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revision 83 by nigel, Sat Feb 24 21:41:06 2007 UTC revision 153 by ph10, Wed Apr 18 09:12:14 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  Last updated: 15 August 2005  
463  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
464    
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.
656         rithm.  
657    
658    AUTHOR
659    
660  Last updated: 28 February 2005         Philip Hazel
661  Copyright (c) 1997-2005 University of Cambridge.         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 782  CHECKING BUILD-TIME OPTIONS Line 916  CHECKING BUILD-TIME OPTIONS
916    
917           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
918    
919         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
920         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
921         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,
922         operating system.         and  -1  for  ANY. The default should normally be the standard sequence
923           for your operating system.
924    
925           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
926    
927         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
928         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
929         4.  Larger  values  allow larger regular expressions to be compiled, at         4. Larger values allow larger regular expressions to  be  compiled,  at
930         the expense of slower matching. The default value of  2  is  sufficient         the  expense  of  slower matching. The default value of 2 is sufficient
931         for  all  but  the  most massive patterns, since it allows the compiled         for all but the most massive patterns, since  it  allows  the  compiled
932         pattern to be up to 64K in size.         pattern to be up to 64K in size.
933    
934           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
935    
936         The output is an integer that contains the threshold  above  which  the         The  output  is  an integer that contains the threshold above which the
937         POSIX  interface  uses malloc() for output vectors. Further details are         POSIX interface uses malloc() for output vectors. Further  details  are
938         given in the pcreposix documentation.         given in the pcreposix documentation.
939    
940           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
941    
942         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
943         internal  matching  function  calls in a pcre_exec() execution. Further         internal matching function calls in a  pcre_exec()  execution.  Further
944         details are given with pcre_exec() below.         details are given with pcre_exec() below.
945    
946             PCRE_CONFIG_MATCH_LIMIT_RECURSION
947    
948           The  output is an integer that gives the default limit for the depth of
949           recursion when calling the internal matching function in a  pcre_exec()
950           execution. Further details are given with pcre_exec() below.
951    
952           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
953    
954         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
955         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
956         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
957         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
958         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
959         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
960         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
961    
962    
# Line 832  COMPILING A PATTERN Line 973  COMPILING A PATTERN
973    
974         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
975         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
976         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
977         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
978    
979         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
980         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
981         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
982         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
983         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
984         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
985         required.         longer required.
986    
987         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
988         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
989         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
990         ment, which is an address (see below).         ment, which is an address (see below).
991    
992         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
993         tion.  It  should  be  zero  if  no options are required. The available         pilation. It should be zero if no options are required.  The  available
994         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them, in particular, those that
995         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
996         pattern (see the detailed description  in  the  pcrepattern  documenta-         pattern  (see  the  detailed  description in the pcrepattern documenta-
997         tion).  For  these options, the contents of the options argument speci-         tion). For these options, the contents of the options  argument  speci-
998         fies their initial settings at the start of compilation and  execution.         fies  their initial settings at the start of compilation and execution.
999         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
1000         at compile time.         of matching as well as at compile time.
1001    
1002         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1003         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1004         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-
1005         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
1006         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-
1007         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
1008           by  erroffset,  which must not be NULL. If it is, an immediate error is
1009         given.         given.
1010    
1011         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 1068  COMPILING A PATTERN
1068    
1069         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
1070         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
1071         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
1072         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1073         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
1074         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1075    
1076           PCRE_DOTALL           PCRE_DOTALL
1077    
1078         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-
1079         acters, including newlines. Without it,  newlines  are  excluded.  This         acters, including those that indicate newline. Without it, a  dot  does
1080         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
1081         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
1082         always  matches a newline character, independent of the setting of this         by  a (?s) option setting. A negative class such as [^a] always matches
1083         option.         newline characters, independent of the setting of this option.
1084    
1085             PCRE_DUPNAMES
1086    
1087           If this bit is set, names used to identify capturing  subpatterns  need
1088           not be unique. This can be helpful for certain types of pattern when it
1089           is known that only one instance of the named  subpattern  can  ever  be
1090           matched.  There  are  more details of named subpatterns below; see also
1091           the pcrepattern documentation.
1092    
1093           PCRE_EXTENDED           PCRE_EXTENDED
1094    
# Line 946  COMPILING A PATTERN Line 1096  COMPILING A PATTERN
1096         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1097         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1098         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1099         line character, inclusive, are also  ignored.  This  is  equivalent  to         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1100         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-
1101         option setting.         ting.
1102    
1103         This option makes it possible to include  comments  inside  complicated         This option makes it possible to include  comments  inside  complicated
1104         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 1114  COMPILING A PATTERN
1114         letter  that  has  no  special  meaning causes an error, thus reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1115         these combinations for future expansion. By  default,  as  in  Perl,  a         these combinations for future expansion. By  default,  as  in  Perl,  a
1116         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
1117         literal. There are at present no  other  features  controlled  by  this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1118         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
1119           can also be set by a (?X) option setting within a pattern.
1120    
1121           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1122    
1123         If  this  option  is  set,  an  unanchored pattern is required to match         If this option is set, an  unanchored  pattern  is  required  to  match
1124         before or at the first newline character in the subject string,  though         before  or  at  the  first  newline  in  the subject string, though the
1125         the matched text may continue over the newline.         matched text may continue over the newline.
1126    
1127           PCRE_MULTILINE           PCRE_MULTILINE
1128    
1129         By  default,  PCRE  treats the subject string as consisting of a single         By default, PCRE treats the subject string as consisting  of  a  single
1130         line of characters (even if it actually contains newlines). The  "start         line  of characters (even if it actually contains newlines). The "start
1131         of  line"  metacharacter  (^)  matches only at the start of the string,         of line" metacharacter (^) matches only at the  start  of  the  string,
1132         while the "end of line" metacharacter ($) matches only at  the  end  of         while  the  "end  of line" metacharacter ($) matches only at the end of
1133         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1134         is set). This is the same as Perl.         is set). This is the same as Perl.
1135    
1136         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"
1137         constructs  match  immediately following or immediately before any new-         constructs match immediately following or immediately  before  internal
1138         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
1139         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
1140         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-
1141         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,
1142         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1143    
1144             PCRE_NEWLINE_CR
1145             PCRE_NEWLINE_LF
1146             PCRE_NEWLINE_CRLF
1147             PCRE_NEWLINE_ANYCRLF
1148             PCRE_NEWLINE_ANY
1149    
1150           These  options  override the default newline definition that was chosen
1151           when PCRE was built. Setting the first or the second specifies  that  a
1152           newline  is  indicated  by a single character (CR or LF, respectively).
1153           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1154           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1155           that any of the three preceding sequences should be recognized. Setting
1156           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1157           recognized. The Unicode newline sequences are the three just mentioned,
1158           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1159           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1160           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1161           UTF-8 mode.
1162    
1163           The newline setting in the  options  word  uses  three  bits  that  are
1164           treated as a number, giving eight possibilities. Currently only six are
1165           used (default plus the five values above). This means that if  you  set
1166           more  than one newline option, the combination may or may not be sensi-
1167           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1168           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1169           cause an error.
1170    
1171           The only time that a line break is specially recognized when  compiling
1172           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1173           character class is encountered. This indicates  a  comment  that  lasts
1174           until  after the next line break sequence. In other circumstances, line
1175           break  sequences  are  treated  as  literal  data,   except   that   in
1176           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1177           and are therefore ignored.
1178    
1179           The newline option that is set at compile time becomes the default that
1180           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1181    
1182           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1183    
1184         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 1220  COMPILATION ERROR CODES
1220    
1221         The following table lists the error  codes  than  may  be  returned  by         The following table lists the error  codes  than  may  be  returned  by
1222         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(),  along with the error messages that may be returned by
1223         both compiling functions.         both compiling functions. As PCRE has developed, some error codes  have
1224           fallen out of use. To avoid confusion, they have not been re-used.
1225    
1226            0  no error            0  no error
1227            1  \ at end of pattern            1  \ at end of pattern
# Line 1043  COMPILATION ERROR CODES Line 1233  COMPILATION ERROR CODES
1233            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1234            8  range out of order in character class            8  range out of order in character class
1235            9  nothing to repeat            9  nothing to repeat
1236           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1237           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1238           12  unrecognized character after (?           12  unrecognized character after (?
1239           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 1242  COMPILATION ERROR CODES
1242           16  erroffset passed as NULL           16  erroffset passed as NULL
1243           17  unknown option bit(s) set           17  unknown option bit(s) set
1244           18  missing ) after comment           18  missing ) after comment
1245           19  parentheses nested too deeply           19  [this code is not in use]
1246           20  regular expression too large           20  regular expression too large
1247           21  failed to get memory           21  failed to get memory
1248           22  unmatched parentheses           22  unmatched parentheses
1249           23  internal error: code overflow           23  internal error: code overflow
1250           24  unrecognized character after (?<           24  unrecognized character after (?<
1251           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1252           26  malformed number after (?(           26  malformed number or name after (?(
1253           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1254           28  assertion expected after (?(           28  assertion expected after (?(
1255           29  (?R or (?digits must be followed by )           29  (?R or (?digits must be followed by )
1256           30  unknown POSIX class name           30  unknown POSIX class name
1257           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1258           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1259           33  spare error           33  [this code is not in use]
1260           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1261           35  invalid condition (?(0)           35  invalid condition (?(0)
1262           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1075  COMPILATION ERROR CODES Line 1265  COMPILATION ERROR CODES
1265           39  closing ) for (?C expected           39  closing ) for (?C expected
1266           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1267           41  unrecognized character after (?P           41  unrecognized character after (?P
1268           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1269           43  two named groups have the same name           43  two named subpatterns have the same name
1270           44  invalid UTF-8 string           44  invalid UTF-8 string
1271           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1272           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1273           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1274             48  subpattern name is too long (maximum 32 characters)
1275             49  too many named subpatterns (maximum 10,000)
1276             50  repeated subpattern is too long
1277             51  octal value is greater than \377 (not in UTF-8 mode)
1278             52  internal error: overran compiling workspace
1279             53   internal  error:  previously-checked  referenced  subpattern not
1280           found
1281             54  DEFINE group contains more than one branch
1282             55  repeating a DEFINE group is not allowed
1283             56  inconsistent NEWLINE options"
1284    
1285    
1286  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1111  STUDYING A PATTERN Line 1311  STUDYING A PATTERN
1311    
1312         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.
1313         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1314         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
1315         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
1316         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
1317           after calling pcre_study(), to be sure that it has run successfully.
1318    
1319         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1320    
# Line 1124  STUDYING A PATTERN Line 1325  STUDYING A PATTERN
1325             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1326    
1327         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1328         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-
1329         ble starting bytes is created.         ble starting bytes is created.
1330    
1331    
1332  LOCALE SUPPORT  LOCALE SUPPORT
1333    
1334         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1335         letters digits, or whatever, by reference to a set of  tables,  indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1336         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
1337         characters with codes less than 128. Higher-valued  codes  never  match         characters  with  codes  less than 128. Higher-valued codes never match
1338         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
1339         with Unicode character property support.         with  Unicode  character property support. The use of locales with Uni-
1340           code is discouraged. If you are handling characters with codes  greater
1341         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
1342         is  built.  This  is  used when the final argument of pcre_compile() is         not try to mix the two.
1343         NULL, and is sufficient for many applications. An  alternative  set  of  
1344         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
1345         locale from the default. As more and more applications change to  using         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1346         Unicode, the need for this locale support is expected to die away.         applications.  Normally, the internal tables recognize only ASCII char-
1347           acters. However, when PCRE is built, it is possible to cause the inter-
1348         External  tables  are  built by calling the pcre_maketables() function,         nal tables to be rebuilt in the default "C" locale of the local system,
1349         which has no arguments, in the relevant locale. The result can then  be         which may cause them to be different.
1350         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For  
1351         example, to build and use tables that are appropriate  for  the  French         The  internal tables can always be overridden by tables supplied by the
1352         locale  (where  accented  characters  with  values greater than 128 are         application that calls PCRE. These may be created in a different locale
1353           from  the  default.  As more and more applications change to using Uni-
1354           code, the need for this locale support is expected to die away.
1355    
1356           External tables are built by calling  the  pcre_maketables()  function,
1357           which  has no arguments, in the relevant locale. The result can then be
1358           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1359           example,  to  build  and use tables that are appropriate for the French
1360           locale (where accented characters with  values  greater  than  128  are
1361         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1362    
1363           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1364           tables = pcre_maketables();           tables = pcre_maketables();
1365           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1366    
1367           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1368           if you are using Windows, the name for the French locale is "french".
1369    
1370         When pcre_maketables() runs, the tables are built  in  memory  that  is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1371         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1372         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 1412  INFORMATION ABOUT A PATTERN
1412         pattern:         pattern:
1413    
1414           int rc;           int rc;
1415           unsigned long int length;           size_t length;
1416           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1417             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1418             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
# Line 1232  INFORMATION ABOUT A PATTERN Line 1444  INFORMATION ABOUT A PATTERN
1444           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1445    
1446         Return  information  about  the first byte of any matched string, for a         Return  information  about  the first byte of any matched string, for a
1447         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored pattern. The fourth argument should point to an int  vari-
1448         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1449         compatibility.)         is still recognized for backwards compatibility.)
1450    
1451         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
1452         (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  
1453    
1454         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1455         branch starts with "^", or         branch starts with "^", or
1456    
1457         (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
1458         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1459    
1460         -1 is returned, indicating that the pattern matches only at  the  start         -1  is  returned, indicating that the pattern matches only at the start
1461         of  a  subject string or after any newline within the string. Otherwise         of a subject string or after any newline within the  string.  Otherwise
1462         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1463    
1464           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1465    
1466         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
1467         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
1468         matching string, a pointer to the table is returned. Otherwise NULL  is         matching  string, a pointer to the table is returned. Otherwise NULL is
1469         returned.  The fourth argument should point to an unsigned char * vari-         returned. The fourth argument should point to an unsigned char *  vari-
1470         able.         able.
1471    
1472           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1473    
1474         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
1475         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
1476         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1477         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
1478         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1479         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
1480         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1481    
# Line 1272  INFORMATION ABOUT A PATTERN Line 1483  INFORMATION ABOUT A PATTERN
1483           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1484           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1485    
1486         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1487         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1488         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1489         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1490         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
1491         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
1492         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1493         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
1494         which is described by these three values.         described by these three values.
1495    
1496         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
1497         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1498         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
1499         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1500         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
1501         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-
1502         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-
1503         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1504         For example, consider the following pattern  (assume  PCRE_EXTENDED  is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1505         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1506           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1507           ignored):
1508    
1509           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1510           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1511    
1512         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1513         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,
1514         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1515         as ??:         as ??:
1516    
# Line 1306  INFORMATION ABOUT A PATTERN Line 1519  INFORMATION ABOUT A PATTERN
1519           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1520           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1521    
1522         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1523         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
1524         be different for each compiled pattern.         to be different for each compiled pattern.
1525    
1526           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1527    
1528         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
1529         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1530         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1531         by any top-level option settings within the pattern itself.         by any top-level option settings within the pattern itself.
1532    
1533         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
1534         alternatives begin with one of the following:         alternatives begin with one of the following:
1535    
1536           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1331  INFORMATION ABOUT A PATTERN Line 1544  INFORMATION ABOUT A PATTERN
1544    
1545           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1546    
1547         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
1548         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
1549         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
1550         size_t variable.         size_t variable.
# Line 1339  INFORMATION ABOUT A PATTERN Line 1552  INFORMATION ABOUT A PATTERN
1552           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1553    
1554         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
1555         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
1556         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
1557         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
1558         variable.         variable.
1559    
1560    
# Line 1349  OBSOLETE INFO FUNCTION Line 1562  OBSOLETE INFO FUNCTION
1562    
1563         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1564    
1565         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1566         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1567         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1568         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-
1569         lowing negative numbers:         lowing negative numbers:
1570    
1571           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1572           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1573    
1574         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
1575         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
1576         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1577    
1578         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1579         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
1580         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1581    
1582    
# Line 1371  REFERENCE COUNTS Line 1584  REFERENCE COUNTS
1584    
1585         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1586    
1587         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1588         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
1589         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1590         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1591         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.
1592    
1593         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1594         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
1595         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
1596         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
1597         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
1598         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1599    
1600         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1601         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
1602         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1603    
1604    
# Line 1395  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1608  MATCHING A PATTERN: THE TRADITIONAL FUNC
1608              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1609              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1610    
1611         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
1612         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1613         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
1614         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1615         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
1616         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1617         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1618    
1619         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1620         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1621         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
1622         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1623         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1624    
1625         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 1638  MATCHING A PATTERN: THE TRADITIONAL FUNC
1638    
1639     Extra data for pcre_exec()     Extra data for pcre_exec()
1640    
1641         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
1642         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
1643         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-
1644         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
1645         lows:         fields (not necessarily in this order):
1646    
1647           unsigned long int flags;           unsigned long int flags;
1648           void *study_data;           void *study_data;
1649           unsigned long int match_limit;           unsigned long int match_limit;
1650             unsigned long int match_limit_recursion;
1651           void *callout_data;           void *callout_data;
1652           const unsigned char *tables;           const unsigned char *tables;
1653    
1654         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
1655         are set. The flag bits are:         are set. The flag bits are:
1656    
1657           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1658           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1659             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1660           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1661           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1662    
1663         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
1664         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1665         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
1666         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1667         flag bits.         flag bits.
1668    
1669         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
1670         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
1671         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1672         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1673         repeats.         repeats.
1674    
1675         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1676         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly  (sometimes  recursively). The limit set by match_limit is imposed
1677         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
1678         limiting the amount of recursion and backtracking that can take  place.         has  the  effect  of  limiting the amount of backtracking that can take
1679         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
1680         position in the subject string.         for each position in the subject string.
1681    
1682         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
1683         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1684         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1685         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra    block    in    which    match_limit    is    set,     and
1686         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
1687         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1688    
1689         The  pcre_callout  field is used in conjunction with the "callout" fea-         The match_limit_recursion field is similar to match_limit, but  instead
1690           of limiting the total number of times that match() is called, it limits
1691           the depth of recursion. The recursion depth is a  smaller  number  than
1692           the  total number of calls, because not all calls to match() are recur-
1693           sive.  This limit is of use only if it is set smaller than match_limit.
1694    
1695           Limiting  the  recursion  depth  limits the amount of stack that can be
1696           used, or, when PCRE has been compiled to use memory on the heap instead
1697           of the stack, the amount of heap memory that can be used.
1698    
1699           The  default  value  for  match_limit_recursion can be set when PCRE is
1700           built; the default default  is  the  same  value  as  the  default  for
1701           match_limit.  You can override the default by suppling pcre_exec() with
1702           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1703           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1704           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1705    
1706           The pcre_callout field is used in conjunction with the  "callout"  fea-
1707         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1708    
1709         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1710         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
1711         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
1712         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1713         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
1714         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-
1715         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
1716         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
1717         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1718         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1719    
1720     Option bits for pcre_exec()     Option bits for pcre_exec()
1721    
1722         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.
1723         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,
1724         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1725           PCRE_PARTIAL.
1726    
1727           PCRE_ANCHORED           PCRE_ANCHORED
1728    
# Line 1498  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1731  MATCHING A PATTERN: THE TRADITIONAL FUNC
1731         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
1732         unachored at matching time.         unachored at matching time.
1733    
1734             PCRE_NEWLINE_CR
1735             PCRE_NEWLINE_LF
1736             PCRE_NEWLINE_CRLF
1737             PCRE_NEWLINE_ANYCRLF
1738             PCRE_NEWLINE_ANY
1739    
1740           These options override  the  newline  definition  that  was  chosen  or
1741           defaulted  when the pattern was compiled. For details, see the descrip-
1742           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1743           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1744           ters. It may also alter the way the match position is advanced after  a
1745           match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,
1746           PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a  match  attempt
1747           fails  when the current position is at a CRLF sequence, the match posi-
1748           tion is advanced by two characters instead of one, in other  words,  to
1749           after the CRLF.
1750    
1751           PCRE_NOTBOL           PCRE_NOTBOL
1752    
1753         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1754         the  beginning  of  a  line, so the circumflex metacharacter should not         the beginning of a line, so the  circumflex  metacharacter  should  not
1755         match before it. Setting this without PCRE_MULTILINE (at compile  time)         match  before it. Setting this without PCRE_MULTILINE (at compile time)
1756         causes  circumflex  never to match. This option affects only the behav-         causes circumflex never to match. This option affects only  the  behav-
1757         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1758    
1759           PCRE_NOTEOL           PCRE_NOTEOL
1760    
1761         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
1762         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
1763         in multiline mode) a newline immediately before it. Setting this  with-         in  multiline mode) a newline immediately before it. Setting this with-
1764         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1765         option affects only the behaviour of the dollar metacharacter. It  does         option  affects only the behaviour of the dollar metacharacter. It does
1766         not affect \Z or \z.         not affect \Z or \z.
1767    
1768           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1769    
1770         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
1771         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
1772         the  alternatives  match  the empty string, the entire match fails. For         the alternatives match the empty string, the entire  match  fails.  For
1773         example, if the pattern         example, if the pattern
1774    
1775           a?b?           a?b?
1776    
1777         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
1778         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
1779         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-
1780         rences of "a" or "b".         rences of "a" or "b".
1781    
1782         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-
1783         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()
1784         function,  and  when  using  the /g modifier. It is possible to emulate         function, and when using the /g modifier. It  is  possible  to  emulate
1785         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
1786         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
1787         if that fails by advancing the starting offset (see below)  and  trying         if  that  fails by advancing the starting offset (see below) and trying
1788         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
1789         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
1790    
1791           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1792    
1793         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
1794         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8 string is automatically checked when pcre_exec() is  subsequently
1795         called.  The value of startoffset is also checked  to  ensure  that  it         called.   The  value  of  startoffset is also checked to ensure that it
1796         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
1797         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
1798         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is
1799         returned.         returned.
1800    
1801         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
1802         these    checks    for   performance   reasons,   you   can   set   the         these   checks   for   performance   reasons,   you   can    set    the
1803         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
1804         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
1805         making repeated calls to find all  the  matches  in  a  single  subject         making  repeated  calls  to  find  all  the matches in a single subject
1806         string.  However,  you  should  be  sure  that the value of startoffset         string. However, you should be  sure  that  the  value  of  startoffset
1807         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
1808         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
1809         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-
1810         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1811    
1812           PCRE_PARTIAL           PCRE_PARTIAL
1813    
1814         This  option  turns  on  the  partial  matching feature. If the subject         This option turns on the  partial  matching  feature.  If  the  subject
1815         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-
1816         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
1817         partially matches the pattern and the failure to  match  occurred  only         partially  matches  the  pattern and the failure to match occurred only
1818         because  there were not enough subject characters), pcre_exec() returns         because there were not enough subject characters), pcre_exec()  returns
1819         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1820         used,  there  are restrictions on what may appear in the pattern. These         used, there are restrictions on what may appear in the  pattern.  These
1821         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1822    
1823     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1824    
1825         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
1826         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
1827         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.
1828         Unlike  the  pattern string, the subject may contain binary zero bytes.         Unlike the pattern string, the subject may contain binary  zero  bytes.
1829         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
1830         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.
1831    
1832         A  non-zero  starting offset is useful when searching for another match         A non-zero starting offset is useful when searching for  another  match
1833         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-
1834         cess.   Setting  startoffset differs from just passing over a shortened         cess.  Setting startoffset differs from just passing over  a  shortened
1835         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
1836         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1837    
1838           \Biss\B           \Biss\B
1839    
1840         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
1841         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.)
1842         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
1843         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
1844         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
1845         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
1846         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
1847         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-
1848         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
1849         discover that it is preceded by a letter.         discover that it is preceded by a letter.
1850    
1851         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,
1852         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
1853         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
1854         subject.         subject.
1855    
1856     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
1857    
1858         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
1859         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
1860         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
1861         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
1862         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-
1863         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
1864         that do not cause substrings to be captured.         that do not cause substrings to be captured.
1865    
1866         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of  integer
1867         offsets whose address is passed in ovector. The number of  elements  in         offsets  whose  address is passed in ovector. The number of elements in
1868         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.
1869         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
1870    
1871         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-
1872         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
1873         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-
1874         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
1875         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
1876         it is not, it is rounded down.         it is not, it is rounded down.
1877    
1878         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
1879         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
1880         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
1881         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-
1882         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
1883         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-
1884         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1], identify the portion of  the  subject  string  matched  by  the
1885         entire pattern. The next pair is used for the first  capturing  subpat-         entire  pattern.  The next pair is used for the first capturing subpat-
1886         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
1887         pairs that have been set. If there are no  capturing  subpatterns,  the         highest numbered pair that has been set. For example, if two substrings
1888         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
1889         first pair of offsets has been set.         subpatterns,  the return value from a successful match is 1, indicating
1890           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.  
1891    
1892         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1893         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 1901  MATCHING A PATTERN: THE TRADITIONAL FUNC
1901         substrings,  PCRE has to get additional memory for use during matching.         substrings,  PCRE has to get additional memory for use during matching.
1902         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1903    
1904         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
1905         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns  there  are  in  a  compiled pattern. The smallest size for
1906         that will allow for n captured substrings, in addition to  the  offsets         ovector that will allow for n captured substrings, in addition  to  the
1907         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.
1908    
1909           It  is  possible for capturing subpattern number n+1 to match some part
1910           of the subject when subpattern n has not been used at all. For example,
1911           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
1912           return from the function is 4, and subpatterns 1 and 3 are matched, but
1913           2  is  not.  When  this happens, both values in the offset pairs corre-
1914           sponding to unused subpatterns are set to -1.
1915    
1916           Offset values that correspond to unused subpatterns at the end  of  the
1917           expression  are  also  set  to  -1. For example, if the string "abc" is
1918           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
1919           matched.  The  return  from the function is 2, because the highest used
1920           capturing subpattern number is 1. However, you can refer to the offsets
1921           for  the  second  and third capturing subpatterns if you wish (assuming
1922           the vector is large enough, of course).
1923    
1924           Some convenience functions are provided  for  extracting  the  captured
1925           substrings as separate strings. These are described below.
1926    
1927     Return values from pcre_exec()     Error return values from pcre_exec()
1928    
1929         If  pcre_exec()  fails, it returns a negative number. The following are         If  pcre_exec()  fails, it returns a negative number. The following are
1930         defined in the header file:         defined in the header file:
# Line 1691  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1950  MATCHING A PATTERN: THE TRADITIONAL FUNC
1950         an environment with the other endianness. This is the error  that  PCRE         an environment with the other endianness. This is the error  that  PCRE
1951         gives when the magic number is not present.         gives when the magic number is not present.
1952    
1953           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1954    
1955         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1956         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 1972  MATCHING A PATTERN: THE TRADITIONAL FUNC
1972    
1973           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
1974    
1975         The  recursion  and backtracking limit, as specified by the match_limit         The  backtracking  limit,  as  specified  by the match_limit field in a
1976         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra structure (or defaulted) was reached.  See  the  description
1977         description above.         above.
1978    
1979           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
1980    
# Line 1754  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2013  MATCHING A PATTERN: THE TRADITIONAL FUNC
2013    
2014         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.
2015    
2016             PCRE_ERROR_RECURSIONLIMIT (-21)
2017    
2018           The internal recursion limit, as specified by the match_limit_recursion
2019           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2020           description above.
2021    
2022             PCRE_ERROR_NULLWSLIMIT    (-22)
2023    
2024           When  a  group  that  can  match an empty substring is repeated with an
2025           unbounded upper limit, the subject position at the start of  the  group
2026           must be remembered, so that a test for an empty string can be made when
2027           the end of the group is reached. Some workspace is required  for  this;
2028           if it runs out, this error is given.
2029    
2030             PCRE_ERROR_BADNEWLINE     (-23)
2031    
2032           An invalid combination of PCRE_NEWLINE_xxx options was given.
2033    
2034           Error numbers -16 to -20 are not used by pcre_exec().
2035    
2036    
2037  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2038    
# Line 1774  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2053  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2053         string_list() are provided for extracting captured substrings  as  new,         string_list() are provided for extracting captured substrings  as  new,
2054         separate,  zero-terminated strings. These functions identify substrings         separate,  zero-terminated strings. These functions identify substrings
2055         by number. The next section describes functions  for  extracting  named         by number. The next section describes functions  for  extracting  named
2056         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2057         extracted and has a further zero added on the end, but  the  result  is  
2058         not, of course, a C string.         A  substring that contains a binary zero is correctly extracted and has
2059           a further zero added on the end, but the result is not, of course, a  C
2060           string.   However,  you  can  process such a string by referring to the
2061           length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2062           string().  Unfortunately, the interface to pcre_get_substring_list() is
2063           not adequate for handling strings containing binary zeros, because  the
2064           end of the final string is not independently indicated.
2065    
2066         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-
2067         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 2081  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2081         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2082         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2083         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
2084         the terminating zero, or one of         the terminating zero, or one of these error codes:
2085    
2086           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2087    
# Line 1812  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2097  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2097         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
2098         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
2099         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
2100         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
2101           error code
2102    
2103           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2104    
2105         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2106    
2107         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2108         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2109         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
2110         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2111         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2112         tive for unset substrings.         tive for unset substrings.
2113    
2114         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2115         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
2116         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2117         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2118         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.
2119         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-
2120         cial  interface  to  another  programming  language  which  cannot  use         cial   interface  to  another  programming  language  that  cannot  use
2121         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-
2122         vided.         vided.
2123    
2124    
# Line 1851  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2137  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2137              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2138              const char **stringptr);              const char **stringptr);
2139    
2140         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-
2141         ber.  For example, for this pattern         ber.  For example, for this pattern
2142    
2143           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2144    
2145         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
2146         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
2147         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-
2148         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
2149         there is no subpattern of that name.         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2150           subpattern of that name.
2151    
2152         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
2153         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 2166  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2166    
2167         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2168         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2169         ate.         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2170           behaviour may not be what you want (see the next section).
2171    
2172    
2173    DUPLICATE SUBPATTERN NAMES
2174    
2175           int pcre_get_stringtable_entries(const pcre *code,
2176                const char *name, char **first, char **last);
2177    
2178           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2179           subpatterns are not required to  be  unique.  Normally,  patterns  with
2180           duplicate  names  are such that in any one match, only one of the named
2181           subpatterns participates. An example is shown in the pcrepattern  docu-
2182           mentation. When duplicates are present, pcre_copy_named_substring() and
2183           pcre_get_named_substring() return the first substring corresponding  to
2184           the  given  name  that  is  set.  If  none  are set, an empty string is
2185           returned.  The pcre_get_stringnumber() function returns one of the num-
2186           bers  that are associated with the name, but it is not defined which it
2187           is.
2188    
2189           If you want to get full details of all captured substrings for a  given
2190           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2191           first argument is the compiled pattern, and the second is the name. The
2192           third  and  fourth  are  pointers to variables which are updated by the
2193           function. After it has run, they point to the first and last entries in
2194           the  name-to-number  table  for  the  given  name.  The function itself
2195           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2196           there  are none. The format of the table is described above in the sec-
2197           tion entitled Information about a  pattern.   Given  all  the  relevant
2198           entries  for the name, you can extract each of their numbers, and hence
2199           the captured data, if any.
2200    
2201    
2202  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
# Line 1908  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2225  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2225              int *workspace, int wscount);              int *workspace, int wscount);
2226    
2227         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2228         against a compiled pattern, using a "DFA" matching algorithm. This  has         against a compiled pattern, using a matching algorithm that  scans  the
2229         different  characteristics to the normal algorithm, and is not compati-         subject  string  just  once, and does not backtrack. This has different
2230         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics to the normal algorithm, and  is  not  compatible  with
2231         Nevertheless, there are times when this kind of matching can be useful.         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2232         For a discussion of the two matching algorithms, see  the  pcrematching         theless, there are times when this kind of matching can be useful.  For
2233         documentation.         a discussion of the two matching algorithms, see the pcrematching docu-
2234           mentation.
2235    
2236         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
2237         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-
2238         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2239         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
2240         repeated here.         repeated here.
2241    
2242         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2243         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2244         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2245         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2246         lot of possible matches.         lot of potential matches.
2247    
2248         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2249    
2250           int rc;           int rc;
2251           int ovector[10];           int ovector[10];
2252           int wspace[20];           int wspace[20];
2253           rc = pcre_exec(           rc = pcre_dfa_exec(
2254             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2255             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2256             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1946  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2264  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2264    
2265     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2266    
2267         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
2268         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-
2269         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2270         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
2271         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
2272         repeated here.         not repeated here.
2273    
2274           PCRE_PARTIAL           PCRE_PARTIAL
2275    
2276         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
2277         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2278         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2279         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
2280         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-
2281         sibility.  The portion of the string that provided the partial match is         sibility. The portion of the string that provided the partial match  is
2282         set as the first matching string.         set as the first matching string.
2283    
2284           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2285    
2286         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2287         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-
2288         algorithm works, this is necessarily the shortest possible match at the         tive  algorithm  works, this is necessarily the shortest possible match
2289         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2290    
2291           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2292    
2293         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2294         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-
2295         tional  subject  characters,  and have it continue with the same match.         tional subject characters, and have it continue with  the  same  match.
2296         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
2297         workspace  and wscount options must reference the same vector as before         workspace and wscount options must reference the same vector as  before
2298         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
2299         match.  There  is  more  discussion of this facility in the pcrepartial         match. There is more discussion of this  facility  in  the  pcrepartial
2300         documentation.         documentation.
2301    
2302     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2303    
2304         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-
2305         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
2306         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
2307         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2308         if the pattern         if the pattern
2309    
2310           <.*>           <.*>
# Line 2001  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2319  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2319           <something> <something else>           <something> <something else>
2320           <something> <something else> <something further>           <something> <something else> <something further>
2321    
2322         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,
2323         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2324         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2325         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
2326         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
2327         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
2328         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility  with  the  way pcre_exec() returns data, even though the
2329         strings is different.)         meaning of the strings is different.)
2330    
2331         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-
2332         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
2333         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
2334         filled with the longest matches.         filled with the longest matches.
2335    
2336     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2337    
2338         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2339         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
2340         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2341         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2342    
2343           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2344    
2345         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-
2346         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
2347         reference.         reference.
2348    
2349           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2350    
2351         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
2352         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
2353         supported.         in a specific group. These are not supported.
2354    
2355           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2356    
2357         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
2358         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
2359         (it is meaningless).         (it is meaningless).
2360    
2361           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2362    
2363         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
2364         workspace vector.         workspace vector.
2365    
2366           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2367    
2368         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2369         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2370         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
2371         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2372    
2373  Last updated: 16 May 2005  
2374  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2375    
2376           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2377           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2378    
2379    
2380    AUTHOR
2381    
2382           Philip Hazel
2383           University Computing Service
2384           Cambridge CB2 3QH, England.
2385    
2386    
2387    REVISION
2388    
2389           Last updated: 16 April 2007
2390           Copyright (c) 1997-2007 University of Cambridge.
2391  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2392    
2393    
# Line 2211  RETURN VALUES Line 2545  RETURN VALUES
2545         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
2546         itself.         itself.
2547    
2548  Last updated: 28 February 2005  
2549  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2550    
2551           Philip Hazel
2552           University Computing Service
2553           Cambridge CB2 3QH, England.
2554    
2555    
2556    REVISION
2557    
2558           Last updated: 06 March 2007
2559           Copyright (c) 1997-2007 University of Cambridge.
2560  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2561    
2562    
# Line 2226  NAME Line 2570  NAME
2570  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2571    
2572         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2573         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2574         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2575           tures that are expected to be in the forthcoming Perl 5.10.
2576         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2577         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
2578           of  what  it does have are given in the section on UTF-8 support in the
2579           main pcre page.
2580    
2581         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2582         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 2603  DIFFERENCES BETWEEN PCRE AND PERL
2603         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
2604         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2605         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-
2606         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2607           derived properties Any and L&.
2608    
2609         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2610         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2611         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2612         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2613         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2614    
2615             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2272  DIFFERENCES BETWEEN PCRE AND PERL Line 2619  DIFFERENCES BETWEEN PCRE AND PERL
2619             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2620             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2621    
2622         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2623         classes.         classes.
2624    
2625         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2626         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2627         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
2628         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2629         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2630    
2631         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2632         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2633         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2634    
2635           10.  There are some differences that are concerned with the settings of
2636           captured strings when part of  a  pattern  is  repeated.  For  example,
2637           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2638         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2639    
2640         10. PCRE provides some extensions to the Perl regular expression facil-         11. PCRE provides some extensions to the Perl regular expression facil-
2641         ities:         ities.   Perl  5.10  will  include new features that are not in earlier
2642           versions, some of which (such as named parentheses) have been  in  PCRE
2643           for some time. This list is with respect to Perl 5.10:
2644    
2645         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2646         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2647         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2648    
2649         (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 $
2650         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2651    
2652         (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-
2653         cial meaning is faulted.         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2654           ignored. (Perl can be made to issue a warning.)
2655    
2656         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2657         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 2663  DIFFERENCES BETWEEN PCRE AND PERL
2663         (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-
2664         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2665    
2666         (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.)  
2667    
2668         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The partial matching facility is PCRE-specific.
2669    
2670         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2671         Sun's Java package.         even on different hosts that have the other endianness.
2672    
2673         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2674           different way and is not Perl-compatible.
2675    
        (k) The callout facility is PCRE-specific.  
2676    
2677         (l) The partial matching facility is PCRE-specific.  AUTHOR
2678    
2679         (m) Patterns compiled by PCRE can be saved and re-used at a later time,         Philip Hazel
2680         even on different hosts that have the other endianness.         University Computing Service
2681           Cambridge CB2 3QH, England.
2682    
        (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  
        different way and is not Perl-compatible.  
2683    
2684  Last updated: 28 February 2005  REVISION
2685  Copyright (c) 1997-2005 University of Cambridge.  
2686           Last updated: 06 March 2007
2687           Copyright (c) 1997-2007 University of Cambridge.
2688  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2689    
2690    
# Line 2367  PCRE REGULAR EXPRESSION DETAILS Line 2720  PCRE REGULAR EXPRESSION DETAILS
2720         function, and how it differs from the normal function, are discussed in         function, and how it differs from the normal function, are discussed in
2721         the pcrematching page.         the pcrematching page.
2722    
2723    
2724    CHARACTERS AND METACHARACTERS
2725    
2726         A regular expression is a pattern that is  matched  against  a  subject         A regular expression is a pattern that is  matched  against  a  subject
2727         string  from  left  to right. Most characters stand for themselves in a         string  from  left  to right. Most characters stand for themselves in a
2728         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 2747  PCRE REGULAR EXPRESSION DETAILS
2747    
2748         There are two different sets of metacharacters: those that  are  recog-         There are two different sets of metacharacters: those that  are  recog-
2749         nized  anywhere in the pattern except within square brackets, and those         nized  anywhere in the pattern except within square brackets, and those
2750         that are recognized in square brackets. Outside  square  brackets,  the         that are recognized within square brackets.  Outside  square  brackets,
2751         metacharacters are as follows:         the metacharacters are as follows:
2752    
2753           \      general escape character with several uses           \      general escape character with several uses
2754           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2439  BACKSLASH Line 2795  BACKSLASH
2795    
2796         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2797         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
2798         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2799         An escaping backslash can be used to include a whitespace or #  charac-         ing backslash can be used to include a whitespace  or  #  character  as
2800         ter as part of the pattern.         part of the pattern.
2801    
2802         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-
2803         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 2833  BACKSLASH
2833           \t        tab (hex 09)           \t        tab (hex 09)
2834           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
2835           \xhh      character with hex code hh           \xhh      character with hex code hh
2836           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
2837    
2838         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,
2839         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 2841  BACKSLASH
2841         becomes hex 7B.         becomes hex 7B.
2842    
2843         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
2844         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
2845         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
2846         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,
2847         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than
2848         \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-
2849         recognized. Instead, the initial \x will  be  interpreted  as  a  basic         nating }, this form of escape is not recognized.  Instead, the  initial
2850         hexadecimal  escape, with no following digits, giving a character whose         \x will be interpreted as a basic hexadecimal escape, with no following
2851         value is zero.         digits, giving a character whose value is zero.
2852    
2853         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
2854         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-
2855         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}.
2856         \x{dc}.  
2857           After \0 up to two further octal digits are read. If  there  are  fewer
2858         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
2859         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
2860         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
2861         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.  
2862    
2863         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-
2864         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 2870  BACKSLASH
2870    
2871         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
2872         and  there have not been that many capturing subpatterns, PCRE re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
2873         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-
2874         gle byte from the least significant 8 bits of the value. Any subsequent         erate  a data character. Any subsequent digits stand for themselves. In
2875         digits stand for themselves.  For example:         non-UTF-8 mode, the value of a character specified  in  octal  must  be
2876           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
2877           example:
2878    
2879           \040   is another way of writing a space           \040   is another way of writing a space
2880           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2538  BACKSLASH Line 2894  BACKSLASH
2894         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
2895         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2896    
2897         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
2898         character (in UTF-8 mode) can be used both inside and outside character         inside and outside character classes. In addition, inside  a  character
2899         classes.  In  addition,  inside  a  character class, the sequence \b is         class,  the  sequence \b is interpreted as the backspace character (hex
2900         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"
2901         interpreted  as  the  character  "X".  Outside a character class, these         and  "X", respectively. Outside a character class, these sequences have
2902         sequences have different meanings (see below).         different meanings (see below).
2903    
2904       Absolute and relative back references
2905    
2906           The sequence \g followed by a positive or negative  number,  optionally
2907           enclosed  in  braces,  is  an absolute or relative back reference. Back
2908           references are discussed later, following the discussion  of  parenthe-
2909           sized subpatterns.
2910    
2911     Generic character types     Generic character types
2912    
2913         The third use of backslash is for specifying generic  character  types.         Another use of backslash is for specifying generic character types. The
2914         The following are always recognized:         following are always recognized:
2915    
2916           \d     any decimal digit           \d     any decimal digit
2917           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 2558  BACKSLASH Line 2921  BACKSLASH
2921           \W     any "non-word" character           \W     any "non-word" character
2922    
2923         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
2924         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
2925         of each pair.         of each pair.
2926    
2927         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
2928         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
2929         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
2930         of them fail, since there is no character to match.         of them fail, since there is no character to match.
2931    
2932         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
2933         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
2934         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
2935           "use locale;" is included in a Perl script, \s may match the VT charac-
2936           ter. In PCRE, it never does.)
2937    
2938         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
2939         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-
2940         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-
2941         specific  matching is taking place (see "Locale support" in the pcreapi         specific matching is taking place (see "Locale support" in the  pcreapi
2942         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
2943         codes  greater  than  128  are used for accented letters, and these are         systems, or "french" in Windows, some character codes greater than  128
2944         matched by \w.         are used for accented letters, and these are matched by \w.
2945    
2946         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,
2947         \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-
2948         code character property support is available.         code  character  property support is available. The use of locales with
2949           Unicode is discouraged.
2950    
2951       Newline sequences
2952    
2953           Outside a character class, the escape sequence \R matches  any  Unicode
2954           newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2955           equivalent to the following:
2956    
2957             (?>\r\n|\n|\x0b|\f|\r|\x85)
2958    
2959           This is an example of an "atomic group", details  of  which  are  given
2960           below.  This particular group matches either the two-character sequence
2961           CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
2962           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2963           return, U+000D), or NEL (next line, U+0085). The two-character sequence
2964           is treated as a single unit that cannot be split.
2965    
2966           In  UTF-8  mode, two additional characters whose codepoints are greater
2967           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2968           rator,  U+2029).   Unicode character property support is not needed for
2969           these characters to be recognized.
2970    
2971           Inside a character class, \R matches the letter "R".
2972    
2973     Unicode character properties     Unicode character properties
2974    
2975         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
2976         tional  escape sequences to match generic character types are available         tional  escape  sequences  to  match character properties are available
2977         when UTF-8 mode is selected. They are:         when UTF-8 mode is selected. They are:
2978    
2979          \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
2980          \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
2981          \X       an extended Unicode sequence           \X       an extended Unicode sequence
2982    
2983         The property names represented by xx above are limited to  the  Unicode         The property names represented by xx above are limited to  the  Unicode
2984         general  category properties. Each character has exactly one such prop-         script names, the general category properties, and "Any", which matches
2985         erty, specified by a two-letter abbreviation.  For  compatibility  with         any character (including newline). Other properties such as "InMusical-
2986         Perl,  negation  can be specified by including a circumflex between the         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
2987         opening brace and the property name. For example, \p{^Lu} is  the  same         not match any characters, so always causes a match failure.
2988         as \P{Lu}.  
2989           Sets of Unicode characters are defined as belonging to certain scripts.
2990         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.
2991         properties that start with that letter. In this case, in the absence of         For example:
2992         negation, the curly brackets in the escape sequence are optional; these  
2993         two examples have the same effect:           \p{Greek}
2994             \P{Han}
2995    
2996           Those that are not part of an identified script are lumped together  as
2997           "Common". The current list of scripts is:
2998    
2999           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3000           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
3001           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3002           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
3003           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
3004           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3005           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
3006           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3007           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3008    
3009           Each  character has exactly one general category property, specified by
3010           a two-letter abbreviation. For compatibility with Perl, negation can be
3011           specified  by  including a circumflex between the opening brace and the
3012           property name. For example, \p{^Lu} is the same as \P{Lu}.
3013    
3014           If only one letter is specified with \p or \P, it includes all the gen-
3015           eral  category properties that start with that letter. In this case, in
3016           the absence of negation, the curly brackets in the escape sequence  are
3017           optional; these two examples have the same effect:
3018    
3019           \p{L}           \p{L}
3020           \pL           \pL
3021    
3022         The following property codes are supported:         The following general category property codes are supported:
3023    
3024           C     Other           C     Other
3025           Cc    Control           Cc    Control
# Line 2653  BACKSLASH Line 3065  BACKSLASH
3065           Zp    Paragraph separator           Zp    Paragraph separator
3066           Zs    Space separator           Zs    Space separator
3067    
3068         Extended properties such as "Greek" or "InMusicalSymbols" are not  sup-         The  special property L& is also supported: it matches a character that
3069         ported by PCRE.         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
3070           classified as a modifier or "other".
3071    
3072           The  long  synonyms  for  these  properties that Perl supports (such as
3073           \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3074           any of these properties with "Is".
3075    
3076           No character that is in the Unicode table has the Cn (unassigned) prop-
3077           erty.  Instead, this property is assumed for any code point that is not
3078           in the Unicode table.
3079    
3080         Specifying  caseless  matching  does not affect these escape sequences.         Specifying  caseless  matching  does not affect these escape sequences.
3081         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
# Line 2676  BACKSLASH Line 3097  BACKSLASH
3097    
3098     Simple assertions     Simple assertions
3099    
3100         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3101         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
3102         a  match, without consuming any characters from the subject string. The         a  match, without consuming any characters from the subject string. The
3103         use of subpatterns for more complicated assertions is described  below.         use of subpatterns for more complicated assertions is described  below.
# Line 2684  BACKSLASH Line 3105  BACKSLASH
3105    
3106           \b     matches at a word boundary           \b     matches at a word boundary
3107           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3108           \A     matches at start of subject           \A     matches at the start of the subject
3109           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3110           \z     matches at end of subject                   also matches before a newline at the end of the subject
3111           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3112             \G     matches at the first matching position in the subject
3113    
3114         These  assertions may not appear in character classes (but note that \b         These  assertions may not appear in character classes (but note that \b
3115         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 3129  BACKSLASH
3129         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3130         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
3131         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
3132         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
3133         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.
3134         the end.  
3135           The \G assertion is true only when the current matching position is  at
3136         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
3137         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
3138         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-  
3139         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-
3140         mentation where \G can be useful.         mentation where \G can be useful.
3141    
3142         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
3143         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
3144         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
3145         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3146         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3147    
3148         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
3149         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3150         in the compiled regular expression.         in the compiled regular expression.
3151    
# Line 2732  BACKSLASH Line 3153  BACKSLASH
3153  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3154    
3155         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3156         character  is  an  assertion  that is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3157         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-
3158         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
3159         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3160         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3161    
3162         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
3163         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
3164         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
3165         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3166         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-
3167         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
3168         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3169    
3170         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
3171         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3172         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
3173         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
3174         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
3175         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.  
3176    
3177         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
3178         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
3179         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3180    
3181         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3182         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
3183         ately  after  and  immediately  before  an  internal newline character,         matches  immediately after internal newlines as well as at the start of
3184         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
3185         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         string.  A dollar matches before any newlines in the string, as well as
3186         string "def\nabc" (where \n represents a newline character)  in  multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3187         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3188         in single line mode because all branches start with ^ are not  anchored         not indicate newlines.
3189         in  multiline  mode,  and  a  match for circumflex is possible when the  
3190         startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3191         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3192           Consequently, patterns that are anchored in single  line  mode  because
3193         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
3194         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
3195         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
3196         not.         PCRE_MULTILINE is set.
3197    
3198           Note that the sequences \A, \Z, and \z can be used to match  the  start
3199           and  end of the subject in both modes, and if all branches of a pattern
3200           start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3201           set.
3202    
3203    
3204  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3205    
3206         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-
3207         ter  in  the  subject,  including a non-printing character, but not (by         ter in the subject string except (by default) a character  that  signi-
3208         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
3209         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3210         the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-  
3211         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
3212         dollar, the only relationship being  that  they  both  involve  newline         that  character; when the two-character sequence CRLF is used, dot does
3213         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3214           matches  all characters (including isolated CRs and LFs). When any Uni-
3215           code line endings are being recognized, dot does not match CR or LF  or
3216           any of the other line ending characters.
3217    
3218           The  behaviour  of  dot  with regard to newlines can be changed. If the
3219           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3220           exception. If the two-character sequence CRLF is present in the subject
3221           string, it takes two dots to match it.
3222    
3223           The handling of dot is entirely independent of the handling of  circum-
3224           flex  and  dollar,  the  only relationship being that they both involve
3225           newlines. Dot has no special meaning in a character class.
3226    
3227    
3228  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3229    
3230         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3231         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
3232         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
3233         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-
3234         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-
3235         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3236           avoided.
3237    
3238         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3239         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 3280  SQUARE BRACKETS AND CHARACTER CLASSES
3280         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
3281         support.         support.
3282    
3283         The newline character is never treated in any special way in  character         Characters that might indicate line breaks are  never  treated  in  any
3284         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         special  way  when  matching  character  classes,  whatever line-ending
3285         options is. A class such as [^a] will always match a newline.         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3286           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3287           of these characters.
3288    
3289         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-
3290         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 3310  SQUARE BRACKETS AND CHARACTER CLASSES
3310         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,
3311         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
3312         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3313         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
3314         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
3315         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3316         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 2945  VERTICAL BAR Line 3385  VERTICAL BAR
3385    
3386         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3387         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3388         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3389         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
3390         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3391         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.  
3392    
3393    
3394  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 2977  INTERNAL OPTION SETTING Line 3416  INTERNAL OPTION SETTING
3416         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
3417         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3418    
3419         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
3420         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3421           it, so
3422    
3423           (a(?i)b)c           (a(?i)b)c
3424    
3425         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
3426         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3427         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3428         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3429         example,         example,
3430    
3431           (a(?i)b|c)           (a(?i)b|c)
3432    
3433         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3434         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3435         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3436         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3437    
3438         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3439         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
3440         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.  
3441    
3442    
3443  SUBPATTERNS  SUBPATTERNS
# Line 3013  SUBPATTERNS Line 3450  SUBPATTERNS
3450           cat(aract|erpillar|)           cat(aract|erpillar|)
3451    
3452         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3453         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3454         string.         string.
3455    
3456         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 3479  SUBPATTERNS
3479           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3480    
3481         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3482         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.  
3483    
3484         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3485         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 3501  NAMED SUBPATTERNS
3501         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3502         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3503         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3504         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3505         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3506         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3507           tax.
3508    
3509           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3510           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3511           to capturing parentheses from other parts of the pattern, such as back-
3512           references,  recursion,  and conditions, can be made by name as well as
3513           by number.
3514    
3515           Names consist of up to  32  alphanumeric  characters  and  underscores.
3516         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3517         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
3518         number  translation table from a compiled pattern. There is also a con-         function calls for extracting the name-to-number translation table from
3519         venience function for extracting a captured substring by name. For fur-         a compiled pattern. There is also a convenience function for extracting
3520         ther details see the pcreapi documentation.         a captured substring by name.
3521    
3522           By  default, a name must be unique within a pattern, but it is possible
3523           to relax this constraint by setting the PCRE_DUPNAMES option at compile
3524           time.  This  can  be useful for patterns where only one instance of the
3525           named parentheses can match. Suppose you want to match the  name  of  a
3526           weekday,  either as a 3-letter abbreviation or as the full name, and in
3527           both cases you want to extract the abbreviation. This pattern (ignoring
3528           the line breaks) does the job:
3529    
3530             (?<DN>Mon|Fri|Sun)(?:day)?|
3531             (?<DN>Tue)(?:sday)?|
3532             (?<DN>Wed)(?:nesday)?|
3533             (?<DN>Thu)(?:rsday)?|
3534             (?<DN>Sat)(?:urday)?
3535    
3536           There  are  five capturing substrings, but only one is ever set after a
3537           match.  The convenience  function  for  extracting  the  data  by  name
3538           returns  the  substring  for  the first (and in this example, the only)
3539           subpattern of that name that matched.  This  saves  searching  to  find
3540           which  numbered  subpattern  it  was. If you make a reference to a non-
3541           unique named subpattern from elsewhere in the  pattern,  the  one  that
3542           corresponds  to  the  lowest number is used. For further details of the
3543           interfaces for handling named subpatterns, see the  pcreapi  documenta-
3544           tion.
3545    
3546    
3547  REPETITION  REPETITION
# Line 3083  REPETITION Line 3550  REPETITION
3550         following items:         following items:
3551    
3552           a literal data character           a literal data character
3553           the . metacharacter           the dot metacharacter
3554           the \C escape sequence           the \C escape sequence
3555           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3556             the \R escape sequence
3557           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3558           a character class           a character class
3559           a back reference (see next section)           a back reference (see next section)
# Line 3125  REPETITION Line 3593  REPETITION
3593         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3594         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3595    
3596         For  convenience  (and  historical compatibility) the three most common         For  convenience, the three most common quantifiers have single-charac-
3597         quantifiers have single-character abbreviations:         ter abbreviations:
3598    
3599           *    is equivalent to {0,}           *    is equivalent to {0,}
3600           +    is equivalent to {1,}           +    is equivalent to {1,}
# Line 3178  REPETITION Line 3646  REPETITION
3646         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
3647         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3648    
3649         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
3650         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3651         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
3652         words, it inverts the default behaviour.         words, it inverts the default behaviour.
# Line 3189  REPETITION Line 3657  REPETITION
3657         minimum or maximum.         minimum or maximum.
3658    
3659         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-
3660         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,
3661         pattern is implicitly anchored, because whatever follows will be  tried         the pattern is implicitly anchored, because whatever  follows  will  be
3662         against  every character position in the subject string, so there is no         tried  against every character position in the subject string, so there
3663         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
3664         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
3665           by \A.
3666    
3667         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-
3668         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-
3669         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3670    
3671         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3672         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3673         backreference  elsewhere in the pattern, a match at the start may fail,         backreference elsewhere in the pattern, a match at the start  may  fail
3674         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3675    
3676           (.*)abc\1           (.*)abc\1
3677    
3678         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3679         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3680    
3681         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 3684  REPETITION
3684           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
3685    
3686         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
3687         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
3688         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
3689         tions. For example, after         tions. For example, after
3690    
3691           /(a|(b))+/           /(a|(b))+/
# Line 3226  REPETITION Line 3695  REPETITION
3695    
3696  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
3697    
3698         With both maximizing and minimizing repetition, failure of what follows         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
3699         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition,  failure  of what follows normally causes the repeated item
3700         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
3701         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,
3702         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
3703         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
3704           no point in carrying on.
3705    
3706         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider, for example, the pattern \d+foo when applied to  the  subject
3707         line         line
# Line 3245  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3715  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3715         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
3716         to be re-evaluated in this way.         to be re-evaluated in this way.
3717    
3718         If we use atomic grouping for the previous example, the  matcher  would         If we use atomic grouping for the previous example, the  matcher  gives
3719         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
3720         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:  
3721    
3722           (?>\d+)foo           (?>\d+)foo
3723    
# Line 3280  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3749  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3749         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
3750         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
3751         simpler forms of atomic group. However, there is no difference  in  the         simpler forms of atomic group. However, there is no difference  in  the
3752         meaning  or  processing  of  a possessive quantifier and the equivalent         meaning  of  a  possessive  quantifier and the equivalent atomic group,
3753         atomic group.         though there may be a performance  difference;  possessive  quantifiers
3754           should be slightly faster.
3755         The possessive quantifier syntax is an extension to the Perl syntax. It  
3756         originates in Sun's Java package.         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
3757           tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first
3758         When  a  pattern  contains an unlimited repeat inside a subpattern that         edition of his book. Mike McCloskey liked it, so implemented it when he
3759         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
3760         atomic  group  is  the  only way to avoid some failing matches taking a         found its way into Perl at release 5.10.
3761    
3762           PCRE has an optimization that automatically "possessifies" certain sim-
3763           ple pattern constructs. For example, the sequence  A+B  is  treated  as
3764           A++B  because  there is no point in backtracking into a sequence of A's
3765           when B must follow.
3766    
3767           When a pattern contains an unlimited repeat inside  a  subpattern  that
3768           can  itself  be  repeated  an  unlimited number of times, the use of an
3769           atomic group is the only way to avoid some  failing  matches  taking  a
3770         very long time indeed. The pattern         very long time indeed. The pattern
3771    
3772           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
3773    
3774         matches an unlimited number of substrings that either consist  of  non-         matches  an  unlimited number of substrings that either consist of non-
3775         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it
3776         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
3777    
3778           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
3779    
3780         it takes a long time before reporting  failure.  This  is  because  the         it  takes  a  long  time  before reporting failure. This is because the
3781         string  can be divided between the internal \D+ repeat and the external         string can be divided between the internal \D+ repeat and the  external
3782         * 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
3783         example  uses  [!?]  rather than a single character at the end, because         example uses [!?] rather than a single character at  the  end,  because
3784         both PCRE and Perl have an optimization that allows  for  fast  failure         both  PCRE  and  Perl have an optimization that allows for fast failure
3785         when  a single character is used. They remember the last single charac-         when a single character is used. They remember the last single  charac-
3786         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
3787         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
3788         group, like this:         group, like this:
3789    
3790           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
3791    
3792         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences  of non-digits cannot be broken, and failure happens quickly.
3793    
3794    
3795  BACK REFERENCES  BACK REFERENCES
3796    
3797         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
3798         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-
3799         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
3800         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
3801    
3802         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
3803         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
3804         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
3805         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
3806         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
3807         tion  entitled  "Non-printing  characters" above for further details of         reference" of this type can make sense when a  repetition  is  involved
3808         the handling of digits following a backslash.         and  the  subpattern to the right has participated in an earlier itera-
3809           tion.
3810    
3811         A back reference matches whatever actually matched the  capturing  sub-         It is not possible to have a numerical "forward back  reference"  to  a
3812         pattern  in  the  current subject string, rather than anything matching         subpattern  whose  number  is  10  or  more using this syntax because a
3813           sequence such as \50 is interpreted as a character  defined  in  octal.
3814           See the subsection entitled "Non-printing characters" above for further
3815           details of the handling of digits following a backslash.  There  is  no
3816           such  problem  when named parentheses are used. A back reference to any
3817           subpattern is possible using named parentheses (see below).
3818    
3819           Another way of avoiding the ambiguity inherent in  the  use  of  digits
3820           following a backslash is to use the \g escape sequence, which is a fea-
3821           ture introduced in Perl 5.10. This escape must be followed by  a  posi-
3822           tive  or  a negative number, optionally enclosed in braces. These exam-
3823           ples are all identical:
3824    
3825             (ring), \1
3826             (ring), \g1
3827             (ring), \g{1}
3828    
3829           A positive number specifies an absolute reference without the ambiguity
3830           that  is  present  in  the older syntax. It is also useful when literal
3831           digits follow the reference. A negative number is a relative reference.
3832           Consider this example:
3833    
3834             (abc(def)ghi)\g{-1}
3835    
3836           The sequence \g{-1} is a reference to the most recently started captur-
3837           ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,
3838           \g{-2} would be equivalent to \1. The use of relative references can be
3839           helpful in long patterns, and also in  patterns  that  are  created  by
3840           joining together fragments that contain references within themselves.
3841    
3842           A  back  reference matches whatever actually matched the capturing sub-
3843           pattern in the current subject string, rather  than  anything  matching
3844         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
3845         of doing that). So the pattern         of doing that). So the pattern
3846    
3847           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
3848    
3849         matches  "sense and sensibility" and "response and responsibility", but         matches "sense and sensibility" and "response and responsibility",  but
3850         not "sense and responsibility". If caseful matching is in force at  the         not  "sense and responsibility". If caseful matching is in force at the
3851         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-
3852         ple,         ple,
3853    
3854           ((?i)rah)\s+\1           ((?i)rah)\s+\1
3855    
3856         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
3857         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
3858    
3859         Back  references  to named subpatterns use the Python syntax (?P=name).         Back references to named subpatterns use the Perl  syntax  \k<name>  or
3860         We could rewrite the above example as follows:         \k'name'  or  the  Python  syntax (?P=name). We could rewrite the above
3861           example in either of the following ways:
3862    
3863           (?<p1>(?i)rah)\s+(?P=p1)           (?<p1>(?i)rah)\s+\k<p1>
3864             (?P<p1>(?i)rah)\s+(?P=p1)
3865    
3866         There may be more than one back reference to the same subpattern. If  a         A subpattern that is referenced by  name  may  appear  in  the  pattern
3867         subpattern  has  not actually been used in a particular match, any back         before or after the reference.
3868    
3869           There  may be more than one back reference to the same subpattern. If a
3870           subpattern has not actually been used in a particular match,  any  back
3871         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
3872    
3873           (a|(bc))\2           (a|(bc))\2
3874    
3875         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
3876         may  be  many  capturing parentheses in a pattern, all digits following         may be many capturing parentheses in a pattern,  all  digits  following
3877         the backslash are taken as part of a potential back  reference  number.         the  backslash  are taken as part of a potential back reference number.
3878         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
3879         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         used  to  terminate  the back reference. If the PCRE_EXTENDED option is
3880         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-
3881         ments" below) can be used.         ments" below) can be used.
3882    
3883         A back reference that occurs inside the parentheses to which it  refers         A  back reference that occurs inside the parentheses to which it refers
3884         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
3885         matches.  However, such references can be useful inside  repeated  sub-         matches.   However,  such references can be useful inside repeated sub-
3886         patterns. For example, the pattern         patterns. For example, the pattern
3887    
3888           (a|b\1)+           (a|b\1)+
3889    
3890         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-
3891         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
3892         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
3893         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
3894         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
3895         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
3896    
3897    
3898  ASSERTIONS  ASSERTIONS
3899    
3900         An assertion is a test on the characters  following  or  preceding  the         An  assertion  is  a  test on the characters following or preceding the
3901         current  matching  point that does not actually consume any characters.         current matching point that does not actually consume  any  characters.
3902         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
3903         described above.         described above.
3904    
3905         More  complicated  assertions  are  coded as subpatterns. There are two         More complicated assertions are coded as  subpatterns.  There  are  two
3906         kinds: those that look ahead of the current  position  in  the  subject         kinds:  those  that  look  ahead of the current position in the subject
3907         string,  and  those  that  look  behind  it. An assertion subpattern is         string, and those that look  behind  it.  An  assertion  subpattern  is
3908         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
3909         matching position to be changed.         matching position to be changed.
3910    
3911         Assertion  subpatterns  are  not  capturing subpatterns, and may not be         Assertion subpatterns are not capturing subpatterns,  and  may  not  be
3912         repeated, because it makes no sense to assert the  same  thing  several         repeated,  because  it  makes no sense to assert the same thing several
3913         times.  If  any kind of assertion contains capturing subpatterns within         times. If any kind of assertion contains capturing  subpatterns  within
3914         it, these are counted for the purposes of numbering the capturing  sub-         it,  these are counted for the purposes of numbering the capturing sub-
3915         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
3916         out only for positive assertions, because it does not  make  sense  for         out  only  for  positive assertions, because it does not make sense for
3917         negative assertions.         negative assertions.
3918    
3919     Lookahead assertions     Lookahead assertions
# Line 3408  ASSERTIONS Line 3923  ASSERTIONS
3923    
3924           \w+(?=;)           \w+(?=;)
3925    
3926         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-
3927         colon in the match, and         colon in the match, and
3928    
3929           foo(?!bar)           foo(?!bar)
3930    
3931         matches  any  occurrence  of  "foo" that is not followed by "bar". Note         matches any occurrence of "foo" that is not  followed  by  "bar".  Note
3932         that the apparently similar pattern         that the apparently similar pattern
3933    
3934           (?!foo)bar           (?!foo)bar
3935    
3936         does not find an occurrence of "bar"  that  is  preceded  by  something         does  not  find  an  occurrence  of "bar" that is preceded by something
3937         other  than "foo"; it finds any occurrence of "bar" whatsoever, because         other than "foo"; it finds any occurrence of "bar" whatsoever,  because
3938         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
3939         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
3940    
3941         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
3942         most convenient way to do it is  with  (?!)  because  an  empty  string         most  convenient  way  to  do  it  is with (?!) because an empty string
3943         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
3944         string must always fail.         string must always fail.
3945    
3946     Lookbehind assertions     Lookbehind assertions
3947    
3948         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
3949         for negative assertions. For example,         for negative assertions. For example,
3950    
3951           (?<!foo)bar           (?<!foo)bar
3952    
3953         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
3954         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
3955         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-
3956         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
3957         Thus         fixed length. Thus
3958    
3959           (?<=bullock|donkey)           (?<=bullock|donkey)
3960    
# Line 3447  ASSERTIONS Line 3962  ASSERTIONS
3962    
3963           (?<!dogs?|cats?)           (?<!dogs?|cats?)
3964    
3965         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
3966         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
3967         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
3968         requires all branches to match the same length of string. An  assertion         requires  all branches to match the same length of string. An assertion
3969         such as         such as
3970    
3971           (?<=ab(c|de))           (?<=ab(c|de))
3972    
3973         is  not  permitted,  because  its single top-level branch can match two         is not permitted, because its single top-level  branch  can  match  two
3974         different lengths, but it is acceptable if rewritten to  use  two  top-         different  lengths,  but  it is acceptable if rewritten to use two top-
3975         level branches:         level branches:
3976    
3977           (?<=abc|abde)           (?<=abc|abde)
3978    
3979         The  implementation  of lookbehind assertions is, for each alternative,         The implementation of lookbehind assertions is, for  each  alternative,
3980         to temporarily move the current position back by the  fixed  width  and         to  temporarily  move the current position back by the fixed length and
3981         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
3982         rent position, the match is deemed to fail.         rent position, the assertion fails.
3983    
3984         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
3985         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode) to appear in lookbehind assertions, because it makes it  impossi-
3986         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,
3987         match different numbers of bytes, is also not permitted.         which can match different numbers of bytes, are also not permitted.
3988    
3989         Atomic  groups can be used in conjunction with lookbehind assertions to         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind
3990         specify efficient matching at the end of the subject string. Consider a         assertions  to  specify  efficient  matching  at the end of the subject
3991         simple pattern such as         string. Consider a simple pattern such as
3992    
3993           abcd$           abcd$
3994    
3995         when  applied  to  a  long string that does not match. Because matching         when applied to a long string that does  not  match.  Because  matching
3996         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
3997         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
3998         pattern is specified as         pattern is specified as
3999    
4000           ^.*abcd$           ^.*abcd$
4001    
4002         the initial .* matches the entire string at first, but when this  fails         the  initial .* matches the entire string at first, but when this fails
4003         (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
4004         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
4005         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,
4006         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
4007    
          ^(?>.*)(?<=abcd)  
   
        or, equivalently, using the possessive quantifier syntax,  
   
4008           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4009    
4010         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
4011         entire  string.  The subsequent lookbehind assertion does a single test         entire string. The subsequent lookbehind assertion does a  single  test
4012         on the last four characters. If it fails, the match fails  immediately.         on  the last four characters. If it fails, the match fails immediately.
4013         For  long  strings, this approach makes a significant difference to the         For long strings, this approach makes a significant difference  to  the
4014         processing time.         processing time.
4015    
4016     Using multiple assertions     Using multiple assertions
# Line 3508  ASSERTIONS Line 4019  ASSERTIONS
4019    
4020           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4021    
4022         matches "foo" preceded by three digits that are not "999". Notice  that         matches  "foo" preceded by three digits that are not "999". Notice that
4023         each  of  the  assertions is applied independently at the same point in         each of the assertions is applied independently at the  same  point  in
4024         the subject string. First there is a  check  that  the  previous  three         the  subject  string.  First  there  is a check that the previous three
4025         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
4026         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4027         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
4028         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-
4029         foo". A pattern to do that is         foo". A pattern to do that is
4030    
4031           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4032    
4033         This  time  the  first assertion looks at the preceding six characters,         This time the first assertion looks at the  preceding  six  characters,
4034         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4035         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4036    
# Line 3527  ASSERTIONS Line 4038  ASSERTIONS
4038    
4039           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4040    
4041         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
4042         is not preceded by "foo", while         is not preceded by "foo", while
4043    
4044           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4045    
4046         is another pattern that matches "foo" preceded by three digits and  any         is  another pattern that matches "foo" preceded by three digits and any
4047         three characters that are not "999".         three characters that are not "999".
4048    
4049    
4050  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4051    
4052         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-
4053         ditionally or to choose between two alternative subpatterns,  depending         ditionally  or to choose between two alternative subpatterns, depending
4054         on  the result of an assertion, or whether a previous capturing subpat-         on the result of an assertion, or whether a previous capturing  subpat-
4055         tern matched or not. The two possible forms of  conditional  subpattern         tern  matched  or not. The two possible forms of conditional subpattern
4056         are         are
4057    
4058           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4059           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4060    
4061         If  the  condition is satisfied, the yes-pattern is used; otherwise the         If the condition is satisfied, the yes-pattern is used;  otherwise  the
4062         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-
4063         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4064    
4065         There are three kinds of condition. If the text between the parentheses         There are four kinds of condition: references  to  subpatterns,  refer-
4066         consists of a sequence of digits, the condition  is  satisfied  if  the         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4067         capturing  subpattern of that number has previously matched. The number  
4068         must be greater than zero. Consider the following pattern,  which  con-     Checking for a used subpattern by number
4069         tains  non-significant white space to make it more readable (assume the  
4070         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,
4071         discussion:         the condition is true if the capturing subpattern of  that  number  has
4072           previously matched.
4073    
4074           Consider  the  following  pattern, which contains non-significant white
4075           space to make it more readable (assume the PCRE_EXTENDED option) and to
4076           divide it into three parts for ease of discussion:
4077    
4078           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4079    
# Line 3572  CONDITIONAL SUBPATTERNS Line 4088  CONDITIONAL SUBPATTERNS
4088         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other  words,  this  pattern  matches  a  sequence  of non-parentheses,
4089         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4090    
4091         If the condition is the string (R), it is satisfied if a recursive call     Checking for a used subpattern by name
4092         to  the pattern or subpattern has been made. At "top level", the condi-  
4093         tion is false.  This  is  a  PCRE  extension.  Recursive  patterns  are         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a
4094         described in the next section.         used  subpattern  by  name.  For compatibility with earlier versions of
4095           PCRE, which had this facility before Perl, the syntax  (?(name)...)  is
4096           also  recognized. However, there is a possible ambiguity with this syn-
4097           tax, because subpattern names may  consist  entirely  of  digits.  PCRE
4098           looks  first for a named subpattern; if it cannot find one and the name
4099           consists entirely of digits, PCRE looks for a subpattern of  that  num-
4100           ber,  which must be greater than zero. Using subpattern names that con-
4101           sist entirely of digits is not recommended.
4102    
4103           Rewriting the above example to use a named subpattern gives this:
4104    
4105             (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
4106    
4107         If  the  condition  is  not  a sequence of digits or (R), it must be an  
4108       Checking for pattern recursion
4109    
4110           If the condition is the string (R), and there is no subpattern with the
4111           name  R, the condition is true if a recursive call to the whole pattern
4112           or any subpattern has been made. If digits or a name preceded by amper-
4113           sand follow the letter R, for example:
4114    
4115             (?(R3)...) or (?(R&name)...)
4116    
4117           the  condition is true if the most recent recursion is into the subpat-
4118           tern whose number or name is given. This condition does not  check  the
4119           entire recursion stack.
4120    
4121           At  "top  level", all these recursion test conditions are false. Recur-
4122           sive patterns are described below.
4123    
4124       Defining subpatterns for use by reference only
4125    
4126           If the condition is the string (DEFINE), and  there  is  no  subpattern
4127           with  the  name  DEFINE,  the  condition is always false. In this case,
4128           there may be only one alternative  in  the  subpattern.  It  is  always
4129           skipped  if  control  reaches  this  point  in the pattern; the idea of
4130           DEFINE is that it can be used to define "subroutines" that can be  ref-
4131           erenced  from elsewhere. (The use of "subroutines" is described below.)
4132           For example, a pattern to match an IPv4 address could be  written  like
4133           this (ignore whitespace and line breaks):
4134    
4135             (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
4136             \b (?&byte) (\.(?&byte)){3} \b
4137    
4138           The  first part of the pattern is a DEFINE group inside which a another
4139           group named "byte" is defined. This matches an individual component  of
4140</