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revision 83 by nigel, Sat Feb 24 21:41:06 2007 UTC revision 172 by ph10, Tue Jun 5 10:40:13 2007 UTC
# Line 18  INTRODUCTION Line 18  INTRODUCTION
18    
19         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
20         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
21         just  a  few  differences.  The current implementation of PCRE (release         just  a  few differences. (Certain features that appeared in Python and
22         6.x) corresponds approximately with Perl  5.8,  including  support  for         PCRE before they appeared in Perl are also available using  the  Python
23         UTF-8 encoded strings and Unicode general category properties. However,         syntax.)
24         this support has to be explicitly enabled; it is not the default.  
25           The  current  implementation of PCRE (release 7.x) corresponds approxi-
26         In addition to the Perl-compatible matching function,  PCRE  also  con-         mately with Perl 5.10, including support for UTF-8 encoded strings  and
27         tains  an  alternative matching function that matches the same compiled         Unicode general category properties. However, UTF-8 and Unicode support
28         patterns in a different way. In certain circumstances, the  alternative         has to be explicitly enabled; it is not the default. The Unicode tables
29         function  has  some  advantages.  For  a discussion of the two matching         correspond to Unicode release 5.0.0.
30         algorithms, see the pcrematching page.  
31           In  addition to the Perl-compatible matching function, PCRE contains an
32         PCRE is written in C and released as a C library. A  number  of  people         alternative matching function that matches the same  compiled  patterns
33         have  written  wrappers and interfaces of various kinds. In particular,         in  a different way. In certain circumstances, the alternative function
34         Google Inc.  have provided a comprehensive C++  wrapper.  This  is  now         has some advantages. For a discussion of the two  matching  algorithms,
35           see the pcrematching page.
36    
37           PCRE  is  written  in C and released as a C library. A number of people
38           have written wrappers and interfaces of various kinds.  In  particular,
39           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
40         included as part of the PCRE distribution. The pcrecpp page has details         included as part of the PCRE distribution. The pcrecpp page has details
41         of this interface. Other people's contributions can  be  found  in  the         of  this  interface.  Other  people's contributions can be found in the
42         Contrib directory at the primary FTP site, which is:         Contrib directory at the primary FTP site, which is:
43    
44         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
45    
46         Details  of  exactly which Perl regular expression features are and are         Details of exactly which Perl regular expression features are  and  are
47         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
48         tern and pcrecompat pages.         tern and pcrecompat pages.
49    
50         Some  features  of  PCRE can be included, excluded, or changed when the         Some features of PCRE can be included, excluded, or  changed  when  the
51         library is built. The pcre_config() function makes it  possible  for  a         library  is  built.  The pcre_config() function makes it possible for a
52         client  to  discover  which  features are available. The features them-         client to discover which features are  available.  The  features  them-
53         selves are described in the pcrebuild page. Documentation about  build-         selves  are described in the pcrebuild page. Documentation about build-
54         ing  PCRE for various operating systems can be found in the README file         ing PCRE for various operating systems can be found in the README  file
55         in the source distribution.         in the source distribution.
56    
57         The library contains a number of undocumented  internal  functions  and         The  library  contains  a number of undocumented internal functions and
58         data  tables  that  are  used by more than one of the exported external         data tables that are used by more than one  of  the  exported  external
59         functions, but which are not intended  for  use  by  external  callers.         functions,  but  which  are  not  intended for use by external callers.
60         Their  names  all begin with "_pcre_", which hopefully will not provoke         Their names all begin with "_pcre_", which hopefully will  not  provoke
61         any name clashes. In some environments, it is possible to control which         any name clashes. In some environments, it is possible to control which
62         external  symbols  are  exported when a shared library is built, and in         external symbols are exported when a shared library is  built,  and  in
63         these cases the undocumented symbols are not exported.         these cases the undocumented symbols are not exported.
64    
65    
66  USER DOCUMENTATION  USER DOCUMENTATION
67    
68         The user documentation for PCRE comprises a number  of  different  sec-         The  user  documentation  for PCRE comprises a number of different sec-
69         tions.  In the "man" format, each of these is a separate "man page". In         tions. In the "man" format, each of these is a separate "man page".  In
70         the HTML format, each is a separate page, linked from the  index  page.         the  HTML  format, each is a separate page, linked from the index page.
71         In  the  plain text format, all the sections are concatenated, for ease         In the plain text format, all the sections are concatenated,  for  ease
72         of searching. The sections are as follows:         of searching. The sections are as follows:
73    
74           pcre              this document           pcre              this document
75             pcre-config       show PCRE installation configuration information
76           pcreapi           details of PCRE's native C API           pcreapi           details of PCRE's native C API
77           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
78           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
# Line 81  USER DOCUMENTATION Line 87  USER DOCUMENTATION
87           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
88           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
89           pcresample        discussion of the sample program           pcresample        discussion of the sample program
90             pcrestack         discussion of stack usage
91           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
92    
93         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
94         each C library function, listing its arguments and results.         each C library function, listing its arguments and results.
95    
96    
97  LIMITATIONS  LIMITATIONS
98    
99         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
100         never in practice be relevant.         never in practice be relevant.
101    
102         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
103         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
104         process  regular  expressions  that are truly enormous, you can compile         process regular expressions that are truly enormous,  you  can  compile
105         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
106         the  source  distribution and the pcrebuild documentation for details).         the source distribution and the pcrebuild documentation  for  details).
107         In these cases the limit is substantially larger.  However,  the  speed         In  these  cases the limit is substantially larger.  However, the speed
108         of execution will be slower.         of execution is slower.
109    
110         All values in repeating quantifiers must be less than 65536.  The maxi-         All values in repeating quantifiers must be less than 65536. The  maxi-
111         mum number of capturing subpatterns is 65535.         mum  compiled  length  of  subpattern  with an explicit repeat count is
112           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.  
113    
114         The  maximum  length of a subject string is the largest positive number         There is no limit to the number of parenthesized subpatterns, but there
115         that an integer variable can hold. However, when using the  traditional         can be no more than 65535 capturing subpatterns.
116    
117           The maximum length of name for a named subpattern is 32 characters, and
118           the maximum number of named subpatterns is 10000.
119    
120           The maximum length of a subject string is the largest  positive  number
121           that  an integer variable can hold. However, when using the traditional
122         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
123         inite repetition.  This means that the available stack space may  limit         inite  repetition.  This means that the available stack space may limit
124         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.
125           For a discussion of stack issues, see the pcrestack documentation.
126    
127    
128  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
129    
130         From release 3.3, PCRE has  had  some  support  for  character  strings         From  release  3.3,  PCRE  has  had  some support for character strings
131         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
132         to cover most common requirements, and in release 5.0  additional  sup-         to  cover  most common requirements, and in release 5.0 additional sup-
133         port for Unicode general category properties was added.         port for Unicode general category properties was added.
134    
135         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
136         support in the code, and, in addition,  you  must  call  pcre_compile()         support  in  the  code,  and, in addition, you must call pcre_compile()
137         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
138         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
139         strings instead of just strings of bytes.         strings instead of just strings of bytes.
140    
141         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,
142         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
143         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
144         not be very large.         very big.
145    
146         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
147         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
148         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
149         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
150         for a decimal number. A full list is given in the pcrepattern  documen-         for  a  decimal number, the Unicode script names such as Arabic or Han,
151         tation. The PCRE library is increased in size by about 90K when Unicode         and the derived properties Any and L&. A full  list  is  given  in  the
152         property support is included.         pcrepattern documentation. Only the short names for properties are sup-
153           ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
154           ter},  is  not  supported.   Furthermore,  in Perl, many properties may
155           optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
156           does not support this.
157    
158         The following comments apply when PCRE is running in UTF-8 mode:         The following comments apply when PCRE is running in UTF-8 mode:
159    
160         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
161         subjects  are  checked for validity on entry to the relevant functions.         subjects are checked for validity on entry to the  relevant  functions.
162         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
163         situations,  you  may  already  know  that  your strings are valid, and         situations, you may already know  that  your  strings  are  valid,  and
164         therefore want to skip these checks in order to improve performance. If         therefore want to skip these checks in order to improve performance. If
165         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,
166         PCRE assumes that the pattern or subject  it  is  given  (respectively)         PCRE  assumes  that  the  pattern or subject it is given (respectively)
167         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
168         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
169         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
170         crash.         crash.
171    
172         2. In a pattern, the escape sequence \x{...}, where the contents of the         2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
173         braces  is  a  string  of hexadecimal digits, is interpreted as a UTF-8         two-byte UTF-8 character if the value is greater than 127.
        character whose code number is the given hexadecimal number, for  exam-  
        ple:  \x{1234}.  If a non-hexadecimal digit appears between the braces,  
        the item is not recognized.  This escape sequence can be used either as  
        a literal, or within a character class.  
174    
175         3.  The  original hexadecimal escape sequence, \xhh, matches a two-byte         3. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
176         UTF-8 character if the value is greater than 127.         characters for values greater than \177.
177    
178         4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
179         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
180    
181         5.  The dot metacharacter matches one UTF-8 character instead of a sin-         5. The dot metacharacter matches one UTF-8 character instead of a  sin-
182         gle byte.         gle byte.
183    
184         6. The escape sequence \C can be used to match a single byte  in  UTF-8         6.  The  escape sequence \C can be used to match a single byte in UTF-8
185         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
186         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
187    
188         7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly         7.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
189         test  characters of any code value, but the characters that PCRE recog-         test characters of any code value, but the characters that PCRE  recog-
190         nizes as digits, spaces, or word characters  remain  the  same  set  as         nizes  as  digits,  spaces,  or  word characters remain the same set as
191         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
192         includes Unicode property support, because to do otherwise  would  slow         includes  Unicode  property support, because to do otherwise would slow
193         down  PCRE in many common cases. If you really want to test for a wider         down PCRE in many common cases. If you really want to test for a  wider
194         sense of, say, "digit", you must use Unicode  property  tests  such  as         sense  of,  say,  "digit",  you must use Unicode property tests such as
195         \p{Nd}.         \p{Nd}.
196    
197         8.  Similarly,  characters that match the POSIX named character classes         8. Similarly, characters that match the POSIX named  character  classes
198         are all low-valued characters.         are all low-valued characters.
199    
200         9. Case-insensitive matching applies only to  characters  whose  values         9.  Case-insensitive  matching  applies only to characters whose values
201         are  less than 128, unless PCRE is built with Unicode property support.         are less than 128, unless PCRE is built with Unicode property  support.
202         Even when Unicode property support is available, PCRE  still  uses  its         Even  when  Unicode  property support is available, PCRE still uses its
203         own  character  tables when checking the case of low-valued characters,         own character tables when checking the case of  low-valued  characters,
204         so as not to degrade performance.  The Unicode property information  is         so  as not to degrade performance.  The Unicode property information is
205         used only for characters with higher values.         used only for characters with higher values. Even when Unicode property
206           support is available, PCRE supports case-insensitive matching only when
207           there is a one-to-one mapping between a letter's  cases.  There  are  a
208           small  number  of  many-to-one  mappings in Unicode; these are not sup-
209           ported by PCRE.
210    
211    
212  AUTHOR  AUTHOR
213    
214         Philip Hazel         Philip Hazel
215         University Computing Service,         University Computing Service
216         Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
217    
218           Putting an actual email address here seems to have been a spam  magnet,
219           so  I've  taken  it away. If you want to email me, use my two initials,
220           followed by the two digits 10, at the domain cam.ac.uk.
221    
222    
223         Putting  an actual email address here seems to have been a spam magnet,  REVISION
        so I've taken it away. If you want to email me, use my initial and sur-  
        name, separated by a dot, at the domain ucs.cam.ac.uk.  
224    
225  Last updated: 07 March 2005         Last updated: 18 April 2007
226  Copyright (c) 1997-2005 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
227  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
228    
229    
# Line 228  PCRE BUILD-TIME OPTIONS Line 245  PCRE BUILD-TIME OPTIONS
245    
246           ./configure --help           ./configure --help
247    
248         The following sections describe certain options whose names begin  with         The following sections include  descriptions  of  options  whose  names
249         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
250         for the configure command. Because of the  way  that  configure  works,         defaults for the configure command. Because of the way  that  configure
251         --enable  and  --disable  always  come  in  pairs, so the complementary         works,  --enable  and --disable always come in pairs, so the complemen-
252         option always exists as well, but as it specifies the  default,  it  is         tary option always exists as well, but as it specifies the default,  it
253         not described.         is not described.
254    
255    
256  C++ SUPPORT  C++ SUPPORT
# Line 272  UNICODE CHARACTER PROPERTY SUPPORT Line 289  UNICODE CHARACTER PROPERTY SUPPORT
289         to the configure command. This implies UTF-8 support, even if you  have         to the configure command. This implies UTF-8 support, even if you  have
290         not explicitly requested it.         not explicitly requested it.
291    
292         Including  Unicode  property  support  adds around 90K of tables to the         Including  Unicode  property  support  adds around 30K of tables to the
293         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE library. Only the general category properties such as  Lu  and  Nd
294         gory  properties  such as Lu and Nd are supported. Details are given in         are supported. Details are given in the pcrepattern documentation.
        the pcrepattern documentation.  
295    
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-anycrlf
317    
318           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
319           CRLF as indicating a line ending. Finally, a fifth option, specified by
320    
321             --enable-newline-is-any
322    
323           causes PCRE to recognize any Unicode newline sequence.
324    
325           Whatever line ending convention is selected when PCRE is built  can  be
326           overridden  when  the library functions are called. At build time it is
327           conventional to use the standard for your operating system.
328    
329    
330  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
# Line 319  POSIX MALLOC USAGE Line 355  POSIX MALLOC USAGE
355         to the configure command.         to the configure command.
356    
357    
 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.  
   
   
358  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
359    
360         Within  a  compiled  pattern,  offset values are used to point from one         Within  a  compiled  pattern,  offset values are used to point from one
# Line 353  HANDLING VERY LARGE PATTERNS Line 372  HANDLING VERY LARGE PATTERNS
372         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
373         additional bytes when handling them.         additional bytes when handling them.
374    
        If you build PCRE with an increased link size, test 2 (and  test  5  if  
        you  are using UTF-8) will fail. Part of the output of these tests is a  
        representation of the compiled pattern, and this changes with the  link  
        size.  
   
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    CREATING CHARACTER TABLES AT BUILD TIME
433    
434           PCRE uses fixed tables for processing characters whose code values  are
435           less  than 256. By default, PCRE is built with a set of tables that are
436           distributed in the file pcre_chartables.c.dist. These  tables  are  for
437           ASCII codes only. If you add
438    
439             --enable-rebuild-chartables
440    
441           to  the  configure  command, the distributed tables are no longer used.
442           Instead, a program called dftables is compiled and  run.  This  outputs
443           the source for new set of tables, created in the default locale of your
444           C runtime system. (This method of replacing the tables does not work if
445           you  are cross compiling, because dftables is run on the local host. If
446           you need to create alternative tables when cross  compiling,  you  will
447           have to do so "by hand".)
448    
449    
450  USING EBCDIC CODE  USING EBCDIC CODE
451    
452         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
453         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
454         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by
455         adding         adding
456    
457           --enable-ebcdic           --enable-ebcdic
458    
459         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
460           bles.
461    
462    
463    SEE ALSO
464    
465  Last updated: 15 August 2005         pcreapi(3), pcre_config(3).
466  Copyright (c) 1997-2005 University of Cambridge.  
467    
468    AUTHOR
469    
470           Philip Hazel
471           University Computing Service
472           Cambridge CB2 3QH, England.
473    
474    
475    REVISION
476    
477           Last updated: 16 April 2007
478           Copyright (c) 1997-2007 University of Cambridge.
479  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
480    
481    
# Line 431  PCRE MATCHING ALGORITHMS Line 511  PCRE MATCHING ALGORITHMS
511           <something> <something else> <something further>           <something> <something else> <something further>
512    
513         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
514         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
515    
516    
517  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 440  REGULAR EXPRESSIONS AS TREES Line 520  REGULAR EXPRESSIONS AS TREES
520         resented  as  a  tree structure. An unlimited repetition in the pattern         resented  as  a  tree structure. An unlimited repetition in the pattern
521         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
522         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
523         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
524         search  a  tree: depth-first and breadth-first, and these correspond to         tree:  depth-first  and  breadth-first, and these correspond to the two
525         the two matching algorithms provided by PCRE.         matching algorithms provided by PCRE.
526    
527    
528  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
529    
530         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
531         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
532         depth-first search of the pattern tree. That is, it  proceeds  along  a         depth-first search of the pattern tree. That is, it  proceeds  along  a
533         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
534         required. When there is a mismatch, the algorithm  tries  any  alterna-         required. When there is a mismatch, the algorithm  tries  any  alterna-
# Line 472  THE STANDARD MATCHING ALGORITHM Line 552  THE STANDARD MATCHING ALGORITHM
552         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
553    
554    
555  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
556    
557         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
558         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
559         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
560         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
561         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",
562         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
563           keeps multiple states active simultaneously).
564         The  scan  continues until either the end of the subject is reached, or  
565         there are no more unterminated paths. At this point,  terminated  paths         The scan continues until either the end of the subject is  reached,  or
566         represent  the different matching possibilities (if there are none, the         there  are  no more unterminated paths. At this point, terminated paths
567         match has failed).  Thus, if there is more  than  one  possible  match,         represent the different matching possibilities (if there are none,  the
568           match  has  failed).   Thus,  if there is more than one possible match,
569         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-
570         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
571         match (which is necessarily the shortest) has been found.         match (which is necessarily the shortest) has been found.
572    
573         Note that all the matches that are found start at the same point in the         Note that all the matches that are found start at the same point in the
# Line 494  THE DFA MATCHING ALGORITHM Line 575  THE DFA MATCHING ALGORITHM
575    
576           cat(er(pillar)?)           cat(er(pillar)?)
577    
578         is matched against the string "the caterpillar catchment",  the  result         is  matched  against the string "the caterpillar catchment", the result
579         will  be the three strings "cat", "cater", and "caterpillar" that start         will be the three strings "cat", "cater", and "caterpillar" that  start
580         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
581         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
582    
583         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
584         supported by the DFA matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
585    
586         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1.  Because  the  algorithm  finds  all possible matches, the greedy or
587         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
588         ungreedy quantifiers are treated in exactly the same way.         ungreedy quantifiers are treated in exactly the same way. However, pos-
589           sessive quantifiers can make a difference when what follows could  also
590           match what is quantified, for example in a pattern like this:
591    
592             ^a++\w!
593    
594           This  pattern matches "aaab!" but not "aaa!", which would be matched by
595           a non-possessive quantifier. Similarly, if an atomic group is  present,
596           it  is matched as if it were a standalone pattern at the current point,
597           and the longest match is then "locked in" for the rest of  the  overall
598           pattern.
599    
600         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
601         is  not  straightforward  to  keep track of captured substrings for the         is not straightforward to keep track of  captured  substrings  for  the
602         different matching possibilities, and  PCRE's  implementation  of  this         different  matching  possibilities,  and  PCRE's implementation of this
603         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-
604         strings are available.         strings are available.
605    
606         3. Because no substrings are captured, back references within the  pat-         3.  Because no substrings are captured, back references within the pat-
607         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
608    
609         4.  For  the same reason, conditional expressions that use a backrefer-         4. For the same reason, conditional expressions that use  a  backrefer-
610         ence as the condition are not supported.         ence  as  the  condition or test for a specific group recursion are not
611           supported.
612    
613           5. Because many paths through the tree may be  active,  the  \K  escape
614           sequence, which resets the start of the match when encountered (but may
615           be on some paths and not on others), is not  supported.  It  causes  an
616           error if encountered.
617    
618         5. Callouts are supported, but the value of the  capture_top  field  is         6.  Callouts  are  supported, but the value of the capture_top field is
619         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.
620    
621         6.  The \C escape sequence, which (in the standard algorithm) matches a         7.  The \C escape sequence, which (in the standard algorithm) matches a
622         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-
623         rithm moves through the subject string one character at a time, for all         tive algorithm moves through the subject  string  one  character  at  a
624         active paths through the tree.         time, for all active paths through the tree.
625    
626    
627  ADVANTAGES OF THE DFA ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
628    
629         Using the DFA matching algorithm provides the following advantages:         Using  the alternative matching algorithm provides the following advan-
630           tages:
631    
632         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-
633         ically  found,  and  in particular, the longest match is found. To find         ically  found,  and  in particular, the longest match is found. To find
# Line 538  ADVANTAGES OF THE DFA ALGORITHM Line 636  ADVANTAGES OF THE DFA ALGORITHM
636    
637         2.  There is much better support for partial matching. The restrictions         2.  There is much better support for partial matching. The restrictions
638         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-
639         rithm  for partial matching do not apply to the DFA algorithm. For non-         rithm  for  partial matching do not apply to the alternative algorithm.
640         anchored patterns, the starting position of a partial match  is  avail-         For non-anchored patterns, the starting position of a partial match  is
641         able.         available.
642    
643         3.  Because  the  DFA algorithm scans the subject string just once, and         3.  Because  the  alternative  algorithm  scans the subject string just
644         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
645         strings  to  the matching function in several pieces, checking for par-         subject  strings  to  the matching function in several pieces, checking
646         tial matching each time.         for partial matching each time.
647    
648    
649  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
650    
651         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
652    
653         1. It is substantially slower than  the  standard  algorithm.  This  is         1. It is substantially slower than  the  standard  algorithm.  This  is
654         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
# Line 558  DISADVANTAGES OF THE DFA ALGORITHM Line 656  DISADVANTAGES OF THE DFA ALGORITHM
656    
657         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
658    
659         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
660         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
661         rithm.  
662    
663    AUTHOR
664    
665           Philip Hazel
666           University Computing Service
667           Cambridge CB2 3QH, England.
668    
669  Last updated: 28 February 2005  
670  Copyright (c) 1997-2005 University of Cambridge.  REVISION
671    
672           Last updated: 29 May 2007
673           Copyright (c) 1997-2007 University of Cambridge.
674  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
675    
676    
# Line 616  PCRE NATIVE API Line 723  PCRE NATIVE API
723         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
724              const char *name);              const char *name);
725    
726           int pcre_get_stringtable_entries(const pcre *code,
727                const char *name, char **first, char **last);
728    
729         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
730              int stringcount, int stringnumber,              int stringcount, int stringnumber,
731              const char **stringptr);              const char **stringptr);
# Line 654  PCRE NATIVE API Line 764  PCRE NATIVE API
764  PCRE API OVERVIEW  PCRE API OVERVIEW
765    
766         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
767         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
768         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
769         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
770         distributed with PCRE. It is documented in the pcrecpp page.         distributed with PCRE. It is documented in the pcrecpp page.
# Line 676  PCRE API OVERVIEW Line 786  PCRE API OVERVIEW
786    
787         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
788         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
789         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
790         the  subject),  not  just  one. However, this algorithm does not return         point  in  the subject), and scans the subject just once. However, this
791         captured substrings. A description of the two matching  algorithms  and         algorithm does not return captured substrings. A description of the two
792         their  advantages  and disadvantages is given in the pcrematching docu-         matching  algorithms and their advantages and disadvantages is given in
793         mentation.         the pcrematching documentation.
794    
795         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
796         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 692  PCRE API OVERVIEW Line 802  PCRE API OVERVIEW
802           pcre_get_named_substring()           pcre_get_named_substring()
803           pcre_get_substring_list()           pcre_get_substring_list()
804           pcre_get_stringnumber()           pcre_get_stringnumber()
805             pcre_get_stringtable_entries()
806    
807         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
808         to free the memory used for extracted strings.         to free the memory used for extracted strings.
# Line 723  PCRE API OVERVIEW Line 834  PCRE API OVERVIEW
834         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
835         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
836         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
837         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
838         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-
839         management, it runs more slowly.  Separate functions  are  provided  so         ments that have limited stacks. Because of the greater  use  of  memory
840         that  special-purpose  external  code  can  be used for this case. When         management,  it  runs  more  slowly. Separate functions are provided so
841         used, these functions are always called in a  stack-like  manner  (last         that special-purpose external code can be  used  for  this  case.  When
842         obtained,  first freed), and always for memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
843           obtained, first freed), and always for memory blocks of the same  size.
844           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
845           mentation.
846    
847         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
848         by  the  caller  to  a "callout" function, which PCRE will then call at         by  the  caller  to  a "callout" function, which PCRE will then call at
# Line 736  PCRE API OVERVIEW Line 850  PCRE API OVERVIEW
850         pcrecallout documentation.         pcrecallout documentation.
851    
852    
853    NEWLINES
854    
855           PCRE  supports five different conventions for indicating line breaks in
856           strings: a single CR (carriage return) character, a  single  LF  (line-
857           feed) character, the two-character sequence CRLF, any of the three pre-
858           ceding, or any Unicode newline sequence. The Unicode newline  sequences
859           are  the  three just mentioned, plus the single characters VT (vertical
860           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
861           separator, U+2028), and PS (paragraph separator, U+2029).
862    
863           Each  of  the first three conventions is used by at least one operating
864           system as its standard newline sequence. When PCRE is built, a  default
865           can  be  specified.  The default default is LF, which is the Unix stan-
866           dard. When PCRE is run, the default can be overridden,  either  when  a
867           pattern is compiled, or when it is matched.
868    
869           In the PCRE documentation the word "newline" is used to mean "the char-
870           acter or pair of characters that indicate a line break". The choice  of
871           newline  convention  affects  the  handling of the dot, circumflex, and
872           dollar metacharacters, the handling of #-comments in /x mode, and, when
873           CRLF  is a recognized line ending sequence, the match position advance-
874           ment for a non-anchored pattern. The choice of newline convention  does
875           not affect the interpretation of the \n or \r escape sequences.
876    
877    
878  MULTITHREADING  MULTITHREADING
879    
880         The  PCRE  functions  can be used in multi-threading applications, with         The  PCRE  functions  can be used in multi-threading applications, with
# Line 753  SAVING PRECOMPILED PATTERNS FOR LATER US Line 892  SAVING PRECOMPILED PATTERNS FOR LATER US
892         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
893         later time, possibly by a different program, and even on a  host  other         later time, possibly by a different program, and even on a  host  other
894         than  the  one  on  which  it  was  compiled.  Details are given in the         than  the  one  on  which  it  was  compiled.  Details are given in the
895         pcreprecompile documentation.         pcreprecompile documentation. However, compiling a  regular  expression
896           with  one version of PCRE for use with a different version is not guar-
897           anteed to work and may cause crashes.
898    
899    
900  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
# Line 782  CHECKING BUILD-TIME OPTIONS Line 923  CHECKING BUILD-TIME OPTIONS
923    
924           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
925    
926         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
927         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
928         return (13), and should normally be the  standard  character  for  your         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
929         operating system.         and  -1  for  ANY. The default should normally be the standard sequence
930           for your operating system.
931    
932           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
933    
934         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
935         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
936         4.  Larger  values  allow larger regular expressions to be compiled, at         4. Larger values allow larger regular expressions to  be  compiled,  at
937         the expense of slower matching. The default value of  2  is  sufficient         the  expense  of  slower matching. The default value of 2 is sufficient
938         for  all  but  the  most massive patterns, since it allows the compiled         for all but the most massive patterns, since  it  allows  the  compiled
939         pattern to be up to 64K in size.         pattern to be up to 64K in size.
940    
941           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
942    
943         The output is an integer that contains the threshold  above  which  the         The  output  is  an integer that contains the threshold above which the
944         POSIX  interface  uses malloc() for output vectors. Further details are         POSIX interface uses malloc() for output vectors. Further  details  are
945         given in the pcreposix documentation.         given in the pcreposix documentation.
946    
947           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
948    
949         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
950         internal  matching  function  calls in a pcre_exec() execution. Further         internal matching function calls in a  pcre_exec()  execution.  Further
951         details are given with pcre_exec() below.         details are given with pcre_exec() below.
952    
953             PCRE_CONFIG_MATCH_LIMIT_RECURSION
954    
955           The  output is an integer that gives the default limit for the depth of
956           recursion when calling the internal matching function in a  pcre_exec()
957           execution. Further details are given with pcre_exec() below.
958    
959           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
960    
961         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
962         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
963         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
964         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
965         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
966         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
967         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
968    
969    
# Line 832  COMPILING A PATTERN Line 980  COMPILING A PATTERN
980    
981         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
982         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
983         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
984         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
985    
986         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
987         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
988         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
989         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
990         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
991         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
992         required.         longer required.
993    
994         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
995         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
996         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
997         ment, which is an address (see below).         ment, which is an address (see below).
998    
999         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
1000         tion.  It  should  be  zero  if  no options are required. The available         pilation. It should be zero if no options are required.  The  available
1001         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them, in particular, those that
1002         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
1003         pattern (see the detailed description  in  the  pcrepattern  documenta-         pattern  (see  the  detailed  description in the pcrepattern documenta-
1004         tion).  For  these options, the contents of the options argument speci-         tion). For these options, the contents of the options  argument  speci-
1005         fies their initial settings at the start of compilation and  execution.         fies  their initial settings at the start of compilation and execution.
1006         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
1007         at compile time.         of matching as well as at compile time.
1008    
1009         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1010         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1011         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-
1012         sage.  The  offset from the start of the pattern to the character where         sage. This is a static string that is part of the library. You must not
1013         the error was discovered is  placed  in  the  variable  pointed  to  by         try to free it. The offset from the start of the pattern to the charac-
1014         erroffset,  which  must  not  be  NULL. If it is, an immediate error is         ter where the error was discovered is placed in the variable pointed to
1015           by  erroffset,  which must not be NULL. If it is, an immediate error is
1016         given.         given.
1017    
1018         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
# Line 926  COMPILING A PATTERN Line 1075  COMPILING A PATTERN
1075    
1076         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
1077         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
1078         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
1079         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1080         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
1081         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1082    
1083           PCRE_DOTALL           PCRE_DOTALL
1084    
1085         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-
1086         acters, including newlines. Without it,  newlines  are  excluded.  This         acters, including those that indicate newline. Without it, a  dot  does
1087         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
1088         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
1089         always  matches a newline character, independent of the setting of this         by  a (?s) option setting. A negative class such as [^a] always matches
1090         option.         newline characters, independent of the setting of this option.
1091    
1092             PCRE_DUPNAMES
1093    
1094           If this bit is set, names used to identify capturing  subpatterns  need
1095           not be unique. This can be helpful for certain types of pattern when it
1096           is known that only one instance of the named  subpattern  can  ever  be
1097           matched.  There  are  more details of named subpatterns below; see also
1098           the pcrepattern documentation.
1099    
1100           PCRE_EXTENDED           PCRE_EXTENDED
1101    
# Line 946  COMPILING A PATTERN Line 1103  COMPILING A PATTERN
1103         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1104         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1105         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1106         line character, inclusive, are also  ignored.  This  is  equivalent  to         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1107         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-
1108         option setting.         ting.
1109    
1110         This option makes it possible to include  comments  inside  complicated         This option makes it possible to include  comments  inside  complicated
1111         patterns.   Note,  however,  that this applies only to data characters.         patterns.   Note,  however,  that this applies only to data characters.
# Line 964  COMPILING A PATTERN Line 1121  COMPILING A PATTERN
1121         letter  that  has  no  special  meaning causes an error, thus reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1122         these combinations for future expansion. By  default,  as  in  Perl,  a         these combinations for future expansion. By  default,  as  in  Perl,  a
1123         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
1124         literal. There are at present no  other  features  controlled  by  this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1125         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
1126           can also be set by a (?X) option setting within a pattern.
1127    
1128           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1129    
1130         If  this  option  is  set,  an  unanchored pattern is required to match         If this option is set, an  unanchored  pattern  is  required  to  match
1131         before or at the first newline character in the subject string,  though         before  or  at  the  first  newline  in  the subject string, though the
1132         the matched text may continue over the newline.         matched text may continue over the newline.
1133    
1134           PCRE_MULTILINE           PCRE_MULTILINE
1135    
1136         By  default,  PCRE  treats the subject string as consisting of a single         By default, PCRE treats the subject string as consisting  of  a  single
1137         line of characters (even if it actually contains newlines). The  "start         line  of characters (even if it actually contains newlines). The "start
1138         of  line"  metacharacter  (^)  matches only at the start of the string,         of line" metacharacter (^) matches only at the  start  of  the  string,
1139         while the "end of line" metacharacter ($) matches only at  the  end  of         while  the  "end  of line" metacharacter ($) matches only at the end of
1140         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1141         is set). This is the same as Perl.         is set). This is the same as Perl.
1142    
1143         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"
1144         constructs  match  immediately following or immediately before any new-         constructs match immediately following or immediately  before  internal
1145         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
1146         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
1147         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-
1148         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,
1149         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1150    
1151             PCRE_NEWLINE_CR
1152             PCRE_NEWLINE_LF
1153             PCRE_NEWLINE_CRLF
1154             PCRE_NEWLINE_ANYCRLF
1155             PCRE_NEWLINE_ANY
1156    
1157           These  options  override the default newline definition that was chosen
1158           when PCRE was built. Setting the first or the second specifies  that  a
1159           newline  is  indicated  by a single character (CR or LF, respectively).
1160           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1161           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1162           that any of the three preceding sequences should be recognized. Setting
1163           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1164           recognized. The Unicode newline sequences are the three just mentioned,
1165           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1166           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1167           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1168           UTF-8 mode.
1169    
1170           The newline setting in the  options  word  uses  three  bits  that  are
1171           treated as a number, giving eight possibilities. Currently only six are
1172           used (default plus the five values above). This means that if  you  set
1173           more  than one newline option, the combination may or may not be sensi-
1174           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1175           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1176           cause an error.
1177    
1178           The only time that a line break is specially recognized when  compiling
1179           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1180           character class is encountered. This indicates  a  comment  that  lasts
1181           until  after the next line break sequence. In other circumstances, line
1182           break  sequences  are  treated  as  literal  data,   except   that   in
1183           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1184           and are therefore ignored.
1185    
1186           The newline option that is set at compile time becomes the default that
1187           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1188    
1189           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1190    
1191         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
# Line 1031  COMPILATION ERROR CODES Line 1227  COMPILATION ERROR CODES
1227    
1228         The following table lists the error  codes  than  may  be  returned  by         The following table lists the error  codes  than  may  be  returned  by
1229         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(),  along with the error messages that may be returned by
1230         both compiling functions.         both compiling functions. As PCRE has developed, some error codes  have
1231           fallen out of use. To avoid confusion, they have not been re-used.
1232    
1233            0  no error            0  no error
1234            1  \ at end of pattern            1  \ at end of pattern
# Line 1043  COMPILATION ERROR CODES Line 1240  COMPILATION ERROR CODES
1240            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1241            8  range out of order in character class            8  range out of order in character class
1242            9  nothing to repeat            9  nothing to repeat
1243           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1244           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1245           12  unrecognized character after (?           12  unrecognized character after (?
1246           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
# Line 1052  COMPILATION ERROR CODES Line 1249  COMPILATION ERROR CODES
1249           16  erroffset passed as NULL           16  erroffset passed as NULL
1250           17  unknown option bit(s) set           17  unknown option bit(s) set
1251           18  missing ) after comment           18  missing ) after comment
1252           19  parentheses nested too deeply           19  [this code is not in use]
1253           20  regular expression too large           20  regular expression too large
1254           21  failed to get memory           21  failed to get memory
1255           22  unmatched parentheses           22  unmatched parentheses
1256           23  internal error: code overflow           23  internal error: code overflow
1257           24  unrecognized character after (?<           24  unrecognized character after (?<
1258           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1259           26  malformed number after (?(           26  malformed number or name after (?(
1260           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1261           28  assertion expected after (?(           28  assertion expected after (?(
1262           29  (?R or (?digits must be followed by )           29  (?R or (?digits must be followed by )
1263           30  unknown POSIX class name           30  unknown POSIX class name
1264           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1265           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1266           33  spare error           33  [this code is not in use]
1267           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1268           35  invalid condition (?(0)           35  invalid condition (?(0)
1269           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1075  COMPILATION ERROR CODES Line 1272  COMPILATION ERROR CODES
1272           39  closing ) for (?C expected           39  closing ) for (?C expected
1273           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1274           41  unrecognized character after (?P           41  unrecognized character after (?P
1275           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1276           43  two named groups have the same name           43  two named subpatterns have the same name
1277           44  invalid UTF-8 string           44  invalid UTF-8 string
1278           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1279           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1280           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1281             48  subpattern name is too long (maximum 32 characters)
1282             49  too many named subpatterns (maximum 10,000)
1283             50  repeated subpattern is too long
1284             51  octal value is greater than \377 (not in UTF-8 mode)
1285             52  internal error: overran compiling workspace
1286             53   internal  error:  previously-checked  referenced  subpattern not
1287           found
1288             54  DEFINE group contains more than one branch
1289             55  repeating a DEFINE group is not allowed
1290             56  inconsistent NEWLINE options"
1291    
1292    
1293  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1111  STUDYING A PATTERN Line 1318  STUDYING A PATTERN
1318    
1319         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.
1320         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1321         points  to  is set to NULL. Otherwise it points to a textual error mes-         points  to  is  set  to NULL. Otherwise it is set to point to a textual
1322         sage. You should therefore test the error pointer for NULL after  call-         error message. This is a static string that is part of the library. You
1323         ing pcre_study(), to be sure that it has run successfully.         must  not  try  to  free it. You should test the error pointer for NULL
1324           after calling pcre_study(), to be sure that it has run successfully.
1325    
1326         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1327    
# Line 1124  STUDYING A PATTERN Line 1332  STUDYING A PATTERN
1332             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1333    
1334         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1335         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-
1336         ble starting bytes is created.         ble starting bytes is created.
1337    
1338    
1339  LOCALE SUPPORT  LOCALE SUPPORT
1340    
1341         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1342         letters digits, or whatever, by reference to a set of  tables,  indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1343         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
1344         characters with codes less than 128. Higher-valued  codes  never  match         characters  with  codes  less than 128. Higher-valued codes never match
1345         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
1346         with Unicode character property support.         with  Unicode  character property support. The use of locales with Uni-
1347           code is discouraged. If you are handling characters with codes  greater
1348         An internal set of tables is created in the default C locale when  PCRE         than  128, you should either use UTF-8 and Unicode, or use locales, but
1349         is  built.  This  is  used when the final argument of pcre_compile() is         not try to mix the two.
1350         NULL, and is sufficient for many applications. An  alternative  set  of  
1351         tables  can,  however, be supplied. These may be created in a different         PCRE contains an internal set of tables that are used  when  the  final
1352         locale from the default. As more and more applications change to  using         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1353         Unicode, the need for this locale support is expected to die away.         applications.  Normally, the internal tables recognize only ASCII char-
1354           acters. However, when PCRE is built, it is possible to cause the inter-
1355         External  tables  are  built by calling the pcre_maketables() function,         nal tables to be rebuilt in the default "C" locale of the local system,
1356         which has no arguments, in the relevant locale. The result can then  be         which may cause them to be different.
1357         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For  
1358         example, to build and use tables that are appropriate  for  the  French         The  internal tables can always be overridden by tables supplied by the
1359         locale  (where  accented  characters  with  values greater than 128 are         application that calls PCRE. These may be created in a different locale
1360           from  the  default.  As more and more applications change to using Uni-
1361           code, the need for this locale support is expected to die away.
1362    
1363           External tables are built by calling  the  pcre_maketables()  function,
1364           which  has no arguments, in the relevant locale. The result can then be
1365           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1366           example,  to  build  and use tables that are appropriate for the French
1367           locale (where accented characters with  values  greater  than  128  are
1368         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1369    
1370           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1371           tables = pcre_maketables();           tables = pcre_maketables();
1372           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1373    
1374           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1375           if you are using Windows, the name for the French locale is "french".
1376    
1377         When pcre_maketables() runs, the tables are built  in  memory  that  is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1378         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1379         that the memory containing the tables remains available for as long  as         that the memory containing the tables remains available for as long  as
# Line 1200  INFORMATION ABOUT A PATTERN Line 1419  INFORMATION ABOUT A PATTERN
1419         pattern:         pattern:
1420    
1421           int rc;           int rc;
1422           unsigned long int length;           size_t length;
1423           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1424             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1425             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
# Line 1232  INFORMATION ABOUT A PATTERN Line 1451  INFORMATION ABOUT A PATTERN
1451           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1452    
1453         Return  information  about  the first byte of any matched string, for a         Return  information  about  the first byte of any matched string, for a
1454         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored pattern. The fourth argument should point to an int  vari-
1455         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1456         compatibility.)         is still recognized for backwards compatibility.)
1457    
1458         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
1459         (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  
1460    
1461         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1462         branch starts with "^", or         branch starts with "^", or
1463    
1464         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1465         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1466    
1467         -1 is returned, indicating that the pattern matches only at  the  start         -1  is  returned, indicating that the pattern matches only at the start
1468         of  a  subject string or after any newline within the string. Otherwise         of a subject string or after any newline within the  string.  Otherwise
1469         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1470    
1471           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1472    
1473         If the pattern was studied, and this resulted in the construction of  a         If  the pattern was studied, and this resulted in the construction of a
1474         256-bit table indicating a fixed set of bytes for the first byte in any         256-bit table indicating a fixed set of bytes for the first byte in any
1475         matching string, a pointer to the table is returned. Otherwise NULL  is         matching  string, a pointer to the table is returned. Otherwise NULL is
1476         returned.  The fourth argument should point to an unsigned char * vari-         returned. The fourth argument should point to an unsigned char *  vari-
1477         able.         able.
1478    
1479             PCRE_INFO_JCHANGED
1480    
1481           Return  1  if the (?J) option setting is used in the pattern, otherwise
1482           0. The fourth argument should point to an int variable. The (?J) inter-
1483           nal option setting changes the local PCRE_DUPNAMES value.
1484    
1485           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1486    
1487         Return the value of the rightmost literal byte that must exist  in  any         Return  the  value of the rightmost literal byte that must exist in any
1488         matched  string,  other  than  at  its  start,  if such a byte has been         matched string, other than at its  start,  if  such  a  byte  has  been
1489         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1490         is  no such byte, -1 is returned. For anchored patterns, a last literal         is no such byte, -1 is returned. For anchored patterns, a last  literal
1491         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1492         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1493         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1494    
# Line 1272  INFORMATION ABOUT A PATTERN Line 1496  INFORMATION ABOUT A PATTERN
1496           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1497           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1498    
1499         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1500         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1501         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1502         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1503         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
1504         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
1505         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1506         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
1507         which is described by these three values.         described by these three values.
1508    
1509         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
1510         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1511         of each entry; both of these  return  an  int  value.  The  entry  size         of  each  entry;  both  of  these  return  an int value. The entry size
1512         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1513         a pointer to the first entry of the table  (a  pointer  to  char).  The         a  pointer  to  the  first  entry of the table (a pointer to char). The
1514         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-
1515         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-
1516         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1517         For example, consider the following pattern  (assume  PCRE_EXTENDED  is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1518         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1519           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1520           ignored):
1521    
1522           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1523           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1524    
1525         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1526         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,
1527         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1528         as ??:         as ??:
1529    
# Line 1306  INFORMATION ABOUT A PATTERN Line 1532  INFORMATION ABOUT A PATTERN
1532           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1533           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1534    
1535         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1536         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
1537         be different for each compiled pattern.         to be different for each compiled pattern.
1538    
1539             PCRE_INFO_OKPARTIAL
1540    
1541           Return  1 if the pattern can be used for partial matching, otherwise 0.
1542           The fourth argument should point to an int  variable.  The  pcrepartial
1543           documentation  lists  the restrictions that apply to patterns when par-
1544           tial matching is used.
1545    
1546           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1547    
# Line 1428  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1661  MATCHING A PATTERN: THE TRADITIONAL FUNC
1661         If the extra argument is not NULL, it must point to a  pcre_extra  data         If the extra argument is not NULL, it must point to a  pcre_extra  data
1662         block.  The pcre_study() function returns such a block (when it doesn't         block.  The pcre_study() function returns such a block (when it doesn't
1663         return NULL), but you can also create one for yourself, and pass  addi-         return NULL), but you can also create one for yourself, and pass  addi-
1664         tional  information in it. The fields in a pcre_extra block are as fol-         tional  information  in it. The pcre_extra block contains the following
1665         lows:         fields (not necessarily in this order):
1666    
1667           unsigned long int flags;           unsigned long int flags;
1668           void *study_data;           void *study_data;
1669           unsigned long int match_limit;           unsigned long int match_limit;
1670             unsigned long int match_limit_recursion;
1671           void *callout_data;           void *callout_data;
1672           const unsigned char *tables;           const unsigned char *tables;
1673    
# Line 1442  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1676  MATCHING A PATTERN: THE TRADITIONAL FUNC
1676    
1677           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1678           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1679             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1680           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1681           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1682    
# Line 1458  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1693  MATCHING A PATTERN: THE TRADITIONAL FUNC
1693         repeats.         repeats.
1694    
1695         Internally,  PCRE uses a function called match() which it calls repeat-         Internally,  PCRE uses a function called match() which it calls repeat-
1696         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly (sometimes recursively). The limit set by match_limit  is  imposed
1697         times  this  function is called during a match, which has the effect of         on  the  number  of times this function is called during a match, which
1698         limiting the amount of recursion and backtracking that can take  place.         has the effect of limiting the amount of  backtracking  that  can  take
1699         For patterns that are not anchored, the count starts from zero for each         place. For patterns that are not anchored, the count restarts from zero
1700         position in the subject string.         for each position in the subject string.
1701    
1702         The default limit for the library can be set when PCRE  is  built;  the         The default value for the limit can be set  when  PCRE  is  built;  the
1703         default  default  is 10 million, which handles all but the most extreme         default  default  is 10 million, which handles all but the most extreme
1704         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases. You can override the default  by  suppling  pcre_exec()  with  a
1705         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra     block    in    which    match_limit    is    set,    and
1706         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is
1707         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1708    
1709           The  match_limit_recursion field is similar to match_limit, but instead
1710           of limiting the total number of times that match() is called, it limits
1711           the  depth  of  recursion. The recursion depth is a smaller number than
1712           the total number of calls, because not all calls to match() are  recur-
1713           sive.  This limit is of use only if it is set smaller than match_limit.
1714    
1715           Limiting the recursion depth limits the amount of  stack  that  can  be
1716           used, or, when PCRE has been compiled to use memory on the heap instead
1717           of the stack, the amount of heap memory that can be used.
1718    
1719           The default value for match_limit_recursion can be  set  when  PCRE  is
1720           built;  the  default  default  is  the  same  value  as the default for
1721           match_limit. You can override the default by suppling pcre_exec()  with
1722           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1723           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1724           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1725    
1726         The  pcre_callout  field is used in conjunction with the "callout" fea-         The  pcre_callout  field is used in conjunction with the "callout" fea-
1727         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1728    
# Line 1488  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1740  MATCHING A PATTERN: THE TRADITIONAL FUNC
1740     Option bits for pcre_exec()     Option bits for pcre_exec()
1741    
1742         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.
1743         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,
1744         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1745           PCRE_PARTIAL.
1746    
1747           PCRE_ANCHORED           PCRE_ANCHORED
1748    
1749         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
1750         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
1751         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
1752         unachored at matching time.         unachored at matching time.
1753    
1754             PCRE_NEWLINE_CR
1755             PCRE_NEWLINE_LF
1756             PCRE_NEWLINE_CRLF
1757             PCRE_NEWLINE_ANYCRLF
1758             PCRE_NEWLINE_ANY
1759    
1760           These  options  override  the  newline  definition  that  was chosen or
1761           defaulted when the pattern was compiled. For details, see the  descrip-
1762           tion  of  pcre_compile()  above.  During  matching,  the newline choice
1763           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1764           ters.  It may also alter the way the match position is advanced after a
1765           match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,
1766           PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY is set, and a match attempt
1767           fails when the current position is at a CRLF sequence, the match  posi-
1768           tion  is  advanced by two characters instead of one, in other words, to
1769           after the CRLF.
1770    
1771           PCRE_NOTBOL           PCRE_NOTBOL
1772    
1773         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
# Line 1633  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1903  MATCHING A PATTERN: THE TRADITIONAL FUNC
1903         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-
1904         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1],  identify  the  portion  of  the  subject string matched by the
1905         entire pattern. The next pair is used for the first  capturing  subpat-         entire pattern. The next pair is used for the first  capturing  subpat-
1906         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
1907         pairs that have been set. If there are no  capturing  subpatterns,  the         highest numbered pair that has been set. For example, if two substrings
1908         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
1909         first pair of offsets has been set.         subpatterns, the return value from a successful match is 1,  indicating
1910           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.  
1911    
1912         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1913         of the string that it matched that is returned.         of the string that it matched that is returned.
1914    
1915         If  the vector is too small to hold all the captured substring offsets,         If the vector is too small to hold all the captured substring  offsets,
1916         it is used as far as possible (up to two-thirds of its length), and the         it is used as far as possible (up to two-thirds of its length), and the
1917         function  returns a value of zero. In particular, if the substring off-         function returns a value of zero. In particular, if the substring  off-
1918         sets are not of interest, pcre_exec() may be called with ovector passed         sets are not of interest, pcre_exec() may be called with ovector passed
1919         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         as NULL and ovecsize as zero. However, if  the  pattern  contains  back
1920         references and the ovector is not big enough to  remember  the  related         references  and  the  ovector is not big enough to remember the related
1921         substrings,  PCRE has to get additional memory for use during matching.         substrings, PCRE has to get additional memory for use during  matching.
1922         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1923    
1924         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
1925         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
1926         that will allow for n captured substrings, in addition to  the  offsets         ovector  that  will allow for n captured substrings, in addition to the
1927         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.
1928    
1929           It is possible for capturing subpattern number n+1 to match  some  part
1930           of the subject when subpattern n has not been used at all. For example,
1931           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1932           return from the function is 4, and subpatterns 1 and 3 are matched, but
1933           2 is not. When this happens, both values in  the  offset  pairs  corre-
1934           sponding to unused subpatterns are set to -1.
1935    
1936           Offset  values  that correspond to unused subpatterns at the end of the
1937           expression are also set to -1. For example,  if  the  string  "abc"  is
1938           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1939           matched. The return from the function is 2, because  the  highest  used
1940           capturing subpattern number is 1. However, you can refer to the offsets
1941           for the second and third capturing subpatterns if  you  wish  (assuming
1942           the vector is large enough, of course).
1943    
1944     Return values from pcre_exec()         Some  convenience  functions  are  provided for extracting the captured
1945           substrings as separate strings. These are described below.
1946    
1947         If  pcre_exec()  fails, it returns a negative number. The following are     Error return values from pcre_exec()
1948    
1949           If pcre_exec() fails, it returns a negative number. The  following  are
1950         defined in the header file:         defined in the header file:
1951    
1952           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1676  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1955  MATCHING A PATTERN: THE TRADITIONAL FUNC
1955    
1956           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
1957    
1958         Either code or subject was passed as NULL,  or  ovector  was  NULL  and         Either  code  or  subject  was  passed as NULL, or ovector was NULL and
1959         ovecsize was not zero.         ovecsize was not zero.
1960    
1961           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1685  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1964  MATCHING A PATTERN: THE TRADITIONAL FUNC
1964    
1965           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
1966    
1967         PCRE  stores a 4-byte "magic number" at the start of the compiled code,         PCRE stores a 4-byte "magic number" at the start of the compiled  code,
1968         to catch the case when it is passed a junk pointer and to detect when a         to catch the case when it is passed a junk pointer and to detect when a
1969         pattern that was compiled in an environment of one endianness is run in         pattern that was compiled in an environment of one endianness is run in
1970         an environment with the other endianness. This is the error  that  PCRE         an  environment  with the other endianness. This is the error that PCRE
1971         gives when the magic number is not present.         gives when the magic number is not present.
1972    
1973           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1974    
1975         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1976         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
1977         overwriting of the compiled pattern.         overwriting of the compiled pattern.
1978    
1979           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
1980    
1981         If  a  pattern contains back references, but the ovector that is passed         If a pattern contains back references, but the ovector that  is  passed
1982         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
1983         PCRE  gets  a  block of memory at the start of matching to use for this         PCRE gets a block of memory at the start of matching to  use  for  this
1984         purpose. If the call via pcre_malloc() fails, this error is given.  The         purpose.  If the call via pcre_malloc() fails, this error is given. The
1985         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
1986    
1987           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
1988    
1989         This  error is used by the pcre_copy_substring(), pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
1990         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
1991         returned by pcre_exec().         returned by pcre_exec().
1992    
1993           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
1994    
1995         The  recursion  and backtracking limit, as specified by the match_limit         The backtracking limit, as specified by  the  match_limit  field  in  a
1996         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra  structure  (or  defaulted) was reached. See the description
1997         description above.         above.
1998    
1999           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2000    
2001         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
2002         use by callout functions that want to yield a distinctive  error  code.         use  by  callout functions that want to yield a distinctive error code.
2003         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2004    
2005           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2006    
2007         A  string  that contains an invalid UTF-8 byte sequence was passed as a         A string that contains an invalid UTF-8 byte sequence was passed  as  a
2008         subject.         subject.
2009    
2010           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2011    
2012         The UTF-8 byte sequence that was passed as a subject was valid, but the         The UTF-8 byte sequence that was passed as a subject was valid, but the
2013         value  of startoffset did not point to the beginning of a UTF-8 charac-         value of startoffset did not point to the beginning of a UTF-8  charac-
2014         ter.         ter.
2015    
2016           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2017    
2018         The subject string did not match, but it did match partially.  See  the         The  subject  string did not match, but it did match partially. See the
2019         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2020    
2021           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2022    
2023         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
2024         items that are not supported for partial matching. See the  pcrepartial         items  that are not supported for partial matching. See the pcrepartial
2025         documentation for details of partial matching.         documentation for details of partial matching.
2026    
2027           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2028    
2029         An  unexpected  internal error has occurred. This error could be caused         An unexpected internal error has occurred. This error could  be  caused
2030         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2031    
2032           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2033    
2034         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.
2035    
2036             PCRE_ERROR_RECURSIONLIMIT (-21)
2037    
2038           The internal recursion limit, as specified by the match_limit_recursion
2039           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2040           description above.
2041    
2042             PCRE_ERROR_NULLWSLIMIT    (-22)
2043    
2044           When a group that can match an empty  substring  is  repeated  with  an
2045           unbounded  upper  limit, the subject position at the start of the group
2046           must be remembered, so that a test for an empty string can be made when
2047           the  end  of the group is reached. Some workspace is required for this;
2048           if it runs out, this error is given.
2049    
2050             PCRE_ERROR_BADNEWLINE     (-23)
2051    
2052           An invalid combination of PCRE_NEWLINE_xxx options was given.
2053    
2054           Error numbers -16 to -20 are not used by pcre_exec().
2055    
2056    
2057  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 1768  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2067  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2067         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2068              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2069    
2070         Captured  substrings  can  be  accessed  directly  by using the offsets         Captured substrings can be  accessed  directly  by  using  the  offsets
2071         returned by pcre_exec() in  ovector.  For  convenience,  the  functions         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2072         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2073         string_list() are provided for extracting captured substrings  as  new,         string_list()  are  provided for extracting captured substrings as new,
2074         separate,  zero-terminated strings. These functions identify substrings         separate, zero-terminated strings. These functions identify  substrings
2075         by number. The next section describes functions  for  extracting  named         by  number.  The  next section describes functions for extracting named
2076         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2077         extracted and has a further zero added on the end, but  the  result  is  
2078         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2079           a  further zero added on the end, but the result is not, of course, a C
2080           string.  However, you can process such a string  by  referring  to  the
2081           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2082           string().  Unfortunately, the interface to pcre_get_substring_list() is
2083           not  adequate for handling strings containing binary zeros, because the
2084           end of the final string is not independently indicated.
2085    
2086         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-
2087         tions: subject is the subject string that has  just  been  successfully         tions:  subject  is  the subject string that has just been successfully
2088         matched, ovector is a pointer to the vector of integer offsets that was         matched, ovector is a pointer to the vector of integer offsets that was
2089         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2090         were  captured  by  the match, including the substring that matched the         were captured by the match, including the substring  that  matched  the
2091         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2092         it  is greater than zero. If pcre_exec() returned zero, indicating that         it is greater than zero. If pcre_exec() returned zero, indicating  that
2093         it ran out of space in ovector, the value passed as stringcount  should         it  ran out of space in ovector, the value passed as stringcount should
2094         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2095    
2096         The  functions pcre_copy_substring() and pcre_get_substring() extract a         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2097         single substring, whose number is given as  stringnumber.  A  value  of         single  substring,  whose  number  is given as stringnumber. A value of
2098         zero  extracts  the  substring that matched the entire pattern, whereas         zero extracts the substring that matched the  entire  pattern,  whereas
2099         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2100         string(),  the  string  is  placed  in buffer, whose length is given by         string(), the string is placed in buffer,  whose  length  is  given  by
2101         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2102         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2103         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
2104         the terminating zero, or one of         the terminating zero, or one of these error codes:
2105    
2106           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2107    
2108         The  buffer  was too small for pcre_copy_substring(), or the attempt to         The buffer was too small for pcre_copy_substring(), or the  attempt  to
2109         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2110    
2111           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2112    
2113         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2114    
2115         The pcre_get_substring_list()  function  extracts  all  available  sub-         The  pcre_get_substring_list()  function  extracts  all  available sub-
2116         strings  and  builds  a list of pointers to them. All this is done in a         strings and builds a list of pointers to them. All this is  done  in  a
2117         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
2118         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
2119         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
2120         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
2121           error code
2122    
2123           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2124    
# Line 1831  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2137  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2137         tively.  They  do  nothing  more  than  call the function pointed to by         tively.  They  do  nothing  more  than  call the function pointed to by
2138         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.
2139         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-
2140         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2141         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-
2142         vided.         vided.
2143    
# Line 1854  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2160  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2160         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-
2161         ber.  For example, for this pattern         ber.  For example, for this pattern
2162    
2163           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2164    
2165         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
2166         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
2167         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-
2168         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
2169         there is no subpattern of that name.         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2170           subpattern of that name.
2171    
2172         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
2173         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2174         are also two functions that do the whole job.         are also two functions that do the whole job.
2175    
2176         Most    of    the    arguments   of   pcre_copy_named_substring()   and         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2177         pcre_get_named_substring() are the same  as  those  for  the  similarly         pcre_get_named_substring()  are  the  same  as  those for the similarly
2178         named  functions  that extract by number. As these are described in the         named functions that extract by number. As these are described  in  the
2179         previous section, they are not re-described here. There  are  just  two         previous  section,  they  are not re-described here. There are just two
2180         differences:         differences:
2181    
2182         First,  instead  of a substring number, a substring name is given. Sec-         First, instead of a substring number, a substring name is  given.  Sec-
2183         ond, there is an extra argument, given at the start, which is a pointer         ond, there is an extra argument, given at the start, which is a pointer
2184         to  the compiled pattern. This is needed in order to gain access to the         to the compiled pattern. This is needed in order to gain access to  the
2185         name-to-number translation table.         name-to-number translation table.
2186    
2187         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2188         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2189         ate.         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2190           behaviour may not be what you want (see the next section).
2191    
2192    
2193    DUPLICATE SUBPATTERN NAMES
2194    
2195           int pcre_get_stringtable_entries(const pcre *code,
2196                const char *name, char **first, char **last);
2197    
2198           When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2199           subpatterns  are  not  required  to  be unique. Normally, patterns with
2200           duplicate names are such that in any one match, only one of  the  named
2201           subpatterns  participates. An example is shown in the pcrepattern docu-
2202           mentation. When duplicates are present, pcre_copy_named_substring() and
2203           pcre_get_named_substring()  return the first substring corresponding to
2204           the given name that is set.  If  none  are  set,  an  empty  string  is
2205           returned.  The pcre_get_stringnumber() function returns one of the num-
2206           bers that are associated with the name, but it is not defined which  it
2207           is.
2208    
2209           If  you want to get full details of all captured substrings for a given
2210           name, you must use  the  pcre_get_stringtable_entries()  function.  The
2211           first argument is the compiled pattern, and the second is the name. The
2212           third and fourth are pointers to variables which  are  updated  by  the
2213           function. After it has run, they point to the first and last entries in
2214           the name-to-number table  for  the  given  name.  The  function  itself
2215           returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2216           there are none. The format of the table is described above in the  sec-
2217           tion  entitled  Information  about  a  pattern.  Given all the relevant
2218           entries for the name, you can extract each of their numbers, and  hence
2219           the captured data, if any.
2220    
2221    
2222  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2223    
2224         The traditional matching function uses a  similar  algorithm  to  Perl,         The  traditional  matching  function  uses a similar algorithm to Perl,
2225         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
2226         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
2227         possible  match,  consider using the alternative matching function (see         possible match, consider using the alternative matching  function  (see
2228         below) instead. If you cannot use the alternative function,  but  still         below)  instead.  If you cannot use the alternative function, but still
2229         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
2230         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2231         tation.         tation.
2232    
2233         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-
2234         tern.  When your callout function is called, extract and save the  cur-         tern.   When your callout function is called, extract and save the cur-
2235         rent  matched  substring.  Then  return  1, which forces pcre_exec() to         rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2236         backtrack and try other alternatives. Ultimately, when it runs  out  of         backtrack  and  try other alternatives. Ultimately, when it runs out of
2237         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2238    
2239    
# Line 1907  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2244  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2244              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2245              int *workspace, int wscount);              int *workspace, int wscount);
2246    
2247         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2248         against a compiled pattern, using a "DFA" matching algorithm. This  has         against  a  compiled pattern, using a matching algorithm that scans the
2249         different  characteristics to the normal algorithm, and is not compati-         subject string just once, and does not backtrack.  This  has  different
2250         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics  to  the  normal  algorithm, and is not compatible with
2251         Nevertheless, there are times when this kind of matching can be useful.         Perl. Some of the features of PCRE patterns are not  supported.  Never-
2252         For a discussion of the two matching algorithms, see  the  pcrematching         theless,  there are times when this kind of matching can be useful. For
2253         documentation.         a discussion of the two matching algorithms, see the pcrematching docu-
2254           mentation.
2255    
2256         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
2257         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
# Line 1925  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2263  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2263         workspace vector should contain at least 20 elements. It  is  used  for         workspace vector should contain at least 20 elements. It  is  used  for
2264         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2265         workspace will be needed for patterns and subjects where  there  are  a         workspace will be needed for patterns and subjects where  there  are  a
2266         lot of possible matches.         lot of potential matches.
2267    
2268         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2269    
2270           int rc;           int rc;
2271           int ovector[10];           int ovector[10];
2272           int wspace[20];           int wspace[20];
2273           rc = pcre_exec(           rc = pcre_dfa_exec(
2274             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2275             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2276             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1947  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2285  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2285     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2286    
2287         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
2288         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-
2289         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
2290         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
2291         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
2292         repeated here.         not repeated here.
2293    
2294           PCRE_PARTIAL           PCRE_PARTIAL
2295    
# Line 1966  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2304  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2304           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2305    
2306         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2307         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-
2308         algorithm works, this is necessarily the shortest possible match at the         tive algorithm works, this is necessarily the shortest  possible  match
2309         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2310    
2311           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2312    
# Line 2004  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2342  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2342         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,
2343         which  is  the  number of matched substrings. The substrings themselves         which  is  the  number of matched substrings. The substrings themselves
2344         are returned in ovector. Each string uses two elements;  the  first  is         are returned in ovector. Each string uses two elements;  the  first  is
2345         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
2346         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
2347         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
2348         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility with the way pcre_exec() returns data,  even  though  the
2349         strings is different.)         meaning of the strings is different.)
2350    
2351         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-
2352         est matching string is given first. If there were too many  matches  to         est matching string is given first. If there were too many  matches  to
# Line 2030  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2368  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2368    
2369           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2370    
2371         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
2372         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
2373         supported.         in a specific group. These are not supported.
2374    
2375           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2376    
# Line 2052  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2390  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2390         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
2391         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2392    
2393  Last updated: 16 May 2005  
2394  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2395    
2396           pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2397           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
2398    
2399    
2400    AUTHOR
2401    
2402           Philip Hazel
2403           University Computing Service
2404           Cambridge CB2 3QH, England.
2405    
2406    
2407    REVISION
2408    
2409           Last updated: 04 June 2007
2410           Copyright (c) 1997-2007 University of Cambridge.
2411  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2412    
2413    
# Line 2080  PCRE CALLOUTS Line 2434  PCRE CALLOUTS
2434         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2435         points:         points:
2436    
2437           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2438    
2439         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2440         called, PCRE automatically  inserts  callouts,  all  with  number  255,         called, PCRE automatically  inserts  callouts,  all  with  number  255,
# Line 2155  THE CALLOUT INTERFACE Line 2509  THE CALLOUT INTERFACE
2509         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2510         were passed to pcre_exec().         were passed to pcre_exec().
2511    
2512         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
2513         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
2514         callout function may be called several times from the same point in the         sequence \K has been encountered, this value is changed to reflect  the
2515         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2516           function may be called several times from the same point in the pattern
2517           for different starting points in the subject.
2518    
2519         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
2520         the current match pointer.         the current match pointer.
# Line 2211  RETURN VALUES Line 2567  RETURN VALUES
2567         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
2568         itself.         itself.
2569    
2570  Last updated: 28 February 2005  
2571  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2572    
2573           Philip Hazel
2574           University Computing Service
2575           Cambridge CB2 3QH, England.
2576    
2577    
2578    REVISION
2579    
2580           Last updated: 29 May 2007
2581           Copyright (c) 1997-2007 University of Cambridge.
2582  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2583    
2584    
# Line 2226  NAME Line 2592  NAME
2592  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2593    
2594         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2595         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2596         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2597           tures that are expected to be in the forthcoming Perl 5.10.
2598         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2599         are given in the section on UTF-8 support in the main pcre page.         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2600           of  what  it does have are given in the section on UTF-8 support in the
2601           main pcre page.
2602    
2603         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2604         permits  them,  but they do not mean what you might think. For example,         permits  them,  but they do not mean what you might think. For example,
# Line 2257  DIFFERENCES BETWEEN PCRE AND PERL Line 2625  DIFFERENCES BETWEEN PCRE AND PERL
2625         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
2626         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2627         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-
2628         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2629           derived properties Any and L&.
2630    
2631         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2632         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2633         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2634         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2635         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2636    
2637             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2272  DIFFERENCES BETWEEN PCRE AND PERL Line 2641  DIFFERENCES BETWEEN PCRE AND PERL
2641             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2642             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2643    
2644         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2645         classes.         classes.
2646    
2647         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2648         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2649         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
2650         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2651         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2652    
2653         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2654         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2655         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2656    
2657           10.  There are some differences that are concerned with the settings of
2658           captured strings when part of  a  pattern  is  repeated.  For  example,
2659           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2660         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2661    
2662         10. PCRE provides some extensions to the Perl regular expression facil-         11. PCRE provides some extensions to the Perl regular expression facil-
2663         ities:         ities.   Perl  5.10  will  include new features that are not in earlier
2664           versions, some of which (such as named parentheses) have been  in  PCRE
2665           for some time. This list is with respect to Perl 5.10:
2666    
2667         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2668         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2669         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2670    
2671         (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 $
2672         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2673    
2674         (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-
2675         cial meaning is faulted.         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2676           ignored. (Perl can be made to issue a warning.)
2677    
2678         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2679         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
# Line 2309  DIFFERENCES BETWEEN PCRE AND PERL Line 2685  DIFFERENCES BETWEEN PCRE AND PERL
2685         (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-
2686         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2687    
2688         (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.)  
2689    
2690         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The partial matching facility is PCRE-specific.
2691    
2692           (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2693           even on different hosts that have the other endianness.
2694    
2695         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2696         Sun's Java package.         different way and is not Perl-compatible.
2697    
        (j) The (R) condition, for testing recursion, is a PCRE extension.  
2698    
2699         (k) The callout facility is PCRE-specific.  AUTHOR
2700    
2701         (l) The partial matching facility is PCRE-specific.         Philip Hazel
2702           University Computing Service
2703           Cambridge CB2 3QH, England.
2704    
        (m) Patterns compiled by PCRE can be saved and re-used at a later time,  
        even on different hosts that have the other endianness.  
2705    
2706         (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  REVISION
        different way and is not Perl-compatible.  
2707    
2708  Last updated: 28 February 2005         Last updated: 06 March 2007
2709  Copyright (c) 1997-2005 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2710  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2711    
2712    
# Line 2363  PCRE REGULAR EXPRESSION DETAILS Line 2738  PCRE REGULAR EXPRESSION DETAILS
2738         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2739         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
2740         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
2741         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
2742         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2743         the pcrematching page.         alternative function, and how it differs from the normal function,  are
2744           discussed in the pcrematching page.
2745         A regular expression is a pattern that is  matched  against  a  subject  
2746         string  from  left  to right. Most characters stand for themselves in a  
2747         pattern, and match the corresponding characters in the  subject.  As  a  CHARACTERS AND METACHARACTERS
2748    
2749           A  regular  expression  is  a pattern that is matched against a subject
2750           string from left to right. Most characters stand for  themselves  in  a
2751           pattern,  and  match  the corresponding characters in the subject. As a
2752         trivial example, the pattern         trivial example, the pattern
2753    
2754           The quick brown fox           The quick brown fox
2755    
2756         matches a portion of a subject string that is identical to itself. When         matches a portion of a subject string that is identical to itself. When
2757         caseless matching is specified (the PCRE_CASELESS option), letters  are         caseless  matching is specified (the PCRE_CASELESS option), letters are
2758         matched  independently  of case. In UTF-8 mode, PCRE always understands         matched independently of case. In UTF-8 mode, PCRE  always  understands
2759         the concept of case for characters whose values are less than  128,  so         the  concept  of case for characters whose values are less than 128, so
2760         caseless  matching  is always possible. For characters with higher val-         caseless matching is always possible. For characters with  higher  val-
2761         ues, the concept of case is supported if PCRE is compiled with  Unicode         ues,  the concept of case is supported if PCRE is compiled with Unicode
2762         property  support,  but  not  otherwise.   If  you want to use caseless         property support, but not otherwise.   If  you  want  to  use  caseless
2763         matching for characters 128 and above, you must  ensure  that  PCRE  is         matching  for  characters  128  and above, you must ensure that PCRE is
2764         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
2765    
2766         The  power  of  regular  expressions  comes from the ability to include         The power of regular expressions comes  from  the  ability  to  include
2767         alternatives and repetitions in the pattern. These are encoded  in  the         alternatives  and  repetitions in the pattern. These are encoded in the
2768         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
2769         but instead are interpreted in some special way.         but instead are interpreted in some special way.
2770    
2771         There are two different sets of metacharacters: those that  are  recog-         There  are  two different sets of metacharacters: those that are recog-
2772         nized  anywhere in the pattern except within square brackets, and those         nized anywhere in the pattern except within square brackets, and  those
2773         that are recognized in square brackets. Outside  square  brackets,  the         that  are  recognized  within square brackets. Outside square brackets,
2774         metacharacters are as follows:         the metacharacters are as follows:
2775    
2776           \      general escape character with several uses           \      general escape character with several uses
2777           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2410  PCRE REGULAR EXPRESSION DETAILS Line 2789  PCRE REGULAR EXPRESSION DETAILS
2789                  also "possessive quantifier"                  also "possessive quantifier"
2790           {      start min/max quantifier           {      start min/max quantifier
2791    
2792         Part  of  a  pattern  that is in square brackets is called a "character         Part of a pattern that is in square brackets  is  called  a  "character
2793         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
2794    
2795           \      general escape character           \      general escape character
# Line 2420  PCRE REGULAR EXPRESSION DETAILS Line 2799  PCRE REGULAR EXPRESSION DETAILS
2799                    syntax)                    syntax)
2800           ]      terminates the character class           ]      terminates the character class
2801    
2802         The following sections describe the use of each of the  metacharacters.         The  following sections describe the use of each of the metacharacters.
2803    
2804    
2805  BACKSLASH  BACKSLASH
2806    
2807         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
2808         a non-alphanumeric character, it takes away any  special  meaning  that         a  non-alphanumeric  character,  it takes away any special meaning that
2809         character  may  have.  This  use  of  backslash  as an escape character         character may have. This  use  of  backslash  as  an  escape  character
2810         applies both inside and outside character classes.         applies both inside and outside character classes.
2811    
2812         For example, if you want to match a * character, you write  \*  in  the         For  example,  if  you want to match a * character, you write \* in the
2813         pattern.   This  escaping  action  applies whether or not the following         pattern.  This escaping action applies whether  or  not  the  following
2814         character would otherwise be interpreted as a metacharacter, so  it  is         character  would  otherwise be interpreted as a metacharacter, so it is
2815         always  safe  to  precede  a non-alphanumeric with backslash to specify         always safe to precede a non-alphanumeric  with  backslash  to  specify
2816         that it stands for itself. In particular, if you want to match a  back-         that  it stands for itself. In particular, if you want to match a back-
2817         slash, you write \\.         slash, you write \\.
2818    
2819         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
2820         the pattern (other than in a character class) and characters between  a         the  pattern (other than in a character class) and characters between a
2821         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2822         An escaping backslash can be used to include a whitespace or #  charac-         ing  backslash  can  be  used to include a whitespace or # character as
2823         ter as part of the pattern.         part of the pattern.
2824    
2825         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-
2826         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-
2827         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E
2828         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
2829         tion. Note the following examples:         tion. Note the following examples:
2830    
2831           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2456  BACKSLASH Line 2835  BACKSLASH
2835           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
2836           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
2837    
2838         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2839         classes.         classes.
2840    
2841     Non-printing characters     Non-printing characters
2842    
2843         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
2844         acters  in patterns in a visible manner. There is no restriction on the         acters in patterns in a visible manner. There is no restriction on  the
2845         appearance of non-printing characters, apart from the binary zero  that         appearance  of non-printing characters, apart from the binary zero that
2846         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates a pattern, but when a pattern  is  being  prepared  by  text
2847         editing, it is usually easier  to  use  one  of  the  following  escape         editing,  it  is  usually  easier  to  use  one of the following escape
2848         sequences than the binary character it represents:         sequences than the binary character it represents:
2849    
2850           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
# Line 2477  BACKSLASH Line 2856  BACKSLASH
2856           \t        tab (hex 09)           \t        tab (hex 09)
2857           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
2858           \xhh      character with hex code hh           \xhh      character with hex code hh
2859           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
2860    
2861         The  precise  effect of \cx is as follows: if x is a lower case letter,         The precise effect of \cx is as follows: if x is a lower  case  letter,
2862         it is converted to upper case. Then bit 6 of the character (hex 40)  is         it  is converted to upper case. Then bit 6 of the character (hex 40) is
2863         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;
2864         becomes hex 7B.         becomes hex 7B.
2865    
2866         After \x, from zero to two hexadecimal digits are read (letters can  be         After  \x, from zero to two hexadecimal digits are read (letters can be
2867         in  upper or lower case). In UTF-8 mode, any number of hexadecimal dig-         in upper or lower case). Any number of hexadecimal  digits  may  appear
2868         its may appear between \x{ and }, but the value of the  character  code         between  \x{  and  },  but the value of the character code must be less
2869         must  be  less  than  2**31  (that is, the maximum hexadecimal value is         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode (that is,
2870         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the  maximum  hexadecimal  value is 7FFFFFFF). If characters other than
2871         \x{  and }, or if there is no terminating }, this form of escape is not         hexadecimal digits appear between \x{ and }, or if there is  no  termi-
2872         recognized. Instead, the initial \x will  be  interpreted  as  a  basic         nating  }, this form of escape is not recognized.  Instead, the initial
2873         hexadecimal  escape, with no following digits, giving a character whose         \x will be interpreted as a basic hexadecimal escape, with no following
2874         value is zero.         digits, giving a character whose value is zero.
2875    
2876         Characters whose value is less than 256 can be defined by either of the         Characters whose value is less than 256 can be defined by either of the
2877         two  syntaxes for \x when PCRE is in UTF-8 mode. There is no difference         two syntaxes for \x. There is no difference in the way  they  are  han-
2878         in the way they are handled. For example, \xdc is exactly the  same  as         dled. For example, \xdc is exactly the same as \x{dc}.
2879         \x{dc}.  
2880           After  \0  up  to two further octal digits are read. If there are fewer
2881         After  \0  up  to  two further octal digits are read. In both cases, if         than two digits, just  those  that  are  present  are  used.  Thus  the
2882         there are fewer than two digits, just those that are present are  used.         sequence \0\x\07 specifies two binary zeros followed by a BEL character
2883         Thus  the sequence \0\x\07 specifies two binary zeros followed by a BEL         (code value 7). Make sure you supply two digits after the initial  zero
2884         character (code value 7). Make sure you supply  two  digits  after  the         if the pattern character that follows is itself an octal digit.
        initial  zero  if the pattern character that follows is itself an octal  
        digit.  
2885    
2886         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-
2887         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
2888         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
2889         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
2890         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
2891         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
2892         of parenthesized subpatterns.         of parenthesized subpatterns.
2893    
2894         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
2895         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
2896         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-
2897         gle byte from the least significant 8 bits of the value. Any subsequent         erate a data character. Any subsequent digits stand for themselves.  In
2898         digits stand for themselves.  For example:         non-UTF-8  mode,  the  value  of a character specified in octal must be
2899           less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
2900           example:
2901    
2902           \040   is another way of writing a space           \040   is another way of writing a space
2903           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2535  BACKSLASH Line 2914  BACKSLASH
2914           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
2915                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
2916    
2917         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
2918         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2919    
2920         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
2921         character (in UTF-8 mode) can be used both inside and outside character         inside  and  outside character classes. In addition, inside a character
2922         classes.  In  addition,  inside  a  character class, the sequence \b is         class, the sequence \b is interpreted as the backspace  character  (hex
2923         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"
2924         interpreted  as  the  character  "X".  Outside a character class, these         and "X", respectively. Outside a character class, these sequences  have
2925         sequences have different meanings (see below).         different meanings (see below).
2926    
2927       Absolute and relative back references
2928    
2929           The  sequence  \g followed by a positive or negative number, optionally
2930           enclosed in braces, is an absolute or relative back reference. A  named
2931           back  reference can be coded as \g{name}. Back references are discussed
2932           later, following the discussion of parenthesized subpatterns.
2933    
2934     Generic character types     Generic character types
2935    
2936         The third use of backslash is for specifying generic  character  types.         Another use of backslash is for specifying generic character types. The
2937         The following are always recognized:         following are always recognized:
2938    
2939           \d     any decimal digit           \d     any decimal digit
2940           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 2568  BACKSLASH Line 2954  BACKSLASH
2954    
2955         For compatibility with Perl, \s does not match the VT  character  (code         For compatibility with Perl, \s does not match the VT  character  (code
2956         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
2957         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
2958           "use locale;" is included in a Perl script, \s may match the VT charac-
2959           ter. In PCRE, it never does.)
2960    
2961         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
2962         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-
2963         trolled by PCRE's low-valued character tables, and may vary if  locale-         trolled by PCRE's low-valued character tables, and may vary if  locale-
2964         specific  matching is taking place (see "Locale support" in the pcreapi         specific  matching is taking place (see "Locale support" in the pcreapi
2965         page). For example, in the  "fr_FR"  (French)  locale,  some  character         page). For example, in a French locale such  as  "fr_FR"  in  Unix-like
2966         codes  greater  than  128  are used for accented letters, and these are         systems,  or "french" in Windows, some character codes greater than 128
2967         matched by \w.         are used for accented letters, and these are matched by \w.
2968    
2969         In UTF-8 mode, characters with values greater than 128 never match  \d,         In UTF-8 mode, characters with values greater than 128 never match  \d,
2970         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
2971         code character property support is available.         code character property support is available. The use of  locales  with
2972           Unicode is discouraged.
2973    
2974       Newline sequences
2975    
2976           Outside  a  character class, the escape sequence \R matches any Unicode
2977           newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2978           equivalent to the following:
2979    
2980             (?>\r\n|\n|\x0b|\f|\r|\x85)
2981    
2982           This  is  an  example  of an "atomic group", details of which are given
2983           below.  This particular group matches either the two-character sequence
2984           CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
2985           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2986           return, U+000D), or NEL (next line, U+0085). The two-character sequence
2987           is treated as a single unit that cannot be split.
2988    
2989           In UTF-8 mode, two additional characters whose codepoints  are  greater
2990           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2991           rator, U+2029).  Unicode character property support is not  needed  for
2992           these characters to be recognized.
2993    
2994           Inside a character class, \R matches the letter "R".
2995    
2996     Unicode character properties     Unicode character properties
2997    
2998         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
2999         tional  escape sequences to match generic character types are available         tional escape sequences to match  character  properties  are  available
3000         when UTF-8 mode is selected. They are:         when UTF-8 mode is selected. They are:
3001    
3002          \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3003          \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
3004          \X       an extended Unicode sequence           \X       an extended Unicode sequence
3005    
3006         The property names represented by xx above are limited to  the  Unicode         The  property  names represented by xx above are limited to the Unicode
3007         general  category properties. Each character has exactly one such prop-         script names, the general category properties, and "Any", which matches
3008         erty, specified by a two-letter abbreviation.  For  compatibility  with         any character (including newline). Other properties such as "InMusical-
3009         Perl,  negation  can be specified by including a circumflex between the         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does
3010         opening brace and the property name. For example, \p{^Lu} is  the  same         not match any characters, so always causes a match failure.
3011         as \P{Lu}.  
3012           Sets of Unicode characters are defined as belonging to certain scripts.
3013         If  only  one  letter  is  specified with \p or \P, it includes all the         A character from one of these sets can be matched using a script  name.
3014         properties that start with that letter. In this case, in the absence of         For example:
3015         negation, the curly brackets in the escape sequence are optional; these  
3016         two examples have the same effect:           \p{Greek}
3017             \P{Han}
3018    
3019           Those  that are not part of an identified script are lumped together as
3020           "Common". The current list of scripts is:
3021    
3022           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3023           Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,
3024           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3025           Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
3026           gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,
3027           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3028           Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,
3029           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3030           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3031    
3032           Each character has exactly one general category property, specified  by
3033           a two-letter abbreviation. For compatibility with Perl, negation can be
3034           specified by including a circumflex between the opening brace  and  the
3035           property name. For example, \p{^Lu} is the same as \P{Lu}.
3036    
3037           If only one letter is specified with \p or \P, it includes all the gen-
3038           eral category properties that start with that letter. In this case,  in
3039           the  absence of negation, the curly brackets in the escape sequence are
3040           optional; these two examples have the same effect:
3041    
3042           \p{L}           \p{L}
3043           \pL           \pL
3044    
3045         The following property codes are supported:         The following general category property codes are supported:
3046    
3047           C     Other           C     Other
3048           Cc    Control           Cc    Control
# Line 2653  BACKSLASH Line 3088  BACKSLASH
3088           Zp    Paragraph separator           Zp    Paragraph separator
3089           Zs    Space separator           Zs    Space separator
3090    
3091         Extended properties such as "Greek" or "InMusicalSymbols" are not  sup-         The special property L& is also supported: it matches a character  that
3092         ported by PCRE.         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not
3093           classified as a modifier or "other".
3094    
3095           The long synonyms for these properties  that  Perl  supports  (such  as
3096           \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix
3097           any of these properties with "Is".
3098    
3099           No character that is in the Unicode table has the Cn (unassigned) prop-
3100           erty.  Instead, this property is assumed for any code point that is not
3101           in the Unicode table.
3102    
3103         Specifying  caseless  matching  does not affect these escape sequences.         Specifying caseless matching does not affect  these  escape  sequences.
3104         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3105    
3106         The \X escape matches any number of Unicode  characters  that  form  an         The  \X  escape  matches  any number of Unicode characters that form an
3107         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3108    
3109           (?>\PM\pM*)           (?>\PM\pM*)
3110    
3111         That  is,  it matches a character without the "mark" property, followed         That is, it matches a character without the "mark"  property,  followed
3112         by zero or more characters with the "mark"  property,  and  treats  the         by  zero  or  more  characters with the "mark" property, and treats the
3113         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3114         property are typically accents that affect the preceding character.         property are typically accents that affect the preceding character.
3115    
3116         Matching characters by Unicode property is not fast, because  PCRE  has         Matching  characters  by Unicode property is not fast, because PCRE has
3117         to  search  a  structure  that  contains data for over fifteen thousand         to search a structure that contains  data  for  over  fifteen  thousand
3118         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3119         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3120    
3121       Resetting the match start
3122    
3123           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3124           ously  matched  characters  not  to  be  included  in the final matched
3125           sequence. For example, the pattern:
3126    
3127             foo\Kbar
3128    
3129           matches "foobar", but reports that it has matched "bar".  This  feature
3130           is  similar  to  a lookbehind assertion (described below).  However, in
3131           this case, the part of the subject before the real match does not  have
3132           to  be of fixed length, as lookbehind assertions do. The use of \K does
3133           not interfere with the setting of captured  substrings.   For  example,
3134           when the pattern
3135    
3136             (foo)\Kbar
3137    
3138           matches "foobar", the first substring is still set to "foo".
3139    
3140     Simple assertions     Simple assertions
3141    
3142         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3143         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
3144         a  match, without consuming any characters from the subject string. The         a  match, without consuming any characters from the subject string. The
3145         use of subpatterns for more complicated assertions is described  below.         use of subpatterns for more complicated assertions is described  below.
# Line 2684  BACKSLASH Line 3147  BACKSLASH
3147    
3148           \b     matches at a word boundary           \b     matches at a word boundary
3149           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3150           \A     matches at start of subject           \A     matches at the start of the subject
3151           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3152           \z     matches at end of subject                   also matches before a newline at the end of the subject
3153           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3154             \G     matches at the first matching position in the subject
3155    
3156         These  assertions may not appear in character classes (but note that \b         These  assertions may not appear in character classes (but note that \b
3157         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
# Line 2707  BACKSLASH Line 3171  BACKSLASH
3171         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3172         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
3173         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
3174         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
3175         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.
3176         the end.  
3177           The \G assertion is true only when the current matching position is  at
3178         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
3179         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
3180         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-  
3181         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-
3182         mentation where \G can be useful.         mentation where \G can be useful.
3183    
3184         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
3185         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
3186         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
3187         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3188         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3189    
3190         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
3191         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3192         in the compiled regular expression.         in the compiled regular expression.
3193    
# Line 2732  BACKSLASH Line 3195  BACKSLASH
3195  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3196    
3197         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3198         character  is  an  assertion  that is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3199         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-
3200         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
3201         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3202         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3203    
3204         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
3205         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
3206         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
3207         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3208         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-
3209         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
3210         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3211    
3212         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
3213         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3214         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
3215         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
3216         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
3217         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.  
3218    
3219         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
3220         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
3221         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3222    
3223         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3224         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
3225         ately  after  and  immediately  before  an  internal newline character,         matches  immediately after internal newlines as well as at the start of
3226         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
3227         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         string.  A dollar matches before any newlines in the string, as well as
3228         string "def\nabc" (where \n represents a newline character)  in  multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3229         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3230         in single line mode because all branches start with ^ are not  anchored         not indicate newlines.
3231         in  multiline  mode,  and  a  match for circumflex is possible when the  
3232         startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3233         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3234           Consequently, patterns that are anchored in single  line  mode  because
3235         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
3236         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
3237         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
3238         not.         PCRE_MULTILINE is set.
3239    
3240           Note that the sequences \A, \Z, and \z can be used to match  the  start
3241           and  end of the subject in both modes, and if all branches of a pattern
3242           start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3243           set.
3244    
3245    
3246  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3247    
3248         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-
3249         ter  in  the  subject,  including a non-printing character, but not (by         ter in the subject string except (by default) a character  that  signi-
3250         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
3251         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3252         the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-  
3253         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
3254         dollar, the only relationship being  that  they  both  involve  newline         that  character; when the two-character sequence CRLF is used, dot does
3255         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3256           matches  all characters (including isolated CRs and LFs). When any Uni-
3257           code line endings are being recognized, dot does not match CR or LF  or
3258           any of the other line ending characters.
3259    
3260           The  behaviour  of  dot  with regard to newlines can be changed. If the
3261           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3262           exception. If the two-character sequence CRLF is present in the subject
3263           string, it takes two dots to match it.
3264    
3265           The handling of dot is entirely independent of the handling of  circum-
3266           flex  and  dollar,  the  only relationship being that they both involve
3267           newlines. Dot has no special meaning in a character class.
3268    
3269    
3270  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3271    
3272         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3273         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
3274         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
3275         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-
3276         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-
3277         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3278           avoided.
3279    
3280         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3281         below),  because  in UTF-8 mode this would make it impossible to calcu-         below),  because  in UTF-8 mode this would make it impossible to calcu-
# Line 2842  SQUARE BRACKETS AND CHARACTER CLASSES Line 3322  SQUARE BRACKETS AND CHARACTER CLASSES
3322         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
3323         support.         support.
3324    
3325         The newline character is never treated in any special way in  character         Characters that might indicate line breaks are  never  treated  in  any
3326         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         special  way  when  matching  character  classes,  whatever line-ending
3327         options is. A class such as [^a] will always match a newline.         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3328           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3329           of these characters.
3330    
3331         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-
3332         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters  in  a  character  class.  For  example,  [d-m] matches any letter
# Line 2870  SQUARE BRACKETS AND CHARACTER CLASSES Line 3352  SQUARE BRACKETS AND CHARACTER CLASSES
3352         If a range that includes letters is used when caseless matching is set,         If a range that includes letters is used when caseless matching is set,
3353         it matches the letters in either case. For example, [W-c] is equivalent         it matches the letters in either case. For example, [W-c] is equivalent
3354         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3355         character tables for the "fr_FR" locale are in use, [\xc8-\xcb] matches         character tables for a French locale are in  use,  [\xc8-\xcb]  matches
3356         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the
3357         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3358         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 2945  VERTICAL BAR Line 3427  VERTICAL BAR
3427    
3428         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3429         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3430         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3431         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
3432         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3433         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.  
3434    
3435    
3436  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 2977  INTERNAL OPTION SETTING Line 3458  INTERNAL OPTION SETTING
3458         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
3459         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3460    
3461         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
3462         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3463           it, so
3464    
3465           (a(?i)b)c           (a(?i)b)c
3466    
3467         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
3468         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3469         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3470         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3471         example,         example,
3472    
3473           (a(?i)b|c)           (a(?i)b|c)
3474    
3475         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3476         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3477         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3478         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3479    
3480         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3481         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
3482         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.  
3483    
3484    
3485  SUBPATTERNS  SUBPATTERNS
# Line 3013  SUBPATTERNS Line 3492  SUBPATTERNS
3492           cat(aract|erpillar|)           cat(aract|erpillar|)
3493    
3494         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3495         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3496         string.         string.
3497    
3498         2.  It  sets  up  the  subpattern as a capturing subpattern. This means         2.  It  sets  up  the  subpattern as a capturing subpattern. This means
# Line 3042  SUBPATTERNS Line 3521  SUBPATTERNS
3521           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3522    
3523         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3524         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.  
3525    
3526         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3527         start of a non-capturing subpattern,  the  option  letters  may  appear         start of a non-capturing subpattern,  the  option  letters  may  appear
# Line 3066  NAMED SUBPATTERNS Line 3543  NAMED SUBPATTERNS
3543         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3544         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3545         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3546         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3547         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3548         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3549           tax.
3550    
3551           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3552           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3553           to capturing parentheses from other parts of the pattern, such as back-
3554           references,  recursion,  and conditions, can be made by name as well as
3555           by number.
3556    
3557           Names consist of up to  32  alphanumeric  characters  and  underscores.
3558         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3559         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
3560         number  translation table from a compiled pattern. There is also a con-         function calls for extracting the name-to-number translation table from
3561         venience function for extracting a captured substring by name. For fur-         a compiled pattern. There is also a convenience function for extracting
3562         ther details see the pcreapi documentation.         a captured substring by name.
3563    
3564           By  default, a name must be unique within a pattern, but it is possible
3565           to relax this constraint by setting the PCRE_DUPNAMES option at compile
3566           time.  This  can  be useful for patterns where only one instance of the
3567           named parentheses can match. Suppose you want to match the  name  of  a
3568           weekday,  either as a 3-letter abbreviation or as the full name, and in
3569           both cases you want to extract the abbreviation. This pattern (ignoring
3570           the line breaks) does the job:
3571    
3572             (?<DN>Mon|Fri|Sun)(?:day)?|
3573             (?<DN>Tue)(?:sday)?|
3574             (?<DN>Wed)(?:nesday)?|
3575             (?<DN>Thu)(?:rsday)?|
3576             (?<DN>Sat)(?:urday)?
3577    
3578           There  are  five capturing substrings, but only one is ever set after a
3579           match.  The convenience  function  for  extracting  the  data  by  name
3580           returns  the  substring  for  the first (and in this example, the only)
3581           subpattern of that name that matched.  This  saves  searching  to  find
3582           which  numbered  subpattern  it  was. If you make a reference to a non-
3583           unique named subpattern from elsewhere in the  pattern,  the  one  that
3584           corresponds  to  the  lowest number is used. For further details of the
3585           interfaces for handling named subpatterns, see the  pcreapi  documenta-
3586           tion.
3587    
3588    
3589  REPETITION  REPETITION
# Line 3083  REPETITION Line 3592  REPETITION
3592         following items:         following items:
3593    
3594           a literal data character           a literal data character
3595           the . metacharacter           the dot metacharacter
3596           the \C escape sequence           the \C escape sequence
3597           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3598             the \R escape sequence
3599           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3600           a character class           a character class
3601           a back reference (see next section)           a back reference (see next section)
# Line 3125  REPETITION Line 3635  REPETITION
3635         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3636         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3637    
3638         For  convenience  (and  historical compatibility) the three most common         For  convenience, the three most common quantifiers have single-charac-
3639         quantifiers have single-character abbreviations:         ter abbreviations:
3640    
3641           *    is equivalent to {0,}           *    is equivalent to {0,}
3642           +    is equivalent to {1,}           +    is equivalent to {1,}
# Line 3178  REPETITION Line 3688  REPETITION
3688         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
3689         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3690    
3691         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
3692         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3693         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
3694         words, it inverts the default behaviour.         words, it inverts the default behaviour.
# Line 3189  REPETITION Line 3699  REPETITION
3699         minimum or maximum.         minimum or maximum.
3700    
3701         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-
3702         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,
3703         pattern is implicitly anchored, because whatever follows will be  tried         the pattern is implicitly anchored, because whatever  follows  will  be
3704         against  every character position in the subject string, so there is no         tried  against every character position in the subject string, so there
3705         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
3706         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
3707           by \A.
3708    
3709         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-
3710         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-
3711         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3712    
3713         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3714         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3715         backreference  elsewhere in the pattern, a match at the start may fail,         backreference elsewhere in the pattern, a match at the start  may  fail
3716         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3717    
3718           (.*)abc\1           (.*)abc\1
3719    
3720         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3721         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3722    
3723         When a capturing subpattern is repeated, the value captured is the sub-         When a capturing subpattern is repeated, the value captured is the sub-
# Line 3215  REPETITION Line 3726  REPETITION
3726           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
3727    
3728         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
3729         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
3730         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
3731         tions. For example, after         tions. For example, after
3732    
3733           /(a|(b))+/           /(a|(b))+/
# Line 3226  REPETITION Line 3737  REPETITION
3737    
3738  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
3739    
3740         With both maximizing and minimizing repetition, failure of what follows         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
3741         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition,  failure  of what follows normally causes the repeated item
3742         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
3743         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,
3744         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
3745         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
3746           no point in carrying on.
3747    
3748         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider, for example, the pattern \d+foo when applied to  the  subject
3749         line         line
# Line 3245  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3757  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3757         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
3758         to be re-evaluated in this way.         to be re-evaluated in this way.
3759    
3760         If we use atomic grouping for the previous example, the  matcher  would         If we use atomic grouping for the previous example, the  matcher  gives
3761         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
3762         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:  
3763    
3764           (?>\d+)foo           (?>\d+)foo
3765    
# Line 3280  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3791  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3791         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
3792         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
3793         simpler forms of atomic group. However, there is no difference  in  the         simpler forms of atomic group. However, there is no difference  in  the
3794         meaning  or  processing  of  a possessive quantifier and the equivalent         meaning  of  a  possessive  quantifier and the equivalent atomic group,
3795         atomic group.         though there may be a performance  difference;  possessive  quantifiers
3796           should be slightly faster.
3797         The possessive quantifier syntax is an extension to the Perl syntax. It  
3798         originates in Sun's Java package.         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
3799           tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first
3800         When  a  pattern  contains an unlimited repeat inside a subpattern that         edition of his book. Mike McCloskey liked it, so implemented it when he
3801         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
3802         atomic  group  is  the  only way to avoid some failing matches taking a         found its way into Perl at release 5.10.
3803    
3804           PCRE has an optimization that automatically "possessifies" certain sim-
3805           ple pattern constructs. For example, the sequence  A+B  is  treated  as
3806           A++B  because  there is no point in backtracking into a sequence of A's
3807           when B must follow.
3808    
3809           When a pattern contains an unlimited repeat inside  a  subpattern  that
3810           can  itself  be  repeated  an  unlimited number of times, the use of an
3811           atomic group is the only way to avoid some  failing  matches  taking  a
3812         very long time indeed. The pattern         very long time indeed. The pattern
3813    
3814           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
3815    
3816         matches an unlimited number of substrings that either consist  of  non-         matches  an  unlimited number of substrings that either consist of non-
3817         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it
3818         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
3819    
3820           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
3821    
3822         it takes a long time before reporting  failure.  This  is  because  the         it  takes  a  long  time  before reporting failure. This is because the
3823         string  can be divided between the internal \D+ repeat and the external         string can be divided between the internal \D+ repeat and the  external
3824         * 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
3825         example  uses  [!?]  rather than a single character at the end, because         example uses [!?] rather than a single character at  the  end,  because
3826         both PCRE and Perl have an optimization that allows  for  fast  failure         both  PCRE  and  Perl have an optimization that allows for fast failure
3827         when  a single character is used. They remember the last single charac-         when a single character is used. They remember the last single  charac-
3828         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
3829         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
3830         group, like this:         group, like this:
3831    
3832           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
3833    
3834         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences  of non-digits cannot be broken, and failure happens quickly.
3835    
3836    
3837  BACK REFERENCES  BACK REFERENCES
3838    
3839         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
3840         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-
3841         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
3842         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
3843    
3844         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
3845         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
3846         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
3847         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
3848         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
3849         tion  entitled  "Non-printing  characters" above for further details of         reference" of this type can make sense when a  repetition  is  involved
3850         the handling of digits following a backslash.         and  the  subpattern to the right has participated in an earlier itera-
3851           tion.
3852    
3853           It is not possible to have a numerical "forward back  reference"  to  a
3854           subpattern  whose  number  is  10  or  more using this syntax because a
3855           sequence such as \50 is interpreted as a character  defined  in  octal.
3856           See the subsection entitled "Non-printing characters" above for further
3857           details of the handling of digits following a backslash.  There  is  no
3858           such  problem  when named parentheses are used. A back reference to any
3859           subpattern is possible using named parentheses (see below).
3860    
3861           Another way of avoiding the ambiguity inherent in  the  use  of  digits
3862           following a backslash is to use the \g escape sequence, which is a fea-
3863           ture introduced in Perl 5.10. This escape must be followed by  a  posi-
3864           tive  or  a negative number, optionally enclosed in braces. These exam-
3865           ples are all identical:
3866    
3867             (ring), \1
3868             (ring), \g1
3869             (ring), \g{1}
3870    
3871           A positive number specifies an absolute reference without the ambiguity
3872           that  is  present  in  the older syntax. It is also useful when literal
3873           digits follow the reference. A negative number is a relative reference.
3874           Consider this example:
3875    
3876             (abc(def)ghi)\g{-1}
3877    
3878           The sequence \g{-1} is a reference to the most recently started captur-
3879           ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,
3880           \g{-2} would be equivalent to \1. The use of relative references can be
3881           helpful in long patterns, and also in  patterns  that  are  created  by
3882           joining together fragments that contain references within themselves.
3883    
3884         A back reference matches whatever actually matched the  capturing  sub-         A  back  reference matches whatever actually matched the capturing sub-
3885         pattern  in  the  current subject string, rather than anything matching         pattern in the current subject string, rather  than  anything  matching
3886         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
3887         of doing that). So the pattern         of doing that). So the pattern
3888    
3889           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
3890    
3891         matches  "sense and sensibility" and "response and responsibility", but         matches "sense and sensibility" and "response and responsibility",  but
3892         not "sense and responsibility". If caseful matching is in force at  the         not  "sense and responsibility". If caseful matching is in force at the
3893         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-
3894         ple,         ple,
3895    
3896           ((?i)rah)\s+\1           ((?i)rah)\s+\1
3897    
3898         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
3899         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
3900    
3901         Back  references  to named subpatterns use the Python syntax (?P=name).         There are several different ways of writing back  references  to  named
3902         We could rewrite the above example as follows:         subpatterns.  The  .NET syntax \k{name} and the Perl syntax \k<name> or
3903           \k'name' are supported, as is the Python syntax (?P=name). Perl  5.10's
3904           unified back reference syntax, in which \g can be used for both numeric
3905           and named references, is also supported. We  could  rewrite  the  above
3906           example in any of the following ways:
3907    
3908             (?<p1>(?i)rah)\s+\k<p1>
3909             (?'p1'(?i)rah)\s+\k{p1}
3910             (?P<p1>(?i)rah)\s+(?P=p1)
3911             (?<p1>(?i)rah)\s+\g{p1}
3912    
3913           (?<p1>(?i)rah)\s+(?P=p1)         A  subpattern  that  is  referenced  by  name may appear in the pattern
3914           before or after the reference.
3915    
3916         There may be more than one back reference to the same subpattern. If  a         There may be more than one back reference to the same subpattern. If  a
3917         subpattern  has  not actually been used in a particular match, any back         subpattern  has  not actually been used in a particular match, any back
# Line 3438  ASSERTIONS Line 4000  ASSERTIONS
4000         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
4001         contents of a lookbehind assertion are restricted  such  that  all  the         contents of a lookbehind assertion are restricted  such  that  all  the
4002         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-
4003         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
4004         Thus         fixed length. Thus
4005    
4006           (?<=bullock|donkey)           (?<=bullock|donkey)
4007    
# Line 3461  ASSERTIONS Line 4023  ASSERTIONS
4023    
4024           (?<=abc|abde)           (?<=abc|abde)
4025    
4026           In some cases, the Perl 5.10 escape sequence \K (see above) can be used
4027           instead of a lookbehind assertion; this is not restricted to  a  fixed-
4028           length.
4029    
4030         The  implementation  of lookbehind assertions is, for each alternative,         The  implementation  of lookbehind assertions is, for each alternative,
4031         to temporarily move the current position back by the  fixed  width  and         to temporarily move the current position back by the fixed  length  and
4032         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
4033         rent position, the match is deemed to fail.         rent position, the assertion fails.
4034    
4035         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
4036         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode)  to appear in lookbehind assertions, because it makes it impossi-
4037         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,
4038         match different numbers of bytes, is also not permitted.         which can match different numbers of bytes, are also not permitted.
4039    
4040         Atomic  groups can be used in conjunction with lookbehind assertions to         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind
4041         specify efficient matching at the end of the subject string. Consider a         assertions to specify efficient matching at  the  end  of  the  subject
4042         simple pattern such as         string. Consider a simple pattern such as
4043    
4044           abcd$           abcd$
4045    
# Line 3490  ASSERTIONS Line 4056  ASSERTIONS
4056         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,
4057         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
4058    
          ^(?>.*)(?<=abcd)  
   
        or, equivalently, using the possessive quantifier syntax,  
   
4059           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4060    
4061         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
4062         entire  string.  The subsequent lookbehind assertion does a single test         entire  string.  The subsequent lookbehind assertion does a single test
4063         on the last four characters. If it fails, the match fails  immediately.         on the last four characters. If it fails, the match fails  immediately.
4064         For  long  strings, this approach makes a significant difference to the         For  long  strings, this approach makes a significant difference to the
# Line 3551  CONDITIONAL SUBPATTERNS Line 4113  CONDITIONAL SUBPATTERNS
4113         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-
4114         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4115    
4116         There are three kinds of condition. If the text between the parentheses         There  are  four  kinds of condition: references to subpatterns, refer-
4117         consists of a sequence of digits, the condition  is  satisfied  if  the         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4118         capturing  subpattern of that number has previously matched. The number  
4119         must be greater than zero. Consider the following pattern,  which  con-     Checking for a used subpattern by number
4120         tains  non-significant white space to make it more readable (assume the  
4121         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,
4122         discussion:         the  condition  is  true if the capturing subpattern of that number has
4123           previously matched. An alternative notation is to  precede  the  digits
4124           with a plus or minus sign. In this case, the subpattern number is rela-
4125           tive rather than absolute.  The most recently opened parentheses can be
4126           referenced  by  (?(-1),  the  next most recent by (?(-2), and so on. In
4127           looping constructs it can also make sense to refer to subsequent groups
4128           with constructs such as (?(+2).
4129    
4130           Consider  the  following  pattern, which contains non-significant white
4131           space to make it more readable (assume the PCRE_EXTENDED option) and to
4132           divide it into three parts for ease of discussion:
4133    
4134           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4135    
# Line 3572  CONDITIONAL SUBPATTERNS Line 4144  CONDITIONAL SUBPATTERNS
4144         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other  words,  this  pattern  matches  a  sequence  of non-parentheses,
4145         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4146    
4147         If the condition is the string (R), it is satisfied if a recursive call         If you were embedding this pattern in a larger one,  you  could  use  a
4148         to  the pattern or subpattern has been made. At "top level", the condi-         relative reference:
4149         tion is false.  This  is  a  PCRE  extension.  Recursive  patterns  are  
4150         described in the next section.           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4151    
4152           This  makes  the  fragment independent of the parentheses in the larger
4153           pattern.
4154    
4155       Checking for a used subpattern by name
4156    
4157           Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a
4158           used  subpattern  by  name.  For compatibility with earlier versions of
4159           PCRE, which had this facility before Perl, the syntax  (?(name)...)  is
4160           also  recognized. However, there is a possible ambiguity with this syn-
4161           tax, because subpattern names may  consist  entirely  of  digits.  PCRE
4162           looks  first for a named subpattern; if it cannot find one and the name
4163           consists entirely of digits, PCRE looks for a subpattern of  that  num-
4164           ber,  which must be greater than zero. Using subpattern names that con-
4165           sist entirely of digits is not recommended.
4166    
4167           Rewriting the above example to use a named subpattern gives this:
4168    
4169             (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
4170    
4171    
4172         If  the  condition  is  not  a sequence of digits or (R), it must be an     Checking for pattern recursion
4173    
4174           If the condition is the string (R), and there is no subpattern with the
4175           name  R, the condition is true if a recursive call to the whole pattern
4176           or any subpattern has been made. If digits or a name preceded by amper-
4177           sand follow the letter R, for example:
4178    
4179             (?(R3)...) or (?(R&name)...)
4180    
4181           the  condition is true if the most recent recursion is into the subpat-
4182           tern whose number or name is given. This condition does not  check  the
4183           entire recursion stack.
4184    
4185           At  "top  level", all these recursion test conditions are false. Recur-
4186           sive patterns are described below.
4187    
4188       Defining subpatterns for use by reference only
4189    
4190           If the condition is the string (DEFINE), and  there  is  no  subpattern
4191           with  the  name  DEFINE,  the  condition is always false. In this case,
4192           there may be only one alternative  in  the  subpattern.  It  is  always
4193           skipped  if  control  reaches  this  point  in the pattern; the idea of
4194           DEFINE is that it can be used to define "subroutines" that can be  ref-
4195           erenced  from elsewhere. (The use of "subroutines" is described below.)
4196           For example, a pattern to match an IPv4 address could be  written  like
4197           this (ignore whitespace and line breaks):
4198    
4199             (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
4200             \b (?&byte) (\.(?&byte)){3} \b
4201    
4202           The  first part of the pattern is a DEFINE group inside which a another
4203           group named "byte" is defined. This matches an individual component  of
4204           an  IPv4  address  (a number less than 256). When matching takes place,
4205           this part of the pattern is skipped because DEFINE acts  like  a  false
4206           condition.
4207    
4208           The rest of the pattern uses references to the named group to match the
4209           four dot-separated components of an IPv4 address, insisting on  a  word
4210           boundary at each end.
4211    
4212       Assertion conditions
4213    
4214           If  the  condition  is  not  in any of the above formats, it must be an
4215         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.  This may be a positive or negative lookahead or  lookbehind
4216         assertion.  Consider  this  pattern,  again  containing non-significant         assertion.  Consider  this  pattern,  again  containing non-significant
4217         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
# Line 3602  COMMENTS Line 4236  COMMENTS
4236         at all.         at all.
4237    
4238         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If  the PCRE_EXTENDED option is set, an unescaped # character outside a
4239         character class introduces a comment that continues up to the next new-         character class introduces a  comment  that  continues  to  immediately
4240         line character in the pattern.         after the next newline in the pattern.
4241    
4242    
4243  RECURSIVE PATTERNS  RECURSIVE PATTERNS
# Line 3612  RECURSIVE PATTERNS Line 4246  RECURSIVE PATTERNS
4246         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited nested parentheses. Without the use of  recursion,  the  best
4247         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
4248         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth of nesting. It is not possible to  handle  an  arbitrary  nesting
4249         depth.  Perl  provides  a  facility  that allows regular expressions to         depth.
4250         recurse (amongst other things). It does this by interpolating Perl code  
4251         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-
4252         itself. A Perl pattern to solve the parentheses problem can be  created         sions to recurse (amongst other things). It does this by  interpolating
4253         like this:         Perl  code in the expression at run time, and the code can refer to the
4254           expression itself. A Perl pattern using code interpolation to solve the
4255           parentheses problem can be created like this:
4256    
4257           $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x;           $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x;
4258    
4259         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
4260         refers recursively to the pattern in which it appears. Obviously,  PCRE         refers recursively to the pattern in which it appears.
4261         cannot  support  the  interpolation  of Perl code. Instead, it supports  
4262         some special syntax for recursion of the entire pattern, and  also  for         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4263         individual subpattern recursion.         it  supports  special  syntax  for recursion of the entire pattern, and
4264           also for individual subpattern recursion.  After  its  introduction  in
4265           PCRE  and  Python,  this  kind of recursion was introduced into Perl at
4266           release 5.10.
4267    
4268         The  special item that consists of (? followed by a number greater than         A special item that consists of (? followed by a  number  greater  than
4269         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
4270         the  given  number, provided that it occurs inside that subpattern. (If         the given number, provided that it occurs inside that  subpattern.  (If
4271         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-
4272         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
4273         expression.         regular expression.
4274    
4275           In  PCRE (like Python, but unlike Perl), a recursive subpattern call is
4276           always treated as an atomic group. That is, once it has matched some of
4277           the subject string, it is never re-entered, even if it contains untried
4278           alternatives and there is a subsequent matching failure.
4279    
4280         For example, this PCRE pattern solves the  nested  parentheses  problem         This PCRE pattern solves the nested  parentheses  problem  (assume  the
4281         (assume  the  PCRE_EXTENDED  option  is  set  so  that  white  space is         PCRE_EXTENDED option is set so that white space is ignored):
        ignored):  
4282    
4283           \( ( (?>[^()]+) | (?R) )* \)           \( ( (?>[^()]+) | (?R) )* \)
4284    
4285         First it matches an opening parenthesis. Then it matches any number  of         First  it matches an opening parenthesis. Then it matches any number of
4286         substrings  which  can  either  be  a sequence of non-parentheses, or a         substrings which can either be a  sequence  of  non-parentheses,  or  a
4287         recursive match of the pattern itself (that is  a  correctly  parenthe-         recursive  match  of the pattern itself (that is, a correctly parenthe-
4288         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis.
4289    
4290         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
4291         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4292    
4293           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( (?>[^()]+) | (?1) )* \) )
4294    
4295         We have put the pattern into parentheses, and caused the  recursion  to         We  have  put the pattern into parentheses, and caused the recursion to
4296         refer  to them instead of the whole pattern. In a larger pattern, keep-         refer to them instead of the whole pattern.
4297         ing track of parenthesis numbers can be tricky. It may be  more  conve-  
4298         nient  to use named parentheses instead. For this, PCRE uses (?P>name),         In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be
4299         which is an extension to the Python syntax that  PCRE  uses  for  named         tricky.  This is made easier by the use of relative references. (A Perl
4300         parentheses (Perl does not provide named parentheses). We could rewrite         5.10 feature.)  Instead of (?1) in the  pattern  above  you  can  write
4301         the above example as follows:         (?-2) to refer to the second most recently opened parentheses preceding
4302           the recursion. In other  words,  a  negative  number  counts  capturing
4303           (?P<pn> \( ( (?>[^()]+) | (?P>pn) )* \) )         parentheses leftwards from the point at which it is encountered.
4304    
4305         This particular example pattern contains nested unlimited repeats,  and         It  is  also  possible  to refer to subsequently opened parentheses, by
4306         so  the  use of atomic grouping for matching strings of non-parentheses         writing references such as (?+2). However, these  cannot  be  recursive
4307         is important when applying the pattern to strings that  do  not  match.         because  the  reference  is  not inside the parentheses that are refer-
4308         For example, when this pattern is applied to         enced. They are always "subroutine" calls, as  described  in  the  next
4309           section.
4310    
4311           An  alternative  approach is to use named parentheses instead. The Perl
4312           syntax for this is (?&name); PCRE's earlier syntax  (?P>name)  is  also
4313           supported. We could rewrite the above example as follows:
4314    
4315             (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
4316    
4317           If  there  is more than one subpattern with the same name, the earliest
4318           one is used.
4319    
4320           This particular example pattern that we have been looking  at  contains
4321           nested  unlimited repeats, and so the use of atomic grouping for match-
4322           ing strings of non-parentheses is important when applying  the  pattern
4323           to strings that do not match. For example, when this pattern is applied
4324           to
4325    
4326           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
4327    
4328         it  yields "no match" quickly. However, if atomic grouping is not used,         it yields "no match" quickly. However, if atomic grouping is not  used,
4329         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
4330         different  ways  the  + and * repeats can carve up the subject, and all         different ways the + and * repeats can carve up the  subject,  and  all
4331         have to be tested before failure can be reported.         have to be tested before failure can be reported.
4332    
4333         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
4334         those from the outermost level of the recursion at which the subpattern         those from the outermost level of the recursion at which the subpattern
4335         value is set.  If you want to obtain  intermediate  values,  a  callout         value  is  set.   If  you want to obtain intermediate values, a callout
4336         function can be used (see the next section and the pcrecallout documen-         function can be used (see below and the pcrecallout documentation).  If
4337         tation). If the pattern above is matched against         the pattern above is matched against
4338    
4339           (ab(cd)ef)           (ab(cd)ef)
4340    
4341         the value for the capturing parentheses is  "ef",  which  is  the  last         the  value  for  the  capturing  parentheses is "ef", which is the last
4342         value  taken  on at the top level. If additional parentheses are added,         value taken on at the top level. If additional parentheses  are  added,
4343         giving         giving
4344    
4345           \( ( ( (?>[^()]+) | (?R) )* ) \)           \( ( ( (?>[^()]+) | (?R) )* ) \)
4346              ^                        ^              ^                        ^
4347              ^                        ^              ^                        ^
4348    
4349         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
4350         parentheses.  If there are more than 15 capturing parentheses in a pat-         parentheses. If there are more than 15 capturing parentheses in a  pat-
4351         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,
4352         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-
4353         wards. If  no  memory  can  be  obtained,  the  match  fails  with  the         wards.  If  no  memory  can  be  obtained,  the  match  fails  with the
4354         PCRE_ERROR_NOMEMORY error.         PCRE_ERROR_NOMEMORY error.
4355    
4356         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
4357         recursion.  Consider this pattern, which matches text in  angle  brack-         recursion.   Consider  this pattern, which matches text in angle brack-
4358         ets,  allowing for arbitrary nesting. Only digits are allowed in nested         ets, allowing for arbitrary nesting. Only digits are allowed in  nested
4359         brackets (that is, when recursing), whereas any characters are  permit-         brackets  (that is, when recursing), whereas any characters are permit-
4360         ted at the outer level.         ted at the outer level.
4361    
4362           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >
4363    
4364         In  this  pattern, (?(R) is the start of a conditional subpattern, with         In this pattern, (?(R) is the start of a conditional  subpattern,  with
4365         two different alternatives for the recursive and  non-recursive  cases.         two  different  alternatives for the recursive and non-recursive cases.
4366         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
4367    
4368    
4369  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
4370    
4371         If the syntax for a recursive subpattern reference (either by number or         If the syntax for a recursive subpattern reference (either by number or
4372         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-
4373         ates  like  a  subroutine in a programming language. An earlier example         ates like a subroutine in a programming language. The "called"  subpat-
4374         pointed out that the pattern         tern may be defined before or after the reference. A numbered reference
4375           can be absolute or relative, as in these examples:
4376    
4377             (...(absolute)...)...(?2)...
4378             (...(relative)...)...(?-1)...
4379             (...(?+1)...(relative)...
4380    
4381           An earlier example pointed out that the pattern
4382    
4383           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4384    
# Line 3722  SUBPATTERNS AS SUBROUTINES Line 4388  SUBPATTERNS AS SUBROUTINES
4388           (sens|respons)e and (?1)ibility           (sens|respons)e and (?1)ibility
4389    
4390         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
4391         two strings. Such references must, however, follow  the  subpattern  to         two strings. Another example is  given  in  the  discussion  of  DEFINE
4392         which they refer.         above.
4393    
4394           Like recursive subpatterns, a "subroutine" call is always treated as an
4395           atomic group. That is, once it has matched some of the subject  string,
4396           it  is  never  re-entered, even if it contains untried alternatives and
4397           there is a subsequent matching failure.
4398    
4399           When a subpattern is used as a subroutine, processing options  such  as
4400           case-independence are fixed when the subpattern is defined. They cannot
4401           be changed for different calls. For example, consider this pattern:
4402    
4403             (abc)(?i:(?-1))
4404    
4405           It matches "abcabc". It does not match "abcABC" because the  change  of
4406           processing option does not affect the called subpattern.
4407 &