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revision 83 by nigel, Sat Feb 24 21:41:06 2007 UTC revision 155 by ph10, Tue Apr 24 13:36:11 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  Last updated: 15 August 2005  SEE ALSO
464  Copyright (c) 1997-2005 University of Cambridge.  
465           pcreapi(3), pcre_config(3).
466    
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. Callouts are supported, but the value of the  capture_top  field  is         5. Callouts are supported, but the value of the  capture_top  field  is
614         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.
615    
616         6.  The \C escape sequence, which (in the standard algorithm) matches a         6.  The \C escape sequence, which (in the standard algorithm) matches a
617         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-
618         rithm moves through the subject string one character at a time, for all         tive  algorithm  moves  through  the  subject string one character at a
619         active paths through the tree.         time, for all active paths through the tree.
620    
621    
622  ADVANTAGES OF THE DFA ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
623    
624         Using the DFA matching algorithm provides the following advantages:         Using the alternative matching algorithm provides the following  advan-
625           tages:
626    
627         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-
628         ically  found,  and  in particular, the longest match is found. To find         ically found, and in particular, the longest match is  found.  To  find
629         more than one match using the standard algorithm, you have to do kludgy         more than one match using the standard algorithm, you have to do kludgy
630         things with callouts.         things with callouts.
631    
632         2.  There is much better support for partial matching. The restrictions         2. There is much better support for partial matching. The  restrictions
633         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-
634         rithm  for partial matching do not apply to the DFA algorithm. For non-         rithm for partial matching do not apply to the  alternative  algorithm.
635         anchored patterns, the starting position of a partial match  is  avail-         For  non-anchored patterns, the starting position of a partial match is
636         able.         available.
637    
638         3.  Because  the  DFA algorithm scans the subject string just once, and         3. Because the alternative algorithm  scans  the  subject  string  just
639         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
640         strings  to  the matching function in several pieces, checking for par-         subject strings to the matching function in  several  pieces,  checking
641         tial matching each time.         for partial matching each time.
642    
643    
644  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
645    
646         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
647    
648         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
649         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
650         because it is less susceptible to optimization.         because it is less susceptible to optimization.
651    
652         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
653    
654         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
655         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
        rithm.  
656    
657  Last updated: 28 February 2005  
658  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
659    
660           Philip Hazel
661           University Computing Service
662           Cambridge CB2 3QH, England.
663    
664    
665    REVISION
666    
667           Last updated: 06 March 2007
668           Copyright (c) 1997-2007 University of Cambridge.
669  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
670    
671    
# Line 616  PCRE NATIVE API Line 718  PCRE NATIVE API
718         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
719              const char *name);              const char *name);
720    
721           int pcre_get_stringtable_entries(const pcre *code,
722                const char *name, char **first, char **last);
723    
724         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
725              int stringcount, int stringnumber,              int stringcount, int stringnumber,
726              const char **stringptr);              const char **stringptr);
# Line 654  PCRE NATIVE API Line 759  PCRE NATIVE API
759  PCRE API OVERVIEW  PCRE API OVERVIEW
760    
761         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
762         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
763         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
764         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
765         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 781  PCRE API OVERVIEW
781    
782         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
783         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
784         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
785         the  subject),  not  just  one. However, this algorithm does not return         point  in  the subject), and scans the subject just once. However, this
786         captured substrings. A description of the two matching  algorithms  and         algorithm does not return captured substrings. A description of the two
787         their  advantages  and disadvantages is given in the pcrematching docu-         matching  algorithms and their advantages and disadvantages is given in
788         mentation.         the pcrematching documentation.
789    
790         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
791         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 692  PCRE API OVERVIEW Line 797  PCRE API OVERVIEW
797           pcre_get_named_substring()           pcre_get_named_substring()
798           pcre_get_substring_list()           pcre_get_substring_list()
799           pcre_get_stringnumber()           pcre_get_stringnumber()
800             pcre_get_stringtable_entries()
801    
802         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
803         to free the memory used for extracted strings.         to free the memory used for extracted strings.
# Line 723  PCRE API OVERVIEW Line 829  PCRE API OVERVIEW
829         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
830         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
831         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
832         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
833         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-
834         management, it runs more slowly.  Separate functions  are  provided  so         ments that have limited stacks. Because of the greater  use  of  memory
835         that  special-purpose  external  code  can  be used for this case. When         management,  it  runs  more  slowly. Separate functions are provided so
836         used, these functions are always called in a  stack-like  manner  (last         that special-purpose external code can be  used  for  this  case.  When
837         obtained,  first freed), and always for memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
838           obtained, first freed), and always for memory blocks of the same  size.
839           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
840           mentation.
841    
842         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
843         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 845  PCRE API OVERVIEW
845         pcrecallout documentation.         pcrecallout documentation.
846    
847    
848    NEWLINES
849    
850           PCRE  supports five different conventions for indicating line breaks in
851           strings: a single CR (carriage return) character, a  single  LF  (line-
852           feed) character, the two-character sequence CRLF, any of the three pre-
853           ceding, or any Unicode newline sequence. The Unicode newline  sequences
854           are  the  three just mentioned, plus the single characters VT (vertical
855           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
856           separator, U+2028), and PS (paragraph separator, U+2029).
857    
858           Each  of  the first three conventions is used by at least one operating
859           system as its standard newline sequence. When PCRE is built, a  default
860           can  be  specified.  The default default is LF, which is the Unix stan-
861           dard. When PCRE is run, the default can be overridden,  either  when  a
862           pattern is compiled, or when it is matched.
863    
864           In the PCRE documentation the word "newline" is used to mean "the char-
865           acter or pair of characters that indicate a line break". The choice  of
866           newline  convention  affects  the  handling of the dot, circumflex, and
867           dollar metacharacters, the handling of #-comments in /x mode, and, when
868           CRLF  is a recognized line ending sequence, the match position advance-
869           ment for a non-anchored pattern. The choice of newline convention  does
870           not affect the interpretation of the \n or \r escape sequences.
871    
872    
873  MULTITHREADING  MULTITHREADING
874    
875         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 887  SAVING PRECOMPILED PATTERNS FOR LATER US
887         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
888         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
889         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
890         pcreprecompile documentation.         pcreprecompile documentation. However, compiling a  regular  expression
891           with  one version of PCRE for use with a different version is not guar-
892           anteed to work and may cause crashes.
893    
894    
895  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
# Line 782  CHECKING BUILD-TIME OPTIONS Line 918  CHECKING BUILD-TIME OPTIONS
918    
919           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
920    
921         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
922         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
923         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,
924         operating system.         and  -1  for  ANY. The default should normally be the standard sequence
925           for your operating system.
926    
927           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
928    
929         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
930         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
931         4.  Larger  values  allow larger regular expressions to be compiled, at         4. Larger values allow larger regular expressions to  be  compiled,  at
932         the expense of slower matching. The default value of  2  is  sufficient         the  expense  of  slower matching. The default value of 2 is sufficient
933         for  all  but  the  most massive patterns, since it allows the compiled         for all but the most massive patterns, since  it  allows  the  compiled
934         pattern to be up to 64K in size.         pattern to be up to 64K in size.
935    
936           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
937    
938         The output is an integer that contains the threshold  above  which  the         The  output  is  an integer that contains the threshold above which the
939         POSIX  interface  uses malloc() for output vectors. Further details are         POSIX interface uses malloc() for output vectors. Further  details  are
940         given in the pcreposix documentation.         given in the pcreposix documentation.
941    
942           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
943    
944         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
945         internal  matching  function  calls in a pcre_exec() execution. Further         internal matching function calls in a  pcre_exec()  execution.  Further
946         details are given with pcre_exec() below.         details are given with pcre_exec() below.
947    
948             PCRE_CONFIG_MATCH_LIMIT_RECURSION
949    
950           The  output is an integer that gives the default limit for the depth of
951           recursion when calling the internal matching function in a  pcre_exec()
952           execution. Further details are given with pcre_exec() below.
953    
954           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
955    
956         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
957         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
958         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
959         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
960         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
961         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
962         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
963    
964    
# Line 832  COMPILING A PATTERN Line 975  COMPILING A PATTERN
975    
976         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
977         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
978         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
979         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
980    
981         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
982         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
983         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
984         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
985         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
986         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
987         required.         longer required.
988    
989         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
990         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
991         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
992         ment, which is an address (see below).         ment, which is an address (see below).
993    
994         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
995         tion.  It  should  be  zero  if  no options are required. The available         pilation. It should be zero if no options are required.  The  available
996         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them, in particular, those that
997         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
998         pattern (see the detailed description  in  the  pcrepattern  documenta-         pattern  (see  the  detailed  description in the pcrepattern documenta-
999         tion).  For  these options, the contents of the options argument speci-         tion). For these options, the contents of the options  argument  speci-
1000         fies their initial settings at the start of compilation and  execution.         fies  their initial settings at the start of compilation and execution.
1001         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
1002         at compile time.         of matching as well as at compile time.
1003    
1004         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1005         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1006         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-
1007         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
1008         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-
1009         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
1010           by  erroffset,  which must not be NULL. If it is, an immediate error is
1011         given.         given.
1012    
1013         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 1070  COMPILING A PATTERN
1070    
1071         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
1072         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
1073         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
1074         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1075         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
1076         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1077    
1078           PCRE_DOTALL           PCRE_DOTALL
1079    
1080         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-
1081         acters, including newlines. Without it,  newlines  are  excluded.  This         acters, including those that indicate newline. Without it, a  dot  does
1082         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
1083         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
1084         always  matches a newline character, independent of the setting of this         by  a (?s) option setting. A negative class such as [^a] always matches
1085         option.         newline characters, independent of the setting of this option.
1086    
1087             PCRE_DUPNAMES
1088    
1089           If this bit is set, names used to identify capturing  subpatterns  need
1090           not be unique. This can be helpful for certain types of pattern when it
1091           is known that only one instance of the named  subpattern  can  ever  be
1092           matched.  There  are  more details of named subpatterns below; see also
1093           the pcrepattern documentation.
1094    
1095           PCRE_EXTENDED           PCRE_EXTENDED
1096    
# Line 946  COMPILING A PATTERN Line 1098  COMPILING A PATTERN
1098         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1099         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1100         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1101         line character, inclusive, are also  ignored.  This  is  equivalent  to         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1102         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-
1103         option setting.         ting.
1104    
1105         This option makes it possible to include  comments  inside  complicated         This option makes it possible to include  comments  inside  complicated
1106         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 1116  COMPILING A PATTERN
1116         letter  that  has  no  special  meaning causes an error, thus reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1117         these combinations for future expansion. By  default,  as  in  Perl,  a         these combinations for future expansion. By  default,  as  in  Perl,  a
1118         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
1119         literal. There are at present no  other  features  controlled  by  this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1120         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
1121           can also be set by a (?X) option setting within a pattern.
1122    
1123           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1124    
1125         If  this  option  is  set,  an  unanchored pattern is required to match         If this option is set, an  unanchored  pattern  is  required  to  match
1126         before or at the first newline character in the subject string,  though         before  or  at  the  first  newline  in  the subject string, though the
1127         the matched text may continue over the newline.         matched text may continue over the newline.
1128    
1129           PCRE_MULTILINE           PCRE_MULTILINE
1130    
1131         By  default,  PCRE  treats the subject string as consisting of a single         By default, PCRE treats the subject string as consisting  of  a  single
1132         line of characters (even if it actually contains newlines). The  "start         line  of characters (even if it actually contains newlines). The "start
1133         of  line"  metacharacter  (^)  matches only at the start of the string,         of line" metacharacter (^) matches only at the  start  of  the  string,
1134         while the "end of line" metacharacter ($) matches only at  the  end  of         while  the  "end  of line" metacharacter ($) matches only at the end of
1135         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1136         is set). This is the same as Perl.         is set). This is the same as Perl.
1137    
1138         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"
1139         constructs  match  immediately following or immediately before any new-         constructs match immediately following or immediately  before  internal
1140         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
1141         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
1142         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-
1143         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,
1144         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1145    
1146             PCRE_NEWLINE_CR
1147             PCRE_NEWLINE_LF
1148             PCRE_NEWLINE_CRLF
1149             PCRE_NEWLINE_ANYCRLF
1150             PCRE_NEWLINE_ANY
1151    
1152           These  options  override the default newline definition that was chosen
1153           when PCRE was built. Setting the first or the second specifies  that  a
1154           newline  is  indicated  by a single character (CR or LF, respectively).
1155           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1156           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1157           that any of the three preceding sequences should be recognized. Setting
1158           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1159           recognized. The Unicode newline sequences are the three just mentioned,
1160           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1161           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1162           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1163           UTF-8 mode.
1164    
1165           The newline setting in the  options  word  uses  three  bits  that  are
1166           treated as a number, giving eight possibilities. Currently only six are
1167           used (default plus the five values above). This means that if  you  set
1168           more  than one newline option, the combination may or may not be sensi-
1169           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1170           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1171           cause an error.
1172    
1173           The only time that a line break is specially recognized when  compiling
1174           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1175           character class is encountered. This indicates  a  comment  that  lasts
1176           until  after the next line break sequence. In other circumstances, line
1177           break  sequences  are  treated  as  literal  data,   except   that   in
1178           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1179           and are therefore ignored.
1180    
1181           The newline option that is set at compile time becomes the default that
1182           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1183    
1184           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1185    
1186         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 1222  COMPILATION ERROR CODES
1222    
1223         The following table lists the error  codes  than  may  be  returned  by         The following table lists the error  codes  than  may  be  returned  by
1224         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(),  along with the error messages that may be returned by
1225         both compiling functions.         both compiling functions. As PCRE has developed, some error codes  have
1226           fallen out of use. To avoid confusion, they have not been re-used.
1227    
1228            0  no error            0  no error
1229            1  \ at end of pattern            1  \ at end of pattern
# Line 1043  COMPILATION ERROR CODES Line 1235  COMPILATION ERROR CODES
1235            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1236            8  range out of order in character class            8  range out of order in character class
1237            9  nothing to repeat            9  nothing to repeat
1238           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1239           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1240           12  unrecognized character after (?           12  unrecognized character after (?
1241           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 1244  COMPILATION ERROR CODES
1244           16  erroffset passed as NULL           16  erroffset passed as NULL
1245           17  unknown option bit(s) set           17  unknown option bit(s) set
1246           18  missing ) after comment           18  missing ) after comment
1247           19  parentheses nested too deeply           19  [this code is not in use]
1248           20  regular expression too large           20  regular expression too large
1249           21  failed to get memory           21  failed to get memory
1250           22  unmatched parentheses           22  unmatched parentheses
1251           23  internal error: code overflow           23  internal error: code overflow
1252           24  unrecognized character after (?<           24  unrecognized character after (?<
1253           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1254           26  malformed number after (?(           26  malformed number or name after (?(
1255           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1256           28  assertion expected after (?(           28  assertion expected after (?(
1257           29  (?R or (?digits must be followed by )           29  (?R or (?digits must be followed by )
1258           30  unknown POSIX class name           30  unknown POSIX class name
1259           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1260           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1261           33  spare error           33  [this code is not in use]
1262           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1263           35  invalid condition (?(0)           35  invalid condition (?(0)
1264           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1075  COMPILATION ERROR CODES Line 1267  COMPILATION ERROR CODES
1267           39  closing ) for (?C expected           39  closing ) for (?C expected
1268           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1269           41  unrecognized character after (?P           41  unrecognized character after (?P
1270           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1271           43  two named groups have the same name           43  two named subpatterns have the same name
1272           44  invalid UTF-8 string           44  invalid UTF-8 string
1273           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1274           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1275           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1276             48  subpattern name is too long (maximum 32 characters)
1277             49  too many named subpatterns (maximum 10,000)
1278             50  repeated subpattern is too long
1279             51  octal value is greater than \377 (not in UTF-8 mode)
1280             52  internal error: overran compiling workspace
1281             53   internal  error:  previously-checked  referenced  subpattern not
1282           found
1283             54  DEFINE group contains more than one branch
1284             55  repeating a DEFINE group is not allowed
1285             56  inconsistent NEWLINE options"
1286    
1287    
1288  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1111  STUDYING A PATTERN Line 1313  STUDYING A PATTERN
1313    
1314         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.
1315         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1316         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
1317         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
1318         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
1319           after calling pcre_study(), to be sure that it has run successfully.
1320    
1321         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1322    
# Line 1124  STUDYING A PATTERN Line 1327  STUDYING A PATTERN
1327             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1328    
1329         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1330         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-
1331         ble starting bytes is created.         ble starting bytes is created.
1332    
1333    
1334  LOCALE SUPPORT  LOCALE SUPPORT
1335    
1336         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1337         letters digits, or whatever, by reference to a set of  tables,  indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1338         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
1339         characters with codes less than 128. Higher-valued  codes  never  match         characters  with  codes  less than 128. Higher-valued codes never match
1340         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
1341         with Unicode character property support.         with  Unicode  character property support. The use of locales with Uni-
1342           code is discouraged. If you are handling characters with codes  greater
1343         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
1344         is  built.  This  is  used when the final argument of pcre_compile() is         not try to mix the two.
1345         NULL, and is sufficient for many applications. An  alternative  set  of  
1346         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
1347         locale from the default. As more and more applications change to  using         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1348         Unicode, the need for this locale support is expected to die away.         applications.  Normally, the internal tables recognize only ASCII char-
1349           acters. However, when PCRE is built, it is possible to cause the inter-
1350         External  tables  are  built by calling the pcre_maketables() function,         nal tables to be rebuilt in the default "C" locale of the local system,
1351         which has no arguments, in the relevant locale. The result can then  be         which may cause them to be different.
1352         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For  
1353         example, to build and use tables that are appropriate  for  the  French         The  internal tables can always be overridden by tables supplied by the
1354         locale  (where  accented  characters  with  values greater than 128 are         application that calls PCRE. These may be created in a different locale
1355           from  the  default.  As more and more applications change to using Uni-
1356           code, the need for this locale support is expected to die away.
1357    
1358           External tables are built by calling  the  pcre_maketables()  function,
1359           which  has no arguments, in the relevant locale. The result can then be
1360           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1361           example,  to  build  and use tables that are appropriate for the French
1362           locale (where accented characters with  values  greater  than  128  are
1363         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1364    
1365           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1366           tables = pcre_maketables();           tables = pcre_maketables();
1367           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1368    
1369           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1370           if you are using Windows, the name for the French locale is "french".
1371    
1372         When pcre_maketables() runs, the tables are built  in  memory  that  is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1373         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1374         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 1414  INFORMATION ABOUT A PATTERN
1414         pattern:         pattern:
1415    
1416           int rc;           int rc;
1417           unsigned long int length;           size_t length;
1418           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1419             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1420             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
# Line 1232  INFORMATION ABOUT A PATTERN Line 1446  INFORMATION ABOUT A PATTERN
1446           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1447    
1448         Return  information  about  the first byte of any matched string, for a         Return  information  about  the first byte of any matched string, for a
1449         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored pattern. The fourth argument should point to an int  vari-
1450         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1451         compatibility.)         is still recognized for backwards compatibility.)
1452    
1453         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
1454         (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  
1455    
1456         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1457         branch starts with "^", or         branch starts with "^", or
1458    
1459         (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
1460         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1461    
1462         -1 is returned, indicating that the pattern matches only at  the  start         -1  is  returned, indicating that the pattern matches only at the start
1463         of  a  subject string or after any newline within the string. Otherwise         of a subject string or after any newline within the  string.  Otherwise
1464         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1465    
1466           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1467    
1468         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
1469         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
1470         matching string, a pointer to the table is returned. Otherwise NULL  is         matching  string, a pointer to the table is returned. Otherwise NULL is
1471         returned.  The fourth argument should point to an unsigned char * vari-         returned. The fourth argument should point to an unsigned char *  vari-
1472         able.         able.
1473    
1474           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1475    
1476         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
1477         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
1478         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1479         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
1480         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1481         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
1482         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1483    
# Line 1272  INFORMATION ABOUT A PATTERN Line 1485  INFORMATION ABOUT A PATTERN
1485           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1486           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1487    
1488         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1489         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1490         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1491         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1492         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
1493         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
1494         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1495         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
1496         which is described by these three values.         described by these three values.
1497    
1498         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
1499         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1500         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
1501         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1502         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
1503         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-
1504         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-
1505         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1506         For example, consider the following pattern  (assume  PCRE_EXTENDED  is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1507         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1508           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1509           ignored):
1510    
1511           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1512           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1513    
1514         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1515         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,
1516         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1517         as ??:         as ??:
1518    
# Line 1306  INFORMATION ABOUT A PATTERN Line 1521  INFORMATION ABOUT A PATTERN
1521           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1522           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1523    
1524         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1525         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
1526         be different for each compiled pattern.         to be different for each compiled pattern.
1527    
1528           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1529    
1530         Return a copy of the options with which the pattern was  compiled.  The         Return  a  copy of the options with which the pattern was compiled. The
1531         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1532         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1533         by any top-level option settings within the pattern itself.         by any top-level option settings within the pattern itself.
1534    
1535         A  pattern  is  automatically  anchored by PCRE if all of its top-level         A pattern is automatically anchored by PCRE if  all  of  its  top-level
1536         alternatives begin with one of the following:         alternatives begin with one of the following:
1537    
1538           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1331  INFORMATION ABOUT A PATTERN Line 1546  INFORMATION ABOUT A PATTERN
1546    
1547           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1548    
1549         Return  the  size  of the compiled pattern, that is, the value that was         Return the size of the compiled pattern, that is, the  value  that  was
1550         passed as the argument to pcre_malloc() when PCRE was getting memory in         passed as the argument to pcre_malloc() when PCRE was getting memory in
1551         which to place the compiled data. The fourth argument should point to a         which to place the compiled data. The fourth argument should point to a
1552         size_t variable.         size_t variable.
# Line 1339  INFORMATION ABOUT A PATTERN Line 1554  INFORMATION ABOUT A PATTERN
1554           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1555    
1556         Return the size of the data block pointed to by the study_data field in         Return the size of the data block pointed to by the study_data field in
1557         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to         a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1558         pcre_malloc() when PCRE was getting memory into which to place the data         pcre_malloc() when PCRE was getting memory into which to place the data
1559         created  by  pcre_study(). The fourth argument should point to a size_t         created by pcre_study(). The fourth argument should point to  a  size_t
1560         variable.         variable.
1561    
1562    
# Line 1349  OBSOLETE INFO FUNCTION Line 1564  OBSOLETE INFO FUNCTION
1564    
1565         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1566    
1567         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1568         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1569         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1570         pcre_info()  is the number of capturing subpatterns, or one of the fol-         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1571         lowing negative numbers:         lowing negative numbers:
1572    
1573           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1574           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1575    
1576         If the optptr argument is not NULL, a copy of the  options  with  which         If  the  optptr  argument is not NULL, a copy of the options with which
1577         the  pattern  was  compiled  is placed in the integer it points to (see         the pattern was compiled is placed in the integer  it  points  to  (see
1578         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1579    
1580         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1581         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1582         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1583    
1584    
# Line 1371  REFERENCE COUNTS Line 1586  REFERENCE COUNTS
1586    
1587         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1588    
1589         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1590         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1591         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1592         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1593         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1594    
1595         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1596         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1597         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1598         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1599         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1600         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1601    
1602         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1603         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1604         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1605    
1606    
# Line 1395  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1610  MATCHING A PATTERN: THE TRADITIONAL FUNC
1610              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1611              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1612    
1613         The function pcre_exec() is called to match a subject string against  a         The  function pcre_exec() is called to match a subject string against a
1614         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1615         has been studied, the result of the study should be passed in the extra         has been studied, the result of the study should be passed in the extra
1616         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1617         and it operates in a Perl-like manner. For specialist use there is also         and it operates in a Perl-like manner. For specialist use there is also
1618         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1619         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1620    
1621         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1622         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1623         is possible to save compiled patterns and study data, and then use them         is possible to save compiled patterns and study data, and then use them
1624         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1625         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1626    
1627         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1425  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1640  MATCHING A PATTERN: THE TRADITIONAL FUNC
1640    
1641     Extra data for pcre_exec()     Extra data for pcre_exec()
1642    
1643         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
1644         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
1645         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-
1646         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
1647         lows:         fields (not necessarily in this order):
1648    
1649           unsigned long int flags;           unsigned long int flags;
1650           void *study_data;           void *study_data;
1651           unsigned long int match_limit;           unsigned long int match_limit;
1652             unsigned long int match_limit_recursion;
1653           void *callout_data;           void *callout_data;
1654           const unsigned char *tables;           const unsigned char *tables;
1655    
1656         The flags field is a bitmap that specifies which of  the  other  fields         The  flags  field  is a bitmap that specifies which of the other fields
1657         are set. The flag bits are:         are set. The flag bits are:
1658    
1659           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1660           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1661             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1662           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1663           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1664    
1665         Other  flag  bits should be set to zero. The study_data field is set in         Other flag bits should be set to zero. The study_data field is  set  in
1666         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1667         the appropriate flag bit. You should not set this yourself, but you may         the appropriate flag bit. You should not set this yourself, but you may
1668         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1669         flag bits.         flag bits.
1670    
1671         The match_limit field provides a means of preventing PCRE from using up         The match_limit field provides a means of preventing PCRE from using up
1672         a vast amount of resources when running patterns that are not going  to         a  vast amount of resources when running patterns that are not going to
1673         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1674         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1675         repeats.         repeats.
1676    
1677         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1678         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly  (sometimes  recursively). The limit set by match_limit is imposed
1679         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
1680         limiting the amount of recursion and backtracking that can take  place.         has  the  effect  of  limiting the amount of backtracking that can take
1681         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
1682         position in the subject string.         for each position in the subject string.
1683    
1684         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
1685         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1686         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1687         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra    block    in    which    match_limit    is    set,     and
1688         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
1689         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1690    
1691         The  pcre_callout  field is used in conjunction with the "callout" fea-         The match_limit_recursion field is similar to match_limit, but  instead
1692           of limiting the total number of times that match() is called, it limits
1693           the depth of recursion. The recursion depth is a  smaller  number  than
1694           the  total number of calls, because not all calls to match() are recur-
1695           sive.  This limit is of use only if it is set smaller than match_limit.
1696    
1697           Limiting  the  recursion  depth  limits the amount of stack that can be
1698           used, or, when PCRE has been compiled to use memory on the heap instead
1699           of the stack, the amount of heap memory that can be used.
1700    
1701           The  default  value  for  match_limit_recursion can be set when PCRE is
1702           built; the default default  is  the  same  value  as  the  default  for
1703           match_limit.  You can override the default by suppling pcre_exec() with
1704           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1705           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1706           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1707    
1708           The pcre_callout field is used in conjunction with the  "callout"  fea-
1709         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1710    
1711         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1712         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
1713         pattern. A non-NULL value is stored with the compiled pattern  only  if         pattern.  A  non-NULL value is stored with the compiled pattern only if
1714         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1715         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1716         PCRE's  internal  tables  to be used. This facility is helpful when re-         PCRE's internal tables to be used. This facility is  helpful  when  re-
1717         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
1718         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
1719         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1720         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1721    
1722     Option bits for pcre_exec()     Option bits for pcre_exec()
1723    
1724         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.
1725         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,
1726         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1727           PCRE_PARTIAL.
1728    
1729           PCRE_ANCHORED           PCRE_ANCHORED
1730    
# Line 1498  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1733  MATCHING A PATTERN: THE TRADITIONAL FUNC
1733         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
1734         unachored at matching time.         unachored at matching time.
1735    
1736             PCRE_NEWLINE_CR
1737             PCRE_NEWLINE_LF
1738             PCRE_NEWLINE_CRLF
1739             PCRE_NEWLINE_ANYCRLF
1740             PCRE_NEWLINE_ANY
1741    
1742           These options override  the  newline  definition  that  was  chosen  or
1743           defaulted  when the pattern was compiled. For details, see the descrip-
1744           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1745           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1746           ters. It may also alter the way the match position is advanced after  a
1747           match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,
1748           PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a  match  attempt
1749           fails  when the current position is at a CRLF sequence, the match posi-
1750           tion is advanced by two characters instead of one, in other  words,  to
1751           after the CRLF.
1752    
1753           PCRE_NOTBOL           PCRE_NOTBOL
1754    
1755         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1756         the  beginning  of  a  line, so the circumflex metacharacter should not         the beginning of a line, so the  circumflex  metacharacter  should  not
1757         match before it. Setting this without PCRE_MULTILINE (at compile  time)         match  before it. Setting this without PCRE_MULTILINE (at compile time)
1758         causes  circumflex  never to match. This option affects only the behav-         causes circumflex never to match. This option affects only  the  behav-
1759         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1760    
1761           PCRE_NOTEOL           PCRE_NOTEOL
1762    
1763         This option specifies that the end of the subject string is not the end         This option specifies that the end of the subject string is not the end
1764         of  a line, so the dollar metacharacter should not match it nor (except         of a line, so the dollar metacharacter should not match it nor  (except
1765         in multiline mode) a newline immediately before it. Setting this  with-         in  multiline mode) a newline immediately before it. Setting this with-
1766         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1767         option affects only the behaviour of the dollar metacharacter. It  does         option  affects only the behaviour of the dollar metacharacter. It does
1768         not affect \Z or \z.         not affect \Z or \z.
1769    
1770           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1771    
1772         An empty string is not considered to be a valid match if this option is         An empty string is not considered to be a valid match if this option is
1773         set. If there are alternatives in the pattern, they are tried.  If  all         set.  If  there are alternatives in the pattern, they are tried. If all
1774         the  alternatives  match  the empty string, the entire match fails. For         the alternatives match the empty string, the entire  match  fails.  For
1775         example, if the pattern         example, if the pattern
1776    
1777           a?b?           a?b?
1778    
1779         is applied to a string not beginning with "a" or "b",  it  matches  the         is  applied  to  a string not beginning with "a" or "b", it matches the
1780         empty  string at the start of the subject. With PCRE_NOTEMPTY set, this         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
1781         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
1782         rences of "a" or "b".         rences of "a" or "b".
1783    
1784         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1785         cial case of a pattern match of the empty  string  within  its  split()         cial  case  of  a  pattern match of the empty string within its split()
1786         function,  and  when  using  the /g modifier. It is possible to emulate         function, and when using the /g modifier. It  is  possible  to  emulate
1787         Perl's behaviour after matching a null string by first trying the match         Perl's behaviour after matching a null string by first trying the match
1788         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1789         if that fails by advancing the starting offset (see below)  and  trying         if  that  fails by advancing the starting offset (see below) and trying
1790         an ordinary match again. There is some code that demonstrates how to do         an ordinary match again. There is some code that demonstrates how to do
1791         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
1792    
1793           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1794    
1795         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
1796         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8 string is automatically checked when pcre_exec() is  subsequently
1797         called.  The value of startoffset is also checked  to  ensure  that  it         called.   The  value  of  startoffset is also checked to ensure that it
1798         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence         points to the start of a UTF-8 character. If an invalid UTF-8  sequence
1799         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1800         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is
1801         returned.         returned.
1802    
1803         If you already know that your subject is valid, and you  want  to  skip         If  you  already  know that your subject is valid, and you want to skip
1804         these    checks    for   performance   reasons,   you   can   set   the         these   checks   for   performance   reasons,   you   can    set    the
1805         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
1806         do  this  for the second and subsequent calls to pcre_exec() if you are         do this for the second and subsequent calls to pcre_exec() if  you  are
1807         making repeated calls to find all  the  matches  in  a  single  subject         making  repeated  calls  to  find  all  the matches in a single subject
1808         string.  However,  you  should  be  sure  that the value of startoffset         string. However, you should be  sure  that  the  value  of  startoffset
1809         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
1810         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         set, the effect of passing an invalid UTF-8 string as a subject,  or  a
1811         value of startoffset that does not point to the start of a UTF-8  char-         value  of startoffset that does not point to the start of a UTF-8 char-
1812         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1813    
1814           PCRE_PARTIAL           PCRE_PARTIAL
1815    
1816         This  option  turns  on  the  partial  matching feature. If the subject         This option turns on the  partial  matching  feature.  If  the  subject
1817         string fails to match the pattern, but at some point during the  match-         string  fails to match the pattern, but at some point during the match-
1818         ing  process  the  end of the subject was reached (that is, the subject         ing process the end of the subject was reached (that  is,  the  subject
1819         partially matches the pattern and the failure to  match  occurred  only         partially  matches  the  pattern and the failure to match occurred only
1820         because  there were not enough subject characters), pcre_exec() returns         because there were not enough subject characters), pcre_exec()  returns
1821         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1822         used,  there  are restrictions on what may appear in the pattern. These         used, there are restrictions on what may appear in the  pattern.  These
1823         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1824    
1825     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1826    
1827         The subject string is passed to pcre_exec() as a pointer in subject,  a         The  subject string is passed to pcre_exec() as a pointer in subject, a
1828         length  in  length, and a starting byte offset in startoffset. In UTF-8         length in length, and a starting byte offset in startoffset.  In  UTF-8
1829         mode, the byte offset must point to the start  of  a  UTF-8  character.         mode,  the  byte  offset  must point to the start of a UTF-8 character.
1830         Unlike  the  pattern string, the subject may contain binary zero bytes.         Unlike the pattern string, the subject may contain binary  zero  bytes.
1831         When the starting offset is zero, the search for a match starts at  the         When  the starting offset is zero, the search for a match starts at the
1832         beginning of the subject, and this is by far the most common case.         beginning of the subject, and this is by far the most common case.
1833    
1834         A  non-zero  starting offset is useful when searching for another match         A non-zero starting offset is useful when searching for  another  match
1835         in the same subject by calling pcre_exec() again after a previous  suc-         in  the same subject by calling pcre_exec() again after a previous suc-
1836         cess.   Setting  startoffset differs from just passing over a shortened         cess.  Setting startoffset differs from just passing over  a  shortened
1837         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
1838         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1839    
1840           \Biss\B           \Biss\B
1841    
1842         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
1843         only if the current position in the subject is not  a  word  boundary.)         only  if  the  current position in the subject is not a word boundary.)
1844         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
1845         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
1846         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
1847         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
1848         to  be  a  word  boundary. However, if pcre_exec() is passed the entire         to be a word boundary. However, if pcre_exec()  is  passed  the  entire
1849         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
1850         rence  of "iss" because it is able to look behind the starting point to         rence of "iss" because it is able to look behind the starting point  to
1851         discover that it is preceded by a letter.         discover that it is preceded by a letter.
1852    
1853         If a non-zero starting offset is passed when the pattern  is  anchored,         If  a  non-zero starting offset is passed when the pattern is anchored,
1854         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
1855         if the pattern does not require the match to be at  the  start  of  the         if  the  pattern  does  not require the match to be at the start of the
1856         subject.         subject.
1857    
1858     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
1859    
1860         In  general, a pattern matches a certain portion of the subject, and in         In general, a pattern matches a certain portion of the subject, and  in
1861         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
1862         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
1863         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
1864         subpattern"  is  used for a fragment of a pattern that picks out a sub-         subpattern" is used for a fragment of a pattern that picks out  a  sub-
1865         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
1866         that do not cause substrings to be captured.         that do not cause substrings to be captured.
1867    
1868         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of  integer
1869         offsets whose address is passed in ovector. The number of  elements  in         offsets  whose  address is passed in ovector. The number of elements in
1870         the  vector is passed in ovecsize, which must be a non-negative number.         the vector is passed in ovecsize, which must be a non-negative  number.
1871         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
1872    
1873         The first two-thirds of the vector is used to pass back  captured  sub-         The  first  two-thirds of the vector is used to pass back captured sub-
1874         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
1875         of the vector is used as workspace by pcre_exec() while  matching  cap-         of  the  vector is used as workspace by pcre_exec() while matching cap-
1876         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
1877         The length passed in ovecsize should always be a multiple of three.  If         The  length passed in ovecsize should always be a multiple of three. If
1878         it is not, it is rounded down.         it is not, it is rounded down.
1879    
1880         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
1881         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
1882         and  continuing  up  to two-thirds of its length at the most. The first         and continuing up to two-thirds of its length at the  most.  The  first
1883         element of a pair is set to the offset of the first character in a sub-         element of a pair is set to the offset of the first character in a sub-
1884         string,  and  the  second  is  set to the offset of the first character         string, and the second is set to the  offset  of  the  first  character
1885         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-
1886         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1], identify the portion of  the  subject  string  matched  by  the
1887         entire pattern. The next pair is used for the first  capturing  subpat-         entire  pattern.  The next pair is used for the first capturing subpat-
1888         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
1889         pairs that have been set. If there are no  capturing  subpatterns,  the         highest numbered pair that has been set. For example, if two substrings
1890         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
1891         first pair of offsets has been set.         subpatterns,  the return value from a successful match is 1, indicating
1892           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.  
1893    
1894         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1895         of the string that it matched that is returned.         of the string that it matched that is returned.
# Line 1660  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1903  MATCHING A PATTERN: THE TRADITIONAL FUNC
1903         substrings,  PCRE has to get additional memory for use during matching.         substrings,  PCRE has to get additional memory for use during matching.
1904         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1905    
1906         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
1907         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns  there  are  in  a  compiled pattern. The smallest size for
1908         that will allow for n captured substrings, in addition to  the  offsets         ovector that will allow for n captured substrings, in addition  to  the
1909         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.
1910    
1911           It  is  possible for capturing subpattern number n+1 to match some part
1912           of the subject when subpattern n has not been used at all. For example,
1913           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
1914           return from the function is 4, and subpatterns 1 and 3 are matched, but
1915           2  is  not.  When  this happens, both values in the offset pairs corre-
1916           sponding to unused subpatterns are set to -1.
1917    
1918           Offset values that correspond to unused subpatterns at the end  of  the
1919           expression  are  also  set  to  -1. For example, if the string "abc" is
1920           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
1921           matched.  The  return  from the function is 2, because the highest used
1922           capturing subpattern number is 1. However, you can refer to the offsets
1923           for  the  second  and third capturing subpatterns if you wish (assuming
1924           the vector is large enough, of course).
1925    
1926     Return values from pcre_exec()         Some convenience functions are provided  for  extracting  the  captured
1927           substrings as separate strings. These are described below.
1928    
1929       Error return values from pcre_exec()
1930    
1931         If  pcre_exec()  fails, it returns a negative number. The following are         If  pcre_exec()  fails, it returns a negative number. The following are
1932         defined in the header file:         defined in the header file:
# Line 1691  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1952  MATCHING A PATTERN: THE TRADITIONAL FUNC
1952         an environment with the other endianness. This is the error  that  PCRE         an environment with the other endianness. This is the error  that  PCRE
1953         gives when the magic number is not present.         gives when the magic number is not present.
1954    
1955           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1956    
1957         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1958         compiled pattern. This error could be caused by a bug  in  PCRE  or  by         compiled pattern. This error could be caused by a bug  in  PCRE  or  by
# Line 1713  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1974  MATCHING A PATTERN: THE TRADITIONAL FUNC
1974    
1975           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
1976    
1977         The  recursion  and backtracking limit, as specified by the match_limit         The  backtracking  limit,  as  specified  by the match_limit field in a
1978         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra structure (or defaulted) was reached.  See  the  description
1979         description above.         above.
1980    
1981           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
1982    
# Line 1754  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2015  MATCHING A PATTERN: THE TRADITIONAL FUNC
2015    
2016         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.
2017    
2018             PCRE_ERROR_RECURSIONLIMIT (-21)
2019    
2020           The internal recursion limit, as specified by the match_limit_recursion
2021           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2022           description above.
2023    
2024             PCRE_ERROR_NULLWSLIMIT    (-22)
2025    
2026           When  a  group  that  can  match an empty substring is repeated with an
2027           unbounded upper limit, the subject position at the start of  the  group
2028           must be remembered, so that a test for an empty string can be made when
2029           the end of the group is reached. Some workspace is required  for  this;
2030           if it runs out, this error is given.
2031    
2032             PCRE_ERROR_BADNEWLINE     (-23)
2033    
2034           An invalid combination of PCRE_NEWLINE_xxx options was given.
2035    
2036           Error numbers -16 to -20 are not used by pcre_exec().
2037    
2038    
2039  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2040    
# Line 1774  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2055  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2055         string_list() are provided for extracting captured substrings  as  new,         string_list() are provided for extracting captured substrings  as  new,
2056         separate,  zero-terminated strings. These functions identify substrings         separate,  zero-terminated strings. These functions identify substrings
2057         by number. The next section describes functions  for  extracting  named         by number. The next section describes functions  for  extracting  named
2058         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2059         extracted and has a further zero added on the end, but  the  result  is  
2060         not, of course, a C string.         A  substring that contains a binary zero is correctly extracted and has
2061           a further zero added on the end, but the result is not, of course, a  C
2062           string.   However,  you  can  process such a string by referring to the
2063           length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2064           string().  Unfortunately, the interface to pcre_get_substring_list() is
2065           not adequate for handling strings containing binary zeros, because  the
2066           end of the final string is not independently indicated.
2067    
2068         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-
2069         tions: subject is the subject string that has  just  been  successfully         tions: subject is the subject string that has  just  been  successfully
# Line 1796  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2083  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2083         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2084         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2085         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
2086         the terminating zero, or one of         the terminating zero, or one of these error codes:
2087    
2088           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2089    
# Line 1812  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2099  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2099         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
2100         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
2101         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
2102         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
2103           error code
2104    
2105           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2106    
2107         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2108    
2109         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2110         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2111         the  subject, but subpattern n has not been used at all, they return an         the subject, but subpattern n has not been used at all, they return  an
2112         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2113         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2114         tive for unset substrings.         tive for unset substrings.
2115    
2116         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2117         string_list()  can  be  used  to free the memory returned by a previous         string_list() can be used to free the memory  returned  by  a  previous
2118         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2119         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2120         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.
2121         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-
2122         cial  interface  to  another  programming  language  which  cannot  use         cial   interface  to  another  programming  language  that  cannot  use
2123         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-
2124         vided.         vided.
2125    
2126    
# Line 1851  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2139  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2139              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2140              const char **stringptr);              const char **stringptr);
2141    
2142         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-
2143         ber.  For example, for this pattern         ber.  For example, for this pattern
2144    
2145           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2146    
2147         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
2148         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
2149         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-
2150         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
2151         there is no subpattern of that name.         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2152           subpattern of that name.
2153    
2154         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
2155         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
# Line 1879  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2168  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2168    
2169         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2170         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2171         ate.         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2172           behaviour may not be what you want (see the next section).
2173    
2174    
2175    DUPLICATE SUBPATTERN NAMES
2176    
2177           int pcre_get_stringtable_entries(const pcre *code,
2178                const char *name, char **first, char **last);
2179    
2180           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2181           subpatterns are not required to  be  unique.  Normally,  patterns  with
2182           duplicate  names  are such that in any one match, only one of the named
2183           subpatterns participates. An example is shown in the pcrepattern  docu-
2184           mentation. When duplicates are present, pcre_copy_named_substring() and
2185           pcre_get_named_substring() return the first substring corresponding  to
2186           the  given  name  that  is  set.  If  none  are set, an empty string is
2187           returned.  The pcre_get_stringnumber() function returns one of the num-
2188           bers  that are associated with the name, but it is not defined which it
2189           is.
2190    
2191           If you want to get full details of all captured substrings for a  given
2192           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2193           first argument is the compiled pattern, and the second is the name. The
2194           third  and  fourth  are  pointers to variables which are updated by the
2195           function. After it has run, they point to the first and last entries in
2196           the  name-to-number  table  for  the  given  name.  The function itself
2197           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2198           there  are none. The format of the table is described above in the sec-
2199           tion entitled Information about a  pattern.   Given  all  the  relevant
2200           entries  for the name, you can extract each of their numbers, and hence
2201           the captured data, if any.
2202    
2203    
2204  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
# Line 1908  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2227  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2227              int *workspace, int wscount);              int *workspace, int wscount);
2228    
2229         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2230         against a compiled pattern, using a "DFA" matching algorithm. This  has         against a compiled pattern, using a matching algorithm that  scans  the
2231         different  characteristics to the normal algorithm, and is not compati-         subject  string  just  once, and does not backtrack. This has different
2232         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics to the normal algorithm, and  is  not  compatible  with
2233         Nevertheless, there are times when this kind of matching can be useful.         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2234         For a discussion of the two matching algorithms, see  the  pcrematching         theless, there are times when this kind of matching can be useful.  For
2235         documentation.         a discussion of the two matching algorithms, see the pcrematching docu-
2236           mentation.
2237    
2238         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
2239         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-
2240         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2241         used in the same way as for pcre_exec(), so their  description  is  not         used  in  the  same way as for pcre_exec(), so their description is not
2242         repeated here.         repeated here.
2243    
2244         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2245         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2246         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2247         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2248         lot of possible matches.         lot of potential matches.
2249    
2250         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2251    
2252           int rc;           int rc;
2253           int ovector[10];           int ovector[10];
2254           int wspace[20];           int wspace[20];
2255           rc = pcre_exec(           rc = pcre_dfa_exec(
2256             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2257             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2258             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1946  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2266  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2266    
2267     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2268    
2269         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
2270         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-
2271         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2272         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
2273         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
2274         repeated here.         not repeated here.
2275    
2276           PCRE_PARTIAL           PCRE_PARTIAL
2277    
2278         This has the same general effect as it does for  pcre_exec(),  but  the         This  has  the  same general effect as it does for pcre_exec(), but the
2279         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2280         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2281         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have         PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2282         been no complete matches, but there is still at least one matching pos-         been no complete matches, but there is still at least one matching pos-
2283         sibility.  The portion of the string that provided the partial match is         sibility. The portion of the string that provided the partial match  is
2284         set as the first matching string.         set as the first matching string.
2285    
2286           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2287    
2288         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2289         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-
2290         algorithm works, this is necessarily the shortest possible match at the         tive  algorithm  works, this is necessarily the shortest possible match
2291         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2292    
2293           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2294    
2295         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2296         returns a partial match, it is possible to call it  again,  with  addi-         returns  a  partial  match, it is possible to call it again, with addi-
2297         tional  subject  characters,  and have it continue with the same match.         tional subject characters, and have it continue with  the  same  match.
2298         The PCRE_DFA_RESTART option requests this action; when it is  set,  the         The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2299         workspace  and wscount options must reference the same vector as before         workspace and wscount options must reference the same vector as  before
2300         because data about the match so far is left in  them  after  a  partial         because  data  about  the  match so far is left in them after a partial
2301         match.  There  is  more  discussion of this facility in the pcrepartial         match. There is more discussion of this  facility  in  the  pcrepartial
2302         documentation.         documentation.
2303    
2304     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2305    
2306         When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-         When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2307         string in the subject. Note, however, that all the matches from one run         string in the subject. Note, however, that all the matches from one run
2308         of the function start at the same point in  the  subject.  The  shorter         of  the  function  start  at the same point in the subject. The shorter
2309         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2310         if the pattern         if the pattern
2311    
2312           <.*>           <.*>
# Line 2001  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2321  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2321           <something> <something else>           <something> <something else>
2322           <something> <something else> <something further>           <something> <something else> <something further>
2323    
2324         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,
2325         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2326         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2327         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
2328         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
2329         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
2330         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility  with  the  way pcre_exec() returns data, even though the
2331         strings is different.)         meaning of the strings is different.)
2332    
2333         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-
2334         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
2335         fit  into ovector, the yield of the function is zero, and the vector is         fit into ovector, the yield of the function is zero, and the vector  is
2336         filled with the longest matches.         filled with the longest matches.
2337    
2338     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2339    
2340         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2341         Many  of  the  errors  are  the  same as for pcre_exec(), and these are         Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2342         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2343         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2344    
2345           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2346    
2347         This  return is given if pcre_dfa_exec() encounters an item in the pat-         This return is given if pcre_dfa_exec() encounters an item in the  pat-
2348         tern that it does not support, for instance, the use of \C  or  a  back         tern  that  it  does not support, for instance, the use of \C or a back
2349         reference.         reference.
2350    
2351           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2352    
2353         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
2354         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
2355         supported.         in a specific group. These are not supported.
2356    
2357           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2358    
2359         This  return  is given if pcre_dfa_exec() is called with an extra block         This return is given if pcre_dfa_exec() is called with an  extra  block
2360         that contains a setting of the match_limit field. This is not supported         that contains a setting of the match_limit field. This is not supported
2361         (it is meaningless).         (it is meaningless).
2362    
2363           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2364    
2365         This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the         This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2366         workspace vector.         workspace vector.
2367    
2368           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2369    
2370         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2371         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2372         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
2373         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2374    
2375  Last updated: 16 May 2005  
2376  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2377    
2378           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2379           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2380    
2381    
2382    AUTHOR
2383    
2384           Philip Hazel
2385           University Computing Service
2386           Cambridge CB2 3QH, England.
2387    
2388    
2389    REVISION
2390    
2391           Last updated: 24 April 2007
2392           Copyright (c) 1997-2007 University of Cambridge.
2393  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2394    
2395    
# Line 2080  PCRE CALLOUTS Line 2416  PCRE CALLOUTS
2416         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2417         points:         points:
2418    
2419           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2420    
2421         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
2422         called, PCRE automatically  inserts  callouts,  all  with  number  255,         called, PCRE automatically  inserts  callouts,  all  with  number  255,
# Line 2211  RETURN VALUES Line 2547  RETURN VALUES
2547         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
2548         itself.         itself.
2549    
2550  Last updated: 28 February 2005  
2551  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2552    
2553           Philip Hazel
2554           University Computing Service
2555           Cambridge CB2 3QH, England.
2556    
2557    
2558    REVISION
2559    
2560           Last updated: 06 March 2007
2561           Copyright (c) 1997-2007 University of Cambridge.
2562  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2563    
2564    
# Line 2226  NAME Line 2572  NAME
2572  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2573    
2574         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2575         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2576         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2577           tures that are expected to be in the forthcoming Perl 5.10.
2578         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2579         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
2580           of  what  it does have are given in the section on UTF-8 support in the
2581           main pcre page.
2582    
2583         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2584         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 2605  DIFFERENCES BETWEEN PCRE AND PERL
2605         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
2606         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2607         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-
2608         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2609           derived properties Any and L&.
2610    
2611         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2612         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2613         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2614         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2615         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2616    
2617             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2272  DIFFERENCES BETWEEN PCRE AND PERL Line 2621  DIFFERENCES BETWEEN PCRE AND PERL
2621             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2622             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2623    
2624         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2625         classes.         classes.
2626    
2627         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2628         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2629         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
2630         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2631         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2632    
2633         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2634         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2635         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2636    
2637           10.  There are some differences that are concerned with the settings of
2638           captured strings when part of  a  pattern  is  repeated.  For  example,
2639           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2640         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2641    
2642         10. PCRE provides some extensions to the Perl regular expression facil-         11. PCRE provides some extensions to the Perl regular expression facil-
2643         ities:         ities.   Perl  5.10  will  include new features that are not in earlier
2644           versions, some of which (such as named parentheses) have been  in  PCRE
2645           for some time. This list is with respect to Perl 5.10:
2646    
2647         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2648         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2649         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2650    
2651         (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 $
2652         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2653    
2654         (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-
2655         cial meaning is faulted.         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2656           ignored. (Perl can be made to issue a warning.)
2657    
2658         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2659         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 2665  DIFFERENCES BETWEEN PCRE AND PERL
2665         (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-
2666         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2667    
2668         (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.)  
2669    
2670         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The partial matching facility is PCRE-specific.
2671    
2672         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2673         Sun's Java package.         even on different hosts that have the other endianness.
2674    
2675         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2676           different way and is not Perl-compatible.
2677    
        (k) The callout facility is PCRE-specific.  
2678    
2679         (l) The partial matching facility is PCRE-specific.  AUTHOR
2680    
2681         (m) Patterns compiled by PCRE can be saved and re-used at a later time,         Philip Hazel
2682         even on different hosts that have the other endianness.         University Computing Service
2683           Cambridge CB2 3QH, England.
2684    
        (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  
        different way and is not Perl-compatible.  
2685    
2686  Last updated: 28 February 2005  REVISION
2687  Copyright (c) 1997-2005 University of Cambridge.  
2688           Last updated: 06 March 2007
2689           Copyright (c) 1997-2007 University of Cambridge.
2690  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2691    
2692    
# Line 2367  PCRE REGULAR EXPRESSION DETAILS Line 2722  PCRE REGULAR EXPRESSION DETAILS
2722         function, and how it differs from the normal function, are discussed in         function, and how it differs from the normal function, are discussed in
2723         the pcrematching page.         the pcrematching page.
2724    
2725    
2726    CHARACTERS AND METACHARACTERS
2727    
2728         A regular expression is a pattern that is  matched  against  a  subject         A regular expression is a pattern that is  matched  against  a  subject
2729         string  from  left  to right. Most characters stand for themselves in a         string  from  left  to right. Most characters stand for themselves in a
2730         pattern, and match the corresponding characters in the  subject.  As  a         pattern, and match the corresponding characters in the  subject.  As  a
# Line 2391  PCRE REGULAR EXPRESSION DETAILS Line 2749  PCRE REGULAR EXPRESSION DETAILS
2749    
2750         There are two different sets of metacharacters: those that  are  recog-         There are two different sets of metacharacters: those that  are  recog-
2751         nized  anywhere in the pattern except within square brackets, and those         nized  anywhere in the pattern except within square brackets, and those
2752         that are recognized in square brackets. Outside  square  brackets,  the         that are recognized within square brackets.  Outside  square  brackets,
2753         metacharacters are as follows:         the metacharacters are as follows:
2754    
2755           \      general escape character with several uses           \      general escape character with several uses
2756           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2439  BACKSLASH Line 2797  BACKSLASH
2797    
2798         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2799         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
2800         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2801         An escaping backslash can be used to include a whitespace or #  charac-         ing backslash can be used to include a whitespace  or  #  character  as
2802         ter as part of the pattern.         part of the pattern.
2803    
2804         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-
2805         ters, you can do so by putting them between \Q and \E. This is  differ-         ters, you can do so by putting them between \Q and \E. This is  differ-
# Line 2477  BACKSLASH Line 2835  BACKSLASH
2835           \t        tab (hex 09)           \t        tab (hex 09)
2836           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
2837           \xhh      character with hex code hh           \xhh      character with hex code hh
2838           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
2839    
2840         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,
2841         it is converted to upper case. Then bit 6 of the character (hex 40)  is         it is converted to upper case. Then bit 6 of the character (hex 40)  is
# Line 2485  BACKSLASH Line 2843  BACKSLASH
2843         becomes hex 7B.         becomes hex 7B.
2844    
2845         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
2846         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
2847         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
2848         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,
2849         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than
2850         \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-
2851         recognized. Instead, the initial \x will  be  interpreted  as  a  basic         nating }, this form of escape is not recognized.  Instead, the  initial
2852         hexadecimal  escape, with no following digits, giving a character whose         \x will be interpreted as a basic hexadecimal escape, with no following
2853         value is zero.         digits, giving a character whose value is zero.
2854    
2855         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
2856         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-
2857         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}.
2858         \x{dc}.  
2859           After \0 up to two further octal digits are read. If  there  are  fewer
2860         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
2861         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
2862         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
2863         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.  
2864    
2865         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-
2866         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
# Line 2516  BACKSLASH Line 2872  BACKSLASH
2872    
2873         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
2874         and  there have not been that many capturing subpatterns, PCRE re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
2875         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-
2876         gle byte from the least significant 8 bits of the value. Any subsequent         erate  a data character. Any subsequent digits stand for themselves. In
2877         digits stand for themselves.  For example:         non-UTF-8 mode, the value of a character specified  in  octal  must  be
2878           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
2879           example:
2880    
2881           \040   is another way of writing a space           \040   is another way of writing a space
2882           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2538  BACKSLASH Line 2896  BACKSLASH
2896         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
2897         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2898    
2899         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
2900         character (in UTF-8 mode) can be used both inside and outside character         inside and outside character classes. In addition, inside  a  character
2901         classes.  In  addition,  inside  a  character class, the sequence \b is         class,  the  sequence \b is interpreted as the backspace character (hex
2902         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"
2903         interpreted  as  the  character  "X".  Outside a character class, these         and  "X", respectively. Outside a character class, these sequences have
2904         sequences have different meanings (see below).         different meanings (see below).
2905    
2906       Absolute and relative back references
2907    
2908           The sequence \g followed by a positive or negative  number,  optionally
2909           enclosed  in  braces,  is  an absolute or relative back reference. Back
2910           references are discussed later, following the discussion  of  parenthe-
2911           sized subpatterns.
2912    
2913     Generic character types     Generic character types
2914    
2915         The third use of backslash is for specifying generic  character  types.         Another use of backslash is for specifying generic character types. The
2916         The following are always recognized:         following are always recognized:
2917    
2918           \d     any decimal digit           \d     any decimal digit
2919           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 2558  BACKSLASH Line 2923  BACKSLASH
2923           \W     any "non-word" character           \W     any "non-word" character
2924    
2925         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
2926         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
2927         of each pair.         of each pair.
2928    
2929         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
2930         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
2931         If  the current matching point is at the end of the subject string, all         If the current matching point is at the end of the subject string,  all
2932         of them fail, since there is no character to match.         of them fail, since there is no character to match.
2933    
2934         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
2935         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
2936         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
2937           "use locale;" is included in a Perl script, \s may match the VT charac-
2938           ter. In PCRE, it never does.)
2939    
2940         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
2941         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-
2942         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-
2943         specific  matching is taking place (see "Locale support" in the pcreapi         specific matching is taking place (see "Locale support" in the  pcreapi
2944         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
2945         codes  greater  than  128  are used for accented letters, and these are         systems, or "french" in Windows, some character codes greater than  128
2946         matched by \w.         are used for accented letters, and these are matched by \w.
2947    
2948         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,
2949         \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-
2950         code character property support is available.         code  character  property support is available. The use of locales with
2951           Unicode is discouraged.
2952    
2953       Newline sequences
2954    
2955           Outside a character class, the escape sequence \R matches  any  Unicode
2956           newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2957           equivalent to the following:
2958    
2959             (?>\r\n|\n|\x0b|\f|\r|\x85)
2960    
2961           This is an example of an "atomic group", details  of  which  are  given
2962           below.  This particular group matches either the two-character sequence
2963           CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
2964           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2965           return, U+000D), or NEL (next line, U+0085). The two-character sequence
2966           is treated as a single unit that cannot be split.
2967    
2968           In  UTF-8  mode, two additional characters whose codepoints are greater
2969           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2970           rator,  U+2029).   Unicode character property support is not needed for
2971           these characters to be recognized.
2972    
2973           Inside a character class, \R matches the letter "R".
2974    
2975     Unicode character properties     Unicode character properties
2976    
2977         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
2978         tional  escape sequences to match generic character types are available         tional  escape  sequences  to  match character properties are available
2979         when UTF-8 mode is selected. They are:         when UTF-8 mode is selected. They are:
2980    
2981          \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
2982          \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
2983          \X       an extended Unicode sequence           \X       an extended Unicode sequence
2984    
2985         The property names represented by xx above are limited to  the  Unicode         The property names represented by xx above are limited to  the  Unicode
2986         general  category properties. Each character has exactly one such prop-         script names, the general category properties, and "Any", which matches
2987         erty, specified by a two-letter abbreviation.  For  compatibility  with         any character (including newline). Other properties such as "InMusical-
2988         Perl,  negation  can be specified by including a circumflex between the         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
2989         opening brace and the property name. For example, \p{^Lu} is  the  same         not match any characters, so always causes a match failure.
2990         as \P{Lu}.  
2991           Sets of Unicode characters are defined as belonging to certain scripts.
2992         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.
2993         properties that start with that letter. In this case, in the absence of         For example:
2994         negation, the curly brackets in the escape sequence are optional; these  
2995         two examples have the same effect:           \p{Greek}
2996             \P{Han}
2997    
2998           Those that are not part of an identified script are lumped together  as
2999           "Common". The current list of scripts is:
3000    
3001           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3002           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
3003           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3004           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
3005           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
3006           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3007           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
3008           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3009           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3010    
3011           Each  character has exactly one general category property, specified by
3012           a two-letter abbreviation. For compatibility with Perl, negation can be
3013           specified  by  including a circumflex between the opening brace and the
3014           property name. For example, \p{^Lu} is the same as \P{Lu}.
3015    
3016           If only one letter is specified with \p or \P, it includes all the gen-
3017           eral  category properties that start with that letter. In this case, in
3018           the absence of negation, the curly brackets in the escape sequence  are
3019           optional; these two examples have the same effect:
3020    
3021           \p{L}           \p{L}
3022           \pL           \pL
3023    
3024         The following property codes are supported:         The following general category property codes are supported:
3025    
3026           C     Other           C     Other
3027           Cc    Control           Cc    Control
# Line 2653  BACKSLASH Line 3067  BACKSLASH
3067           Zp    Paragraph separator           Zp    Paragraph separator
3068           Zs    Space separator           Zs    Space separator
3069    
3070         Extended properties such as "Greek" or "InMusicalSymbols" are not  sup-         The  special property L& is also supported: it matches a character that
3071         ported by PCRE.         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
3072           classified as a modifier or "other".
3073    
3074           The  long  synonyms  for  these  properties that Perl supports (such as
3075           \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3076           any of these properties with "Is".
3077    
3078           No character that is in the Unicode table has the Cn (unassigned) prop-
3079           erty.  Instead, this property is assumed for any code point that is not
3080           in the Unicode table.
3081    
3082         Specifying  caseless  matching  does not affect these escape sequences.         Specifying  caseless  matching  does not affect these escape sequences.
3083         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
# Line 2676  BACKSLASH Line 3099  BACKSLASH
3099    
3100     Simple assertions     Simple assertions
3101    
3102         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3103         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
3104         a  match, without consuming any characters from the subject string. The         a  match, without consuming any characters from the subject string. The
3105         use of subpatterns for more complicated assertions is described  below.         use of subpatterns for more complicated assertions is described  below.
# Line 2684  BACKSLASH Line 3107  BACKSLASH
3107    
3108           \b     matches at a word boundary           \b     matches at a word boundary
3109           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3110           \A     matches at start of subject           \A     matches at the start of the subject
3111           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3112           \z     matches at end of subject                   also matches before a newline at the end of the subject
3113           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3114             \G     matches at the first matching position in the subject
3115    
3116         These  assertions may not appear in character classes (but note that \b         These  assertions may not appear in character classes (but note that \b
3117         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 3131  BACKSLASH
3131         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3132         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
3133         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
3134         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
3135         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.
3136         the end.  
3137           The \G assertion is true only when the current matching position is  at
3138         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
3139         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
3140         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-  
3141         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-
3142         mentation where \G can be useful.         mentation where \G can be useful.
3143    
3144         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
3145         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
3146         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
3147         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3148         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3149    
3150         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
3151         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3152         in the compiled regular expression.         in the compiled regular expression.
3153    
# Line 2732  BACKSLASH Line 3155  BACKSLASH
3155  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3156    
3157         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3158         character  is  an  assertion  that is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3159         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-
3160         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
3161         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3162         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3163    
3164         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
3165         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
3166         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
3167         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3168         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-
3169         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
3170         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3171    
3172         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
3173         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3174         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
3175         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
3176         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
3177         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.  
3178    
3179         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
3180         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
3181         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3182    
3183         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3184         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
3185         ately  after  and  immediately  before  an  internal newline character,         matches  immediately after internal newlines as well as at the start of
3186         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
3187         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         string.  A dollar matches before any newlines in the string, as well as
3188         string "def\nabc" (where \n represents a newline character)  in  multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3189         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3190         in single line mode because all branches start with ^ are not  anchored         not indicate newlines.
3191         in  multiline  mode,  and  a  match for circumflex is possible when the  
3192         startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3193         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3194           Consequently, patterns that are anchored in single  line  mode  because
3195         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
3196         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
3197         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
3198         not.         PCRE_MULTILINE is set.
3199    
3200           Note that the sequences \A, \Z, and \z can be used to match  the  start
3201           and  end of the subject in both modes, and if all branches of a pattern
3202           start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3203           set.
3204    
3205    
3206  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3207    
3208         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-
3209         ter  in  the  subject,  including a non-printing character, but not (by         ter in the subject string except (by default) a character  that  signi-
3210         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
3211         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3212         the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-  
3213         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
3214         dollar, the only relationship being  that  they  both  involve  newline         that  character; when the two-character sequence CRLF is used, dot does
3215         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3216           matches  all characters (including isolated CRs and LFs). When any Uni-
3217           code line endings are being recognized, dot does not match CR or LF  or
3218           any of the other line ending characters.
3219    
3220           The  behaviour  of  dot  with regard to newlines can be changed. If the
3221           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3222           exception. If the two-character sequence CRLF is present in the subject
3223           string, it takes two dots to match it.
3224    
3225           The handling of dot is entirely independent of the handling of  circum-
3226           flex  and  dollar,  the  only relationship being that they both involve
3227           newlines. Dot has no special meaning in a character class.
3228    
3229    
3230  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3231    
3232         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3233         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
3234         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
3235         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-
3236         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-
3237         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3238           avoided.
3239    
3240         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3241         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 3282  SQUARE BRACKETS AND CHARACTER CLASSES
3282         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
3283         support.         support.
3284    
3285         The newline character is never treated in any special way in  character         Characters that might indicate line breaks are  never  treated  in  any
3286         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         special  way  when  matching  character  classes,  whatever line-ending
3287         options is. A class such as [^a] will always match a newline.         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3288           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3289           of these characters.
3290    
3291         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-
3292         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 3312  SQUARE BRACKETS AND CHARACTER CLASSES
3312         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,
3313         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
3314         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3315         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
3316         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
3317         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3318         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 2945  VERTICAL BAR Line 3387  VERTICAL BAR
3387    
3388         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3389         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3390         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3391         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
3392         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3393         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.  
3394    
3395    
3396  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 2977  INTERNAL OPTION SETTING Line 3418  INTERNAL OPTION SETTING
3418         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
3419         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3420    
3421         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
3422         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3423           it, so
3424    
3425           (a(?i)b)c           (a(?i)b)c
3426    
3427         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
3428         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3429         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3430         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3431         example,         example,
3432    
3433           (a(?i)b|c)           (a(?i)b|c)
3434    
3435         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3436         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3437         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3438         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3439    
3440         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3441         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
3442         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.  
3443    
3444    
3445  SUBPATTERNS  SUBPATTERNS
# Line 3013  SUBPATTERNS Line 3452  SUBPATTERNS
3452           cat(aract|erpillar|)           cat(aract|erpillar|)
3453    
3454         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3455         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3456         string.         string.
3457    
3458         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 3481  SUBPATTERNS
3481           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3482    
3483         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3484         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.  
3485    
3486         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3487         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 3503  NAMED SUBPATTERNS
3503         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3504         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3505         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3506         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3507         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3508         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3509           tax.
3510    
3511           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3512           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3513           to capturing parentheses from other parts of the pattern, such as back-
3514           references,  recursion,  and conditions, can be made by name as well as
3515           by number.
3516    
3517           Names consist of up to  32  alphanumeric  characters  and  underscores.
3518         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3519         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
3520         number  translation table from a compiled pattern. There is also a con-         function calls for extracting the name-to-number translation table from
3521         venience function for extracting a captured substring by name. For fur-         a compiled pattern. There is also a convenience function for extracting
3522         ther details see the pcreapi documentation.         a captured substring by name.
3523    
3524           By  default, a name must be unique within a pattern, but it is possible
3525           to relax this constraint by setting the PCRE_DUPNAMES option at compile
3526           time.  This  can  be useful for patterns where only one instance of the
3527           named parentheses can match. Suppose you want to match the  name  of  a
3528           weekday,  either as a 3-letter abbreviation or as the full name, and in
3529           both cases you want to extract the abbreviation. This pattern (ignoring
3530           the line breaks) does the job:
3531    
3532             (?<DN>Mon|Fri|Sun)(?:day)?|
3533             (?<DN>Tue)(?:sday)?|
3534             (?<DN>Wed)(?:nesday)?|
3535             (?<DN>Thu)(?:rsday)?|
3536             (?<DN>Sat)(?:urday)?
3537    
3538           There  are  five capturing substrings, but only one is ever set after a
3539           match.  The convenience  function  for  extracting  the  data  by  name
3540           returns  the  substring  for  the first (and in this example, the only)
3541           subpattern of that name that matched.  This  saves  searching  to  find
3542           which  numbered  subpattern  it  was. If you make a reference to a non-
3543           unique named subpattern from elsewhere in the  pattern,  the  one  that
3544           corresponds  to  the  lowest number is used. For further details of the
3545           interfaces for handling named subpatterns, see the  pcreapi  documenta-
3546           tion.
3547    
3548    
3549  REPETITION  REPETITION
# Line 3083  REPETITION Line 3552  REPETITION
3552         following items:         following items:
3553    
3554           a literal data character           a literal data character
3555           the . metacharacter           the dot metacharacter
3556           the \C escape sequence           the \C escape sequence
3557           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3558             the \R escape sequence
3559           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3560           a character class           a character class
3561           a back reference (see next section)           a back reference (see next section)
# Line 3125  REPETITION Line 3595  REPETITION
3595         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3596         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3597    
3598         For  convenience  (and  historical compatibility) the three most common         For  convenience, the three most common quantifiers have single-charac-
3599         quantifiers have single-character abbreviations:         ter abbreviations:
3600    
3601           *    is equivalent to {0,}           *    is equivalent to {0,}
3602           +    is equivalent to {1,}           +    is equivalent to {1,}
# Line 3178  REPETITION Line 3648  REPETITION
3648         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
3649         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3650    
3651         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
3652         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3653         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
3654         words, it inverts the default behaviour.         words, it inverts the default behaviour.
# Line 3189  REPETITION Line 3659  REPETITION
3659         minimum or maximum.         minimum or maximum.
3660    
3661         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-
3662         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,
3663         pattern is implicitly anchored, because whatever follows will be  tried         the pattern is implicitly anchored, because whatever  follows  will  be
3664         against  every character position in the subject string, so there is no         tried  against every character position in the subject string, so there
3665         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
3666         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
3667           by \A.
3668    
3669         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-
3670         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-
3671         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3672    
3673         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3674         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3675         backreference  elsewhere in the pattern, a match at the start may fail,         backreference elsewhere in the pattern, a match at the start  may  fail
3676         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3677    
3678           (.*)abc\1           (.*)abc\1
3679    
3680         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3681         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3682    
3683         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 3686  REPETITION
3686           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
3687    
3688         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
3689         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
3690         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
3691         tions. For example, after         tions. For example, after
3692    
3693           /(a|(b))+/           /(a|(b))+/
# Line 3226  REPETITION Line 3697  REPETITION
3697    
3698  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
3699    
3700         With both maximizing and minimizing repetition, failure of what follows         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
3701         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition,  failure  of what follows normally causes the repeated item
3702         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
3703         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,
3704         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
3705         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
3706           no point in carrying on.
3707    
3708         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider, for example, the pattern \d+foo when applied to  the  subject
3709         line         line
# Line 3245  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3717  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3717         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
3718         to be re-evaluated in this way.         to be re-evaluated in this way.
3719    
3720         If we use atomic grouping for the previous example, the  matcher  would         If we use atomic grouping for the previous example, the  matcher  gives
3721         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
3722         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:  
3723    
3724           (?>\d+)foo           (?>\d+)foo
3725    
# Line 3280  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3751  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3751         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
3752         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
3753         simpler forms of atomic group. However, there is no difference  in  the         simpler forms of atomic group. However, there is no difference  in  the
3754         meaning  or  processing  of  a possessive quantifier and the equivalent         meaning  of  a  possessive  quantifier and the equivalent atomic group,
3755         atomic group.         though there may be a performance  difference;  possessive  quantifiers
3756           should be slightly faster.
3757         The possessive quantifier syntax is an extension to the Perl syntax. It  
3758         originates in Sun's Java package.         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
3759           tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first
3760         When  a  pattern  contains an unlimited repeat inside a subpattern that         edition of his book. Mike McCloskey liked it, so implemented it when he
3761         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
3762         atomic  group  is  the  only way to avoid some failing matches taking a         found its way into Perl at release 5.10.
3763    
3764           PCRE has an optimization that automatically "possessifies" certain sim-
3765           ple pattern constructs. For example, the sequence  A+B  is  treated  as
3766           A++B  because  there is no point in backtracking into a sequence of A's
3767           when B must follow.
3768    
3769           When a pattern contains an unlimited repeat inside  a  subpattern  that
3770           can  itself  be  repeated  an  unlimited number of times, the use of an
3771           atomic group is the only way to avoid some  failing  matches  taking  a
3772         very long time indeed. The pattern         very long time indeed. The pattern
3773    
3774           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
3775    
3776         matches an unlimited number of substrings that either consist  of  non-         matches  an  unlimited number of substrings that either consist of non-
3777         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it
3778         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
3779    
3780           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
3781    
3782         it takes a long time before reporting  failure.  This  is  because  the         it  takes  a  long  time  before reporting failure. This is because the
3783         string  can be divided between the internal \D+ repeat and the external         string can be divided between the internal \D+ repeat and the  external
3784         * 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
3785         example  uses  [!?]  rather than a single character at the end, because         example uses [!?] rather than a single character at  the  end,  because
3786         both PCRE and Perl have an optimization that allows  for  fast  failure         both  PCRE  and  Perl have an optimization that allows for fast failure
3787         when  a single character is used. They remember the last single charac-         when a single character is used. They remember the last single  charac-
3788         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
3789         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
3790         group, like this:         group, like this:
3791    
3792           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
3793    
3794         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences  of non-digits cannot be broken, and failure happens quickly.
3795    
3796    
3797  BACK REFERENCES  BACK REFERENCES
3798    
3799         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
3800         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-
3801         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
3802         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
3803    
3804         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
3805         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
3806         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
3807         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
3808         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
3809         tion  entitled  "Non-printing  characters" above for further details of         reference" of this type can make sense when a  repetition  is  involved
3810         the handling of digits following a backslash.         and  the  subpattern to the right has participated in an earlier itera-
3811           tion.
3812    
3813           It is not possible to have a numerical "forward back  reference"  to  a
3814           subpattern  whose  number  is  10  or  more using this syntax because a
3815           sequence such as \50 is interpreted as a character  defined  in  octal.
3816           See the subsection entitled "Non-printing characters" above for further
3817           details of the handling of digits following a backslash.  There  is  no
3818           such  problem  when named parentheses are used. A back reference to any
3819           subpattern is possible using named parentheses (see below).
3820    
3821           Another way of avoiding the ambiguity inherent in  the  use  of  digits
3822           following a backslash is to use the \g escape sequence, which is a fea-
3823           ture introduced in Perl 5.10. This escape must be followed by  a  posi-
3824           tive  or  a negative number, optionally enclosed in braces. These exam-
3825           ples are all identical:
3826    
3827             (ring), \1
3828             (ring), \g1
3829             (ring), \g{1}
3830    
3831           A positive number specifies an absolute reference without the ambiguity
3832           that  is  present  in  the older syntax. It is also useful when literal
3833           digits follow the reference. A negative number is a relative reference.
3834           Consider this example:
3835    
3836             (abc(def)ghi)\g{-1}
3837    
3838           The sequence \g{-1} is a reference to the most recently started captur-
3839           ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,
3840           \g{-2} would be equivalent to \1. The use of relative references can be
3841           helpful in long patterns, and also in  patterns  that  are  created  by
3842           joining together fragments that contain references within themselves.
3843    
3844         A back reference matches whatever actually matched the  capturing  sub-         A  back  reference matches whatever actually matched the capturing sub-
3845         pattern  in  the  current subject string, rather than anything matching         pattern in the current subject string, rather  than  anything  matching
3846         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
3847         of doing that). So the pattern         of doing that). So the pattern
3848    
3849           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
3850    
3851         matches  "sense and sensibility" and "response and responsibility", but         matches "sense and sensibility" and "response and responsibility",  but
3852         not "sense and responsibility". If caseful matching is in force at  the         not  "sense and responsibility". If caseful matching is in force at the
3853         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-
3854         ple,         ple,
3855    
3856           ((?i)rah)\s+\1           ((?i)rah)\s+\1
3857    
3858         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
3859         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
3860    
3861         Back  references  to named subpatterns use the Python syntax (?P=name).         Back references to named subpatterns use the Perl  syntax  \k<name>  or
3862         We could rewrite the above example as follows:         \k'name'  or  the  Python  syntax (?P=name). We could rewrite the above
3863           example in either of the following ways:
3864    
3865             (?<p1>(?i)rah)\s+\k<p1>
3866             (?P<p1>(?i)rah)\s+(?P=p1)
3867    
3868           (?<p1>(?i)rah)\s+(?P=p1)         A subpattern that is referenced by  name  may  appear  in  the  pattern
3869           before or after the reference.
3870    
3871         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
3872         subpattern  has  not actually been used in a particular match, any back         subpattern has not actually been used in a particular match,  any  back
3873         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
3874    
3875           (a|(bc))\2           (a|(bc))\2
3876    
3877         always fails if it starts to match "a" rather than "bc". Because  there         always  fails if it starts to match "a" rather than "bc". Because there
3878         may  be  many  capturing parentheses in a pattern, all digits following         may be many capturing parentheses in a pattern,  all  digits  following
3879         the backslash are taken as part of a potential back  reference  number.         the  backslash  are taken as part of a potential back reference number.
3880         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
3881         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         used  to  terminate  the back reference. If the PCRE_EXTENDED option is
3882         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-
3883         ments" below) can be used.         ments" below) can be used.
3884    
3885         A back reference that occurs inside the parentheses to which it  refers         A  back reference that occurs inside the parentheses to which it refers
3886         fails  when  the subpattern is first used, so, for example, (a\1) never         fails when the subpattern is first used, so, for example,  (a\1)  never
3887         matches.  However, such references can be useful inside  repeated  sub-         matches.   However,  such references can be useful inside repeated sub-
3888         patterns. For example, the pattern         patterns. For example, the pattern
3889    
3890           (a|b\1)+           (a|b\1)+
3891    
3892         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-
3893         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
3894         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
3895         work, the pattern must be such that the first iteration does  not  need         work,  the  pattern must be such that the first iteration does not need
3896         to  match the back reference. This can be done using alternation, as in         to match the back reference. This can be done using alternation, as  in
3897         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
3898    
3899    
3900  ASSERTIONS  ASSERTIONS
3901    
3902         An assertion is a test on the characters  following  or  preceding  the         An  assertion  is  a  test on the characters following or preceding the
3903         current  matching  point that does not actually consume any characters.         current matching point that does not actually consume  any  characters.
3904         The simple assertions coded as \b, \B, \A, \G, \Z,  \z,  ^  and  $  are         The  simple  assertions  coded  as  \b, \B, \A, \G, \Z, \z, ^ and $ are
3905         described above.         described above.
3906    
3907         More  complicated  assertions  are  coded as subpatterns. There are two         More complicated assertions are coded as  subpatterns.  There  are  two
3908         kinds: those that look ahead of the current  position  in  the  subject         kinds:  those  that  look  ahead of the current position in the subject
3909         string,  and  those  that  look  behind  it. An assertion subpattern is         string, and those that look  behind  it.  An  assertion  subpattern  is
3910         matched in the normal way, except that it does not  cause  the  current         matched  in  the  normal way, except that it does not cause the current
3911         matching position to be changed.         matching position to be changed.
3912    
3913         Assertion  subpatterns  are  not  capturing subpatterns, and may not be         Assertion subpatterns are not capturing subpatterns,  and  may  not  be
3914         repeated, because it makes no sense to assert the  same  thing  several         repeated,  because  it  makes no sense to assert the same thing several
3915         times.  If  any kind of assertion contains capturing subpatterns within         times. If any kind of assertion contains capturing  subpatterns  within
3916         it, these are counted for the purposes of numbering the capturing  sub-         it,  these are counted for the purposes of numbering the capturing sub-
3917         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
3918         out only for positive assertions, because it does not  make  sense  for         out  only  for  positive assertions, because it does not make sense for
3919         negative assertions.         negative assertions.
3920    
3921     Lookahead assertions     Lookahead assertions
# Line 3408  ASSERTIONS Line 3925  ASSERTIONS
3925    
3926           \w+(?=;)           \w+(?=;)
3927    
3928         matches a word followed by a semicolon, but does not include the  semi-         matches  a word followed by a semicolon, but does not include the semi-
3929         colon in the match, and         colon in the match, and
3930    
3931           foo(?!bar)           foo(?!bar)
3932    
3933         matches  any  occurrence  of  "foo" that is not followed by "bar". Note         matches any occurrence of "foo" that is not  followed  by  "bar".  Note
3934         that the apparently similar pattern         that the apparently similar pattern
3935    
3936           (?!foo)bar           (?!foo)bar
3937    
3938         does not find an occurrence of "bar"  that  is  preceded  by  something         does  not  find  an  occurrence  of "bar" that is preceded by something
3939         other  than "foo"; it finds any occurrence of "bar" whatsoever, because         other than "foo"; it finds any occurrence of "bar" whatsoever,  because
3940         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
3941         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
3942    
3943         If you want to force a matching failure at some point in a pattern, the         If you want to force a matching failure at some point in a pattern, the
3944         most convenient way to do it is  with  (?!)  because  an  empty  string         most  convenient  way  to  do  it  is with (?!) because an empty string
3945         always  matches, so an assertion that requires there not to be an empty         always matches, so an assertion that requires there not to be an  empty
3946         string must always fail.         string must always fail.
3947    
3948     Lookbehind assertions     Lookbehind assertions
3949    
3950         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
3951         for negative assertions. For example,         for negative assertions. For example,
3952    
3953           (?<!foo)bar           (?<!foo)bar
3954    
3955         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
3956         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
3957         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-
3958         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
3959         Thus         fixed length. Thus
3960    
3961           (?<=bullock|donkey)           (?<=bullock|donkey)
3962    
# Line 3447  ASSERTIONS Line 3964  ASSERTIONS
3964    
3965           (?<!dogs?|cats?)           (?<!dogs?|cats?)
3966    
3967         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
3968         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
3969         This  is  an  extension  compared  with  Perl (at least for 5.8), which         This is an extension compared with  Perl  (at  least  for  5.8),  which
3970         requires all branches to match the same length of string. An  assertion         requires  all branches to match the same length of string. An assertion
3971         such as         such as
3972    
3973           (?<=ab(c|de))           (?<=ab(c|de))
3974    
3975         is  not  permitted,  because  its single top-level branch can match two         is not permitted, because its single top-level  branch  can  match  two
3976         different lengths, but it is acceptable if rewritten to  use  two  top-         different  lengths,  but  it is acceptable if rewritten to use two top-
3977         level branches:         level branches:
3978    
3979           (?<=abc|abde)           (?<=abc|abde)
3980    
3981         The  implementation  of lookbehind assertions is, for each alternative,         The implementation of lookbehind assertions is, for  each  alternative,
3982         to temporarily move the current position back by the  fixed  width  and         to  temporarily  move the current position back by the fixed length and
3983         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
3984         rent position, the match is deemed to fail.         rent position, the assertion fails.
3985    
3986         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
3987         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode) to appear in lookbehind assertions, because it makes it  impossi-
3988         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,
3989         match different numbers of bytes, is also not permitted.         which can match different numbers of bytes, are also not permitted.
3990    
3991         Atomic  groups can be used in conjunction with lookbehind assertions to         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind
3992         specify efficient matching at the end of the subject string. Consider a         assertions  to  specify  efficient  matching  at the end of the subject
3993         simple pattern such as         string. Consider a simple pattern such as
3994    
3995           abcd$           abcd$
3996    
3997         when  applied  to  a  long string that does not match. Because matching         when applied to a long string that does  not  match.  Because  matching
3998         proceeds from left to right, PCRE will look for each "a" in the subject         proceeds from left to right, PCRE will look for each "a" in the subject
3999         and  then  see  if what follows matches the rest of the pattern. If the         and then see if what follows matches the rest of the  pattern.  If  the
4000         pattern is specified as         pattern is specified as
4001    
4002           ^.*abcd$           ^.*abcd$
4003    
4004         the initial .* matches the entire string at first, but when this  fails         the  initial .* matches the entire string at first, but when this fails
4005         (because there is no following "a"), it backtracks to match all but the         (because there is no following "a"), it backtracks to match all but the
4006         last character, then all but the last two characters, and so  on.  Once         last  character,  then all but the last two characters, and so on. Once
4007         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,
4008         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
4009    
          ^(?>.*)(?<=abcd)  
   
        or, equivalently, using the possessive quantifier syntax,  
   
4010           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4011    
4012         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
4013         entire  string.  The subsequent lookbehind assertion does a single test         entire string. The subsequent lookbehind assertion does a  single  test
4014         on the last four characters. If it fails, the match fails  immediately.         on  the last four characters. If it fails, the match fails immediately.
4015         For  long  strings, this approach makes a significant difference to the         For long strings, this approach makes a significant difference  to  the
4016         processing time.         processing time.
4017    
4018     Using multiple assertions     Using multiple assertions
# Line 3508  ASSERTIONS Line 4021  ASSERTIONS
4021    
4022           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4023    
4024         matches "foo" preceded by three digits that are not "999". Notice  that         matches  "foo" preceded by three digits that are not "999". Notice that
4025         each  of  the  assertions is applied independently at the same point in         each of the assertions is applied independently at the  same  point  in
4026         the subject string. First there is a  check  that  the  previous  three         the  subject  string.  First  there  is a check that the previous three
4027         characters  are  all  digits,  and  then there is a check that the same         characters are all digits, and then there is  a  check  that  the  same
4028         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4029         ceded  by  six  characters,  the first of which are digits and the last         ceded by six characters, the first of which are  digits  and  the  last
4030         three of which are not "999". For example, it  doesn't  match  "123abc-         three  of  which  are not "999". For example, it doesn't match "123abc-
4031         foo". A pattern to do that is         foo". A pattern to do that is
4032    
4033           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4034    
4035         This  time  the  first assertion looks at the preceding six characters,         This time the first assertion looks at the  preceding  six  characters,
4036         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4037         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4038    
# Line 3527  ASSERTIONS Line 4040  ASSERTIONS
4040    
4041           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4042    
4043         matches  an occurrence of "baz" that is preceded by "bar" which in turn         matches an occurrence of "baz" that is preceded by "bar" which in  turn
4044         is not preceded by "foo", while         is not preceded by "foo", while
4045    
4046           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4047    
4048         is another pattern that matches "foo" preceded by three digits and  any         is  another pattern that matches "foo" preceded by three digits and any
4049         three characters that are not "999".         three characters that are not "999".
4050    
4051    
4052  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4053    
4054         It  is possible to cause the matching process to obey a subpattern con-         It is possible to cause the matching process to obey a subpattern  con-
4055         ditionally or to choose between two alternative subpatterns,  depending         ditionally  or to choose between two alternative subpatterns, depending
4056         on  the result of an assertion, or whether a previous capturing subpat-         on the result of an assertion, or whether a previous capturing  subpat-
4057         tern matched or not. The two possible forms of  conditional  subpattern         tern  matched  or not. The two possible forms of conditional subpattern
4058         are         are
4059    
4060           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4061           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4062    
4063         If  the  condition is satisfied, the yes-pattern is used; otherwise the         If the condition is satisfied, the yes-pattern is used;  otherwise  the
4064         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-
4065         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4066    
4067         There are three kinds of condition. If the text between the parentheses         There are four kinds of condition: references  to  subpatterns,  refer-
4068         consists of a sequence of digits, the condition  is  satisfied  if  the         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4069         capturing  subpattern of that number has previously matched. The number  
4070         must be greater than zero. Consider the following pattern,  which  con-     Checking for a used subpattern by number
4071         tains  non-significant white space to make it more readable (assume the  
4072         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,
4073         discussion:         the condition is true if the capturing subpattern of  that  number  has
4074           previously matched.
4075    
4076           Consider  the  following  pattern, which contains non-significant white
4077           space to make it more readable (assume the PCRE_EXTENDED option) and to
4078           divide it into three parts for ease of discussion:
4079    
4080           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4081    
# Line 3572  CONDITIONAL SUBPATTERNS Line 4090  CONDITIONAL SUBPATTERNS
4090         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other  words,  this  pattern  matches  a  sequence  of non-parentheses,
4091         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4092    
4093         If the condition is the string (R), it is satisfied if a recursive call     Checking for a used subpattern by name
4094         to  the pattern or subpattern has been made. At "top level", the condi-  
4095         tion is false.  This  is  a  PCRE  extension.  Recursive  patterns  are         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a
4096         described in the next section.         used  subpattern  by  name.  For compatibility with earlier versions of
4097           PCRE, which had this facility before Perl, the syntax  (?(name)...)  is
4098           also  recognized. However, there is a possible ambiguity with this syn-
4099           tax, because subpattern names may  consist  entirely  of  digits.  PCRE
4100           looks  first for a named subpattern; if it cannot find one and the name
4101           consists entirely of digits, PCRE looks for a subpattern of  that  num-
4102           ber,  which must be greater than zero. Using subpattern names that con-
4103           sist entirely of digits is not recommended.
4104    
4105           Rewriting the above example to use a named subpattern gives this:
4106    
4107             (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
4108    
4109    
4110         If  the  condition  is  not  a sequence of digits or (R), it must be an     Checking for pattern recursion
4111    
4112           If the condition is the string (R), and there is no subpattern with the
4113           name  R, the condition is true if a recursive call to the whole pattern
4114           or any subpattern has been made. If digits or a name preceded by amper-
4115           sand follow the letter R, for example:
4116    
4117             (?(R3)...) or (?(R&name)...)
4118    
4119           the  condition is true if the most recent recursion is into the subpat-
4120           tern whose number or name is given. This condition does not  check  the
4121