/[pcre]/code/trunk/doc/pcre.txt
ViewVC logotype

Diff of /code/trunk/doc/pcre.txt

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 73 by nigel, Sat Feb 24 21:40:30 2007 UTC revision 123 by ph10, Mon Mar 12 15:19:06 2007 UTC
# Line 1  Line 1 
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           pcreapi           details of PCRE's native C API
76           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
77           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
78           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
79             pcrecpp           details of the C++ wrapper
80           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
81             pcrematching      discussion of the two matching algorithms
82             pcrepartial       details of the partial matching facility
83           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
84                               regular expressions                               regular expressions
85           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
86           pcreposix         the POSIX-compatible API           pcreposix         the POSIX-compatible C API
87             pcreprecompile    details of saving and re-using precompiled patterns
88           pcresample        discussion of the sample program           pcresample        discussion of the sample program
89           pcretest          the pcretest testing command           pcrestack         discussion of stack usage
90             pcretest          description of the pcretest testing command
91    
92         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
93         each library function, listing its arguments and results.         each C library function, listing its arguments and results.
94    
95    
96  LIMITATIONS  LIMITATIONS
97    
98         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
99         never in practice be relevant.         never in practice be relevant.
100    
101         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
102         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
103         process  regular  expressions  that are truly enormous, you can compile         process regular expressions that are truly enormous,  you  can  compile
104         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
105         the  source  distribution and the pcrebuild documentation for details).         the source distribution and the pcrebuild documentation  for  details).
106         If these cases the limit is substantially larger.  However,  the  speed         In  these  cases the limit is substantially larger.  However, the speed
107         of execution will be slower.         of execution is slower.
108    
109         All values in repeating quantifiers must be less than 65536.  The maxi-         All values in repeating quantifiers must be less than 65536. The  maxi-
110         mum number of capturing subpatterns is 65535.         mum  compiled  length  of  subpattern  with an explicit repeat count is
111           30000 bytes. The maximum number of capturing subpatterns is 65535.
112         There is no limit to the number of non-capturing subpatterns,  but  the  
113         maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,         There is no limit to the number of parenthesized subpatterns, but there
114         including capturing subpatterns, assertions, and other types of subpat-         can be no more than 65535 capturing subpatterns.
115         tern, is 200.  
116           The maximum length of name for a named subpattern is 32 characters, and
117         The  maximum  length of a subject string is the largest positive number         the maximum number of named subpatterns is 10000.
118         that an integer variable can hold. However, PCRE uses recursion to han-  
119         dle  subpatterns  and indefinite repetition. This means that the avail-         The maximum length of a subject string is the largest  positive  number
120         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
121         processed by certain patterns.         matching function, PCRE uses recursion to handle subpatterns and indef-
122           inite  repetition.  This means that the available stack space may limit
123           the size of a subject string that can be processed by certain patterns.
124  UTF-8 SUPPORT         For a discussion of stack issues, see the pcrestack documentation.
125    
126         Starting  at  release  3.3,  PCRE  has  had  some support for character  
127         strings encoded in the UTF-8 format. For  release  4.0  this  has  been  UTF-8 AND UNICODE PROPERTY SUPPORT
128         greatly extended to cover most common requirements.  
129           From  release  3.3,  PCRE  has  had  some support for character strings
130         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
131         support in the code, and, in addition,  you  must  call  pcre_compile()         to  cover  most common requirements, and in release 5.0 additional sup-
132         with  the PCRE_UTF8 option flag. When you do this, both the pattern and         port for Unicode general category properties was added.
133         any subject strings that are matched against it are  treated  as  UTF-8  
134           In order process UTF-8 strings, you must build PCRE  to  include  UTF-8
135           support  in  the  code,  and, in addition, you must call pcre_compile()
136           with the PCRE_UTF8 option flag. When you do this, both the pattern  and
137           any  subject  strings  that are matched against it are treated as UTF-8
138         strings instead of just strings of bytes.         strings instead of just strings of bytes.
139    
140         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,
141         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
142         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
143         not be very large.         very big.
144    
145           If PCRE is built with Unicode character property support (which implies
146           UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
147           ported.  The available properties that can be tested are limited to the
148           general category properties such as Lu for an upper case letter  or  Nd
149           for  a  decimal number, the Unicode script names such as Arabic or Han,
150           and the derived properties Any and L&. A full  list  is  given  in  the
151           pcrepattern documentation. Only the short names for properties are sup-
152           ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
153           ter},  is  not  supported.   Furthermore,  in Perl, many properties may
154           optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
155           does not support this.
156    
157         The following comments apply when PCRE is running in UTF-8 mode:         The following comments apply when PCRE is running in UTF-8 mode:
158    
159         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
160         subjects  are  checked for validity on entry to the relevant functions.         subjects are checked for validity on entry to the  relevant  functions.
161         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
162         situations,  you  may  already  know  that  your strings are valid, and         situations, you may already know  that  your  strings  are  valid,  and
163         therefore want to skip these checks in order to improve performance. If         therefore want to skip these checks in order to improve performance. If
164         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,
165         PCRE assumes that the pattern or subject  it  is  given  (respectively)         PCRE  assumes  that  the  pattern or subject it is given (respectively)
166         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
167         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
168         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
169         crash.         crash.
170    
171         2. In a pattern, the escape sequence \x{...}, where the contents of the         2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
172         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.  
173    
174         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
175         UTF-8 character if the value is greater than 127.         characters for values greater than \177.
176    
177         4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
178         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
179    
180         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-
181         single byte.         gle byte.
182    
183         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
184         mode, but its use can lead to some strange effects.         mode, but its use can lead to some strange effects.  This  facility  is
185           not available in the alternative matching function, pcre_dfa_exec().
186    
187         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
188         test characters of any code value, but the characters that PCRE  recog-         test characters of any code value, but the characters that PCRE  recog-
189         nizes  as  digits,  spaces,  or  word characters remain the same set as         nizes  as  digits,  spaces,  or  word characters remain the same set as
190         before, all with values less than 256.         before, all with values less than 256. This remains true even when PCRE
191           includes  Unicode  property support, because to do otherwise would slow
192           down PCRE in many common cases. If you really want to test for a  wider
193           sense  of,  say,  "digit",  you must use Unicode property tests such as
194           \p{Nd}.
195    
196           8. Similarly, characters that match the POSIX named  character  classes
197           are all low-valued characters.
198    
199           9.  Case-insensitive  matching  applies only to characters whose values
200           are less than 128, unless PCRE is built with Unicode property  support.
201           Even  when  Unicode  property support is available, PCRE still uses its
202           own character tables when checking the case of  low-valued  characters,
203           so  as not to degrade performance.  The Unicode property information is
204           used only for characters with higher values. Even when Unicode property
205           support is available, PCRE supports case-insensitive matching only when
206           there is a one-to-one mapping between a letter's  cases.  There  are  a
207           small  number  of  many-to-one  mappings in Unicode; these are not sup-
208           ported by PCRE.
209    
        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.  
210    
211         9. PCRE does not support the use of Unicode tables  and  properties  or  AUTHOR
        the Perl escapes \p, \P, and \X.  
212    
213           Philip Hazel
214           University Computing Service
215           Cambridge CB2 3QH, England.
216    
217  AUTHOR         Putting an actual email address here seems to have been a spam  magnet,
218           so I've taken it away. If you want to email me, use my initial and sur-
219           name, separated by a dot, at the domain ucs.cam.ac.uk.
220    
        Philip Hazel <ph10@cam.ac.uk>  
        University Computing Service,  
        Cambridge CB2 3QG, England.  
        Phone: +44 1223 334714  
221    
222  Last updated: 20 August 2003  REVISION
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
223    
224  PCRE(3)                                                                PCRE(3)         Last updated: 06 March 2007
225           Copyright (c) 1997-2007 University of Cambridge.
226    ------------------------------------------------------------------------------
227    
228    
229    PCREBUILD(3)                                                      PCREBUILD(3)
230    
231    
232  NAME  NAME
233         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
234    
235    
236  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
237    
238         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
239         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. They are all selected, or  dese-
240         lected,  by  providing  options  to  the  configure script which is run         lected, by providing options to the configure script that is run before
241         before the make command. The complete list  of  options  for  configure         the make command. The complete list of  options  for  configure  (which
242         (which  includes the standard ones such as the selection of the instal-         includes  the  standard  ones such as the selection of the installation
243         lation directory) can be obtained by running         directory) can be obtained by running
244    
245           ./configure --help           ./configure --help
246    
# Line 192  PCRE BUILD-TIME OPTIONS Line 252  PCRE BUILD-TIME OPTIONS
252         not described.         not described.
253    
254    
255    C++ SUPPORT
256    
257           By default, the configure script will search for a C++ compiler and C++
258           header files. If it finds them, it automatically builds the C++ wrapper
259           library for PCRE. You can disable this by adding
260    
261             --disable-cpp
262    
263           to the configure command.
264    
265    
266  UTF-8 SUPPORT  UTF-8 SUPPORT
267    
268         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 character strings, add
# Line 204  UTF-8 SUPPORT Line 275  UTF-8 SUPPORT
275         function.         function.
276    
277    
278    UNICODE CHARACTER PROPERTY SUPPORT
279    
280           UTF-8 support allows PCRE to process character values greater than  255
281           in  the  strings that it handles. On its own, however, it does not pro-
282           vide any facilities for accessing the properties of such characters. If
283           you  want  to  be able to use the pattern escapes \P, \p, and \X, which
284           refer to Unicode character properties, you must add
285    
286             --enable-unicode-properties
287    
288           to the configure command. This implies UTF-8 support, even if you  have
289           not explicitly requested it.
290    
291           Including  Unicode  property  support  adds around 90K of tables to the
292           PCRE library, approximately doubling its size. Only the  general  cate-
293           gory  properties  such as Lu and Nd are supported. Details are given in
294           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-any
317    
318           which causes PCRE to recognize any Unicode newline sequence.
319    
320           Whatever  line  ending convention is selected when PCRE is built can be
321           overridden when the library functions are called. At build time  it  is
322           conventional to use the standard for your operating system.
323    
324    
325  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
326    
327         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
328         Unix  libraries by default. You can suppress one of these by adding one         Unix libraries by default. You can suppress one of these by adding  one
329         of         of
330    
331           --disable-shared           --disable-shared
# Line 231  BUILDING SHARED AND STATIC LIBRARIES Line 336  BUILDING SHARED AND STATIC LIBRARIES
336    
337  POSIX MALLOC USAGE  POSIX MALLOC USAGE
338    
339         When PCRE is called through the  POSIX  interface  (see  the  pcreposix         When PCRE is called through the POSIX interface (see the pcreposix doc-
340         documentation),  additional working storage is required for holding the         umentation), additional working storage is  required  for  holding  the
341         pointers to capturing substrings because PCRE requires  three  integers         pointers  to capturing substrings, because PCRE requires three integers
342         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
343         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
344         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.
345         The default threshold above which the stack is no longer used is 10; it         The default threshold above which the stack is no longer used is 10; it
# Line 245  POSIX MALLOC USAGE Line 350  POSIX MALLOC USAGE
350         to the configure command.         to the configure command.
351    
352    
 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.  
   
   
353  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
354    
355         Within  a  compiled  pattern,  offset values are used to point from one         Within a compiled pattern, offset values are used  to  point  from  one
356         part to another (for example, from an opening parenthesis to an  alter-         part  to another (for example, from an opening parenthesis to an alter-
357         nation  metacharacter).  By  default two-byte values are used for these         nation metacharacter). By default, two-byte values are used  for  these
358         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets,  leading  to  a  maximum size for a compiled pattern of around
359         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
360         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless,  some  people do want to process enormous patterns, so it
361         is  possible  to compile PCRE to use three-byte or four-byte offsets by         is possible to compile PCRE to use three-byte or four-byte  offsets  by
362         adding a setting such as         adding a setting such as
363    
364           --with-link-size=3           --with-link-size=3
365    
366         to the configure command. The value given must be 2,  3,  or  4.  Using         to  the  configure  command.  The value given must be 2, 3, or 4. Using
367         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
368         additional bytes when handling them.         additional bytes when handling them.
369    
370         If you build PCRE with an increased link size, test 2 (and  test  5  if         If  you  build  PCRE with an increased link size, test 2 (and test 5 if
371         you  are using UTF-8) will fail. Part of the output of these tests is a         you are using UTF-8) will fail. Part of the output of these tests is  a
372         representation of the compiled pattern, and this changes with the  link         representation  of the compiled pattern, and this changes with the link
373         size.         size.
374    
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  USING EBCDIC CODE  USING EBCDIC CODE
433    
434         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
435         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).
436         can, however, be compiled to run in an EBCDIC environment by adding         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by
437           adding
438    
439           --enable-ebcdic           --enable-ebcdic
440    
441         to the configure command.         to the configure command.
442    
 Last updated: 09 December 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
443    
444  PCRE(3)                                                                PCRE(3)  SEE ALSO
445    
446           pcreapi(3), pcre_config(3).
447    
448    
449    AUTHOR
450    
451           Philip Hazel
452           University Computing Service
453           Cambridge CB2 3QH, England.
454    
455    
456    REVISION
457    
458           Last updated: 06 March 2007
459           Copyright (c) 1997-2007 University of Cambridge.
460    ------------------------------------------------------------------------------
461    
462    
463    PCREMATCHING(3)                                                PCREMATCHING(3)
464    
465    
466    NAME
467           PCRE - Perl-compatible regular expressions
468    
469    
470    PCRE MATCHING ALGORITHMS
471    
472           This document describes the two different algorithms that are available
473           in PCRE for matching a compiled regular expression against a given sub-
474           ject  string.  The  "standard"  algorithm  is  the  one provided by the
475           pcre_exec() function.  This works in the same was  as  Perl's  matching
476           function, and provides a Perl-compatible matching operation.
477    
478           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
479           this operates in a different way, and is not  Perl-compatible.  It  has
480           advantages  and disadvantages compared with the standard algorithm, and
481           these are described below.
482    
483           When there is only one possible way in which a given subject string can
484           match  a pattern, the two algorithms give the same answer. A difference
485           arises, however, when there are multiple possibilities. For example, if
486           the pattern
487    
488             ^<.*>
489    
490           is matched against the string
491    
492             <something> <something else> <something further>
493    
494           there are three possible answers. The standard algorithm finds only one
495           of them, whereas the alternative algorithm finds all three.
496    
497    
498    REGULAR EXPRESSIONS AS TREES
499    
500           The set of strings that are matched by a regular expression can be rep-
501           resented  as  a  tree structure. An unlimited repetition in the pattern
502           makes the tree of infinite size, but it is still a tree.  Matching  the
503           pattern  to a given subject string (from a given starting point) can be
504           thought of as a search of the tree.  There are two  ways  to  search  a
505           tree:  depth-first  and  breadth-first, and these correspond to the two
506           matching algorithms provided by PCRE.
507    
508    
509    THE STANDARD MATCHING ALGORITHM
510    
511           In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-
512           sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a
513           depth-first search of the pattern tree. That is, it  proceeds  along  a
514           single path through the tree, checking that the subject matches what is
515           required. When there is a mismatch, the algorithm  tries  any  alterna-
516           tives  at  the  current point, and if they all fail, it backs up to the
517           previous branch point in the  tree,  and  tries  the  next  alternative
518           branch  at  that  level.  This often involves backing up (moving to the
519           left) in the subject string as well.  The  order  in  which  repetition
520           branches  are  tried  is controlled by the greedy or ungreedy nature of
521           the quantifier.
522    
523           If a leaf node is reached, a matching string has  been  found,  and  at
524           that  point the algorithm stops. Thus, if there is more than one possi-
525           ble match, this algorithm returns the first one that it finds.  Whether
526           this  is the shortest, the longest, or some intermediate length depends
527           on the way the greedy and ungreedy repetition quantifiers are specified
528           in the pattern.
529    
530           Because  it  ends  up  with a single path through the tree, it is rela-
531           tively straightforward for this algorithm to keep  track  of  the  sub-
532           strings  that  are  matched  by portions of the pattern in parentheses.
533           This provides support for capturing parentheses and back references.
534    
535    
536    THE ALTERNATIVE MATCHING ALGORITHM
537    
538           This algorithm conducts a breadth-first search of  the  tree.  Starting
539           from  the  first  matching  point  in the subject, it scans the subject
540           string from left to right, once, character by character, and as it does
541           this,  it remembers all the paths through the tree that represent valid
542           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
543           though  it is not implemented as a traditional finite state machine (it
544           keeps multiple states active simultaneously).
545    
546           The scan continues until either the end of the subject is  reached,  or
547           there  are  no more unterminated paths. At this point, terminated paths
548           represent the different matching possibilities (if there are none,  the
549           match  has  failed).   Thus,  if there is more than one possible match,
550           this algorithm finds all of them, and in particular, it finds the long-
551           est.  In PCRE, there is an option to stop the algorithm after the first
552           match (which is necessarily the shortest) has been found.
553    
554           Note that all the matches that are found start at the same point in the
555           subject. If the pattern
556    
557             cat(er(pillar)?)
558    
559           is  matched  against the string "the caterpillar catchment", the result
560           will be the three strings "cat", "cater", and "caterpillar" that  start
561           at the fourth character of the subject. The algorithm does not automat-
562           ically move on to find matches that start at later positions.
563    
564           There are a number of features of PCRE regular expressions that are not
565           supported by the alternative matching algorithm. They are as follows:
566    
567           1.  Because  the  algorithm  finds  all possible matches, the greedy or
568           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
569           ungreedy quantifiers are treated in exactly the same way. However, pos-
570           sessive quantifiers can make a difference when what follows could  also
571           match what is quantified, for example in a pattern like this:
572    
573             ^a++\w!
574    
575           This  pattern matches "aaab!" but not "aaa!", which would be matched by
576           a non-possessive quantifier. Similarly, if an atomic group is  present,
577           it  is matched as if it were a standalone pattern at the current point,
578           and the longest match is then "locked in" for the rest of  the  overall
579           pattern.
580    
581           2. When dealing with multiple paths through the tree simultaneously, it
582           is not straightforward to keep track of  captured  substrings  for  the
583           different  matching  possibilities,  and  PCRE's implementation of this
584           algorithm does not attempt to do this. This means that no captured sub-
585           strings are available.
586    
587           3.  Because no substrings are captured, back references within the pat-
588           tern are not supported, and cause errors if encountered.
589    
590           4. For the same reason, conditional expressions that use  a  backrefer-
591           ence  as  the  condition or test for a specific group recursion are not
592           supported.
593    
594           5. Callouts are supported, but the value of the  capture_top  field  is
595           always 1, and the value of the capture_last field is always -1.
596    
597           6.  The \C escape sequence, which (in the standard algorithm) matches a
598           single byte, even in UTF-8 mode, is not supported because the  alterna-
599           tive  algorithm  moves  through  the  subject string one character at a
600           time, for all active paths through the tree.
601    
602    
603    ADVANTAGES OF THE ALTERNATIVE ALGORITHM
604    
605           Using the alternative matching algorithm provides the following  advan-
606           tages:
607    
608           1. All possible matches (at a single point in the subject) are automat-
609           ically found, and in particular, the longest match is  found.  To  find
610           more than one match using the standard algorithm, you have to do kludgy
611           things with callouts.
612    
613           2. There is much better support for partial matching. The  restrictions
614           on  the content of the pattern that apply when using the standard algo-
615           rithm for partial matching do not apply to the  alternative  algorithm.
616           For  non-anchored patterns, the starting position of a partial match is
617           available.
618    
619           3. Because the alternative algorithm  scans  the  subject  string  just
620           once,  and  never  needs to backtrack, it is possible to pass very long
621           subject strings to the matching function in  several  pieces,  checking
622           for partial matching each time.
623    
624    
625    DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
626    
627           The alternative algorithm suffers from a number of disadvantages:
628    
629           1.  It  is  substantially  slower  than the standard algorithm. This is
630           partly because it has to search for all possible matches, but  is  also
631           because it is less susceptible to optimization.
632    
633           2. Capturing parentheses and back references are not supported.
634    
635           3. Although atomic groups are supported, their use does not provide the
636           performance advantage that it does for the standard algorithm.
637    
638    
639    AUTHOR
640    
641           Philip Hazel
642           University Computing Service
643           Cambridge CB2 3QH, England.
644    
645    
646    REVISION
647    
648           Last updated: 06 March 2007
649           Copyright (c) 1997-2007 University of Cambridge.
650    ------------------------------------------------------------------------------
651    
652    
653    PCREAPI(3)                                                          PCREAPI(3)
654    
655    
656  NAME  NAME
657         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
658    
659  SYNOPSIS OF PCRE API  
660    PCRE NATIVE API
661    
662         #include <pcre.h>         #include <pcre.h>
663    
# Line 335  SYNOPSIS OF PCRE API Line 665  SYNOPSIS OF PCRE API
665              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
666              const unsigned char *tableptr);              const unsigned char *tableptr);
667    
668           pcre *pcre_compile2(const char *pattern, int options,
669                int *errorcodeptr,
670                const char **errptr, int *erroffset,
671                const unsigned char *tableptr);
672    
673         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options,
674              const char **errptr);              const char **errptr);
675    
# Line 342  SYNOPSIS OF PCRE API Line 677  SYNOPSIS OF PCRE API
677              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
678              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
679    
680           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
681                const char *subject, int length, int startoffset,
682                int options, int *ovector, int ovecsize,
683                int *workspace, int wscount);
684    
685         int pcre_copy_named_substring(const pcre *code,         int pcre_copy_named_substring(const pcre *code,
686              const char *subject, int *ovector,              const char *subject, int *ovector,
687              int stringcount, const char *stringname,              int stringcount, const char *stringname,
# Line 359  SYNOPSIS OF PCRE API Line 699  SYNOPSIS OF PCRE API
699         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
700              const char *name);              const char *name);
701    
702           int pcre_get_stringtable_entries(const pcre *code,
703                const char *name, char **first, char **last);
704    
705         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
706              int stringcount, int stringnumber,              int stringcount, int stringnumber,
707              const char **stringptr);              const char **stringptr);
# Line 377  SYNOPSIS OF PCRE API Line 720  SYNOPSIS OF PCRE API
720    
721         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
722    
723           int pcre_refcount(pcre *code, int adjust);
724    
725         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
726    
727         char *pcre_version(void);         char *pcre_version(void);
# Line 392  SYNOPSIS OF PCRE API Line 737  SYNOPSIS OF PCRE API
737         int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
738    
739    
740  PCRE API  PCRE API OVERVIEW
741    
742         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
743         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
744         expression API.  These are described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
745           Both of these APIs define a set of C function calls. A C++  wrapper  is
746         The  native  API  function  prototypes  are  defined in the header file         distributed with PCRE. It is documented in the pcrecpp page.
747         pcre.h, and on Unix systems the library itself is called libpcre.a,  so  
748         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
749         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
750         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
751         library. Applications can use these to include  support  for  different         application  that  uses  PCRE.  The  header  file  defines  the  macros
752         releases.         PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
753           bers for the library.  Applications can use these  to  include  support
754         The  functions  pcre_compile(),  pcre_study(), and pcre_exec() are used         for different releases of PCRE.
755         for compiling and matching regular expressions. A sample  program  that  
756         demonstrates  the simplest way of using them is given in the file pcre-         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
757         demo.c. The pcresample documentation describes how to run it.         pcre_exec() are used for compiling and matching regular expressions  in
758           a  Perl-compatible  manner. A sample program that demonstrates the sim-
759         There are convenience functions for extracting captured substrings from         plest way of using them is provided in the file  called  pcredemo.c  in
760         a matched subject string. They are:         the  source distribution. The pcresample documentation describes how to
761           run it.
762    
763           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
764           ble,  is  also provided. This uses a different algorithm for the match-
765           ing. The alternative algorithm finds all possible matches (at  a  given
766           point  in  the subject), and scans the subject just once. However, this
767           algorithm does not return captured substrings. A description of the two
768           matching  algorithms and their advantages and disadvantages is given in
769           the pcrematching documentation.
770    
771           In addition to the main compiling and  matching  functions,  there  are
772           convenience functions for extracting captured substrings from a subject
773           string that is matched by pcre_exec(). They are:
774    
775           pcre_copy_substring()           pcre_copy_substring()
776           pcre_copy_named_substring()           pcre_copy_named_substring()
777           pcre_get_substring()           pcre_get_substring()
778           pcre_get_named_substring()           pcre_get_named_substring()
779           pcre_get_substring_list()           pcre_get_substring_list()
780             pcre_get_stringnumber()
781             pcre_get_stringtable_entries()
782    
783         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
784         to free the memory used for extracted strings.         to free the memory used for extracted strings.
785    
786         The function pcre_maketables() is used (optionally) to build a  set  of         The  function  pcre_maketables()  is  used  to build a set of character
787         character tables in the current locale for passing to pcre_compile().         tables  in  the  current  locale   for   passing   to   pcre_compile(),
788           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
789         The  function  pcre_fullinfo()  is used to find out information about a         provided for specialist use.  Most  commonly,  no  special  tables  are
790         compiled pattern; pcre_info() is an obsolete version which returns only         passed,  in  which case internal tables that are generated when PCRE is
791         some  of  the available information, but is retained for backwards com-         built are used.
792         patibility.  The function pcre_version() returns a pointer to a  string  
793           The function pcre_fullinfo() is used to find out  information  about  a
794           compiled  pattern; pcre_info() is an obsolete version that returns only
795           some of the available information, but is retained for  backwards  com-
796           patibility.   The function pcre_version() returns a pointer to a string
797         containing the version of PCRE and its date of release.         containing the version of PCRE and its date of release.
798    
799         The  global  variables  pcre_malloc and pcre_free initially contain the         The function pcre_refcount() maintains a  reference  count  in  a  data
800         entry points of the standard  malloc()  and  free()  functions  respec-         block  containing  a compiled pattern. This is provided for the benefit
801           of object-oriented applications.
802    
803           The global variables pcre_malloc and pcre_free  initially  contain  the
804           entry  points  of  the  standard malloc() and free() functions, respec-
805         tively. PCRE calls the memory management functions via these variables,         tively. PCRE calls the memory management functions via these variables,
806         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
807         calls. This should be done before calling any PCRE functions.         calls. This should be done before calling any PCRE functions.
808    
809         The  global  variables  pcre_stack_malloc  and pcre_stack_free are also         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
810         indirections to memory management functions.  These  special  functions         indirections  to  memory  management functions. These special functions
811         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
812         data, instead of recursive function calls. This is a  non-standard  way         data, instead of recursive function calls, when running the pcre_exec()
813         of  building  PCRE,  for  use in environments that have limited stacks.         function. See the pcrebuild documentation for  details  of  how  to  do
814         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-
815         Separate  functions  are provided so that special-purpose external code         ments that have limited stacks. Because of the greater  use  of  memory
816         can be used for this case. When used, these functions are always called         management,  it  runs  more  slowly. Separate functions are provided so
817         in  a  stack-like  manner  (last obtained, first freed), and always for         that special-purpose external code can be  used  for  this  case.  When
818         memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
819           obtained, first freed), and always for memory blocks of the same  size.
820           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
821           mentation.
822    
823         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
824         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 826  PCRE API
826         pcrecallout documentation.         pcrecallout documentation.
827    
828    
829    NEWLINES
830    
831           PCRE  supports four different conventions for indicating line breaks in
832           strings: a single CR (carriage return) character, a  single  LF  (line-
833           feed)  character,  the two-character sequence CRLF, or any Unicode new-
834           line sequence.  The Unicode newline sequences are the three  just  men-
835           tioned, plus the single characters VT (vertical tab, U+000B), FF (form-
836           feed, U+000C), NEL (next line, U+0085), LS  (line  separator,  U+2028),
837           and PS (paragraph separator, U+2029).
838    
839           Each  of  the first three conventions is used by at least one operating
840           system as its standard newline sequence. When PCRE is built, a  default
841           can  be  specified.  The default default is LF, which is the Unix stan-
842           dard. When PCRE is run, the default can be overridden,  either  when  a
843           pattern is compiled, or when it is matched.
844    
845           In the PCRE documentation the word "newline" is used to mean "the char-
846           acter or pair of characters that indicate a line break". The choice  of
847           newline  convention  affects  the  handling of the dot, circumflex, and
848           dollar metacharacters, the handling of #-comments in /x mode, and, when
849           CRLF  is a recognized line ending sequence, the match position advance-
850           ment for a non-anchored pattern. The choice of newline convention  does
851           not affect the interpretation of the \n or \r escape sequences.
852    
853    
854  MULTITHREADING  MULTITHREADING
855    
856         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 863  MULTITHREADING
863         at once.         at once.
864    
865    
866    SAVING PRECOMPILED PATTERNS FOR LATER USE
867    
868           The compiled form of a regular expression can be saved and re-used at a
869           later time, possibly by a different program, and even on a  host  other
870           than  the  one  on  which  it  was  compiled.  Details are given in the
871           pcreprecompile documentation.
872    
873    
874  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
875    
876         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
877    
878         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-
879         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
880         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
881         tures.         tures.
882    
883         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
884         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
885         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
886         available:         available:
887    
888           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
889    
890         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-
891         able; otherwise it is set to zero.         able; otherwise it is set to zero.
892    
893             PCRE_CONFIG_UNICODE_PROPERTIES
894    
895           The  output  is  an  integer  that is set to one if support for Unicode
896           character properties is available; otherwise it is set to zero.
897    
898           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
899    
900         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
901         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
902         return (13), and should normally be the  standard  character  for  your         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, and -1 for ANY.
903         operating system.         The default should normally be the standard sequence for your operating
904           system.
905    
906           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
907    
908         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
909         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
910         4.  Larger  values  allow larger regular expressions to be compiled, at         4. Larger values allow larger regular expressions to  be  compiled,  at
911         the expense of slower matching. The default value of  2  is  sufficient         the  expense  of  slower matching. The default value of 2 is sufficient
912         for  all  but  the  most massive patterns, since it allows the compiled         for all but the most massive patterns, since  it  allows  the  compiled
913         pattern to be up to 64K in size.         pattern to be up to 64K in size.
914    
915           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
916    
917         The output is an integer that contains the threshold  above  which  the         The  output  is  an integer that contains the threshold above which the
918         POSIX  interface  uses malloc() for output vectors. Further details are         POSIX interface uses malloc() for output vectors. Further  details  are
919         given in the pcreposix documentation.         given in the pcreposix documentation.
920    
921           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
922    
923         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
924         internal  matching  function  calls in a pcre_exec() execution. Further         internal matching function calls in a  pcre_exec()  execution.  Further
925         details are given with pcre_exec() below.         details are given with pcre_exec() below.
926    
927             PCRE_CONFIG_MATCH_LIMIT_RECURSION
928    
929           The  output is an integer that gives the default limit for the depth of
930           recursion when calling the internal matching function in a  pcre_exec()
931           execution. Further details are given with pcre_exec() below.
932    
933           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
934    
935         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
936         implemented  by recursive function calls that use the stack to remember         running pcre_exec() is implemented by recursive function calls that use
937         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
938         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
939         recursive  function  calls.  In  this   case,   pcre_stack_malloc   and         on  the  heap  instead  of  recursive  function  calls.  In  this case,
940         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
941         avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
942    
943    
944  COMPILING A PATTERN  COMPILING A PATTERN
# Line 531  COMPILING A PATTERN Line 947  COMPILING A PATTERN
947              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
948              const unsigned char *tableptr);              const unsigned char *tableptr);
949    
950           pcre *pcre_compile2(const char *pattern, int options,
951                int *errorcodeptr,
952                const char **errptr, int *erroffset,
953                const unsigned char *tableptr);
954    
955         The function pcre_compile() is called to  compile  a  pattern  into  an         Either of the functions pcre_compile() or pcre_compile2() can be called
956         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
957         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,
958         memory  that is obtained via pcre_malloc is returned. This contains the         errorcodeptr, via which a numerical error code can be returned.
959         compiled code and related data.  The  pcre  type  is  defined  for  the  
960         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
961         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
962         it is no longer required.         obtained via pcre_malloc is returned. This contains the  compiled  code
963           and related data. The pcre type is defined for the returned block; this
964           is a typedef for a structure whose contents are not externally defined.
965           It is up to the caller to free the memory (via pcre_free) when it is no
966           longer required.
967    
968         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
969         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
970         fully relocatable, because it contains a copy of the tableptr argument,         fully relocatable, because it may contain a copy of the tableptr  argu-
971         which is an address (see below).         ment, which is an address (see below).
972    
973         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
974         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
975         options, in particular, those that are compatible with Perl,  can  also         options  are  described  below. Some of them, in particular, those that
976         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
977         of regular expressions in the  pcrepattern  documentation).  For  these         pattern  (see  the  detailed  description in the pcrepattern documenta-
978         options,  the  contents of the options argument specifies their initial         tion). For these options, the contents of the options  argument  speci-
979         settings at the start of compilation and execution.  The  PCRE_ANCHORED         fies  their initial settings at the start of compilation and execution.
980         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
981           of matching as well as at compile time.
982    
983         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
984         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
985         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-
986         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
987         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-
988         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
989           by  erroffset,  which must not be NULL. If it is, an immediate error is
990         given.         given.
991    
992           If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
993           codeptr  argument is not NULL, a non-zero error code number is returned
994           via this argument in the event of an error. This is in addition to  the
995           textual error message. Error codes and messages are listed below.
996    
997         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
998         character tables which are built when it is compiled, using the default         character tables that are  built  when  PCRE  is  compiled,  using  the
999         C  locale.  Otherwise,  tableptr  must  be  the  result  of  a  call to         default  C  locale.  Otherwise, tableptr must be an address that is the
1000         pcre_maketables(). See the section on locale support below.         result of a call to pcre_maketables(). This value is  stored  with  the
1001           compiled  pattern,  and used again by pcre_exec(), unless another table
1002           pointer is passed to it. For more discussion, see the section on locale
1003           support below.
1004    
1005         This code fragment shows a typical straightforward  call  to  pcre_com-         This  code  fragment  shows a typical straightforward call to pcre_com-
1006         pile():         pile():
1007    
1008           pcre *re;           pcre *re;
# Line 581  COMPILING A PATTERN Line 1015  COMPILING A PATTERN
1015             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1016             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1017    
1018         The following option bits are defined:         The following names for option bits are defined in  the  pcre.h  header
1019           file:
1020    
1021           PCRE_ANCHORED           PCRE_ANCHORED
1022    
1023         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
1024         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
1025         which is being searched (the "subject string"). This effect can also be         that  is being searched (the "subject string"). This effect can also be
1026         achieved by appropriate constructs in the pattern itself, which is  the         achieved by appropriate constructs in the pattern itself, which is  the
1027         only way to do it in Perl.         only way to do it in Perl.
1028    
1029             PCRE_AUTO_CALLOUT
1030    
1031           If this bit is set, pcre_compile() automatically inserts callout items,
1032           all with number 255, before each pattern item. For  discussion  of  the
1033           callout facility, see the pcrecallout documentation.
1034    
1035           PCRE_CASELESS           PCRE_CASELESS
1036    
1037         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
1038         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
1039         changed within a pattern by a (?i) option setting.         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
1040           always understands the concept of case for characters whose values  are
1041           less  than 128, so caseless matching is always possible. For characters
1042           with higher values, the concept of case is supported if  PCRE  is  com-
1043           piled  with Unicode property support, but not otherwise. If you want to
1044           use caseless matching for characters 128 and  above,  you  must  ensure
1045           that  PCRE  is  compiled  with Unicode property support as well as with
1046           UTF-8 support.
1047    
1048           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1049    
1050         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
1051         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
1052         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
1053         not before any  other  newlines).  The  PCRE_DOLLAR_ENDONLY  option  is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1054         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
1055         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1056    
1057           PCRE_DOTALL           PCRE_DOTALL
1058    
1059         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-
1060         acters,  including  newlines.  Without  it, newlines are excluded. This         acters, including those that indicate newline. Without it, a  dot  does
1061         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
1062         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
1063         always matches a newline character, independent of the setting of  this         by  a (?s) option setting. A negative class such as [^a] always matches
1064         option.         newline characters, independent of the setting of this option.
1065    
1066             PCRE_DUPNAMES
1067    
1068           If this bit is set, names used to identify capturing  subpatterns  need
1069           not be unique. This can be helpful for certain types of pattern when it
1070           is known that only one instance of the named  subpattern  can  ever  be
1071           matched.  There  are  more details of named subpatterns below; see also
1072           the pcrepattern documentation.
1073    
1074           PCRE_EXTENDED           PCRE_EXTENDED
1075    
1076         If  this  bit  is  set,  whitespace  data characters in the pattern are         If this bit is set, whitespace  data  characters  in  the  pattern  are
1077         totally ignored except  when  escaped  or  inside  a  character  class.         totally ignored except when escaped or inside a character class. White-
1078         Whitespace  does  not  include the VT character (code 11). In addition,         space does not include the VT character (code 11). In addition, charac-
1079         characters between an unescaped # outside a  character  class  and  the         ters between an unescaped # outside a character class and the next new-
1080         next newline character, inclusive, are also ignored. This is equivalent         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1081         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-
1082         option setting.         ting.
1083    
1084         This  option  makes  it possible to include comments inside complicated         This option makes it possible to include  comments  inside  complicated
1085         patterns.  Note, however, that this applies only  to  data  characters.         patterns.   Note,  however,  that this applies only to data characters.
1086         Whitespace   characters  may  never  appear  within  special  character         Whitespace  characters  may  never  appear  within  special   character
1087         sequences in a pattern, for  example  within  the  sequence  (?(  which         sequences  in  a  pattern,  for  example  within the sequence (?( which
1088         introduces a conditional subpattern.         introduces a conditional subpattern.
1089    
1090           PCRE_EXTRA           PCRE_EXTRA
1091    
1092         This  option  was invented in order to turn on additional functionality         This option was invented in order to turn on  additional  functionality
1093         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
1094         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
1095         letter that has no special meaning  causes  an  error,  thus  reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1096         these  combinations  for  future  expansion.  By default, as in Perl, a         these combinations for future expansion. By  default,  as  in  Perl,  a
1097         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
1098         literal.  There  are  at  present  no other features controlled by this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1099         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
1100           can also be set by a (?X) option setting within a pattern.
1101    
1102             PCRE_FIRSTLINE
1103    
1104           If this option is set, an  unanchored  pattern  is  required  to  match
1105           before  or  at  the  first  newline  in  the subject string, though the
1106           matched text may continue over the newline.
1107    
1108           PCRE_MULTILINE           PCRE_MULTILINE
1109    
1110         By default, PCRE treats the subject string as consisting  of  a  single         By default, PCRE treats the subject string as consisting  of  a  single
1111         "line"  of  characters (even if it actually contains several newlines).         line  of characters (even if it actually contains newlines). The "start
1112         The "start of line" metacharacter (^) matches only at the start of  the         of line" metacharacter (^) matches only at the  start  of  the  string,
1113         string,  while  the "end of line" metacharacter ($) matches only at the         while  the  "end  of line" metacharacter ($) matches only at the end of
1114         end of the string, or before a terminating  newline  (unless  PCRE_DOL-         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1115         LAR_ENDONLY is set). This is the same as Perl.         is set). This is the same as Perl.
1116    
1117         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"
1118         constructs match immediately following or immediately before  any  new-         constructs match immediately following or immediately  before  internal
1119         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
1120         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
1121         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-
1122         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,
1123         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1124    
1125             PCRE_NEWLINE_CR
1126             PCRE_NEWLINE_LF
1127             PCRE_NEWLINE_CRLF
1128             PCRE_NEWLINE_ANY
1129    
1130           These  options  override the default newline definition that was chosen
1131           when PCRE was built. Setting the first or the second specifies  that  a
1132           newline  is  indicated  by a single character (CR or LF, respectively).
1133           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1134           two-character  CRLF  sequence.  Setting PCRE_NEWLINE_ANY specifies that
1135           any Unicode newline sequence should be recognized. The Unicode  newline
1136           sequences  are  the three just mentioned, plus the single characters VT
1137           (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085),
1138           LS  (line separator, U+2028), and PS (paragraph separator, U+2029). The
1139           last two are recognized only in UTF-8 mode.
1140    
1141           The newline setting in the  options  word  uses  three  bits  that  are
1142           treated  as  a  number, giving eight possibilities. Currently only five
1143           are used (default plus the four values above). This means that  if  you
1144           set  more  than  one  newline option, the combination may or may not be
1145           sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is  equiva-
1146           lent  to PCRE_NEWLINE_CRLF, but other combinations yield unused numbers
1147           and cause an error.
1148    
1149           The only time that a line break is specially recognized when  compiling
1150           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1151           character class is encountered. This indicates  a  comment  that  lasts
1152           until  after the next line break sequence. In other circumstances, line
1153           break  sequences  are  treated  as  literal  data,   except   that   in
1154           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1155           and are therefore ignored.
1156    
1157           The newline option that is set at compile time becomes the default that
1158           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1159    
1160           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1161    
1162         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-
1163         theses in the pattern. Any opening parenthesis that is not followed  by         theses  in the pattern. Any opening parenthesis that is not followed by
1164         ?  behaves as if it were followed by ?: but named parentheses can still         ? behaves as if it were followed by ?: but named parentheses can  still
1165         be used for capturing (and they acquire  numbers  in  the  usual  way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1166         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1167    
1168           PCRE_UNGREEDY           PCRE_UNGREEDY
1169    
1170         This  option  inverts  the "greediness" of the quantifiers so that they         This option inverts the "greediness" of the quantifiers  so  that  they
1171         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
1172         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
1173         within the pattern.         within the pattern.
1174    
1175           PCRE_UTF8           PCRE_UTF8
1176    
1177         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
1178         strings  of  UTF-8 characters instead of single-byte character strings.         strings of UTF-8 characters instead of single-byte  character  strings.
1179         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-
1180         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
1181         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
1182         on UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1183    
1184           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1185    
1186         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
1187         automatically checked. If an invalid UTF-8 sequence of bytes is  found,         automatically  checked. If an invalid UTF-8 sequence of bytes is found,
1188         pcre_compile()  returns an error. If you already know that your pattern         pcre_compile() returns an error. If you already know that your  pattern
1189         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
1190         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
1191         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
1192         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
1193         pressing the checking of subject strings passed to pcre_exec().         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1194           ing of subject strings.
1195    
1196    
1197    COMPILATION ERROR CODES
1198    
1199           The following table lists the error  codes  than  may  be  returned  by
1200           pcre_compile2(),  along with the error messages that may be returned by
1201           both compiling functions. As PCRE has developed, some error codes  have
1202           fallen out of use. To avoid confusion, they have not been re-used.
1203    
1204              0  no error
1205              1  \ at end of pattern
1206              2  \c at end of pattern
1207              3  unrecognized character follows \
1208              4  numbers out of order in {} quantifier
1209              5  number too big in {} quantifier
1210              6  missing terminating ] for character class
1211              7  invalid escape sequence in character class
1212              8  range out of order in character class
1213              9  nothing to repeat
1214             10  [this code is not in use]
1215             11  internal error: unexpected repeat
1216             12  unrecognized character after (?
1217             13  POSIX named classes are supported only within a class
1218             14  missing )
1219             15  reference to non-existent subpattern
1220             16  erroffset passed as NULL
1221             17  unknown option bit(s) set
1222             18  missing ) after comment
1223             19  [this code is not in use]
1224             20  regular expression too large
1225             21  failed to get memory
1226             22  unmatched parentheses
1227             23  internal error: code overflow
1228             24  unrecognized character after (?<
1229             25  lookbehind assertion is not fixed length
1230             26  malformed number or name after (?(
1231             27  conditional group contains more than two branches
1232             28  assertion expected after (?(
1233             29  (?R or (?digits must be followed by )
1234             30  unknown POSIX class name
1235             31  POSIX collating elements are not supported
1236             32  this version of PCRE is not compiled with PCRE_UTF8 support
1237             33  [this code is not in use]
1238             34  character value in \x{...} sequence is too large
1239             35  invalid condition (?(0)
1240             36  \C not allowed in lookbehind assertion
1241             37  PCRE does not support \L, \l, \N, \U, or \u
1242             38  number after (?C is > 255
1243             39  closing ) for (?C expected
1244             40  recursive call could loop indefinitely
1245             41  unrecognized character after (?P
1246             42  syntax error in subpattern name (missing terminator)
1247             43  two named subpatterns have the same name
1248             44  invalid UTF-8 string
1249             45  support for \P, \p, and \X has not been compiled
1250             46  malformed \P or \p sequence
1251             47  unknown property name after \P or \p
1252             48  subpattern name is too long (maximum 32 characters)
1253             49  too many named subpatterns (maximum 10,000)
1254             50  repeated subpattern is too long
1255             51  octal value is greater than \377 (not in UTF-8 mode)
1256             52  internal error: overran compiling workspace
1257             53   internal  error:  previously-checked  referenced  subpattern not
1258           found
1259             54  DEFINE group contains more than one branch
1260             55  repeating a DEFINE group is not allowed
1261             56  inconsistent NEWLINE options"
1262    
1263    
1264  STUDYING A PATTERN  STUDYING A PATTERN
1265    
1266         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1267              const char **errptr);              const char **errptr);
1268    
1269         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
1270         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
1271         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-
1272         its first argument. If studing the pattern produces additional informa-         tern as its first argument. If studying the pattern produces additional
1273         tion that will help speed up matching, pcre_study() returns  a  pointer         information that will help speed up matching,  pcre_study()  returns  a
1274         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
1275         results of the study.         the results of the study.
1276    
1277         The returned value from  a  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1278         pcre_exec().  However,  the pcre_extra block also contains other fields         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1279         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
1280         described  below.  If  studying  the pattern does not produce any addi-         described below in the section on matching a pattern.
1281         tional information, pcre_study() returns NULL. In that circumstance, if  
1282         the  calling  program  wants  to  pass  some  of  the  other  fields to         If  studying  the  pattern  does not produce any additional information
1283         pcre_exec(), it must set up its own pcre_extra block.         pcre_study() returns NULL. In that circumstance, if the calling program
1284           wants  to  pass  any of the other fields to pcre_exec(), it must set up
1285           its own pcre_extra block.
1286    
1287         The second argument contains option bits. At present,  no  options  are         The second argument of pcre_study() contains option bits.  At  present,
1288         defined for pcre_study(), and this argument should always be zero.         no options are defined, and this argument should always be zero.
1289    
1290         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.
1291         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1292         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
1293         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
1294         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
1295           after calling pcre_study(), to be sure that it has run successfully.
1296    
1297         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1298    
# Line 735  STUDYING A PATTERN Line 1303  STUDYING A PATTERN
1303             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1304    
1305         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1306         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-
1307         ble starting characters is created.         ble starting bytes is created.
1308    
1309    
1310  LOCALE SUPPORT  LOCALE SUPPORT
1311    
1312         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1313         letters, digits, or whatever, by reference to a  set  of  tables.  When         letters  digits,  or whatever, by reference to a set of tables, indexed
1314         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
1315         than 256. The library contains a default set of tables that is  created         characters  with  codes  less than 128. Higher-valued codes never match
1316         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
1317         final argument of pcre_compile() is NULL, and is  sufficient  for  many         with  Unicode  character property support. The use of locales with Uni-
1318         applications.         code is discouraged.
1319    
1320         An alternative set of tables can, however, be supplied. Such tables are         An internal set of tables is created in the default C locale when  PCRE
1321         built by calling the pcre_maketables() function,  which  has  no  argu-         is  built.  This  is  used when the final argument of pcre_compile() is
1322         ments,  in  the  relevant  locale.  The  result  can  then be passed to         NULL, and is sufficient for many applications. An  alternative  set  of
1323         pcre_compile() as often as necessary. For example,  to  build  and  use         tables  can,  however, be supplied. These may be created in a different
1324         tables that are appropriate for the French locale (where accented char-         locale from the default. As more and more applications change to  using
1325         acters with codes greater than 128 are treated as letters), the follow-         Unicode, the need for this locale support is expected to die away.
1326         ing code could be used:  
1327           External  tables  are  built by calling the pcre_maketables() function,
1328           which has no arguments, in the relevant locale. The result can then  be
1329           passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
1330           example, to build and use tables that are appropriate  for  the  French
1331           locale  (where  accented  characters  with  values greater than 128 are
1332           treated as letters), the following code could be used:
1333    
1334           setlocale(LC_CTYPE, "fr");           setlocale(LC_CTYPE, "fr_FR");
1335           tables = pcre_maketables();           tables = pcre_maketables();
1336           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1337    
1338         The  tables  are  built in memory that is obtained via pcre_malloc. The         When pcre_maketables() runs, the tables are built  in  memory  that  is
1339         pointer that is passed to pcre_compile is saved with the compiled  pat-         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1340         tern, and the same tables are used via this pointer by pcre_study() and         that the memory containing the tables remains available for as long  as
1341         pcre_exec(). Thus, for any single pattern,  compilation,  studying  and         it is needed.
1342         matching  all  happen in the same locale, but different patterns can be  
1343         compiled in different locales. It is  the  caller's  responsibility  to         The pointer that is passed to pcre_compile() is saved with the compiled
1344         ensure  that  the memory containing the tables remains available for as         pattern, and the same tables are used via this pointer by  pcre_study()
1345         long as it is needed.         and normally also by pcre_exec(). Thus, by default, for any single pat-
1346           tern, compilation, studying and matching all happen in the same locale,
1347           but different patterns can be compiled in different locales.
1348    
1349           It  is  possible to pass a table pointer or NULL (indicating the use of
1350           the internal tables) to pcre_exec(). Although  not  intended  for  this
1351           purpose,  this facility could be used to match a pattern in a different
1352           locale from the one in which it was compiled. Passing table pointers at
1353           run time is discussed below in the section on matching a pattern.
1354    
1355    
1356  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
# Line 776  INFORMATION ABOUT A PATTERN Line 1358  INFORMATION ABOUT A PATTERN
1358         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1359              int what, void *where);              int what, void *where);
1360    
1361         The pcre_fullinfo() function returns information about a compiled  pat-         The  pcre_fullinfo() function returns information about a compiled pat-
1362         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1363         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1364    
1365         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1366         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
1367         the pattern was not studied. The third argument specifies  which  piece         the  pattern  was not studied. The third argument specifies which piece
1368         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
1369         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
1370         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1371    
1372           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 792  INFORMATION ABOUT A PATTERN Line 1374  INFORMATION ABOUT A PATTERN
1374           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1375           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1376    
1377         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
1378         compiled pattern:         an  simple check against passing an arbitrary memory pointer. Here is a
1379           typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1380           pattern:
1381    
1382           int rc;           int rc;
1383           unsigned long int length;           size_t length;
1384           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1385             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1386             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1387             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1388             &length);         /* where to put the data */             &length);         /* where to put the data */
1389    
1390         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
1391         are as follows:         are as follows:
1392    
1393           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1394    
1395         Return  the  number  of  the highest back reference in the pattern. The         Return the number of the highest back reference  in  the  pattern.  The
1396         fourth argument should point to an int variable. Zero  is  returned  if         fourth  argument  should  point to an int variable. Zero is returned if
1397         there are no back references.         there are no back references.
1398    
1399           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1400    
1401         Return  the  number of capturing subpatterns in the pattern. The fourth         Return the number of capturing subpatterns in the pattern.  The  fourth
1402         argument should point to an int variable.         argument should point to an int variable.
1403    
1404             PCRE_INFO_DEFAULT_TABLES
1405    
1406           Return  a pointer to the internal default character tables within PCRE.
1407           The fourth argument should point to an unsigned char *  variable.  This
1408           information call is provided for internal use by the pcre_study() func-
1409           tion. External callers can cause PCRE to use  its  internal  tables  by
1410           passing a NULL table pointer.
1411    
1412           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1413    
1414         Return information about the first byte of any matched  string,  for  a         Return  information  about  the first byte of any matched string, for a
1415         non-anchored    pattern.    (This    option    used    to   be   called         non-anchored pattern. The fourth argument should point to an int  vari-
1416         PCRE_INFO_FIRSTCHAR; the old name is  still  recognized  for  backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1417         compatibility.)         is still recognized for backwards compatibility.)
1418    
1419         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
1420         (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  
1421    
1422         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1423         branch starts with "^", or         branch starts with "^", or
# Line 862  INFORMATION ABOUT A PATTERN Line 1453  INFORMATION ABOUT A PATTERN
1453    
1454         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1455         ses. The names are just an additional way of identifying the  parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1456         ses,  which still acquire a number. A caller that wants to extract data         ses, which still acquire numbers. Several convenience functions such as
1457         from a named subpattern must convert the name to a number in  order  to         pcre_get_named_substring() are provided for  extracting  captured  sub-
1458         access  the  correct  pointers  in  the  output  vector (described with         strings  by  name. It is also possible to extract the data directly, by
1459         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
1460         values to obtain the name-to-number mapping table for the pattern.         pointers in the output vector (described with pcre_exec() below). To do
1461           the conversion, you need  to  use  the  name-to-number  map,  which  is
1462           described by these three values.
1463    
1464         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
1465         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 1469  INFORMATION ABOUT A PATTERN
1469         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-
1470         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-
1471         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1472         For  example,  consider  the following pattern (assume PCRE_EXTENDED is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1473         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1474           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1475           ignored):
1476    
1477           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1478           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1479    
1480         There are four named subpatterns, so the table has  four  entries,  and         There are four named subpatterns, so the table has  four  entries,  and
1481         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,
1482         with non-printing bytes shows in hex, and undefined bytes shown as ??:         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1483           as ??:
1484    
1485           00 01 d  a  t  e  00 ??           00 01 d  a  t  e  00 ??
1486           00 05 d  a  y  00 ?? ??           00 05 d  a  y  00 ?? ??
1487           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1488           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1489    
1490         When writing code to extract data from named subpatterns, remember that         When  writing  code  to  extract  data from named subpatterns using the
1491         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
1492           to be different for each compiled pattern.
1493    
1494           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1495    
# Line 922  INFORMATION ABOUT A PATTERN Line 1519  INFORMATION ABOUT A PATTERN
1519    
1520           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1521    
1522         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
1523         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
1524         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
1525         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
1526         variable.         variable.
# Line 951  OBSOLETE INFO FUNCTION Line 1548  OBSOLETE INFO FUNCTION
1548         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1549    
1550    
1551  MATCHING A PATTERN  REFERENCE COUNTS
1552    
1553           int pcre_refcount(pcre *code, int adjust);
1554    
1555           The  pcre_refcount()  function is used to maintain a reference count in
1556           the data block that contains a compiled pattern. It is provided for the
1557           benefit  of  applications  that  operate  in an object-oriented manner,
1558           where different parts of the application may be using the same compiled
1559           pattern, but you want to free the block when they are all done.
1560    
1561           When a pattern is compiled, the reference count field is initialized to
1562           zero.  It is changed only by calling this function, whose action is  to
1563           add  the  adjust  value  (which may be positive or negative) to it. The
1564           yield of the function is the new value. However, the value of the count
1565           is  constrained to lie between 0 and 65535, inclusive. If the new value
1566           is outside these limits, it is forced to the appropriate limit value.
1567    
1568           Except when it is zero, the reference count is not correctly  preserved
1569           if  a  pattern  is  compiled on one host and then transferred to a host
1570           whose byte-order is different. (This seems a highly unlikely scenario.)
1571    
1572    
1573    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1574    
1575         int pcre_exec(const pcre *code, const pcre_extra *extra,         int pcre_exec(const pcre *code, const pcre_extra *extra,
1576              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1577              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1578    
1579         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
1580         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
1581         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
1582         extra argument.         argument. This function is the main matching facility of  the  library,
1583           and it operates in a Perl-like manner. For specialist use there is also
1584           an alternative matching function, which is described below in the  sec-
1585           tion about the pcre_dfa_exec() function.
1586    
1587           In  most applications, the pattern will have been compiled (and option-
1588           ally studied) in the same process that calls pcre_exec().  However,  it
1589           is possible to save compiled patterns and study data, and then use them
1590           later in different processes, possibly even on different hosts.  For  a
1591           discussion about this, see the pcreprecompile documentation.
1592    
1593         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
1594    
# Line 973  MATCHING A PATTERN Line 1601  MATCHING A PATTERN
1601             11,             /* the length of the subject string */             11,             /* the length of the subject string */
1602             0,              /* start at offset 0 in the subject */             0,              /* start at offset 0 in the subject */
1603             0,              /* default options */             0,              /* default options */
1604             ovector,        /* vector for substring information */             ovector,        /* vector of integers for substring information */
1605             30);            /* number of elements in the vector */             30);            /* number of elements (NOT size in bytes) */
1606    
1607       Extra data for pcre_exec()
1608    
1609         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
1610         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
1611         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-
1612         tional information in it. The fields in the block are as follows:         tional information in it. The pcre_extra block contains  the  following
1613           fields (not necessarily in this order):
1614    
1615           unsigned long int flags;           unsigned long int flags;
1616           void *study_data;           void *study_data;
1617           unsigned long int match_limit;           unsigned long int match_limit;
1618             unsigned long int match_limit_recursion;
1619           void *callout_data;           void *callout_data;
1620             const unsigned char *tables;
1621    
1622         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
1623         are set. The flag bits are:         are set. The flag bits are:
1624    
1625           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1626           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1627             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1628           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1629             PCRE_EXTRA_TABLES
1630    
1631         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
1632         the  pcre_extra  block  that is returned by pcre_study(), together with         the  pcre_extra  block  that is returned by pcre_study(), together with
1633         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
1634         add to the block by setting the other fields.         add  to  the  block by setting the other fields and their corresponding
1635           flag bits.
1636    
1637         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
1638         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
1639         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1640         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1641         repeats. Internally, PCRE uses a function called match() which it calls         repeats.
1642         repeatedly (sometimes recursively). The limit is imposed on the  number  
1643         of  times  this function is called during a match, which has the effect         Internally, PCRE uses a function called match() which it calls  repeat-
1644         of limiting the amount of recursion  and  backtracking  that  can  take         edly  (sometimes  recursively). The limit set by match_limit is imposed
1645         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
1646           has  the  effect  of  limiting the amount of backtracking that can take
1647           place. For patterns that are not anchored, the count restarts from zero
1648         for each position in the subject string.         for each position in the subject string.
1649    
1650         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
1651         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1652         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1653         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra    block    in    which    match_limit    is    set,     and
1654         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
1655         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1656    
1657         The  pcre_callout  field is used in conjunction with the "callout" fea-         The match_limit_recursion field is similar to match_limit, but  instead
1658           of limiting the total number of times that match() is called, it limits
1659           the depth of recursion. The recursion depth is a  smaller  number  than
1660           the  total number of calls, because not all calls to match() are recur-
1661           sive.  This limit is of use only if it is set smaller than match_limit.
1662    
1663           Limiting  the  recursion  depth  limits the amount of stack that can be
1664           used, or, when PCRE has been compiled to use memory on the heap instead
1665           of the stack, the amount of heap memory that can be used.
1666    
1667           The  default  value  for  match_limit_recursion can be set when PCRE is
1668           built; the default default  is  the  same  value  as  the  default  for
1669           match_limit.  You can override the default by suppling pcre_exec() with
1670           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1671           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1672           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1673    
1674           The pcre_callout field is used in conjunction with the  "callout"  fea-
1675         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1676    
1677         The PCRE_ANCHORED option can be passed in the options  argument,  whose         The  tables  field  is  used  to  pass  a  character  tables pointer to
1678         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
1679         first matching position.  However,  if  a  pattern  was  compiled  with         pattern.  A  non-NULL value is stored with the compiled pattern only if
1680         PCRE_ANCHORED,  or turned out to be anchored by virtue of its contents,         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1681         it cannot be made unachored at matching time.         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1682           PCRE's internal tables to be used. This facility is  helpful  when  re-
1683         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
1684         a  UTF-8  string is automatically checked, and the value of startoffset         set of tables, because the external tables  might  be  at  a  different
1685         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-
1686         acter.  If  an  invalid  UTF-8  sequence of bytes is found, pcre_exec()         tion for a discussion of saving compiled patterns for later use.
1687         returns  the  error  PCRE_ERROR_BADUTF8.  If  startoffset  contains  an  
1688         invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.     Option bits for pcre_exec()
1689    
1690         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.
1691         these   checks   for   performance   reasons,   you   can    set    the         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1692         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1693         do this for the second and subsequent calls to pcre_exec() if  you  are         PCRE_PARTIAL.
1694         making  repeated  calls  to  find  all  the matches in a single subject  
1695         string. However, you should be  sure  that  the  value  of  startoffset           PCRE_ANCHORED
        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.  
1696    
1697         There are also three further options that can be set only  at  matching         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1698         time:         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1699           turned  out to be anchored by virtue of its contents, it cannot be made
1700           unachored at matching time.
1701    
1702             PCRE_NEWLINE_CR
1703             PCRE_NEWLINE_LF
1704             PCRE_NEWLINE_CRLF
1705             PCRE_NEWLINE_ANY
1706    
1707           These options override  the  newline  definition  that  was  chosen  or
1708           defaulted  when the pattern was compiled. For details, see the descrip-
1709           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1710           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1711           ters. It may also alter the way the match position is advanced after  a
1712           match  failure  for  an  unanchored  pattern. When PCRE_NEWLINE_CRLF or
1713           PCRE_NEWLINE_ANY is set, and a match attempt  fails  when  the  current
1714           position  is  at a CRLF sequence, the match position is advanced by two
1715           characters instead of one, in other words, to after the CRLF.
1716    
1717           PCRE_NOTBOL           PCRE_NOTBOL
1718    
1719         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
1720         the circumflex metacharacter should not match before it.  Setting  this         the  beginning  of  a  line, so the circumflex metacharacter should not
1721         without  PCRE_MULTILINE  (at  compile  time) causes circumflex never to         match before it. Setting this without PCRE_MULTILINE (at compile  time)
1722         match.         causes  circumflex  never to match. This option affects only the behav-
1723           iour of the circumflex metacharacter. It does not affect \A.
1724    
1725           PCRE_NOTEOL           PCRE_NOTEOL
1726    
1727         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
1728         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
1729         immediately before it. Setting this without PCRE_MULTILINE (at  compile         in multiline mode) a newline immediately before it. Setting this  with-
1730         time) causes dollar never to match.         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1731           option affects only the behaviour of the dollar metacharacter. It  does
1732           not affect \Z or \z.
1733    
1734           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1735    
# Line 1078  MATCHING A PATTERN Line 1749  MATCHING A PATTERN
1749         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()
1750         function,  and  when  using  the /g modifier. It is possible to emulate         function,  and  when  using  the /g modifier. It is possible to emulate
1751         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
1752         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
1753         by advancing the starting offset (see below)  and  trying  an  ordinary         if that fails by advancing the starting offset (see below)  and  trying
1754         match again.         an ordinary match again. There is some code that demonstrates how to do
1755           this in the pcredemo.c sample program.
1756         The  subject string is passed to pcre_exec() as a pointer in subject, a  
1757         length in length, and a starting byte offset in startoffset. Unlike the           PCRE_NO_UTF8_CHECK
1758         pattern  string,  the  subject  may contain binary zero bytes. When the  
1759         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
1760         of the subject, and this is by far the most common case.         UTF-8  string is automatically checked when pcre_exec() is subsequently
1761           called.  The value of startoffset is also checked  to  ensure  that  it
1762         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
1763         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
1764         offset  must point to the beginning of a UTF-8 character. If an invalid         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is
1765         UTF-8 string or offset is passed, an error  (either  PCRE_ERROR_BADUTF8         returned.
1766         or   PCRE_ERROR_BADUTF8_OFFSET)   is   returned,   unless   the  option  
1767         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
1768         defined.         these    checks    for   performance   reasons,   you   can   set   the
1769           PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
1770           do  this  for the second and subsequent calls to pcre_exec() if you are
1771           making repeated calls to find all  the  matches  in  a  single  subject
1772           string.  However,  you  should  be  sure  that the value of startoffset
1773           points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
1774           set,  the  effect of passing an invalid UTF-8 string as a subject, or a
1775           value of startoffset that does not point to the start of a UTF-8  char-
1776           acter, is undefined. Your program may crash.
1777    
1778             PCRE_PARTIAL
1779    
1780           This  option  turns  on  the  partial  matching feature. If the subject
1781           string fails to match the pattern, but at some point during the  match-
1782           ing  process  the  end of the subject was reached (that is, the subject
1783           partially matches the pattern and the failure to  match  occurred  only
1784           because  there were not enough subject characters), pcre_exec() returns
1785           PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1786           used,  there  are restrictions on what may appear in the pattern. These
1787           are discussed in the pcrepartial documentation.
1788    
1789       The string to be matched by pcre_exec()
1790    
1791           The subject string is passed to pcre_exec() as a pointer in subject,  a
1792           length  in  length, and a starting byte offset in startoffset. In UTF-8
1793           mode, the byte offset must point to the start  of  a  UTF-8  character.
1794           Unlike  the  pattern string, the subject may contain binary zero bytes.
1795           When the starting offset is zero, the search for a match starts at  the
1796           beginning of the subject, and this is by far the most common case.
1797    
1798         A  non-zero  starting offset is useful when searching for another match         A  non-zero  starting offset is useful when searching for another match
1799         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 1810  MATCHING A PATTERN
1810         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the  remainder  of  the  subject,  namely  "issipi", it does not match,
1811         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
1812         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
1813         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-
1814         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
1815         point to discover that it is preceded by a letter.         discover that it is preceded by a letter.
1816    
1817         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,
1818         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
1819         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
1820         the subject.         subject.
1821    
1822       How pcre_exec() returns captured substrings
1823    
1824         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
1825         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 1831  MATCHING A PATTERN
1831    
1832         Captured  substrings are returned to the caller via a vector of integer         Captured  substrings are returned to the caller via a vector of integer
1833         offsets whose address is passed in ovector. The number of  elements  in         offsets whose address is passed in ovector. The number of  elements  in
1834         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.
1835         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.  
   
        Some  convenience  functions  are  provided for extracting the captured  
        substrings as separate strings. These are described  in  the  following  
        section.  
1836    
1837         It  is  possible  for  an capturing subpattern number n+1 to match some         The first two-thirds of the vector is used to pass back  captured  sub-
1838         part of the subject when subpattern n has not been  used  at  all.  For         strings,  each  substring using a pair of integers. The remaining third
1839         example, if the string "abc" is matched against the pattern (a|(z))(bc)         of the vector is used as workspace by pcre_exec() while  matching  cap-
1840         subpatterns 1 and 3 are matched, but 2 is not. When this happens,  both         turing  subpatterns, and is not available for passing back information.
1841         offset values corresponding to the unused subpattern are set to -1.         The length passed in ovecsize should always be a multiple of three.  If
1842           it is not, it is rounded down.
1843    
1844           When  a  match  is successful, information about captured substrings is
1845           returned in pairs of integers, starting at the  beginning  of  ovector,
1846           and  continuing  up  to two-thirds of its length at the most. The first
1847           element of a pair is set to the offset of the first character in a sub-
1848           string,  and  the  second  is  set to the offset of the first character
1849           after the end of a substring. The  first  pair,  ovector[0]  and  ovec-
1850           tor[1],  identify  the  portion  of  the  subject string matched by the
1851           entire pattern. The next pair is used for the first  capturing  subpat-
1852           tern, and so on. The value returned by pcre_exec() is one more than the
1853           highest numbered pair that has been set. For example, if two substrings
1854           have  been captured, the returned value is 3. If there are no capturing
1855           subpatterns, the return value from a successful match is 1,  indicating
1856           that just the first pair of offsets has been set.
1857    
1858         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1859         of the string that it matched that gets returned.         of the string that it matched that is returned.
1860    
1861         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,
1862         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
1863         tion returns a value of zero. In particular, if the  substring  offsets         function returns a value of zero. In particular, if the substring  off-
1864         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
1865         NULL and ovecsize as zero. However, if the pattern contains back refer-         as NULL and ovecsize as zero. However, if  the  pattern  contains  back
1866         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
1867         strings, PCRE has to get additional memory  for  use  during  matching.         substrings, PCRE has to get additional memory for use during  matching.
1868         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1869    
1870         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
1871         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
1872         that  will  allow for n captured substrings, in addition to the offsets         ovector  that  will allow for n captured substrings, in addition to the
1873         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.
1874    
1875           It is possible for capturing subpattern number n+1 to match  some  part
1876           of the subject when subpattern n has not been used at all. For example,
1877           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1878           return from the function is 4, and subpatterns 1 and 3 are matched, but
1879           2 is not. When this happens, both values in  the  offset  pairs  corre-
1880           sponding to unused subpatterns are set to -1.
1881    
1882           Offset  values  that correspond to unused subpatterns at the end of the
1883           expression are also set to -1. For example,  if  the  string  "abc"  is
1884           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1885           matched. The return from the function is 2, because  the  highest  used
1886           capturing subpattern number is 1. However, you can refer to the offsets
1887           for the second and third capturing subpatterns if  you  wish  (assuming
1888           the vector is large enough, of course).
1889    
1890           Some  convenience  functions  are  provided for extracting the captured
1891           substrings as separate strings. These are described below.
1892    
1893       Error return values from pcre_exec()
1894    
1895         If pcre_exec() fails, it returns a negative number. The  following  are         If pcre_exec() fails, it returns a negative number. The  following  are
1896         defined in the header file:         defined in the header file:
# Line 1196  MATCHING A PATTERN Line 1911  MATCHING A PATTERN
1911           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
1912    
1913         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,
1914         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
1915         it gives when the magic number isn't present.         pattern that was compiled in an environment of one endianness is run in
1916           an  environment  with the other endianness. This is the error that PCRE
1917           gives when the magic number is not present.
1918    
1919           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1920    
1921         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1922         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 1928  MATCHING A PATTERN
1928         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
1929         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
1930         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
1931         memory is freed at the end of matching.         memory is automatically freed at the end of matching.
1932    
1933           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
1934    
# Line 1221  MATCHING A PATTERN Line 1938  MATCHING A PATTERN
1938    
1939           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
1940    
1941         The recursion and backtracking limit, as specified by  the  match_limit         The backtracking limit, as specified by  the  match_limit  field  in  a
1942         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         pcre_extra  structure  (or  defaulted) was reached. See the description
1943         description above.         above.
1944    
1945           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
1946    
# Line 1242  MATCHING A PATTERN Line 1959  MATCHING A PATTERN
1959         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-
1960         ter.         ter.
1961    
1962             PCRE_ERROR_PARTIAL        (-12)
1963    
1964           The  subject  string did not match, but it did match partially. See the
1965           pcrepartial documentation for details of partial matching.
1966    
1967             PCRE_ERROR_BADPARTIAL     (-13)
1968    
1969           The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
1970           items  that are not supported for partial matching. See the pcrepartial
1971           documentation for details of partial matching.
1972    
1973             PCRE_ERROR_INTERNAL       (-14)
1974    
1975           An unexpected internal error has occurred. This error could  be  caused
1976           by a bug in PCRE or by overwriting of the compiled pattern.
1977    
1978             PCRE_ERROR_BADCOUNT       (-15)
1979    
1980           This  error is given if the value of the ovecsize argument is negative.
1981    
1982             PCRE_ERROR_RECURSIONLIMIT (-21)
1983    
1984           The internal recursion limit, as specified by the match_limit_recursion
1985           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
1986           description above.
1987    
1988             PCRE_ERROR_NULLWSLIMIT    (-22)
1989    
1990           When a group that can match an empty  substring  is  repeated  with  an
1991           unbounded  upper  limit, the subject position at the start of the group
1992           must be remembered, so that a test for an empty string can be made when
1993           the  end  of the group is reached. Some workspace is required for this;
1994           if it runs out, this error is given.
1995    
1996             PCRE_ERROR_BADNEWLINE     (-23)
1997    
1998           An invalid combination of PCRE_NEWLINE_xxx options was given.
1999    
2000           Error numbers -16 to -20 are not used by pcre_exec().
2001    
2002    
2003  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2004    
# Line 1256  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2013  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2013         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2014              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2015    
2016         Captured  substrings  can  be  accessed  directly  by using the offsets         Captured substrings can be  accessed  directly  by  using  the  offsets
2017         returned by pcre_exec() in  ovector.  For  convenience,  the  functions         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2018         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2019         string_list() are provided for extracting captured substrings  as  new,         string_list()  are  provided for extracting captured substrings as new,
2020         separate,  zero-terminated strings. These functions identify substrings         separate, zero-terminated strings. These functions identify  substrings
2021         by number. The next section describes functions  for  extracting  named         by  number.  The  next section describes functions for extracting named
2022         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2023         extracted and has a further zero added on the end, but  the  result  is  
2024         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2025           a  further zero added on the end, but the result is not, of course, a C
2026           string.  However, you can process such a string  by  referring  to  the
2027           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2028           string().  Unfortunately, the interface to pcre_get_substring_list() is
2029           not  adequate for handling strings containing binary zeros, because the
2030           end of the final string is not independently indicated.
2031    
2032         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-
2033         tions: subject is the subject string which has just  been  successfully         tions:  subject  is  the subject string that has just been successfully
2034         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
2035         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2036         were  captured  by  the match, including the substring that matched the         were captured by the match, including the substring  that  matched  the
2037         entire regular expression. This is the value returned by  pcre_exec  if         entire regular expression. This is the value returned by pcre_exec() if
2038         it  is greater than zero. If pcre_exec() returned zero, indicating that         it is greater than zero. If pcre_exec() returned zero, indicating  that
2039         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
2040         be the size of the vector divided by three.         be the number of elements in the vector divided by three.
2041    
2042         The  functions pcre_copy_substring() and pcre_get_substring() extract a         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2043         single substring, whose number is given as  stringnumber.  A  value  of         single  substring,  whose  number  is given as stringnumber. A value of
2044         zero  extracts  the  substring  that  matched the entire pattern, while         zero extracts the substring that matched the  entire  pattern,  whereas
2045         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2046         string(),  the  string  is  placed  in buffer, whose length is given by         string(), the string is placed in buffer,  whose  length  is  given  by
2047         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2048         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2049         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
2050         the terminating zero, or one of         the terminating zero, or one of these error codes:
2051    
2052           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2053    
2054         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
2055         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2056    
2057           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2058    
2059         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2060    
2061         The pcre_get_substring_list()  function  extracts  all  available  sub-         The  pcre_get_substring_list()  function  extracts  all  available sub-
2062         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
2063         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
2064         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
2065         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
2066         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
2067           error code
2068    
2069           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2070    
# Line 1313  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2077  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2077         string  by inspecting the appropriate offset in ovector, which is nega-         string  by inspecting the appropriate offset in ovector, which is nega-
2078         tive for unset substrings.         tive for unset substrings.
2079    
2080         The    two    convenience    functions    pcre_free_substring()     and         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2081         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
2082         previous call  of  pcre_get_substring()  or  pcre_get_substring_list(),         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2083         respectively. They do nothing more than call the function pointed to by         tively.  They  do  nothing  more  than  call the function pointed to by
2084         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.
2085         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-
2086         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2087         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-
2088         vided.         vided.
2089    
2090    
2091  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2092    
2093           int pcre_get_stringnumber(const pcre *code,
2094                const char *name);
2095    
2096         int pcre_copy_named_substring(const pcre *code,         int pcre_copy_named_substring(const pcre *code,
2097              const char *subject, int *ovector,              const char *subject, int *ovector,
2098              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2099              char *buffer, int buffersize);              char *buffer, int buffersize);
2100    
        int pcre_get_stringnumber(const pcre *code,  
             const char *name);  
   
2101         int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2102              const char *subject, int *ovector,              const char *subject, int *ovector,
2103              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2104              const char **stringptr);              const char **stringptr);
2105    
2106         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-
2107         ber.  This  can  be  done by calling pcre_get_stringnumber(). The first         ber.  For example, for this pattern
2108         argument is the compiled pattern, and the second is the name. For exam-  
2109         ple, for this pattern           (a+)b(?<xxx>\d+)...
2110    
2111           ab(?<xxx>\d+)...         the number of the subpattern called "xxx" is 2. If the name is known to
2112           be unique (PCRE_DUPNAMES was not set), you can find the number from the
2113         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-
2114         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
2115         described  in the previous section. For convenience, there are also two         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2116         functions that do the whole job.         subpattern of that name.
2117    
2118           Given the number, you can extract the substring directly, or use one of
2119           the functions described in the previous section. For convenience, there
2120           are also two functions that do the whole job.
2121    
2122         Most   of   the   arguments    of    pcre_copy_named_substring()    and         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2123         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
2124         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
2125         differences.         previous  section,  they  are not re-described here. There are just two
2126           differences:
2127    
2128         First,  instead  of a substring number, a substring name is given. Sec-         First, instead of a substring number, a substring name is  given.  Sec-
2129         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
2130         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
2131         name-to-number translation table.         name-to-number translation table.
2132    
2133         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2134         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2135         ate.         ate.
2136    
 Last updated: 09 December 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2137    
2138  PCRE(3)                                                                PCRE(3)  DUPLICATE SUBPATTERN NAMES
2139    
2140           int pcre_get_stringtable_entries(const pcre *code,
2141                const char *name, char **first, char **last);
2142    
2143           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2144           subpatterns are not required to  be  unique.  Normally,  patterns  with
2145           duplicate  names  are such that in any one match, only one of the named
2146           subpatterns participates. An example is shown in the pcrepattern  docu-
2147           mentation. When duplicates are present, pcre_copy_named_substring() and
2148           pcre_get_named_substring() return the first substring corresponding  to
2149           the  given  name  that  is  set.  If  none  are set, an empty string is
2150           returned.  The pcre_get_stringnumber() function returns one of the num-
2151           bers  that are associated with the name, but it is not defined which it
2152           is.
2153    
2154           If you want to get full details of all captured substrings for a  given
2155           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2156           first argument is the compiled pattern, and the second is the name. The
2157           third  and  fourth  are  pointers to variables which are updated by the
2158           function. After it has run, they point to the first and last entries in
2159           the  name-to-number  table  for  the  given  name.  The function itself
2160           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2161           there  are none. The format of the table is described above in the sec-
2162           tion entitled Information about a  pattern.   Given  all  the  relevant
2163           entries  for the name, you can extract each of their numbers, and hence
2164           the captured data, if any.
2165    
2166    
2167    FINDING ALL POSSIBLE MATCHES
2168    
2169           The traditional matching function uses a  similar  algorithm  to  Perl,
2170           which stops when it finds the first match, starting at a given point in
2171           the subject. If you want to find all possible matches, or  the  longest
2172           possible  match,  consider using the alternative matching function (see
2173           below) instead. If you cannot use the alternative function,  but  still
2174           need  to  find all possible matches, you can kludge it up by making use
2175           of the callout facility, which is described in the pcrecallout documen-
2176           tation.
2177    
2178           What you have to do is to insert a callout right at the end of the pat-
2179           tern.  When your callout function is called, extract and save the  cur-
2180           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2181           backtrack and try other alternatives. Ultimately, when it runs  out  of
2182           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2183    
2184    
2185    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2186    
2187           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2188                const char *subject, int length, int startoffset,
2189                int options, int *ovector, int ovecsize,
2190                int *workspace, int wscount);
2191    
2192           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2193           against a compiled pattern, using a matching algorithm that  scans  the
2194           subject  string  just  once, and does not backtrack. This has different
2195           characteristics to the normal algorithm, and  is  not  compatible  with
2196           Perl.  Some  of the features of PCRE patterns are not supported. Never-
2197           theless, there are times when this kind of matching can be useful.  For
2198           a discussion of the two matching algorithms, see the pcrematching docu-
2199           mentation.
2200    
2201           The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2202           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2203           ent way, and this is described below. The other  common  arguments  are
2204           used  in  the  same way as for pcre_exec(), so their description is not
2205           repeated here.
2206    
2207           The two additional arguments provide workspace for  the  function.  The
2208           workspace  vector  should  contain at least 20 elements. It is used for
2209           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2210           workspace  will  be  needed for patterns and subjects where there are a
2211           lot of potential matches.
2212    
2213           Here is an example of a simple call to pcre_dfa_exec():
2214    
2215             int rc;
2216             int ovector[10];
2217             int wspace[20];
2218             rc = pcre_dfa_exec(
2219               re,             /* result of pcre_compile() */
2220               NULL,           /* we didn't study the pattern */
2221               "some string",  /* the subject string */
2222               11,             /* the length of the subject string */
2223               0,              /* start at offset 0 in the subject */
2224               0,              /* default options */
2225               ovector,        /* vector of integers for substring information */
2226               10,             /* number of elements (NOT size in bytes) */
2227               wspace,         /* working space vector */
2228               20);            /* number of elements (NOT size in bytes) */
2229    
2230       Option bits for pcre_dfa_exec()
2231    
2232           The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2233           zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2234           LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2235           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2236           three of these are the same as for pcre_exec(), so their description is
2237           not repeated here.
2238    
2239             PCRE_PARTIAL
2240    
2241           This  has  the  same general effect as it does for pcre_exec(), but the
2242           details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2243           pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2244           PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2245           been no complete matches, but there is still at least one matching pos-
2246           sibility. The portion of the string that provided the partial match  is
2247           set as the first matching string.
2248    
2249             PCRE_DFA_SHORTEST
2250    
2251           Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2252           stop as soon as it has found one match. Because of the way the alterna-
2253           tive  algorithm  works, this is necessarily the shortest possible match
2254           at the first possible matching point in the subject string.
2255    
2256             PCRE_DFA_RESTART
2257    
2258           When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2259           returns  a  partial  match, it is possible to call it again, with addi-
2260           tional subject characters, and have it continue with  the  same  match.
2261           The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2262           workspace and wscount options must reference the same vector as  before
2263           because  data  about  the  match so far is left in them after a partial
2264           match. There is more discussion of this  facility  in  the  pcrepartial
2265           documentation.
2266    
2267       Successful returns from pcre_dfa_exec()
2268    
2269           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2270           string in the subject. Note, however, that all the matches from one run
2271           of  the  function  start  at the same point in the subject. The shorter
2272           matches are all initial substrings of the longer matches. For  example,
2273           if the pattern
2274    
2275             <.*>
2276    
2277           is matched against the string
2278    
2279             This is <something> <something else> <something further> no more
2280    
2281           the three matched strings are
2282    
2283             <something>
2284             <something> <something else>
2285             <something> <something else> <something further>
2286    
2287           On  success,  the  yield of the function is a number greater than zero,
2288           which is the number of matched substrings.  The  substrings  themselves
2289           are  returned  in  ovector. Each string uses two elements; the first is
2290           the offset to the start, and the second is the offset to  the  end.  In
2291           fact,  all  the  strings  have the same start offset. (Space could have
2292           been saved by giving this only once, but it was decided to retain  some
2293           compatibility  with  the  way pcre_exec() returns data, even though the
2294           meaning of the strings is different.)
2295    
2296           The strings are returned in reverse order of length; that is, the long-
2297           est  matching  string is given first. If there were too many matches to
2298           fit into ovector, the yield of the function is zero, and the vector  is
2299           filled with the longest matches.
2300    
2301       Error returns from pcre_dfa_exec()
2302    
2303           The  pcre_dfa_exec()  function returns a negative number when it fails.
2304           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2305           described  above.   There are in addition the following errors that are
2306           specific to pcre_dfa_exec():
2307    
2308             PCRE_ERROR_DFA_UITEM      (-16)
2309    
2310           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2311           tern  that  it  does not support, for instance, the use of \C or a back
2312           reference.
2313    
2314             PCRE_ERROR_DFA_UCOND      (-17)
2315    
2316           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2317           that  uses  a back reference for the condition, or a test for recursion
2318           in a specific group. These are not supported.
2319    
2320             PCRE_ERROR_DFA_UMLIMIT    (-18)
2321    
2322           This return is given if pcre_dfa_exec() is called with an  extra  block
2323           that contains a setting of the match_limit field. This is not supported
2324           (it is meaningless).
2325    
2326             PCRE_ERROR_DFA_WSSIZE     (-19)
2327    
2328           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2329           workspace vector.
2330    
2331             PCRE_ERROR_DFA_RECURSE    (-20)
2332    
2333           When  a  recursive subpattern is processed, the matching function calls
2334           itself recursively, using private vectors for  ovector  and  workspace.
2335           This  error  is  given  if  the output vector is not large enough. This
2336           should be extremely rare, as a vector of size 1000 is used.
2337    
2338    
2339    SEE ALSO
2340    
2341           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2342           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2343    
2344    
2345    AUTHOR
2346    
2347           Philip Hazel
2348           University Computing Service
2349           Cambridge CB2 3QH, England.
2350    
2351    
2352    REVISION
2353    
2354           Last updated: 06 March 2007
2355           Copyright (c) 1997-2007 University of Cambridge.
2356    ------------------------------------------------------------------------------
2357    
2358    
2359    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2360    
2361    
2362  NAME  NAME
2363         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2364    
2365    
2366  PCRE CALLOUTS  PCRE CALLOUTS
2367    
2368         int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
# Line 1392  PCRE CALLOUTS Line 2379  PCRE CALLOUTS
2379         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2380         points:         points:
2381    
2382           (?C1)abc(?C2)def           (?C1)eabc(?C2)def
2383    
2384           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2385           called, PCRE automatically  inserts  callouts,  all  with  number  255,
2386           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2387           used with the pattern
2388    
2389             A(\d{2}|--)
2390    
2391           it is processed as if it were
2392    
2393           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2394    
2395           Notice that there is a callout before and after  each  parenthesis  and
2396           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2397           progress of pattern matching. The pcretest command has an  option  that
2398           sets  automatic callouts; when it is used, the output indicates how the
2399           pattern is matched. This is useful information when you are  trying  to
2400           optimize the performance of a particular pattern.
2401    
2402         During matching, when PCRE reaches a callout point (and pcre_callout is  
2403         set), the external function is called. Its only argument is  a  pointer  MISSING CALLOUTS
2404         to a pcre_callout block. This contains the following variables:  
2405           You  should  be  aware  that,  because of optimizations in the way PCRE
2406           matches patterns, callouts sometimes do not happen. For example, if the
2407           pattern is
2408    
2409             ab(?C4)cd
2410    
2411           PCRE knows that any matching string must contain the letter "d". If the
2412           subject string is "abyz", the lack of "d" means that  matching  doesn't
2413           ever  start,  and  the  callout is never reached. However, with "abyd",
2414           though the result is still no match, the callout is obeyed.
2415    
2416    
2417    THE CALLOUT INTERFACE
2418    
2419           During matching, when PCRE reaches a callout point, the external  func-
2420           tion  defined by pcre_callout is called (if it is set). This applies to
2421           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2422           only  argument  to  the callout function is a pointer to a pcre_callout
2423           block. This structure contains the following fields:
2424    
2425           int          version;           int          version;
2426           int          callout_number;           int          callout_number;
# Line 1408  PCRE CALLOUTS Line 2432  PCRE CALLOUTS
2432           int          capture_top;           int          capture_top;
2433           int          capture_last;           int          capture_last;
2434           void        *callout_data;           void        *callout_data;
2435             int          pattern_position;
2436             int          next_item_length;
2437    
2438         The  version  field  is an integer containing the version number of the         The version field is an integer containing the version  number  of  the
2439         block format. The current version  is  zero.  The  version  number  may         block  format. The initial version was 0; the current version is 1. The
2440         change  in  future if additional fields are added, but the intention is         version number will change again in future  if  additional  fields  are
2441         never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2442    
2443         The callout_number field contains the number of the  callout,  as  com-         The callout_number field contains the number of the  callout,  as  com-
2444         piled into the pattern (that is, the number after ?C).         piled  into  the pattern (that is, the number after ?C for manual call-
2445           outs, and 255 for automatically generated callouts).
2446    
2447         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
2448         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
2449         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
2450         way as for extracting substrings after a match has completed.         substrings  that  have  been  matched  so  far,  in the same way as for
2451           extracting substrings after a match has completed. For  pcre_dfa_exec()
2452           this field is not useful.
2453    
2454         The subject and subject_length fields contain copies  the  values  that         The subject and subject_length fields contain copies of the values that
2455         were passed to pcre_exec().         were passed to pcre_exec().
2456    
2457         The  start_match  field contains the offset within the subject at which         The start_match field contains the offset within the subject  at  which
2458         the current match attempt started. If the pattern is not anchored,  the         the  current match attempt started. If the pattern is not anchored, the
2459         callout  function  may  be  called several times for different starting         callout function may be called several times from the same point in the
2460         points.         pattern for different starting points in the subject.
2461    
2462         The current_position field contains the offset within  the  subject  of         The  current_position  field  contains the offset within the subject of
2463         the current match pointer.         the current match pointer.
2464    
2465         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
2466         numbered  captured  substring  so  far.  If  no  substrings  have  been         one  more than the number of the highest numbered captured substring so
2467         captured, the value of capture_top is one.         far. If no substrings have been captured, the value of  capture_top  is
2468           one.  This  is always the case when pcre_dfa_exec() is used, because it
2469         The  capture_last  field  contains the number of the most recently cap-         does not support captured substrings.
2470         tured substring.  
2471           The capture_last field contains the number of the  most  recently  cap-
2472           tured  substring. If no substrings have been captured, its value is -1.
2473           This is always the case when pcre_dfa_exec() is used.
2474    
2475         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()
2476         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-
2477         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
2478         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
2479         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
2480         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2481    
2482           The  pattern_position field is present from version 1 of the pcre_call-
2483           out structure. It contains the offset to the next item to be matched in
2484           the pattern string.
2485    
2486           The  next_item_length field is present from version 1 of the pcre_call-
2487           out structure. It contains the length of the next item to be matched in
2488           the  pattern  string. When the callout immediately precedes an alterna-
2489           tion bar, a closing parenthesis, or the end of the pattern, the  length
2490           is  zero.  When the callout precedes an opening parenthesis, the length
2491           is that of the entire subpattern.
2492    
2493           The pattern_position and next_item_length fields are intended  to  help
2494           in  distinguishing between different automatic callouts, which all have
2495           the same callout number. However, they are set for all callouts.
2496    
2497    
2498  RETURN VALUES  RETURN VALUES
2499    
2500         The callout function returns an integer. If the value is zero, matching         The external callout function returns an integer to PCRE. If the  value
2501         proceeds as normal. If the value is greater than zero,  matching  fails         is  zero,  matching  proceeds  as  normal. If the value is greater than
2502         at the current point, but backtracking to test other possibilities goes         zero, matching fails at the current point, but  the  testing  of  other
2503         ahead, just as if a lookahead assertion had failed.  If  the  value  is         matching possibilities goes ahead, just as if a lookahead assertion had
2504         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
2505         value.         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2506    
2507         Negative  values  should  normally  be   chosen   from   the   set   of         Negative   values   should   normally   be   chosen  from  the  set  of
2508         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2509         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2510         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
2511         itself.         itself.
2512    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2513    
2514  PCRE(3)                                                                PCRE(3)  AUTHOR
2515    
2516           Philip Hazel
2517           University Computing Service
2518           Cambridge CB2 3QH, England.
2519    
2520    
2521    REVISION
2522    
2523           Last updated: 06 March 2007
2524           Copyright (c) 1997-2007 University of Cambridge.
2525    ------------------------------------------------------------------------------
2526    
2527    
2528    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2529    
2530    
2531  NAME  NAME
2532         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2533    
 DIFFERENCES FROM PERL  
2534    
2535         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.  
2536    
2537         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
2538         are given in the section on UTF-8 support in the main pcre page.         handle regular expressions. The differences described here  are  mainly
2539           with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2540           tures that are expected to be in the forthcoming Perl 5.10.
2541    
2542           1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2543           of  what  it does have are given in the section on UTF-8 support in the
2544           main pcre page.
2545    
2546         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2547         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 2557  DIFFERENCES FROM PERL
2557    
2558         4. Though binary zero characters are supported in the  subject  string,         4. Though binary zero characters are supported in the  subject  string,
2559         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-
2560         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
2561         in the pattern to represent a binary zero.         the pattern to represent a binary zero.
2562    
2563         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2564         \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-
2565         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
2566         of these are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
2567    
2568           6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2569           is  built  with Unicode character property support. The properties that
2570           can be tested with \p and \P are limited to the general category  prop-
2571           erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2572           derived properties Any and L&.
2573    
2574         6. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2575         ters  in  between  are  treated as literals. This is slightly different         ters  in  between  are  treated as literals. This is slightly different
2576         from Perl in that $ and @ are  also  handled  as  literals  inside  the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2577         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 2587  DIFFERENCES FROM PERL
2587         The \Q...\E sequence is recognized both inside  and  outside  character         The \Q...\E sequence is recognized both inside  and  outside  character
2588         classes.         classes.
2589    
2590         7. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2591         constructions. However, there is some experimental support  for  recur-         constructions. However, there is support for recursive  patterns.  This
2592         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
2593         Also, the PCRE "callout" feature allows  an  external  function  to  be         "callout" feature allows an external function to be called during  pat-
2594         called during pattern matching.         tern matching. See the pcrecallout documentation for details.
2595    
2596           9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2597           always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2598           unlike Perl.
2599    
2600         8.  There  are some differences that are concerned with the settings of         10.  There are some differences that are concerned with the settings of
2601         captured strings when part of  a  pattern  is  repeated.  For  example,         captured strings when part of  a  pattern  is  repeated.  For  example,
2602         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2603         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2604    
2605         9. PCRE  provides  some  extensions  to  the  Perl  regular  expression         11. PCRE provides some extensions to the Perl regular expression facil-
2606         facilities:         ities.   Perl  5.10  will  include new features that are not in earlier
2607           versions, some of which (such as named parentheses) have been  in  PCRE
2608           for some time. This list is with respect to Perl 5.10:
2609    
2610         (a)  Although  lookbehind  assertions  must match fixed length strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2611         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 2615  DIFFERENCES FROM PERL
2615         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2616    
2617         (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-
2618         cial meaning is faulted.         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2619           ignored. (Perl can be made to issue a warning.)
2620    
2621         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2622         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-
2623         lowed by a question mark they are.         lowed by a question mark they are.
2624    
2625         (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
2626         the first matching position in the subject string.         tried only at the first matching position in the subject string.
2627    
2628         (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-
2629         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2630    
2631         (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.)  
2632    
2633         (h)  PCRE supports named capturing substrings, using the Python syntax.         (h) The partial matching facility is PCRE-specific.
2634    
2635         (i) PCRE supports the possessive quantifier  "++"  syntax,  taken  from         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2636         Sun's Java package.         even on different hosts that have the other endianness.
2637    
2638         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2639           different way and is not Perl-compatible.
2640    
        (k) The callout facility is PCRE-specific.  
2641    
2642  Last updated: 09 December 2003  AUTHOR
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2643    
2644  PCRE(3)                                                                PCRE(3)         Philip Hazel
2645           University Computing Service
2646           Cambridge CB2 3QH, England.
2647    
2648    
2649    REVISION
2650    
2651           Last updated: 06 March 2007
2652           Copyright (c) 1997-2007 University of Cambridge.
2653    ------------------------------------------------------------------------------
2654    
2655    
2656    PCREPATTERN(3)                                                  PCREPATTERN(3)
2657    
2658    
2659  NAME  NAME
2660         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2661    
2662    
2663  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2664    
2665         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax  and semantics of the regular expressions supported by PCRE
2666         are described below. Regular expressions are also described in the Perl         are described below. Regular expressions are also described in the Perl
2667         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
2668         ous examples. Jeffrey Friedl's "Mastering  Regular  Expressions",  pub-         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published
2669         lished  by  O'Reilly, covers them in great detail. The description here         by  O'Reilly, covers regular expressions in great detail. This descrip-
2670         is intended as reference documentation.         tion of PCRE's regular expressions is intended as reference material.
2671    
2672         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.
2673         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
2674         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
2675         the  PCRE_UTF8  option.  How  this affects the pattern matching is men-         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern
2676         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
2677         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
2678           page.
2679         A  regular  expression  is  a pattern that is matched against a subject  
2680         string from left to right. Most characters stand for  themselves  in  a         The remainder of this document discusses the  patterns  that  are  sup-
2681         pattern,  and  match  the corresponding characters in the subject. As a         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2682           From  release  6.0,   PCRE   offers   a   second   matching   function,
2683           pcre_dfa_exec(),  which matches using a different algorithm that is not
2684           Perl-compatible. The advantages and disadvantages  of  the  alternative
2685           function, and how it differs from the normal function, are discussed in
2686           the pcrematching page.
2687    
2688    
2689    CHARACTERS AND METACHARACTERS
2690    
2691           A regular expression is a pattern that is  matched  against  a  subject
2692           string  from  left  to right. Most characters stand for themselves in a
2693           pattern, and match the corresponding characters in the  subject.  As  a
2694         trivial example, the pattern         trivial example, the pattern
2695    
2696           The quick brown fox           The quick brown fox
2697    
2698         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
2699         power of regular expressions comes from the ability to include alterna-         caseless matching is specified (the PCRE_CASELESS option), letters  are
2700         tives and repetitions in the pattern. These are encoded in the  pattern         matched  independently  of case. In UTF-8 mode, PCRE always understands
2701         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
2702         instead are interpreted in some special way.         caseless  matching  is always possible. For characters with higher val-
2703           ues, the concept of case is supported if PCRE is compiled with  Unicode
2704           property  support,  but  not  otherwise.   If  you want to use caseless
2705           matching for characters 128 and above, you must  ensure  that  PCRE  is
2706           compiled with Unicode property support as well as with UTF-8 support.
2707    
2708           The  power  of  regular  expressions  comes from the ability to include
2709           alternatives and repetitions in the pattern. These are encoded  in  the
2710           pattern by the use of metacharacters, which do not stand for themselves
2711           but instead are interpreted in some special way.
2712    
2713         There are two different sets of meta-characters: those that are  recog-         There are two different sets of metacharacters: those that  are  recog-
2714         nized  anywhere in the pattern except within square brackets, and those         nized  anywhere in the pattern except within square brackets, and those
2715         that are recognized in square brackets. Outside  square  brackets,  the         that are recognized within square brackets.  Outside  square  brackets,
2716         meta-characters are as follows:         the metacharacters are as follows:
2717    
2718           \      general escape character with several uses           \      general escape character with several uses
2719           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 1631  PCRE REGULAR EXPRESSION DETAILS Line 2732  PCRE REGULAR EXPRESSION DETAILS
2732           {      start min/max quantifier           {      start min/max quantifier
2733    
2734         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
2735         class". In a character class the only meta-characters are:         class". In a character class the only metacharacters are:
2736    
2737           \      general escape character           \      general escape character
2738           ^      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 2741  PCRE REGULAR EXPRESSION DETAILS
2741                    syntax)                    syntax)
2742           ]      terminates the character class           ]      terminates the character class
2743    
2744         The following sections describe the use of each of the meta-characters.         The following sections describe the use of each of the  metacharacters.
2745    
2746    
2747  BACKSLASH  BACKSLASH
2748    
2749         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
2750         a non-alphameric character, it takes  away  any  special  meaning  that         a non-alphanumeric character, it takes away any  special  meaning  that
2751         character  may  have.  This  use  of  backslash  as an escape character         character  may  have.  This  use  of  backslash  as an escape character
2752         applies both inside and outside character classes.         applies both inside and outside character classes.
2753    
2754         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
2755         pattern.   This  escaping  action  applies whether or not the following         pattern.   This  escaping  action  applies whether or not the following
2756         character would otherwise be interpreted as a meta-character, so it  is         character would otherwise be interpreted as a metacharacter, so  it  is
2757         always  safe to precede a non-alphameric with backslash to specify that         always  safe  to  precede  a non-alphanumeric with backslash to specify
2758         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-
2759         you write \\.         slash, you write \\.
2760    
2761         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2762         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
2763         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2764         An escaping backslash can be used to include a whitespace or #  charac-         ing backslash can be used to include a whitespace  or  #  character  as
2765         ter as part of the pattern.         part of the pattern.
2766    
2767         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-
2768         ters, you can do so by putting them between \Q and \E. This is  differ-         ters, you can do so by putting them between \Q and \E. This is  differ-
# Line 1679  BACKSLASH Line 2780  BACKSLASH
2780         The  \Q...\E  sequence  is recognized both inside and outside character         The  \Q...\E  sequence  is recognized both inside and outside character
2781         classes.         classes.
2782    
2783       Non-printing characters
2784    
2785         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-
2786         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
2787         appearance of non-printing characters, apart from the binary zero  that         appearance of non-printing characters, apart from the binary zero  that
# Line 1695  BACKSLASH Line 2798  BACKSLASH
2798           \t        tab (hex 09)           \t        tab (hex 09)
2799           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
2800           \xhh      character with hex code hh           \xhh      character with hex code hh
2801           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
2802    
2803         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,
2804         it is converted to upper case. Then bit 6 of the character (hex 40)  is         it is converted to upper case. Then bit 6 of the character (hex 40)  is
# Line 1703  BACKSLASH Line 2806  BACKSLASH
2806         becomes hex 7B.         becomes hex 7B.
2807    
2808         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
2809         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
2810         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
2811         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,
2812         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than
2813         \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-
2814         recognized. Instead, the initial \x will be interpreted as a basic hex-         nating }, this form of escape is not recognized.  Instead, the  initial
2815         adecimal escape, with no following digits, giving a byte whose value is         \x will be interpreted as a basic hexadecimal escape, with no following
2816         zero.         digits, giving a character whose value is zero.
2817    
2818         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
2819         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-
2820         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}.
2821         \x{dc}.  
2822           After \0 up to two further octal digits are read. If  there  are  fewer
2823         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
2824         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
2825         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
2826         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.  
2827    
2828         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-
2829         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
2830         its  as  a  decimal  number. If the number is less than 10, or if there         its as a decimal number. If the number is less than  10,  or  if  there
2831         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
2832         expression,  the  entire  sequence  is  taken  as  a  back reference. A         expression, the entire  sequence  is  taken  as  a  back  reference.  A
2833         description of how this works is given later, following the  discussion         description  of how this works is given later, following the discussion
2834         of parenthesized subpatterns.         of parenthesized subpatterns.
2835    
2836         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
2837         and there have not been that many capturing subpatterns, PCRE  re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
2838         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-
2839         gle byte from the least significant 8 bits of the value. Any subsequent         erate  a data character. Any subsequent digits stand for themselves. In
2840         digits stand for themselves.  For example:         non-UTF-8 mode, the value of a character specified  in  octal  must  be
2841           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
2842           example:
2843    
2844           \040   is another way of writing a space           \040   is another way of writing a space
2845           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 1752  BACKSLASH Line 2856  BACKSLASH
2856           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
2857                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
2858    
2859         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
2860         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2861    
2862         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
2863         character (in UTF-8 mode) can be used both inside and outside character         inside and outside character classes. In addition, inside  a  character
2864         classes. In addition, inside a character  class,  the  sequence  \b  is         class,  the  sequence \b is interpreted as the backspace character (hex
2865         interpreted  as  the  backspace character (hex 08). Outside a character         08), and the sequences \R and \X are interpreted as the characters  "R"
2866         class it has a different meaning (see below).         and  "X", respectively. Outside a character class, these sequences have
2867           different meanings (see below).
2868    
2869       Absolute and relative back references
2870    
2871           The sequence \g followed by a positive or negative  number,  optionally
2872           enclosed  in  braces,  is  an absolute or relative back reference. Back
2873           references are discussed later, following the discussion  of  parenthe-
2874           sized subpatterns.
2875    
2876       Generic character types
2877    
2878         The third use of backslash is for specifying generic character types:         Another use of backslash is for specifying generic character types. The
2879           following are always recognized:
2880    
2881           \d     any decimal digit           \d     any decimal digit
2882           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 1771  BACKSLASH Line 2886  BACKSLASH
2886           \W     any "non-word" character           \W     any "non-word" character
2887    
2888         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
2889         into  two disjoint sets. Any given character matches one, and only one,         into  two disjoint sets. Any given character matches one, and only one,
2890         of each pair.         of each pair.
   
        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.  
2891    
2892         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
2893         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
2894         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
2895         of them fail, since there is no character to match.         of them fail, since there is no character to match.
2896    
2897         The fourth use of backslash is for certain simple assertions. An asser-         For  compatibility  with Perl, \s does not match the VT character (code
2898         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
2899         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
2900         use  of subpatterns for more complicated assertions is described below.         "use locale;" is included in a Perl script, \s may match the VT charac-
2901         The backslashed assertions are         ter. In PCRE, it never does.)
2902    
2903           A "word" character is an underscore or any character less than 256 that
2904           is a letter or digit. The definition of  letters  and  digits  is  con-
2905           trolled  by PCRE's low-valued character tables, and may vary if locale-
2906           specific matching is taking place (see "Locale support" in the  pcreapi
2907           page).  For  example,  in  the  "fr_FR" (French) locale, some character
2908           codes greater than 128 are used for accented  letters,  and  these  are
2909           matched by \w.
2910    
2911           In  UTF-8 mode, characters with values greater than 128 never match \d,
2912           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
2913           code  character  property support is available. The use of locales with
2914           Unicode is discouraged.
2915    
2916       Newline sequences
2917    
2918           Outside a character class, the escape sequence \R matches  any  Unicode
2919           newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2920           equivalent to the following:
2921    
2922             (?>\r\n|\n|\x0b|\f|\r|\x85)
2923    
2924           This is an example of an "atomic group", details  of  which  are  given
2925           below.  This particular group matches either the two-character sequence
2926           CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
2927           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2928           return, U+000D), or NEL (next line, U+0085). The two-character sequence
2929           is treated as a single unit that cannot be split.
2930    
2931           In  UTF-8  mode, two additional characters whose codepoints are greater
2932           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2933           rator,  U+2029).   Unicode character property support is not needed for
2934           these characters to be recognized.
2935    
2936           Inside a character class, \R matches the letter "R".
2937    
2938       Unicode character properties
2939    
2940           When PCRE is built with Unicode character property support, three addi-
2941           tional  escape  sequences  to  match character properties are available
2942           when UTF-8 mode is selected. They are:
2943    
2944             \p{xx}   a character with the xx property
2945             \P{xx}   a character without the xx property
2946             \X       an extended Unicode sequence
2947    
2948           The property names represented by xx above are limited to  the  Unicode
2949           script names, the general category properties, and "Any", which matches
2950           any character (including newline). Other properties such as "InMusical-
2951           Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
2952           not match any characters, so always causes a match failure.
2953    
2954           Sets of Unicode characters are defined as belonging to certain scripts.
2955           A  character from one of these sets can be matched using a script name.
2956           For example:
2957    
2958             \p{Greek}
2959             \P{Han}
2960    
2961           Those that are not part of an identified script are lumped together  as
2962           "Common". The current list of scripts is:
2963    
2964           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
2965           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
2966           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
2967           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
2968           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
2969           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
2970           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
2971           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
2972           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
2973    
2974           Each  character has exactly one general category property, specified by
2975           a two-letter abbreviation. For compatibility with Perl, negation can be
2976           specified  by  including a circumflex between the opening brace and the
2977           property name. For example, \p{^Lu} is the same as \P{Lu}.
2978    
2979           If only one letter is specified with \p or \P, it includes all the gen-
2980           eral  category properties that start with that letter. In this case, in
2981           the absence of negation, the curly brackets in the escape sequence  are
2982           optional; these two examples have the same effect:
2983    
2984             \p{L}
2985             \pL
2986    
2987           The following general category property codes are supported:
2988    
2989             C     Other
2990             Cc    Control
2991             Cf    Format
2992             Cn    Unassigned
2993             Co    Private use
2994             Cs    Surrogate
2995    
2996             L     Letter
2997             Ll    Lower case letter
2998             Lm    Modifier letter
2999             Lo    Other letter
3000             Lt    Title case letter
3001             Lu    Upper case letter
3002    
3003             M     Mark
3004             Mc    Spacing mark
3005             Me    Enclosing mark
3006             Mn    Non-spacing mark
3007    
3008             N     Number
3009             Nd    Decimal number
3010             Nl    Letter number
3011             No    Other number
3012    
3013             P     Punctuation
3014             Pc    Connector punctuation
3015             Pd    Dash punctuation
3016             Pe    Close punctuation
3017             Pf    Final punctuation
3018             Pi    Initial punctuation
3019             Po    Other punctuation
3020             Ps    Open punctuation
3021    
3022             S     Symbol
3023             Sc    Currency symbol
3024             Sk    Modifier symbol
3025             Sm    Mathematical symbol
3026             So    Other symbol
3027    
3028             Z     Separator
3029             Zl    Line separator
3030             Zp    Paragraph separator
3031             Zs    Space separator
3032    
3033           The  special property L& is also supported: it matches a character that
3034           has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
3035           classified as a modifier or "other".
3036    
3037           The  long  synonyms  for  these  properties that Perl supports (such as
3038           \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3039           any of these properties with "Is".
3040    
3041           No character that is in the Unicode table has the Cn (unassigned) prop-
3042           erty.  Instead, this property is assumed for any code point that is not
3043           in the Unicode table.
3044    
3045           Specifying  caseless  matching  does not affect these escape sequences.
3046           For example, \p{Lu} always matches only upper case letters.
3047    
3048           The \X escape matches any number of Unicode  characters  that  form  an
3049           extended Unicode sequence. \X is equivalent to
3050    
3051             (?>\PM\pM*)
3052    
3053           That  is,  it matches a character without the "mark" property, followed
3054           by zero or more characters with the "mark"  property,  and  treats  the
3055           sequence  as  an  atomic group (see below).  Characters with the "mark"
3056           property are typically accents that affect the preceding character.
3057    
3058           Matching characters by Unicode property is not fast, because  PCRE  has
3059           to  search  a  structure  that  contains data for over fifteen thousand
3060           characters. That is why the traditional escape sequences such as \d and
3061           \w do not use Unicode properties in PCRE.
3062    
3063       Simple assertions
3064    
3065           The  final use of backslash is for certain simple assertions. An asser-
3066           tion specifies a condition that has to be met at a particular point  in
3067           a  match, without consuming any characters from the subject string. The
3068           use of subpatterns for more complicated assertions is described  below.
3069           The backslashed assertions are:
3070    
3071           \b     matches at a word boundary           \b     matches at a word boundary
3072           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3073           \A     matches at start of subject           \A     matches at the start of the subject
3074           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3075           \z     matches at end of subject                   also matches before a newline at the end of the subject
3076           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3077             \G     matches at the first matching position in the subject
3078    
3079         These assertions may not appear in character classes (but note that  \b         These  assertions may not appear in character classes (but note that \b
3080         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3081         acter class).         acter class).
3082    
3083         A word boundary is a position in the subject string where  the  current         A  word  boundary is a position in the subject string where the current
3084         character  and  the previous character do not both match \w or \W (i.e.         character and the previous character do not both match \w or  \W  (i.e.
3085         one matches \w and the other matches \W), or the start or  end  of  the         one  matches  \w  and the other matches \W), or the start or end of the
3086         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
3087    
3088         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The \A, \Z, and \z assertions differ from  the  traditional  circumflex
3089         and dollar (described below) in that they only ever match at  the  very         and dollar (described in the next section) in that they only ever match
3090         start  and  end  of the subject string, whatever options are set. Thus,         at the very start and end of the subject string, whatever  options  are
3091         they are independent of multiline mode.         set.  Thus,  they are independent of multiline mode. These three asser-
3092           tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3093         They are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options. If the         affect  only the behaviour of the circumflex and dollar metacharacters.
3094         startoffset argument of pcre_exec() is non-zero, indicating that match-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3095         ing is to start at a point other than the beginning of the subject,  \A         cating that matching is to start at a point other than the beginning of
3096         can  never  match.  The difference between \Z and \z is that \Z matches         the subject, \A can never match. The difference between \Z  and  \z  is
3097         before a newline that is the last character of the string as well as at         that \Z matches before a newline at the end of the string as well as at
3098         the end of the string, whereas \z matches only at the end.         the very end, whereas \z matches only at the end.
3099    
3100         The  \G assertion is true only when the current matching position is at         The \G assertion is true only when the current matching position is  at
3101         the start point of the match, as specified by the startoffset  argument         the  start point of the match, as specified by the startoffset argument
3102         of  pcre_exec().  It  differs  from \A when the value of startoffset is         of pcre_exec(). It differs from \A when the  value  of  startoffset  is
3103         non-zero. By calling pcre_exec() multiple times with appropriate  argu-         non-zero.  By calling pcre_exec() multiple times with appropriate argu-
3104         ments, you can mimic Perl's /g option, and it is in this kind of imple-         ments, you can mimic Perl's /g option, and it is in this kind of imple-
3105         mentation where \G can be useful.         mentation where \G can be useful.
3106    
3107         Note, however, that PCRE's interpretation of \G, as the  start  of  the         Note,  however,  that  PCRE's interpretation of \G, as the start of the
3108         current match, is subtly different from Perl's, which defines it as the         current match, is subtly different from Perl's, which defines it as the
3109         end of the previous match. In Perl, these can  be  different  when  the         end  of  the  previous  match. In Perl, these can be different when the
3110         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3111         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3112    
3113         If all the alternatives of a pattern begin with \G, the  expression  is         If  all  the alternatives of a pattern begin with \G, the expression is
3114         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3115         in the compiled regular expression.         in the compiled regular expression.
3116    
# Line 1849  BACKSLASH Line 3118  BACKSLASH
3118  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3119    
3120         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3121         character  is  an  assertion which is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3122         point is at the start of the subject string. If the  startoffset  argu-         point  is  at the start of the subject string. If the startoffset argu-
3123         ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the         ment of pcre_exec() is non-zero, circumflex  can  never  match  if  the
3124         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3125         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3126    
3127         Circumflex  need  not be the first character of the pattern if a number         Circumflex need not be the first character of the pattern if  a  number
3128         of alternatives are involved, but it should be the first thing in  each         of  alternatives are involved, but it should be the first thing in each
3129         alternative  in  which  it appears if the pattern is ever to match that         alternative in which it appears if the pattern is ever  to  match  that
3130         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3131         if  the  pattern  is constrained to match only at the start of the sub-         if the pattern is constrained to match only at the start  of  the  sub-
3132         ject, it is said to be an "anchored" pattern.  (There  are  also  other         ject,  it  is  said  to be an "anchored" pattern. (There are also other
3133         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3134    
3135         A  dollar  character  is an assertion which is true only if the current         A dollar character is an assertion that is true  only  if  the  current
3136         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3137         before a newline character that is the last character in the string (by         before a newline at the end of the string (by default). Dollar need not
3138         default). Dollar need not be the last character of  the  pattern  if  a         be  the  last  character of the pattern if a number of alternatives are
3139         number  of alternatives are involved, but it should be the last item in         involved, but it should be the last item in  any  branch  in  which  it
3140         any branch in which it appears.  Dollar has no  special  meaning  in  a         appears. Dollar has no special meaning in a character class.
        character class.  
3141    
3142         The  meaning  of  dollar  can be changed so that it matches only at the         The  meaning  of  dollar  can be changed so that it matches only at the
3143         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at
3144         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3145    
3146         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3147         PCRE_MULTILINE option is set. When this is the case, they match immedi-         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex
3148         ately  after  and  immediately  before  an  internal newline character,         matches  immediately after internal newlines as well as at the start of
3149         respectively, in addition to matching at the start and end of the  sub-         the subject string. It does not match after a  newline  that  ends  the
3150         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         string.  A dollar matches before any newlines in the string, as well as
3151         string "def\nabc" in multiline mode, but not  otherwise.  Consequently,         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3152         patterns  that  are  anchored  in single line mode because all branches         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3153         start with ^ are not anchored in multiline mode, and a match  for  cir-         not indicate newlines.
3154         cumflex  is  possible  when  the startoffset argument of pcre_exec() is  
3155         non-zero. The PCRE_DOLLAR_ENDONLY option is ignored  if  PCRE_MULTILINE         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3156         is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3157           Consequently, patterns that are anchored in single  line  mode  because
3158         Note  that  the sequences \A, \Z, and \z can be used to match the start         all  branches  start  with  ^ are not anchored in multiline mode, and a
3159         and end of the subject in both modes, and if all branches of a  pattern         match for circumflex is  possible  when  the  startoffset  argument  of
3160         start  with  \A it is always anchored, whether PCRE_MULTILINE is set or         pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
3161         not.         PCRE_MULTILINE is set.
3162    
3163           Note that the sequences \A, \Z, and \z can be used to match  the  start
3164           and  end of the subject in both modes, and if all branches of a pattern
3165           start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3166           set.
3167    
3168