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1    -----------------------------------------------------------------------------
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
# Line 5  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  DESCRIPTION  
17    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         4.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.   However,  this  support has to be explicitly         syntax.)
24         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. However, a number  of         mately with Perl 5.10, including support for UTF-8 encoded strings  and
27         people  have  written  wrappers  and interfaces of various kinds. A C++         Unicode general category properties. However, UTF-8 and Unicode support
28         class is included in these contributions, which can  be  found  in  the         has to be explicitly enabled; it is not the default. The Unicode tables
29           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:         Contrib directory at the primary FTP site, which is:
43    
44         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
45    
46         Details  of  exactly which Perl regular expression features are and are         Details of exactly which Perl regular expression features are  and  are
47         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
48         tern and pcrecompat pages.         tern and pcrecompat pages.
49    
50         Some  features  of  PCRE can be included, excluded, or changed when the         Some features of PCRE can be included, excluded, or  changed  when  the
51         library is built. The pcre_config() function makes it  possible  for  a         library  is  built.  The pcre_config() function makes it possible for a
52         client  to  discover  which features are available. Documentation about         client to discover which features are  available.  The  features  them-
53         building PCRE for various operating systems can be found in the  README         selves  are described in the pcrebuild page. Documentation about build-
54         file in the source distribution.         ing PCRE for various operating systems can be found in the README  file
55           in the source distribution.
56    
57           The  library  contains  a number of undocumented internal functions and
58           data tables that are used by more than one  of  the  exported  external
59           functions,  but  which  are  not  intended for use by external callers.
60           Their names all begin with "_pcre_", which hopefully will  not  provoke
61           any name clashes. In some environments, it is possible to control which
62           external symbols are exported when a shared library is  built,  and  in
63           these cases the undocumented symbols are not exported.
64    
65    
66  USER DOCUMENTATION  USER DOCUMENTATION
67    
68         The user documentation for PCRE has been split up into a number of dif-         The  user  documentation  for PCRE comprises a number of different sec-
69         ferent sections. In the "man" format, each of these is a separate  "man         tions. In the "man" format, each of these is a separate "man page".  In
70         page".  In  the  HTML  format, each is a separate page, linked from the         the  HTML  format, each is a separate page, linked from the index page.
71         index page. In the plain text format, all  the  sections  are  concate-         In the plain text format, all the sections are concatenated,  for  ease
72         nated, for ease of searching. The sections are as follows:         of searching. The sections are as follows:
73    
74           pcre              this document           pcre              this document
75           pcreapi           details of PCRE's native API           pcre-config       show PCRE installation configuration information
76             pcreapi           details of PCRE's native C API
77           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
78           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
79           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
80             pcrecpp           details of the C++ wrapper
81           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
82             pcrematching      discussion of the two matching algorithms
83             pcrepartial       details of the partial matching facility
84           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
85                               regular expressions                               regular expressions
86           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
87           pcreposix         the POSIX-compatible API           pcreposix         the POSIX-compatible C API
88             pcreprecompile    details of saving and re-using precompiled patterns
89           pcresample        discussion of the sample program           pcresample        discussion of the sample program
90           pcretest          the pcretest testing command           pcrestack         discussion of stack usage
91             pcretest          description of the pcretest testing command
92    
93         In  addition,  in the "man" and HTML formats, there is a short page for         In addition, in the "man" and HTML formats, there is a short  page  for
94         each library function, listing its arguments and results.         each C library function, listing its arguments and results.
95    
96    
97  LIMITATIONS  LIMITATIONS
98    
99         There are some size limitations in PCRE but it is hoped that they  will         There  are some size limitations in PCRE but it is hoped that they will
100         never in practice be relevant.         never in practice be relevant.
101    
102         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE         The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE
103         is compiled with the default internal linkage size of 2. If you want to         is compiled with the default internal linkage size of 2. If you want to
104         process  regular  expressions  that are truly enormous, you can compile         process regular expressions that are truly enormous,  you  can  compile
105         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in         PCRE  with  an  internal linkage size of 3 or 4 (see the README file in
106         the  source  distribution and the pcrebuild documentation for details).         the source distribution and the pcrebuild documentation  for  details).
107         If these cases the limit is substantially larger.  However,  the  speed         In  these  cases the limit is substantially larger.  However, the speed
108         of execution will be slower.         of execution is slower.
109    
110         All values in repeating quantifiers must be less than 65536.  The maxi-         All values in repeating quantifiers must be less than 65536. The  maxi-
111         mum number of capturing subpatterns is 65535.         mum  compiled  length  of  subpattern  with an explicit repeat count is
112           30000 bytes. The maximum number of capturing subpatterns is 65535.
113         There is no limit to the number of non-capturing subpatterns,  but  the  
114         maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,         There is no limit to the number of parenthesized subpatterns, but there
115         including capturing subpatterns, assertions, and other types of subpat-         can be no more than 65535 capturing subpatterns.
116         tern, is 200.  
117           The maximum length of name for a named subpattern is 32 characters, and
118         The  maximum  length of a subject string is the largest positive number         the maximum number of named subpatterns is 10000.
119         that an integer variable can hold. However, PCRE uses recursion to han-  
120         dle  subpatterns  and indefinite repetition. This means that the avail-         The maximum length of a subject string is the largest  positive  number
121         able stack space may limit the size of a subject  string  that  can  be         that  an integer variable can hold. However, when using the traditional
122         processed by certain patterns.         matching function, PCRE uses recursion to handle subpatterns and indef-
123           inite  repetition.  This means that the available stack space may limit
124           the size of a subject string that can be processed by certain patterns.
125  UTF-8 SUPPORT         For a discussion of stack issues, see the pcrestack documentation.
126    
127         Starting  at  release  3.3,  PCRE  has  had  some support for character  
128         strings encoded in the UTF-8 format. For  release  4.0  this  has  been  UTF-8 AND UNICODE PROPERTY SUPPORT
129         greatly extended to cover most common requirements.  
130           From  release  3.3,  PCRE  has  had  some support for character strings
131         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         encoded in the UTF-8 format. For release 4.0 this was greatly  extended
132         support in the code, and, in addition,  you  must  call  pcre_compile()         to  cover  most common requirements, and in release 5.0 additional sup-
133         with  the PCRE_UTF8 option flag. When you do this, both the pattern and         port for Unicode general category properties was added.
134         any subject strings that are matched against it are  treated  as  UTF-8  
135           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()
137           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
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
147           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
149           general category properties such as Lu for an upper case letter  or  Nd
150           for  a  decimal number, the Unicode script names such as Arabic or Han,
151           and the derived properties Any and L&. A full  list  is  given  in  the
152           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         5. The dot metacharacter matches one UTF-8 character instead of a  sin-
182         single 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-
190         nizes  as  digits,  spaces,  or  word characters remain the same set as         nizes  as  digits,  spaces,  or  word characters remain the same set as
191         before, all with values less than 256.         before, all with values less than 256. This remains true even when PCRE
192           includes  Unicode  property support, because to do otherwise would slow
193           down PCRE in many common cases. If you really want to test for a  wider
194           sense  of,  say,  "digit",  you must use Unicode property tests such as
195           \p{Nd}.
196    
197           8. Similarly, characters that match the POSIX named  character  classes
198           are all low-valued characters.
199    
200           9.  Case-insensitive  matching  applies only to characters whose values
201           are less than 128, unless PCRE is built with Unicode property  support.
202           Even  when  Unicode  property support is available, PCRE still uses its
203           own character tables when checking the case of  low-valued  characters,
204           so  as not to degrade performance.  The Unicode property information is
205           used only for characters with higher values. Even when Unicode property
206           support is available, PCRE supports case-insensitive matching only when
207           there is a one-to-one mapping between a letter's  cases.  There  are  a
208           small  number  of  many-to-one  mappings in Unicode; these are not sup-
209           ported by PCRE.
210    
        8. Case-insensitive matching applies only to  characters  whose  values  
        are  less  than  256.  PCRE  does  not support the notion of "case" for  
        higher-valued characters.  
211    
212         9. PCRE does not support the use of Unicode tables  and  properties  or  AUTHOR
        the Perl escapes \p, \P, and \X.  
213    
214           Philip Hazel
215           University Computing Service
216           Cambridge CB2 3QH, England.
217    
218  AUTHOR         Putting an actual email address here seems to have been a spam  magnet,
219           so  I've  taken  it away. If you want to email me, use my two initials,
220           followed by the two digits 10, at the domain cam.ac.uk.
221    
        Philip Hazel <ph10@cam.ac.uk>  
        University Computing Service,  
        Cambridge CB2 3QG, England.  
        Phone: +44 1223 334714  
222    
223  Last updated: 20 August 2003  REVISION
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
224    
225  PCRE(3)                                                                PCRE(3)         Last updated: 18 April 2007
226           Copyright (c) 1997-2007 University of Cambridge.
227    ------------------------------------------------------------------------------
228    
229    
230    PCREBUILD(3)                                                      PCREBUILD(3)
231    
232    
233  NAME  NAME
234         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
235    
236    
237  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
238    
239         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
240         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. They are all selected, or  dese-
241         lected,  by  providing  options  to  the  configure script which is run         lected, by providing options to the configure script that is run before
242         before the make command. The complete list  of  options  for  configure         the make command. The complete list of  options  for  configure  (which
243         (which  includes the standard ones such as the selection of the instal-         includes  the  standard  ones such as the selection of the installation
244         lation directory) can be obtained by running         directory) can be obtained by running
245    
246           ./configure --help           ./configure --help
247    
248         The following sections describe certain options whose names begin  with         The following sections include  descriptions  of  options  whose  names
249         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
250         for the configure command. Because of the  way  that  configure  works,         defaults for the configure command. Because of the way  that  configure
251         --enable  and  --disable  always  come  in  pairs, so the complementary         works,  --enable  and --disable always come in pairs, so the complemen-
252         option always exists as well, but as it specifies the  default,  it  is         tary option always exists as well, but as it specifies the default,  it
253         not described.         is not described.
254    
255    
256    C++ SUPPORT
257    
258           By default, the configure script will search for a C++ compiler and C++
259           header files. If it finds them, it automatically builds the C++ wrapper
260           library for PCRE. You can disable this by adding
261    
262             --disable-cpp
263    
264           to the configure command.
265    
266    
267  UTF-8 SUPPORT  UTF-8 SUPPORT
# Line 204  UTF-8 SUPPORT Line 276  UTF-8 SUPPORT
276         function.         function.
277    
278    
279    UNICODE CHARACTER PROPERTY SUPPORT
280    
281           UTF-8 support allows PCRE to process character values greater than  255
282           in  the  strings that it handles. On its own, however, it does not pro-
283           vide any facilities for accessing the properties of such characters. If
284           you  want  to  be able to use the pattern escapes \P, \p, and \X, which
285           refer to Unicode character properties, you must add
286    
287             --enable-unicode-properties
288    
289           to the configure command. This implies UTF-8 support, even if you  have
290           not explicitly requested it.
291    
292           Including  Unicode  property  support  adds around 30K of tables to the
293           PCRE library. Only the general category properties such as  Lu  and  Nd
294           are supported. Details are given in the pcrepattern documentation.
295    
296    
297  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
298    
299         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating
300         ter. This is the normal newline character on Unix-like systems. You can         the end of a line. This is the normal newline  character  on  Unix-like
301         compile PCRE to use character 13 (carriage return) instead by adding         systems. You can compile PCRE to use character 13 (carriage return, CR)
302           instead, by adding
303    
304           --enable-newline-is-cr           --enable-newline-is-cr
305    
306         to the configure command. For completeness there is  also  a  --enable-         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
307         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
308         line character.  
309           Alternatively, you can specify that line endings are to be indicated by
310           the two character sequence CRLF. If you want this, add
311    
312             --enable-newline-is-crlf
313    
314           to the configure command. There is a fourth option, specified by
315    
316             --enable-newline-is-anycrlf
317    
318           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
319           CRLF as indicating a line ending. Finally, a fifth option, specified by
320    
321             --enable-newline-is-any
322    
323           causes PCRE to recognize any Unicode newline sequence.
324    
325           Whatever line ending convention is selected when PCRE is built  can  be
326           overridden  when  the library functions are called. At build time it is
327           conventional to use the standard for your operating system.
328    
329    
330  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
# Line 231  BUILDING SHARED AND STATIC LIBRARIES Line 341  BUILDING SHARED AND STATIC LIBRARIES
341    
342  POSIX MALLOC USAGE  POSIX MALLOC USAGE
343    
344         When PCRE is called through the  POSIX  interface  (see  the  pcreposix         When PCRE is called through the POSIX interface (see the pcreposix doc-
345         documentation),  additional working storage is required for holding the         umentation),  additional  working  storage  is required for holding the
346         pointers to capturing substrings because PCRE requires  three  integers         pointers to capturing substrings, because PCRE requires three  integers
347         per  substring,  whereas  the POSIX interface provides only two. If the         per  substring,  whereas  the POSIX interface provides only two. If the
348         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
349         on the stack, because this is faster than using malloc() for each call.         on the stack, because this is faster than using malloc() for each call.
# Line 245  POSIX MALLOC USAGE Line 355  POSIX MALLOC USAGE
355         to the configure command.         to the configure command.
356    
357    
 LIMITING PCRE RESOURCE USAGE  
   
        Internally,  PCRE  has a function called match() which it calls repeat-  
        edly (possibly recursively) when performing a  matching  operation.  By  
        limiting  the  number of times this function may be called, a limit can  
        be placed on the resources used by a single call  to  pcre_exec().  The  
        limit  can be changed at run time, as described in the pcreapi documen-  
        tation. The default is 10 million, but this can be changed by adding  a  
        setting such as  
   
          --with-match-limit=500000  
   
        to the configure command.  
   
   
358  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
359    
360         Within  a  compiled  pattern,  offset values are used to point from one         Within  a  compiled  pattern,  offset values are used to point from one
361         part to another (for example, from an opening parenthesis to an  alter-         part to another (for example, from an opening parenthesis to an  alter-
362         nation  metacharacter).  By  default two-byte values are used for these         nation  metacharacter).  By default, two-byte values are used for these
363         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets, leading to a maximum size for a  compiled  pattern  of  around
364         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K.  This  is sufficient to handle all but the most gigantic patterns.
365         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless, some people do want to process enormous patterns,  so  it
# Line 277  HANDLING VERY LARGE PATTERNS Line 372  HANDLING VERY LARGE PATTERNS
372         longer  offsets slows down the operation of PCRE because it has to load         longer  offsets slows down the operation of PCRE because it has to load
373         additional bytes when handling them.         additional bytes when handling them.
374    
        If you build PCRE with an increased link size, test 2 (and  test  5  if  
        you  are using UTF-8) will fail. Part of the output of these tests is a  
        representation of the compiled pattern, and this changes with the  link  
        size.  
   
375    
376  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
377    
378         PCRE  implements  backtracking while matching by making recursive calls         When matching with the pcre_exec() function, PCRE implements backtrack-
379         to an internal function called match(). In environments where the  size         ing  by  making recursive calls to an internal function called match().
380         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-
381         Unix environment does not usually suffer from this problem.) An  alter-         verely  limit  PCRE's operation. (The Unix environment does not usually
382         native  approach  that  uses  memory  from  the  heap to remember data,         suffer from this problem, but it may sometimes be necessary to increase
383         instead of using recursive function calls, has been implemented to work         the  maximum  stack size.  There is a discussion in the pcrestack docu-
384         round  this  problem. If you want to build a version of PCRE that works         mentation.) An alternative approach to recursion that uses memory  from
385         this way, add         the  heap  to remember data, instead of using recursive function calls,
386           has been implemented to work round the problem of limited  stack  size.
387           If you want to build a version of PCRE that works this way, add
388    
389           --disable-stack-for-recursion           --disable-stack-for-recursion
390    
391         to the configure command. With this configuration, PCRE  will  use  the         to  the  configure  command. With this configuration, PCRE will use the
392         pcre_stack_malloc   and   pcre_stack_free   variables  to  call  memory         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
393         management functions. Separate functions are provided because the usage         ment  functions.  Separate  functions are provided because the usage is
394         is very predictable: the block sizes requested are always the same, and         very predictable: the block sizes requested are always  the  same,  and
395         the blocks are always freed in reverse order. A calling  program  might         the  blocks  are always freed in reverse order. A calling program might
396         be  able  to implement optimized functions that perform better than the         be able to implement optimized functions that perform better  than  the
397         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more
398         slowly when built in this way.         slowly when built in this way. This option affects only the pcre_exec()
399           function; it is not relevant for the the pcre_dfa_exec() function.
400    
401    
402    LIMITING PCRE RESOURCE USAGE
403    
404           Internally,  PCRE has a function called match(), which it calls repeat-
405           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
406           pcre_exec()  function.  By controlling the maximum number of times this
407           function may be called during a single matching operation, a limit  can
408           be  placed  on  the resources used by a single call to pcre_exec(). The
409           limit can be changed at run time, as described in the pcreapi  documen-
410           tation.  The default is 10 million, but this can be changed by adding a
411           setting such as
412    
413             --with-match-limit=500000
414    
415           to  the  configure  command.  This  setting  has  no  effect   on   the
416           pcre_dfa_exec() matching function.
417    
418           In  some  environments  it is desirable to limit the depth of recursive
419           calls of match() more strictly than the total number of calls, in order
420           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
421           for-recursion is specified) that is used. A second limit controls this;
422           it  defaults  to  the  value  that is set for --with-match-limit, which
423           imposes no additional constraints. However, you can set a  lower  limit
424           by adding, for example,
425    
426             --with-match-limit-recursion=10000
427    
428           to  the  configure  command.  This  value can also be overridden at run
429           time.
430    
431    
432    CREATING CHARACTER TABLES AT BUILD TIME
433    
434           PCRE uses fixed tables for processing characters whose code values  are
435           less  than 256. By default, PCRE is built with a set of tables that are
436           distributed in the file pcre_chartables.c.dist. These  tables  are  for
437           ASCII codes only. If you add
438    
439             --enable-rebuild-chartables
440    
441           to  the  configure  command, the distributed tables are no longer used.
442           Instead, a program called dftables is compiled and  run.  This  outputs
443           the source for new set of tables, created in the default locale of your
444           C runtime system. (This method of replacing the tables does not work if
445           you  are cross compiling, because dftables is run on the local host. If
446           you need to create alternative tables when cross  compiling,  you  will
447           have to do so "by hand".)
448    
449    
450  USING EBCDIC CODE  USING EBCDIC CODE
451    
452         PCRE  assumes  by  default that it will run in an environment where the         PCRE  assumes  by  default that it will run in an environment where the
453         character code is ASCII (or UTF-8, which is a superset of ASCII).  PCRE         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
454         can, however, be compiled to run in an EBCDIC environment by adding         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by
455           adding
456    
457           --enable-ebcdic           --enable-ebcdic
458    
459         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
460           bles.
461    
 Last updated: 09 December 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
462    
463  PCRE(3)                                                                PCRE(3)  SEE ALSO
464    
465           pcreapi(3), pcre_config(3).
466    
467    
468    AUTHOR
469    
470           Philip Hazel
471           University Computing Service
472           Cambridge CB2 3QH, England.
473    
474    
475    REVISION
476    
477           Last updated: 16 April 2007
478           Copyright (c) 1997-2007 University of Cambridge.
479    ------------------------------------------------------------------------------
480    
481    
482    PCREMATCHING(3)                                                PCREMATCHING(3)
483    
484    
485    NAME
486           PCRE - Perl-compatible regular expressions
487    
488    
489    PCRE MATCHING ALGORITHMS
490    
491           This document describes the two different algorithms that are available
492           in PCRE for matching a compiled regular expression against a given sub-
493           ject  string.  The  "standard"  algorithm  is  the  one provided by the
494           pcre_exec() function.  This works in the same was  as  Perl's  matching
495           function, and provides a Perl-compatible matching operation.
496    
497           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
498           this operates in a different way, and is not  Perl-compatible.  It  has
499           advantages  and disadvantages compared with the standard algorithm, and
500           these are described below.
501    
502           When there is only one possible way in which a given subject string can
503           match  a pattern, the two algorithms give the same answer. A difference
504           arises, however, when there are multiple possibilities. For example, if
505           the pattern
506    
507             ^<.*>
508    
509           is matched against the string
510    
511             <something> <something else> <something further>
512    
513           there are three possible answers. The standard algorithm finds only one
514           of them, whereas the alternative algorithm finds all three.
515    
516    
517    REGULAR EXPRESSIONS AS TREES
518    
519           The set of strings that are matched by a regular expression can be rep-
520           resented  as  a  tree structure. An unlimited repetition in the pattern
521           makes the tree of infinite size, but it is still a tree.  Matching  the
522           pattern  to a given subject string (from a given starting point) can be
523           thought of as a search of the tree.  There are two  ways  to  search  a
524           tree:  depth-first  and  breadth-first, and these correspond to the two
525           matching algorithms provided by PCRE.
526    
527    
528    THE STANDARD MATCHING ALGORITHM
529    
530           In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
531           sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
532           depth-first search of the pattern tree. That is, it  proceeds  along  a
533           single path through the tree, checking that the subject matches what is
534           required. When there is a mismatch, the algorithm  tries  any  alterna-
535           tives  at  the  current point, and if they all fail, it backs up to the
536           previous branch point in the  tree,  and  tries  the  next  alternative
537           branch  at  that  level.  This often involves backing up (moving to the
538           left) in the subject string as well.  The  order  in  which  repetition
539           branches  are  tried  is controlled by the greedy or ungreedy nature of
540           the quantifier.
541    
542           If a leaf node is reached, a matching string has  been  found,  and  at
543           that  point the algorithm stops. Thus, if there is more than one possi-
544           ble match, this algorithm returns the first one that it finds.  Whether
545           this  is the shortest, the longest, or some intermediate length depends
546           on the way the greedy and ungreedy repetition quantifiers are specified
547           in the pattern.
548    
549           Because  it  ends  up  with a single path through the tree, it is rela-
550           tively straightforward for this algorithm to keep  track  of  the  sub-
551           strings  that  are  matched  by portions of the pattern in parentheses.
552           This provides support for capturing parentheses and back references.
553    
554    
555    THE ALTERNATIVE MATCHING ALGORITHM
556    
557           This algorithm conducts a breadth-first search of  the  tree.  Starting
558           from  the  first  matching  point  in the subject, it scans the subject
559           string from left to right, once, character by character, and as it does
560           this,  it remembers all the paths through the tree that represent valid
561           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
562           though  it is not implemented as a traditional finite state machine (it
563           keeps multiple states active simultaneously).
564    
565           The scan continues until either the end of the subject is  reached,  or
566           there  are  no more unterminated paths. At this point, terminated paths
567           represent the different matching possibilities (if there are none,  the
568           match  has  failed).   Thus,  if there is more than one possible match,
569           this algorithm finds all of them, and in particular, it finds the long-
570           est.  In PCRE, there is an option to stop the algorithm after the first
571           match (which is necessarily the shortest) has been found.
572    
573           Note that all the matches that are found start at the same point in the
574           subject. If the pattern
575    
576             cat(er(pillar)?)
577    
578           is  matched  against the string "the caterpillar catchment", the result
579           will be the three strings "cat", "cater", and "caterpillar" that  start
580           at the fourth character of the subject. The algorithm does not automat-
581           ically move on to find matches that start at later positions.
582    
583           There are a number of features of PCRE regular expressions that are not
584           supported by the alternative matching algorithm. They are as follows:
585    
586           1.  Because  the  algorithm  finds  all possible matches, the greedy or
587           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
588           ungreedy quantifiers are treated in exactly the same way. However, pos-
589           sessive quantifiers can make a difference when what follows could  also
590           match what is quantified, for example in a pattern like this:
591    
592             ^a++\w!
593    
594           This  pattern matches "aaab!" but not "aaa!", which would be matched by
595           a non-possessive quantifier. Similarly, if an atomic group is  present,
596           it  is matched as if it were a standalone pattern at the current point,
597           and the longest match is then "locked in" for the rest of  the  overall
598           pattern.
599    
600           2. When dealing with multiple paths through the tree simultaneously, it
601           is not straightforward to keep track of  captured  substrings  for  the
602           different  matching  possibilities,  and  PCRE's implementation of this
603           algorithm does not attempt to do this. This means that no captured sub-
604           strings are available.
605    
606           3.  Because no substrings are captured, back references within the pat-
607           tern are not supported, and cause errors if encountered.
608    
609           4. For the same reason, conditional expressions that use  a  backrefer-
610           ence  as  the  condition or test for a specific group recursion are not
611           supported.
612    
613           5. Because many paths through the tree may be  active,  the  \K  escape
614           sequence, which resets the start of the match when encountered (but may
615           be on some paths and not on others), is not  supported.  It  causes  an
616           error if encountered.
617    
618           6.  Callouts  are  supported, but the value of the capture_top field is
619           always 1, and the value of the capture_last field is always -1.
620    
621           7.  The \C escape sequence, which (in the standard algorithm) matches a
622           single  byte, even in UTF-8 mode, is not supported because the alterna-
623           tive algorithm moves through the subject  string  one  character  at  a
624           time, for all active paths through the tree.
625    
626    
627    ADVANTAGES OF THE ALTERNATIVE ALGORITHM
628    
629           Using  the alternative matching algorithm provides the following advan-
630           tages:
631    
632           1. All possible matches (at a single point in the subject) are automat-
633           ically  found,  and  in particular, the longest match is found. To find
634           more than one match using the standard algorithm, you have to do kludgy
635           things with callouts.
636    
637           2.  There is much better support for partial matching. The restrictions
638           on the content of the pattern that apply when using the standard  algo-
639           rithm  for  partial matching do not apply to the alternative algorithm.
640           For non-anchored patterns, the starting position of a partial match  is
641           available.
642    
643           3.  Because  the  alternative  algorithm  scans the subject string just
644           once, and never needs to backtrack, it is possible to  pass  very  long
645           subject  strings  to  the matching function in several pieces, checking
646           for partial matching each time.
647    
648    
649    DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
650    
651           The alternative algorithm suffers from a number of disadvantages:
652    
653           1. It is substantially slower than  the  standard  algorithm.  This  is
654           partly  because  it has to search for all possible matches, but is also
655           because it is less susceptible to optimization.
656    
657           2. Capturing parentheses and back references are not supported.
658    
659           3. Although atomic groups are supported, their use does not provide the
660           performance advantage that it does for the standard algorithm.
661    
662    
663    AUTHOR
664    
665           Philip Hazel
666           University Computing Service
667           Cambridge CB2 3QH, England.
668    
669    
670    REVISION
671    
672           Last updated: 29 May 2007
673           Copyright (c) 1997-2007 University of Cambridge.
674    ------------------------------------------------------------------------------
675    
676    
677    PCREAPI(3)                                                          PCREAPI(3)
678    
679    
680  NAME  NAME
681         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
682    
683  SYNOPSIS OF PCRE API  
684    PCRE NATIVE API
685    
686         #include <pcre.h>         #include <pcre.h>
687    
# Line 335  SYNOPSIS OF PCRE API Line 689  SYNOPSIS OF PCRE API
689              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
690              const unsigned char *tableptr);              const unsigned char *tableptr);
691    
692           pcre *pcre_compile2(const char *pattern, int options,
693                int *errorcodeptr,
694                const char **errptr, int *erroffset,
695                const unsigned char *tableptr);
696    
697         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options,
698              const char **errptr);              const char **errptr);
699    
# Line 342  SYNOPSIS OF PCRE API Line 701  SYNOPSIS OF PCRE API
701              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
702              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
703    
704           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
705                const char *subject, int length, int startoffset,
706                int options, int *ovector, int ovecsize,
707                int *workspace, int wscount);
708    
709         int pcre_copy_named_substring(const pcre *code,         int pcre_copy_named_substring(const pcre *code,
710              const char *subject, int *ovector,              const char *subject, int *ovector,
711              int stringcount, const char *stringname,              int stringcount, const char *stringname,
# Line 359  SYNOPSIS OF PCRE API Line 723  SYNOPSIS OF PCRE API
723         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
724              const char *name);              const char *name);
725    
726           int pcre_get_stringtable_entries(const pcre *code,
727                const char *name, char **first, char **last);
728    
729         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
730              int stringcount, int stringnumber,              int stringcount, int stringnumber,
731              const char **stringptr);              const char **stringptr);
# Line 377  SYNOPSIS OF PCRE API Line 744  SYNOPSIS OF PCRE API
744    
745         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
746    
747           int pcre_refcount(pcre *code, int adjust);
748    
749         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
750    
751         char *pcre_version(void);         char *pcre_version(void);
# Line 392  SYNOPSIS OF PCRE API Line 761  SYNOPSIS OF PCRE API
761         int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
762    
763    
764  PCRE API  PCRE API OVERVIEW
765    
766         PCRE has its own native API, which is described in this document. There         PCRE has its own native API, which is described in this document. There
767         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
768         expression API.  These are described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
769           Both of these APIs define a set of C function calls. A C++  wrapper  is
770         The  native  API  function  prototypes  are  defined in the header file         distributed with PCRE. It is documented in the pcrecpp page.
771         pcre.h, and on Unix systems the library itself is called libpcre.a,  so  
772         can be accessed by adding -lpcre to the command for linking an applica-         The  native  API  C  function prototypes are defined in the header file
773         tion which calls it. The header file defines the macros PCRE_MAJOR  and         pcre.h, and on Unix systems the library itself is called  libpcre.   It
774         PCRE_MINOR  to  contain  the  major  and  minor release numbers for the         can normally be accessed by adding -lpcre to the command for linking an
775         library. Applications can use these to include  support  for  different         application  that  uses  PCRE.  The  header  file  defines  the  macros
776         releases.         PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
777           bers for the library.  Applications can use these  to  include  support
778         The  functions  pcre_compile(),  pcre_study(), and pcre_exec() are used         for different releases of PCRE.
779         for compiling and matching regular expressions. A sample  program  that  
780         demonstrates  the simplest way of using them is given in the file pcre-         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
781         demo.c. The pcresample documentation describes how to run it.         pcre_exec() are used for compiling and matching regular expressions  in
782           a  Perl-compatible  manner. A sample program that demonstrates the sim-
783         There are convenience functions for extracting captured substrings from         plest way of using them is provided in the file  called  pcredemo.c  in
784         a matched subject string. They are:         the  source distribution. The pcresample documentation describes how to
785           run it.
786    
787           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
788           ble,  is  also provided. This uses a different algorithm for the match-
789           ing. The alternative algorithm finds all possible matches (at  a  given
790           point  in  the subject), and scans the subject just once. However, this
791           algorithm does not return captured substrings. A description of the two
792           matching  algorithms and their advantages and disadvantages is given in
793           the pcrematching documentation.
794    
795           In addition to the main compiling and  matching  functions,  there  are
796           convenience functions for extracting captured substrings from a subject
797           string that is matched by pcre_exec(). They are:
798    
799           pcre_copy_substring()           pcre_copy_substring()
800           pcre_copy_named_substring()           pcre_copy_named_substring()
801           pcre_get_substring()           pcre_get_substring()
802           pcre_get_named_substring()           pcre_get_named_substring()
803           pcre_get_substring_list()           pcre_get_substring_list()
804             pcre_get_stringnumber()
805             pcre_get_stringtable_entries()
806    
807         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
808         to free the memory used for extracted strings.         to free the memory used for extracted strings.
809    
810         The function pcre_maketables() is used (optionally) to build a  set  of         The  function  pcre_maketables()  is  used  to build a set of character
811         character tables in the current locale for passing to pcre_compile().         tables  in  the  current  locale   for   passing   to   pcre_compile(),
812           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
813         The  function  pcre_fullinfo()  is used to find out information about a         provided for specialist use.  Most  commonly,  no  special  tables  are
814         compiled pattern; pcre_info() is an obsolete version which returns only         passed,  in  which case internal tables that are generated when PCRE is
815         some  of  the available information, but is retained for backwards com-         built are used.
816         patibility.  The function pcre_version() returns a pointer to a  string  
817           The function pcre_fullinfo() is used to find out  information  about  a
818           compiled  pattern; pcre_info() is an obsolete version that returns only
819           some of the available information, but is retained for  backwards  com-
820           patibility.   The function pcre_version() returns a pointer to a string
821         containing the version of PCRE and its date of release.         containing the version of PCRE and its date of release.
822    
823         The  global  variables  pcre_malloc and pcre_free initially contain the         The function pcre_refcount() maintains a  reference  count  in  a  data
824         entry points of the standard  malloc()  and  free()  functions  respec-         block  containing  a compiled pattern. This is provided for the benefit
825           of object-oriented applications.
826    
827           The global variables pcre_malloc and pcre_free  initially  contain  the
828           entry  points  of  the  standard malloc() and free() functions, respec-
829         tively. PCRE calls the memory management functions via these variables,         tively. PCRE calls the memory management functions via these variables,
830         so a calling program can replace them if it  wishes  to  intercept  the         so  a  calling  program  can replace them if it wishes to intercept the
831         calls. This should be done before calling any PCRE functions.         calls. This should be done before calling any PCRE functions.
832    
833         The  global  variables  pcre_stack_malloc  and pcre_stack_free are also         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
834         indirections to memory management functions.  These  special  functions         indirections  to  memory  management functions. These special functions
835         are  used  only  when  PCRE is compiled to use the heap for remembering         are used only when PCRE is compiled to use  the  heap  for  remembering
836         data, instead of recursive function calls. This is a  non-standard  way         data, instead of recursive function calls, when running the pcre_exec()
837         of  building  PCRE,  for  use in environments that have limited stacks.         function. See the pcrebuild documentation for  details  of  how  to  do
838         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-
839         Separate  functions  are provided so that special-purpose external code         ments that have limited stacks. Because of the greater  use  of  memory
840         can be used for this case. When used, these functions are always called         management,  it  runs  more  slowly. Separate functions are provided so
841         in  a  stack-like  manner  (last obtained, first freed), and always for         that special-purpose external code can be  used  for  this  case.  When
842         memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
843           obtained, first freed), and always for memory blocks of the same  size.
844           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
845           mentation.
846    
847         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
848         by  the  caller  to  a "callout" function, which PCRE will then call at         by  the  caller  to  a "callout" function, which PCRE will then call at
# Line 455  PCRE API Line 850  PCRE API
850         pcrecallout documentation.         pcrecallout documentation.
851    
852    
853    NEWLINES
854    
855           PCRE  supports five different conventions for indicating line breaks in
856           strings: a single CR (carriage return) character, a  single  LF  (line-
857           feed) character, the two-character sequence CRLF, any of the three pre-
858           ceding, or any Unicode newline sequence. The Unicode newline  sequences
859           are  the  three just mentioned, plus the single characters VT (vertical
860           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
861           separator, U+2028), and PS (paragraph separator, U+2029).
862    
863           Each  of  the first three conventions is used by at least one operating
864           system as its standard newline sequence. When PCRE is built, a  default
865           can  be  specified.  The default default is LF, which is the Unix stan-
866           dard. When PCRE is run, the default can be overridden,  either  when  a
867           pattern is compiled, or when it is matched.
868    
869           In the PCRE documentation the word "newline" is used to mean "the char-
870           acter or pair of characters that indicate a line break". The choice  of
871           newline  convention  affects  the  handling of the dot, circumflex, and
872           dollar metacharacters, the handling of #-comments in /x mode, and, when
873           CRLF  is a recognized line ending sequence, the match position advance-
874           ment for a non-anchored pattern. The choice of newline convention  does
875           not affect the interpretation of the \n or \r escape sequences.
876    
877    
878  MULTITHREADING  MULTITHREADING
879    
880         The  PCRE  functions  can be used in multi-threading applications, with         The  PCRE  functions  can be used in multi-threading applications, with
# Line 467  MULTITHREADING Line 887  MULTITHREADING
887         at once.         at once.
888    
889    
890    SAVING PRECOMPILED PATTERNS FOR LATER USE
891    
892           The compiled form of a regular expression can be saved and re-used at a
893           later time, possibly by a different program, and even on a  host  other
894           than  the  one  on  which  it  was  compiled.  Details are given in the
895           pcreprecompile documentation. However, compiling a  regular  expression
896           with  one version of PCRE for use with a different version is not guar-
897           anteed to work and may cause crashes.
898    
899    
900  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
901    
902         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
903    
904         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-
905         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
906         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
907         tures.         tures.
908    
909         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
910         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
911         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
912         available:         available:
913    
914           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
915    
916         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-
917         able; otherwise it is set to zero.         able; otherwise it is set to zero.
918    
919             PCRE_CONFIG_UNICODE_PROPERTIES
920    
921           The  output  is  an  integer  that is set to one if support for Unicode
922           character properties is available; otherwise it is set to zero.
923    
924           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
925    
926         The output is an integer that is set to the value of the code  that  is         The output is an integer whose value specifies  the  default  character
927         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
928         return (13), and should normally be the  standard  character  for  your         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
929         operating system.         and  -1  for  ANY. The default should normally be the standard sequence
930           for your operating system.
931    
932           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
933    
934         The  output  is  an  integer that contains the number of bytes used for         The output is an integer that contains the number  of  bytes  used  for
935         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
936         4.  Larger  values  allow larger regular expressions to be compiled, at         4. Larger values allow larger regular expressions to  be  compiled,  at
937         the expense of slower matching. The default value of  2  is  sufficient         the  expense  of  slower matching. The default value of 2 is sufficient
938         for  all  but  the  most massive patterns, since it allows the compiled         for all but the most massive patterns, since  it  allows  the  compiled
939         pattern to be up to 64K in size.         pattern to be up to 64K in size.
940    
941           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
942    
943         The output is an integer that contains the threshold  above  which  the         The  output  is  an integer that contains the threshold above which the
944         POSIX  interface  uses malloc() for output vectors. Further details are         POSIX interface uses malloc() for output vectors. Further  details  are
945         given in the pcreposix documentation.         given in the pcreposix documentation.
946    
947           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
948    
949         The output is an integer that gives the default limit for the number of         The output is an integer that gives the default limit for the number of
950         internal  matching  function  calls in a pcre_exec() execution. Further         internal matching function calls in a  pcre_exec()  execution.  Further
951         details are given with pcre_exec() below.         details are given with pcre_exec() below.
952    
953             PCRE_CONFIG_MATCH_LIMIT_RECURSION
954    
955           The  output is an integer that gives the default limit for the depth of
956           recursion when calling the internal matching function in a  pcre_exec()
957           execution. Further details are given with pcre_exec() below.
958    
959           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
960    
961         The output is an integer that is set to one if  internal  recursion  is         The  output is an integer that is set to one if internal recursion when
962         implemented  by recursive function calls that use the stack to remember         running pcre_exec() is implemented by recursive function calls that use
963         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
964         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
965         recursive  function  calls.  In  this   case,   pcre_stack_malloc   and         on  the  heap  instead  of  recursive  function  calls.  In  this case,
966         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
967         avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
968    
969    
970  COMPILING A PATTERN  COMPILING A PATTERN
# Line 531  COMPILING A PATTERN Line 973  COMPILING A PATTERN
973              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
974              const unsigned char *tableptr);              const unsigned char *tableptr);
975    
976           pcre *pcre_compile2(const char *pattern, int options,
977                int *errorcodeptr,
978                const char **errptr, int *erroffset,
979                const unsigned char *tableptr);
980    
981         The function pcre_compile() is called to  compile  a  pattern  into  an         Either of the functions pcre_compile() or pcre_compile2() can be called
982         internal  form.  The pattern is a C string terminated by a binary zero,         to compile a pattern into an internal form. The only difference between
983         and is passed in the argument pattern. A pointer to a single  block  of         the  two interfaces is that pcre_compile2() has an additional argument,
984         memory  that is obtained via pcre_malloc is returned. This contains the         errorcodeptr, via which a numerical error code can be returned.
985         compiled code and related data.  The  pcre  type  is  defined  for  the  
986         returned  block;  this  is a typedef for a structure whose contents are         The pattern is a C string terminated by a binary zero, and is passed in
987         not externally defined. It is up to the caller to free the memory  when         the  pattern  argument.  A  pointer to a single block of memory that is
988         it is no longer required.         obtained via pcre_malloc is returned. This contains the  compiled  code
989           and related data. The pcre type is defined for the returned block; this
990           is a typedef for a structure whose contents are not externally defined.
991           It is up to the caller to free the memory (via pcre_free) when it is no
992           longer required.
993    
994         Although  the compiled code of a PCRE regex is relocatable, that is, it         Although the compiled code of a PCRE regex is relocatable, that is,  it
995         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
996         fully relocatable, because it contains a copy of the tableptr argument,         fully relocatable, because it may contain a copy of the tableptr  argu-
997         which is an address (see below).         ment, which is an address (see below).
998    
999         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
1000         tion.  It  should  be  zero  if  no  options  are required. Some of the         pilation. It should be zero if no options are required.  The  available
1001         options, in particular, those that are compatible with Perl,  can  also         options  are  described  below. Some of them, in particular, those that
1002         be  set and unset from within the pattern (see the detailed description         are compatible with Perl, can also be set and  unset  from  within  the
1003         of regular expressions in the  pcrepattern  documentation).  For  these         pattern  (see  the  detailed  description in the pcrepattern documenta-
1004         options,  the  contents of the options argument specifies their initial         tion). For these options, the contents of the options  argument  speci-
1005         settings at the start of compilation and execution.  The  PCRE_ANCHORED         fies  their initial settings at the start of compilation and execution.
1006         option can be set at the time of matching as well as at compile time.         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time
1007           of matching as well as at compile time.
1008    
1009         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1010         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1011         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
1012         sage. The offset from the start of the pattern to the  character  where         sage. This is a static string that is part of the library. You must not
1013         the  error  was  discovered  is  placed  in  the variable pointed to by         try to free it. The offset from the start of the pattern to the charac-
1014         erroffset, which must not be NULL. If it  is,  an  immediate  error  is         ter where the error was discovered is placed in the variable pointed to
1015           by  erroffset,  which must not be NULL. If it is, an immediate error is
1016         given.         given.
1017    
1018           If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
1019           codeptr  argument is not NULL, a non-zero error code number is returned
1020           via this argument in the event of an error. This is in addition to  the
1021           textual error message. Error codes and messages are listed below.
1022    
1023         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
1024         character tables which are built when it is compiled, using the default         character tables that are  built  when  PCRE  is  compiled,  using  the
1025         C  locale.  Otherwise,  tableptr  must  be  the  result  of  a  call to         default  C  locale.  Otherwise, tableptr must be an address that is the
1026         pcre_maketables(). See the section on locale support below.         result of a call to pcre_maketables(). This value is  stored  with  the
1027           compiled  pattern,  and used again by pcre_exec(), unless another table
1028           pointer is passed to it. For more discussion, see the section on locale
1029           support below.
1030    
1031         This code fragment shows a typical straightforward  call  to  pcre_com-         This  code  fragment  shows a typical straightforward call to pcre_com-
1032         pile():         pile():
1033    
1034           pcre *re;           pcre *re;
# Line 581  COMPILING A PATTERN Line 1041  COMPILING A PATTERN
1041             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1042             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1043    
1044         The following option bits are defined:         The following names for option bits are defined in  the  pcre.h  header
1045           file:
1046    
1047           PCRE_ANCHORED           PCRE_ANCHORED
1048    
1049         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
1050         is constrained to match only at the first matching point in the  string         is constrained to match only at the first matching point in the  string
1051         which is being searched (the "subject string"). This effect can also be         that  is being searched (the "subject string"). This effect can also be
1052         achieved by appropriate constructs in the pattern itself, which is  the         achieved by appropriate constructs in the pattern itself, which is  the
1053         only way to do it in Perl.         only way to do it in Perl.
1054    
1055             PCRE_AUTO_CALLOUT
1056    
1057           If this bit is set, pcre_compile() automatically inserts callout items,
1058           all with number 255, before each pattern item. For  discussion  of  the
1059           callout facility, see the pcrecallout documentation.
1060    
1061           PCRE_CASELESS           PCRE_CASELESS
1062    
1063         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
1064         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
1065         changed within a pattern by a (?i) option setting.         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
1066           always understands the concept of case for characters whose values  are
1067           less  than 128, so caseless matching is always possible. For characters
1068           with higher values, the concept of case is supported if  PCRE  is  com-
1069           piled  with Unicode property support, but not otherwise. If you want to
1070           use caseless matching for characters 128 and  above,  you  must  ensure
1071           that  PCRE  is  compiled  with Unicode property support as well as with
1072           UTF-8 support.
1073    
1074           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1075    
1076         If  this bit is set, a dollar metacharacter in the pattern matches only         If this bit is set, a dollar metacharacter in the pattern matches  only
1077         at the end of the subject string. Without this option,  a  dollar  also         at  the  end  of the subject string. Without this option, a dollar also
1078         matches  immediately before the final character if it is a newline (but         matches immediately before a newline at the end of the string (but  not
1079         not before any  other  newlines).  The  PCRE_DOLLAR_ENDONLY  option  is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1080         ignored if PCRE_MULTILINE is set. There is no equivalent to this option         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in
1081         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1082    
1083           PCRE_DOTALL           PCRE_DOTALL
1084    
1085         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharater in the pattern matches all char-
1086         acters,  including  newlines.  Without  it, newlines are excluded. This         acters, including those that indicate newline. Without it, a  dot  does
1087         option is equivalent to Perl's /s option, and it can be changed  within         not  match  when  the  current position is at a newline. This option is
1088         a  pattern  by  a  (?s)  option  setting. A negative class such as [^a]         equivalent to Perl's /s option, and it can be changed within a  pattern
1089         always matches a newline character, independent of the setting of  this         by  a (?s) option setting. A negative class such as [^a] always matches
1090         option.         newline characters, independent of the setting of this option.
1091    
1092             PCRE_DUPNAMES
1093    
1094           If this bit is set, names used to identify capturing  subpatterns  need
1095           not be unique. This can be helpful for certain types of pattern when it
1096           is known that only one instance of the named  subpattern  can  ever  be
1097           matched.  There  are  more details of named subpatterns below; see also
1098           the pcrepattern documentation.
1099    
1100           PCRE_EXTENDED           PCRE_EXTENDED
1101    
1102         If  this  bit  is  set,  whitespace  data characters in the pattern are         If this bit is set, whitespace  data  characters  in  the  pattern  are
1103         totally ignored except  when  escaped  or  inside  a  character  class.         totally ignored except when escaped or inside a character class. White-
1104         Whitespace  does  not  include the VT character (code 11). In addition,         space does not include the VT character (code 11). In addition, charac-
1105         characters between an unescaped # outside a  character  class  and  the         ters between an unescaped # outside a character class and the next new-
1106         next newline character, inclusive, are also ignored. This is equivalent         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1107         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-
1108         option setting.         ting.
1109    
1110         This  option  makes  it possible to include comments inside complicated         This option makes it possible to include  comments  inside  complicated
1111         patterns.  Note, however, that this applies only  to  data  characters.         patterns.   Note,  however,  that this applies only to data characters.
1112         Whitespace   characters  may  never  appear  within  special  character         Whitespace  characters  may  never  appear  within  special   character
1113         sequences in a pattern, for  example  within  the  sequence  (?(  which         sequences  in  a  pattern,  for  example  within the sequence (?( which
1114         introduces a conditional subpattern.         introduces a conditional subpattern.
1115    
1116           PCRE_EXTRA           PCRE_EXTRA
1117    
1118         This  option  was invented in order to turn on additional functionality         This option was invented in order to turn on  additional  functionality
1119         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
1120         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
1121         letter that has no special meaning  causes  an  error,  thus  reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1122         these  combinations  for  future  expansion.  By default, as in Perl, a         these combinations for future expansion. By  default,  as  in  Perl,  a
1123         backslash followed by a letter with no special meaning is treated as  a         backslash  followed by a letter with no special meaning is treated as a
1124         literal.  There  are  at  present  no other features controlled by this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1125         option. It can also be set by a (?X) option setting within a pattern.         There  are  at  present no other features controlled by this option. It
1126           can also be set by a (?X) option setting within a pattern.
1127    
1128             PCRE_FIRSTLINE
1129    
1130           If this option is set, an  unanchored  pattern  is  required  to  match
1131           before  or  at  the  first  newline  in  the subject string, though the
1132           matched text may continue over the newline.
1133    
1134           PCRE_MULTILINE           PCRE_MULTILINE
1135    
1136         By default, PCRE treats the subject string as consisting  of  a  single         By default, PCRE treats the subject string as consisting  of  a  single
1137         "line"  of  characters (even if it actually contains several newlines).         line  of characters (even if it actually contains newlines). The "start
1138         The "start of line" metacharacter (^) matches only at the start of  the         of line" metacharacter (^) matches only at the  start  of  the  string,
1139         string,  while  the "end of line" metacharacter ($) matches only at the         while  the  "end  of line" metacharacter ($) matches only at the end of
1140         end of the string, or before a terminating  newline  (unless  PCRE_DOL-         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1141         LAR_ENDONLY is set). This is the same as Perl.         is set). This is the same as Perl.
1142    
1143         When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"         When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1144         constructs match immediately following or immediately before  any  new-         constructs match immediately following or immediately  before  internal
1145         line  in the subject string, respectively, as well as at the very start         newlines  in  the  subject string, respectively, as well as at the very
1146         and end. This is equivalent to Perl's /m option, and it can be  changed         start and end. This is equivalent to Perl's /m option, and  it  can  be
1147         within a pattern by a (?m) option setting. If there are no "\n" charac-         changed within a pattern by a (?m) option setting. If there are no new-
1148         ters in a subject string, or no occurrences of ^ or  $  in  a  pattern,         lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1149         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1150    
1151             PCRE_NEWLINE_CR
1152             PCRE_NEWLINE_LF
1153             PCRE_NEWLINE_CRLF
1154             PCRE_NEWLINE_ANYCRLF
1155             PCRE_NEWLINE_ANY
1156    
1157           These  options  override the default newline definition that was chosen
1158           when PCRE was built. Setting the first or the second specifies  that  a
1159           newline  is  indicated  by a single character (CR or LF, respectively).
1160           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1161           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1162           that any of the three preceding sequences should be recognized. Setting
1163           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1164           recognized. The Unicode newline sequences are the three just mentioned,
1165           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1166           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1167           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1168           UTF-8 mode.
1169    
1170           The newline setting in the  options  word  uses  three  bits  that  are
1171           treated as a number, giving eight possibilities. Currently only six are
1172           used (default plus the five values above). This means that if  you  set
1173           more  than one newline option, the combination may or may not be sensi-
1174           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1175           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1176           cause an error.
1177    
1178           The only time that a line break is specially recognized when  compiling
1179           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1180           character class is encountered. This indicates  a  comment  that  lasts
1181           until  after the next line break sequence. In other circumstances, line
1182           break  sequences  are  treated  as  literal  data,   except   that   in
1183           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1184           and are therefore ignored.
1185    
1186           The newline option that is set at compile time becomes the default that
1187           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1188    
1189           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1190    
1191         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
1192         theses in the pattern. Any opening parenthesis that is not followed  by         theses  in the pattern. Any opening parenthesis that is not followed by
1193         ?  behaves as if it were followed by ?: but named parentheses can still         ? behaves as if it were followed by ?: but named parentheses can  still
1194         be used for capturing (and they acquire  numbers  in  the  usual  way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1195         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1196    
1197           PCRE_UNGREEDY           PCRE_UNGREEDY
1198    
1199         This  option  inverts  the "greediness" of the quantifiers so that they         This option inverts the "greediness" of the quantifiers  so  that  they
1200         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
1201         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
1202         within the pattern.         within the pattern.
1203    
1204           PCRE_UTF8           PCRE_UTF8
1205    
1206         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
1207         strings  of  UTF-8 characters instead of single-byte character strings.         strings of UTF-8 characters instead of single-byte  character  strings.
1208         However, it is available only if PCRE has been built to  include  UTF-8         However,  it is available only when PCRE is built to include UTF-8 sup-
1209         support.  If  not, the use of this option provokes an error. Details of         port. If not, the use of this option provokes an error. Details of  how
1210         how this option changes the behaviour of PCRE are given in the  section         this  option  changes the behaviour of PCRE are given in the section on
1211         on UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1212    
1213           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1214    
1215         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
1216         automatically checked. If an invalid UTF-8 sequence of bytes is  found,         automatically  checked. If an invalid UTF-8 sequence of bytes is found,
1217         pcre_compile()  returns an error. If you already know that your pattern         pcre_compile() returns an error. If you already know that your  pattern
1218         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
1219         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
1220         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
1221         your  program  to  crash.  Note that there is a similar option for sup-         your program to crash.  Note that this option can  also  be  passed  to
1222         pressing the checking of subject strings passed to pcre_exec().         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1223           ing of subject strings.
1224    
1225    
1226    COMPILATION ERROR CODES
1227    
1228           The following table lists the error  codes  than  may  be  returned  by
1229           pcre_compile2(),  along with the error messages that may be returned by
1230           both compiling functions. As PCRE has developed, some error codes  have
1231           fallen out of use. To avoid confusion, they have not been re-used.
1232    
1233              0  no error
1234              1  \ at end of pattern
1235              2  \c at end of pattern
1236              3  unrecognized character follows \
1237              4  numbers out of order in {} quantifier
1238              5  number too big in {} quantifier
1239              6  missing terminating ] for character class
1240              7  invalid escape sequence in character class
1241              8  range out of order in character class
1242              9  nothing to repeat
1243             10  [this code is not in use]
1244             11  internal error: unexpected repeat
1245             12  unrecognized character after (?
1246             13  POSIX named classes are supported only within a class
1247             14  missing )
1248             15  reference to non-existent subpattern
1249             16  erroffset passed as NULL
1250             17  unknown option bit(s) set
1251             18  missing ) after comment
1252             19  [this code is not in use]
1253             20  regular expression too large
1254             21  failed to get memory
1255             22  unmatched parentheses
1256             23  internal error: code overflow
1257             24  unrecognized character after (?<
1258             25  lookbehind assertion is not fixed length
1259             26  malformed number or name after (?(
1260             27  conditional group contains more than two branches
1261             28  assertion expected after (?(
1262             29  (?R or (?digits must be followed by )
1263             30  unknown POSIX class name
1264             31  POSIX collating elements are not supported
1265             32  this version of PCRE is not compiled with PCRE_UTF8 support
1266             33  [this code is not in use]
1267             34  character value in \x{...} sequence is too large
1268             35  invalid condition (?(0)
1269             36  \C not allowed in lookbehind assertion
1270             37  PCRE does not support \L, \l, \N, \U, or \u
1271             38  number after (?C is > 255
1272             39  closing ) for (?C expected
1273             40  recursive call could loop indefinitely
1274             41  unrecognized character after (?P
1275             42  syntax error in subpattern name (missing terminator)
1276             43  two named subpatterns have the same name
1277             44  invalid UTF-8 string
1278             45  support for \P, \p, and \X has not been compiled
1279             46  malformed \P or \p sequence
1280             47  unknown property name after \P or \p
1281             48  subpattern name is too long (maximum 32 characters)
1282             49  too many named subpatterns (maximum 10,000)
1283             50  repeated subpattern is too long
1284             51  octal value is greater than \377 (not in UTF-8 mode)
1285             52  internal error: overran compiling workspace
1286             53   internal  error:  previously-checked  referenced  subpattern not
1287           found
1288             54  DEFINE group contains more than one branch
1289             55  repeating a DEFINE group is not allowed
1290             56  inconsistent NEWLINE options"
1291    
1292    
1293  STUDYING A PATTERN  STUDYING A PATTERN
1294    
1295         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1296              const char **errptr);              const char **errptr);
1297    
1298         When a pattern is going to be used several times, it is worth  spending         If a compiled pattern is going to be used several times,  it  is  worth
1299         more  time  analyzing it in order to speed up the time taken for match-         spending more time analyzing it in order to speed up the time taken for
1300         ing. The function pcre_study() takes a pointer to a compiled pattern as         matching. The function pcre_study() takes a pointer to a compiled  pat-
1301         its first argument. If studing the pattern produces additional informa-         tern as its first argument. If studying the pattern produces additional
1302         tion that will help speed up matching, pcre_study() returns  a  pointer         information that will help speed up matching,  pcre_study()  returns  a
1303         to  a  pcre_extra  block,  in  which the study_data field points to the         pointer  to a pcre_extra block, in which the study_data field points to
1304         results of the study.         the results of the study.
1305    
1306         The returned value from  a  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1307         pcre_exec().  However,  the pcre_extra block also contains other fields         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1308         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
1309         described  below.  If  studying  the pattern does not produce any addi-         described below in the section on matching a pattern.
1310         tional information, pcre_study() returns NULL. In that circumstance, if  
1311         the  calling  program  wants  to  pass  some  of  the  other  fields to         If  studying  the  pattern  does not produce any additional information
1312         pcre_exec(), it must set up its own pcre_extra block.         pcre_study() returns NULL. In that circumstance, if the calling program
1313           wants  to  pass  any of the other fields to pcre_exec(), it must set up
1314           its own pcre_extra block.
1315    
1316         The second argument contains option bits. At present,  no  options  are         The second argument of pcre_study() contains option bits.  At  present,
1317         defined for pcre_study(), and this argument should always be zero.         no options are defined, and this argument should always be zero.
1318    
1319         The  third argument for pcre_study() is a pointer for an error message.         The  third argument for pcre_study() is a pointer for an error message.
1320         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1321         points  to  is set to NULL. Otherwise it points to a textual error mes-         points  to  is  set  to NULL. Otherwise it is set to point to a textual
1322         sage. You should therefore test the error pointer for NULL after  call-         error message. This is a static string that is part of the library. You
1323         ing pcre_study(), to be sure that it has run successfully.         must  not  try  to  free it. You should test the error pointer for NULL
1324           after calling pcre_study(), to be sure that it has run successfully.
1325    
1326         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1327    
# Line 735  STUDYING A PATTERN Line 1332  STUDYING A PATTERN
1332             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1333    
1334         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1335         that do not have a single fixed starting character. A bitmap of  possi-         that  do not have a single fixed starting character. A bitmap of possi-
1336         ble starting characters is created.         ble starting bytes is created.
1337    
1338    
1339  LOCALE SUPPORT  LOCALE SUPPORT
1340    
1341         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1342         letters, digits, or whatever, by reference to a  set  of  tables.  When         letters,  digits, or whatever, by reference to a set of tables, indexed
1343         running  in UTF-8 mode, this applies only to characters with codes less         by character value. When running in UTF-8 mode, this  applies  only  to
1344         than 256. The library contains a default set of tables that is  created         characters  with  codes  less than 128. Higher-valued codes never match
1345         in  the  default  C locale when PCRE is compiled. This is used when the         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
1346         final argument of pcre_compile() is NULL, and is  sufficient  for  many         with  Unicode  character property support. The use of locales with Uni-
1347         applications.         code is discouraged. If you are handling characters with codes  greater
1348           than  128, you should either use UTF-8 and Unicode, or use locales, but
1349         An alternative set of tables can, however, be supplied. Such tables are         not try to mix the two.
1350         built by calling the pcre_maketables() function,  which  has  no  argu-  
1351         ments,  in  the  relevant  locale.  The  result  can  then be passed to         PCRE contains an internal set of tables that are used  when  the  final
1352         pcre_compile() as often as necessary. For example,  to  build  and  use         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1353         tables that are appropriate for the French locale (where accented char-         applications.  Normally, the internal tables recognize only ASCII char-
1354         acters with codes greater than 128 are treated as letters), the follow-         acters. However, when PCRE is built, it is possible to cause the inter-
1355         ing code could be used:         nal tables to be rebuilt in the default "C" locale of the local system,
1356           which may cause them to be different.
1357    
1358           The  internal tables can always be overridden by tables supplied by the
1359           application that calls PCRE. These may be created in a different locale
1360           from  the  default.  As more and more applications change to using Uni-
1361           code, the need for this locale support is expected to die away.
1362    
1363           External tables are built by calling  the  pcre_maketables()  function,
1364           which  has no arguments, in the relevant locale. The result can then be
1365           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1366           example,  to  build  and use tables that are appropriate for the French
1367           locale (where accented characters with  values  greater  than  128  are
1368           treated as letters), the following code could be used:
1369    
1370           setlocale(LC_CTYPE, "fr");           setlocale(LC_CTYPE, "fr_FR");
1371           tables = pcre_maketables();           tables = pcre_maketables();
1372           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1373    
1374         The  tables  are  built in memory that is obtained via pcre_malloc. The         The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1375         pointer that is passed to pcre_compile is saved with the compiled  pat-         if you are using Windows, the name for the French locale is "french".
1376         tern, and the same tables are used via this pointer by pcre_study() and  
1377         pcre_exec(). Thus, for any single pattern,  compilation,  studying  and         When pcre_maketables() runs, the tables are built  in  memory  that  is
1378         matching  all  happen in the same locale, but different patterns can be         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1379         compiled in different locales. It is  the  caller's  responsibility  to         that the memory containing the tables remains available for as long  as
1380         ensure  that  the memory containing the tables remains available for as         it is needed.
1381         long as it is needed.  
1382           The pointer that is passed to pcre_compile() is saved with the compiled
1383           pattern, and the same tables are used via this pointer by  pcre_study()
1384           and normally also by pcre_exec(). Thus, by default, for any single pat-
1385           tern, compilation, studying and matching all happen in the same locale,
1386           but different patterns can be compiled in different locales.
1387    
1388           It  is  possible to pass a table pointer or NULL (indicating the use of
1389           the internal tables) to pcre_exec(). Although  not  intended  for  this
1390           purpose,  this facility could be used to match a pattern in a different
1391           locale from the one in which it was compiled. Passing table pointers at
1392           run time is discussed below in the section on matching a pattern.
1393    
1394    
1395  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
# Line 776  INFORMATION ABOUT A PATTERN Line 1397  INFORMATION ABOUT A PATTERN
1397         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1398              int what, void *where);              int what, void *where);
1399    
1400         The pcre_fullinfo() function returns information about a compiled  pat-         The  pcre_fullinfo() function returns information about a compiled pat-
1401         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1402         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1403    
1404         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1405         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
1406         the pattern was not studied. The third argument specifies  which  piece         the  pattern  was not studied. The third argument specifies which piece
1407         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
1408         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
1409         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1410    
1411           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 792  INFORMATION ABOUT A PATTERN Line 1413  INFORMATION ABOUT A PATTERN
1413           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1414           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1415    
1416         Here  is a typical call of pcre_fullinfo(), to obtain the length of the         The "magic number" is placed at the start of each compiled  pattern  as
1417         compiled pattern:         an  simple check against passing an arbitrary memory pointer. Here is a
1418           typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1419           pattern:
1420    
1421           int rc;           int rc;
1422           unsigned long int length;           size_t length;
1423           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1424             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1425             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1426             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1427             &length);         /* where to put the data */             &length);         /* where to put the data */
1428    
1429         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
1430         are as follows:         are as follows:
1431    
1432           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1433    
1434         Return  the  number  of  the highest back reference in the pattern. The         Return the number of the highest back reference  in  the  pattern.  The
1435         fourth argument should point to an int variable. Zero  is  returned  if         fourth  argument  should  point to an int variable. Zero is returned if
1436         there are no back references.         there are no back references.
1437    
1438           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1439    
1440         Return  the  number of capturing subpatterns in the pattern. The fourth         Return the number of capturing subpatterns in the pattern.  The  fourth
1441         argument should point to an int variable.         argument should point to an int variable.
1442    
1443             PCRE_INFO_DEFAULT_TABLES
1444    
1445           Return  a pointer to the internal default character tables within PCRE.
1446           The fourth argument should point to an unsigned char *  variable.  This
1447           information call is provided for internal use by the pcre_study() func-
1448           tion. External callers can cause PCRE to use  its  internal  tables  by
1449           passing a NULL table pointer.
1450    
1451           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1452    
1453         Return information about the first byte of any matched  string,  for  a         Return  information  about  the first byte of any matched string, for a
1454         non-anchored    pattern.    (This    option    used    to   be   called         non-anchored pattern. The fourth argument should point to an int  vari-
1455         PCRE_INFO_FIRSTCHAR; the old name is  still  recognized  for  backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1456         compatibility.)         is still recognized for backwards compatibility.)
1457    
1458         If  there  is  a  fixed  first  byte,  e.g.  from  a  pattern  such  as         If there is a fixed first byte, for example, from  a  pattern  such  as
1459         (cat|cow|coyote), it is returned in the integer pointed  to  by  where.         (cat|cow|coyote), its value is returned. Otherwise, if either
        Otherwise, if either  
1460    
1461         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1462         branch starts with "^", or         branch starts with "^", or
# Line 846  INFORMATION ABOUT A PATTERN Line 1476  INFORMATION ABOUT A PATTERN
1476         returned. The fourth argument should point to an unsigned char *  vari-         returned. The fourth argument should point to an unsigned char *  vari-
1477         able.         able.
1478    
1479             PCRE_INFO_JCHANGED
1480    
1481           Return  1  if the (?J) option setting is used in the pattern, otherwise
1482           0. The fourth argument should point to an int variable. The (?J) inter-
1483           nal option setting changes the local PCRE_DUPNAMES value.
1484    
1485           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1486    
1487         Return  the  value of the rightmost literal byte that must exist in any         Return  the  value of the rightmost literal byte that must exist in any
# Line 862  INFORMATION ABOUT A PATTERN Line 1498  INFORMATION ABOUT A PATTERN
1498    
1499         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1500         ses. The names are just an additional way of identifying the  parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1501         ses,  which still acquire a number. A caller that wants to extract data         ses, which still acquire numbers. Several convenience functions such as
1502         from a named subpattern must convert the name to a number in  order  to         pcre_get_named_substring() are provided for  extracting  captured  sub-
1503         access  the  correct  pointers  in  the  output  vector (described with         strings  by  name. It is also possible to extract the data directly, by
1504         pcre_exec() below). In order to do this, it must first use these  three         first converting the name to a number in order to  access  the  correct
1505         values to obtain the name-to-number mapping table for the pattern.         pointers in the output vector (described with pcre_exec() below). To do
1506           the conversion, you need  to  use  the  name-to-number  map,  which  is
1507           described by these three values.
1508    
1509         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1510         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
# Line 876  INFORMATION ABOUT A PATTERN Line 1514  INFORMATION ABOUT A PATTERN
1514         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1515         sis,  most  significant byte first. The rest of the entry is the corre-         sis,  most  significant byte first. The rest of the entry is the corre-
1516         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1517         For  example,  consider  the following pattern (assume PCRE_EXTENDED is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1518         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1519           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1520           ignored):
1521    
1522           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1523           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1524    
1525         There are four named subpatterns, so the table has  four  entries,  and         There are four named subpatterns, so the table has  four  entries,  and
1526         each  entry  in the table is eight bytes long. The table is as follows,         each  entry  in the table is eight bytes long. The table is as follows,
1527         with non-printing bytes shows in hex, and undefined bytes shown as ??:         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1528           as ??:
1529    
1530           00 01 d  a  t  e  00 ??           00 01 d  a  t  e  00 ??
1531           00 05 d  a  y  00 ?? ??           00 05 d  a  y  00 ?? ??
1532           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1533           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1534    
1535         When writing code to extract data from named subpatterns, remember that         When  writing  code  to  extract  data from named subpatterns using the
1536         the length of each entry may be different for each compiled pattern.         name-to-number map, remember that the length of the entries  is  likely
1537           to be different for each compiled pattern.
1538    
1539             PCRE_INFO_OKPARTIAL
1540    
1541           Return  1 if the pattern can be used for partial matching, otherwise 0.
1542           The fourth argument should point to an int  variable.  The  pcrepartial
1543           documentation  lists  the restrictions that apply to patterns when par-
1544           tial matching is used.
1545    
1546           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1547    
1548         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
1549         fourth argument should point to an unsigned long  int  variable.  These         fourth  argument  should  point to an unsigned long int variable. These
1550         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1551         by any top-level option settings within the pattern itself.         by any top-level option settings within the pattern itself.
1552    
1553         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
1554         alternatives begin with one of the following:         alternatives begin with one of the following:
1555    
1556           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 915  INFORMATION ABOUT A PATTERN Line 1564  INFORMATION ABOUT A PATTERN
1564    
1565           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1566    
1567         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
1568         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
1569         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
1570         size_t variable.         size_t variable.
1571    
1572           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1573    
1574         Returns  the  size of the data block pointed to by the study_data field         Return the size of the data block pointed to by the study_data field in
1575         in 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
1576         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
1577         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
1578         variable.         variable.
1579    
1580    
# Line 933  OBSOLETE INFO FUNCTION Line 1582  OBSOLETE INFO FUNCTION
1582    
1583         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1584    
1585         The  pcre_info()  function is now obsolete because its interface is too         The pcre_info() function is now obsolete because its interface  is  too
1586         restrictive to return all the available data about a compiled  pattern.         restrictive  to return all the available data about a compiled pattern.
1587         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1588         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-
1589         lowing negative numbers:         lowing negative numbers:
1590    
1591           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1592           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1593    
1594         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
1595         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
1596         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1597    
1598         If  the  pattern  is  not anchored and the firstcharptr argument is not         If the pattern is not anchored and the  firstcharptr  argument  is  not
1599         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
1600         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1601    
1602    
1603  MATCHING A PATTERN  REFERENCE COUNTS
1604    
1605           int pcre_refcount(pcre *code, int adjust);
1606    
1607           The pcre_refcount() function is used to maintain a reference  count  in
1608           the data block that contains a compiled pattern. It is provided for the
1609           benefit of applications that  operate  in  an  object-oriented  manner,
1610           where different parts of the application may be using the same compiled
1611           pattern, but you want to free the block when they are all done.
1612    
1613           When a pattern is compiled, the reference count field is initialized to
1614           zero.   It is changed only by calling this function, whose action is to
1615           add the adjust value (which may be positive or  negative)  to  it.  The
1616           yield of the function is the new value. However, the value of the count
1617           is constrained to lie between 0 and 65535, inclusive. If the new  value
1618           is outside these limits, it is forced to the appropriate limit value.
1619    
1620           Except  when it is zero, the reference count is not correctly preserved
1621           if a pattern is compiled on one host and then  transferred  to  a  host
1622           whose byte-order is different. (This seems a highly unlikely scenario.)
1623    
1624    
1625    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1626    
1627         int pcre_exec(const pcre *code, const pcre_extra *extra,         int pcre_exec(const pcre *code, const pcre_extra *extra,
1628              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1629              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1630    
1631         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
1632         pre-compiled pattern, which is passed in the code argument. If the pat-         compiled  pattern, which is passed in the code argument. If the pattern
1633         tern  has been studied, the result of the study should be passed in the         has been studied, the result of the study should be passed in the extra
1634         extra argument.         argument.  This  function is the main matching facility of the library,
1635           and it operates in a Perl-like manner. For specialist use there is also
1636           an  alternative matching function, which is described below in the sec-
1637           tion about the pcre_dfa_exec() function.
1638    
1639           In most applications, the pattern will have been compiled (and  option-
1640           ally  studied)  in the same process that calls pcre_exec(). However, it
1641           is possible to save compiled patterns and study data, and then use them
1642           later  in  different processes, possibly even on different hosts. For a
1643           discussion about this, see the pcreprecompile documentation.
1644    
1645         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
1646    
# Line 973  MATCHING A PATTERN Line 1653  MATCHING A PATTERN
1653             11,             /* the length of the subject string */             11,             /* the length of the subject string */
1654             0,              /* start at offset 0 in the subject */             0,              /* start at offset 0 in the subject */
1655             0,              /* default options */             0,              /* default options */
1656             ovector,        /* vector for substring information */             ovector,        /* vector of integers for substring information */
1657             30);            /* number of elements in the vector */             30);            /* number of elements (NOT size in bytes) */
1658    
1659       Extra data for pcre_exec()
1660    
1661         If the extra argument is not NULL, it must point to a  pcre_extra  data         If the extra argument is not NULL, it must point to a  pcre_extra  data
1662         block.  The pcre_study() function returns such a block (when it doesn't         block.  The pcre_study() function returns such a block (when it doesn't
1663         return NULL), but you can also create one for yourself, and pass  addi-         return NULL), but you can also create one for yourself, and pass  addi-
1664         tional information in it. The fields in the block are as follows:         tional  information  in it. The pcre_extra block contains the following
1665           fields (not necessarily in this order):
1666    
1667           unsigned long int flags;           unsigned long int flags;
1668           void *study_data;           void *study_data;
1669           unsigned long int match_limit;           unsigned long int match_limit;
1670             unsigned long int match_limit_recursion;
1671           void *callout_data;           void *callout_data;
1672             const unsigned char *tables;
1673    
1674         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
1675         are set. The flag bits are:         are set. The flag bits are:
1676    
1677           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1678           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1679             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1680           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1681             PCRE_EXTRA_TABLES
1682    
1683         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
1684         the  pcre_extra  block  that is returned by pcre_study(), together with         the pcre_extra block that is returned by  pcre_study(),  together  with
1685         the appropriate flag bit. You should not set this yourself, but you can         the appropriate flag bit. You should not set this yourself, but you may
1686         add to the block by setting the other fields.         add to the block by setting the other fields  and  their  corresponding
1687           flag bits.
1688    
1689         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
1690         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
1691         match,  but  which  have  a very large number of possibilities in their         match,  but  which  have  a very large number of possibilities in their
1692         search trees. The classic  example  is  the  use  of  nested  unlimited         search trees. The classic  example  is  the  use  of  nested  unlimited
1693         repeats. Internally, PCRE uses a function called match() which it calls         repeats.
1694         repeatedly (sometimes recursively). The limit is imposed on the  number  
1695         of  times  this function is called during a match, which has the effect         Internally,  PCRE uses a function called match() which it calls repeat-
1696         of limiting the amount of recursion  and  backtracking  that  can  take         edly (sometimes recursively). The limit set by match_limit  is  imposed
1697         place.  For  patterns that are not anchored, the count starts from zero         on  the  number  of times this function is called during a match, which
1698           has the effect of limiting the amount of  backtracking  that  can  take
1699           place. For patterns that are not anchored, the count restarts from zero
1700         for each position in the subject string.         for each position in the subject string.
1701    
1702         The default limit for the library can be set when PCRE  is  built;  the         The default value for the limit can be set  when  PCRE  is  built;  the
1703         default  default  is 10 million, which handles all but the most extreme         default  default  is 10 million, which handles all but the most extreme
1704         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases. You can override the default  by  suppling  pcre_exec()  with  a
1705         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra     block    in    which    match_limit    is    set,    and
1706         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is
1707         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1708    
1709           The  match_limit_recursion field is similar to match_limit, but instead
1710           of limiting the total number of times that match() is called, it limits
1711           the  depth  of  recursion. The recursion depth is a smaller number than
1712           the total number of calls, because not all calls to match() are  recur-
1713           sive.  This limit is of use only if it is set smaller than match_limit.
1714    
1715           Limiting the recursion depth limits the amount of  stack  that  can  be
1716           used, or, when PCRE has been compiled to use memory on the heap instead
1717           of the stack, the amount of heap memory that can be used.
1718    
1719           The default value for match_limit_recursion can be  set  when  PCRE  is
1720           built;  the  default  default  is  the  same  value  as the default for
1721           match_limit. You can override the default by suppling pcre_exec()  with
1722           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1723           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1724           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1725    
1726         The  pcre_callout  field is used in conjunction with the "callout" fea-         The  pcre_callout  field is used in conjunction with the "callout" fea-
1727         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1728    
1729         The PCRE_ANCHORED option can be passed in the options  argument,  whose         The tables field  is  used  to  pass  a  character  tables  pointer  to
1730         unused  bits  must  be zero. This limits pcre_exec() to matching at the         pcre_exec();  this overrides the value that is stored with the compiled
1731         first matching position.  However,  if  a  pattern  was  compiled  with         pattern. A non-NULL value is stored with the compiled pattern  only  if
1732         PCRE_ANCHORED,  or turned out to be anchored by virtue of its contents,         custom  tables  were  supplied to pcre_compile() via its tableptr argu-
1733         it cannot be made unachored at matching time.         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1734           PCRE's  internal  tables  to be used. This facility is helpful when re-
1735         When PCRE_UTF8 was set at compile time, the validity of the subject  as         using patterns that have been saved after compiling  with  an  external
1736         a  UTF-8  string is automatically checked, and the value of startoffset         set  of  tables,  because  the  external tables might be at a different
1737         is also checked to ensure that it points to the start of a UTF-8  char-         address when pcre_exec() is called. See the  pcreprecompile  documenta-
1738         acter.  If  an  invalid  UTF-8  sequence of bytes is found, pcre_exec()         tion for a discussion of saving compiled patterns for later use.
1739         returns  the  error  PCRE_ERROR_BADUTF8.  If  startoffset  contains  an  
1740         invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.     Option bits for pcre_exec()
1741    
1742         If  you  already  know that your subject is valid, and you want to skip         The  unused  bits of the options argument for pcre_exec() must be zero.
1743         these   checks   for   performance   reasons,   you   can    set    the         The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
1744         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1745         do this for the second and subsequent calls to pcre_exec() if  you  are         PCRE_PARTIAL.
        making  repeated  calls  to  find  all  the matches in a single subject  
        string. However, you should be  sure  that  the  value  of  startoffset  
        points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is  
        set, the effect of passing an invalid UTF-8 string as a subject,  or  a  
        value  of startoffset that does not point to the start of a UTF-8 char-  
        acter, is undefined. Your program may crash.  
1746    
1747         There are also three further options that can be set only  at  matching           PCRE_ANCHORED
1748         time:  
1749           The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
1750           matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
1751           turned out to be anchored by virtue of its contents, it cannot be  made
1752           unachored at matching time.
1753    
1754             PCRE_NEWLINE_CR
1755             PCRE_NEWLINE_LF
1756             PCRE_NEWLINE_CRLF
1757             PCRE_NEWLINE_ANYCRLF
1758             PCRE_NEWLINE_ANY
1759    
1760           These  options  override  the  newline  definition  that  was chosen or
1761           defaulted when the pattern was compiled. For details, see the  descrip-
1762           tion  of  pcre_compile()  above.  During  matching,  the newline choice
1763           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1764           ters.  It may also alter the way the match position is advanced after a
1765           match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,
1766           PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY is set, and a match attempt
1767           fails when the current position is at a CRLF sequence, the match  posi-
1768           tion  is  advanced by two characters instead of one, in other words, to
1769           after the CRLF.
1770    
1771           PCRE_NOTBOL           PCRE_NOTBOL
1772    
1773         The  first  character  of the string is not the beginning of a line, so         This option specifies that first character of the subject string is not
1774         the circumflex metacharacter should not match before it.  Setting  this         the  beginning  of  a  line, so the circumflex metacharacter should not
1775         without  PCRE_MULTILINE  (at  compile  time) causes circumflex never to         match before it. Setting this without PCRE_MULTILINE (at compile  time)
1776         match.         causes  circumflex  never to match. This option affects only the behav-
1777           iour of the circumflex metacharacter. It does not affect \A.
1778    
1779           PCRE_NOTEOL           PCRE_NOTEOL
1780    
1781         The end of the string is not the end of a line, so the dollar metachar-         This option specifies that the end of the subject string is not the end
1782         acter  should  not  match  it  nor (except in multiline mode) a newline         of  a line, so the dollar metacharacter should not match it nor (except
1783         immediately before it. Setting this without PCRE_MULTILINE (at  compile         in multiline mode) a newline immediately before it. Setting this  with-
1784         time) causes dollar never to match.         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1785           option affects only the behaviour of the dollar metacharacter. It  does
1786           not affect \Z or \z.
1787    
1788           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1789    
# Line 1078  MATCHING A PATTERN Line 1803  MATCHING A PATTERN
1803         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()
1804         function,  and  when  using  the /g modifier. It is possible to emulate         function,  and  when  using  the /g modifier. It is possible to emulate
1805         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
1806         again at the same offset with PCRE_NOTEMPTY set, and then if that fails         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1807         by advancing the starting offset (see below)  and  trying  an  ordinary         if that fails by advancing the starting offset (see below)  and  trying
1808         match again.         an ordinary match again. There is some code that demonstrates how to do
1809           this in the pcredemo.c sample program.
1810         The  subject string is passed to pcre_exec() as a pointer in subject, a  
1811         length in length, and a starting byte offset in startoffset. Unlike the           PCRE_NO_UTF8_CHECK
1812         pattern  string,  the  subject  may contain binary zero bytes. When the  
1813         starting offset is zero, the search for a match starts at the beginning         When PCRE_UTF8 is set at compile time, the validity of the subject as a
1814         of the subject, and this is by far the most common case.         UTF-8  string is automatically checked when pcre_exec() is subsequently
1815           called.  The value of startoffset is also checked  to  ensure  that  it
1816         If the pattern was compiled with the PCRE_UTF8 option, the subject must         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence
1817         be a sequence of bytes that is a valid UTF-8 string, and  the  starting         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1818         offset  must point to the beginning of a UTF-8 character. If an invalid         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is
1819         UTF-8 string or offset is passed, an error  (either  PCRE_ERROR_BADUTF8         returned.
1820         or   PCRE_ERROR_BADUTF8_OFFSET)   is   returned,   unless   the  option  
1821         PCRE_NO_UTF8_CHECK is set,  in  which  case  PCRE's  behaviour  is  not         If you already know that your subject is valid, and you  want  to  skip
1822         defined.         these    checks    for   performance   reasons,   you   can   set   the
1823           PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
1824           do  this  for the second and subsequent calls to pcre_exec() if you are
1825           making repeated calls to find all  the  matches  in  a  single  subject
1826           string.  However,  you  should  be  sure  that the value of startoffset
1827           points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
1828           set,  the  effect of passing an invalid UTF-8 string as a subject, or a
1829           value of startoffset that does not point to the start of a UTF-8  char-
1830           acter, is undefined. Your program may crash.
1831    
1832             PCRE_PARTIAL
1833    
1834           This  option  turns  on  the  partial  matching feature. If the subject
1835           string fails to match the pattern, but at some point during the  match-
1836           ing  process  the  end of the subject was reached (that is, the subject
1837           partially matches the pattern and the failure to  match  occurred  only
1838           because  there were not enough subject characters), pcre_exec() returns
1839           PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1840           used,  there  are restrictions on what may appear in the pattern. These
1841           are discussed in the pcrepartial documentation.
1842    
1843       The string to be matched by pcre_exec()
1844    
1845           The subject string is passed to pcre_exec() as a pointer in subject,  a
1846           length  in  length, and a starting byte offset in startoffset. In UTF-8
1847           mode, the byte offset must point to the start  of  a  UTF-8  character.
1848           Unlike  the  pattern string, the subject may contain binary zero bytes.
1849           When the starting offset is zero, the search for a match starts at  the
1850           beginning of the subject, and this is by far the most common case.
1851    
1852         A  non-zero  starting offset is useful when searching for another match         A  non-zero  starting offset is useful when searching for another match
1853         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-
# Line 1111  MATCHING A PATTERN Line 1864  MATCHING A PATTERN
1864         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the  remainder  of  the  subject,  namely  "issipi", it does not match,
1865         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
1866         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
1867         string again, but with startoffset  set  to  4,  it  finds  the  second         string again, but with startoffset set to 4, it finds the second occur-
1868         occurrence  of  "iss"  because  it  is able to look behind the starting         rence  of "iss" because it is able to look behind the starting point to
1869         point to discover that it is preceded by a letter.         discover that it is preceded by a letter.
1870    
1871         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,
1872         one  attempt  to match at the given offset is tried. This can only suc-         one attempt to match at the given offset is made. This can only succeed
1873         ceed if the pattern does not require the match to be at  the  start  of         if the pattern does not require the match to be at  the  start  of  the
1874         the subject.         subject.
1875    
1876       How pcre_exec() returns captured substrings
1877    
1878         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
1879         addition, further substrings from the subject  may  be  picked  out  by         addition, further substrings from the subject  may  be  picked  out  by
# Line 1130  MATCHING A PATTERN Line 1885  MATCHING A PATTERN
1885    
1886         Captured  substrings are returned to the caller via a vector of integer         Captured  substrings are returned to the caller via a vector of integer
1887         offsets whose address is passed in ovector. The number of  elements  in         offsets whose address is passed in ovector. The number of  elements  in
1888         the vector is passed in ovecsize. The first two-thirds of the vector is         the  vector is passed in ovecsize, which must be a non-negative number.
1889         used to pass back captured substrings, each substring using a  pair  of         Note: this argument is NOT the size of ovector in bytes.
        integers.  The  remaining  third  of the vector is used as workspace by  
        pcre_exec() while matching capturing subpatterns, and is not  available  
        for  passing  back  information.  The  length passed in ovecsize should  
        always be a multiple of three. If it is not, it is rounded down.  
   
        When a match has been successful, information about captured substrings  
        is returned in pairs of integers, starting at the beginning of ovector,  
        and continuing up to two-thirds of its length at the  most.  The  first  
        element of a pair is set to the offset of the first character in a sub-  
        string, and the second is set to the  offset  of  the  first  character  
        after  the  end  of  a  substring. The first pair, ovector[0] and ovec-  
        tor[1], identify the portion of  the  subject  string  matched  by  the  
        entire  pattern.  The next pair is used for the first capturing subpat-  
        tern, and so on. The value returned by pcre_exec()  is  the  number  of  
        pairs  that  have  been set. If there are no capturing subpatterns, the  
        return value from a successful match is 1,  indicating  that  just  the  
        first pair of offsets has been set.  
1890    
1891         Some  convenience  functions  are  provided for extracting the captured         The first two-thirds of the vector is used to pass back  captured  sub-
1892         substrings as separate strings. These are described  in  the  following         strings,  each  substring using a pair of integers. The remaining third
1893         section.         of the vector is used as workspace by pcre_exec() while  matching  cap-
1894           turing  subpatterns, and is not available for passing back information.
1895         It  is  possible  for  an capturing subpattern number n+1 to match some         The length passed in ovecsize should always be a multiple of three.  If
1896         part of the subject when subpattern n has not been  used  at  all.  For         it is not, it is rounded down.
1897         example, if the string "abc" is matched against the pattern (a|(z))(bc)  
1898         subpatterns 1 and 3 are matched, but 2 is not. When this happens,  both         When  a  match  is successful, information about captured substrings is
1899         offset values corresponding to the unused subpattern are set to -1.         returned in pairs of integers, starting at the  beginning  of  ovector,
1900           and  continuing  up  to two-thirds of its length at the most. The first
1901           element of a pair is set to the offset of the first character in a sub-
1902           string,  and  the  second  is  set to the offset of the first character
1903           after the end of a substring. The  first  pair,  ovector[0]  and  ovec-
1904           tor[1],  identify  the  portion  of  the  subject string matched by the
1905           entire pattern. The next pair is used for the first  capturing  subpat-
1906           tern, and so on. The value returned by pcre_exec() is one more than the
1907           highest numbered pair that has been set. For example, if two substrings
1908           have  been captured, the returned value is 3. If there are no capturing
1909           subpatterns, the return value from a successful match is 1,  indicating
1910           that just the first pair of offsets has been set.
1911    
1912         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1913         of the string that it matched that gets returned.         of the string that it matched that is returned.
1914    
1915         If the vector is too small to hold all the captured substrings,  it  is         If the vector is too small to hold all the captured substring  offsets,
1916         used as far as possible (up to two-thirds of its length), and the func-         it is used as far as possible (up to two-thirds of its length), and the
1917         tion returns a value of zero. In particular, if the  substring  offsets         function returns a value of zero. In particular, if the substring  off-
1918         are  not  of interest, pcre_exec() may be called with ovector passed as         sets are not of interest, pcre_exec() may be called with ovector passed
1919         NULL and ovecsize as zero. However, if the pattern contains back refer-         as NULL and ovecsize as zero. However, if  the  pattern  contains  back
1920         ences  and  the  ovector  isn't big enough to remember the related sub-         references  and  the  ovector is not big enough to remember the related
1921         strings, PCRE has to get additional memory  for  use  during  matching.         substrings, PCRE has to get additional memory for use during  matching.
1922         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1923    
1924         Note  that  pcre_info() can be used to find out how many capturing sub-         The  pcre_info()  function  can  be used to find out how many capturing
1925         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
1926         that  will  allow for n captured substrings, in addition to the offsets         ovector  that  will allow for n captured substrings, in addition to the
1927         of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
1928    
1929           It is possible for capturing subpattern number n+1 to match  some  part
1930           of the subject when subpattern n has not been used at all. For example,
1931           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1932           return from the function is 4, and subpatterns 1 and 3 are matched, but
1933           2 is not. When this happens, both values in  the  offset  pairs  corre-
1934           sponding to unused subpatterns are set to -1.
1935    
1936           Offset  values  that correspond to unused subpatterns at the end of the
1937           expression are also set to -1. For example,  if  the  string  "abc"  is
1938           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1939           matched. The return from the function is 2, because  the  highest  used
1940           capturing subpattern number is 1. However, you can refer to the offsets
1941           for the second and third capturing subpatterns if  you  wish  (assuming
1942           the vector is large enough, of course).
1943    
1944           Some  convenience  functions  are  provided for extracting the captured
1945           substrings as separate strings. These are described below.
1946    
1947       Error return values from pcre_exec()
1948    
1949         If pcre_exec() fails, it returns a negative number. The  following  are         If pcre_exec() fails, it returns a negative number. The  following  are
1950         defined in the header file:         defined in the header file:
# Line 1196  MATCHING A PATTERN Line 1965  MATCHING A PATTERN
1965           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
1966    
1967         PCRE stores a 4-byte "magic number" at the start of the compiled  code,         PCRE stores a 4-byte "magic number" at the start of the compiled  code,
1968         to  catch  the case when it is passed a junk pointer. This is the error         to catch the case when it is passed a junk pointer and to detect when a
1969         it gives when the magic number isn't present.         pattern that was compiled in an environment of one endianness is run in
1970           an  environment  with the other endianness. This is the error that PCRE
1971           gives when the magic number is not present.
1972    
1973           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1974    
1975         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1976         compiled  pattern.  This  error  could be caused by a bug in PCRE or by         compiled  pattern.  This  error  could be caused by a bug in PCRE or by
# Line 1211  MATCHING A PATTERN Line 1982  MATCHING A PATTERN
1982         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
1983         PCRE gets a block of memory at the start of matching to  use  for  this         PCRE gets a block of memory at the start of matching to  use  for  this
1984         purpose.  If the call via pcre_malloc() fails, this error is given. The         purpose.  If the call via pcre_malloc() fails, this error is given. The
1985         memory is freed at the end of matching.         memory is automatically freed at the end of matching.
1986    
1987           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
1988    
# Line 1221  MATCHING A PATTERN Line 1992  MATCHING A PATTERN
1992    
1993           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
1994    
1995         The recursion and backtracking limit, as specified by  the  match_limit         The backtracking limit, as specified by  the  match_limit  field  in  a
1996         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         pcre_extra  structure  (or  defaulted) was reached. See the description
1997         description above.         above.
1998    
1999           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2000    
# Line 1242  MATCHING A PATTERN Line 2013  MATCHING A PATTERN
2013         value of startoffset did not point to the beginning of a UTF-8  charac-         value of startoffset did not point to the beginning of a UTF-8  charac-
2014         ter.         ter.
2015    
2016             PCRE_ERROR_PARTIAL        (-12)
2017    
2018           The  subject  string did not match, but it did match partially. See the
2019           pcrepartial documentation for details of partial matching.
2020    
2021             PCRE_ERROR_BADPARTIAL     (-13)
2022    
2023           The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
2024           items  that are not supported for partial matching. See the pcrepartial
2025           documentation for details of partial matching.
2026    
2027             PCRE_ERROR_INTERNAL       (-14)
2028    
2029           An unexpected internal error has occurred. This error could  be  caused
2030           by a bug in PCRE or by overwriting of the compiled pattern.
2031    
2032             PCRE_ERROR_BADCOUNT       (-15)
2033    
2034           This  error is given if the value of the ovecsize argument is negative.
2035    
2036             PCRE_ERROR_RECURSIONLIMIT (-21)
2037    
2038           The internal recursion limit, as specified by the match_limit_recursion
2039           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2040           description above.
2041    
2042             PCRE_ERROR_NULLWSLIMIT    (-22)
2043    
2044           When a group that can match an empty  substring  is  repeated  with  an
2045           unbounded  upper  limit, the subject position at the start of the group
2046           must be remembered, so that a test for an empty string can be made when
2047           the  end  of the group is reached. Some workspace is required for this;
2048           if it runs out, this error is given.
2049    
2050             PCRE_ERROR_BADNEWLINE     (-23)
2051    
2052           An invalid combination of PCRE_NEWLINE_xxx options was given.
2053    
2054           Error numbers -16 to -20 are not used by pcre_exec().
2055    
2056    
2057  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2058    
# Line 1256  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2067  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2067         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2068              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2069    
2070         Captured  substrings  can  be  accessed  directly  by using the offsets         Captured substrings can be  accessed  directly  by  using  the  offsets
2071         returned by pcre_exec() in  ovector.  For  convenience,  the  functions         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2072         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2073         string_list() are provided for extracting captured substrings  as  new,         string_list()  are  provided for extracting captured substrings as new,
2074         separate,  zero-terminated strings. These functions identify substrings         separate, zero-terminated strings. These functions identify  substrings
2075         by number. The next section describes functions  for  extracting  named         by  number.  The  next section describes functions for extracting named
2076         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2077         extracted and has a further zero added on the end, but  the  result  is  
2078         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2079           a  further zero added on the end, but the result is not, of course, a C
2080           string.  However, you can process such a string  by  referring  to  the
2081           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2082           string().  Unfortunately, the interface to pcre_get_substring_list() is
2083           not  adequate for handling strings containing binary zeros, because the
2084           end of the final string is not independently indicated.
2085    
2086         The  first  three  arguments  are the same for all three of these func-         The first three arguments are the same for all  three  of  these  func-
2087         tions: subject is the subject string which has just  been  successfully         tions:  subject  is  the subject string that has just been successfully
2088         matched, ovector is a pointer to the vector of integer offsets that was         matched, ovector is a pointer to the vector of integer offsets that was
2089         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2090         were  captured  by  the match, including the substring that matched the         were captured by the match, including the substring  that  matched  the
2091         entire regular expression. This is the value returned by  pcre_exec  if         entire regular expression. This is the value returned by pcre_exec() if
2092         it  is greater than zero. If pcre_exec() returned zero, indicating that         it is greater than zero. If pcre_exec() returned zero, indicating  that
2093         it ran out of space in ovector, the value passed as stringcount  should         it  ran out of space in ovector, the value passed as stringcount should
2094         be the size of the vector divided by three.         be the number of elements in the vector divided by three.
2095    
2096         The  functions pcre_copy_substring() and pcre_get_substring() extract a         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2097         single substring, whose number is given as  stringnumber.  A  value  of         single  substring,  whose  number  is given as stringnumber. A value of
2098         zero  extracts  the  substring  that  matched the entire pattern, while         zero extracts the substring that matched the  entire  pattern,  whereas
2099         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2100         string(),  the  string  is  placed  in buffer, whose length is given by         string(), the string is placed in buffer,  whose  length  is  given  by
2101         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2102         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2103         The yield of the function is the length of the  string,  not  including         The  yield  of  the function is the length of the string, not including
2104         the terminating zero, or one of         the terminating zero, or one of these error codes:
2105    
2106           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2107    
2108         The  buffer  was too small for pcre_copy_substring(), or the attempt to         The buffer was too small for pcre_copy_substring(), or the  attempt  to
2109         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2110    
2111           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2112    
2113         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2114    
2115         The pcre_get_substring_list()  function  extracts  all  available  sub-         The  pcre_get_substring_list()  function  extracts  all  available sub-
2116         strings  and  builds  a list of pointers to them. All this is done in a         strings and builds a list of pointers to them. All this is  done  in  a
2117         single block of memory which is obtained via pcre_malloc.  The  address         single block of memory that is obtained via pcre_malloc. The address of
2118         of the memory block is returned via listptr, which is also the start of         the memory block is returned via listptr, which is also  the  start  of
2119         the list of string pointers. The end of the list is marked  by  a  NULL         the  list  of  string pointers. The end of the list is marked by a NULL
2120         pointer. The yield of the function is zero if all went well, or         pointer. The yield of the function is zero if all  went  well,  or  the
2121           error code
2122    
2123           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2124    
# Line 1313  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2131  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2131         string  by inspecting the appropriate offset in ovector, which is nega-         string  by inspecting the appropriate offset in ovector, which is nega-
2132         tive for unset substrings.         tive for unset substrings.
2133    
2134         The    two    convenience    functions    pcre_free_substring()     and         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2135         pcre_free_substring_list() can be used to free the memory returned by a         string_list()  can  be  used  to free the memory returned by a previous
2136         previous call  of  pcre_get_substring()  or  pcre_get_substring_list(),         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2137         respectively. They do nothing more than call the function pointed to by         tively.  They  do  nothing  more  than  call the function pointed to by
2138         pcre_free, which of course could be called directly from a  C  program.         pcre_free, which of course could be called directly from a  C  program.
2139         However,  PCRE is used in some situations where it is linked via a spe-         However,  PCRE is used in some situations where it is linked via a spe-
2140         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2141         pcre_free  directly;  it is for these cases that the functions are pro-         pcre_free  directly;  it is for these cases that the functions are pro-
2142         vided.         vided.
2143    
2144    
2145  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2146    
2147           int pcre_get_stringnumber(const pcre *code,
2148                const char *name);
2149    
2150         int pcre_copy_named_substring(const pcre *code,         int pcre_copy_named_substring(const pcre *code,
2151              const char *subject, int *ovector,              const char *subject, int *ovector,
2152              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2153              char *buffer, int buffersize);              char *buffer, int buffersize);
2154    
        int pcre_get_stringnumber(const pcre *code,  
             const char *name);  
   
2155         int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2156              const char *subject, int *ovector,              const char *subject, int *ovector,
2157              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2158              const char **stringptr);              const char **stringptr);
2159    
2160         To extract a substring by name, you first have to find associated  num-         To extract a substring by name, you first have to find associated  num-
2161         ber.  This  can  be  done by calling pcre_get_stringnumber(). The first         ber.  For example, for this pattern
2162         argument is the compiled pattern, and the second is the name. For exam-  
2163         ple, for this pattern           (a+)b(?<xxx>\d+)...
2164    
2165           ab(?<xxx>\d+)...         the number of the subpattern called "xxx" is 2. If the name is known to
2166           be unique (PCRE_DUPNAMES was not set), you can find the number from the
2167         the  number  of the subpattern called "xxx" is 1. Given the number, you         name by calling pcre_get_stringnumber(). The first argument is the com-
2168         can then extract the substring directly, or use one  of  the  functions         piled pattern, and the second is the name. The yield of the function is
2169         described  in the previous section. For convenience, there are also two         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2170         functions that do the whole job.         subpattern of that name.
2171    
2172           Given the number, you can extract the substring directly, or use one of
2173           the functions described in the previous section. For convenience, there
2174           are also two functions that do the whole job.
2175    
2176         Most   of   the   arguments    of    pcre_copy_named_substring()    and         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2177         pcre_get_named_substring() are the same as those for the functions that         pcre_get_named_substring()  are  the  same  as  those for the similarly
2178         extract by number, and so are not re-described here. There are just two         named functions that extract by number. As these are described  in  the
2179         differences.         previous  section,  they  are not re-described here. There are just two
2180           differences:
2181    
2182         First,  instead  of a substring number, a substring name is given. Sec-         First, instead of a substring number, a substring name is  given.  Sec-
2183         ond, there is an extra argument, given at the start, which is a pointer         ond, there is an extra argument, given at the start, which is a pointer
2184         to  the compiled pattern. This is needed in order to gain access to the         to the compiled pattern. This is needed in order to gain access to  the
2185         name-to-number translation table.         name-to-number translation table.
2186    
2187         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2188         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2189         ate.         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2190           behaviour may not be what you want (see the next section).
2191    
2192    
2193    DUPLICATE SUBPATTERN NAMES
2194    
2195           int pcre_get_stringtable_entries(const pcre *code,
2196                const char *name, char **first, char **last);
2197    
2198           When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2199           subpatterns  are  not  required  to  be unique. Normally, patterns with
2200           duplicate names are such that in any one match, only one of  the  named
2201           subpatterns  participates. An example is shown in the pcrepattern docu-
2202           mentation. When duplicates are present, pcre_copy_named_substring() and
2203           pcre_get_named_substring()  return the first substring corresponding to
2204           the given name that is set.  If  none  are  set,  an  empty  string  is
2205           returned.  The pcre_get_stringnumber() function returns one of the num-
2206           bers that are associated with the name, but it is not defined which  it
2207           is.
2208    
2209           If  you want to get full details of all captured substrings for a given
2210           name, you must use  the  pcre_get_stringtable_entries()  function.  The
2211           first argument is the compiled pattern, and the second is the name. The
2212           third and fourth are pointers to variables which  are  updated  by  the
2213           function. After it has run, they point to the first and last entries in
2214           the name-to-number table  for  the  given  name.  The  function  itself
2215           returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2216           there are none. The format of the table is described above in the  sec-
2217           tion  entitled  Information  about  a  pattern.  Given all the relevant
2218           entries for the name, you can extract each of their numbers, and  hence
2219           the captured data, if any.
2220    
2221    
2222    FINDING ALL POSSIBLE MATCHES
2223    
2224           The  traditional  matching  function  uses a similar algorithm to Perl,
2225           which stops when it finds the first match, starting at a given point in
2226           the  subject.  If you want to find all possible matches, or the longest
2227           possible match, consider using the alternative matching  function  (see
2228           below)  instead.  If you cannot use the alternative function, but still
2229           need to find all possible matches, you can kludge it up by  making  use
2230           of the callout facility, which is described in the pcrecallout documen-
2231           tation.
2232    
2233  Last updated: 09 December 2003         What you have to do is to insert a callout right at the end of the pat-
2234  Copyright (c) 1997-2003 University of Cambridge.         tern.   When your callout function is called, extract and save the cur-
2235  -----------------------------------------------------------------------------         rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2236           backtrack  and  try other alternatives. Ultimately, when it runs out of
2237           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2238    
 PCRE(3)                                                                PCRE(3)  
2239    
2240    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2241    
2242           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2243                const char *subject, int length, int startoffset,
2244                int options, int *ovector, int ovecsize,
2245                int *workspace, int wscount);
2246    
2247           The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2248           against  a  compiled pattern, using a matching algorithm that scans the
2249           subject string just once, and does not backtrack.  This  has  different
2250           characteristics  to  the  normal  algorithm, and is not compatible with
2251           Perl. Some of the features of PCRE patterns are not  supported.  Never-
2252           theless,  there are times when this kind of matching can be useful. For
2253           a discussion of the two matching algorithms, see the pcrematching docu-
2254           mentation.
2255    
2256           The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2257           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2258           ent  way,  and  this is described below. The other common arguments are
2259           used in the same way as for pcre_exec(), so their  description  is  not
2260           repeated here.
2261    
2262           The  two  additional  arguments provide workspace for the function. The
2263           workspace vector should contain at least 20 elements. It  is  used  for
2264           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2265           workspace will be needed for patterns and subjects where  there  are  a
2266           lot of potential matches.
2267    
2268           Here is an example of a simple call to pcre_dfa_exec():
2269    
2270             int rc;
2271             int ovector[10];
2272             int wspace[20];
2273             rc = pcre_dfa_exec(
2274               re,             /* result of pcre_compile() */
2275               NULL,           /* we didn't study the pattern */
2276               "some string",  /* the subject string */
2277               11,             /* the length of the subject string */
2278               0,              /* start at offset 0 in the subject */
2279               0,              /* default options */
2280               ovector,        /* vector of integers for substring information */
2281               10,             /* number of elements (NOT size in bytes) */
2282               wspace,         /* working space vector */
2283               20);            /* number of elements (NOT size in bytes) */
2284    
2285       Option bits for pcre_dfa_exec()
2286    
2287           The  unused  bits  of  the options argument for pcre_dfa_exec() must be
2288           zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2289           LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
2290           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2291           three of these are the same as for pcre_exec(), so their description is
2292           not repeated here.
2293    
2294             PCRE_PARTIAL
2295    
2296           This has the same general effect as it does for  pcre_exec(),  but  the
2297           details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for
2298           pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into
2299           PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have
2300           been no complete matches, but there is still at least one matching pos-
2301           sibility.  The portion of the string that provided the partial match is
2302           set as the first matching string.
2303    
2304             PCRE_DFA_SHORTEST
2305    
2306           Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2307           stop as soon as it has found one match. Because of the way the alterna-
2308           tive algorithm works, this is necessarily the shortest  possible  match
2309           at the first possible matching point in the subject string.
2310    
2311             PCRE_DFA_RESTART
2312    
2313           When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and
2314           returns a partial match, it is possible to call it  again,  with  addi-
2315           tional  subject  characters,  and have it continue with the same match.
2316           The PCRE_DFA_RESTART option requests this action; when it is  set,  the
2317           workspace  and wscount options must reference the same vector as before
2318           because data about the match so far is left in  them  after  a  partial
2319           match.  There  is  more  discussion of this facility in the pcrepartial
2320           documentation.
2321    
2322       Successful returns from pcre_dfa_exec()
2323    
2324           When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-
2325           string in the subject. Note, however, that all the matches from one run
2326           of the function start at the same point in  the  subject.  The  shorter
2327           matches  are all initial substrings of the longer matches. For example,
2328           if the pattern
2329    
2330             <.*>
2331    
2332           is matched against the string
2333    
2334             This is <something> <something else> <something further> no more
2335    
2336           the three matched strings are
2337    
2338             <something>
2339             <something> <something else>
2340             <something> <something else> <something further>
2341    
2342           On success, the yield of the function is a number  greater  than  zero,
2343           which  is  the  number of matched substrings. The substrings themselves
2344           are returned in ovector. Each string uses two elements;  the  first  is
2345           the  offset  to  the start, and the second is the offset to the end. In
2346           fact, all the strings have the same start  offset.  (Space  could  have
2347           been  saved by giving this only once, but it was decided to retain some
2348           compatibility with the way pcre_exec() returns data,  even  though  the
2349           meaning of the strings is different.)
2350    
2351           The strings are returned in reverse order of length; that is, the long-
2352           est matching string is given first. If there were too many  matches  to
2353           fit  into ovector, the yield of the function is zero, and the vector is
2354           filled with the longest matches.
2355    
2356       Error returns from pcre_dfa_exec()
2357    
2358           The pcre_dfa_exec() function returns a negative number when  it  fails.
2359           Many  of  the  errors  are  the  same as for pcre_exec(), and these are
2360           described above.  There are in addition the following errors  that  are
2361           specific to pcre_dfa_exec():
2362    
2363             PCRE_ERROR_DFA_UITEM      (-16)
2364    
2365           This  return is given if pcre_dfa_exec() encounters an item in the pat-
2366           tern that it does not support, for instance, the use of \C  or  a  back
2367           reference.
2368    
2369             PCRE_ERROR_DFA_UCOND      (-17)
2370    
2371           This  return  is  given  if pcre_dfa_exec() encounters a condition item
2372           that uses a back reference for the condition, or a test  for  recursion
2373           in a specific group. These are not supported.
2374    
2375             PCRE_ERROR_DFA_UMLIMIT    (-18)
2376    
2377           This  return  is given if pcre_dfa_exec() is called with an extra block
2378           that contains a setting of the match_limit field. This is not supported
2379           (it is meaningless).
2380    
2381             PCRE_ERROR_DFA_WSSIZE     (-19)
2382    
2383           This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the
2384           workspace vector.
2385    
2386             PCRE_ERROR_DFA_RECURSE    (-20)
2387    
2388           When a recursive subpattern is processed, the matching  function  calls
2389           itself  recursively,  using  private vectors for ovector and workspace.
2390           This error is given if the output vector  is  not  large  enough.  This
2391           should be extremely rare, as a vector of size 1000 is used.
2392    
2393    
2394    SEE ALSO
2395    
2396           pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2397           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
2398    
2399    
2400    AUTHOR
2401    
2402           Philip Hazel
2403           University Computing Service
2404           Cambridge CB2 3QH, England.
2405    
2406    
2407    REVISION
2408    
2409           Last updated: 04 June 2007
2410           Copyright (c) 1997-2007 University of Cambridge.
2411    ------------------------------------------------------------------------------
2412    
2413    
2414    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2415    
2416    
2417  NAME  NAME
2418         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2419    
2420    
2421  PCRE CALLOUTS  PCRE CALLOUTS
2422    
2423         int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
# Line 1394  PCRE CALLOUTS Line 2436  PCRE CALLOUTS
2436    
2437           (?C1)abc(?C2)def           (?C1)abc(?C2)def
2438    
2439         During matching, when PCRE reaches a callout point (and pcre_callout is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2440         set), the external function is called. Its only argument is  a  pointer         called, PCRE automatically  inserts  callouts,  all  with  number  255,
2441         to a pcre_callout block. This contains the following variables:         before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2442           used with the pattern
2443    
2444             A(\d{2}|--)
2445    
2446           it is processed as if it were
2447    
2448           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2449    
2450           Notice that there is a callout before and after  each  parenthesis  and
2451           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2452           progress of pattern matching. The pcretest command has an  option  that
2453           sets  automatic callouts; when it is used, the output indicates how the
2454           pattern is matched. This is useful information when you are  trying  to
2455           optimize the performance of a particular pattern.
2456    
2457    
2458    MISSING CALLOUTS
2459    
2460           You  should  be  aware  that,  because of optimizations in the way PCRE
2461           matches patterns, callouts sometimes do not happen. For example, if the
2462           pattern is
2463    
2464             ab(?C4)cd
2465    
2466           PCRE knows that any matching string must contain the letter "d". If the
2467           subject string is "abyz", the lack of "d" means that  matching  doesn't
2468           ever  start,  and  the  callout is never reached. However, with "abyd",
2469           though the result is still no match, the callout is obeyed.
2470    
2471    
2472    THE CALLOUT INTERFACE
2473    
2474           During matching, when PCRE reaches a callout point, the external  func-
2475           tion  defined by pcre_callout is called (if it is set). This applies to
2476           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2477           only  argument  to  the callout function is a pointer to a pcre_callout
2478           block. This structure contains the following fields:
2479    
2480           int          version;           int          version;
2481           int          callout_number;           int          callout_number;
# Line 1408  PCRE CALLOUTS Line 2487  PCRE CALLOUTS
2487           int          capture_top;           int          capture_top;
2488           int          capture_last;           int          capture_last;
2489           void        *callout_data;           void        *callout_data;
2490             int          pattern_position;
2491             int          next_item_length;
2492    
2493         The  version  field  is an integer containing the version number of the         The version field is an integer containing the version  number  of  the
2494         block format. The current version  is  zero.  The  version  number  may         block  format. The initial version was 0; the current version is 1. The
2495         change  in  future if additional fields are added, but the intention is         version number will change again in future  if  additional  fields  are
2496         never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2497    
2498         The callout_number field contains the number of the  callout,  as  com-         The callout_number field contains the number of the  callout,  as  com-
2499         piled into the pattern (that is, the number after ?C).         piled  into  the pattern (that is, the number after ?C for manual call-
2500           outs, and 255 for automatically generated callouts).
2501    
2502         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
2503         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
2504         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
2505         way as for extracting substrings after a match has completed.         substrings  that  have  been  matched  so  far,  in the same way as for
2506           extracting substrings after a match has completed. For  pcre_dfa_exec()
2507           this field is not useful.
2508    
2509         The subject and subject_length fields contain copies  the  values  that         The subject and subject_length fields contain copies of the values that
2510         were passed to pcre_exec().         were passed to pcre_exec().
2511    
2512         The  start_match  field contains the offset within the subject at which         The start_match field normally contains the offset within  the  subject
2513         the current match attempt started. If the pattern is not anchored,  the         at  which  the  current  match  attempt started. However, if the escape
2514         callout  function  may  be  called several times for different starting         sequence \K has been encountered, this value is changed to reflect  the
2515         points.         modified  starting  point.  If the pattern is not anchored, the callout
2516           function may be called several times from the same point in the pattern
2517           for different starting points in the subject.
2518    
2519         The current_position field contains the offset within  the  subject  of         The  current_position  field  contains the offset within the subject of
2520         the current match pointer.         the current match pointer.
2521    
2522         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
2523         numbered  captured  substring  so  far.  If  no  substrings  have  been         one  more than the number of the highest numbered captured substring so
2524         captured, the value of capture_top is one.         far. If no substrings have been captured, the value of  capture_top  is
2525           one.  This  is always the case when pcre_dfa_exec() is used, because it
2526         The  capture_last  field  contains the number of the most recently cap-         does not support captured substrings.
2527         tured substring.  
2528           The capture_last field contains the number of the  most  recently  cap-
2529           tured  substring. If no substrings have been captured, its value is -1.
2530           This is always the case when pcre_dfa_exec() is used.
2531    
2532         The callout_data field contains a value that is passed  to  pcre_exec()         The callout_data field contains a value that is passed  to  pcre_exec()
2533         by  the  caller specifically so that it can be passed back in callouts.         or  pcre_dfa_exec() specifically so that it can be passed back in call-
2534         It is passed in the pcre_callout field of the  pcre_extra  data  struc-         outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2535         ture.  If  no  such  data  was  passed,  the value of callout_data in a         structure.  If  no such data was passed, the value of callout_data in a
2536         pcre_callout block is NULL. There is a description  of  the  pcre_extra         pcre_callout block is NULL. There is a description  of  the  pcre_extra
2537         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2538    
2539           The  pattern_position field is present from version 1 of the pcre_call-
2540           out structure. It contains the offset to the next item to be matched in
2541           the pattern string.
2542    
2543           The  next_item_length field is present from version 1 of the pcre_call-
2544           out structure. It contains the length of the next item to be matched in
2545           the  pattern  string. When the callout immediately precedes an alterna-
2546           tion bar, a closing parenthesis, or the end of the pattern, the  length
2547           is  zero.  When the callout precedes an opening parenthesis, the length
2548           is that of the entire subpattern.
2549    
2550           The pattern_position and next_item_length fields are intended  to  help
2551           in  distinguishing between different automatic callouts, which all have
2552           the same callout number. However, they are set for all callouts.
2553    
2554    
2555  RETURN VALUES  RETURN VALUES
2556    
2557         The callout function returns an integer. If the value is zero, matching         The external callout function returns an integer to PCRE. If the  value
2558         proceeds as normal. If the value is greater than zero,  matching  fails         is  zero,  matching  proceeds  as  normal. If the value is greater than
2559         at the current point, but backtracking to test other possibilities goes         zero, matching fails at the current point, but  the  testing  of  other
2560         ahead, just as if a lookahead assertion had failed.  If  the  value  is         matching possibilities goes ahead, just as if a lookahead assertion had
2561         less  than  zero,  the  match is abandoned, and pcre_exec() returns the         failed. If the value is less than zero, the  match  is  abandoned,  and
2562         value.         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2563    
2564         Negative  values  should  normally  be   chosen   from   the   set   of         Negative   values   should   normally   be   chosen  from  the  set  of
2565         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2566         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2567         reserved  for  use  by callout functions; it will never be used by PCRE         reserved for use by callout functions; it will never be  used  by  PCRE
2568         itself.         itself.
2569    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2570    
2571  PCRE(3)                                                                PCRE(3)  AUTHOR
2572    
2573           Philip Hazel
2574           University Computing Service
2575           Cambridge CB2 3QH, England.
2576    
2577    
2578    REVISION
2579    
2580           Last updated: 29 May 2007
2581           Copyright (c) 1997-2007 University of Cambridge.
2582    ------------------------------------------------------------------------------
2583    
2584    
2585    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2586    
2587    
2588  NAME  NAME
2589         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2590    
 DIFFERENCES FROM PERL  
2591    
2592         This  document describes the differences in the ways that PCRE and Perl  DIFFERENCES BETWEEN PCRE AND PERL
        handle regular expressions. The differences  described  here  are  with  
        respect to Perl 5.8.  
2593    
2594         1.  PCRE does not have full UTF-8 support. Details of what it does have         This  document describes the differences in the ways that PCRE and Perl
2595         are given in the section on UTF-8 support in the main pcre page.         handle regular expressions. The differences described here  are  mainly
2596           with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2597           tures that are expected to be in the forthcoming Perl 5.10.
2598    
2599           1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2600           of  what  it does have are given in the section on UTF-8 support in the
2601           main pcre page.
2602    
2603         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2604         permits  them,  but they do not mean what you might think. For example,         permits  them,  but they do not mean what you might think. For example,
# Line 1498  DIFFERENCES FROM PERL Line 2614  DIFFERENCES FROM PERL
2614    
2615         4. Though binary zero characters are supported in the  subject  string,         4. Though binary zero characters are supported in the  subject  string,
2616         they are not allowed in a pattern string because it is passed as a nor-         they are not allowed in a pattern string because it is passed as a nor-
2617         mal C string, terminated by zero. The escape sequence "\0" can be  used         mal C string, terminated by zero. The escape sequence \0 can be used in
2618         in the pattern to represent a binary zero.         the pattern to represent a binary zero.
2619    
2620         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2621         \U, \P, \p, \N, and \X. In fact these are implemented by Perl's general         \U, and \N. In fact these are implemented by Perl's general string-han-
2622         string-handling and are not part of its pattern matching engine. If any         dling  and are not part of its pattern matching engine. If any of these
2623         of these are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
2624    
2625           6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2626           is  built  with Unicode character property support. The properties that
2627           can be tested with \p and \P are limited to the general category  prop-
2628           erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2629           derived properties Any and L&.
2630    
2631         6. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2632         ters  in  between  are  treated as literals. This is slightly different         ters  in  between  are  treated as literals. This is slightly different
2633         from Perl in that $ and @ are  also  handled  as  literals  inside  the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2634         quotes.  In Perl, they cause variable interpolation (but of course PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
# Line 1522  DIFFERENCES FROM PERL Line 2644  DIFFERENCES FROM PERL
2644         The \Q...\E sequence is recognized both inside  and  outside  character         The \Q...\E sequence is recognized both inside  and  outside  character
2645         classes.         classes.
2646    
2647         7. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2648         constructions. However, there is some experimental support  for  recur-         constructions. However, there is support for recursive  patterns.  This
2649         sive  patterns  using the non-Perl items (?R), (?number) and (?P>name).         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2650         Also, the PCRE "callout" feature allows  an  external  function  to  be         "callout" feature allows an external function to be called during  pat-
2651         called during pattern matching.         tern matching. See the pcrecallout documentation for details.
2652    
2653           9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2654           always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2655           unlike Perl.
2656    
2657         8.  There  are some differences that are concerned with the settings of         10.  There are some differences that are concerned with the settings of
2658         captured strings when part of  a  pattern  is  repeated.  For  example,         captured strings when part of  a  pattern  is  repeated.  For  example,
2659         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2660         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2661    
2662         9. PCRE  provides  some  extensions  to  the  Perl  regular  expression         11. PCRE provides some extensions to the Perl regular expression facil-
2663         facilities:         ities.   Perl  5.10  will  include new features that are not in earlier
2664           versions, some of which (such as named parentheses) have been  in  PCRE
2665           for some time. This list is with respect to Perl 5.10:
2666    
2667         (a)  Although  lookbehind  assertions  must match fixed length strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2668         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
# Line 1544  DIFFERENCES FROM PERL Line 2672  DIFFERENCES FROM PERL
2672         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2673    
2674         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2675         cial meaning is faulted.         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2676           ignored. (Perl can be made to issue a warning.)
2677    
2678         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2679         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
2680         lowed by a question mark they are.         lowed by a question mark they are.
2681    
2682         (e)  PCRE_ANCHORED  can  be used to force a pattern to be tried only at         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
2683         the first matching position in the subject string.         tried only at the first matching position in the subject string.
2684    
2685         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and  PCRE_NO_AUTO_CAP-         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2686         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2687    
2688         (g)  The (?R), (?number), and (?P>name) constructs allows for recursive         (g) The callout facility is PCRE-specific.
        pattern matching (Perl can do  this  using  the  (?p{code})  construct,  
        which PCRE cannot support.)  
2689    
2690         (h)  PCRE supports named capturing substrings, using the Python syntax.         (h) The partial matching facility is PCRE-specific.
2691    
2692         (i) PCRE supports the possessive quantifier  "++"  syntax,  taken  from         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2693         Sun's Java package.         even on different hosts that have the other endianness.
2694    
2695         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2696           different way and is not Perl-compatible.
2697    
        (k) The callout facility is PCRE-specific.  
2698    
2699  Last updated: 09 December 2003  AUTHOR
2700  Copyright (c) 1997-2003 University of Cambridge.  
2701  -----------------------------------------------------------------------------         Philip Hazel
2702           University Computing Service
2703           Cambridge CB2 3QH, England.
2704    
 PCRE(3)                                                                PCRE(3)  
2705    
2706    REVISION
2707    
2708           Last updated: 06 March 2007
2709           Copyright (c) 1997-2007 University of Cambridge.
2710    ------------------------------------------------------------------------------
2711    
2712    
2713    PCREPATTERN(3)                                                  PCREPATTERN(3)
2714    
2715    
2716  NAME  NAME
2717         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2718    
2719    
2720  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2721    
2722         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax  and semantics of the regular expressions supported by PCRE
2723         are described below. Regular expressions are also described in the Perl         are described below. Regular expressions are also described in the Perl
2724         documentation  and in a number of other books, some of which have copi-         documentation  and  in  a  number  of books, some of which have copious
2725         ous examples. Jeffrey Friedl's "Mastering  Regular  Expressions",  pub-         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published
2726         lished  by  O'Reilly, covers them in great detail. The description here         by  O'Reilly, covers regular expressions in great detail. This descrip-
2727         is intended as reference documentation.         tion of PCRE's regular expressions is intended as reference material.
2728    
2729         The basic operation of PCRE is on strings of bytes. However,  there  is         The original operation of PCRE was on strings of  one-byte  characters.
2730         also  support for UTF-8 character strings. To use this support you must         However,  there is now also support for UTF-8 character strings. To use
2731         build PCRE to include UTF-8 support, and then call pcre_compile()  with         this, you must build PCRE to  include  UTF-8  support,  and  then  call
2732         the  PCRE_UTF8  option.  How  this affects the pattern matching is men-         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern
2733         tioned in several places below. There is also a summary of  UTF-8  fea-         matching is mentioned in several places below. There is also a  summary
2734         tures in the section on UTF-8 support in the main pcre page.         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
2735           page.
2736    
2737           The remainder of this document discusses the  patterns  that  are  sup-
2738           ported  by  PCRE when its main matching function, pcre_exec(), is used.
2739           From  release  6.0,   PCRE   offers   a   second   matching   function,
2740           pcre_dfa_exec(),  which matches using a different algorithm that is not
2741           Perl-compatible. Some of the features discussed below are not available
2742           when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2743           alternative function, and how it differs from the normal function,  are
2744           discussed in the pcrematching page.
2745    
2746    
2747    CHARACTERS AND METACHARACTERS
2748    
2749         A  regular  expression  is  a pattern that is matched against a subject         A  regular  expression  is  a pattern that is matched against a subject
2750         string from left to right. Most characters stand for  themselves  in  a         string from left to right. Most characters stand for  themselves  in  a
# Line 1603  PCRE REGULAR EXPRESSION DETAILS Line 2753  PCRE REGULAR EXPRESSION DETAILS
2753    
2754           The quick brown fox           The quick brown fox
2755    
2756         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
2757         power of regular expressions comes from the ability to include alterna-         caseless  matching is specified (the PCRE_CASELESS option), letters are
2758         tives and repetitions in the pattern. These are encoded in the  pattern         matched independently of case. In UTF-8 mode, PCRE  always  understands
2759         by  the  use  of meta-characters, which do not stand for themselves but         the  concept  of case for characters whose values are less than 128, so
2760         instead are interpreted in some special way.         caseless matching is always possible. For characters with  higher  val-
2761           ues,  the concept of case is supported if PCRE is compiled with Unicode
2762         There are two different sets of meta-characters: those that are  recog-         property support, but not otherwise.   If  you  want  to  use  caseless
2763         nized  anywhere in the pattern except within square brackets, and those         matching  for  characters  128  and above, you must ensure that PCRE is
2764         that are recognized in square brackets. Outside  square  brackets,  the         compiled with Unicode property support as well as with UTF-8 support.
2765         meta-characters are as follows:  
2766           The power of regular expressions comes  from  the  ability  to  include
2767           alternatives  and  repetitions in the pattern. These are encoded in the
2768           pattern by the use of metacharacters, which do not stand for themselves
2769           but instead are interpreted in some special way.
2770    
2771           There  are  two different sets of metacharacters: those that are recog-
2772           nized anywhere in the pattern except within square brackets, and  those
2773           that  are  recognized  within square brackets. Outside square brackets,
2774           the metacharacters are as follows:
2775    
2776           \      general escape character with several uses           \      general escape character with several uses
2777           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 1630  PCRE REGULAR EXPRESSION DETAILS Line 2789  PCRE REGULAR EXPRESSION DETAILS
2789                  also "possessive quantifier"                  also "possessive quantifier"
2790           {      start min/max quantifier           {      start min/max quantifier
2791    
2792         Part  of  a  pattern  that is in square brackets is called a "character         Part of a pattern that is in square brackets  is  called  a  "character
2793         class". In a character class the only meta-characters are:         class". In a character class the only metacharacters are:
2794    
2795           \      general escape character           \      general escape character
2796           ^      negate the class, but only if the first character           ^      negate the class, but only if the first character
# Line 1640  PCRE REGULAR EXPRESSION DETAILS Line 2799  PCRE REGULAR EXPRESSION DETAILS
2799                    syntax)                    syntax)
2800           ]      terminates the character class           ]      terminates the character class
2801    
2802         The following sections describe the use of each of the meta-characters.         The  following sections describe the use of each of the metacharacters.
2803    
2804    
2805  BACKSLASH  BACKSLASH
2806    
2807         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
2808         a non-alphameric character, it takes  away  any  special  meaning  that         a  non-alphanumeric  character,  it takes away any special meaning that
2809         character  may  have.  This  use  of  backslash  as an escape character         character may have. This  use  of  backslash  as  an  escape  character
2810         applies both inside and outside character classes.         applies both inside and outside character classes.
2811    
2812         For example, if you want to match a * character, you write  \*  in  the         For  example,  if  you want to match a * character, you write \* in the
2813         pattern.   This  escaping  action  applies whether or not the following         pattern.  This escaping action applies whether  or  not  the  following
2814         character would otherwise be interpreted as a meta-character, so it  is         character  would  otherwise be interpreted as a metacharacter, so it is
2815         always  safe to precede a non-alphameric with backslash to specify that         always safe to precede a non-alphanumeric  with  backslash  to  specify
2816         it stands for itself. In particular, if you want to match a  backslash,         that  it stands for itself. In particular, if you want to match a back-
2817         you write \\.         slash, you write \\.
2818    
2819         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
2820         the pattern (other than in a character class) and characters between  a         the  pattern (other than in a character class) and characters between a
2821         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2822         An escaping backslash can be used to include a whitespace or #  charac-         ing  backslash  can  be  used to include a whitespace or # character as
2823         ter as part of the pattern.         part of the pattern.
2824    
2825         If  you  want  to remove the special meaning from a sequence of charac-         If you want to remove the special meaning from a  sequence  of  charac-
2826         ters, you can do so by putting them between \Q and \E. This is  differ-         ters,  you can do so by putting them between \Q and \E. This is differ-
2827         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E
2828         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
2829         tion. Note the following examples:         tion. Note the following examples:
2830    
2831           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 1676  BACKSLASH Line 2835  BACKSLASH
2835           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
2836           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
2837    
2838         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2839         classes.         classes.
2840    
2841       Non-printing characters
2842    
2843         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
2844         acters  in patterns in a visible manner. There is no restriction on the         acters in patterns in a visible manner. There is no restriction on  the
2845         appearance of non-printing characters, apart from the binary zero  that         appearance  of non-printing characters, apart from the binary zero that
2846         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates a pattern, but when a pattern  is  being  prepared  by  text
2847         editing, it is usually easier  to  use  one  of  the  following  escape         editing,  it  is  usually  easier  to  use  one of the following escape
2848         sequences than the binary character it represents:         sequences than the binary character it represents:
2849    
2850           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
# Line 1695  BACKSLASH Line 2856  BACKSLASH
2856           \t        tab (hex 09)           \t        tab (hex 09)
2857           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
2858           \xhh      character with hex code hh           \xhh      character with hex code hh
2859           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
2860    
2861         The  precise  effect of \cx is as follows: if x is a lower case letter,         The precise effect of \cx is as follows: if x is a lower  case  letter,
2862         it is converted to upper case. Then bit 6 of the character (hex 40)  is         it  is converted to upper case. Then bit 6 of the character (hex 40) is
2863         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;
2864         becomes hex 7B.         becomes hex 7B.
2865    
2866         After \x, from zero to two hexadecimal digits are read (letters can  be         After  \x, from zero to two hexadecimal digits are read (letters can be
2867         in  upper or lower case). In UTF-8 mode, any number of hexadecimal dig-         in upper or lower case). Any number of hexadecimal  digits  may  appear
2868         its may appear between \x{ and }, but the value of the  character  code         between  \x{  and  },  but the value of the character code must be less
2869         must  be  less  than  2**31  (that is, the maximum hexadecimal value is         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode (that is,
2870         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the  maximum  hexadecimal  value is 7FFFFFFF). If characters other than
2871         \x{  and }, or if there is no terminating }, this form of escape is not         hexadecimal digits appear between \x{ and }, or if there is  no  termi-
2872         recognized. Instead, the initial \x will be interpreted as a basic hex-         nating  }, this form of escape is not recognized.  Instead, the initial
2873         adecimal escape, with no following digits, giving a byte whose value is         \x will be interpreted as a basic hexadecimal escape, with no following
2874         zero.         digits, giving a character whose value is zero.
2875    
2876         Characters whose value is less than 256 can be defined by either of the         Characters whose value is less than 256 can be defined by either of the
2877         two  syntaxes for \x when PCRE is in UTF-8 mode. There is no difference         two syntaxes for \x. There is no difference in the way  they  are  han-
2878         in the way they are handled. For example, \xdc is exactly the  same  as         dled. For example, \xdc is exactly the same as \x{dc}.
2879         \x{dc}.  
2880           After  \0  up  to two further octal digits are read. If there are fewer
2881         After  \0  up  to  two further octal digits are read. In both cases, if         than two digits, just  those  that  are  present  are  used.  Thus  the
2882         there are fewer than two digits, just those that are present are  used.         sequence \0\x\07 specifies two binary zeros followed by a BEL character
2883         Thus  the sequence \0\x\07 specifies two binary zeros followed by a BEL         (code value 7). Make sure you supply two digits after the initial  zero
2884         character (code value 7). Make sure you supply  two  digits  after  the         if the pattern character that follows is itself an octal digit.
        initial zero if the character that follows is itself an octal digit.  
2885    
2886         The handling of a backslash followed by a digit other than 0 is compli-         The handling of a backslash followed by a digit other than 0 is compli-
2887         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
# Line 1733  BACKSLASH Line 2893  BACKSLASH
2893    
2894         Inside  a  character  class, or if the decimal number is greater than 9         Inside  a  character  class, or if the decimal number is greater than 9
2895         and there have not been that many capturing subpatterns, PCRE  re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
2896         up  to three octal digits following the backslash, and generates a sin-         up to three octal digits following the backslash, and uses them to gen-
2897         gle byte from the least significant 8 bits of the value. Any subsequent         erate a data character. Any subsequent digits stand for themselves.  In
2898         digits stand for themselves.  For example:         non-UTF-8  mode,  the  value  of a character specified in octal must be
2899           less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
2900           example:
2901    
2902           \040   is another way of writing a space           \040   is another way of writing a space
2903           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 1755  BACKSLASH Line 2917  BACKSLASH
2917         Note  that  octal  values of 100 or greater must not be introduced by a         Note  that  octal  values of 100 or greater must not be introduced by a
2918         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2919    
2920         All the sequences that define a single byte value  or  a  single  UTF-8         All the sequences that define a single character value can be used both
2921         character (in UTF-8 mode) can be used both inside and outside character         inside  and  outside character classes. In addition, inside a character
2922         classes. In addition, inside a character  class,  the  sequence  \b  is         class, the sequence \b is interpreted as the backspace  character  (hex
2923         interpreted  as  the  backspace character (hex 08). Outside a character         08),  and the sequences \R and \X are interpreted as the characters "R"
2924         class it has a different meaning (see below).         and "X", respectively. Outside a character class, these sequences  have
2925           different meanings (see below).
2926    
2927       Absolute and relative back references
2928    
2929           The  sequence  \g followed by a positive or negative number, optionally
2930           enclosed in braces, is an absolute or relative back reference. A  named
2931           back  reference can be coded as \g{name}. Back references are discussed
2932           later, following the discussion of parenthesized subpatterns.
2933    
2934         The third use of backslash is for specifying generic character types:     Generic character types
2935    
2936           Another use of backslash is for specifying generic character types. The
2937           following are always recognized:
2938    
2939           \d     any decimal digit           \d     any decimal digit
2940           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 1771  BACKSLASH Line 2944  BACKSLASH
2944           \W     any "non-word" character           \W     any "non-word" character
2945    
2946         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
2947         into  two disjoint sets. Any given character matches one, and only one,         into two disjoint sets. Any given character matches one, and only  one,
2948         of each pair.         of each pair.
2949    
        In UTF-8 mode, characters with values greater than 255 never match  \d,  
        \s, or \w, and always match \D, \S, and \W.  
   
        For  compatibility  with Perl, \s does not match the VT character (code  
        11).  This makes it different from the the POSIX "space" class. The  \s  
        characters are HT (9), LF (10), FF (12), CR (13), and space (32).  
   
        A  "word" character is any letter or digit or the underscore character,  
        that is, any character which can be part of a Perl "word". The  defini-  
        tion  of  letters  and digits is controlled by PCRE's character tables,  
        and may vary if locale- specific matching is taking place (see  "Locale  
        support"  in  the  pcreapi  page).  For  example,  in the "fr" (French)  
        locale, some character codes greater than 128  are  used  for  accented  
        letters, and these are matched by \w.  
   
2950         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
2951         acter classes. They each match one character of the  appropriate  type.         acter classes. They each match one character of the  appropriate  type.
2952         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
2953         of them fail, since there is no character to match.         of them fail, since there is no character to match.
2954    
2955         The fourth use of backslash is for certain simple assertions. An asser-         For compatibility with Perl, \s does not match the VT  character  (code
2956         tion  specifies a condition that has to be met at a particular point in         11).   This makes it different from the the POSIX "space" class. The \s
2957         a match, without consuming any characters from the subject string.  The         characters are HT (9), LF (10), FF (12), CR (13), and space  (32).  (If
2958         use  of subpatterns for more complicated assertions is described below.         "use locale;" is included in a Perl script, \s may match the VT charac-
2959         The backslashed assertions are         ter. In PCRE, it never does.)
2960    
2961           A "word" character is an underscore or any character less than 256 that
2962           is  a  letter  or  digit.  The definition of letters and digits is con-
2963           trolled by PCRE's low-valued character tables, and may vary if  locale-
2964           specific  matching is taking place (see "Locale support" in the pcreapi
2965           page). For example, in a French locale such  as  "fr_FR"  in  Unix-like
2966           systems,  or "french" in Windows, some character codes greater than 128
2967           are used for accented letters, and these are matched by \w.
2968    
2969           In UTF-8 mode, characters with values greater than 128 never match  \d,
2970           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
2971           code character property support is available. The use of  locales  with
2972           Unicode is discouraged.
2973    
2974       Newline sequences
2975    
2976           Outside  a  character class, the escape sequence \R matches any Unicode
2977           newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2978           equivalent to the following:
2979    
2980             (?>\r\n|\n|\x0b|\f|\r|\x85)
2981    
2982           This  is  an  example  of an "atomic group", details of which are given
2983           below.  This particular group matches either the two-character sequence
2984           CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
2985           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2986           return, U+000D), or NEL (next line, U+0085). The two-character sequence
2987           is treated as a single unit that cannot be split.
2988    
2989           In UTF-8 mode, two additional characters whose codepoints  are  greater
2990           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2991           rator, U+2029).  Unicode character property support is not  needed  for
2992           these characters to be recognized.
2993    
2994           Inside a character class, \R matches the letter "R".
2995    
2996       Unicode character properties
2997    
2998           When PCRE is built with Unicode character property support, three addi-
2999           tional escape sequences to match  character  properties  are  available
3000           when UTF-8 mode is selected. They are:
3001    
3002             \p{xx}   a character with the xx property
3003             \P{xx}   a character without the xx property
3004             \X       an extended Unicode sequence
3005    
3006           The  property  names represented by xx above are limited to the Unicode
3007           script names, the general category properties, and "Any", which matches
3008           any character (including newline). Other properties such as "InMusical-
3009           Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does
3010           not match any characters, so always causes a match failure.
3011    
3012           Sets of Unicode characters are defined as belonging to certain scripts.
3013           A character from one of these sets can be matched using a script  name.
3014           For example:
3015    
3016             \p{Greek}
3017             \P{Han}
3018    
3019           Those  that are not part of an identified script are lumped together as
3020           "Common". The current list of scripts is:
3021    
3022           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3023           Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,
3024           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3025           Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
3026           gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,
3027           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3028           Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,
3029           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3030           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3031    
3032           Each character has exactly one general category property, specified  by
3033           a two-letter abbreviation. For compatibility with Perl, negation can be
3034           specified by including a circumflex between the opening brace  and  the
3035           property name. For example, \p{^Lu} is the same as \P{Lu}.
3036    
3037           If only one letter is specified with \p or \P, it includes all the gen-
3038           eral category properties that start with that letter. In this case,  in
3039           the  absence of negation, the curly brackets in the escape sequence are
3040           optional; these two examples have the same effect:
3041    
3042             \p{L}
3043             \pL
3044    
3045           The following general category property codes are supported:
3046    
3047             C     Other
3048             Cc    Control
3049             Cf    Format
3050             Cn    Unassigned
3051             Co    Private use
3052             Cs    Surrogate
3053    
3054             L     Letter
3055             Ll    Lower case letter
3056             Lm    Modifier letter
3057             Lo    Other letter
3058             Lt    Title case letter
3059             Lu    Upper case letter
3060    
3061             M     Mark
3062             Mc    Spacing mark
3063             Me    Enclosing mark
3064             Mn    Non-spacing mark
3065    
3066             N     Number
3067             Nd    Decimal number
3068             Nl    Letter number
3069             No    Other number
3070    
3071             P     Punctuation
3072             Pc    Connector punctuation
3073             Pd    Dash punctuation
3074             Pe    Close punctuation
3075             Pf    Final punctuation
3076             Pi    Initial punctuation
3077             Po    Other punctuation
3078             Ps    Open punctuation
3079    
3080             S     Symbol
3081             Sc    Currency symbol
3082             Sk    Modifier symbol
3083             Sm    Mathematical symbol
3084             So    Other symbol
3085    
3086             Z     Separator
3087             Zl    Line separator
3088             Zp    Paragraph separator
3089             Zs    Space separator
3090    
3091           The special property L& is also supported: it matches a character  that
3092           has  the  Lu,  Ll, or Lt property, in other words, a letter that is not
3093           classified as a modifier or "other".
3094    
3095           The long synonyms for these properties  that  Perl  supports  (such  as
3096           \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix
3097           any of these properties with "Is".
3098    
3099           No character that is in the Unicode table has the Cn (unassigned) prop-
3100           erty.  Instead, this property is assumed for any code point that is not
3101           in the Unicode table.
3102    
3103           Specifying caseless matching does not affect  these  escape  sequences.
3104           For example, \p{Lu} always matches only upper case letters.
3105    
3106           The  \X  escape  matches  any number of Unicode characters that form an
3107           extended Unicode sequence. \X is equivalent to
3108    
3109             (?>\PM\pM*)
3110    
3111           That is, it matches a character without the "mark"  property,  followed
3112           by  zero  or  more  characters with the "mark" property, and treats the
3113           sequence as an atomic group (see below).  Characters  with  the  "mark"
3114           property are typically accents that affect the preceding character.
3115    
3116           Matching  characters  by Unicode property is not fast, because PCRE has
3117           to search a structure that contains  data  for  over  fifteen  thousand
3118           characters. That is why the traditional escape sequences such as \d and
3119           \w do not use Unicode properties in PCRE.
3120    
3121       Resetting the match start
3122    
3123           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3124           ously  matched  characters  not  to  be  included  in the final matched
3125           sequence. For example, the pattern:
3126    
3127             foo\Kbar
3128    
3129           matches "foobar", but reports that it has matched "bar".  This  feature
3130           is  similar  to  a lookbehind assertion (described below).  However, in
3131           this case, the part of the subject before the real match does not  have
3132           to  be of fixed length, as lookbehind assertions do. The use of \K does
3133           not interfere with the setting of captured  substrings.   For  example,
3134           when the pattern
3135    
3136             (foo)\Kbar
3137    
3138           matches "foobar", the first substring is still set to "foo".
3139    
3140       Simple assertions
3141    
3142           The  final use of backslash is for certain simple assertions. An asser-
3143           tion specifies a condition that has to be met at a particular point  in
3144           a  match, without consuming any characters from the subject string. The
3145           use of subpatterns for more complicated assertions is described  below.
3146           The backslashed assertions are:
3147    
3148           \b     matches at a word boundary           \b     matches at a word boundary
3149           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3150           \A     matches at start of subject           \A     matches at the start of the subject
3151           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3152           \z     matches at end of subject                   also matches before a newline at the end of the subject
3153           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3154             \G     matches at the first matching position in the subject
3155