular expressions to         depth.
4151         recurse (amongst other things). It does this by interpolating Perl code  
4152         in the expression at run time, and the code can refer to the expression         For some time, Perl has provided a facility that allows regular expres-
4153         itself. A Perl pattern to solve the parentheses problem can be  created         sions to recurse (amongst other things). It does this by  interpolating
4154         like this:         Perl  code in the expression at run time, and the code can refer to the
4155           expression itself. A Perl pattern using code interpolation to solve the
4156           parentheses problem can be created like this:
4157    
4158           $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x;           $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x;
4159    
4160         The (?p{...}) item interpolates Perl code at run time, and in this case         The (?p{...}) item interpolates Perl code at run time, and in this case
4161         refers recursively to the pattern in which it appears. Obviously,  PCRE         refers recursively to the pattern in which it appears.
        cannot  support  the  interpolation  of Perl code. Instead, it supports  
        some special syntax for recursion of the entire pattern, and  also  for  
        individual subpattern recursion.  
4162    
4163         The  special item that consists of (? followed by a number greater than         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4164           it  supports  special  syntax  for recursion of the entire pattern, and
4165           also for individual subpattern recursion.  After  its  introduction  in
4166           PCRE  and  Python,  this  kind of recursion was introduced into Perl at
4167           release 5.10.
4168    
4169           A special item that consists of (? followed by a  number  greater  than
4170         zero and a closing parenthesis is a recursive call of the subpattern of         zero and a closing parenthesis is a recursive call of the subpattern of
4171         the  given  number, provided that it occurs inside that subpattern. (If         the given number, provided that it occurs inside that  subpattern.  (If
4172         not, it is a "subroutine" call, which is described  in  the  next  sec-         not,  it  is  a  "subroutine" call, which is described in the next sec-
4173         tion.)  The special item (?R) is a recursive call of the entire regular         tion.) The special item (?R) or (?0) is a recursive call of the  entire
4174         expression.         regular expression.
4175    
4176         A recursive subpattern call is always treated as an atomic group.  That         In  PCRE (like Python, but unlike Perl), a recursive subpattern call is
4177         is,  once  it  has  matched some of the subject string, it is never re-         always treated as an atomic group. That is, once it has matched some of
4178         entered, even if it contains untried alternatives and there is a subse-         the subject string, it is never re-entered, even if it contains untried
4179         quent matching failure.         alternatives and there is a subsequent matching failure.
4180    
4181         This  PCRE  pattern  solves  the nested parentheses problem (assume the         This PCRE pattern solves the nested  parentheses  problem  (assume  the
4182         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4183    
4184           \( ( (?>[^()]+) | (?R) )* \)           \( ( (?>[^()]+) | (?R) )* \)
4185    
4186         First it matches an opening parenthesis. Then it matches any number  of         First  it matches an opening parenthesis. Then it matches any number of
4187         substrings  which  can  either  be  a sequence of non-parentheses, or a         substrings which can either be a  sequence  of  non-parentheses,  or  a
4188         recursive match of the pattern itself (that is, a  correctly  parenthe-         recursive  match  of the pattern itself (that is, a correctly parenthe-
4189         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis.
4190    
4191         If  this  were  part of a larger pattern, you would not want to recurse         If this were part of a larger pattern, you would not  want  to  recurse
4192         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4193    
4194           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( (?>[^()]+) | (?1) )* \) )
4195    
4196         We have put the pattern into parentheses, and caused the  recursion  to         We  have  put the pattern into parentheses, and caused the recursion to
4197         refer  to them instead of the whole pattern. In a larger pattern, keep-         refer to them instead of the whole pattern. In a larger pattern,  keep-
4198         ing track of parenthesis numbers can be tricky. It may be  more  conve-         ing  track  of parenthesis numbers can be tricky. It may be more conve-
4199         nient  to use named parentheses instead. For this, PCRE uses (?P>name),         nient to use named parentheses instead. The Perl  syntax  for  this  is
4200         which is an extension to the Python syntax that  PCRE  uses  for  named         (?&name);  PCRE's  earlier syntax (?P>name) is also supported. We could
4201         parentheses (Perl does not provide named parentheses). We could rewrite         rewrite the above example as follows:
4202         the above example as follows:  
4203             (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
4204           (?P<pn> \( ( (?>[^()]+) | (?P>pn) )* \) )  
4205           If there is more than one subpattern with the same name,  the  earliest
4206         This particular example pattern contains nested unlimited repeats,  and         one  is used. This particular example pattern contains nested unlimited
4207         so  the  use of atomic grouping for matching strings of non-parentheses         repeats, and so the use of atomic grouping for matching strings of non-
4208         is important when applying the pattern to strings that  do  not  match.         parentheses  is  important when applying the pattern to strings that do
4209         For example, when this pattern is applied to         not match. For example, when this pattern is applied to
4210    
4211           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
4212    
4213         it  yields "no match" quickly. However, if atomic grouping is not used,         it yields "no match" quickly. However, if atomic grouping is not  used,
4214         the match runs for a very long time indeed because there  are  so  many         the  match  runs  for a very long time indeed because there are so many
4215         different  ways  the  + and * repeats can carve up the subject, and all         different ways the + and * repeats can carve up the  subject,  and  all
4216         have to be tested before failure can be reported.         have to be tested before failure can be reported.
4217    
4218         At the end of a match, the values set for any capturing subpatterns are         At the end of a match, the values set for any capturing subpatterns are
4219         those from the outermost level of the recursion at which the subpattern         those from the outermost level of the recursion at which the subpattern
4220         value is set.  If you want to obtain  intermediate  values,  a  callout         value  is  set.   If  you want to obtain intermediate values, a callout
4221         function can be used (see the next section and the pcrecallout documen-         function can be used (see below and the pcrecallout documentation).  If
4222         tation). If the pattern above is matched against         the pattern above is matched against
4223    
4224           (ab(cd)ef)           (ab(cd)ef)
4225    
4226         the value for the capturing parentheses is  "ef",  which  is  the  last         the  value  for  the  capturing  parentheses is "ef", which is the last
4227         value  taken  on at the top level. If additional parentheses are added,         value taken on at the top level. If additional parentheses  are  added,
4228         giving         giving
4229    
4230           \( ( ( (?>[^()]+) | (?R) )* ) \)           \( ( ( (?>[^()]+) | (?R) )* ) \)
4231              ^                        ^              ^                        ^
4232              ^                        ^              ^                        ^
4233    
4234         the string they capture is "ab(cd)ef", the contents of  the  top  level         the  string  they  capture is "ab(cd)ef", the contents of the top level
4235         parentheses.  If there are more than 15 capturing parentheses in a pat-         parentheses. If there are more than 15 capturing parentheses in a  pat-
4236         tern, PCRE has to obtain extra memory to store data during a recursion,         tern, PCRE has to obtain extra memory to store data during a recursion,
4237         which  it  does  by  using pcre_malloc, freeing it via pcre_free after-         which it does by using pcre_malloc, freeing  it  via  pcre_free  after-
4238         wards. If  no  memory  can  be  obtained,  the  match  fails  with  the         wards.  If  no  memory  can  be  obtained,  the  match  fails  with the
4239         PCRE_ERROR_NOMEMORY error.         PCRE_ERROR_NOMEMORY error.
4240    
4241         Do  not  confuse  the (?R) item with the condition (R), which tests for         Do not confuse the (?R) item with the condition (R),  which  tests  for
4242         recursion.  Consider this pattern, which matches text in  angle  brack-         recursion.   Consider  this pattern, which matches text in angle brack-
4243         ets,  allowing for arbitrary nesting. Only digits are allowed in nested         ets, allowing for arbitrary nesting. Only digits are allowed in  nested
4244         brackets (that is, when recursing), whereas any characters are  permit-         brackets  (that is, when recursing), whereas any characters are permit-
4245         ted at the outer level.         ted at the outer level.
4246    
4247           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >
4248    
4249         In  this  pattern, (?(R) is the start of a conditional subpattern, with         In this pattern, (?(R) is the start of a conditional  subpattern,  with
4250         two different alternatives for the recursive and  non-recursive  cases.         two  different  alternatives for the recursive and non-recursive cases.
4251         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
4252    
4253    
4254  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
4255    
4256         If the syntax for a recursive subpattern reference (either by number or         If the syntax for a recursive subpattern reference (either by number or
4257         by name) is used outside the parentheses to which it refers,  it  oper-         by  name)  is used outside the parentheses to which it refers, it oper-
4258         ates  like  a  subroutine in a programming language. An earlier example         ates like a subroutine in a programming language. The "called"  subpat-
4259           tern  may  be defined before or after the reference. An earlier example
4260         pointed out that the pattern         pointed out that the pattern
4261    
4262           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
# Line 3796  SUBPATTERNS AS SUBROUTINES Line 4267  SUBPATTERNS AS SUBROUTINES
4267           (sens|respons)e and (?1)ibility           (sens|respons)e and (?1)ibility
4268    
4269         is  used, it does match "sense and responsibility" as well as the other         is  used, it does match "sense and responsibility" as well as the other
4270         two strings. Such references must, however, follow  the  subpattern  to         two strings. Another example is  given  in  the  discussion  of  DEFINE
4271         which they refer.         above.
4272    
4273         Like recursive subpatterns, a "subroutine" call is always treated as an         Like recursive subpatterns, a "subroutine" call is always treated as an
4274         atomic group. That is, once it has matched some of the subject  string,         atomic group. That is, once it has matched some of the subject  string,
4275         it  is  never  re-entered, even if it contains untried alternatives and         it  is  never  re-entered, even if it contains untried alternatives and
4276         there is a subsequent matching failure.         there is a subsequent matching failure.
4277    
4278           When a subpattern is used as a subroutine, processing options  such  as
4279           case-independence are fixed when the subpattern is defined. They cannot
4280           be changed for different calls. For example, consider this pattern:
4281    
4282             (abc)(?i:(?1))
4283    
4284           It matches "abcabc". It does not match "abcABC" because the  change  of
4285           processing option does not affect the called subpattern.
4286    
4287    
4288  CALLOUTS  CALLOUTS
4289    
4290         Perl has a feature whereby using the sequence (?{...}) causes arbitrary         Perl has a feature whereby using the sequence (?{...}) causes arbitrary
4291         Perl  code to be obeyed in the middle of matching a regular expression.         Perl code to be obeyed in the middle of matching a regular  expression.
4292         This makes it possible, amongst other things, to extract different sub-         This makes it possible, amongst other things, to extract different sub-
4293         strings that match the same pair of parentheses when there is a repeti-         strings that match the same pair of parentheses when there is a repeti-
4294         tion.         tion.
4295    
4296         PCRE provides a similar feature, but of course it cannot obey arbitrary         PCRE provides a similar feature, but of course it cannot obey arbitrary
4297         Perl code. The feature is called "callout". The caller of PCRE provides         Perl code. The feature is called "callout". The caller of PCRE provides
4298         an external function by putting its entry point in the global  variable         an  external function by putting its entry point in the global variable
4299         pcre_callout.   By default, this variable contains NULL, which disables         pcre_callout.  By default, this variable contains NULL, which  disables
4300         all calling out.         all calling out.
4301    
4302         Within a regular expression, (?C) indicates the  points  at  which  the         Within  a  regular  expression,  (?C) indicates the points at which the
4303         external  function  is  to be called. If you want to identify different         external function is to be called. If you want  to  identify  different
4304         callout points, you can put a number less than 256 after the letter  C.         callout  points, you can put a number less than 256 after the letter C.
4305         The  default  value is zero.  For example, this pattern has two callout         The default value is zero.  For example, this pattern has  two  callout
4306         points:         points:
4307    
4308           (?C1)abc(?C2)def           (?C1)abc(?C2)def
4309    
4310         If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are         If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are
4311         automatically  installed  before each item in the pattern. They are all         automatically installed before each item in the pattern. They  are  all
4312         numbered 255.         numbered 255.
4313    
4314         During matching, when PCRE reaches a callout point (and pcre_callout is         During matching, when PCRE reaches a callout point (and pcre_callout is
4315         set),  the  external function is called. It is provided with the number         set), the external function is called. It is provided with  the  number
4316         of the callout, the position in the pattern, and, optionally, one  item         of  the callout, the position in the pattern, and, optionally, one item
4317         of  data  originally supplied by the caller of pcre_exec(). The callout         of data originally supplied by the caller of pcre_exec().  The  callout
4318         function may cause matching to proceed, to backtrack,