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revision 75 by nigel, Sat Feb 24 21:40:37 2007 UTC revision 208 by ph10, Mon Aug 6 15:23:29 2007 UTC
# Line 6  synopses of each function in the library Line 6  synopses of each function in the library
6  separate text files for the pcregrep and pcretest commands.  separate text files for the pcregrep and pcretest commands.
7  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
8    
 PCRE(3)                                                                PCRE(3)  
9    
10    PCRE(3)                                                                PCRE(3)
11    
12    
13  NAME  NAME
14         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
15    
16    
17  INTRODUCTION  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         5.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         PCRE is written in C and released as a C library. A  number  of  people         mately with Perl 5.10, including support for UTF-8 encoded strings  and
27         have  written  wrappers and interfaces of various kinds. A C++ class is         Unicode general category properties. However, UTF-8 and Unicode support
28         included in these contributions, which can  be  found  in  the  Contrib         has to be explicitly enabled; it is not the default. The Unicode tables
29         directory at the primary FTP site, which is:         correspond to Unicode release 5.0.0.
30    
31           In  addition to the Perl-compatible matching function, PCRE contains an
32           alternative matching function that matches the same  compiled  patterns
33           in  a different way. In certain circumstances, the alternative function
34           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
41           of  this  interface.  Other  people's contributions can be found in the
42           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. There is a syntax summary in the  pcresyntax
49           page.
50    
51         Some  features  of  PCRE can be included, excluded, or changed when the         Some  features  of  PCRE can be included, excluded, or changed when the
52         library is built. The pcre_config() function makes it  possible  for  a         library is built. The pcre_config() function makes it  possible  for  a
# Line 40  INTRODUCTION Line 55  INTRODUCTION
55         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
56         in the source distribution.         in the source distribution.
57    
58           The library contains a number of undocumented  internal  functions  and
59           data  tables  that  are  used by more than one of the exported external
60           functions, but which are not intended  for  use  by  external  callers.
61           Their  names  all begin with "_pcre_", which hopefully will not provoke
62           any name clashes. In some environments, it is possible to control which
63           external  symbols  are  exported when a shared library is built, and in
64           these cases the undocumented symbols are not exported.
65    
66    
67  USER DOCUMENTATION  USER DOCUMENTATION
68    
# Line 50  USER DOCUMENTATION Line 73  USER DOCUMENTATION
73         of searching. The sections are as follows:         of searching. The sections are as follows:
74    
75           pcre              this document           pcre              this document
76           pcreapi           details of PCRE's native API           pcre-config       show PCRE installation configuration information
77             pcreapi           details of PCRE's native C API
78           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
79           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
80           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
81             pcrecpp           details of the C++ wrapper
82           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
83             pcrematching      discussion of the two matching algorithms
84           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
85           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
86                               regular expressions                               regular expressions
87             pcresyntax        quick syntax reference
88           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
89           pcreposix         the POSIX-compatible API           pcreposix         the POSIX-compatible C API
90           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
91           pcresample        discussion of the sample program           pcresample        discussion of the sample program
92             pcrestack         discussion of stack usage
93           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
94    
95         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
96         each library function, listing its arguments and results.         each C library function, listing its arguments and results.
97    
98    
99  LIMITATIONS  LIMITATIONS
# Line 79  LIMITATIONS Line 107  LIMITATIONS
107         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
108         the  source  distribution and the pcrebuild documentation for details).         the  source  distribution and the pcrebuild documentation for details).
109         In these cases the limit is substantially larger.  However,  the  speed         In these cases the limit is substantially larger.  However,  the  speed
110         of execution will be slower.         of execution is slower.
111    
112           All values in repeating quantifiers must be less than 65536.
113    
114         All values in repeating quantifiers must be less than 65536.  The maxi-         There is no limit to the number of parenthesized subpatterns, but there
115         mum number of capturing subpatterns is 65535.         can be no more than 65535 capturing subpatterns.
116    
117         There is no limit to the number of non-capturing subpatterns,  but  the         The maximum length of name for a named subpattern is 32 characters, and
118         maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,         the maximum number of named subpatterns is 10000.
        including capturing subpatterns, assertions, and other types of subpat-  
        tern, is 200.  
119    
120         The  maximum  length of a subject string is the largest positive number         The  maximum  length of a subject string is the largest positive number
121         that an integer variable can hold. However, PCRE uses recursion to han-         that an integer variable can hold. However, when using the  traditional
122         dle  subpatterns  and indefinite repetition. This means that the avail-         matching function, PCRE uses recursion to handle subpatterns and indef-
123         able stack space may limit the size of a subject  string  that  can  be         inite repetition.  This means that the available stack space may  limit
124         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.         mode,  but  its  use can lead to some strange effects. This facility is
186           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-
# Line 167  UTF-8 AND UNICODE PROPERTY SUPPORT Line 197  UTF-8 AND UNICODE PROPERTY SUPPORT
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. However, the Perl 5.10 horizontal and vertical  whitespace  matching
201           escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
202           acters.
203    
204           10. Case-insensitive matching applies only to characters  whose  values
205         are  less than 128, unless PCRE is built with Unicode property support.         are  less than 128, unless PCRE is built with Unicode property support.
206         Even when Unicode property support is available, PCRE  still  uses  its         Even when Unicode property support is available, PCRE  still  uses  its
207         own  character  tables when checking the case of low-valued characters,         own  character  tables when checking the case of low-valued characters,
208         so as not to degrade performance.  The Unicode property information  is         so as not to degrade performance.  The Unicode property information  is
209         used only for characters with higher values.         used only for characters with higher values. Even when Unicode property
210           support is available, PCRE supports case-insensitive matching only when
211           there  is  a  one-to-one  mapping between a letter's cases. There are a
212           small number of many-to-one mappings in Unicode;  these  are  not  sup-
213           ported by PCRE.
214    
215    
216  AUTHOR  AUTHOR
217    
218         Philip Hazel <ph10@cam.ac.uk>         Philip Hazel
219         University Computing Service,         University Computing Service
220         Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
        Phone: +44 1223 334714  
221    
222  Last updated: 09 September 2004         Putting  an actual email address here seems to have been a spam magnet,
223  Copyright (c) 1997-2004 University of Cambridge.         so I've taken it away. If you want to email me, use  my  two  initials,
224  -----------------------------------------------------------------------------         followed by the two digits 10, at the domain cam.ac.uk.
225    
226  PCRE(3)                                                                PCRE(3)  
227    REVISION
228    
229           Last updated: 06 August 2007
230           Copyright (c) 1997-2007 University of Cambridge.
231    ------------------------------------------------------------------------------
232    
233    
234    PCREBUILD(3)                                                      PCREBUILD(3)
235    
236    
237  NAME  NAME
238         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
239    
240    
241  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
242    
243         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
# Line 204  PCRE BUILD-TIME OPTIONS Line 249  PCRE BUILD-TIME OPTIONS
249    
250           ./configure --help           ./configure --help
251    
252         The following sections describe certain options whose names begin  with         The following sections include  descriptions  of  options  whose  names
253         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
254         for the configure command. Because of the  way  that  configure  works,         defaults for the configure command. Because of the way  that  configure
255         --enable  and  --disable  always  come  in  pairs, so the complementary         works,  --enable  and --disable always come in pairs, so the complemen-
256         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
257         not described.         is not described.
258    
259    
260    C++ SUPPORT
261    
262           By default, the configure script will search for a C++ compiler and C++
263           header files. If it finds them, it automatically builds the C++ wrapper
264           library for PCRE. You can disable this by adding
265    
266             --disable-cpp
267    
268           to the configure command.
269    
270    
271  UTF-8 SUPPORT  UTF-8 SUPPORT
# Line 237  UNICODE CHARACTER PROPERTY SUPPORT Line 293  UNICODE CHARACTER PROPERTY SUPPORT
293         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
294         not explicitly requested it.         not explicitly requested it.
295    
296         Including  Unicode  property  support  adds around 90K of tables to the         Including  Unicode  property  support  adds around 30K of tables to the
297         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE library. Only the general category properties such as  Lu  and  Nd
298         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.  
299    
300    
301  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
302    
303         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating
304         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
305         compile PCRE to use character 13 (carriage return) instead by adding         systems. You can compile PCRE to use character 13 (carriage return, CR)
306           instead, by adding
307    
308           --enable-newline-is-cr           --enable-newline-is-cr
309    
310         to the configure command. For completeness there is  also  a  --enable-         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
311         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
312         line character.  
313           Alternatively, you can specify that line endings are to be indicated by
314           the two character sequence CRLF. If you want this, add
315    
316             --enable-newline-is-crlf
317    
318           to the configure command. There is a fourth option, specified by
319    
320             --enable-newline-is-anycrlf
321    
322           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
323           CRLF as indicating a line ending. Finally, a fifth option, specified by
324    
325             --enable-newline-is-any
326    
327           causes PCRE to recognize any Unicode newline sequence.
328    
329           Whatever line ending convention is selected when PCRE is built  can  be
330           overridden  when  the library functions are called. At build time it is
331           conventional to use the standard for your operating system.
332    
333    
334  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
# Line 284  POSIX MALLOC USAGE Line 359  POSIX MALLOC USAGE
359         to the configure command.         to the configure command.
360    
361    
 LIMITING PCRE RESOURCE USAGE  
   
        Internally,  PCRE has a function called match(), which it calls repeat-  
        edly (possibly recursively) when matching a pattern. 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 documentation. The default is 10 million,  but  
        this can be changed by adding a setting such as  
   
          --with-match-limit=500000  
   
        to the configure command.  
   
   
362  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
363    
364         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 316  HANDLING VERY LARGE PATTERNS Line 376  HANDLING VERY LARGE PATTERNS
376         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
377         additional bytes when handling them.         additional bytes when handling them.
378    
        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.  
   
379    
380  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
381    
382         PCRE  implements  backtracking while matching by making recursive calls         When matching with the pcre_exec() function, PCRE implements backtrack-
383         to an internal function called match(). In environments where the  size         ing  by  making recursive calls to an internal function called match().
384         of the stack is limited, this can severely limit PCRE's operation. (The         In environments where the size of the stack is limited,  this  can  se-
385         Unix environment does not usually suffer from this problem.) An  alter-         verely  limit  PCRE's operation. (The Unix environment does not usually
386         native  approach  that  uses  memory  from  the  heap to remember data,         suffer from this problem, but it may sometimes be necessary to increase
387         instead of using recursive function calls, has been implemented to work         the  maximum  stack size.  There is a discussion in the pcrestack docu-
388         round  this  problem. If you want to build a version of PCRE that works         mentation.) An alternative approach to recursion that uses memory  from
389         this way, add         the  heap  to remember data, instead of using recursive function calls,
390           has been implemented to work round the problem of limited  stack  size.
391           If you want to build a version of PCRE that works this way, add
392    
393           --disable-stack-for-recursion           --disable-stack-for-recursion
394    
395         to the configure command. With this configuration, PCRE  will  use  the         to  the  configure  command. With this configuration, PCRE will use the
396         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
397         ment functions. Separate functions are provided because  the  usage  is         ment  functions. By default these point to malloc() and free(), but you
398         very  predictable:  the  block sizes requested are always the same, and         can replace the pointers so that your own functions are used.
399         the blocks are always freed in reverse order. A calling  program  might  
400         be  able  to implement optimized functions that perform better than the         Separate functions are  provided  rather  than  using  pcre_malloc  and
401         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         pcre_free  because  the  usage  is  very  predictable:  the block sizes
402         slowly when built in this way.         requested are always the same, and  the  blocks  are  always  freed  in
403           reverse  order.  A calling program might be able to implement optimized
404           functions that perform better  than  malloc()  and  free().  PCRE  runs
405           noticeably more slowly when built in this way. This option affects only
406           the  pcre_exec()  function;  it   is   not   relevant   for   the   the
407           pcre_dfa_exec() function.
408    
409    
410    LIMITING PCRE RESOURCE USAGE
411    
412           Internally,  PCRE has a function called match(), which it calls repeat-
413           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
414           pcre_exec()  function.  By controlling the maximum number of times this
415           function may be called during a single matching operation, a limit  can
416           be  placed  on  the resources used by a single call to pcre_exec(). The
417           limit can be changed at run time, as described in the pcreapi  documen-
418           tation.  The default is 10 million, but this can be changed by adding a
419           setting such as
420    
421             --with-match-limit=500000
422    
423           to  the  configure  command.  This  setting  has  no  effect   on   the
424           pcre_dfa_exec() matching function.
425    
426           In  some  environments  it is desirable to limit the depth of recursive
427           calls of match() more strictly than the total number of calls, in order
428           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
429           for-recursion is specified) that is used. A second limit controls this;
430           it  defaults  to  the  value  that is set for --with-match-limit, which
431           imposes no additional constraints. However, you can set a  lower  limit
432           by adding, for example,
433    
434             --with-match-limit-recursion=10000
435    
436           to  the  configure  command.  This  value can also be overridden at run
437           time.
438    
439    
440    CREATING CHARACTER TABLES AT BUILD TIME
441    
442           PCRE uses fixed tables for processing characters whose code values  are
443           less  than 256. By default, PCRE is built with a set of tables that are
444           distributed in the file pcre_chartables.c.dist. These  tables  are  for
445           ASCII codes only. If you add
446    
447             --enable-rebuild-chartables
448    
449           to  the  configure  command, the distributed tables are no longer used.
450           Instead, a program called dftables is compiled and  run.  This  outputs
451           the source for new set of tables, created in the default locale of your
452           C runtime system. (This method of replacing the tables does not work if
453           you  are cross compiling, because dftables is run on the local host. If
454           you need to create alternative tables when cross  compiling,  you  will
455           have to do so "by hand".)
456    
457    
458  USING EBCDIC CODE  USING EBCDIC CODE
459    
460         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
461         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
462         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by         This  is  the  case for most computer operating systems. PCRE can, how-
463         adding         ever, be compiled to run in an EBCDIC environment by adding
464    
465           --enable-ebcdic           --enable-ebcdic
466    
467         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
468           bles.  You  should  only  use  it if you know that you are in an EBCDIC
469           environment (for example, an IBM mainframe operating system).
470    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
471    
472  PCRE(3)                                                                PCRE(3)  SEE ALSO
473    
474           pcreapi(3), pcre_config(3).
475    
476    
477    AUTHOR
478    
479           Philip Hazel
480           University Computing Service
481           Cambridge CB2 3QH, England.
482    
483    
484    REVISION
485    
486           Last updated: 30 July 2007
487           Copyright (c) 1997-2007 University of Cambridge.
488    ------------------------------------------------------------------------------
489    
490    
491    PCREMATCHING(3)                                                PCREMATCHING(3)
492    
493    
494    NAME
495           PCRE - Perl-compatible regular expressions
496    
497    
498    PCRE MATCHING ALGORITHMS
499    
500           This document describes the two different algorithms that are available
501           in PCRE for matching a compiled regular expression against a given sub-
502           ject  string.  The  "standard"  algorithm  is  the  one provided by the
503           pcre_exec() function.  This works in the same was  as  Perl's  matching
504           function, and provides a Perl-compatible matching operation.
505    
506           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
507           this operates in a different way, and is not  Perl-compatible.  It  has
508           advantages  and disadvantages compared with the standard algorithm, and
509           these are described below.
510    
511           When there is only one possible way in which a given subject string can
512           match  a pattern, the two algorithms give the same answer. A difference
513           arises, however, when there are multiple possibilities. For example, if
514           the pattern
515    
516             ^<.*>
517    
518           is matched against the string
519    
520             <something> <something else> <something further>
521    
522           there are three possible answers. The standard algorithm finds only one
523           of them, whereas the alternative algorithm finds all three.
524    
525    
526    REGULAR EXPRESSIONS AS TREES
527    
528           The set of strings that are matched by a regular expression can be rep-
529           resented  as  a  tree structure. An unlimited repetition in the pattern
530           makes the tree of infinite size, but it is still a tree.  Matching  the
531           pattern  to a given subject string (from a given starting point) can be
532           thought of as a search of the tree.  There are two  ways  to  search  a
533           tree:  depth-first  and  breadth-first, and these correspond to the two
534           matching algorithms provided by PCRE.
535    
536    
537    THE STANDARD MATCHING ALGORITHM
538    
539           In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
540           sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
541           depth-first search of the pattern tree. That is, it  proceeds  along  a
542           single path through the tree, checking that the subject matches what is
543           required. When there is a mismatch, the algorithm  tries  any  alterna-
544           tives  at  the  current point, and if they all fail, it backs up to the
545           previous branch point in the  tree,  and  tries  the  next  alternative
546           branch  at  that  level.  This often involves backing up (moving to the
547           left) in the subject string as well.  The  order  in  which  repetition
548           branches  are  tried  is controlled by the greedy or ungreedy nature of
549           the quantifier.
550    
551           If a leaf node is reached, a matching string has  been  found,  and  at
552           that  point the algorithm stops. Thus, if there is more than one possi-
553           ble match, this algorithm returns the first one that it finds.  Whether
554           this  is the shortest, the longest, or some intermediate length depends
555           on the way the greedy and ungreedy repetition quantifiers are specified
556           in the pattern.
557    
558           Because  it  ends  up  with a single path through the tree, it is rela-
559           tively straightforward for this algorithm to keep  track  of  the  sub-
560           strings  that  are  matched  by portions of the pattern in parentheses.
561           This provides support for capturing parentheses and back references.
562    
563    
564    THE ALTERNATIVE MATCHING ALGORITHM
565    
566           This algorithm conducts a breadth-first search of  the  tree.  Starting
567           from  the  first  matching  point  in the subject, it scans the subject
568           string from left to right, once, character by character, and as it does
569           this,  it remembers all the paths through the tree that represent valid
570           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
571           though  it is not implemented as a traditional finite state machine (it
572           keeps multiple states active simultaneously).
573    
574           The scan continues until either the end of the subject is  reached,  or
575           there  are  no more unterminated paths. At this point, terminated paths
576           represent the different matching possibilities (if there are none,  the
577           match  has  failed).   Thus,  if there is more than one possible match,
578           this algorithm finds all of them, and in particular, it finds the long-
579           est.  In PCRE, there is an option to stop the algorithm after the first
580           match (which is necessarily the shortest) has been found.
581    
582           Note that all the matches that are found start at the same point in the
583           subject. If the pattern
584    
585             cat(er(pillar)?)
586    
587           is  matched  against the string "the caterpillar catchment", the result
588           will be the three strings "cat", "cater", and "caterpillar" that  start
589           at the fourth character of the subject. The algorithm does not automat-
590           ically move on to find matches that start at later positions.
591    
592           There are a number of features of PCRE regular expressions that are not
593           supported by the alternative matching algorithm. They are as follows:
594    
595           1.  Because  the  algorithm  finds  all possible matches, the greedy or
596           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
597           ungreedy quantifiers are treated in exactly the same way. However, pos-
598           sessive quantifiers can make a difference when what follows could  also
599           match what is quantified, for example in a pattern like this:
600    
601             ^a++\w!
602    
603           This  pattern matches "aaab!" but not "aaa!", which would be matched by
604           a non-possessive quantifier. Similarly, if an atomic group is  present,
605           it  is matched as if it were a standalone pattern at the current point,
606           and the longest match is then "locked in" for the rest of  the  overall
607           pattern.
608    
609           2. When dealing with multiple paths through the tree simultaneously, it
610           is not straightforward to keep track of  captured  substrings  for  the
611           different  matching  possibilities,  and  PCRE's implementation of this
612           algorithm does not attempt to do this. This means that no captured sub-
613           strings are available.
614    
615           3.  Because no substrings are captured, back references within the pat-
616           tern are not supported, and cause errors if encountered.
617    
618           4. For the same reason, conditional expressions that use  a  backrefer-
619           ence  as  the  condition or test for a specific group recursion are not
620           supported.
621    
622           5. Because many paths through the tree may be  active,  the  \K  escape
623           sequence, which resets the start of the match when encountered (but may
624           be on some paths and not on others), is not  supported.  It  causes  an
625           error if encountered.
626    
627           6.  Callouts  are  supported, but the value of the capture_top field is
628           always 1, and the value of the capture_last field is always -1.
629    
630           7.  The \C escape sequence, which (in the standard algorithm) matches a
631           single  byte, even in UTF-8 mode, is not supported because the alterna-
632           tive algorithm moves through the subject  string  one  character  at  a
633           time, for all active paths through the tree.
634    
635    
636    ADVANTAGES OF THE ALTERNATIVE ALGORITHM
637    
638           Using  the alternative matching algorithm provides the following advan-
639           tages:
640    
641           1. All possible matches (at a single point in the subject) are automat-
642           ically  found,  and  in particular, the longest match is found. To find
643           more than one match using the standard algorithm, you have to do kludgy
644           things with callouts.
645    
646           2.  There is much better support for partial matching. The restrictions
647           on the content of the pattern that apply when using the standard  algo-
648           rithm  for  partial matching do not apply to the alternative algorithm.
649           For non-anchored patterns, the starting position of a partial match  is
650           available.
651    
652           3.  Because  the  alternative  algorithm  scans the subject string just
653           once, and never needs to backtrack, it is possible to  pass  very  long
654           subject  strings  to  the matching function in several pieces, checking
655           for partial matching each time.
656    
657    
658    DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
659    
660           The alternative algorithm suffers from a number of disadvantages:
661    
662           1. It is substantially slower than  the  standard  algorithm.  This  is
663           partly  because  it has to search for all possible matches, but is also
664           because it is less susceptible to optimization.
665    
666           2. Capturing parentheses and back references are not supported.
667    
668           3. Although atomic groups are supported, their use does not provide the
669           performance advantage that it does for the standard algorithm.
670    
671    
672    AUTHOR
673    
674           Philip Hazel
675           University Computing Service
676           Cambridge CB2 3QH, England.
677    
678    
679    REVISION
680    
681           Last updated: 29 May 2007
682           Copyright (c) 1997-2007 University of Cambridge.
683    ------------------------------------------------------------------------------
684    
685    
686    PCREAPI(3)                                                          PCREAPI(3)
687    
688    
689  NAME  NAME
690         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
691    
692    
693  PCRE NATIVE API  PCRE NATIVE API
694    
695         #include <pcre.h>         #include <pcre.h>
# Line 375  PCRE NATIVE API Line 698  PCRE NATIVE API
698              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
699              const unsigned char *tableptr);              const unsigned char *tableptr);
700    
701           pcre *pcre_compile2(const char *pattern, int options,
702                int *errorcodeptr,
703                const char **errptr, int *erroffset,
704                const unsigned char *tableptr);
705    
706         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options,
707              const char **errptr);              const char **errptr);
708    
# Line 382  PCRE NATIVE API Line 710  PCRE NATIVE API
710              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
711              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
712    
713           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
714                const char *subject, int length, int startoffset,
715                int options, int *ovector, int ovecsize,
716                int *workspace, int wscount);
717    
718         int pcre_copy_named_substring(const pcre *code,         int pcre_copy_named_substring(const pcre *code,
719              const char *subject, int *ovector,              const char *subject, int *ovector,
720              int stringcount, const char *stringname,              int stringcount, const char *stringname,
# Line 399  PCRE NATIVE API Line 732  PCRE NATIVE API
732         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
733              const char *name);              const char *name);
734    
735           int pcre_get_stringtable_entries(const pcre *code,
736                const char *name, char **first, char **last);
737    
738         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
739              int stringcount, int stringnumber,              int stringcount, int stringnumber,
740              const char **stringptr);              const char **stringptr);
# Line 417  PCRE NATIVE API Line 753  PCRE NATIVE API
753    
754         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
755    
756           int pcre_refcount(pcre *code, int adjust);
757    
758         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
759    
760         char *pcre_version(void);         char *pcre_version(void);
# Line 435  PCRE NATIVE API Line 773  PCRE NATIVE API
773  PCRE API OVERVIEW  PCRE API OVERVIEW
774    
775         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
776         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
777         expression API.  These are described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
778           Both of these APIs define a set of C function calls. A C++  wrapper  is
779           distributed with PCRE. It is documented in the pcrecpp page.
780    
781         The  native  API  function  prototypes  are  defined in the header file         The  native  API  C  function prototypes are defined in the header file
782         pcre.h, and on Unix systems the library itself is  called  libpcre.  It         pcre.h, and on Unix systems the library itself is called  libpcre.   It
783         can normally be accessed by adding -lpcre to the command for linking an         can normally be accessed by adding -lpcre to the command for linking an
784         application  that  uses  PCRE.  The  header  file  defines  the  macros         application  that  uses  PCRE.  The  header  file  defines  the  macros
785         PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-         PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
786         bers for the library.  Applications can use these  to  include  support         bers for the library.  Applications can use these  to  include  support
787         for different releases of PCRE.         for different releases of PCRE.
788    
789         The  functions  pcre_compile(),  pcre_study(), and pcre_exec() are used         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
790         for compiling and matching regular expressions. A sample  program  that         pcre_exec() are used for compiling and matching regular expressions  in
791         demonstrates  the  simplest  way  of using them is provided in the file         a  Perl-compatible  manner. A sample program that demonstrates the sim-
792         called pcredemo.c in the source distribution. The pcresample documenta-         plest way of using them is provided in the file  called  pcredemo.c  in
793         tion describes how to run it.         the  source distribution. The pcresample documentation describes how to
794           run it.
795         In  addition  to  the  main compiling and matching functions, there are  
796         convenience functions for extracting captured substrings from a matched         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
797         subject string.  They are:         ble,  is  also provided. This uses a different algorithm for the match-
798           ing. The alternative algorithm finds all possible matches (at  a  given
799           point  in  the subject), and scans the subject just once. However, this
800           algorithm does not return captured substrings. A description of the two
801           matching  algorithms and their advantages and disadvantages is given in
802           the pcrematching documentation.
803    
804           In addition to the main compiling and  matching  functions,  there  are
805           convenience functions for extracting captured substrings from a subject
806           string that is matched by pcre_exec(). They are:
807    
808           pcre_copy_substring()           pcre_copy_substring()
809           pcre_copy_named_substring()           pcre_copy_named_substring()
# Line 462  PCRE API OVERVIEW Line 811  PCRE API OVERVIEW
811           pcre_get_named_substring()           pcre_get_named_substring()
812           pcre_get_substring_list()           pcre_get_substring_list()
813           pcre_get_stringnumber()           pcre_get_stringnumber()
814             pcre_get_stringtable_entries()
815    
816         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
817         to free the memory used for extracted strings.         to free the memory used for extracted strings.
818    
819         The function pcre_maketables() is used to  build  a  set  of  character         The  function  pcre_maketables()  is  used  to build a set of character
820         tables   in  the  current  locale  for  passing  to  pcre_compile()  or         tables  in  the  current  locale   for   passing   to   pcre_compile(),
821         pcre_exec().  This is an optional facility that is  provided  for  spe-         pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
822         cialist use. Most commonly, no special tables are passed, in which case         provided for specialist use.  Most  commonly,  no  special  tables  are
823         internal tables that are generated when PCRE is built are used.         passed,  in  which case internal tables that are generated when PCRE is
824           built are used.
825    
826         The function pcre_fullinfo() is used to find out  information  about  a         The function pcre_fullinfo() is used to find out  information  about  a
827         compiled  pattern; pcre_info() is an obsolete version that returns only         compiled  pattern; pcre_info() is an obsolete version that returns only
# Line 478  PCRE API OVERVIEW Line 829  PCRE API OVERVIEW
829         patibility.   The function pcre_version() returns a pointer to a string         patibility.   The function pcre_version() returns a pointer to a string
830         containing the version of PCRE and its date of release.         containing the version of PCRE and its date of release.
831    
832           The function pcre_refcount() maintains a  reference  count  in  a  data
833           block  containing  a compiled pattern. This is provided for the benefit
834           of object-oriented applications.
835    
836         The global variables pcre_malloc and pcre_free  initially  contain  the         The global variables pcre_malloc and pcre_free  initially  contain  the
837         entry  points  of  the  standard malloc() and free() functions, respec-         entry  points  of  the  standard malloc() and free() functions, respec-
838         tively. PCRE calls the memory management functions via these variables,         tively. PCRE calls the memory management functions via these variables,
# Line 487  PCRE API OVERVIEW Line 842  PCRE API OVERVIEW
842         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
843         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
844         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
845         data,  instead  of recursive function calls. This is a non-standard way         data, instead of recursive function calls, when running the pcre_exec()
846         of building PCRE, for use in environments  that  have  limited  stacks.         function. See the pcrebuild documentation for  details  of  how  to  do
847         Because  of  the greater use of memory management, it runs more slowly.         this.  It  is  a non-standard way of building PCRE, for use in environ-
848         Separate functions are provided so that special-purpose  external  code         ments that have limited stacks. Because of the greater  use  of  memory
849         can be used for this case. When used, these functions are always called         management,  it  runs  more  slowly. Separate functions are provided so
850         in a stack-like manner (last obtained, first  freed),  and  always  for         that special-purpose external code can be  used  for  this  case.  When
851         memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
852           obtained, first freed), and always for memory blocks of the same  size.
853           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
854           mentation.
855    
856         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
857         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
858         specified  points during a matching operation. Details are given in the         specified points during a matching operation. Details are given in  the
859         pcrecallout documentation.         pcrecallout documentation.
860    
861    
862    NEWLINES
863    
864           PCRE  supports five different conventions for indicating line breaks in
865           strings: a single CR (carriage return) character, a  single  LF  (line-
866           feed) character, the two-character sequence CRLF, any of the three pre-
867           ceding, or any Unicode newline sequence. The Unicode newline  sequences
868           are  the  three just mentioned, plus the single characters VT (vertical
869           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
870           separator, U+2028), and PS (paragraph separator, U+2029).
871    
872           Each  of  the first three conventions is used by at least one operating
873           system as its standard newline sequence. When PCRE is built, a  default
874           can  be  specified.  The default default is LF, which is the Unix stan-
875           dard. When PCRE is run, the default can be overridden,  either  when  a
876           pattern is compiled, or when it is matched.
877    
878           In the PCRE documentation the word "newline" is used to mean "the char-
879           acter or pair of characters that indicate a line break". The choice  of
880           newline  convention  affects  the  handling of the dot, circumflex, and
881           dollar metacharacters, the handling of #-comments in /x mode, and, when
882           CRLF  is a recognized line ending sequence, the match position advance-
883           ment for a non-anchored pattern. The choice of newline convention  does
884           not affect the interpretation of the \n or \r escape sequences.
885    
886    
887  MULTITHREADING  MULTITHREADING
888    
889         The PCRE functions can be used in  multi-threading  applications,  with         The  PCRE  functions  can be used in multi-threading applications, with
890         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
891         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
892         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
893    
894         The compiled form of a regular expression is not altered during  match-         The  compiled form of a regular expression is not altered during match-
895         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
896         at once.         at once.
897    
# Line 516  MULTITHREADING Line 899  MULTITHREADING
899  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
900    
901         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
902         later  time,  possibly by a different program, and even on a host other         later time, possibly by a different program, and even on a  host  other
903         than the one on which  it  was  compiled.  Details  are  given  in  the         than  the  one  on  which  it  was  compiled.  Details are given in the
904         pcreprecompile documentation.         pcreprecompile documentation. However, compiling a  regular  expression
905           with  one version of PCRE for use with a different version is not guar-
906           anteed to work and may cause crashes.
907    
908    
909  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
910    
911         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
912    
913         The  function pcre_config() makes it possible for a PCRE client to dis-         The function pcre_config() makes it possible for a PCRE client to  dis-
914         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
915         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
916         tures.         tures.
917    
918         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
919         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
920         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
921         available:         available:
922    
923           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
924    
925         The  output is an integer that is set to one if UTF-8 support is avail-         The output is an integer that is set to one if UTF-8 support is  avail-
926         able; otherwise it is set to zero.         able; otherwise it is set to zero.
927    
928           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
929    
930         The output is an integer that is set to  one  if  support  for  Unicode         The  output  is  an  integer  that is set to one if support for Unicode
931         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
932    
933           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
934    
935         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
936         used for the newline character. It is either linefeed (10) or  carriage         sequence  that is recognized as meaning "newline". The four values that
937         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,
938         operating system.         and  -1  for  ANY. The default should normally be the standard sequence
939           for your operating system.
940    
941           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
942    
# Line 573  CHECKING BUILD-TIME OPTIONS Line 959  CHECKING BUILD-TIME OPTIONS
959         internal matching function calls in a  pcre_exec()  execution.  Further         internal matching function calls in a  pcre_exec()  execution.  Further
960         details are given with pcre_exec() below.         details are given with pcre_exec() below.
961    
962             PCRE_CONFIG_MATCH_LIMIT_RECURSION
963    
964           The  output is an integer that gives the default limit for the depth of
965           recursion when calling the internal matching function in a  pcre_exec()
966           execution. Further details are given with pcre_exec() below.
967    
968           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
969    
970         The  output  is  an integer that is set to one if internal recursion is         The  output is an integer that is set to one if internal recursion when
971         implemented by recursive function calls that use the stack to  remember         running pcre_exec() is implemented by recursive function calls that use
972         their state. This is the usual way that PCRE is compiled. The output is         the  stack  to remember their state. This is the usual way that PCRE is
973         zero if PCRE was compiled to use blocks of data on the heap instead  of         compiled. The output is zero if PCRE was compiled to use blocks of data
974         recursive   function   calls.   In  this  case,  pcre_stack_malloc  and         on  the  heap  instead  of  recursive  function  calls.  In  this case,
975         pcre_stack_free are called to manage memory blocks on  the  heap,  thus         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
976         avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
977    
978    
979  COMPILING A PATTERN  COMPILING A PATTERN
# Line 590  COMPILING A PATTERN Line 982  COMPILING A PATTERN
982              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
983              const unsigned char *tableptr);              const unsigned char *tableptr);
984    
985         The  function  pcre_compile()  is  called  to compile a pattern into an         pcre *pcre_compile2(const char *pattern, int options,
986         internal form. The pattern is a C string terminated by a  binary  zero,              int *errorcodeptr,
987         and  is  passed in the pattern argument. A pointer to a single block of              const char **errptr, int *erroffset,
988         memory that is obtained via pcre_malloc is returned. This contains  the              const unsigned char *tableptr);
989         compiled  code  and  related  data.  The  pcre  type is defined for the  
990         returned block; this is a typedef for a structure  whose  contents  are         Either of the functions pcre_compile() or pcre_compile2() can be called
991         not  externally defined. It is up to the caller to free the memory when         to compile a pattern into an internal form. The only difference between
992         it is no longer required.         the  two interfaces is that pcre_compile2() has an additional argument,
993           errorcodeptr, via which a numerical error code can be returned.
994    
995           The pattern is a C string terminated by a binary zero, and is passed in
996           the  pattern  argument.  A  pointer to a single block of memory that is
997           obtained via pcre_malloc is returned. This contains the  compiled  code
998           and related data. The pcre type is defined for the returned block; this
999           is a typedef for a structure whose contents are not externally defined.
1000           It is up to the caller to free the memory (via pcre_free) when it is no
1001           longer required.
1002    
1003         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
1004         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
1005         fully relocatable, because it may contain a copy of the tableptr  argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
1006         ment, which is an address (see below).         ment, which is an address (see below).
1007    
1008         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
1009         tion. It should be zero if  no  options  are  required.  The  available         pilation. It should be zero if no options are required.  The  available
1010         options  are  described  below. Some of them, in particular, those that         options  are  described  below. Some of them, in particular, those that
1011         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
1012         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern  (see  the  detailed  description in the pcrepattern documenta-
1013         tion). For these options, the contents of the options  argument  speci-         tion). For these options, the contents of the options  argument  speci-
1014         fies  their initial settings at the start of compilation and execution.         fies  their initial settings at the start of compilation and execution.
1015         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
1016         at compile time.         of matching as well as at compile time.
1017    
1018         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1019         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1020         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-
1021         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
1022         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-
1023         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
1024           by  erroffset,  which must not be NULL. If it is, an immediate error is
1025         given.         given.
1026    
1027           If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
1028           codeptr  argument is not NULL, a non-zero error code number is returned
1029           via this argument in the event of an error. This is in addition to  the
1030           textual error message. Error codes and messages are listed below.
1031    
1032         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of
1033         character tables that are  built  when  PCRE  is  compiled,  using  the         character tables that are  built  when  PCRE  is  compiled,  using  the
1034         default  C  locale.  Otherwise, tableptr must be an address that is the         default  C  locale.  Otherwise, tableptr must be an address that is the
# Line 664  COMPILING A PATTERN Line 1071  COMPILING A PATTERN
1071    
1072         If  this  bit is set, letters in the pattern match both upper and lower         If  this  bit is set, letters in the pattern match both upper and lower
1073         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be
1074         changed  within  a  pattern  by  a (?i) option setting. When running in         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
1075         UTF-8 mode, case support for high-valued characters is  available  only         always understands the concept of case for characters whose values  are
1076         when PCRE is built with Unicode character property support.         less  than 128, so caseless matching is always possible. For characters
1077           with higher values, the concept of case is supported if  PCRE  is  com-
1078           piled  with Unicode property support, but not otherwise. If you want to
1079           use caseless matching for characters 128 and  above,  you  must  ensure
1080           that  PCRE  is  compiled  with Unicode property support as well as with
1081           UTF-8 support.
1082    
1083           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1084    
1085         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
1086         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
1087         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
1088         not before any  other  newlines).  The  PCRE_DOLLAR_ENDONLY  option  is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1089         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
1090         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1091    
1092           PCRE_DOTALL           PCRE_DOTALL
1093    
1094         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-
1095         acters,  including  newlines.  Without  it, newlines are excluded. This         acters, including those that indicate newline. Without it, a  dot  does
1096         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
1097         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
1098         always matches a newline character, independent of the setting of  this         by  a (?s) option setting. A negative class such as [^a] always matches
1099         option.         newline characters, independent of the setting of this option.
1100    
1101             PCRE_DUPNAMES
1102    
1103           If this bit is set, names used to identify capturing  subpatterns  need
1104           not be unique. This can be helpful for certain types of pattern when it
1105           is known that only one instance of the named  subpattern  can  ever  be
1106           matched.  There  are  more details of named subpatterns below; see also
1107           the pcrepattern documentation.
1108    
1109           PCRE_EXTENDED           PCRE_EXTENDED
1110    
1111         If  this  bit  is  set,  whitespace  data characters in the pattern are         If this bit is set, whitespace  data  characters  in  the  pattern  are
1112         totally ignored except  when  escaped  or  inside  a  character  class.         totally ignored except when escaped or inside a character class. White-
1113         Whitespace  does  not  include the VT character (code 11). In addition,         space does not include the VT character (code 11). In addition, charac-
1114         characters between an unescaped # outside a  character  class  and  the         ters between an unescaped # outside a character class and the next new-
1115         next newline character, inclusive, are also ignored. This is equivalent         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1116         to 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-
1117         option setting.         ting.
1118    
1119         This  option  makes  it possible to include comments inside complicated         This option makes it possible to include  comments  inside  complicated
1120         patterns.  Note, however, that this applies only  to  data  characters.         patterns.   Note,  however,  that this applies only to data characters.
1121         Whitespace   characters  may  never  appear  within  special  character         Whitespace  characters  may  never  appear  within  special   character
1122         sequences in a pattern, for  example  within  the  sequence  (?(  which         sequences  in  a  pattern,  for  example  within the sequence (?( which
1123         introduces a conditional subpattern.         introduces a conditional subpattern.
1124    
1125           PCRE_EXTRA           PCRE_EXTRA
1126    
1127         This  option  was invented in order to turn on additional functionality         This option was invented in order to turn on  additional  functionality
1128         of PCRE that is incompatible with Perl, but it  is  currently  of  very         of  PCRE  that  is  incompatible with Perl, but it is currently of very
1129         little  use. When set, any backslash in a pattern that is followed by a         little use. When set, any backslash in a pattern that is followed by  a
1130         letter that has no special meaning  causes  an  error,  thus  reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1131         these  combinations  for  future  expansion.  By default, as in Perl, a         these combinations for future expansion. By  default,  as  in  Perl,  a
1132         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
1133         literal.  There  are  at  present  no other features controlled by this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1134         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
1135           can also be set by a (?X) option setting within a pattern.
1136    
1137             PCRE_FIRSTLINE
1138    
1139           If this option is set, an  unanchored  pattern  is  required  to  match
1140           before  or  at  the  first  newline  in  the subject string, though the
1141           matched text may continue over the newline.
1142    
1143           PCRE_MULTILINE           PCRE_MULTILINE
1144    
# Line 723  COMPILING A PATTERN Line 1150  COMPILING A PATTERN
1150         is set). This is the same as Perl.         is set). This is the same as Perl.
1151    
1152         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"
1153         constructs match immediately following or immediately before  any  new-         constructs match immediately following or immediately  before  internal
1154         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
1155         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
1156         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-
1157         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,
1158         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1159    
1160             PCRE_NEWLINE_CR
1161             PCRE_NEWLINE_LF
1162             PCRE_NEWLINE_CRLF
1163             PCRE_NEWLINE_ANYCRLF
1164             PCRE_NEWLINE_ANY
1165    
1166           These  options  override the default newline definition that was chosen
1167           when PCRE was built. Setting the first or the second specifies  that  a
1168           newline  is  indicated  by a single character (CR or LF, respectively).
1169           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1170           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1171           that any of the three preceding sequences should be recognized. Setting
1172           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1173           recognized. The Unicode newline sequences are the three just mentioned,
1174           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1175           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1176           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1177           UTF-8 mode.
1178    
1179           The newline setting in the  options  word  uses  three  bits  that  are
1180           treated as a number, giving eight possibilities. Currently only six are
1181           used (default plus the five values above). This means that if  you  set
1182           more  than one newline option, the combination may or may not be sensi-
1183           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1184           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1185           cause an error.
1186    
1187           The only time that a line break is specially recognized when  compiling
1188           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1189           character class is encountered. This indicates  a  comment  that  lasts
1190           until  after the next line break sequence. In other circumstances, line
1191           break  sequences  are  treated  as  literal  data,   except   that   in
1192           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1193           and are therefore ignored.
1194    
1195           The newline option that is set at compile time becomes the default that
1196           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1197    
1198           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1199    
1200         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-
1201         theses in the pattern. Any opening parenthesis that is not followed  by         theses  in the pattern. Any opening parenthesis that is not followed by
1202         ?  behaves as if it were followed by ?: but named parentheses can still         ? behaves as if it were followed by ?: but named parentheses can  still
1203         be used for capturing (and they acquire  numbers  in  the  usual  way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1204         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1205    
1206           PCRE_UNGREEDY           PCRE_UNGREEDY
1207    
1208         This  option  inverts  the "greediness" of the quantifiers so that they         This option inverts the "greediness" of the quantifiers  so  that  they
1209         are not greedy by default, but become greedy if followed by "?". It  is         are  not greedy by default, but become greedy if followed by "?". It is
1210         not  compatible  with Perl. It can also be set by a (?U) option setting         not compatible with Perl. It can also be set by a (?U)  option  setting
1211         within the pattern.         within the pattern.
1212    
1213           PCRE_UTF8           PCRE_UTF8
1214    
1215         This option causes PCRE to regard both the pattern and the  subject  as         This  option  causes PCRE to regard both the pattern and the subject as
1216         strings  of  UTF-8 characters instead of single-byte character strings.         strings of UTF-8 characters instead of single-byte  character  strings.
1217         However, it is available only when PCRE is built to include UTF-8  sup-         However,  it is available only when PCRE is built to include UTF-8 sup-
1218         port.  If not, the use of this option provokes an error. Details of how         port. If not, the use of this option provokes an error. Details of  how
1219         this option changes the behaviour of PCRE are given in the  section  on         this  option  changes the behaviour of PCRE are given in the section on
1220         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1221    
1222           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1223    
1224         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1225         automatically checked. If an invalid UTF-8 sequence of bytes is  found,         automatically  checked. If an invalid UTF-8 sequence of bytes is found,
1226         pcre_compile()  returns an error. If you already know that your pattern         pcre_compile() returns an error. If you already know that your  pattern
1227         is valid, and you want to skip this check for performance reasons,  you         is  valid, and you want to skip this check for performance reasons, you
1228         can  set  the  PCRE_NO_UTF8_CHECK option. When it is set, the effect of         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of
1229         passing an invalid UTF-8 string as a pattern is undefined. It may cause         passing an invalid UTF-8 string as a pattern is undefined. It may cause
1230         your  program  to  crash.   Note that this option can also be passed to         your program to crash.  Note that this option can  also  be  passed  to
1231         pcre_exec(),  to  suppress  the  UTF-8  validity  checking  of  subject         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1232         strings.         ing of subject strings.
1233    
1234    
1235    COMPILATION ERROR CODES
1236    
1237           The following table lists the error  codes  than  may  be  returned  by
1238           pcre_compile2(),  along with the error messages that may be returned by
1239           both compiling functions. As PCRE has developed, some error codes  have
1240           fallen out of use. To avoid confusion, they have not been re-used.
1241    
1242              0  no error
1243              1  \ at end of pattern
1244              2  \c at end of pattern
1245              3  unrecognized character follows \
1246              4  numbers out of order in {} quantifier
1247              5  number too big in {} quantifier
1248              6  missing terminating ] for character class
1249              7  invalid escape sequence in character class
1250              8  range out of order in character class
1251              9  nothing to repeat
1252             10  [this code is not in use]
1253             11  internal error: unexpected repeat
1254             12  unrecognized character after (?
1255             13  POSIX named classes are supported only within a class
1256             14  missing )
1257             15  reference to non-existent subpattern
1258             16  erroffset passed as NULL
1259             17  unknown option bit(s) set
1260             18  missing ) after comment
1261             19  [this code is not in use]
1262             20  regular expression too large
1263             21  failed to get memory
1264             22  unmatched parentheses
1265             23  internal error: code overflow
1266             24  unrecognized character after (?<
1267             25  lookbehind assertion is not fixed length
1268             26  malformed number or name after (?(
1269             27  conditional group contains more than two branches
1270             28  assertion expected after (?(
1271             29  (?R or (?[+-]digits must be followed by )
1272             30  unknown POSIX class name
1273             31  POSIX collating elements are not supported
1274             32  this version of PCRE is not compiled with PCRE_UTF8 support
1275             33  [this code is not in use]
1276             34  character value in \x{...} sequence is too large
1277             35  invalid condition (?(0)
1278             36  \C not allowed in lookbehind assertion
1279             37  PCRE does not support \L, \l, \N, \U, or \u
1280             38  number after (?C is > 255
1281             39  closing ) for (?C expected
1282             40  recursive call could loop indefinitely
1283             41  unrecognized character after (?P
1284             42  syntax error in subpattern name (missing terminator)
1285             43  two named subpatterns have the same name
1286             44  invalid UTF-8 string
1287             45  support for \P, \p, and \X has not been compiled
1288             46  malformed \P or \p sequence
1289             47  unknown property name after \P or \p
1290             48  subpattern name is too long (maximum 32 characters)
1291             49  too many named subpatterns (maximum 10,000)
1292             50  [this code is not in use]
1293             51  octal value is greater than \377 (not in UTF-8 mode)
1294             52  internal error: overran compiling workspace
1295             53   internal  error:  previously-checked  referenced  subpattern not
1296           found
1297             54  DEFINE group contains more than one branch
1298             55  repeating a DEFINE group is not allowed
1299             56  inconsistent NEWLINE options"
1300             57  \g is not followed by a braced name or an optionally braced
1301                   non-zero number
1302             58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
1303    
1304    
1305  STUDYING A PATTERN  STUDYING A PATTERN
1306    
1307         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1308              const char **errptr);              const char **errptr);
1309    
1310         If  a  compiled  pattern is going to be used several times, it is worth         If a compiled pattern is going to be used several times,  it  is  worth
1311         spending more time analyzing it in order to speed up the time taken for         spending more time analyzing it in order to speed up the time taken for
1312         matching.  The function pcre_study() takes a pointer to a compiled pat-         matching. The function pcre_study() takes a pointer to a compiled  pat-
1313         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1314         information  that  will  help speed up matching, pcre_study() returns a         information that will help speed up matching,  pcre_study()  returns  a
1315         pointer to a pcre_extra block, in which the study_data field points  to         pointer  to a pcre_extra block, in which the study_data field points to
1316         the results of the study.         the results of the study.
1317    
1318         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1319         pcre_exec(). However, a pcre_extra block  also  contains  other  fields         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1320         that  can  be  set  by the caller before the block is passed; these are         that can be set by the caller before the block  is  passed;  these  are
1321         described below in the section on matching a pattern.         described below in the section on matching a pattern.
1322    
1323         If studying the pattern does not produce  any  additional  information,         If  studying  the  pattern  does not produce any additional information
1324         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1325         wants to pass any of the other fields to pcre_exec(), it  must  set  up         wants  to  pass  any of the other fields to pcre_exec(), it must set up
1326         its own pcre_extra block.         its own pcre_extra block.
1327    
1328         The  second  argument of pcre_study() contains option bits. At present,         The second argument of pcre_study() contains option bits.  At  present,
1329         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1330    
1331         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.
1332         If  studying  succeeds  (even  if no data is returned), the variable it         If studying succeeds (even if no data is  returned),  the  variable  it
1333         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
1334         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
1335         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
1336           after calling pcre_study(), to be sure that it has run successfully.
1337    
1338         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1339    
# Line 816  LOCALE SUPPORT Line 1352  LOCALE SUPPORT
1352    
1353         PCRE handles caseless matching, and determines whether  characters  are         PCRE handles caseless matching, and determines whether  characters  are
1354         letters,  digits, or whatever, by reference to a set of tables, indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1355         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
1356         characters  with  codes  less than 128. Higher-valued codes never match         characters  with  codes  less than 128. Higher-valued codes never match
1357         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
1358         with Unicode character property support.)         with  Unicode  character property support. The use of locales with Uni-
1359           code is discouraged. If you are handling characters with codes  greater
1360         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
1361         is built. This is used when the final  argument  of  pcre_compile()  is         not try to mix the two.
1362         NULL,  and  is  sufficient for many applications. An alternative set of  
1363         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
1364         locale  from the default. As more and more applications change to using         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1365         Unicode, the need for this locale support is expected to die away.         applications.  Normally, the internal tables recognize only ASCII char-
1366           acters. However, when PCRE is built, it is possible to cause the inter-
1367           nal tables to be rebuilt in the default "C" locale of the local system,
1368           which may cause them to be different.
1369    
1370           The  internal tables can always be overridden by tables supplied by the
1371           application that calls PCRE. These may be created in a different locale
1372           from  the  default.  As more and more applications change to using Uni-
1373           code, the need for this locale support is expected to die away.
1374    
1375         External tables are built by calling  the  pcre_maketables()  function,         External tables are built by calling  the  pcre_maketables()  function,
1376         which  has no arguments, in the relevant locale. The result can then be         which  has no arguments, in the relevant locale. The result can then be
# Line 839  LOCALE SUPPORT Line 1383  LOCALE SUPPORT
1383           tables = pcre_maketables();           tables = pcre_maketables();
1384           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1385    
1386         When  pcre_maketables()  runs,  the  tables are built in memory that is         The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1387         obtained via pcre_malloc. It is the caller's responsibility  to  ensure         if you are using Windows, the name for the French locale is "french".
1388         that  the memory containing the tables remains available for as long as  
1389           When pcre_maketables() runs, the tables are built  in  memory  that  is
1390           obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1391           that the memory containing the tables remains available for as long  as
1392         it is needed.         it is needed.
1393    
1394         The pointer that is passed to pcre_compile() is saved with the compiled         The pointer that is passed to pcre_compile() is saved with the compiled
1395         pattern,  and the same tables are used via this pointer by pcre_study()         pattern, and the same tables are used via this pointer by  pcre_study()
1396         and normally also by pcre_exec(). Thus, by default, for any single pat-         and normally also by pcre_exec(). Thus, by default, for any single pat-
1397         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1398         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1399    
1400         It is possible to pass a table pointer or NULL (indicating the  use  of         It  is  possible to pass a table pointer or NULL (indicating the use of
1401         the  internal  tables)  to  pcre_exec(). Although not intended for this         the internal tables) to pcre_exec(). Although  not  intended  for  this
1402         purpose, this facility could be used to match a pattern in a  different         purpose,  this facility could be used to match a pattern in a different
1403         locale from the one in which it was compiled. Passing table pointers at         locale from the one in which it was compiled. Passing table pointers at
1404         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1405    
# Line 862  INFORMATION ABOUT A PATTERN Line 1409  INFORMATION ABOUT A PATTERN
1409         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1410              int what, void *where);              int what, void *where);
1411    
1412         The pcre_fullinfo() function returns information about a compiled  pat-         The  pcre_fullinfo() function returns information about a compiled pat-
1413         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1414         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1415    
1416         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1417         pattern.  The second argument is the result of pcre_study(), or NULL if         pattern. The second argument is the result of pcre_study(), or NULL  if
1418         the pattern was not studied. The third argument specifies  which  piece         the  pattern  was not studied. The third argument specifies which piece
1419         of  information  is required, and the fourth argument is a pointer to a         of information is required, and the fourth argument is a pointer  to  a
1420         variable to receive the data. The yield of the  function  is  zero  for         variable  to  receive  the  data. The yield of the function is zero for
1421         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1422    
1423           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 878  INFORMATION ABOUT A PATTERN Line 1425  INFORMATION ABOUT A PATTERN
1425           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1426           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1427    
1428         The  "magic  number" is placed at the start of each compiled pattern as         The "magic number" is placed at the start of each compiled  pattern  as
1429         an simple check against passing an arbitrary memory pointer. Here is  a         an  simple check against passing an arbitrary memory pointer. Here is a
1430         typical  call  of pcre_fullinfo(), to obtain the length of the compiled         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1431         pattern:         pattern:
1432    
1433           int rc;           int rc;
1434           unsigned long int length;           size_t length;
1435           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1436             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1437             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1438             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1439             &length);         /* where to put the data */             &length);         /* where to put the data */
1440    
1441         The possible values for the third argument are defined in  pcre.h,  and         The  possible  values for the third argument are defined in pcre.h, and
1442         are as follows:         are as follows:
1443    
1444           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1445    
1446         Return  the  number  of  the highest back reference in the pattern. The         Return the number of the highest back reference  in  the  pattern.  The
1447         fourth argument should point to an int variable. Zero  is  returned  if         fourth  argument  should  point to an int variable. Zero is returned if
1448         there are no back references.         there are no back references.
1449    
1450           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1451    
1452         Return  the  number of capturing subpatterns in the pattern. The fourth         Return the number of capturing subpatterns in the pattern.  The  fourth
1453         argument should point to an int variable.         argument should point to an int variable.
1454    
1455           PCRE_INFO_DEFAULTTABLES           PCRE_INFO_DEFAULT_TABLES
1456    
1457         Return a pointer to the internal default character tables within  PCRE.         Return  a pointer to the internal default character tables within PCRE.
1458         The  fourth  argument should point to an unsigned char * variable. This         The fourth argument should point to an unsigned char *  variable.  This
1459         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1460         tion.  External  callers  can  cause PCRE to use its internal tables by         tion. External callers can cause PCRE to use  its  internal  tables  by
1461         passing a NULL table pointer.         passing a NULL table pointer.
1462    
1463           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1464    
1465         Return information about the first byte of any matched  string,  for  a         Return  information  about  the first byte of any matched string, for a
1466         non-anchored    pattern.    (This    option    used    to   be   called         non-anchored pattern. The fourth argument should point to an int  vari-
1467         PCRE_INFO_FIRSTCHAR; the old name is  still  recognized  for  backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1468         compatibility.)         is still recognized for backwards compatibility.)
1469    
1470         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
1471         (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  
1472    
1473         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1474         branch starts with "^", or         branch starts with "^", or
# Line 942  INFORMATION ABOUT A PATTERN Line 1488  INFORMATION ABOUT A PATTERN
1488         returned. The fourth argument should point to an unsigned char *  vari-         returned. The fourth argument should point to an unsigned char *  vari-
1489         able.         able.
1490    
1491             PCRE_INFO_JCHANGED
1492    
1493           Return  1  if the (?J) option setting is used in the pattern, otherwise
1494           0. The fourth argument should point to an int variable. The (?J) inter-
1495           nal option setting changes the local PCRE_DUPNAMES option.
1496    
1497           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1498    
1499         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
# Line 958  INFORMATION ABOUT A PATTERN Line 1510  INFORMATION ABOUT A PATTERN
1510    
1511         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1512         ses. The names are just an additional way of identifying the  parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1513         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1514         pcre_get_named_substring() is provided  for  extracting  an  individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1515         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
1516         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
1517         the  correct  pointers in the output vector (described with pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1518         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
1519         which is described by these three values.         described by these three values.
1520    
1521         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
1522         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
# Line 974  INFORMATION ABOUT A PATTERN Line 1526  INFORMATION ABOUT A PATTERN
1526         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-
1527         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-
1528         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1529         For  example,  consider  the following pattern (assume PCRE_EXTENDED is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1530         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1531           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1532           ignored):
1533    
1534           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1535           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1536    
1537         There are four named subpatterns, so the table has  four  entries,  and         There are four named subpatterns, so the table has  four  entries,  and
1538         each  entry  in the table is eight bytes long. The table is as follows,         each  entry  in the table is eight bytes long. The table is as follows,
# Line 991  INFORMATION ABOUT A PATTERN Line 1545  INFORMATION ABOUT A PATTERN
1545           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1546    
1547         When  writing  code  to  extract  data from named subpatterns using the         When  writing  code  to  extract  data from named subpatterns using the
1548         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
1549         be different for each compiled pattern.         to be different for each compiled pattern.
1550    
1551             PCRE_INFO_OKPARTIAL
1552    
1553           Return  1 if the pattern can be used for partial matching, otherwise 0.
1554           The fourth argument should point to an int  variable.  The  pcrepartial
1555           documentation  lists  the restrictions that apply to patterns when par-
1556           tial matching is used.
1557    
1558           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1559    
1560         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
1561         fourth argument should point to an unsigned long  int  variable.  These         fourth  argument  should  point to an unsigned long int variable. These
1562         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1563         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1564           other words, they are the options that will be in force  when  matching
1565           starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
1566           the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1567           and PCRE_EXTENDED.
1568    
1569         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
1570         alternatives begin with one of the following:         alternatives begin with one of the following:
1571    
1572           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1015  INFORMATION ABOUT A PATTERN Line 1580  INFORMATION ABOUT A PATTERN
1580    
1581           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1582    
1583         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
1584         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
1585         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
1586         size_t variable.         size_t variable.
# Line 1023  INFORMATION ABOUT A PATTERN Line 1588  INFORMATION ABOUT A PATTERN
1588           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1589    
1590         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
1591         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
1592         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
1593         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
1594         variable.         variable.
1595    
1596    
# Line 1033  OBSOLETE INFO FUNCTION Line 1598  OBSOLETE INFO FUNCTION
1598    
1599         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1600    
1601         The  pcre_info()  function is now obsolete because its interface is too         The pcre_info() function is now obsolete because its interface  is  too
1602         restrictive to return all the available data about a compiled  pattern.         restrictive  to return all the available data about a compiled pattern.
1603         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1604         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-
1605         lowing negative numbers:         lowing negative numbers:
1606    
1607           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1608           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1609    
1610         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
1611         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
1612         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1613    
1614         If  the  pattern  is  not anchored and the firstcharptr argument is not         If the pattern is not anchored and the  firstcharptr  argument  is  not
1615         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
1616         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1617    
1618    
1619  MATCHING A PATTERN  REFERENCE COUNTS
1620    
1621           int pcre_refcount(pcre *code, int adjust);
1622    
1623           The pcre_refcount() function is used to maintain a reference  count  in
1624           the data block that contains a compiled pattern. It is provided for the
1625           benefit of applications that  operate  in  an  object-oriented  manner,
1626           where different parts of the application may be using the same compiled
1627           pattern, but you want to free the block when they are all done.
1628    
1629           When a pattern is compiled, the reference count field is initialized to
1630           zero.   It is changed only by calling this function, whose action is to
1631           add the adjust value (which may be positive or  negative)  to  it.  The
1632           yield of the function is the new value. However, the value of the count
1633           is constrained to lie between 0 and 65535, inclusive. If the new  value
1634           is outside these limits, it is forced to the appropriate limit value.
1635    
1636           Except  when it is zero, the reference count is not correctly preserved
1637           if a pattern is compiled on one host and then  transferred  to  a  host
1638           whose byte-order is different. (This seems a highly unlikely scenario.)
1639    
1640    
1641    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1642    
1643         int pcre_exec(const pcre *code, const pcre_extra *extra,         int pcre_exec(const pcre *code, const pcre_extra *extra,
1644              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1645              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1646    
1647         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
1648         compiled pattern, which is passed in the code argument. If the  pattern         compiled  pattern, which is passed in the code argument. If the pattern
1649         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
1650         argument.         argument.  This  function is the main matching facility of the library,
1651           and it operates in a Perl-like manner. For specialist use there is also
1652           an  alternative matching function, which is described below in the sec-
1653           tion about the pcre_dfa_exec() function.
1654    
1655         In most applications, the pattern will have been compiled (and  option-         In most applications, the pattern will have been compiled (and  option-
1656         ally  studied)  in the same process that calls pcre_exec(). However, it         ally  studied)  in the same process that calls pcre_exec(). However, it
# Line 1080  MATCHING A PATTERN Line 1670  MATCHING A PATTERN
1670             0,              /* start at offset 0 in the subject */             0,              /* start at offset 0 in the subject */
1671             0,              /* default options */             0,              /* default options */
1672             ovector,        /* vector of integers for substring information */             ovector,        /* vector of integers for substring information */
1673             30);            /* number of elements in the vector  (NOT  size  in             30);            /* number of elements (NOT size in bytes) */
        bytes) */  
1674    
1675     Extra data for pcre_exec()     Extra data for pcre_exec()
1676    
1677         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
1678         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
1679         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-
1680         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
1681         lows:         fields (not necessarily in this order):
1682    
1683           unsigned long int flags;           unsigned long int flags;
1684           void *study_data;           void *study_data;
1685           unsigned long int match_limit;           unsigned long int match_limit;
1686             unsigned long int match_limit_recursion;
1687           void *callout_data;           void *callout_data;
1688           const unsigned char *tables;           const unsigned char *tables;
1689    
1690         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
1691         are set. The flag bits are:         are set. The flag bits are:
1692    
1693           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1694           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1695             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1696           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1697           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1698    
1699         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
1700         the  pcre_extra  block  that is returned by pcre_study(), together with         the pcre_extra block that is returned by  pcre_study(),  together  with
1701         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
1702         add  to  the  block by setting the other fields and their corresponding         add to the block by setting the other fields  and  their  corresponding
1703         flag bits.         flag bits.
1704    
1705         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
1706         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
1707         match, but which have a very large number  of  possibilities  in  their         match,  but  which  have  a very large number of possibilities in their
1708         search  trees.  The  classic  example  is  the  use of nested unlimited         search trees. The classic  example  is  the  use  of  nested  unlimited
1709         repeats.         repeats.
1710    
1711         Internally, PCRE uses a function called match() which it calls  repeat-         Internally,  PCRE uses a function called match() which it calls repeat-
1712         edly  (sometimes  recursively).  The  limit is imposed on the number of         edly (sometimes recursively). The limit set by match_limit  is  imposed
1713         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
1714         limiting  the amount of recursion and backtracking that can take place.         has the effect of limiting the amount of  backtracking  that  can  take
1715         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
1716         position in the subject string.         for each position in the subject string.
1717    
1718         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
1719         default default is 10 million, which handles all but the  most  extreme         default  default  is 10 million, which handles all but the most extreme
1720         cases.  You  can  reduce  the  default  by  suppling pcre_exec() with a         cases. You can override the default  by  suppling  pcre_exec()  with  a
1721         pcre_extra block in which match_limit is set to a  smaller  value,  and         pcre_extra     block    in    which    match_limit    is    set,    and
1722         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
1723         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1724    
1725         The pcre_callout field is used in conjunction with the  "callout"  fea-         The  match_limit_recursion field is similar to match_limit, but instead
1726           of limiting the total number of times that match() is called, it limits
1727           the  depth  of  recursion. The recursion depth is a smaller number than
1728           the total number of calls, because not all calls to match() are  recur-
1729           sive.  This limit is of use only if it is set smaller than match_limit.
1730    
1731           Limiting the recursion depth limits the amount of  stack  that  can  be
1732           used, or, when PCRE has been compiled to use memory on the heap instead
1733           of the stack, the amount of heap memory that can be used.
1734    
1735           The default value for match_limit_recursion can be  set  when  PCRE  is
1736           built;  the  default  default  is  the  same  value  as the default for
1737           match_limit. You can override the default by suppling pcre_exec()  with
1738           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1739           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1740           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1741    
1742           The  pcre_callout  field is used in conjunction with the "callout" fea-
1743         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1744    
1745         The  tables  field  is  used  to  pass  a  character  tables pointer to         The tables field  is  used  to  pass  a  character  tables  pointer  to
1746         pcre_exec(); this overrides the value that is stored with the  compiled         pcre_exec();  this overrides the value that is stored with the compiled
1747         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
1748         custom tables were supplied to pcre_compile() via  its  tableptr  argu-         custom  tables  were  supplied to pcre_compile() via its tableptr argu-
1749         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
1750         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-
1751         using  patterns  that  have been saved after compiling with an external         using patterns that have been saved after compiling  with  an  external
1752         set of tables, because the external tables  might  be  at  a  different         set  of  tables,  because  the  external tables might be at a different
1753         address  when  pcre_exec() is called. See the pcreprecompile documenta-         address when pcre_exec() is called. See the  pcreprecompile  documenta-
1754         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1755    
1756     Option bits for pcre_exec()     Option bits for pcre_exec()
1757    
1758         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.
1759         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,
1760         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1761           PCRE_PARTIAL.
1762    
1763           PCRE_ANCHORED           PCRE_ANCHORED
1764    
# Line 1158  MATCHING A PATTERN Line 1767  MATCHING A PATTERN
1767         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
1768         unachored at matching time.         unachored at matching time.
1769    
1770             PCRE_NEWLINE_CR
1771             PCRE_NEWLINE_LF
1772             PCRE_NEWLINE_CRLF
1773             PCRE_NEWLINE_ANYCRLF
1774             PCRE_NEWLINE_ANY
1775    
1776           These  options  override  the  newline  definition  that  was chosen or
1777           defaulted when the pattern was compiled. For details, see the  descrip-
1778           tion  of  pcre_compile()  above.  During  matching,  the newline choice
1779           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1780           ters.  It may also alter the way the match position is advanced after a
1781           match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,
1782           PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY is set, and a match attempt
1783           fails when the current position is at a CRLF sequence, the match  posi-
1784           tion  is  advanced by two characters instead of one, in other words, to
1785           after the CRLF.
1786    
1787           PCRE_NOTBOL           PCRE_NOTBOL
1788    
1789         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1790         the beginning of a line, so the  circumflex  metacharacter  should  not         the  beginning  of  a  line, so the circumflex metacharacter should not
1791         match  before it. Setting this without PCRE_MULTILINE (at compile time)         match before it. Setting this without PCRE_MULTILINE (at compile  time)
1792         causes  circumflex  never  to  match.  This  option  affects  only  the         causes  circumflex  never to match. This option affects only the behav-
1793         behaviour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1794    
1795           PCRE_NOTEOL           PCRE_NOTEOL
1796    
1797         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
1798         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
1799         in  multiline mode) a newline immediately before it. Setting this with-         in multiline mode) a newline immediately before it. Setting this  with-
1800         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1801         option  affects only the behaviour of the dollar metacharacter. It does         option affects only the behaviour of the dollar metacharacter. It  does
1802         not affect \Z or \z.         not affect \Z or \z.
1803    
1804           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1805    
1806         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
1807         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
1808         the alternatives match the empty string, the entire  match  fails.  For         the  alternatives  match  the empty string, the entire match fails. For
1809         example, if the pattern         example, if the pattern
1810    
1811           a?b?           a?b?
1812    
1813         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
1814         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
1815         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-
1816         rences of "a" or "b".         rences of "a" or "b".
1817    
1818         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-
1819         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()
1820         function, and when using the /g modifier. It  is  possible  to  emulate         function,  and  when  using  the /g modifier. It is possible to emulate
1821         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
1822         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
1823         if  that  fails by advancing the starting offset (see below) and trying         if that fails by advancing the starting offset (see below)  and  trying
1824         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
1825         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
1826    
1827           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1828    
1829         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
1830         UTF-8 string is automatically checked when pcre_exec() is  subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
1831         called.   The  value  of  startoffset is also checked to ensure that it         called.  The value of startoffset is also checked  to  ensure  that  it
1832         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
1833         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
1834         startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is
1835         returned.         returned.
1836    
1837         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
1838         these   checks   for   performance   reasons,   you   can    set    the         these    checks    for   performance   reasons,   you   can   set   the
1839         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
1840         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
1841         making  repeated  calls  to  find  all  the matches in a single subject         making repeated calls to find all  the  matches  in  a  single  subject
1842         string. However, you should be  sure  that  the  value  of  startoffset         string.  However,  you  should  be  sure  that the value of startoffset
1843         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
1844         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
1845         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-
1846         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1847    
1848           PCRE_PARTIAL           PCRE_PARTIAL
1849    
1850         This option turns on the  partial  matching  feature.  If  the  subject         This  option  turns  on  the  partial  matching feature. If the subject
1851         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-
1852         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
1853         partially  matches  the  pattern and the failure to match occurred only         partially matches the pattern and the failure to  match  occurred  only
1854         because there were not enough subject characters), pcre_exec()  returns         because  there were not enough subject characters), pcre_exec() returns
1855         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1856         used, there are restrictions on what may appear in the  pattern.  These         used,  there  are restrictions on what may appear in the pattern. These
1857         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1858    
1859     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1860    
1861         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
1862         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
1863         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.
1864         Unlike the pattern string, the subject may contain binary  zero  bytes.         Unlike  the  pattern string, the subject may contain binary zero bytes.
1865         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
1866         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.
1867    
1868         A non-zero starting offset is useful when searching for  another  match         A  non-zero  starting offset is useful when searching for another match
1869         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-
1870         cess.  Setting startoffset differs from just passing over  a  shortened         cess.   Setting  startoffset differs from just passing over a shortened
1871         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
1872         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1873    
1874           \Biss\B           \Biss\B
1875    
1876         which finds occurrences of "iss" in the middle of  words.  (\B  matches         which  finds  occurrences  of "iss" in the middle of words. (\B matches
1877         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.)
1878         When applied to the string "Mississipi" the first call  to  pcre_exec()         When  applied  to the string "Mississipi" the first call to pcre_exec()
1879         finds  the  first  occurrence. If pcre_exec() is called again with just         finds the first occurrence. If pcre_exec() is called  again  with  just
1880         the remainder of the subject,  namely  "issipi",  it  does  not  match,         the  remainder  of  the  subject,  namely  "issipi", it does not match,
1881         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
1882         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
1883         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-
1884         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
1885         discover that it is preceded by a letter.         discover that it is preceded by a letter.
1886    
1887         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,
1888         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
1889         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
1890         subject.         subject.
1891    
1892     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
1893    
1894         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
1895         addition,  further  substrings  from  the  subject may be picked out by         addition, further substrings from the subject  may  be  picked  out  by
1896         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,
1897         this  is  called "capturing" in what follows, and the phrase "capturing         this is called "capturing" in what follows, and the  phrase  "capturing
1898         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-
1899         string.  PCRE  supports several other kinds of parenthesized subpattern         string. PCRE supports several other kinds of  parenthesized  subpattern
1900         that do not cause substrings to be captured.         that do not cause substrings to be captured.
1901    
1902         Captured substrings are returned to the caller via a vector of  integer         Captured  substrings are returned to the caller via a vector of integer
1903         offsets  whose  address is passed in ovector. The number of elements in         offsets whose address is passed in ovector. The number of  elements  in
1904         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.
1905         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
1906    
1907         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-
1908         strings, each substring using a pair of integers. The  remaining  third         strings,  each  substring using a pair of integers. The remaining third
1909         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-
1910         turing subpatterns, and is not available for passing back  information.         turing  subpatterns, and is not available for passing back information.
1911         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
1912         it is not, it is rounded down.         it is not, it is rounded down.
1913    
1914         When a match is successful, information about  captured  substrings  is         When  a  match  is successful, information about captured substrings is
1915         returned  in  pairs  of integers, starting at the beginning of ovector,         returned in pairs of integers, starting at the  beginning  of  ovector,
1916         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
1917         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-
1918         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
1919         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-
1920         tor[1], identify the portion of  the  subject  string  matched  by  the         tor[1],  identify  the  portion  of  the  subject string matched by the
1921         entire  pattern.  The next pair is used for the first capturing subpat-         entire pattern. The next pair is used for the first  capturing  subpat-
1922         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
1923         pairs  that  have  been set. If there are no capturing subpatterns, the         highest numbered pair that has been set. For example, if two substrings
1924         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
1925         first pair of offsets has been set.         subpatterns, the return value from a successful match is 1,  indicating
1926           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.  
1927    
1928         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1929         of the string that it matched that is returned.         of the string that it matched that is returned.
# Line 1320  MATCHING A PATTERN Line 1937  MATCHING A PATTERN
1937         substrings, PCRE has to get additional memory for use during  matching.         substrings, PCRE has to get additional memory for use during  matching.
1938         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1939    
1940         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
1941         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
1942         that  will  allow for n captured substrings, in addition to the offsets         ovector  that  will allow for n captured substrings, in addition to the
1943         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.
1944    
1945           It is possible for capturing subpattern number n+1 to match  some  part
1946           of the subject when subpattern n has not been used at all. For example,
1947           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1948           return from the function is 4, and subpatterns 1 and 3 are matched, but
1949           2 is not. When this happens, both values in  the  offset  pairs  corre-
1950           sponding to unused subpatterns are set to -1.
1951    
1952           Offset  values  that correspond to unused subpatterns at the end of the
1953           expression are also set to -1. For example,  if  the  string  "abc"  is
1954           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1955           matched. The return from the function is 2, because  the  highest  used
1956           capturing subpattern number is 1. However, you can refer to the offsets
1957           for the second and third capturing subpatterns if  you  wish  (assuming
1958           the vector is large enough, of course).
1959    
1960           Some  convenience  functions  are  provided for extracting the captured
1961           substrings as separate strings. These are described below.
1962    
1963     Return values from pcre_exec()     Error return values from pcre_exec()
1964    
1965         If pcre_exec() fails, it returns a negative number. The  following  are         If pcre_exec() fails, it returns a negative number. The  following  are
1966         defined in the header file:         defined in the header file:
# Line 1351  MATCHING A PATTERN Line 1986  MATCHING A PATTERN
1986         an  environment  with the other endianness. This is the error that PCRE         an  environment  with the other endianness. This is the error that PCRE
1987         gives when the magic number is not present.         gives when the magic number is not present.
1988    
1989           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1990    
1991         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1992         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 1373  MATCHING A PATTERN Line 2008  MATCHING A PATTERN
2008    
2009           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2010    
2011         The recursion and backtracking limit, as specified by  the  match_limit         The backtracking limit, as specified by  the  match_limit  field  in  a
2012         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         pcre_extra  structure  (or  defaulted) was reached. See the description
2013         description above.         above.
2014    
2015           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2016    
# Line 1394  MATCHING A PATTERN Line 2029  MATCHING A PATTERN
2029         value of startoffset did not point to the beginning of a UTF-8  charac-         value of startoffset did not point to the beginning of a UTF-8  charac-
2030         ter.         ter.
2031    
2032           PCRE_ERROR_PARTIAL (-12)           PCRE_ERROR_PARTIAL        (-12)
2033    
2034         The  subject  string did not match, but it did match partially. See the         The  subject  string did not match, but it did match partially. See the
2035         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2036    
2037           PCRE_ERROR_BAD_PARTIAL (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2038    
2039         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
2040         items  that are not supported for partial matching. See the pcrepartial         items  that are not supported for partial matching. See the pcrepartial
2041         documentation for details of partial matching.         documentation for details of partial matching.
2042    
2043           PCRE_ERROR_INTERNAL (-14)           PCRE_ERROR_INTERNAL       (-14)
2044    
2045         An unexpected internal error has occurred. This error could  be  caused         An unexpected internal error has occurred. This error could  be  caused
2046         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2047    
2048           PCRE_ERROR_BADCOUNT (-15)           PCRE_ERROR_BADCOUNT       (-15)
2049    
2050         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.
2051    
2052             PCRE_ERROR_RECURSIONLIMIT (-21)
2053    
2054           The internal recursion limit, as specified by the match_limit_recursion
2055           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2056           description above.
2057    
2058             PCRE_ERROR_BADNEWLINE     (-23)
2059    
2060           An invalid combination of PCRE_NEWLINE_xxx options was given.
2061    
2062           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2063    
2064    
2065  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2066    
# Line 1434  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2081  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2081         string_list()  are  provided for extracting captured substrings as new,         string_list()  are  provided for extracting captured substrings as new,
2082         separate, zero-terminated strings. These functions identify  substrings         separate, zero-terminated strings. These functions identify  substrings
2083         by  number.  The  next section describes functions for extracting named         by  number.  The  next section describes functions for extracting named
2084         substrings. A substring  that  contains  a  binary  zero  is  correctly         substrings.
2085         extracted  and  has  a further zero added on the end, but the result is  
2086         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2087           a  further zero added on the end, but the result is not, of course, a C
2088           string.  However, you can process such a string  by  referring  to  the
2089           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2090           string().  Unfortunately, the interface to pcre_get_substring_list() is
2091           not  adequate for handling strings containing binary zeros, because the
2092           end of the final string is not independently indicated.
2093    
2094         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-
2095         tions:  subject  is  the subject string that has just been successfully         tions:  subject  is  the subject string that has just been successfully
# Line 1456  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2109  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2109         buffersize,  while  for  pcre_get_substring()  a new block of memory is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2110         obtained via pcre_malloc, and its address is  returned  via  stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2111         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
2112         the terminating zero, or one of         the terminating zero, or one of these error codes:
2113    
2114           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2115    
# Line 1472  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2125  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2125         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
2126         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
2127         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
2128         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
2129           error code
2130    
2131           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2132    
2133         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2134    
2135         When any of these functions encounter a substring that is unset,  which         When  any of these functions encounter a substring that is unset, which
2136         can  happen  when  capturing subpattern number n+1 matches some part of         can happen when capturing subpattern number n+1 matches  some  part  of
2137         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
2138         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2139         string by inspecting the appropriate offset in ovector, which is  nega-         string  by inspecting the appropriate offset in ovector, which is nega-
2140         tive for unset substrings.         tive for unset substrings.
2141    
2142         The  two convenience functions pcre_free_substring() and pcre_free_sub-         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2143         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
2144         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2145         tively. They do nothing more than  call  the  function  pointed  to  by         tively.  They  do  nothing  more  than  call the function pointed to by
2146         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.
2147         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-
2148         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2149         pcre_free directly; it is  for  these  cases  that  the  functions  are         pcre_free  directly;  it is for these cases that the functions are pro-
2150         provided.         vided.
2151    
2152    
2153  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
# Line 1511  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2165  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2165              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2166              const char **stringptr);              const char **stringptr);
2167    
2168         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-
2169         ber.  For example, for this pattern         ber.  For example, for this pattern
2170    
2171           (a+)b(?<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2172    
2173         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
2174         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
2175         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-
2176         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
2177         there is no subpattern of that name.         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2178           subpattern of that name.
2179    
2180         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
2181         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
# Line 1539  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2194  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2194    
2195         These  functions call pcre_get_stringnumber(), and if it succeeds, they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2196         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2197         ate.         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2198           behaviour may not be what you want (see the next section).
2199    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
2200    
2201  PCRE(3)                                                                PCRE(3)  DUPLICATE SUBPATTERN NAMES
2202    
2203           int pcre_get_stringtable_entries(const pcre *code,
2204                const char *name, char **first, char **last);
2205    
2206           When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2207           subpatterns  are  not  required  to  be unique. Normally, patterns with
2208           duplicate names are such that in any one match, only one of  the  named
2209           subpatterns  participates. An example is shown in the pcrepattern docu-
2210           mentation.
2211    
2212           When   duplicates   are   present,   pcre_copy_named_substring()    and
2213           pcre_get_named_substring()  return the first substring corresponding to
2214           the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2215           (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2216           function returns one of the numbers that are associated with the  name,
2217           but it is not defined which it is.
2218    
2219           If  you want to get full details of all captured substrings for a given
2220           name, you must use  the  pcre_get_stringtable_entries()  function.  The
2221           first argument is the compiled pattern, and the second is the name. The
2222           third and fourth are pointers to variables which  are  updated  by  the
2223           function. After it has run, they point to the first and last entries in
2224           the name-to-number table  for  the  given  name.  The  function  itself
2225           returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2226           there are none. The format of the table is described above in the  sec-
2227           tion  entitled  Information  about  a  pattern.  Given all the relevant
2228           entries for the name, you can extract each of their numbers, and  hence
2229           the captured data, if any.
2230    
2231    
2232    FINDING ALL POSSIBLE MATCHES
2233    
2234           The  traditional  matching  function  uses a similar algorithm to Perl,
2235           which stops when it finds the first match, starting at a given point in
2236           the  subject.  If you want to find all possible matches, or the longest
2237           possible match, consider using the alternative matching  function  (see
2238           below)  instead.  If you cannot use the alternative function, but still
2239           need to find all possible matches, you can kludge it up by  making  use
2240           of the callout facility, which is described in the pcrecallout documen-
2241           tation.
2242    
2243           What you have to do is to insert a callout right at the end of the pat-
2244           tern.   When your callout function is called, extract and save the cur-
2245           rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2246           backtrack  and  try other alternatives. Ultimately, when it runs out of
2247           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2248    
2249    
2250    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2251    
2252           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2253                const char *subject, int length, int startoffset,
2254                int options, int *ovector, int ovecsize,
2255                int *workspace, int wscount);
2256    
2257           The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2258           against  a  compiled pattern, using a matching algorithm that scans the
2259           subject string just once, and does not backtrack.  This  has  different
2260           characteristics  to  the  normal  algorithm, and is not compatible with
2261           Perl. Some of the features of PCRE patterns are not  supported.  Never-
2262           theless,  there are times when this kind of matching can be useful. For
2263           a discussion of the two matching algorithms, see the pcrematching docu-
2264           mentation.
2265    
2266           The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2267           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2268           ent  way,  and  this is described below. The other common arguments are
2269           used in the same way as for pcre_exec(), so their  description  is  not
2270           repeated here.
2271    
2272           The  two  additional  arguments provide workspace for the function. The
2273           workspace vector should contain at least 20 elements. It  is  used  for
2274           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2275           workspace will be needed for patterns and subjects where  there  are  a
2276           lot of potential matches.
2277    
2278           Here is an example of a simple call to pcre_dfa_exec():
2279    
2280             int rc;
2281             int ovector[10];
2282             int wspace[20];
2283             rc = pcre_dfa_exec(
2284               re,             /* result of pcre_compile() */
2285               NULL,           /* we didn't study the pattern */
2286               "some string",  /* the subject string */
2287               11,             /* the length of the subject string */
2288               0,              /* start at offset 0 in the subject */
2289               0,              /* default options */
2290               ovector,        /* vector of integers for substring information */
2291               10,             /* number of elements (NOT size in bytes) */
2292               wspace,         /* working space vector */
2293               20);            /* number of elements (NOT size in bytes) */
2294    
2295       Option bits for pcre_dfa_exec()
2296    
2297           The  unused  bits  of  the options argument for pcre_dfa_exec() must be
2298           zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2299           LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
2300           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2301           three of these are the same as for pcre_exec(), so their description is
2302           not repeated here.
2303    
2304             PCRE_PARTIAL
2305    
2306           This has the same general effect as it does for  pcre_exec(),  but  the
2307           details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for
2308           pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into
2309           PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have
2310           been no complete matches, but there is still at least one matching pos-
2311           sibility.  The portion of the string that provided the partial match is
2312           set as the first matching string.
2313    
2314             PCRE_DFA_SHORTEST
2315    
2316           Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2317           stop as soon as it has found one match. Because of the way the alterna-
2318           tive algorithm works, this is necessarily the shortest  possible  match
2319           at the first possible matching point in the subject string.
2320    
2321             PCRE_DFA_RESTART
2322    
2323           When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and
2324           returns a partial match, it is possible to call it  again,  with  addi-
2325           tional  subject  characters,  and have it continue with the same match.
2326           The PCRE_DFA_RESTART option requests this action; when it is  set,  the
2327           workspace  and wscount options must reference the same vector as before
2328           because data about the match so far is left in  them  after  a  partial
2329           match.  There  is  more  discussion of this facility in the pcrepartial
2330           documentation.
2331    
2332       Successful returns from pcre_dfa_exec()
2333    
2334           When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-
2335           string in the subject. Note, however, that all the matches from one run
2336           of the function start at the same point in  the  subject.  The  shorter
2337           matches  are all initial substrings of the longer matches. For example,
2338           if the pattern
2339    
2340             <.*>
2341    
2342           is matched against the string
2343    
2344             This is <something> <something else> <something further> no more
2345    
2346           the three matched strings are
2347    
2348             <something>
2349             <something> <something else>
2350             <something> <something else> <something further>
2351    
2352           On success, the yield of the function is a number  greater  than  zero,
2353           which  is  the  number of matched substrings. The substrings themselves
2354           are returned in ovector. Each string uses two elements;  the  first  is
2355           the  offset  to  the start, and the second is the offset to the end. In
2356           fact, all the strings have the same start  offset.  (Space  could  have
2357           been  saved by giving this only once, but it was decided to retain some
2358           compatibility with the way pcre_exec() returns data,  even  though  the
2359           meaning of the strings is different.)
2360    
2361           The strings are returned in reverse order of length; that is, the long-
2362           est matching string is given first. If there were too many  matches  to
2363           fit  into ovector, the yield of the function is zero, and the vector is
2364           filled with the longest matches.
2365    
2366       Error returns from pcre_dfa_exec()
2367    
2368           The pcre_dfa_exec() function returns a negative number when  it  fails.
2369           Many  of  the  errors  are  the  same as for pcre_exec(), and these are
2370           described above.  There are in addition the following errors  that  are
2371           specific to pcre_dfa_exec():
2372    
2373             PCRE_ERROR_DFA_UITEM      (-16)
2374    
2375           This  return is given if pcre_dfa_exec() encounters an item in the pat-
2376           tern that it does not support, for instance, the use of \C  or  a  back
2377           reference.
2378    
2379             PCRE_ERROR_DFA_UCOND      (-17)
2380    
2381           This  return  is  given  if pcre_dfa_exec() encounters a condition item
2382           that uses a back reference for the condition, or a test  for  recursion
2383           in a specific group. These are not supported.
2384    
2385             PCRE_ERROR_DFA_UMLIMIT    (-18)
2386    
2387           This  return  is given if pcre_dfa_exec() is called with an extra block
2388           that contains a setting of the match_limit field. This is not supported
2389           (it is meaningless).
2390    
2391             PCRE_ERROR_DFA_WSSIZE     (-19)
2392    
2393           This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the
2394           workspace vector.
2395    
2396             PCRE_ERROR_DFA_RECURSE    (-20)
2397    
2398           When a recursive subpattern is processed, the matching  function  calls
2399           itself  recursively,  using  private vectors for ovector and workspace.
2400           This error is given if the output vector  is  not  large  enough.  This
2401           should be extremely rare, as a vector of size 1000 is used.
2402    
2403    
2404    SEE ALSO
2405    
2406           pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2407           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
2408    
2409    
2410    AUTHOR
2411    
2412           Philip Hazel
2413           University Computing Service
2414           Cambridge CB2 3QH, England.
2415    
2416    
2417    REVISION
2418    
2419           Last updated: 30 July 2007
2420           Copyright (c) 1997-2007 University of Cambridge.
2421    ------------------------------------------------------------------------------
2422    
2423    
2424    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2425    
2426    
2427  NAME  NAME
2428         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2429    
2430    
2431  PCRE CALLOUTS  PCRE CALLOUTS
2432    
2433         int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
# Line 1568  PCRE CALLOUTS Line 2444  PCRE CALLOUTS
2444         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2445         points:         points:
2446    
2447           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2448    
2449         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2450         called, PCRE automatically  inserts  callouts,  all  with  number  255,         called, PCRE automatically  inserts  callouts,  all  with  number  255,
# Line 1606  MISSING CALLOUTS Line 2482  MISSING CALLOUTS
2482  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2483    
2484         During matching, when PCRE reaches a callout point, the external  func-         During matching, when PCRE reaches a callout point, the external  func-
2485         tion  defined  by pcre_callout is called (if it is set). The only argu-         tion  defined by pcre_callout is called (if it is set). This applies to
2486         ment is a pointer to a pcre_callout block. This structure contains  the         both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2487         following fields:         only  argument  to  the callout function is a pointer to a pcre_callout
2488           block. This structure contains the following fields:
2489    
2490           int          version;           int          version;
2491           int          callout_number;           int          callout_number;
# Line 1623  THE CALLOUT INTERFACE Line 2500  THE CALLOUT INTERFACE
2500           int          pattern_position;           int          pattern_position;
2501           int          next_item_length;           int          next_item_length;
2502    
2503         The  version  field  is an integer containing the version number of the         The version field is an integer containing the version  number  of  the
2504         block format. The initial version was 0; the current version is 1.  The         block  format. The initial version was 0; the current version is 1. The
2505         version  number  will  change  again in future if additional fields are         version number will change again in future  if  additional  fields  are
2506         added, but the intention is never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2507    
2508         The  callout_number  field  contains the number of the callout, as com-         The callout_number field contains the number of the  callout,  as  com-
2509         piled into the pattern (that is, the number after ?C for  manual  call-         piled  into  the pattern (that is, the number after ?C for manual call-
2510         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2511    
2512         The  offset_vector field is a pointer to the vector of offsets that was         The offset_vector field is a pointer to the vector of offsets that  was
2513         passed by the caller to pcre_exec(). The contents can be  inspected  in         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2514         order  to extract substrings that have been matched so far, in the same         pcre_exec() is used, the contents can be inspected in order to  extract
2515         way as for extracting substrings after a match has completed.         substrings  that  have  been  matched  so  far,  in the same way as for
2516           extracting substrings after a match has completed. For  pcre_dfa_exec()
2517           this field is not useful.
2518    
2519         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2520         were passed to pcre_exec().         were passed to pcre_exec().
2521    
2522         The  start_match  field contains the offset within the subject at which         The start_match field normally contains the offset within  the  subject
2523         the current match attempt started. If the pattern is not anchored,  the         at  which  the  current  match  attempt started. However, if the escape
2524         callout function may be called several times from the same point in the         sequence \K has been encountered, this value is changed to reflect  the
2525         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2526           function may be called several times from the same point in the pattern
2527           for different starting points in the subject.
2528    
2529         The current_position field contains the offset within  the  subject  of         The  current_position  field  contains the offset within the subject of
2530         the current match pointer.         the current match pointer.
2531    
2532         The  capture_top field contains one more than the number of the highest         When the pcre_exec() function is used, the capture_top  field  contains
2533         numbered captured substring so far. If no  substrings  have  been  cap-         one  more than the number of the highest numbered captured substring so
2534         tured, the value of capture_top is one.         far. If no substrings have been captured, the value of  capture_top  is
2535           one.  This  is always the case when pcre_dfa_exec() is used, because it
2536         The  capture_last  field  contains the number of the most recently cap-         does not support captured substrings.
2537         tured substring. If no substrings have been captured, its value is  -1.  
2538           The capture_last field contains the number of the  most  recently  cap-
2539         The  callout_data  field contains a value that is passed to pcre_exec()         tured  substring. If no substrings have been captured, its value is -1.
2540         by the caller specifically so that it can be passed back  in  callouts.         This is always the case when pcre_dfa_exec() is used.
2541         It  is  passed  in the pcre_callout field of the pcre_extra data struc-  
2542         ture. If no such data was  passed,  the  value  of  callout_data  in  a         The callout_data field contains a value that is passed  to  pcre_exec()
2543         pcre_callout  block  is  NULL. There is a description of the pcre_extra         or  pcre_dfa_exec() specifically so that it can be passed back in call-
2544           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2545           structure.  If  no such data was passed, the value of callout_data in a
2546           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2547         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2548    
2549         The pattern_position field is present from version 1 of the  pcre_call-         The  pattern_position field is present from version 1 of the pcre_call-
2550         out structure. It contains the offset to the next item to be matched in         out structure. It contains the offset to the next item to be matched in
2551         the pattern string.         the pattern string.
2552    
2553         The next_item_length field is present from version 1 of the  pcre_call-         The  next_item_length field is present from version 1 of the pcre_call-
2554         out structure. It contains the length of the next item to be matched in         out structure. It contains the length of the next item to be matched in
2555         the pattern string. When the callout immediately precedes  an  alterna-         the  pattern  string. When the callout immediately precedes an alterna-
2556         tion  bar, a closing parenthesis, or the end of the pattern, the length         tion bar, a closing parenthesis, or the end of the pattern, the  length
2557         is zero. When the callout precedes an opening parenthesis,  the  length         is  zero.  When the callout precedes an opening parenthesis, the length
2558         is that of the entire subpattern.         is that of the entire subpattern.
2559    
2560         The  pattern_position  and next_item_length fields are intended to help         The pattern_position and next_item_length fields are intended  to  help
2561         in distinguishing between different automatic callouts, which all  have         in  distinguishing between different automatic callouts, which all have
2562         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
2563    
2564    
2565  RETURN VALUES  RETURN VALUES
2566    
2567         The  external callout function returns an integer to PCRE. If the value         The external callout function returns an integer to PCRE. If the  value
2568         is zero, matching proceeds as normal. If  the  value  is  greater  than         is  zero,  matching  proceeds  as  normal. If the value is greater than
2569         zero,  matching  fails  at  the current point, but backtracking to test         zero, matching fails at the current point, but  the  testing  of  other
2570         other matching possibilities goes ahead, just as if a lookahead  asser-         matching possibilities goes ahead, just as if a lookahead assertion had
2571         tion  had  failed.  If  the value is less than zero, the match is aban-         failed. If the value is less than zero, the  match  is  abandoned,  and
2572         doned, and pcre_exec() returns the negative value.         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2573    
2574         Negative  values  should  normally  be   chosen   from   the   set   of         Negative   values   should   normally   be   chosen  from  the  set  of
2575         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2576         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2577         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
2578         itself.         itself.
2579    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
2580    
2581  PCRE(3)                                                                PCRE(3)  AUTHOR
2582    
2583           Philip Hazel
2584           University Computing Service
2585           Cambridge CB2 3QH, England.
2586    
2587    
2588    REVISION
2589    
2590           Last updated: 29 May 2007
2591           Copyright (c) 1997-2007 University of Cambridge.
2592    ------------------------------------------------------------------------------
2593    
2594    
2595    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2596    
2597    
2598  NAME  NAME
2599         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2600    
2601    
2602  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2603    
2604         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2605         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2606         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2607           some features that are expected to be in the forthcoming Perl 5.10.
2608         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2609         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
2610           of  what  it does have are given in the section on UTF-8 support in the
2611           main pcre page.
2612    
2613         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2614         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 1738  DIFFERENCES BETWEEN PCRE AND PERL Line 2635  DIFFERENCES BETWEEN PCRE AND PERL
2635         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
2636         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2637         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-
2638         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2639           derived properties Any and L&.
2640    
2641         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2642         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2643         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2644         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2645         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2646    
2647             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 1753  DIFFERENCES BETWEEN PCRE AND PERL Line 2651  DIFFERENCES BETWEEN PCRE AND PERL
2651             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2652             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2653    
2654         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2655         classes.         classes.
2656    
2657         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2658         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2659         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
2660         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2661         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2662    
2663         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2664         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2665         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2666    
2667           10.  There are some differences that are concerned with the settings of
2668           captured strings when part of  a  pattern  is  repeated.  For  example,
2669           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2670         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2671    
2672         10. PCRE provides some extensions to the Perl regular expression facil-         11. PCRE provides some extensions to the Perl regular expression facil-
2673         ities:         ities.   Perl  5.10  will  include new features that are not in earlier
2674           versions, some of which (such as named parentheses) have been  in  PCRE
2675           for some time. This list is with respect to Perl 5.10:
2676    
2677         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2678         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2679         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2680    
2681         (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 $
2682         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2683    
2684         (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-
2685         cial meaning is faulted.         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2686           ignored.  (Perl can be made to issue a warning.)
2687    
2688         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2689         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 1790  DIFFERENCES BETWEEN PCRE AND PERL Line 2695  DIFFERENCES BETWEEN PCRE AND PERL
2695         (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-
2696         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2697    
2698         (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.)  
2699    
2700         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The partial matching facility is PCRE-specific.
2701    
2702         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2703         Sun's Java package.         even on different hosts that have the other endianness.
2704    
2705         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2706           different way and is not Perl-compatible.
2707    
        (k) The callout facility is PCRE-specific.  
2708    
2709         (l) The partial matching facility is PCRE-specific.  AUTHOR
2710    
2711         (m) Patterns compiled by PCRE can be saved and re-used at a later time,         Philip Hazel
2712         even on different hosts that have the other endianness.         University Computing Service
2713           Cambridge CB2 3QH, England.
2714    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
2715    
2716  PCRE(3)                                                                PCRE(3)  REVISION
2717    
2718           Last updated: 13 June 2007
2719           Copyright (c) 1997-2007 University of Cambridge.
2720    ------------------------------------------------------------------------------
2721    
2722    
2723    PCREPATTERN(3)                                                  PCREPATTERN(3)
2724    
2725    
2726  NAME  NAME
2727         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2728    
2729    
2730  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2731    
2732         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2733         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2734         documentation  and  in  a  number  of books, some of which have copious         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are
2735         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         described in its own documentation, and regular expressions in  general
2736         by  O'Reilly, covers regular expressions in great detail. This descrip-         are  covered in a number of books, some of which have copious examples.
2737         tion of PCRE's regular expressions is intended as reference material.         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by
2738           O'Reilly,  covers regular expressions in great detail. This description
2739           of PCRE's regular expressions is intended as reference material.
2740    
2741         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2742         However,  there is now also support for UTF-8 character strings. To use         However,  there is now also support for UTF-8 character strings. To use
# Line 1836  PCRE REGULAR EXPRESSION DETAILS Line 2746  PCRE REGULAR EXPRESSION DETAILS
2746         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
2747         page.         page.
2748    
2749         A regular expression is a pattern that is  matched  against  a  subject         The remainder of this document discusses the  patterns  that  are  sup-
2750         string  from  left  to right. Most characters stand for themselves in a         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2751         pattern, and match the corresponding characters in the  subject.  As  a         From  release  6.0,   PCRE   offers   a   second   matching   function,
2752           pcre_dfa_exec(),  which matches using a different algorithm that is not
2753           Perl-compatible. Some of the features discussed below are not available
2754           when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2755           alternative function, and how it differs from the normal function,  are
2756           discussed in the pcrematching page.
2757    
2758    
2759    CHARACTERS AND METACHARACTERS
2760    
2761           A  regular  expression  is  a pattern that is matched against a subject
2762           string from left to right. Most characters stand for  themselves  in  a
2763           pattern,  and  match  the corresponding characters in the subject. As a
2764         trivial example, the pattern         trivial example, the pattern
2765    
2766           The quick brown fox           The quick brown fox
2767    
2768         matches  a portion of a subject string that is identical to itself. The         matches a portion of a subject string that is identical to itself. When
2769         power of regular expressions comes from the ability to include alterna-         caseless  matching is specified (the PCRE_CASELESS option), letters are
2770         tives  and repetitions in the pattern. These are encoded in the pattern         matched independently of case. In UTF-8 mode, PCRE  always  understands
2771         by the use of metacharacters, which do not  stand  for  themselves  but         the  concept  of case for characters whose values are less than 128, so
2772         instead are interpreted in some special way.         caseless matching is always possible. For characters with  higher  val-
2773           ues,  the concept of case is supported if PCRE is compiled with Unicode
2774           property support, but not otherwise.   If  you  want  to  use  caseless
2775           matching  for  characters  128  and above, you must ensure that PCRE is
2776           compiled with Unicode property support as well as with UTF-8 support.
2777    
2778           The power of regular expressions comes  from  the  ability  to  include
2779           alternatives  and  repetitions in the pattern. These are encoded in the
2780           pattern by the use of metacharacters, which do not stand for themselves
2781           but instead are interpreted in some special way.
2782    
2783         There  are  two different sets of metacharacters: those that are recog-         There  are  two different sets of metacharacters: those that are recog-
2784         nized anywhere in the pattern except within square brackets, and  those         nized anywhere in the pattern except within square brackets, and  those
2785         that  are  recognized  in square brackets. Outside square brackets, the         that  are  recognized  within square brackets. Outside square brackets,
2786         metacharacters are as follows:         the metacharacters are as follows:
2787    
2788           \      general escape character with several uses           \      general escape character with several uses
2789           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 1899  BACKSLASH Line 2830  BACKSLASH
2830    
2831         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
2832         the  pattern (other than in a character class) and characters between a         the  pattern (other than in a character class) and characters between a
2833         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2834         An  escaping backslash can be used to include a whitespace or # charac-         ing  backslash  can  be  used to include a whitespace or # character as
2835         ter as part of the pattern.         part of the pattern.
2836    
2837         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-
2838         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 1937  BACKSLASH Line 2868  BACKSLASH
2868           \t        tab (hex 09)           \t        tab (hex 09)
2869           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
2870           \xhh      character with hex code hh           \xhh      character with hex code hh
2871           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
2872    
2873         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,
2874         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 1945  BACKSLASH Line 2876  BACKSLASH
2876         becomes hex 7B.         becomes hex 7B.
2877    
2878         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
2879         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
2880         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
2881         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,
2882         7FFFFFFF).  If  characters other than hexadecimal digits appear between         the  maximum  hexadecimal  value is 7FFFFFFF). If characters other than
2883         \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-
2884         recognized. Instead, the initial \x will be interpreted as a basic hex-         nating  }, this form of escape is not recognized.  Instead, the initial
2885         adecimal escape, with no following digits,  giving  a  character  whose         \x will be interpreted as a basic hexadecimal escape, with no following
2886         value is zero.         digits, giving a character whose value is zero.
2887    
2888         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
2889         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-
2890         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}.
2891         \x{dc}.  
2892           After  \0  up  to two further octal digits are read. If there are fewer
2893         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
2894         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
2895         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
2896         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.  
2897    
2898         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-
2899         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 1976  BACKSLASH Line 2905  BACKSLASH
2905    
2906         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
2907         and there have not been that many capturing subpatterns, PCRE  re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
2908         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-
2909         gle byte from the least significant 8 bits of the value. Any subsequent         erate a data character. Any subsequent digits stand for themselves.  In
2910         digits stand for themselves.  For example:         non-UTF-8  mode,  the  value  of a character specified in octal must be
2911           less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
2912           example:
2913    
2914           \040   is another way of writing a space           \040   is another way of writing a space
2915           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 1998  BACKSLASH Line 2929  BACKSLASH
2929         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
2930         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2931    
2932         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
2933         character (in UTF-8 mode) can be used both inside and outside character         inside  and  outside character classes. In addition, inside a character
2934         classes. In addition, inside a character  class,  the  sequence  \b  is         class, the sequence \b is interpreted as the backspace  character  (hex
2935         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"
2936         interpreted as the character "X".  Outside  a  character  class,  these         and "X", respectively. Outside a character class, these sequences  have
2937         sequences have different meanings (see below).         different meanings (see below).
2938    
2939       Absolute and relative back references
2940    
2941           The  sequence  \g followed by an unsigned or a negative number, option-
2942           ally enclosed in braces, is an absolute or relative back  reference.  A
2943           named back reference can be coded as \g{name}. Back references are dis-
2944           cussed later, following the discussion of parenthesized subpatterns.
2945    
2946     Generic character types     Generic character types
2947    
2948         The  third  use of backslash is for specifying generic character types.         Another use of backslash is for specifying generic character types. The
2949         The following are always recognized:         following are always recognized:
2950    
2951           \d     any decimal digit           \d     any decimal digit
2952           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
2953             \h     any horizontal whitespace character
2954             \H     any character that is not a horizontal whitespace character
2955           \s     any whitespace character           \s     any whitespace character
2956           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
2957             \v     any vertical whitespace character
2958             \V     any character that is not a vertical whitespace character
2959           \w     any "word" character           \w     any "word" character
2960           \W     any "non-word" character           \W     any "non-word" character
2961    
2962         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
2963         into  two disjoint sets. Any given character matches one, and only one,         into two disjoint sets. Any given character matches one, and only  one,
2964         of each pair.         of each pair.
2965    
2966         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
2967         acter  classes.  They each match one character of the appropriate type.         acter classes. They each match one character of the  appropriate  type.
2968         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
2969         of them fail, since there is no character to match.         of them fail, since there is no character to match.
2970    
2971         For  compatibility  with Perl, \s does not match the VT character (code         For compatibility with Perl, \s does not match the VT  character  (code
2972         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
2973         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
2974           "use locale;" is included in a Perl script, \s may match the VT charac-
2975           ter. In PCRE, it never does.
2976    
2977           In UTF-8 mode, characters with values greater than 128 never match  \d,
2978           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
2979           code character property support is available.  These  sequences  retain
2980           their original meanings from before UTF-8 support was available, mainly
2981           for efficiency reasons.
2982    
2983           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
2984           the  other  sequences, these do match certain high-valued codepoints in
2985           UTF-8 mode.  The horizontal space characters are:
2986    
2987             U+0009     Horizontal tab
2988             U+0020     Space
2989             U+00A0     Non-break space
2990             U+1680     Ogham space mark
2991             U+180E     Mongolian vowel separator
2992             U+2000     En quad
2993             U+2001     Em quad
2994             U+2002     En space
2995             U+2003     Em space
2996             U+2004     Three-per-em space
2997             U+2005     Four-per-em space
2998             U+2006     Six-per-em space
2999             U+2007     Figure space
3000             U+2008     Punctuation space
3001             U+2009     Thin space
3002             U+200A     Hair space
3003             U+202F     Narrow no-break space
3004             U+205F     Medium mathematical space
3005             U+3000     Ideographic space
3006    
3007           The vertical space characters are:
3008    
3009             U+000A     Linefeed
3010             U+000B     Vertical tab
3011             U+000C     Formfeed
3012             U+000D     Carriage return
3013             U+0085     Next line
3014             U+2028     Line separator
3015             U+2029     Paragraph separator
3016    
3017         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
3018         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-
3019         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-
3020         specific matching is taking place (see "Locale support" in the  pcreapi         specific  matching is taking place (see "Locale support" in the pcreapi
3021         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
3022         codes greater than 128 are used for accented  letters,  and  these  are         systems,  or "french" in Windows, some character codes greater than 128
3023         matched by \w.         are used for accented letters, and these are matched by \w. The use  of
3024           locales with Unicode is discouraged.
3025    
3026       Newline sequences
3027    
3028           Outside  a  character class, the escape sequence \R matches any Unicode
3029           newline sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \R  is
3030           equivalent to the following:
3031    
3032             (?>\r\n|\n|\x0b|\f|\r|\x85)
3033    
3034           This  is  an  example  of an "atomic group", details of which are given
3035           below.  This particular group matches either the two-character sequence
3036           CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
3037           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3038           return, U+000D), or NEL (next line, U+0085). The two-character sequence
3039           is treated as a single unit that cannot be split.
3040    
3041           In UTF-8 mode, two additional characters whose codepoints  are  greater
3042           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3043           rator, U+2029).  Unicode character property support is not  needed  for
3044           these characters to be recognized.
3045    
3046         In  UTF-8 mode, characters with values greater than 128 never match \d,         Inside a character class, \R matches the letter "R".
        \s, or \w, and always match \D, \S, and \W. This is true even when Uni-  
        code character property support is available.  
3047    
3048     Unicode character properties     Unicode character properties
3049    
3050         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3051         tional escape sequences to match generic character types are  available         tional escape sequences that match characters with specific  properties
3052         when UTF-8 mode is selected. They are:         are  available.   When not in UTF-8 mode, these sequences are of course
3053           limited to testing characters whose codepoints are less than  256,  but
3054          \p{xx}   a character with the xx property         they do work in this mode.  The extra escape sequences are:
3055          \P{xx}   a character without the xx property  
3056          \X       an extended Unicode sequence           \p{xx}   a character with the xx property
3057             \P{xx}   a character without the xx property
3058             \X       an extended Unicode sequence
3059    
3060         The  property  names represented by xx above are limited to the Unicode         The  property  names represented by xx above are limited to the Unicode
3061         general category properties. Each character has exactly one such  prop-         script names, the general category properties, and "Any", which matches
3062         erty,  specified  by  a two-letter abbreviation. For compatibility with         any character (including newline). Other properties such as "InMusical-
3063         Perl, negation can be specified by including a circumflex  between  the         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does
3064         opening  brace  and the property name. For example, \p{^Lu} is the same         not match any characters, so always causes a match failure.
3065         as \P{Lu}.  
3066           Sets of Unicode characters are defined as belonging to certain scripts.
3067         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.
3068         properties that start with that letter. In this case, in the absence of         For example:
3069         negation, the curly brackets in the escape sequence are optional; these  
3070         two examples have the same effect:           \p{Greek}
3071             \P{Han}
3072    
3073           Those  that are not part of an identified script are lumped together as
3074           "Common". The current list of scripts is:
3075    
3076           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3077           Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,
3078           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3079           Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
3080           gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,
3081           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3082           Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,
3083           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3084           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3085    
3086           Each character has exactly one general category property, specified  by
3087           a two-letter abbreviation. For compatibility with Perl, negation can be
3088           specified by including a circumflex between the opening brace  and  the
3089           property name. For example, \p{^Lu} is the same as \P{Lu}.
3090    
3091           If only one letter is specified with \p or \P, it includes all the gen-
3092           eral category properties that start with that letter. In this case,  in
3093           the  absence of negation, the curly brackets in the escape sequence are
3094           optional; these two examples have the same effect:
3095    
3096           \p{L}           \p{L}
3097           \pL           \pL
3098    
3099         The following property codes are supported:         The following general category property codes are supported:
3100    
3101           C     Other           C     Other
3102           Cc    Control           Cc    Control
# Line 2113  BACKSLASH Line 3142  BACKSLASH
3142           Zp    Paragraph separator           Zp    Paragraph separator
3143           Zs    Space separator           Zs    Space separator
3144    
3145         Extended  properties such as "Greek" or "InMusicalSymbols" are not sup-         The special property L& is also supported: it matches a character  that
3146         ported by PCRE.         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not
3147           classified as a modifier or "other".
3148    
3149           The long synonyms for these properties  that  Perl  supports  (such  as
3150           \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix
3151           any of these properties with "Is".
3152    
3153           No character that is in the Unicode table has the Cn (unassigned) prop-
3154           erty.  Instead, this property is assumed for any code point that is not
3155           in the Unicode table.
3156    
3157         Specifying caseless matching does not affect  these  escape  sequences.         Specifying caseless matching does not affect  these  escape  sequences.
3158         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
# Line 2127  BACKSLASH Line 3165  BACKSLASH
3165         That is, it matches a character without the "mark"  property,  followed         That is, it matches a character without the "mark"  property,  followed
3166         by  zero  or  more  characters with the "mark" property, and treats the         by  zero  or  more  characters with the "mark" property, and treats the
3167         sequence as an atomic group (see below).  Characters  with  the  "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3168         property are typically accents that affect the preceding character.         property  are  typically  accents  that affect the preceding character.
3169           None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
3170           matches any one character.
3171    
3172         Matching  characters  by Unicode property is not fast, because PCRE has         Matching  characters  by Unicode property is not fast, because PCRE has
3173         to search a structure that contains  data  for  over  fifteen  thousand         to search a structure that contains  data  for  over  fifteen  thousand
3174         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3175         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3176    
3177       Resetting the match start
3178    
3179           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3180           ously  matched  characters  not  to  be  included  in the final matched
3181           sequence. For example, the pattern:
3182    
3183             foo\Kbar
3184    
3185           matches "foobar", but reports that it has matched "bar".  This  feature
3186           is  similar  to  a lookbehind assertion (described below).  However, in
3187           this case, the part of the subject before the real match does not  have
3188           to  be of fixed length, as lookbehind assertions do. The use of \K does
3189           not interfere with the setting of captured  substrings.   For  example,
3190           when the pattern
3191    
3192             (foo)\Kbar
3193    
3194           matches "foobar", the first substring is still set to "foo".
3195    
3196     Simple assertions     Simple assertions
3197    
3198         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3199         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
3200         a match, without consuming any characters from the subject string.  The         a  match, without consuming any characters from the subject string. The
3201         use  of subpatterns for more complicated assertions is described below.         use of subpatterns for more complicated assertions is described  below.
3202         The backslashed assertions are:         The backslashed assertions are:
3203    
3204           \b     matches at a word boundary           \b     matches at a word boundary
3205           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3206           \A     matches at start of subject           \A     matches at the start of the subject
3207           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3208           \z     matches at end of subject                   also matches before a newline at the end of the subject
3209           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3210             \G     matches at the first matching position in the subject
3211    
3212         These assertions may not appear in character classes (but note that  \b         These  assertions may not appear in character classes (but note that \b
3213         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3214         acter class).         acter class).
3215    
3216         A word boundary is a position in the subject string where  the  current         A  word  boundary is a position in the subject string where the current
3217         character  and  the previous character do not both match \w or \W (i.e.         character and the previous character do not both match \w or  \W  (i.e.
3218         one matches \w and the other matches \W), or the start or  end  of  the         one  matches  \w  and the other matches \W), or the start or end of the
3219         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
3220    
3221         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The \A, \Z, and \z assertions differ from  the  traditional  circumflex
3222         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
3223         at  the  very start and end of the subject string, whatever options are         at the very start and end of the subject string, whatever  options  are
3224         set. Thus, they are independent of multiline mode. These  three  asser-         set.  Thus,  they are independent of multiline mode. These three asser-
3225         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3226         affect only the behaviour of the circumflex and dollar  metacharacters.         affect  only the behaviour of the circumflex and dollar metacharacters.
3227         However,  if the startoffset argument of pcre_exec() is non-zero, indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3228         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
3229         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
3230         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
3231         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.
        the end.  
3232    
3233         The \G assertion is true only when the current matching position is  at         The \G assertion is true only when the current matching position is  at
3234         the  start point of the match, as specified by the startoffset argument         the  start point of the match, as specified by the startoffset argument
# Line 2208  CIRCUMFLEX AND DOLLAR Line 3267  CIRCUMFLEX AND DOLLAR
3267    
3268         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
3269         matching  point  is  at  the  end of the subject string, or immediately         matching  point  is  at  the  end of the subject string, or immediately
3270         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
3271         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
3272         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
3273         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.  
3274    
3275         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
3276         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
3277         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3278    
3279         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3280         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
3281         ately after and  immediately  before  an  internal  newline  character,         matches  immediately after internal newlines as well as at the start of
3282         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
3283         ject string. For example,  the  pattern  /^abc$/  matches  the  subject         string.  A dollar matches before any newlines in the string, as well as
3284         string  "def\nabc"  (where \n represents a newline character) in multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3285         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3286         in  single line mode because all branches start with ^ are not anchored         not indicate newlines.
3287         in multiline mode, and a match for  circumflex  is  possible  when  the  
3288         startoffset   argument   of  pcre_exec()  is  non-zero.  The  PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3289         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3290           Consequently, patterns that are anchored in single  line  mode  because
3291           all  branches  start  with  ^ are not anchored in multiline mode, and a
3292           match for circumflex is  possible  when  the  startoffset  argument  of
3293           pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
3294           PCRE_MULTILINE is set.
3295    
3296         Note that the sequences \A, \Z, and \z can be used to match  the  start         Note that the sequences \A, \Z, and \z can be used to match  the  start
3297         and  end of the subject in both modes, and if all branches of a pattern         and  end of the subject in both modes, and if all branches of a pattern
3298         start with \A it is always anchored, whether PCRE_MULTILINE is  set  or         start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3299         not.         set.
3300    
3301    
3302  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3303    
3304         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-
3305         ter in the subject, including a non-printing  character,  but  not  (by         ter in the subject string except (by default) a character  that  signi-
3306         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
3307         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3308         the  PCRE_DOTALL  option  is set, dots match newlines as well. The han-  
3309         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
3310         dollar,  the  only  relationship  being  that they both involve newline         that  character; when the two-character sequence CRLF is used, dot does
3311         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3312           matches  all characters (including isolated CRs and LFs). When any Uni-
3313           code line endings are being recognized, dot does not match CR or LF  or
3314           any of the other line ending characters.
3315    
3316           The  behaviour  of  dot  with regard to newlines can be changed. If the
3317           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3318           exception. If the two-character sequence CRLF is present in the subject
3319           string, it takes two dots to match it.
3320    
3321           The handling of dot is entirely independent of the handling of  circum-
3322           flex  and  dollar,  the  only relationship being that they both involve
3323           newlines. Dot has no special meaning in a character class.
3324    
3325    
3326  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3327    
3328         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3329         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
3330         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
3331         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-
3332         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-
3333         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3334           avoided.
3335    
3336         PCRE  does  not  allow \C to appear in lookbehind assertions (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3337         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-
3338         late the length of the lookbehind.         late the length of the lookbehind.
3339    
3340    
# Line 2267  SQUARE BRACKETS AND CHARACTER CLASSES Line 3343  SQUARE BRACKETS AND CHARACTER CLASSES
3343         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3344         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3345         cial. If a closing square bracket is required as a member of the class,         cial. If a closing square bracket is required as a member of the class,
3346         it should be the first data character in the class  (after  an  initial         it  should  be  the first data character in the class (after an initial
3347         circumflex, if present) or escaped with a backslash.         circumflex, if present) or escaped with a backslash.
3348    
3349         A  character  class matches a single character in the subject. In UTF-8         A character class matches a single character in the subject.  In  UTF-8
3350         mode, the character may occupy more than one byte. A matched  character         mode,  the character may occupy more than one byte. A matched character
3351         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3352         character in the class definition is a circumflex, in  which  case  the         character  in  the  class definition is a circumflex, in which case the
3353         subject  character  must  not  be in the set defined by the class. If a         subject character must not be in the set defined by  the  class.  If  a
3354         circumflex is actually required as a member of the class, ensure it  is         circumflex  is actually required as a member of the class, ensure it is
3355         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3356    
3357         For  example, the character class [aeiou] matches any lower case vowel,         For example, the character class [aeiou] matches any lower case  vowel,
3358         while [^aeiou] matches any character that is not a  lower  case  vowel.         while  [^aeiou]  matches  any character that is not a lower case vowel.
3359         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3360         characters that are in the class by enumerating those that are  not.  A         characters  that  are in the class by enumerating those that are not. A
3361         class  that starts with a circumflex is not an assertion: it still con-         class that starts with a circumflex is not an assertion: it still  con-
3362         sumes a character from the subject string, and therefore  it  fails  if         sumes  a  character  from the subject string, and therefore it fails if
3363         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3364    
3365         In  UTF-8 mode, characters with values greater than 255 can be included         In UTF-8 mode, characters with values greater than 255 can be  included
3366         in a class as a literal string of bytes, or by using the  \x{  escaping         in  a  class as a literal string of bytes, or by using the \x{ escaping
3367         mechanism.         mechanism.
3368    
3369         When  caseless  matching  is set, any letters in a class represent both         When caseless matching is set, any letters in a  class  represent  both
3370         their upper case and lower case versions, so for  example,  a  caseless         their  upper  case  and lower case versions, so for example, a caseless
3371         [aeiou]  matches  "A"  as well as "a", and a caseless [^aeiou] does not         [aeiou] matches "A" as well as "a", and a caseless  [^aeiou]  does  not
3372         match "A", whereas a caseful version would. When running in UTF-8 mode,         match  "A", whereas a caseful version would. In UTF-8 mode, PCRE always
3373         PCRE  supports  the  concept of case for characters with values greater         understands the concept of case for characters whose  values  are  less
3374         than 128 only when it is compiled with Unicode property support.         than  128, so caseless matching is always possible. For characters with
3375           higher values, the concept of case is supported  if  PCRE  is  compiled
3376         The newline character is never treated in any special way in  character         with  Unicode  property support, but not otherwise.  If you want to use
3377         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         caseless matching for characters 128 and above, you  must  ensure  that
3378         options is. A class such as [^a] will always match a newline.         PCRE  is  compiled  with Unicode property support as well as with UTF-8
3379           support.
3380    
3381           Characters that might indicate line breaks are  never  treated  in  any
3382           special  way  when  matching  character  classes,  whatever line-ending
3383           sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3384           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3385           of these characters.
3386    
3387         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-
3388         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 2325  SQUARE BRACKETS AND CHARACTER CLASSES Line 3408  SQUARE BRACKETS AND CHARACTER CLASSES
3408         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,
3409         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
3410         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3411         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
3412         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
3413         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3414         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 2400  VERTICAL BAR Line 3483  VERTICAL BAR
3483    
3484         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3485         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3486         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3487         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
3488         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3489         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.  
3490    
3491    
3492  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 2432  INTERNAL OPTION SETTING Line 3514  INTERNAL OPTION SETTING
3514         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
3515         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3516    
3517         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
3518         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3519           it, so
3520    
3521           (a(?i)b)c           (a(?i)b)c
3522    
3523         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
3524         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3525