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revision 81 by nigel, Sat Feb 24 21:40:59 2007 UTC revision 96 by nigel, Fri Mar 2 13:10:43 2007 UTC
# Line 18  INTRODUCTION Line 18  INTRODUCTION
18    
19         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
20         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
21         just  a  few  differences.  The current implementation of PCRE (release         just  a  few differences. (Certain features that appeared in Python and
22         6.x) corresponds approximately with Perl  5.8,  including  support  for         PCRE before they appeared in Perl are also available using  the  Python
23         UTF-8 encoded strings and Unicode general category properties. However,         syntax.)
24         this support has to be explicitly enabled; it is not the default.  
25           The  current  implementation of PCRE (release 7.x) corresponds approxi-
26         In addition to the Perl-compatible matching function,  PCRE  also  con-         mately with Perl 5.10, including support for UTF-8 encoded strings  and
27         tains  an  alternative matching function that matches the same compiled         Unicode general category properties. However, UTF-8 and Unicode support
28         patterns in a different way. In certain circumstances, the  alternative         has to be explicitly enabled; it is not the default. The Unicode tables
29         function  has  some  advantages.  For  a discussion of the two matching         correspond to Unicode release 5.0.0.
30         algorithms, see the pcrematching page.  
31           In  addition to the Perl-compatible matching function, PCRE contains an
32         PCRE is written in C and released as a C library. A  number  of  people         alternative matching function that matches the same  compiled  patterns
33         have  written  wrappers and interfaces of various kinds. In particular,         in  a different way. In certain circumstances, the alternative function
34         Google Inc.  have provided a comprehensive C++  wrapper.  This  is  now         has some advantages. For a discussion of the two  matching  algorithms,
35           see the pcrematching page.
36    
37           PCRE  is  written  in C and released as a C library. A number of people
38           have written wrappers and interfaces of various kinds.  In  particular,
39           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
40         included as part of the PCRE distribution. The pcrecpp page has details         included as part of the PCRE distribution. The pcrecpp page has details
41         of this interface. Other people's contributions can  be  found  in  the         of  this  interface.  Other  people's contributions can be found in the
42         Contrib directory at the primary FTP site, which is:         Contrib directory at the primary FTP site, which is:
43    
44         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
45    
46         Details  of  exactly which Perl regular expression features are and are         Details of exactly which Perl regular expression features are  and  are
47         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
48         tern and pcrecompat pages.         tern and pcrecompat pages.
49    
50         Some  features  of  PCRE can be included, excluded, or changed when the         Some features of PCRE can be included, excluded, or  changed  when  the
51         library is built. The pcre_config() function makes it  possible  for  a         library  is  built.  The pcre_config() function makes it possible for a
52         client  to  discover  which  features are available. The features them-         client to discover which features are  available.  The  features  them-
53         selves are described in the pcrebuild page. Documentation about  build-         selves  are described in the pcrebuild page. Documentation about build-
54         ing  PCRE for various operating systems can be found in the README file         ing PCRE for various operating systems can be found in the README  file
55         in the source distribution.         in the source distribution.
56    
57         The library contains a number of undocumented  internal  functions  and         The  library  contains  a number of undocumented internal functions and
58         data  tables  that  are  used by more than one of the exported external         data tables that are used by more than one  of  the  exported  external
59         functions, but which are not intended  for  use  by  external  callers.         functions,  but  which  are  not  intended for use by external callers.
60         Their  names  all begin with "_pcre_", which hopefully will not provoke         Their names all begin with "_pcre_", which hopefully will  not  provoke
61         any name clashes.         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 comprises a number  of  different  sec-         The  user  documentation  for PCRE comprises a number of different sec-
69         tions.  In the "man" format, each of these is a separate "man page". In         tions. In the "man" format, each of these is a separate "man page".  In
70         the HTML format, each is a separate page, linked from the  index  page.         the  HTML  format, each is a separate page, linked from the index page.
71         In  the  plain text format, all the sections are concatenated, for ease         In the plain text format, all the sections are concatenated,  for  ease
72         of searching. The sections are as follows:         of searching. The sections are as follows:
73    
74           pcre              this document           pcre              this document
# Line 79  USER DOCUMENTATION Line 86  USER DOCUMENTATION
86           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
87           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
88           pcresample        discussion of the sample program           pcresample        discussion of the sample program
89             pcrestack         discussion of stack usage
90           pcretest          description of the pcretest testing command           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 C 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         In 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.
        There is no limit to the number of non-capturing subpatterns,  but  the  
        maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,  
        including capturing subpatterns, assertions, and other types of subpat-  
        tern, is 200.  
112    
113         The  maximum  length of a subject string is the largest positive number         There is no limit to the number of parenthesized subpatterns, but there
114         that an integer variable can hold. However, when using the  traditional         can be no more than 65535 capturing subpatterns.
115    
116           The maximum length of name for a named subpattern is 32 characters, and
117           the maximum number of named subpatterns is 10000.
118    
119           The maximum length of a subject string is the largest  positive  number
120           that  an integer variable can hold. However, when using the traditional
121         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
122         inite repetition.  This means that the available stack space may  limit         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.         the size of a subject string that can be processed by certain patterns.
124           For a discussion of stack issues, see the pcrestack documentation.
125    
126    
127  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
128    
129         From release 3.3, PCRE has  had  some  support  for  character  strings         From  release  3.3,  PCRE  has  had  some support for character strings
130         encoded  in the UTF-8 format. For release 4.0 this was greatly extended         encoded in the UTF-8 format. For release 4.0 this was greatly  extended
131         to cover most common requirements, and in release 5.0  additional  sup-         to  cover  most common requirements, and in release 5.0 additional sup-
132         port for Unicode general category properties was added.         port for Unicode general category properties was added.
133    
134         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         In order process UTF-8 strings, you must build PCRE  to  include  UTF-8
135         support in the code, and, in addition,  you  must  call  pcre_compile()         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         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         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         If PCRE is built with Unicode character property support (which implies
146         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         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         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         general category properties such as Lu for an upper case letter  or  Nd
149         for a decimal number. A full list is given in the pcrepattern  documen-         for  a  decimal number, the Unicode script names such as Arabic or Han,
150         tation. The PCRE library is increased in size by about 90K when Unicode         and the derived properties Any and L&. A full  list  is  given  in  the
151         property support is included.         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 sin-         5. The dot metacharacter matches one UTF-8 character instead of a  sin-
181         gle 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. This facility is         mode, but its use can lead to some strange effects.  This  facility  is
185         not available in the alternative matching function, pcre_dfa_exec().         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. This remains true even when PCRE         before, all with values less than 256. This remains true even when PCRE
191         includes Unicode property support, because to do otherwise  would  slow         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         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         sense  of,  say,  "digit",  you must use Unicode property tests such as
194         \p{Nd}.         \p{Nd}.
195    
196         8.  Similarly,  characters that match the POSIX named character classes         8. Similarly, characters that match the POSIX named  character  classes
197         are all low-valued characters.         are all low-valued characters.
198    
199         9. Case-insensitive matching applies only to  characters  whose  values         9.  Case-insensitive  matching  applies only to characters whose values
200         are  less than 128, unless PCRE is built with Unicode property support.         are less than 128, unless PCRE is built with Unicode property  support.
201         Even when Unicode property support is available, PCRE  still  uses  its         Even  when  Unicode  property support is available, PCRE still uses its
202         own  character  tables when checking the case of low-valued characters,         own character tables when checking the case of  low-valued  characters,
203         so as not to degrade performance.  The Unicode property information  is         so  as not to degrade performance.  The Unicode property information is
204         used only for characters with higher values.         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    
210    
211  AUTHOR  AUTHOR
212    
213         Philip Hazel         Philip Hazel
214         University Computing Service,         University Computing Service,
215         Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
216    
217         Putting  an actual email address here seems to have been a spam magnet,         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-         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.         name, separated by a dot, at the domain ucs.cam.ac.uk.
220    
221  Last updated: 07 March 2005  Last updated: 23 November 2006
222  Copyright (c) 1997-2005 University of Cambridge.  Copyright (c) 1997-2006 University of Cambridge.
223  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
224    
225    
# Line 234  PCRE BUILD-TIME OPTIONS Line 249  PCRE BUILD-TIME OPTIONS
249         not described.         not described.
250    
251    
252    C++ SUPPORT
253    
254           By default, the configure script will search for a C++ compiler and C++
255           header files. If it finds them, it automatically builds the C++ wrapper
256           library for PCRE. You can disable this by adding
257    
258             --disable-cpp
259    
260           to the configure command.
261    
262    
263  UTF-8 SUPPORT  UTF-8 SUPPORT
264    
265         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 character strings, add
# Line 267  UNICODE CHARACTER PROPERTY SUPPORT Line 293  UNICODE CHARACTER PROPERTY SUPPORT
293    
294  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
295    
296         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating
297         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
298         compile PCRE to use character 13 (carriage return) instead by adding         systems. You can compile PCRE to use character 13 (carriage return, CR)
299           instead, by adding
300    
301           --enable-newline-is-cr           --enable-newline-is-cr
302    
303         to the configure command. For completeness there is  also  a  --enable-         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
304         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
305         line character.  
306           Alternatively, you can specify that line endings are to be indicated by
307           the two character sequence CRLF. If you want this, add
308    
309             --enable-newline-is-crlf
310    
311           to the configure command. There is a fourth option, specified by
312    
313             --enable-newline-is-any
314    
315           which causes PCRE to recognize any Unicode newline sequence.
316    
317           Whatever  line  ending convention is selected when PCRE is built can be
318           overridden when the library functions are called. At build time  it  is
319           conventional to use the standard for your operating system.
320    
321    
322  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
323    
324         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
325         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
326         of         of
327    
328           --disable-shared           --disable-shared
# Line 293  BUILDING SHARED AND STATIC LIBRARIES Line 334  BUILDING SHARED AND STATIC LIBRARIES
334  POSIX MALLOC USAGE  POSIX MALLOC USAGE
335    
336         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
337         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
338         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
339         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
340         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
341         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.
342         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 306  POSIX MALLOC USAGE Line 347  POSIX MALLOC USAGE
347         to the configure command.         to the configure command.
348    
349    
 LIMITING PCRE RESOURCE USAGE  
   
        Internally,  PCRE has a function called match(), which it calls repeat-  
        edly  (possibly  recursively)  when  matching  a   pattern   with   the  
        pcre_exec()  function.  By controlling the maximum number of times this  
        function may be called during a single matching operation, a limit  can  
        be  placed  on  the resources used by a single call to pcre_exec(). The  
        limit can be changed at run time, as described in the pcreapi  documen-  
        tation.  The default is 10 million, but this can be changed by adding a  
        setting such as  
   
          --with-match-limit=500000  
   
        to  the  configure  command.  This  setting  has  no  effect   on   the  
        pcre_dfa_exec() matching function.  
   
   
350  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
351    
352         Within  a  compiled  pattern,  offset values are used to point from one         Within a compiled pattern, offset values are used  to  point  from  one
353         part to another (for example, from an opening parenthesis to an  alter-         part  to another (for example, from an opening parenthesis to an alter-
354         nation  metacharacter).  By default, two-byte values are used for these         nation metacharacter). By default, two-byte values are used  for  these
355         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets,  leading  to  a  maximum size for a compiled pattern of around
356         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
357         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless,  some  people do want to process enormous patterns, so it
358         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
359         adding a setting such as         adding a setting such as
360    
361           --with-link-size=3           --with-link-size=3
362    
363         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
364         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
365         additional bytes when handling them.         additional bytes when handling them.
366    
367         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
368         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
369         representation of the compiled pattern, and this changes with the  link         representation  of the compiled pattern, and this changes with the link
370         size.         size.
371    
372    
373  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
374    
375         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
376         ing by making recursive calls to an internal function  called  match().         ing  by  making recursive calls to an internal function called match().
377         In  environments  where  the size of the stack is limited, this can se-         In environments where the size of the stack is limited,  this  can  se-
378         verely limit PCRE's operation. (The Unix environment does  not  usually         verely  limit  PCRE's operation. (The Unix environment does not usually
379         suffer  from  this  problem.)  An alternative approach that uses memory         suffer from this problem, but it may sometimes be necessary to increase
380         from the heap to remember data, instead  of  using  recursive  function         the  maximum  stack size.  There is a discussion in the pcrestack docu-
381         calls,  has been implemented to work round this problem. If you want to         mentation.) An alternative approach to recursion that uses memory  from
382         build a version of PCRE that works this way, add         the  heap  to remember data, instead of using recursive function calls,
383           has been implemented to work round the problem of limited  stack  size.
384           If you want to build a version of PCRE that works this way, add
385    
386           --disable-stack-for-recursion           --disable-stack-for-recursion
387    
388         to the configure command. With this configuration, PCRE  will  use  the         to  the  configure  command. With this configuration, PCRE will use the
389         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
390         ment functions. Separate functions are provided because  the  usage  is         ment  functions.  Separate  functions are provided because the usage is
391         very  predictable:  the  block sizes requested are always the same, and         very predictable: the block sizes requested are always  the  same,  and
392         the blocks are always freed in reverse order. A calling  program  might         the  blocks  are always freed in reverse order. A calling program might
393         be  able  to implement optimized functions that perform better than the         be able to implement optimized functions that perform better  than  the
394         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more
395         slowly when built in this way. This option affects only the pcre_exec()         slowly when built in this way. This option affects only the pcre_exec()
396         function; it is not relevant for the the pcre_dfa_exec() function.         function; it is not relevant for the the pcre_dfa_exec() function.
397    
398    
399    LIMITING PCRE RESOURCE USAGE
400    
401           Internally,  PCRE has a function called match(), which it calls repeat-
402           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
403           pcre_exec()  function.  By controlling the maximum number of times this
404           function may be called during a single matching operation, a limit  can
405           be  placed  on  the resources used by a single call to pcre_exec(). The
406           limit can be changed at run time, as described in the pcreapi  documen-
407           tation.  The default is 10 million, but this can be changed by adding a
408           setting such as
409    
410             --with-match-limit=500000
411    
412           to  the  configure  command.  This  setting  has  no  effect   on   the
413           pcre_dfa_exec() matching function.
414    
415           In  some  environments  it is desirable to limit the depth of recursive
416           calls of match() more strictly than the total number of calls, in order
417           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
418           for-recursion is specified) that is used. A second limit controls this;
419           it  defaults  to  the  value  that is set for --with-match-limit, which
420           imposes no additional constraints. However, you can set a  lower  limit
421           by adding, for example,
422    
423             --with-match-limit-recursion=10000
424    
425           to  the  configure  command.  This  value can also be overridden at run
426           time.
427    
428    
429  USING EBCDIC CODE  USING EBCDIC CODE
430    
431         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
# Line 381  USING EBCDIC CODE Line 437  USING EBCDIC CODE
437    
438         to the configure command.         to the configure command.
439    
440  Last updated: 28 February 2005  
441  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
442    
443           pcreapi(3), pcre_config(3).
444    
445    Last updated: 30 November 2006
446    Copyright (c) 1997-2006 University of Cambridge.
447  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
448    
449    
# Line 418  PCRE MATCHING ALGORITHMS Line 479  PCRE MATCHING ALGORITHMS
479           <something> <something else> <something further>           <something> <something else> <something further>
480    
481         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
482         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
483    
484    
485  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 427  REGULAR EXPRESSIONS AS TREES Line 488  REGULAR EXPRESSIONS AS TREES
488         resented  as  a  tree structure. An unlimited repetition in the pattern         resented  as  a  tree structure. An unlimited repetition in the pattern
489         makes the tree of infinite size, but it is still a tree.  Matching  the         makes the tree of infinite size, but it is still a tree.  Matching  the
490         pattern  to a given subject string (from a given starting point) can be         pattern  to a given subject string (from a given starting point) can be
491         thought of as a search of the tree.  There are  two  standard  ways  to         thought of as a search of the tree.  There are two  ways  to  search  a
492         search  a  tree: depth-first and breadth-first, and these correspond to         tree:  depth-first  and  breadth-first, and these correspond to the two
493         the two matching algorithms provided by PCRE.         matching algorithms provided by PCRE.
494    
495    
496  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
# Line 459  THE STANDARD MATCHING ALGORITHM Line 520  THE STANDARD MATCHING ALGORITHM
520         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
521    
522    
523  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
524    
525         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
526         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
527         first search of the tree. Starting from the first matching point in the         string from left to right, once, character by character, and as it does
528         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
529         ter by character, and as it does  this,  it  remembers  all  the  paths         matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
530         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
531           keeps multiple states active simultaneously).
532         The  scan  continues until either the end of the subject is reached, or  
533         there are no more unterminated paths. At this point,  terminated  paths         The scan continues until either the end of the subject is  reached,  or
534         represent  the different matching possibilities (if there are none, the         there  are  no more unterminated paths. At this point, terminated paths
535         match has failed).  Thus, if there is more  than  one  possible  match,         represent the different matching possibilities (if there are none,  the
536           match  has  failed).   Thus,  if there is more than one possible match,
537         this algorithm finds all of them, and in particular, it finds the long-         this algorithm finds all of them, and in particular, it finds the long-
538         est. In PCRE, there is an option to stop the algorithm after the  first         est.  In PCRE, there is an option to stop the algorithm after the first
539         match (which is necessarily the shortest) has been found.         match (which is necessarily the shortest) has been found.
540    
541         Note that all the matches that are found start at the same point in the         Note that all the matches that are found start at the same point in the
# Line 481  THE DFA MATCHING ALGORITHM Line 543  THE DFA MATCHING ALGORITHM
543    
544           cat(er(pillar)?)           cat(er(pillar)?)
545    
546         is matched against the string "the caterpillar catchment",  the  result         is  matched  against the string "the caterpillar catchment", the result
547         will  be the three strings "cat", "cater", and "caterpillar" that start         will be the three strings "cat", "cater", and "caterpillar" that  start
548         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
549         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
550    
551         There are a number of features of PCRE regular expressions that are not         There are a number of features of PCRE regular expressions that are not
552         supported by the DFA matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
553    
554         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1.  Because  the  algorithm  finds  all possible matches, the greedy or
555         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
556         ungreedy quantifiers are treated in exactly the same way.         ungreedy quantifiers are treated in exactly the same way. However, pos-
557           sessive quantifiers can make a difference when what follows could  also
558           match what is quantified, for example in a pattern like this:
559    
560             ^a++\w!
561    
562           This  pattern matches "aaab!" but not "aaa!", which would be matched by
563           a non-possessive quantifier. Similarly, if an atomic group is  present,
564           it  is matched as if it were a standalone pattern at the current point,
565           and the longest match is then "locked in" for the rest of  the  overall
566           pattern.
567    
568         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
569         is  not  straightforward  to  keep track of captured substrings for the         is not straightforward to keep track of  captured  substrings  for  the
570         different matching possibilities, and  PCRE's  implementation  of  this         different  matching  possibilities,  and  PCRE's implementation of this
571         algorithm does not attempt to do this. This means that no captured sub-         algorithm does not attempt to do this. This means that no captured sub-
572         strings are available.         strings are available.
573    
574         3. Because no substrings are captured, back references within the  pat-         3.  Because no substrings are captured, back references within the pat-
575         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
576    
577         4.  For  the same reason, conditional expressions that use a backrefer-         4. For the same reason, conditional expressions that use  a  backrefer-
578         ence as the condition are not supported.         ence  as  the  condition or test for a specific group recursion are not
579           supported.
580    
581         5. Callouts are supported, but the value of the  capture_top  field  is         5. Callouts are supported, but the value of the  capture_top  field  is
582         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
583    
584         6.  The \C escape sequence, which (in the standard algorithm) matches a         6.  The \C escape sequence, which (in the standard algorithm) matches a
585         single byte, even in UTF-8 mode, is not supported because the DFA algo-         single byte, even in UTF-8 mode, is not supported because the  alterna-
586         rithm moves through the subject string one character at a time, for all         tive  algorithm  moves  through  the  subject string one character at a
587         active paths through the tree.         time, for all active paths through the tree.
588    
589    
590  ADVANTAGES OF THE DFA ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
591    
592         Using the DFA matching algorithm provides the following advantages:         Using the alternative matching algorithm provides the following  advan-
593           tages:
594    
595         1. All possible matches (at a single point in the subject) are automat-         1. All possible matches (at a single point in the subject) are automat-
596         ically  found,  and  in particular, the longest match is found. To find         ically found, and in particular, the longest match is  found.  To  find
597         more than one match using the standard algorithm, you have to do kludgy         more than one match using the standard algorithm, you have to do kludgy
598         things with callouts.         things with callouts.
599    
600         2.  There is much better support for partial matching. The restrictions         2. There is much better support for partial matching. The  restrictions
601         on the content of the pattern that apply when using the standard  algo-         on  the content of the pattern that apply when using the standard algo-
602         rithm  for partial matching do not apply to the DFA algorithm. For non-         rithm for partial matching do not apply to the  alternative  algorithm.
603         anchored patterns, the starting position of a partial match  is  avail-         For  non-anchored patterns, the starting position of a partial match is
604         able.         available.
605    
606         3.  Because  the  DFA algorithm scans the subject string just once, and         3. Because the alternative algorithm  scans  the  subject  string  just
607         never needs to backtrack, it is possible  to  pass  very  long  subject         once,  and  never  needs to backtrack, it is possible to pass very long
608         strings  to  the matching function in several pieces, checking for par-         subject strings to the matching function in  several  pieces,  checking
609         tial matching each time.         for partial matching each time.
610    
611    
612  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
613    
614         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
615    
616         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
617         partly  because  it has to search for all possible matches, but is also         partly because it has to search for all possible matches, but  is  also
618         because it is less susceptible to optimization.         because it is less susceptible to optimization.
619    
620         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
621    
622         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
623         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
        rithm.  
624    
625  Last updated: 28 February 2005  Last updated: 24 November 2006
626  Copyright (c) 1997-2005 University of Cambridge.  Copyright (c) 1997-2006 University of Cambridge.
627  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
628    
629    
# Line 603  PCRE NATIVE API Line 676  PCRE NATIVE API
676         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
677              const char *name);              const char *name);
678    
679           int pcre_get_stringtable_entries(const pcre *code,
680                const char *name, char **first, char **last);
681    
682         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
683              int stringcount, int stringnumber,              int stringcount, int stringnumber,
684              const char **stringptr);              const char **stringptr);
# Line 641  PCRE NATIVE API Line 717  PCRE NATIVE API
717  PCRE API OVERVIEW  PCRE API OVERVIEW
718    
719         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
720         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
721         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
722         Both of these APIs define a set of C function calls. A C++  wrapper  is         Both of these APIs define a set of C function calls. A C++  wrapper  is
723         distributed with PCRE. It is documented in the pcrecpp page.         distributed with PCRE. It is documented in the pcrecpp page.
# Line 663  PCRE API OVERVIEW Line 739  PCRE API OVERVIEW
739    
740         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
741         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
742         ing. This allows it to find all possible matches (at a given  point  in         ing. The alternative algorithm finds all possible matches (at  a  given
743         the  subject),  not  just  one. However, this algorithm does not return         point  in  the subject), and scans the subject just once. However, this
744         captured substrings. A description of the two matching  algorithms  and         algorithm does not return captured substrings. A description of the two
745         their  advantages  and disadvantages is given in the pcrematching docu-         matching  algorithms and their advantages and disadvantages is given in
746         mentation.         the pcrematching documentation.
747    
748         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
749         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 679  PCRE API OVERVIEW Line 755  PCRE API OVERVIEW
755           pcre_get_named_substring()           pcre_get_named_substring()
756           pcre_get_substring_list()           pcre_get_substring_list()
757           pcre_get_stringnumber()           pcre_get_stringnumber()
758             pcre_get_stringtable_entries()
759    
760         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
761         to free the memory used for extracted strings.         to free the memory used for extracted strings.
# Line 710  PCRE API OVERVIEW Line 787  PCRE API OVERVIEW
787         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
788         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
789         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
790         function. This is a non-standard way of building PCRE, for use in envi-         function. See the pcrebuild documentation for  details  of  how  to  do
791         ronments that have limited stacks. Because of the greater use of memory         this.  It  is  a non-standard way of building PCRE, for use in environ-
792         management, it runs more slowly.  Separate functions  are  provided  so         ments that have limited stacks. Because of the greater  use  of  memory
793         that  special-purpose  external  code  can  be used for this case. When         management,  it  runs  more  slowly. Separate functions are provided so
794         used, these functions are always called in a  stack-like  manner  (last         that special-purpose external code can be  used  for  this  case.  When
795         obtained,  first freed), and always for memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
796           obtained, first freed), and always for memory blocks of the same  size.
797           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
798           mentation.
799    
800         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
801         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 723  PCRE API OVERVIEW Line 803  PCRE API OVERVIEW
803         pcrecallout documentation.         pcrecallout documentation.
804    
805    
806    NEWLINES
807    
808           PCRE  supports four different conventions for indicating line breaks in
809           strings: a single CR (carriage return) character, a  single  LF  (line-
810           feed)  character,  the two-character sequence CRLF, or any Unicode new-
811           line sequence.  The Unicode newline sequences are the three  just  men-
812           tioned, plus the single characters VT (vertical tab, U+000B), FF (form-
813           feed, U+000C), NEL (next line, U+0085), LS  (line  separator,  U+2028),
814           and PS (paragraph separator, U+2029).
815    
816           Each  of  the first three conventions is used by at least one operating
817           system as its standard newline sequence. When PCRE is built, a  default
818           can  be  specified.  The default default is LF, which is the Unix stan-
819           dard. When PCRE is run, the default can be overridden,  either  when  a
820           pattern is compiled, or when it is matched.
821    
822           In the PCRE documentation the word "newline" is used to mean "the char-
823           acter or pair of characters that indicate a line break". The choice  of
824           newline  convention  affects  the  handling of the dot, circumflex, and
825           dollar metacharacters, the handling of #-comments in /x mode, and, when
826           CRLF  is a recognized line ending sequence, the match position advance-
827           ment for a non-anchored pattern. The choice of newline convention  does
828           not affect the interpretation of the \n or \r escape sequences.
829    
830    
831  MULTITHREADING  MULTITHREADING
832    
833         The  PCRE  functions  can be used in multi-threading applications, with         The  PCRE  functions  can be used in multi-threading applications, with
# Line 769  CHECKING BUILD-TIME OPTIONS Line 874  CHECKING BUILD-TIME OPTIONS
874    
875           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
876    
877         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
878         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
879         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.
880         operating system.         The default should normally be the standard sequence for your operating
881           system.
882    
883           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
884    
885         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
886         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
887         4.  Larger  values  allow larger regular expressions to be compiled, at         4. Larger values allow larger regular expressions to  be  compiled,  at
888         the expense of slower matching. The default value of  2  is  sufficient         the  expense  of  slower matching. The default value of 2 is sufficient
889         for  all  but  the  most massive patterns, since it allows the compiled         for all but the most massive patterns, since  it  allows  the  compiled
890         pattern to be up to 64K in size.         pattern to be up to 64K in size.
891    
892           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
893    
894         The output is an integer that contains the threshold  above  which  the         The  output  is  an integer that contains the threshold above which the
895         POSIX  interface  uses malloc() for output vectors. Further details are         POSIX interface uses malloc() for output vectors. Further  details  are
896         given in the pcreposix documentation.         given in the pcreposix documentation.
897    
898           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
899    
900         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
901         internal  matching  function  calls in a pcre_exec() execution. Further         internal matching function calls in a  pcre_exec()  execution.  Further
902         details are given with pcre_exec() below.         details are given with pcre_exec() below.
903    
904             PCRE_CONFIG_MATCH_LIMIT_RECURSION
905    
906           The  output is an integer that gives the default limit for the depth of
907           recursion when calling the internal matching function in a  pcre_exec()
908           execution. Further details are given with pcre_exec() below.
909    
910           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
911    
912         The output is an integer that is set to one if internal recursion  when         The  output is an integer that is set to one if internal recursion when
913         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
914         the stack to remember their state. This is the usual way that  PCRE  is         the  stack  to remember their state. This is the usual way that PCRE is
915         compiled. The output is zero if PCRE was compiled to use blocks of data         compiled. The output is zero if PCRE was compiled to use blocks of data
916         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
917         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
918         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
919    
920    
# Line 819  COMPILING A PATTERN Line 931  COMPILING A PATTERN
931    
932         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
933         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
934         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
935         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
936    
937         The pattern is a C string terminated by a binary zero, and is passed in         The pattern is a C string terminated by a binary zero, and is passed in
938         the pattern argument. A pointer to a single block  of  memory  that  is         the  pattern  argument.  A  pointer to a single block of memory that is
939         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
940         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
941         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
942         It is up to the caller  to  free  the  memory  when  it  is  no  longer         It is up to the caller to free the memory (via pcre_free) when it is no
943         required.         longer required.
944    
945         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
946         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
947         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
948         ment, which is an address (see below).         ment, which is an address (see below).
949    
950         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
951         tion.  It  should  be  zero  if  no options are required. The available         pilation. It should be zero if no options are required.  The  available
952         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them, in particular, those that
953         are  compatible  with  Perl,  can also be set and unset from within the         are compatible with Perl, can also be set and  unset  from  within  the
954         pattern (see the detailed description  in  the  pcrepattern  documenta-         pattern  (see  the  detailed  description in the pcrepattern documenta-
955         tion).  For  these options, the contents of the options argument speci-         tion). For these options, the contents of the options  argument  speci-
956         fies their initial settings at the start of compilation and  execution.         fies  their initial settings at the start of compilation and execution.
957         The  PCRE_ANCHORED option can be set at the time of matching as well as         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time
958         at compile time.         of matching as well as at compile time.
959    
960         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
961         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
962         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-
963         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
964         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-
965         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
966           by  erroffset,  which must not be NULL. If it is, an immediate error is
967         given.         given.
968    
969         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
# Line 913  COMPILING A PATTERN Line 1026  COMPILING A PATTERN
1026    
1027         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
1028         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
1029         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
1030         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1031         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
1032         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1033    
1034           PCRE_DOTALL           PCRE_DOTALL
1035    
1036         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-
1037         acters, including newlines. Without it,  newlines  are  excluded.  This         acters, including those that indicate newline. Without it, a  dot  does
1038         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
1039         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
1040         always  matches a newline character, independent of the setting of this         by  a (?s) option setting. A negative class such as [^a] always matches
1041         option.         newline characters, independent of the setting of this option.
1042    
1043             PCRE_DUPNAMES
1044    
1045           If this bit is set, names used to identify capturing  subpatterns  need
1046           not be unique. This can be helpful for certain types of pattern when it
1047           is known that only one instance of the named  subpattern  can  ever  be
1048           matched.  There  are  more details of named subpatterns below; see also
1049           the pcrepattern documentation.
1050    
1051           PCRE_EXTENDED           PCRE_EXTENDED
1052    
# Line 933  COMPILING A PATTERN Line 1054  COMPILING A PATTERN
1054         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1055         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1056         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1057         line character, inclusive, are also  ignored.  This  is  equivalent  to         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1058         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-
1059         option setting.         ting.
1060    
1061         This option makes it possible to include  comments  inside  complicated         This option makes it possible to include  comments  inside  complicated
1062         patterns.   Note,  however,  that this applies only to data characters.         patterns.   Note,  however,  that this applies only to data characters.
# Line 951  COMPILING A PATTERN Line 1072  COMPILING A PATTERN
1072         letter  that  has  no  special  meaning causes an error, thus reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1073         these combinations for future expansion. By  default,  as  in  Perl,  a         these combinations for future expansion. By  default,  as  in  Perl,  a
1074         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
1075         literal. There are at present no  other  features  controlled  by  this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1076         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
1077           can also be set by a (?X) option setting within a pattern.
1078    
1079           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1080    
1081         If  this  option  is  set,  an  unanchored pattern is required to match         If this option is set, an  unanchored  pattern  is  required  to  match
1082         before or at the first newline character in the subject string,  though         before  or  at  the  first  newline  in  the subject string, though the
1083         the matched text may continue over the newline.         matched text may continue over the newline.
1084    
1085           PCRE_MULTILINE           PCRE_MULTILINE
1086    
1087         By  default,  PCRE  treats the subject string as consisting of a single         By default, PCRE treats the subject string as consisting  of  a  single
1088         line of characters (even if it actually contains newlines). The  "start         line  of characters (even if it actually contains newlines). The "start
1089         of  line"  metacharacter  (^)  matches only at the start of the string,         of line" metacharacter (^) matches only at the  start  of  the  string,
1090         while the "end of line" metacharacter ($) matches only at  the  end  of         while  the  "end  of line" metacharacter ($) matches only at the end of
1091         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1092         is set). This is the same as Perl.         is set). This is the same as Perl.
1093    
1094         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"
1095         constructs  match  immediately following or immediately before any new-         constructs match immediately following or immediately  before  internal
1096         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
1097         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
1098         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-
1099         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,
1100         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1101    
1102             PCRE_NEWLINE_CR
1103             PCRE_NEWLINE_LF
1104             PCRE_NEWLINE_CRLF
1105             PCRE_NEWLINE_ANY
1106    
1107           These  options  override the default newline definition that was chosen
1108           when PCRE was built. Setting the first or the second specifies  that  a
1109           newline  is  indicated  by a single character (CR or LF, respectively).
1110           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1111           two-character  CRLF  sequence.  Setting PCRE_NEWLINE_ANY specifies that
1112           any Unicode newline sequence should be recognized. The Unicode  newline
1113           sequences  are  the three just mentioned, plus the single characters VT
1114           (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085),
1115           LS  (line separator, U+2028), and PS (paragraph separator, U+2029). The
1116           last two are recognized only in UTF-8 mode.
1117    
1118           The newline setting in the  options  word  uses  three  bits  that  are
1119           treated  as  a  number, giving eight possibilities. Currently only five
1120           are used (default plus the four values above). This means that  if  you
1121           set  more  than  one  newline option, the combination may or may not be
1122           sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is  equiva-
1123           lent  to PCRE_NEWLINE_CRLF, but other combinations yield unused numbers
1124           and cause an error.
1125    
1126           The only time that a line break is specially recognized when  compiling
1127           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1128           character class is encountered. This indicates  a  comment  that  lasts
1129           until  after the next line break sequence. In other circumstances, line
1130           break  sequences  are  treated  as  literal  data,   except   that   in
1131           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1132           and are therefore ignored.
1133    
1134           The newline option that is set at compile time becomes the default that
1135           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1136    
1137           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1138    
1139         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
# Line 1018  COMPILATION ERROR CODES Line 1175  COMPILATION ERROR CODES
1175    
1176         The following table lists the error  codes  than  may  be  returned  by         The following table lists the error  codes  than  may  be  returned  by
1177         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(),  along with the error messages that may be returned by
1178         both compiling functions.         both compiling functions. As PCRE has developed, some error codes  have
1179           fallen out of use. To avoid confusion, they have not been re-used.
1180    
1181            0  no error            0  no error
1182            1  \ at end of pattern            1  \ at end of pattern
# Line 1030  COMPILATION ERROR CODES Line 1188  COMPILATION ERROR CODES
1188            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1189            8  range out of order in character class            8  range out of order in character class
1190            9  nothing to repeat            9  nothing to repeat
1191           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1192           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1193           12  unrecognized character after (?           12  unrecognized character after (?
1194           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
# Line 1039  COMPILATION ERROR CODES Line 1197  COMPILATION ERROR CODES
1197           16  erroffset passed as NULL           16  erroffset passed as NULL
1198           17  unknown option bit(s) set           17  unknown option bit(s) set
1199           18  missing ) after comment           18  missing ) after comment
1200           19  parentheses nested too deeply           19  [this code is not in use]
1201           20  regular expression too large           20  regular expression too large
1202           21  failed to get memory           21  failed to get memory
1203           22  unmatched parentheses           22  unmatched parentheses
1204           23  internal error: code overflow           23  internal error: code overflow
1205           24  unrecognized character after (?<           24  unrecognized character after (?<
1206           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1207           26  malformed number after (?(           26  malformed number or name after (?(
1208           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1209           28  assertion expected after (?(           28  assertion expected after (?(
1210           29  (?R or (?digits must be followed by )           29  (?R or (?digits must be followed by )
1211           30  unknown POSIX class name           30  unknown POSIX class name
1212           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1213           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1214           33  spare error           33  [this code is not in use]
1215           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1216           35  invalid condition (?(0)           35  invalid condition (?(0)
1217           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1062  COMPILATION ERROR CODES Line 1220  COMPILATION ERROR CODES
1220           39  closing ) for (?C expected           39  closing ) for (?C expected
1221           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1222           41  unrecognized character after (?P           41  unrecognized character after (?P
1223           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1224           43  two named groups have the same name           43  two named subpatterns have the same name
1225           44  invalid UTF-8 string           44  invalid UTF-8 string
1226           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1227           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1228           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1229             48  subpattern name is too long (maximum 32 characters)
1230             49  too many named subpatterns (maximum 10,000)
1231             50  repeated subpattern is too long
1232             51  octal value is greater than \377 (not in UTF-8 mode)
1233             52  internal error: overran compiling workspace
1234             53   internal  error:  previously-checked  referenced  subpattern not
1235           found
1236             54  DEFINE group contains more than one branch
1237             55  repeating a DEFINE group is not allowed
1238             56  inconsistent NEWLINE options"
1239    
1240    
1241  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1098  STUDYING A PATTERN Line 1266  STUDYING A PATTERN
1266    
1267         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.
1268         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1269         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
1270         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
1271         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
1272           after calling pcre_study(), to be sure that it has run successfully.
1273    
1274         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1275    
# Line 1111  STUDYING A PATTERN Line 1280  STUDYING A PATTERN
1280             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1281    
1282         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1283         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-
1284         ble starting bytes is created.         ble starting bytes is created.
1285    
1286    
1287  LOCALE SUPPORT  LOCALE SUPPORT
1288    
1289         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1290         letters digits, or whatever, by reference to a set of  tables,  indexed         letters  digits,  or whatever, by reference to a set of tables, indexed
1291         by  character  value.  When running in UTF-8 mode, this applies only to         by character value. When running in UTF-8 mode, this  applies  only  to
1292         characters with codes less than 128. Higher-valued  codes  never  match         characters  with  codes  less than 128. Higher-valued codes never match
1293         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
1294         with Unicode character property support.         with  Unicode  character property support. The use of locales with Uni-
1295           code is discouraged.
1296    
1297         An internal set of tables is created in the default C locale when  PCRE         An internal set of tables is created in the default C locale when  PCRE
1298         is  built.  This  is  used when the final argument of pcre_compile() is         is  built.  This  is  used when the final argument of pcre_compile() is
# Line 1187  INFORMATION ABOUT A PATTERN Line 1357  INFORMATION ABOUT A PATTERN
1357         pattern:         pattern:
1358    
1359           int rc;           int rc;
1360           unsigned long int length;           size_t length;
1361           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1362             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1363             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
# Line 1219  INFORMATION ABOUT A PATTERN Line 1389  INFORMATION ABOUT A PATTERN
1389           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1390    
1391         Return  information  about  the first byte of any matched string, for a         Return  information  about  the first byte of any matched string, for a
1392         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored pattern. The fourth argument should point to an int  vari-
1393         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1394         compatibility.)         is still recognized for backwards compatibility.)
1395    
1396         If there is a fixed first byte, for example, from  a  pattern  such  as         If there is a fixed first byte, for example, from  a  pattern  such  as
1397         (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  
1398    
1399         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1400         branch starts with "^", or         branch starts with "^", or
1401    
1402         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1403         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1404    
1405         -1 is returned, indicating that the pattern matches only at  the  start         -1  is  returned, indicating that the pattern matches only at the start
1406         of  a  subject string or after any newline within the string. Otherwise         of a subject string or after any newline within the  string.  Otherwise
1407         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1408    
1409           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1410    
1411         If the pattern was studied, and this resulted in the construction of  a         If  the pattern was studied, and this resulted in the construction of a
1412         256-bit table indicating a fixed set of bytes for the first byte in any         256-bit table indicating a fixed set of bytes for the first byte in any
1413         matching string, a pointer to the table is returned. Otherwise NULL  is         matching  string, a pointer to the table is returned. Otherwise NULL is
1414         returned.  The fourth argument should point to an unsigned char * vari-         returned. The fourth argument should point to an unsigned char *  vari-
1415         able.         able.
1416    
1417           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1418    
1419         Return the value of the rightmost literal byte that must exist  in  any         Return  the  value of the rightmost literal byte that must exist in any
1420         matched  string,  other  than  at  its  start,  if such a byte has been         matched string, other than at its  start,  if  such  a  byte  has  been
1421         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1422         is  no such byte, -1 is returned. For anchored patterns, a last literal         is no such byte, -1 is returned. For anchored patterns, a last  literal
1423         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1424         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1425         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1426    
# Line 1259  INFORMATION ABOUT A PATTERN Line 1428  INFORMATION ABOUT A PATTERN
1428           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1429           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1430    
1431         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1432         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1433         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1434         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1435         captured substring by name. It is also possible  to  extract  the  data         strings  by  name. It is also possible to extract the data directly, by
1436         directly,  by  first converting the name to a number in order to access         first converting the name to a number in order to  access  the  correct
1437         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1438         below).  To  do the conversion, you need to use the name-to-number map,         the conversion, you need  to  use  the  name-to-number  map,  which  is
1439         which is described by these three values.         described by these three values.
1440    
1441         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
1442         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1443         of each entry; both of these  return  an  int  value.  The  entry  size         of  each  entry;  both  of  these  return  an int value. The entry size
1444         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1445         a pointer to the first entry of the table  (a  pointer  to  char).  The         a  pointer  to  the  first  entry of the table (a pointer to char). The
1446         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-
1447         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-
1448         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1449         For example, consider the following pattern  (assume  PCRE_EXTENDED  is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1450         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1451           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1452           ignored):
1453    
1454           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1455           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1456    
1457         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1458         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,
1459         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1460         as ??:         as ??:
1461    
# Line 1293  INFORMATION ABOUT A PATTERN Line 1464  INFORMATION ABOUT A PATTERN
1464           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1465           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1466    
1467         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1468         name-to-number map, remember that the length of each entry is likely to         name-to-number map, remember that the length of the entries  is  likely
1469         be different for each compiled pattern.         to be different for each compiled pattern.
1470    
1471           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1472    
1473         Return a copy of the options with which the pattern was  compiled.  The         Return  a  copy of the options with which the pattern was compiled. The
1474         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1475         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1476         by any top-level option settings within the pattern itself.         by any top-level option settings within the pattern itself.
1477    
1478         A  pattern  is  automatically  anchored by PCRE if all of its top-level         A pattern is automatically anchored by PCRE if  all  of  its  top-level
1479         alternatives begin with one of the following:         alternatives begin with one of the following:
1480    
1481           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1318  INFORMATION ABOUT A PATTERN Line 1489  INFORMATION ABOUT A PATTERN
1489    
1490           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1491    
1492         Return  the  size  of the compiled pattern, that is, the value that was         Return the size of the compiled pattern, that is, the  value  that  was
1493         passed as the argument to pcre_malloc() when PCRE was getting memory in         passed as the argument to pcre_malloc() when PCRE was getting memory in
1494         which to place the compiled data. The fourth argument should point to a         which to place the compiled data. The fourth argument should point to a
1495         size_t variable.         size_t variable.
# Line 1326  INFORMATION ABOUT A PATTERN Line 1497  INFORMATION ABOUT A PATTERN
1497           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1498    
1499         Return the size of the data block pointed to by the study_data field in         Return the size of the data block pointed to by the study_data field in
1500         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
1501         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
1502         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
1503         variable.         variable.
1504    
1505    
# Line 1336  OBSOLETE INFO FUNCTION Line 1507  OBSOLETE INFO FUNCTION
1507    
1508         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1509    
1510         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1511         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1512         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1513         pcre_info()  is the number of capturing subpatterns, or one of the fol-         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1514         lowing negative numbers:         lowing negative numbers:
1515    
1516           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1517           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1518    
1519         If the optptr argument is not NULL, a copy of the  options  with  which         If  the  optptr  argument is not NULL, a copy of the options with which
1520         the  pattern  was  compiled  is placed in the integer it points to (see         the pattern was compiled is placed in the integer  it  points  to  (see
1521         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1522    
1523         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1524         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1525         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1526    
1527    
# Line 1358  REFERENCE COUNTS Line 1529  REFERENCE COUNTS
1529    
1530         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1531    
1532         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1533         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1534         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1535         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1536         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1537    
1538         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1539         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1540         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1541         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1542         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1543         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1544    
1545         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1546         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1547         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1548    
1549    
# Line 1382  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1553  MATCHING A PATTERN: THE TRADITIONAL FUNC
1553              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1554              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1555    
1556         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
1557         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1558         has been studied, the result of the study should be passed in the extra         has been studied, the result of the study should be passed in the extra
1559         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1560         and it operates in a Perl-like manner. For specialist use there is also         and it operates in a Perl-like manner. For specialist use there is also
1561         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1562         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1563    
1564         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1565         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1566         is possible to save compiled patterns and study data, and then use them         is possible to save compiled patterns and study data, and then use them
1567         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1568         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1569    
1570         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1412  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1583  MATCHING A PATTERN: THE TRADITIONAL FUNC
1583    
1584     Extra data for pcre_exec()     Extra data for pcre_exec()
1585    
1586         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
1587         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
1588         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-
1589         tional  information in it. The fields in a pcre_extra block are as fol-         tional information in it. The pcre_extra block contains  the  following
1590         lows:         fields (not necessarily in this order):
1591    
1592           unsigned long int flags;           unsigned long int flags;
1593           void *study_data;           void *study_data;
1594           unsigned long int match_limit;           unsigned long int match_limit;
1595             unsigned long int match_limit_recursion;
1596           void *callout_data;           void *callout_data;
1597           const unsigned char *tables;           const unsigned char *tables;
1598    
1599         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
1600         are set. The flag bits are:         are set. The flag bits are:
1601    
1602           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1603           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1604             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1605           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1606           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1607    
1608         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
1609         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1610         the appropriate flag bit. You should not set this yourself, but you may         the appropriate flag bit. You should not set this yourself, but you may
1611         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1612         flag bits.         flag bits.
1613    
1614         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
1615         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
1616         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1617         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1618         repeats.         repeats.
1619    
1620         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1621         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly  (sometimes  recursively). The limit set by match_limit is imposed
1622         times  this  function is called during a match, which has the effect of         on the number of times this function is called during  a  match,  which
1623         limiting the amount of recursion and backtracking that can take  place.         has  the  effect  of  limiting the amount of backtracking that can take
1624         For patterns that are not anchored, the count starts from zero for each         place. For patterns that are not anchored, the count restarts from zero
1625         position in the subject string.         for each position in the subject string.
1626    
1627         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
1628         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1629         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1630         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra    block    in    which    match_limit    is    set,     and
1631         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
1632         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1633    
1634         The  pcre_callout  field is used in conjunction with the "callout" fea-         The match_limit_recursion field is similar to match_limit, but  instead
1635           of limiting the total number of times that match() is called, it limits
1636           the depth of recursion. The recursion depth is a  smaller  number  than
1637           the  total number of calls, because not all calls to match() are recur-
1638           sive.  This limit is of use only if it is set smaller than match_limit.
1639    
1640           Limiting  the  recursion  depth  limits the amount of stack that can be
1641           used, or, when PCRE has been compiled to use memory on the heap instead
1642           of the stack, the amount of heap memory that can be used.
1643    
1644           The  default  value  for  match_limit_recursion can be set when PCRE is
1645           built; the default default  is  the  same  value  as  the  default  for
1646           match_limit.  You can override the default by suppling pcre_exec() with
1647           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1648           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1649           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1650    
1651           The pcre_callout field is used in conjunction with the  "callout"  fea-
1652         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1653    
1654         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1655         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
1656         pattern. A non-NULL value is stored with the compiled pattern  only  if         pattern.  A  non-NULL value is stored with the compiled pattern only if
1657         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1658         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1659         PCRE's  internal  tables  to be used. This facility is helpful when re-         PCRE's internal tables to be used. This facility is  helpful  when  re-
1660         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
1661         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
1662         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1663         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1664    
1665     Option bits for pcre_exec()     Option bits for pcre_exec()
1666    
1667         The  unused  bits of the options argument for pcre_exec() must be zero.         The unused bits of the options argument for pcre_exec() must  be  zero.
1668         The  only  bits  that  may  be  set  are  PCRE_ANCHORED,   PCRE_NOTBOL,         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1669         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1670           PCRE_PARTIAL.
1671    
1672           PCRE_ANCHORED           PCRE_ANCHORED
1673    
# Line 1485  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1676  MATCHING A PATTERN: THE TRADITIONAL FUNC
1676         turned  out to be anchored by virtue of its contents, it cannot be made         turned  out to be anchored by virtue of its contents, it cannot be made
1677         unachored at matching time.         unachored at matching time.
1678    
1679             PCRE_NEWLINE_CR
1680             PCRE_NEWLINE_LF
1681             PCRE_NEWLINE_CRLF
1682             PCRE_NEWLINE_ANY
1683    
1684           These options override  the  newline  definition  that  was  chosen  or
1685           defaulted  when the pattern was compiled. For details, see the descrip-
1686           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1687           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1688           ters. It may also alter the way the match position is advanced after  a
1689           match  failure  for  an  unanchored  pattern. When PCRE_NEWLINE_CRLF or
1690           PCRE_NEWLINE_ANY is set, and a match attempt  fails  when  the  current
1691           position  is  at a CRLF sequence, the match position is advanced by two
1692           characters instead of one, in other words, to after the CRLF.
1693    
1694           PCRE_NOTBOL           PCRE_NOTBOL
1695    
1696         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
# Line 1620  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1826  MATCHING A PATTERN: THE TRADITIONAL FUNC
1826         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-
1827         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1],  identify  the  portion  of  the  subject string matched by the
1828         entire pattern. The next pair is used for the first  capturing  subpat-         entire pattern. The next pair is used for the first  capturing  subpat-
1829         tern,  and  so  on.  The value returned by pcre_exec() is the number of         tern, and so on. The value returned by pcre_exec() is one more than the
1830         pairs that have been set. If there are no  capturing  subpatterns,  the         highest numbered pair that has been set. For example, if two substrings
1831         return  value  from  a  successful match is 1, indicating that just the         have  been captured, the returned value is 3. If there are no capturing
1832         first pair of offsets has been set.         subpatterns, the return value from a successful match is 1,  indicating
1833           that just the first pair of offsets has been set.
        Some convenience functions are provided  for  extracting  the  captured  
        substrings  as  separate  strings. These are described in the following  
        section.  
   
        It is possible for an capturing subpattern number  n+1  to  match  some  
        part  of  the  subject  when subpattern n has not been used at all. For  
        example, if the string "abc" is matched against the pattern (a|(z))(bc)  
        subpatterns  1 and 3 are matched, but 2 is not. When this happens, both  
        offset values corresponding to the unused subpattern are set to -1.  
1834    
1835         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1836         of the string that it matched that is returned.         of the string that it matched that is returned.
1837    
1838         If  the vector is too small to hold all the captured substring offsets,         If the vector is too small to hold all the captured substring  offsets,
1839         it is used as far as possible (up to two-thirds of its length), and the         it is used as far as possible (up to two-thirds of its length), and the
1840         function  returns a value of zero. In particular, if the substring off-         function returns a value of zero. In particular, if the substring  off-
1841         sets are not of interest, pcre_exec() may be called with ovector passed         sets are not of interest, pcre_exec() may be called with ovector passed
1842         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         as NULL and ovecsize as zero. However, if  the  pattern  contains  back
1843         references and the ovector is not big enough to  remember  the  related         references  and  the  ovector is not big enough to remember the related
1844         substrings,  PCRE has to get additional memory for use during matching.         substrings, PCRE has to get additional memory for use during  matching.
1845         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1846    
1847         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
1848         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
1849         that will allow for n captured substrings, in addition to  the  offsets         ovector  that  will allow for n captured substrings, in addition to the
1850         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.
1851    
1852           It is possible for capturing subpattern number n+1 to match  some  part
1853           of the subject when subpattern n has not been used at all. For example,
1854           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1855           return from the function is 4, and subpatterns 1 and 3 are matched, but
1856           2 is not. When this happens, both values in  the  offset  pairs  corre-
1857           sponding to unused subpatterns are set to -1.
1858    
1859           Offset  values  that correspond to unused subpatterns at the end of the
1860           expression are also set to -1. For example,  if  the  string  "abc"  is
1861           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1862           matched. The return from the function is 2, because  the  highest  used
1863           capturing subpattern number is 1. However, you can refer to the offsets
1864           for the second and third capturing subpatterns if  you  wish  (assuming
1865           the vector is large enough, of course).
1866    
1867     Return values from pcre_exec()         Some  convenience  functions  are  provided for extracting the captured
1868           substrings as separate strings. These are described below.
1869    
1870         If  pcre_exec()  fails, it returns a negative number. The following are     Error return values from pcre_exec()
1871    
1872           If pcre_exec() fails, it returns a negative number. The  following  are
1873         defined in the header file:         defined in the header file:
1874    
1875           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1663  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1878  MATCHING A PATTERN: THE TRADITIONAL FUNC
1878    
1879           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
1880    
1881         Either code or subject was passed as NULL,  or  ovector  was  NULL  and         Either  code  or  subject  was  passed as NULL, or ovector was NULL and
1882         ovecsize was not zero.         ovecsize was not zero.
1883    
1884           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1672  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1887  MATCHING A PATTERN: THE TRADITIONAL FUNC
1887    
1888           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
1889    
1890         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,
1891         to catch the case when it is passed a junk pointer and to detect when a         to catch the case when it is passed a junk pointer and to detect when a
1892         pattern that was compiled in an environment of one endianness is run in         pattern that was compiled in an environment of one endianness is run in
1893         an environment with the other endianness. This is the error  that  PCRE         an  environment  with the other endianness. This is the error that PCRE
1894         gives when the magic number is not present.         gives when the magic number is not present.
1895    
1896           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1897    
1898         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1899         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
1900         overwriting of the compiled pattern.         overwriting of the compiled pattern.
1901    
1902           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
1903    
1904         If  a  pattern contains back references, but the ovector that is passed         If a pattern contains back references, but the ovector that  is  passed
1905         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
1906         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
1907         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
1908         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
1909    
1910           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
1911    
1912         This  error is used by the pcre_copy_substring(), pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
1913         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
1914         returned by pcre_exec().         returned by pcre_exec().
1915    
1916           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
1917    
1918         The  recursion  and backtracking limit, as specified by the match_limit         The backtracking limit, as specified by  the  match_limit  field  in  a
1919         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra  structure  (or  defaulted) was reached. See the description
1920         description above.         above.
1921    
1922           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
1923    
1924         This error is never generated by pcre_exec() itself. It is provided for         This error is never generated by pcre_exec() itself. It is provided for
1925         use by callout functions that want to yield a distinctive  error  code.         use  by  callout functions that want to yield a distinctive error code.
1926         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
1927    
1928           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
1929    
1930         A  string  that contains an invalid UTF-8 byte sequence was passed as a         A string that contains an invalid UTF-8 byte sequence was passed  as  a
1931         subject.         subject.
1932    
1933           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
1934    
1935         The UTF-8 byte sequence that was passed as a subject was valid, but the         The UTF-8 byte sequence that was passed as a subject was valid, but the
1936         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-
1937         ter.         ter.
1938    
1939           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
1940    
1941         The subject string did not match, but it did match partially.  See  the         The  subject  string did not match, but it did match partially. See the
1942         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
1943    
1944           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
1945    
1946         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
1947         items that are not supported for partial matching. See the  pcrepartial         items  that are not supported for partial matching. See the pcrepartial
1948         documentation for details of partial matching.         documentation for details of partial matching.
1949    
1950           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
1951    
1952         An  unexpected  internal error has occurred. This error could be caused         An unexpected internal error has occurred. This error could  be  caused
1953         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
1954    
1955           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
1956    
1957         This error is given if the value of the ovecsize argument is  negative.         This  error is given if the value of the ovecsize argument is negative.
1958    
1959             PCRE_ERROR_RECURSIONLIMIT (-21)
1960    
1961           The internal recursion limit, as specified by the match_limit_recursion
1962           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
1963           description above.
1964    
1965             PCRE_ERROR_NULLWSLIMIT    (-22)
1966    
1967           When a group that can match an empty  substring  is  repeated  with  an
1968           unbounded  upper  limit, the subject position at the start of the group
1969           must be remembered, so that a test for an empty string can be made when
1970           the  end  of the group is reached. Some workspace is required for this;
1971           if it runs out, this error is given.
1972    
1973             PCRE_ERROR_BADNEWLINE     (-23)
1974    
1975           An invalid combination of PCRE_NEWLINE_xxx options was given.
1976    
1977           Error numbers -16 to -20 are not used by pcre_exec().
1978    
1979    
1980  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 1755  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 1990  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
1990         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
1991              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
1992    
1993         Captured  substrings  can  be  accessed  directly  by using the offsets         Captured substrings can be  accessed  directly  by  using  the  offsets
1994         returned by pcre_exec() in  ovector.  For  convenience,  the  functions         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
1995         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
1996         string_list() are provided for extracting captured substrings  as  new,         string_list()  are  provided for extracting captured substrings as new,
1997         separate,  zero-terminated strings. These functions identify substrings         separate, zero-terminated strings. These functions identify  substrings
1998         by number. The next section describes functions  for  extracting  named         by  number.  The  next section describes functions for extracting named
1999         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2000         extracted and has a further zero added on the end, but  the  result  is  
2001         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2002           a  further zero added on the end, but the result is not, of course, a C
2003           string.  However, you can process such a string  by  referring  to  the
2004           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2005           string().  Unfortunately, the interface to pcre_get_substring_list() is
2006           not  adequate for handling strings containing binary zeros, because the
2007           end of the final string is not independently indicated.
2008    
2009         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-
2010         tions: subject is the subject string that has  just  been  successfully         tions:  subject  is  the subject string that has just been successfully
2011         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
2012         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2013         were  captured  by  the match, including the substring that matched the         were captured by the match, including the substring  that  matched  the
2014         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2015         it  is greater than zero. If pcre_exec() returned zero, indicating that         it is greater than zero. If pcre_exec() returned zero, indicating  that
2016         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
2017         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2018    
2019         The  functions pcre_copy_substring() and pcre_get_substring() extract a         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2020         single substring, whose number is given as  stringnumber.  A  value  of         single  substring,  whose  number  is given as stringnumber. A value of
2021         zero  extracts  the  substring that matched the entire pattern, whereas         zero extracts the substring that matched the  entire  pattern,  whereas
2022         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2023         string(),  the  string  is  placed  in buffer, whose length is given by         string(), the string is placed in buffer,  whose  length  is  given  by
2024         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2025         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2026         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
2027         the terminating zero, or one of         the terminating zero, or one of these error codes:
2028    
2029           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2030    
2031         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
2032         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2033    
2034           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2035    
2036         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2037    
2038         The pcre_get_substring_list()  function  extracts  all  available  sub-         The  pcre_get_substring_list()  function  extracts  all  available sub-
2039         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
2040         single block of memory that is obtained via pcre_malloc. The address of         single block of memory that is obtained via pcre_malloc. The address of
2041         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
2042         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
2043         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
2044           error code
2045    
2046           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2047    
# Line 1818  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2060  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2060         tively.  They  do  nothing  more  than  call the function pointed to by         tively.  They  do  nothing  more  than  call the function pointed to by
2061         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.
2062         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-
2063         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2064         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-
2065         vided.         vided.
2066    
# Line 1841  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2083  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2083         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-
2084         ber.  For example, for this pattern         ber.  For example, for this pattern
2085    
2086           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2087    
2088         the number of the subpattern called "xxx" is 2. You can find the number         the number of the subpattern called "xxx" is 2. If the name is known to
2089         from the name by calling pcre_get_stringnumber(). The first argument is         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2090         the  compiled  pattern,  and  the  second is the name. The yield of the         name by calling pcre_get_stringnumber(). The first argument is the com-
2091         function is the subpattern number, or  PCRE_ERROR_NOSUBSTRING  (-7)  if         piled pattern, and the second is the name. The yield of the function is
2092         there is no subpattern of that name.         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2093           subpattern of that name.
2094    
2095         Given the number, you can extract the substring directly, or use one of         Given the number, you can extract the substring directly, or use one of
2096         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2097         are also two functions that do the whole job.         are also two functions that do the whole job.
2098    
2099         Most    of    the    arguments   of   pcre_copy_named_substring()   and         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2100         pcre_get_named_substring() are the same  as  those  for  the  similarly         pcre_get_named_substring()  are  the  same  as  those for the similarly
2101         named  functions  that extract by number. As these are described in the         named functions that extract by number. As these are described  in  the
2102         previous section, they are not re-described here. There  are  just  two         previous  section,  they  are not re-described here. There are just two
2103         differences:         differences:
2104    
2105         First,  instead  of a substring number, a substring name is given. Sec-         First, instead of a substring number, a substring name is  given.  Sec-
2106         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
2107         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
2108         name-to-number translation table.         name-to-number translation table.
2109    
2110         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2111         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2112         ate.         ate.
2113    
2114    
2115    DUPLICATE SUBPATTERN NAMES
2116    
2117           int pcre_get_stringtable_entries(const pcre *code,
2118                const char *name, char **first, char **last);
2119    
2120           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2121           subpatterns are not required to  be  unique.  Normally,  patterns  with
2122           duplicate  names  are such that in any one match, only one of the named
2123           subpatterns participates. An example is shown in the pcrepattern  docu-
2124           mentation. When duplicates are present, pcre_copy_named_substring() and
2125           pcre_get_named_substring() return the first substring corresponding  to
2126           the  given  name  that  is  set.  If  none  are set, an empty string is
2127           returned.  The pcre_get_stringnumber() function returns one of the num-
2128           bers  that are associated with the name, but it is not defined which it
2129           is.
2130    
2131           If you want to get full details of all captured substrings for a  given
2132           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2133           first argument is the compiled pattern, and the second is the name. The
2134           third  and  fourth  are  pointers to variables which are updated by the
2135           function. After it has run, they point to the first and last entries in
2136           the  name-to-number  table  for  the  given  name.  The function itself
2137           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2138           there  are none. The format of the table is described above in the sec-
2139           tion entitled Information about a  pattern.   Given  all  the  relevant
2140           entries  for the name, you can extract each of their numbers, and hence
2141           the captured data, if any.
2142    
2143    
2144  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2145    
2146         The traditional matching function uses a  similar  algorithm  to  Perl,         The traditional matching function uses a  similar  algorithm  to  Perl,
# Line 1895  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2167  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2167              int *workspace, int wscount);              int *workspace, int wscount);
2168    
2169         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2170         against a compiled pattern, using a "DFA" matching algorithm. This  has         against a compiled pattern, using a matching algorithm that  scans  the
2171         different  characteristics to the normal algorithm, and is not compati-         subject  string  just  once, and does not backtrack. This has different
2172         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics to the normal algorithm, and  is  not  compatible  with
2173         Nevertheless, there are times when this kind of matching can be useful.         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2174         For a discussion of the two matching algorithms, see  the  pcrematching         theless, there are times when this kind of matching can be useful.  For
2175         documentation.         a discussion of the two matching algorithms, see the pcrematching docu-
2176           mentation.
2177    
2178         The  arguments  for  the  pcre_dfa_exec()  function are the same as for         The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2179         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
2180         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2181         used in the same way as for pcre_exec(), so their  description  is  not         used  in  the  same way as for pcre_exec(), so their description is not
2182         repeated here.         repeated here.
2183    
2184         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2185         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2186         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2187         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2188         lot of possible matches.         lot of potential matches.
2189    
2190         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2191    
2192           int rc;           int rc;
2193           int ovector[10];           int ovector[10];
2194           int wspace[20];           int wspace[20];
2195           rc = pcre_exec(           rc = pcre_dfa_exec(
2196             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2197             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2198             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1933  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2206  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2206    
2207     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2208    
2209         The  unused  bits  of  the options argument for pcre_dfa_exec() must be         The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2210         zero. The only bits that may be  set  are  PCRE_ANCHORED,  PCRE_NOTBOL,         zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2211         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2212         PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last  three  of         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2213         these  are  the  same  as  for pcre_exec(), so their description is not         three of these are the same as for pcre_exec(), so their description is
2214         repeated here.         not repeated here.
2215    
2216           PCRE_PARTIAL           PCRE_PARTIAL
2217    
2218         This has the same general effect as it does for  pcre_exec(),  but  the         This  has  the  same general effect as it does for pcre_exec(), but the
2219         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2220         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2221         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have         PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2222         been no complete matches, but there is still at least one matching pos-         been no complete matches, but there is still at least one matching pos-
2223         sibility.  The portion of the string that provided the partial match is         sibility. The portion of the string that provided the partial match  is
2224         set as the first matching string.         set as the first matching string.
2225    
2226           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2227    
2228         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2229         stop  as  soon  as  it  has found one match. Because of the way the DFA         stop as soon as it has found one match. Because of the way the alterna-
2230         algorithm works, this is necessarily the shortest possible match at the         tive  algorithm  works, this is necessarily the shortest possible match
2231         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2232    
2233           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2234    
2235         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2236         returns a partial match, it is possible to call it  again,  with  addi-         returns  a  partial  match, it is possible to call it again, with addi-
2237         tional  subject  characters,  and have it continue with the same match.         tional subject characters, and have it continue with  the  same  match.
2238         The PCRE_DFA_RESTART option requests this action; when it is  set,  the         The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2239         workspace  and wscount options must reference the same vector as before         workspace and wscount options must reference the same vector as  before
2240         because data about the match so far is left in  them  after  a  partial         because  data  about  the  match so far is left in them after a partial
2241         match.  There  is  more  discussion of this facility in the pcrepartial         match. There is more discussion of this  facility  in  the  pcrepartial
2242         documentation.         documentation.
2243    
2244     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2245    
2246         When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-         When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2247         string in the subject. Note, however, that all the matches from one run         string in the subject. Note, however, that all the matches from one run
2248         of the function start at the same point in  the  subject.  The  shorter         of  the  function  start  at the same point in the subject. The shorter
2249         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2250         if the pattern         if the pattern
2251    
2252           <.*>           <.*>
# Line 1988  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2261  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2261           <something> <something else>           <something> <something else>
2262           <something> <something else> <something further>           <something> <something else> <something further>
2263    
2264         On success, the yield of the function is a number  greater  than  zero,         On  success,  the  yield of the function is a number greater than zero,
2265         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2266         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2267         the  offset  to the start, and the second is the offset to the end. All         the offset to the start, and the second is the offset to  the  end.  In
2268         the strings have the same start offset. (Space could have been saved by         fact,  all  the  strings  have the same start offset. (Space could have
2269         giving  this only once, but it was decided to retain some compatibility         been saved by giving this only once, but it was decided to retain  some
2270         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility  with  the  way pcre_exec() returns data, even though the
2271         strings is different.)         meaning of the strings is different.)
2272    
2273         The strings are returned in reverse order of length; that is, the long-         The strings are returned in reverse order of length; that is, the long-
2274         est matching string is given first. If there were too many  matches  to         est  matching  string is given first. If there were too many matches to
2275         fit  into ovector, the yield of the function is zero, and the vector is         fit into ovector, the yield of the function is zero, and the vector  is
2276         filled with the longest matches.         filled with the longest matches.
2277    
2278     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2279    
2280         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2281         Many  of  the  errors  are  the  same as for pcre_exec(), and these are         Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2282         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2283         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2284    
2285           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2286    
2287         This  return is given if pcre_dfa_exec() encounters an item in the pat-         This return is given if pcre_dfa_exec() encounters an item in the  pat-
2288         tern that it does not support, for instance, the use of \C  or  a  back         tern  that  it  does not support, for instance, the use of \C or a back
2289         reference.         reference.
2290    
2291           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2292    
2293         This  return is given if pcre_dfa_exec() encounters a condition item in         This return is given if pcre_dfa_exec()  encounters  a  condition  item
2294         a pattern that uses a back reference for the  condition.  This  is  not         that  uses  a back reference for the condition, or a test for recursion
2295         supported.         in a specific group. These are not supported.
2296    
2297           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2298    
2299         This  return  is given if pcre_dfa_exec() is called with an extra block         This return is given if pcre_dfa_exec() is called with an  extra  block
2300         that contains a setting of the match_limit field. This is not supported         that contains a setting of the match_limit field. This is not supported
2301         (it is meaningless).         (it is meaningless).
2302    
2303           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2304    
2305         This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the         This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2306         workspace vector.         workspace vector.
2307    
2308           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2309    
2310         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2311         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2312         This error is given if the output vector  is  not  large  enough.  This         This  error  is  given  if  the output vector is not large enough. This
2313         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2314    
2315  Last updated: 16 May 2005  
2316  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2317    
2318           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2319           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2320    
2321    Last updated: 30 November 2006
2322    Copyright (c) 1997-2006 University of Cambridge.
2323  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2324    
2325    
# Line 2213  NAME Line 2492  NAME
2492  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2493    
2494         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2495         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2496         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2497           tures that are expected to be in the forthcoming Perl 5.10.
2498         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2499         are given in the section on UTF-8 support in the main pcre page.         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2500           of  what  it does have are given in the section on UTF-8 support in the
2501           main pcre page.
2502    
2503         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2504         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 2244  DIFFERENCES BETWEEN PCRE AND PERL Line 2525  DIFFERENCES BETWEEN PCRE AND PERL
2525         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2526         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2527         can be tested with \p and \P are limited to the general category  prop-         can be tested with \p and \P are limited to the general category  prop-
2528         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2529           derived properties Any and L&.
2530    
2531         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2532         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2533         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2534         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2535         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2536    
2537             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2259  DIFFERENCES BETWEEN PCRE AND PERL Line 2541  DIFFERENCES BETWEEN PCRE AND PERL
2541             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2542             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2543    
2544         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2545         classes.         classes.
2546    
2547         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2548         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2549         the non-Perl items (?R),  (?number),  and  (?P>name).  Also,  the  PCRE         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2550         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2551         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2552    
2553         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2554         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2555         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2556    
2557           10.  There are some differences that are concerned with the settings of
2558           captured strings when part of  a  pattern  is  repeated.  For  example,
2559           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2560         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2561    
2562         10. PCRE provides some extensions to the Perl regular expression facil-         11. PCRE provides some extensions to the Perl regular expression facil-
2563         ities:         ities.   Perl  5.10  will  include new features that are not in earlier
2564           versions, some of which (such as named parentheses) have been  in  PCRE
2565           for some time. This list is with respect to Perl 5.10:
2566    
2567         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2568         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2569         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2570    
2571         (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
2572         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2573    
2574         (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-
2575         cial meaning is faulted.         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2576           ignored. (Perl can be made to issue a warning.)
2577    
2578         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2579         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
# Line 2296  DIFFERENCES BETWEEN PCRE AND PERL Line 2585  DIFFERENCES BETWEEN PCRE AND PERL
2585         (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-
2586         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2587    
2588         (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.)  
2589    
2590         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The partial matching facility is PCRE-specific.
2591    
2592         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
        Sun's Java package.  
   
        (j) The (R) condition, for testing recursion, is a PCRE extension.  
   
        (k) The callout facility is PCRE-specific.  
   
        (l) The partial matching facility is PCRE-specific.  
   
        (m) Patterns compiled by PCRE can be saved and re-used at a later time,  
2593         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2594    
2595         (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2596         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2597    
2598  Last updated: 28 February 2005  Last updated: 28 November 2006
2599  Copyright (c) 1997-2005 University of Cambridge.  Copyright (c) 1997-2006 University of Cambridge.
2600  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2601    
2602    
# Line 2354  PCRE REGULAR EXPRESSION DETAILS Line 2632  PCRE REGULAR EXPRESSION DETAILS
2632         function, and how it differs from the normal function, are discussed in         function, and how it differs from the normal function, are discussed in
2633         the pcrematching page.         the pcrematching page.
2634    
2635    
2636    CHARACTERS AND METACHARACTERS
2637    
2638         A regular expression is a pattern that is  matched  against  a  subject         A regular expression is a pattern that is  matched  against  a  subject
2639         string  from  left  to right. Most characters stand for themselves in a         string  from  left  to right. Most characters stand for themselves in a
2640         pattern, and match the corresponding characters in the  subject.  As  a         pattern, and match the corresponding characters in the  subject.  As  a
# Line 2378  PCRE REGULAR EXPRESSION DETAILS Line 2659  PCRE REGULAR EXPRESSION DETAILS
2659    
2660         There are two different sets of metacharacters: those that  are  recog-         There are two different sets of metacharacters: those that  are  recog-
2661         nized  anywhere in the pattern except within square brackets, and those         nized  anywhere in the pattern except within square brackets, and those
2662         that are recognized in square brackets. Outside  square  brackets,  the         that are recognized within square brackets.  Outside  square  brackets,
2663         metacharacters are as follows:         the metacharacters are as follows:
2664    
2665           \      general escape character with several uses           \      general escape character with several uses
2666           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2426  BACKSLASH Line 2707  BACKSLASH
2707    
2708         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2709         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
2710         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2711         An escaping backslash can be used to include a whitespace or #  charac-         ing backslash can be used to include a whitespace  or  #  character  as
2712         ter as part of the pattern.         part of the pattern.
2713    
2714         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-
2715         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 2464  BACKSLASH Line 2745  BACKSLASH
2745           \t        tab (hex 09)           \t        tab (hex 09)
2746           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
2747           \xhh      character with hex code hh           \xhh      character with hex code hh
2748           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
2749    
2750         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,
2751         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 2472  BACKSLASH Line 2753  BACKSLASH
2753         becomes hex 7B.         becomes hex 7B.
2754    
2755         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
2756         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
2757         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
2758         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,
2759         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than
2760         \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-
2761         recognized. Instead, the initial \x will  be  interpreted  as  a  basic         nating }, this form of escape is not recognized.  Instead, the  initial
2762         hexadecimal  escape, with no following digits, giving a character whose         \x will be interpreted as a basic hexadecimal escape, with no following
2763         value is zero.         digits, giving a character whose value is zero.
2764    
2765         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
2766         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-
2767         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}.
2768         \x{dc}.  
2769           After \0 up to two further octal digits are read. If  there  are  fewer
2770         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
2771         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
2772         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
2773         character (code value 7). Make sure you supply  two  digits  after  the         if the pattern character that follows is itself an octal digit.
        initial  zero  if the pattern character that follows is itself an octal  
        digit.  
2774    
2775         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-
2776         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
# Line 2503  BACKSLASH Line 2782  BACKSLASH
2782    
2783         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
2784         and  there have not been that many capturing subpatterns, PCRE re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
2785         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-
2786         gle byte from the least significant 8 bits of the value. Any subsequent         erate  a data character. Any subsequent digits stand for themselves. In
2787         digits stand for themselves.  For example:         non-UTF-8 mode, the value of a character specified  in  octal  must  be
2788           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
2789           example:
2790    
2791           \040   is another way of writing a space           \040   is another way of writing a space
2792           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2525  BACKSLASH Line 2806  BACKSLASH
2806         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
2807         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2808    
2809         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
2810         character (in UTF-8 mode) can be used both inside and outside character         inside and outside character classes. In addition, inside  a  character
2811         classes.  In  addition,  inside  a  character class, the sequence \b is         class,  the  sequence \b is interpreted as the backspace character (hex
2812         interpreted as the backspace character (hex 08), and the sequence \X is         08), and the sequences \R and \X are interpreted as the characters  "R"
2813         interpreted  as  the  character  "X".  Outside a character class, these         and  "X", respectively. Outside a character class, these sequences have
2814         sequences have different meanings (see below).         different meanings (see below).
2815    
2816       Absolute and relative back references
2817    
2818           The sequence \g followed by a positive or negative  number,  optionally
2819           enclosed  in  braces,  is  an absolute or relative back reference. Back
2820           references are discussed later, following the discussion  of  parenthe-
2821           sized subpatterns.
2822    
2823     Generic character types     Generic character types
2824    
2825         The third use of backslash is for specifying generic  character  types.         Another use of backslash is for specifying generic character types. The
2826         The following are always recognized:         following are always recognized:
2827    
2828           \d     any decimal digit           \d     any decimal digit
2829           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 2545  BACKSLASH Line 2833  BACKSLASH
2833           \W     any "non-word" character           \W     any "non-word" character
2834    
2835         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
2836         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
2837         of each pair.         of each pair.
2838    
2839         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
2840         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
2841         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
2842         of them fail, since there is no character to match.         of them fail, since there is no character to match.
2843    
2844         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
2845         11).   This makes it different from the the POSIX "space" class. The \s         11).  This makes it different from the the POSIX "space" class. The  \s
2846         characters are HT (9), LF (10), FF (12), CR (13), and space (32).         characters  are  HT (9), LF (10), FF (12), CR (13), and space (32). (If
2847           "use locale;" is included in a Perl script, \s may match the VT charac-
2848           ter. In PCRE, it never does.)
2849    
2850         A "word" character is an underscore or any character less than 256 that         A "word" character is an underscore or any character less than 256 that
2851         is  a  letter  or  digit.  The definition of letters and digits is con-         is a letter or digit. The definition of  letters  and  digits  is  con-
2852         trolled by PCRE's low-valued character tables, and may vary if  locale-         trolled  by PCRE's low-valued character tables, and may vary if locale-
2853         specific  matching is taking place (see "Locale support" in the pcreapi         specific matching is taking place (see "Locale support" in the  pcreapi
2854         page). For example, in the  "fr_FR"  (French)  locale,  some  character         page).  For  example,  in  the  "fr_FR" (French) locale, some character
2855         codes  greater  than  128  are used for accented letters, and these are         codes greater than 128 are used for accented  letters,  and  these  are
2856         matched by \w.         matched by \w.
2857    
2858         In UTF-8 mode, characters with values greater than 128 never match  \d,         In  UTF-8 mode, characters with values greater than 128 never match \d,
2859         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
2860         code character property support is available.         code  character  property support is available. The use of locales with
2861           Unicode is discouraged.
2862    
2863       Newline sequences
2864    
2865           Outside a character class, the escape sequence \R matches  any  Unicode
2866           newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2867           equivalent to the following:
2868    
2869             (?>\r\n|\n|\x0b|\f|\r|\x85)
2870    
2871           This is an example of an "atomic group", details  of  which  are  given
2872           below.  This particular group matches either the two-character sequence
2873           CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
2874           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2875           return, U+000D), or NEL (next line, U+0085). The two-character sequence
2876           is treated as a single unit that cannot be split.
2877    
2878           In  UTF-8  mode, two additional characters whose codepoints are greater
2879           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2880           rator,  U+2029).   Unicode character property support is not needed for
2881           these characters to be recognized.
2882    
2883           Inside a character class, \R matches the letter "R".
2884    
2885     Unicode character properties     Unicode character properties
2886    
2887         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
2888         tional  escape sequences to match generic character types are available         tional  escape  sequences  to  match character properties are available
2889         when UTF-8 mode is selected. They are:         when UTF-8 mode is selected. They are:
2890    
2891          \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
2892          \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
2893          \X       an extended Unicode sequence           \X       an extended Unicode sequence
2894    
2895         The property names represented by xx above are limited to  the  Unicode         The property names represented by xx above are limited to  the  Unicode
2896         general  category properties. Each character has exactly one such prop-         script names, the general category properties, and "Any", which matches
2897         erty, specified by a two-letter abbreviation.  For  compatibility  with         any character (including newline). Other properties such as "InMusical-
2898         Perl,  negation  can be specified by including a circumflex between the         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
2899         opening brace and the property name. For example, \p{^Lu} is  the  same         not match any characters, so always causes a match failure.
2900         as \P{Lu}.  
2901           Sets of Unicode characters are defined as belonging to certain scripts.
2902         If  only  one  letter  is  specified with \p or \P, it includes all the         A  character from one of these sets can be matched using a script name.
2903         properties that start with that letter. In this case, in the absence of         For example:
2904         negation, the curly brackets in the escape sequence are optional; these  
2905         two examples have the same effect:           \p{Greek}
2906             \P{Han}
2907    
2908           Those that are not part of an identified script are lumped together  as
2909           "Common". The current list of scripts is:
2910    
2911           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
2912           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
2913           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
2914           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
2915           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
2916           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
2917           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
2918           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
2919           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
2920    
2921           Each  character has exactly one general category property, specified by
2922           a two-letter abbreviation. For compatibility with Perl, negation can be
2923           specified  by  including a circumflex between the opening brace and the
2924           property name. For example, \p{^Lu} is the same as \P{Lu}.
2925    
2926           If only one letter is specified with \p or \P, it includes all the gen-
2927           eral  category properties that start with that letter. In this case, in
2928           the absence of negation, the curly brackets in the escape sequence  are
2929           optional; these two examples have the same effect:
2930    
2931           \p{L}           \p{L}
2932           \pL           \pL
2933    
2934         The following property codes are supported:         The following general category property codes are supported:
2935    
2936           C     Other           C     Other
2937           Cc    Control           Cc    Control
# Line 2640  BACKSLASH Line 2977  BACKSLASH
2977           Zp    Paragraph separator           Zp    Paragraph separator
2978           Zs    Space separator           Zs    Space separator
2979    
2980         Extended properties such as "Greek" or "InMusicalSymbols" are not  sup-         The  special property L& is also supported: it matches a character that
2981         ported by PCRE.         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
2982           classified as a modifier or "other".
2983    
2984           The  long  synonyms  for  these  properties that Perl supports (such as
2985           \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
2986           any of these properties with "Is".
2987    
2988           No character that is in the Unicode table has the Cn (unassigned) prop-
2989           erty.  Instead, this property is assumed for any code point that is not
2990           in the Unicode table.
2991    
2992         Specifying  caseless  matching  does not affect these escape sequences.         Specifying  caseless  matching  does not affect these escape sequences.
2993         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
# Line 2663  BACKSLASH Line 3009  BACKSLASH
3009    
3010     Simple assertions     Simple assertions
3011    
3012         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3013         tion specifies a condition that has to be met at a particular point  in         tion specifies a condition that has to be met at a particular point  in
3014         a  match, without consuming any characters from the subject string. The         a  match, without consuming any characters from the subject string. The
3015         use of subpatterns for more complicated assertions is described  below.         use of subpatterns for more complicated assertions is described  below.
# Line 2671  BACKSLASH Line 3017  BACKSLASH
3017    
3018           \b     matches at a word boundary           \b     matches at a word boundary
3019           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3020           \A     matches at start of subject           \A     matches at the start of the subject
3021           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3022           \z     matches at end of subject                   also matches before a newline at the end of the subject
3023           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3024             \G     matches at the first matching position in the subject
3025    
3026         These  assertions may not appear in character classes (but note that \b         These  assertions may not appear in character classes (but note that \b
3027         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
# Line 2694  BACKSLASH Line 3041  BACKSLASH
3041         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3042         cating that matching is to start at a point other than the beginning of         cating that matching is to start at a point other than the beginning of
3043         the subject, \A can never match. The difference between \Z  and  \z  is         the subject, \A can never match. The difference between \Z  and  \z  is
3044         that  \Z  matches  before  a  newline that is the last character of the         that \Z matches before a newline at the end of the string as well as at
3045         string as well as at the end of the string, whereas \z matches only  at         the very end, whereas \z matches only at the end.
3046         the end.  
3047           The \G assertion is true only when the current matching position is  at
3048         The  \G assertion is true only when the current matching position is at         the  start point of the match, as specified by the startoffset argument
3049         the start point of the match, as specified by the startoffset  argument         of pcre_exec(). It differs from \A when the  value  of  startoffset  is
3050         of  pcre_exec().  It  differs  from \A when the value of startoffset is         non-zero.  By calling pcre_exec() multiple times with appropriate argu-
        non-zero. By calling pcre_exec() multiple times with appropriate  argu-  
3051         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-
3052         mentation where \G can be useful.         mentation where \G can be useful.
3053    
3054         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
3055         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
3056         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
3057         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3058         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3059    
3060         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
3061         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3062         in the compiled regular expression.         in the compiled regular expression.
3063    
# Line 2719  BACKSLASH Line 3065  BACKSLASH
3065  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3066    
3067         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3068         character  is  an  assertion  that is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3069         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-
3070         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
3071         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3072         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3073    
3074         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
3075         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
3076         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
3077         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3078         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-
3079         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
3080         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3081    
3082         A  dollar  character  is  an assertion that is true only if the current         A dollar character is an assertion that is true  only  if  the  current
3083         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3084         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
3085         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
3086         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
3087         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.  
3088    
3089         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
3090         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
3091         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3092    
3093         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3094         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
3095         ately  after  and  immediately  before  an  internal newline character,         matches  immediately after internal newlines as well as at the start of
3096         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
3097         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         string.  A dollar matches before any newlines in the string, as well as
3098         string "def\nabc" (where \n represents a newline character)  in  multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3099         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3100         in single line mode because all branches start with ^ are not  anchored         not indicate newlines.
3101         in  multiline  mode,  and  a  match for circumflex is possible when the  
3102         startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3103         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3104           Consequently, patterns that are anchored in single  line  mode  because
3105         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
3106         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
3107         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
3108         not.         PCRE_MULTILINE is set.
3109    
3110           Note that the sequences \A, \Z, and \z can be used to match  the  start
3111           and  end of the subject in both modes, and if all branches of a pattern
3112           start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3113           set.
3114    
3115    
3116  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3117    
3118         Outside a character class, a dot in the pattern matches any one charac-         Outside a character class, a dot in the pattern matches any one charac-
3119         ter  in  the  subject,  including a non-printing character, but not (by         ter in the subject string except (by default) a character  that  signi-
3120         default) newline.  In UTF-8 mode, a dot matches  any  UTF-8  character,         fies  the  end  of  a line. In UTF-8 mode, the matched character may be
3121         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3122         the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-  
3123         dling  of dot is entirely independent of the handling of circumflex and         When a line ending is defined as a single character, dot never  matches
3124         dollar, the only relationship being  that  they  both  involve  newline         that  character; when the two-character sequence CRLF is used, dot does
3125         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3126           matches  all characters (including isolated CRs and LFs). When any Uni-
3127           code line endings are being recognized, dot does not match CR or LF  or
3128           any of the other line ending characters.
3129    
3130           The  behaviour  of  dot  with regard to newlines can be changed. If the
3131           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3132           exception. If the two-character sequence CRLF is present in the subject
3133           string, it takes two dots to match it.
3134    
3135           The handling of dot is entirely independent of the handling of  circum-
3136           flex  and  dollar,  the  only relationship being that they both involve
3137           newlines. Dot has no special meaning in a character class.
3138    
3139    
3140  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3141    
3142         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3143         both in and out of UTF-8 mode. Unlike a dot, it can  match  a  newline.         both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any
3144         The  feature  is provided in Perl in order to match individual bytes in         line-ending characters. The feature is provided in  Perl  in  order  to
3145         UTF-8 mode. Because it  breaks  up  UTF-8  characters  into  individual         match  individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-
3146         bytes,  what remains in the string may be a malformed UTF-8 string. For         acters into individual bytes, what remains in the string may be a  mal-
3147         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3148           avoided.
3149    
3150         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3151         below),  because  in UTF-8 mode this would make it impossible to calcu-         below),  because  in UTF-8 mode this would make it impossible to calcu-
# Line 2829  SQUARE BRACKETS AND CHARACTER CLASSES Line 3192  SQUARE BRACKETS AND CHARACTER CLASSES
3192         PCRE  is  compiled  with Unicode property support as well as with UTF-8         PCRE  is  compiled  with Unicode property support as well as with UTF-8
3193         support.         support.
3194    
3195         The newline character is never treated in any special way in  character         Characters that might indicate line breaks are  never  treated  in  any
3196         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         special  way  when  matching  character  classes,  whatever line-ending
3197         options is. A class such as [^a] will always match a newline.         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3198           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3199           of these characters.
3200    
3201         The minus (hyphen) character can be used to specify a range of  charac-         The minus (hyphen) character can be used to specify a range of  charac-
3202         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters  in  a  character  class.  For  example,  [d-m] matches any letter
# Line 2932  VERTICAL BAR Line 3297  VERTICAL BAR
3297    
3298         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3299         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3300         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3301         left to right, and the first one that succeeds is used. If the alterna-         to right, and the first one that succeeds is used. If the  alternatives
3302         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3303         ing the rest of the main pattern as well as the alternative in the sub-         rest of the main pattern as well as the alternative in the  subpattern.
        pattern.  
3304    
3305    
3306  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 2964  INTERNAL OPTION SETTING Line 3328  INTERNAL OPTION SETTING
3328         PCRE extracts it into the global options (and it will therefore show up         PCRE extracts it into the global options (and it will therefore show up
3329         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3330    
3331         An option change within a subpattern affects only that part of the cur-         An  option  change  within a subpattern (see below for a description of
3332         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3333           it, so
3334    
3335           (a(?i)b)c           (a(?i)b)c
3336    
3337         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
3338         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3339         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3340         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3341         example,         example,
3342    
3343           (a(?i)b|c)           (a(?i)b|c)
3344    
3345         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3346         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3347         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3348         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3349    
3350         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3351         in the same way as the Perl-compatible options by using the  characters         can  be changed in the same way as the Perl-compatible options by using
3352         U  and X respectively. The (?X) flag setting is special in that it must         the characters J, U and X respectively.
        always occur earlier in the pattern than any of the additional features  
        it  turns on, even when it is at top level. It is best to put it at the  
        start.  
3353    
3354    
3355  SUBPATTERNS  SUBPATTERNS
# Line 3000  SUBPATTERNS Line 3362  SUBPATTERNS
3362           cat(aract|erpillar|)           cat(aract|erpillar|)
3363    
3364         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3365         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3366         string.         string.
3367    
3368         2.  It  sets  up  the  subpattern as a capturing subpattern. This means         2.  It  sets  up  the  subpattern as a capturing subpattern. This means
# Line 3029  SUBPATTERNS Line 3391  SUBPATTERNS
3391           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3392    
3393         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3394         1  and 2. The maximum number of capturing subpatterns is 65535, and the         1 and 2. The maximum number of capturing subpatterns is 65535.
        maximum depth of nesting of all subpatterns, both  capturing  and  non-  
        capturing, is 200.  
3395    
3396         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3397         start of a non-capturing subpattern,  the  option  letters  may  appear         start of a non-capturing subpattern,  the  option  letters  may  appear
# Line 3053  NAMED SUBPATTERNS Line 3413  NAMED SUBPATTERNS
3413         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3414         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3415         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3416         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3417         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3418         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3419           tax.
3420    
3421           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3422           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3423           to capturing parentheses from other parts of the pattern, such as back-
3424           references,  recursion,  and conditions, can be made by name as well as
3425           by number.
3426    
3427           Names consist of up to  32  alphanumeric  characters  and  underscores.
3428         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3429         names. The PCRE API provides function calls for extracting the name-to-         names, exactly as if the names were not present. The PCRE API  provides
3430         number  translation table from a compiled pattern. There is also a con-         function calls for extracting the name-to-number translation table from
3431         venience function for extracting a captured substring by name. For fur-         a compiled pattern. There is also a convenience function for extracting
3432         ther details see the pcreapi documentation.         a captured substring by name.
3433    
3434           By  default, a name must be unique within a pattern, but it is possible
3435           to relax this constraint by setting the PCRE_DUPNAMES option at compile
3436           time.  This  can  be useful for patterns where only one instance of the
3437           named parentheses can match. Suppose you want to match the  name  of  a
3438           weekday,  either as a 3-letter abbreviation or as the full name, and in
3439           both cases you want to extract the abbreviation. This pattern (ignoring
3440           the line breaks) does the job:
3441    
3442             (?<DN>Mon|Fri|Sun)(?:day)?|
3443             (?<DN>Tue)(?:sday)?|
3444             (?<DN>Wed)(?:nesday)?|
3445             (?<DN>Thu)(?:rsday)?|
3446             (?<DN>Sat)(?:urday)?
3447    
3448           There  are  five capturing substrings, but only one is ever set after a
3449           match.  The convenience  function  for  extracting  the  data  by  name
3450           returns  the  substring  for  the first (and in this example, the only)
3451           subpattern of that name that matched.  This  saves  searching  to  find
3452           which  numbered  subpattern  it  was. If you make a reference to a non-
3453           unique named subpattern from elsewhere in the  pattern,  the  one  that
3454           corresponds  to  the  lowest number is used. For further details of the
3455           interfaces for handling named subpatterns, see the  pcreapi  documenta-
3456           tion.
3457    
3458    
3459  REPETITION  REPETITION
# Line 3070  REPETITION Line 3462  REPETITION
3462         following items:         following items:
3463    
3464           a literal data character           a literal data character
3465           the . metacharacter           the dot metacharacter
3466           the \C escape sequence           the \C escape sequence
3467           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3468             the \R escape sequence
3469           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3470           a character class           a character class
3471           a back reference (see next section)           a back reference (see next section)
# Line 3112  REPETITION Line 3505  REPETITION
3505         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3506         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3507    
3508         For  convenience  (and  historical compatibility) the three most common         For  convenience, the three most common quantifiers have single-charac-
3509         quantifiers have single-character abbreviations:         ter abbreviations:
3510    
3511           *    is equivalent to {0,}           *    is equivalent to {0,}
3512           +    is equivalent to {1,}           +    is equivalent to {1,}
# Line 3165  REPETITION Line 3558  REPETITION
3558         which matches one digit by preference, but can match two if that is the         which matches one digit by preference, but can match two if that is the
3559         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3560    
3561         If the PCRE_UNGREEDY option is set (an option which is not available in         If the PCRE_UNGREEDY option is set (an option that is not available  in
3562         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3563         can be made greedy by following them with a  question  mark.  In  other         can be made greedy by following them with a  question  mark.  In  other
3564         words, it inverts the default behaviour.         words, it inverts the default behaviour.
# Line 3176  REPETITION Line 3569  REPETITION
3569         minimum or maximum.         minimum or maximum.
3570    
3571         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
3572         alent  to Perl's /s) is set, thus allowing the . to match newlines, the         alent  to  Perl's  /s) is set, thus allowing the dot to match newlines,
3573         pattern is implicitly anchored, because whatever follows will be  tried         the pattern is implicitly anchored, because whatever  follows  will  be
3574         against  every character position in the subject string, so there is no         tried  against every character position in the subject string, so there
3575         point in retrying the overall match at any position  after  the  first.         is no point in retrying the overall match at  any  position  after  the
3576         PCRE normally treats such a pattern as though it were preceded by \A.         first.  PCRE  normally treats such a pattern as though it were preceded
3577           by \A.
3578    
3579         In  cases  where  it  is known that the subject string contains no new-         In cases where it is known that the subject  string  contains  no  new-
3580         lines, it is worth setting PCRE_DOTALL in order to  obtain  this  opti-         lines,  it  is  worth setting PCRE_DOTALL in order to obtain this opti-
3581         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3582    
3583         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3584         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3585         backreference  elsewhere in the pattern, a match at the start may fail,         backreference elsewhere in the pattern, a match at the start  may  fail
3586         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3587    
3588           (.*)abc\1           (.*)abc\1
3589    
3590         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3591         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3592    
3593         When a capturing subpattern is repeated, the value captured is the sub-         When a capturing subpattern is repeated, the value captured is the sub-
# Line 3202  REPETITION Line 3596  REPETITION
3596           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
3597    
3598         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
3599         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
3600         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
3601         tions. For example, after         tions. For example, after
3602    
3603           /(a|(b))+/           /(a|(b))+/
# Line 3213  REPETITION Line 3607  REPETITION
3607    
3608  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
3609    
3610         With both maximizing and minimizing repetition, failure of what follows         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
3611         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition,  failure  of what follows normally causes the repeated item
3612         ferent number of repeats allows the rest of the pattern to match. Some-         to be re-evaluated to see if a different number of repeats  allows  the
3613         times it is useful to prevent this, either to change the nature of  the         rest  of  the pattern to match. Sometimes it is useful to prevent this,
3614         match,  or  to  cause it fail earlier than it otherwise might, when the         either to change the nature of the match, or to cause it  fail  earlier
3615         author of the pattern knows there is no point in carrying on.         than  it otherwise might, when the author of the pattern knows there is
3616           no point in carrying on.
3617    
3618         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider, for example, the pattern \d+foo when applied to  the  subject
3619         line         line
# Line 3232  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3627  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3627         the  means for specifying that once a subpattern has matched, it is not         the  means for specifying that once a subpattern has matched, it is not
3628         to be re-evaluated in this way.         to be re-evaluated in this way.
3629    
3630         If we use atomic grouping for the previous example, the  matcher  would         If we use atomic grouping for the previous example, the  matcher  gives
3631         give up immediately on failing to match "foo" the first time. The nota-         up  immediately  on failing to match "foo" the first time. The notation
3632         tion is a kind of special parenthesis, starting with  (?>  as  in  this         is a kind of special parenthesis, starting with (?> as in this example:
        example:  
3633    
3634           (?>\d+)foo           (?>\d+)foo
3635    
# Line 3267  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3661  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3661         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
3662         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
3663         simpler forms of atomic group. However, there is no difference  in  the         simpler forms of atomic group. However, there is no difference  in  the
3664         meaning  or  processing  of  a possessive quantifier and the equivalent         meaning  of  a  possessive  quantifier and the equivalent atomic group,
3665         atomic group.         though there may be a performance  difference;  possessive  quantifiers
3666           should be slightly faster.
3667         The possessive quantifier syntax is an extension to the Perl syntax. It  
3668         originates in Sun's Java package.         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
3669           tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first
3670         When  a  pattern  contains an unlimited repeat inside a subpattern that         edition of his book. Mike McCloskey liked it, so implemented it when he
3671         can itself be repeated an unlimited number of  times,  the  use  of  an         built Sun's Java package, and PCRE copied it from there. It  ultimately
3672         atomic  group  is  the  only way to avoid some failing matches taking a         found its way into Perl at release 5.10.
3673    
3674           PCRE has an optimization that automatically "possessifies" certain sim-
3675           ple pattern constructs. For example, the sequence  A+B  is  treated  as
3676           A++B  because  there is no point in backtracking into a sequence of A's
3677           when B must follow.
3678    
3679           When a pattern contains an unlimited repeat inside  a  subpattern  that
3680           can  itself  be  repeated  an  unlimited number of times, the use of an
3681           atomic group is the only way to avoid some  failing  matches  taking  a
3682         very long time indeed. The pattern         very long time indeed. The pattern
3683    
3684           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
3685    
3686         matches an unlimited number of substrings that either consist  of  non-         matches  an  unlimited number of substrings that either consist of non-
3687         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it
3688         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
3689    
3690           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
3691    
3692         it takes a long time before reporting  failure.  This  is  because  the         it  takes  a  long  time  before reporting failure. This is because the
3693         string  can be divided between the internal \D+ repeat and the external         string can be divided between the internal \D+ repeat and the  external
3694         * repeat in a large number of ways, and all  have  to  be  tried.  (The         *  repeat  in  a  large  number of ways, and all have to be tried. (The
3695         example  uses  [!?]  rather than a single character at the end, because         example uses [!?] rather than a single character at  the  end,  because
3696         both PCRE and Perl have an optimization that allows  for  fast  failure         both  PCRE  and  Perl have an optimization that allows for fast failure
3697         when  a single character is used. They remember the last single charac-         when a single character is used. They remember the last single  charac-
3698         ter that is required for a match, and fail early if it is  not  present         ter  that  is required for a match, and fail early if it is not present
3699         in  the  string.)  If  the pattern is changed so that it uses an atomic         in the string.) If the pattern is changed so that  it  uses  an  atomic
3700         group, like this:         group, like this:
3701    
3702           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
3703    
3704         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences  of non-digits cannot be broken, and failure happens quickly.
3705    
3706    
3707  BACK REFERENCES  BACK REFERENCES
3708    
3709         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
3710         0 (and possibly further digits) is a back reference to a capturing sub-         0 (and possibly further digits) is a back reference to a capturing sub-
3711         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
3712         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
3713    
3714         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
3715         it  is  always  taken  as a back reference, and causes an error only if         it is always taken as a back reference, and causes  an  error  only  if
3716         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
3717         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
3718         to the left of the reference for numbers less than 10. See the  subsec-         to  the left of the reference for numbers less than 10. A "forward back
3719         tion  entitled  "Non-printing  characters" above for further details of         reference" of this type can make sense when a  repetition  is  involved
3720         the handling of digits following a backslash.         and  the  subpattern to the right has participated in an earlier itera-
3721           tion.
3722    
3723         A back reference matches whatever actually matched the  capturing  sub-         It is not possible to have a numerical "forward back  reference"  to  a
3724         pattern  in  the  current subject string, rather than anything matching         subpattern  whose  number  is  10  or  more using this syntax because a
3725           sequence such as \50 is interpreted as a character  defined  in  octal.
3726           See the subsection entitled "Non-printing characters" above for further
3727           details of the handling of digits following a backslash.  There  is  no
3728           such  problem  when named parentheses are used. A back reference to any
3729           subpattern is possible using named parentheses (see below).
3730    
3731           Another way of avoiding the ambiguity inherent in  the  use  of  digits
3732           following a backslash is to use the \g escape sequence, which is a fea-
3733           ture introduced in Perl 5.10. This escape must be followed by  a  posi-
3734           tive  or  a negative number, optionally enclosed in braces. These exam-
3735           ples are all identical:
3736    
3737             (ring), \1
3738             (ring), \g1
3739             (ring), \g{1}
3740    
3741           A positive number specifies an absolute reference without the ambiguity
3742           that  is  present  in  the older syntax. It is also useful when literal
3743           digits follow the reference. A negative number is a relative reference.
3744           Consider this example:
3745    
3746             (abc(def)ghi)\g{-1}
3747    
3748           The sequence \g{-1} is a reference to the most recently started captur-
3749           ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,
3750           \g{-2} would be equivalent to \1. The use of relative references can be
3751           helpful in long patterns, and also in  patterns  that  are  created  by
3752           joining together fragments that contain references within themselves.
3753    
3754           A  back  reference matches whatever actually matched the capturing sub-
3755           pattern in the current subject string, rather  than  anything  matching
3756         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
3757         of doing that). So the pattern         of doing that). So the pattern
3758    
3759           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
3760    
3761         matches  "sense and sensibility" and "response and responsibility", but         matches "sense and sensibility" and "response and responsibility",  but
3762         not "sense and responsibility". If caseful matching is in force at  the         not  "sense and responsibility". If caseful matching is in force at the
3763         time  of the back reference, the case of letters is relevant. For exam-         time of the back reference, the case of letters is relevant. For  exam-
3764         ple,         ple,
3765    
3766           ((?i)rah)\s+\1           ((?i)rah)\s+\1
3767    
3768         matches "rah rah" and "RAH RAH", but not "RAH  rah",  even  though  the         matches  "rah  rah"  and  "RAH RAH", but not "RAH rah", even though the
3769         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
3770    
3771         Back  references  to named subpatterns use the Python syntax (?P=name).         Back references to named subpatterns use the Perl  syntax  \k<name>  or
3772         We could rewrite the above example as follows:         \k'name'  or  the  Python  syntax (?P=name). We could rewrite the above
3773           example in either of the following ways:
3774    
3775             (?<p1>(?i)rah)\s+\k<p1>
3776             (?P<p1>(?i)rah)\s+(?P=p1)
3777    
3778           (?<p1>(?i)rah)\s+(?P=p1)         A subpattern that is referenced by  name  may  appear  in  the  pattern
3779           before or after the reference.
3780    
3781         There may be more than one back reference to the same subpattern. If  a         There  may be more than one back reference to the same subpattern. If a
3782         subpattern  has  not actually been used in a particular match, any back         subpattern has not actually been used in a particular match,  any  back
3783         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
3784    
3785           (a|(bc))\2           (a|(bc))\2
3786    
3787         always fails if it starts to match "a" rather than "bc". Because  there         always  fails if it starts to match "a" rather than "bc". Because there
3788         may  be  many  capturing parentheses in a pattern, all digits following         may be many capturing parentheses in a pattern,  all  digits  following
3789         the backslash are taken as part of a potential back  reference  number.         the  backslash  are taken as part of a potential back reference number.
3790         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
3791         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         used  to  terminate  the back reference. If the PCRE_EXTENDED option is
3792         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-
3793         ments" below) can be used.         ments" below) can be used.
3794    
3795         A back reference that occurs inside the parentheses to which it  refers         A  back reference that occurs inside the parentheses to which it refers
3796         fails  when  the subpattern is first used, so, for example, (a\1) never         fails when the subpattern is first used, so, for example,  (a\1)  never
3797         matches.  However, such references can be useful inside  repeated  sub-         matches.   However,  such references can be useful inside repeated sub-
3798         patterns. For example, the pattern         patterns. For example, the pattern
3799    
3800           (a|b\1)+           (a|b\1)+
3801    
3802         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-
3803         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
3804         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
3805         work, the pattern must be such that the first iteration does  not  need         work,  the  pattern must be such that the first iteration does not need
3806         to  match the back reference. This can be done using alternation, as in         to match the back reference. This can be done using alternation, as  in
3807         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
3808    
3809    
3810  ASSERTIONS  ASSERTIONS
3811    
3812         An assertion is a test on the characters  following  or  preceding  the         An  assertion  is  a  test on the characters following or preceding the
3813         current  matching  point that does not actually consume any characters.         current matching point that does not actually consume  any  characters.
3814         The simple assertions coded as \b, \B, \A, \G, \Z,  \z,  ^  and  $  are         The  simple  assertions  coded  as  \b, \B, \A, \G, \Z, \z, ^ and $ are
3815         described above.         described above.
3816    
3817         More  complicated  assertions  are  coded as subpatterns. There are two         More complicated assertions are coded as  subpatterns.  There  are  two
3818         kinds: those that look ahead of the current  position  in  the  subject         kinds:  those  that  look  ahead of the current position in the subject
3819         string,  and  those  that  look  behind  it. An assertion subpattern is         string, and those that look  behind  it.  An  assertion  subpattern  is
3820         matched in the normal way, except that it does not  cause  the  current         matched  in  the  normal way, except that it does not cause the current
3821         matching position to be changed.         matching position to be changed.
3822    
3823         Assertion  subpatterns  are  not  capturing subpatterns, and may not be         Assertion subpatterns are not capturing subpatterns,  and  may  not  be
3824         repeated, because it makes no sense to assert the  same  thing  several         repeated,  because  it  makes no sense to assert the same thing several
3825         times.  If  any kind of assertion contains capturing subpatterns within         times. If any kind of assertion contains capturing  subpatterns  within
3826         it, these are counted for the purposes of numbering the capturing  sub-         it,  these are counted for the purposes of numbering the capturing sub-
3827         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
3828         out only for positive assertions, because it does not  make  sense  for         out  only  for  positive assertions, because it does not make sense for
3829         negative assertions.         negative assertions.
3830    
3831     Lookahead assertions     Lookahead assertions
# Line 3395  ASSERTIONS Line 3835  ASSERTIONS
3835    
3836           \w+(?=;)           \w+(?=;)
3837    
3838         matches a word followed by a semicolon, but does not include the  semi-         matches  a word followed by a semicolon, but does not include the semi-
3839         colon in the match, and         colon in the match, and
3840    
3841           foo(?!bar)           foo(?!bar)
3842    
3843         matches  any  occurrence  of  "foo" that is not followed by "bar". Note         matches any occurrence of "foo" that is not  followed  by  "bar".  Note
3844         that the apparently similar pattern         that the apparently similar pattern
3845    
3846           (?!foo)bar           (?!foo)bar
3847    
3848         does not find an occurrence of "bar"  that  is  preceded  by  something         does  not  find  an  occurrence  of "bar" that is preceded by something
3849         other  than "foo"; it finds any occurrence of "bar" whatsoever, because         other than "foo"; it finds any occurrence of "bar" whatsoever,  because
3850         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
3851         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
3852    
3853         If you want to force a matching failure at some point in a pattern, the         If you want to force a matching failure at some point in a pattern, the
3854         most convenient way to do it is  with  (?!)  because  an  empty  string         most  convenient  way  to  do  it  is with (?!) because an empty string
3855         always  matches, so an assertion that requires there not to be an empty         always matches, so an assertion that requires there not to be an  empty
3856         string must always fail.         string must always fail.
3857    
3858     Lookbehind assertions     Lookbehind assertions
3859    
3860         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
3861         for negative assertions. For example,         for negative assertions. For example,
3862    
3863           (?<!foo)bar           (?<!foo)bar
3864    
3865         does  find  an  occurrence  of "bar" that is not preceded by "foo". The         does find an occurrence of "bar" that is not  preceded  by  "foo".  The
3866         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
3867         strings it matches must have a fixed length. However, if there are sev-         strings it matches must have a fixed length. However, if there are sev-
3868         eral alternatives, they do not all have to have the same fixed  length.         eral  top-level  alternatives,  they  do  not all have to have the same
3869         Thus         fixed length. Thus
3870    
3871           (?<=bullock|donkey)           (?<=bullock|donkey)
3872    
# Line 3434  ASSERTIONS Line 3874  ASSERTIONS
3874    
3875           (?<!dogs?|cats?)           (?<!dogs?|cats?)
3876    
3877         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
3878         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
3879         This  is  an  extension  compared  with  Perl (at least for 5.8), which         This is an extension compared with  Perl  (at  least  for  5.8),  which
3880         requires all branches to match the same length of string. An  assertion         requires  all branches to match the same length of string. An assertion
3881         such as         such as
3882    
3883           (?<=ab(c|de))           (?<=ab(c|de))
3884    
3885         is  not  permitted,  because  its single top-level branch can match two         is not permitted, because its single top-level  branch  can  match  two
3886         different lengths, but it is acceptable if rewritten to  use  two  top-         different  lengths,  but  it is acceptable if rewritten to use two top-
3887         level branches:         level branches:
3888    
3889           (?<=abc|abde)           (?<=abc|abde)
3890    
3891         The  implementation  of lookbehind assertions is, for each alternative,         The implementation of lookbehind assertions is, for  each  alternative,
3892         to temporarily move the current position back by the  fixed  width  and         to  temporarily  move the current position back by the fixed length and
3893         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
3894         rent position, the match is deemed to fail.         rent position, the assertion fails.
3895    
3896         PCRE does not allow the \C escape (which matches a single byte in UTF-8         PCRE does not allow the \C escape (which matches a single byte in UTF-8
3897         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode) to appear in lookbehind assertions, because it makes it  impossi-
3898         ble to calculate the length of the lookbehind. The \X escape, which can         ble  to  calculate the length of the lookbehind. The \X and \R escapes,
3899         match different numbers of bytes, is also not permitted.         which can match different numbers of bytes, are also not permitted.
3900    
3901         Atomic  groups can be used in conjunction with lookbehind assertions to         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind
3902         specify efficient matching at the end of the subject string. Consider a         assertions  to  specify  efficient  matching  at the end of the subject
3903         simple pattern such as         string. Consider a simple pattern such as
3904    
3905           abcd$           abcd$
3906    
3907         when  applied  to  a  long string that does not match. Because matching         when applied to a long string that does  not  match.  Because  matching
3908         proceeds from left to right, PCRE will look for each "a" in the subject         proceeds from left to right, PCRE will look for each "a" in the subject
3909         and  then  see  if what follows matches the rest of the pattern. If the         and then see if what follows matches the rest of the  pattern.  If  the
3910         pattern is specified as         pattern is specified as
3911    
3912           ^.*abcd$           ^.*abcd$
3913    
3914         the initial .* matches the entire string at first, but when this  fails         the  initial .* matches the entire string at first, but when this fails
3915         (because there is no following "a"), it backtracks to match all but the         (because there is no following "a"), it backtracks to match all but the
3916         last character, then all but the last two characters, and so  on.  Once         last  character,  then all but the last two characters, and so on. Once
3917         again  the search for "a" covers the entire string, from right to left,         again the search for "a" covers the entire string, from right to  left,
3918         so we are no better off. However, if the pattern is written as         so we are no better off. However, if the pattern is written as
3919    
          ^(?>.*)(?<=abcd)  
   
        or, equivalently, using the possessive quantifier syntax,  
   
3920           ^.*+(?<=abcd)           ^.*+(?<=abcd)
3921    
3922         there can be no backtracking for the .* item; it  can  match  only  the         there  can  be  no backtracking for the .*+ item; it can match only the
3923         entire  string.  The subsequent lookbehind assertion does a single test         entire string. The subsequent lookbehind assertion does a  single  test
3924         on the last four characters. If it fails, the match fails  immediately.         on  the last four characters. If it fails, the match fails immediately.
3925         For  long  strings, this approach makes a significant difference to the         For long strings, this approach makes a significant difference  to  the
3926         processing time.         processing time.
3927    
3928     Using multiple assertions     Using multiple assertions
# Line 3495  ASSERTIONS Line 3931  ASSERTIONS
3931    
3932           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
3933    
3934         matches "foo" preceded by three digits that are not "999". Notice  that         matches  "foo" preceded by three digits that are not "999". Notice that
3935         each  of  the  assertions is applied independently at the same point in         each of the assertions is applied independently at the  same  point  in
3936         the subject string. First there is a  check  that  the  previous  three         the  subject  string.  First  there  is a check that the previous three
3937         characters  are  all  digits,  and  then there is a check that the same         characters are all digits, and then there is  a  check  that  the  same
3938         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
3939         ceded  by  six  characters,  the first of which are digits and the last         ceded by six characters, the first of which are  digits  and  the  last
3940         three of which are not "999". For example, it  doesn't  match  "123abc-         three  of  which  are not "999". For example, it doesn't match "123abc-
3941         foo". A pattern to do that is         foo". A pattern to do that is
3942    
3943           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
3944    
3945         This  time  the  first assertion looks at the preceding six characters,         This time the first assertion looks at the  preceding  six  characters,
3946         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
3947         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
3948    
# Line 3514  ASSERTIONS Line 3950  ASSERTIONS
3950    
3951           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
3952    
3953         matches  an occurrence of "baz" that is preceded by "bar" which in turn         matches an occurrence of "baz" that is preceded by "bar" which in  turn
3954         is not preceded by "foo", while         is not preceded by "foo", while
3955    
3956           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
3957    
3958         is another pattern that matches "foo" preceded by three digits and  any         is  another pattern that matches "foo" preceded by three digits and any
3959         three characters that are not "999".         three characters that are not "999".
3960    
3961    
3962  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
3963    
3964         It  is possible to cause the matching process to obey a subpattern con-         It is possible to cause the matching process to obey a subpattern  con-
3965         ditionally or to choose between two alternative subpatterns,  depending         ditionally  or to choose between two alternative subpatterns, depending
3966         on  the result of an assertion, or whether a previous capturing subpat-         on the result of an assertion, or whether a previous capturing  subpat-
3967         tern matched or not. The two possible forms of  conditional  subpattern         tern  matched  or not. The two possible forms of conditional subpattern
3968         are         are
3969    
3970           (?(condition)yes-pattern)           (?(condition)yes-pattern)
3971           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
3972    
3973         If  the  condition is satisfied, the yes-pattern is used; otherwise the         If the condition is satisfied, the yes-pattern is used;  otherwise  the
3974         no-pattern (if present) is used. If there are more  than  two  alterna-         no-pattern  (if  present)  is used. If there are more than two alterna-
3975         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
3976    
3977         There are three kinds of condition. If the text between the parentheses         There are four kinds of condition: references  to  subpatterns,  refer-
3978         consists of a sequence of digits, the condition  is  satisfied  if  the         ences to recursion, a pseudo-condition called DEFINE, and assertions.
3979         capturing  subpattern of that number has previously matched. The number  
3980         must be greater than zero. Consider the following pattern,  which  con-     Checking for a used subpattern by number
3981         tains  non-significant white space to make it more readable (assume the  
3982         PCRE_EXTENDED option) and to divide it into three  parts  for  ease  of         If  the  text between the parentheses consists of a sequence of digits,
3983         discussion:         the condition is true if the capturing subpattern of  that  number  has
3984           previously matched.
3985    
3986           Consider  the  following  pattern, which contains non-significant white
3987           space to make it more readable (assume the PCRE_EXTENDED option) and to
3988           divide it into three parts for ease of discussion:
3989    
3990           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
3991    
# Line 3559  CONDITIONAL SUBPATTERNS Line 4000  CONDITIONAL SUBPATTERNS
4000         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other  words,  this  pattern  matches  a  sequence  of non-parentheses,
4001         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4002    
4003         If the condition is the string (R), it is satisfied if a recursive call     Checking for a used subpattern by name
4004         to  the pattern or subpattern has been made. At "top level", the condi-  
4005         tion is false.  This  is  a  PCRE  extension.  Recursive  patterns  are         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a
4006         described in the next section.         used  subpattern  by  name.  For compatibility with earlier versions of
4007           PCRE, which had this facility before Perl, the syntax  (?(name)...)  is
4008           also  recognized. However, there is a possible ambiguity with this syn-
4009           tax, because subpattern names may  consist  entirely  of  digits.  PCRE
4010           looks  first for a named subpattern; if it cannot find one and the name
4011           consists entirely of digits, PCRE looks for a subpattern of  that  num-
4012           ber,  which must be greater than zero. Using subpattern names that con-
4013           sist entirely of digits is not recommended.
4014    
4015           Rewriting the above example to use a named subpattern gives this:
4016    
4017             (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
4018    
4019    
4020       Checking for pattern recursion
4021    
4022           If the condition is the string (R), and there is no subpattern with the
4023           name  R, the condition is true if a recursive call to the whole pattern
4024           or any subpattern has been made. If digits or a name preceded by amper-
4025           sand follow the letter R, for example:
4026    
4027             (?(R3)...) or (?(R&name)...)
4028    
4029           the  condition is true if the most recent recursion is into the subpat-
4030           tern whose number or name is given. This condition does not  check  the
4031           entire recursion stack.
4032    
4033           At  "top  level", all these recursion test conditions are false. Recur-
4034           sive patterns are described below.
4035    
4036       Defining subpatterns for use by reference only
4037    
4038           If the condition is the string (DEFINE), and  there  is  no  subpattern
4039           with  the  name  DEFINE,  the  condition is always false. In this case,
4040           there may be only one alternative  in  the  subpattern.  It  is  always
4041           skipped  if  control  reaches  this  point  in the pattern; the idea of
4042           DEFINE is that it can be used to define "subroutines" that can be  ref-
4043           erenced  from elsewhere. (The use of "subroutines" is described below.)
4044           For example, a pattern to match an IPv4 address could be  written  like
4045           this (ignore whitespace and line breaks):
4046    
4047             (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
4048             \b (?&byte) (\.(?&byte)){3} \b
4049    
4050           The  first part of the pattern is a DEFINE group inside which a another
4051           group named "byte" is defined. This matches an individual component  of
4052           an  IPv4  address  (a number less than 256). When matching takes place,
4053           this part of the pattern is skipped because DEFINE acts  like  a  false
4054           condition.
4055    
4056           The rest of the pattern uses references to the named group to match the
4057           four dot-separated components of an IPv4 address, insisting on  a  word
4058           boundary at each end.
4059    
4060         If  the  condition  is  not  a sequence of digits or (R), it must be an     Assertion conditions
4061    
4062           If  the  condition  is  not  in any of the above formats, it must be an
4063         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.  This may be a positive or negative lookahead or  lookbehind
4064         assertion.  Consider  this  pattern,  again  containing non-significant         assertion.  Consider  this  pattern,  again  containing non-significant
4065         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
# Line 3589  COMMENTS Line 4084  COMMENTS
4084         at all.         at all.
4085    
4086         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If  the PCRE_EXTENDED option is set, an unescaped # character outside a
4087         character class introduces a comment that continues up to the next new-         character class introduces a  comment  that  continues  to  immediately
4088         line character in the pattern.         after the next newline in the pattern.
4089    
4090    
4091  RECURSIVE PATTERNS  RECURSIVE PATTERNS
# Line 3599  RECURSIVE PATTERNS Line 4094  RECURSIVE PATTERNS
4094         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited nested parentheses. Without the use of  recursion,  the  best
4095         that  can  be  done  is  to use a pattern that matches up to some fixed         that  can  be  done  is  to use a pattern that matches up to some fixed
4096         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth of nesting. It is not possible to  handle  an  arbitrary  nesting
4097         depth.  Perl  provides  a  facility  that allows regular expressions to         depth.
4098         recurse (amongst other things). It does this by interpolating Perl code  
4099         in the expression at run time, and the code can refer to the expression         For some time, Perl has provided a facility that allows regular expres-
4100         itself. A Perl pattern to solve the parentheses problem can be  created         sions to recurse (amongst other things). It does this by  interpolating
4101         like this:         Perl  code in the expression at run time, and the code can refer to the
4102           expression itself. A Perl pattern using code interpolation to solve the
4103           parentheses problem can be created like this:
4104    
4105           $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x;           $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x;
4106    
4107         The (?p{...}) item interpolates Perl code at run time, and in this case         The (?p{...}) item interpolates Perl code at run time, and in this case
4108         refers recursively to the pattern in which it appears. Obviously,  PCRE         refers recursively to the pattern in which it appears.
4109         cannot  support  the  interpolation  of Perl code. Instead, it supports  
4110         some special syntax for recursion of the entire pattern, and  also  for         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4111         individual subpattern recursion.         it  supports  special  syntax  for recursion of the entire pattern, and
4112           also for individual subpattern recursion.  After  its  introduction  in
4113           PCRE  and  Python,  this  kind of recursion was introduced into Perl at
4114           release 5.10.
4115    
4116         The  special item that consists of (? followed by a number greater than         A special item that consists of (? followed by a  number  greater  than
4117         zero and a closing parenthesis is a recursive call of the subpattern of         zero and a closing parenthesis is a recursive call of the subpattern of
4118         the  given  number, provided that it occurs inside that subpattern. (If         the given number, provided that it occurs inside that  subpattern.  (If
4119         not, it is a "subroutine" call, which is described  in  the  next  sec-         not,  it  is  a  "subroutine" call, which is described in the next sec-
4120         tion.)  The special item (?R) is a recursive call of the entire regular         tion.) The special item (?R) or (?0) is a recursive call of the  entire
4121         expression.         regular expression.
4122    
4123           In  PCRE (like Python, but unlike Perl), a recursive subpattern call is
4124           always treated as an atomic group. That is, once it has matched some of
4125           the subject string, it is never re-entered, even if it contains untried
4126           alternatives and there is a subsequent matching failure.
4127    
4128         For example, this PCRE pattern solves the  nested  parentheses  problem         This PCRE pattern solves the nested  parentheses  problem  (assume  the
4129         (assume  the  PCRE_EXTENDED  option  is  set  so  that  white  space is         PCRE_EXTENDED option is set so that white space is ignored):
        ignored):  
4130    
4131           \( ( (?>[^()]+) | (?R) )* \)           \( ( (?>[^()]+) | (?R) )* \)
4132    
4133         First it matches an opening parenthesis. Then it matches any number  of         First  it matches an opening parenthesis. Then it matches any number of
4134         substrings  which  can  either  be  a sequence of non-parentheses, or a         substrings which can either be a  sequence  of  non-parentheses,  or  a
4135         recursive match of the pattern itself (that is  a  correctly  parenthe-         recursive  match  of the pattern itself (that is, a correctly parenthe-
4136         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis.
4137    
4138         If  this  were  part of a larger pattern, you would not want to recurse         If this were part of a larger pattern, you would not  want  to  recurse
4139         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4140    
4141           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( (?>[^()]+) | (?1) )* \) )
4142    
4143         We have put the pattern into parentheses, and caused the  recursion  to         We  have  put the pattern into parentheses, and caused the recursion to
4144         refer  to them instead of the whole pattern. In a larger pattern, keep-         refer to them instead of the whole pattern. In a larger pattern,  keep-
4145         ing track of parenthesis numbers can be tricky. It may be  more  conve-         ing  track  of parenthesis numbers can be tricky. It may be more conve-
4146         nient  to use named parentheses instead. For this, PCRE uses (?P>name),         nient to use named parentheses instead. The Perl  syntax  for  this  is
4147         which is an extension to the Python syntax that  PCRE  uses  for  named         (?&name);  PCRE's  earlier syntax (?P>name) is also supported. We could
4148         parentheses (Perl does not provide named parentheses). We could rewrite         rewrite the above example as follows:
4149         the above example as follows:  
4150             (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
4151           (?P<pn> \( ( (?>[^()]+) | (?P>pn) )* \) )  
4152           If there is more than one subpattern with the same name,  the  earliest
4153         This particular example pattern contains nested unlimited repeats,  and         one  is used. This particular example pattern contains nested unlimited
4154         so  the  use of atomic grouping for matching strings of non-parentheses         repeats, and so the use of atomic grouping for matching strings of non-
4155         is important when applying the pattern to strings that  do  not  match.         parentheses  is  important when applying the pattern to strings that do
4156         For example, when this pattern is applied to         not match. For example, when this pattern is applied to
4157    
4158           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
4159    
4160         it  yields "no match" quickly. However, if atomic grouping is not used,         it yields "no match" quickly. However, if atomic grouping is not  used,
4161         the match runs for a very long time indeed because there  are  so  many         the  match  runs  for a very long time indeed because there are so many
4162         different  ways  the  + and * repeats can carve up the subject, and all         different ways the + and * repeats can carve up the  subject,  and  all
4163         have to be tested before failure can be reported.         have to be tested before failure can be reported.
4164    
4165         At the end of a match, the values set for any capturing subpatterns are         At the end of a match, the values set for any capturing subpatterns are
4166         those from the outermost level of the recursion at which the subpattern         those from the outermost level of the recursion at which the subpattern
4167         value is set.  If you want to obtain  intermediate  values,  a  callout         value  is  set.   If  you want to obtain intermediate values, a callout
4168         function can be used (see the next section and the pcrecallout documen-         function can be used (see below and the pcrecallout documentation).  If
4169         tation). If the pattern above is matched against         the pattern above is matched against
4170    
4171           (ab(cd)ef)           (ab(cd)ef)
4172    
4173         the value for the capturing parentheses is  "ef",  which  is  the  last         the  value  for  the  capturing  parentheses is "ef", which is the last
4174         value  taken  on at the top level. If additional parentheses are added,         value taken on at the top level. If additional parentheses  are  added,
4175         giving         giving
4176    
4177           \( ( ( (?>[^()]+) | (?R) )* ) \)           \( ( ( (?>[^()]+) | (?R) )* ) \)
4178              ^                        ^              ^                        ^
4179              ^                        ^              ^                        ^
4180    
4181         the string they capture is "ab(cd)ef", the contents of  the  top  level         the  string  they  capture is "ab(cd)ef", the contents of the top level
4182         parentheses.  If there are more than 15 capturing parentheses in a pat-         parentheses. If there are more than 15 capturing parentheses in a  pat-
4183         tern, PCRE has to obtain extra memory to store data during a recursion,         tern, PCRE has to obtain extra memory to store data during a recursion,
4184         which  it  does  by  using pcre_malloc, freeing it via pcre_free after-         which it does by using pcre_malloc, freeing  it  via  pcre_free  after-
4185         wards. If  no  memory  can  be  obtained,  the  match  fails  with  the         wards.  If  no  memory  can  be  obtained,  the  match  fails  with the
4186         PCRE_ERROR_NOMEMORY error.         PCRE_ERROR_NOMEMORY error.
4187    
4188         Do  not  confuse  the (?R) item with the condition (R), which tests for         Do not confuse the (?R) item with the condition (R),  which  tests  for
4189         recursion.  Consider this pattern, which matches text in  angle  brack-         recursion.   Consider  this pattern, which matches text in angle brack-
4190         ets,  allowing for arbitrary nesting. Only digits are allowed in nested         ets, allowing for arbitrary nesting. Only digits are allowed in  nested
4191         brackets (that is, when recursing), whereas any characters are  permit-         brackets  (that is, when recursing), whereas any characters are permit-
4192         ted at the outer level.         ted at the outer level.
4193    
4194           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >
4195    
4196         In  this  pattern, (?(R) is the start of a conditional subpattern, with         In this pattern, (?(R) is the start of a conditional  subpattern,  with
4197         two different alternatives for the recursive and  non-recursive  cases.         two  different  alternatives for the recursive and non-recursive cases.
4198         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
4199    
4200    
4201  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
4202    
4203         If the syntax for a recursive subpattern reference (either by number or         If the syntax for a recursive subpattern reference (either by number or
4204         by name) is used outside the parentheses to which it refers,  it  oper-         by  name)  is used outside the parentheses to which it refers, it oper-
4205         ates  like  a  subroutine in a programming language. An earlier example         ates like a subroutine in a programming language. The "called"  subpat-
4206           tern  may  be defined before or after the reference. An earlier example
4207         pointed out that the pattern         pointed out that the pattern
4208    
4209           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
# Line 3709  SUBPATTERNS AS SUBROUTINES Line 4214  SUBPATTERNS AS SUBROUTINES
4214           (sens|respons)e and (?1)ibility           (sens|respons)e and (?1)ibility
4215    
4216         is  used, it does match "sense and responsibility" as well as the other         is  used, it does match "sense and responsibility" as well as the other
4217         two strings. Such references must, however, follow  the  subpattern  to         two strings. Another example is  given  in  the  discussion  of  DEFINE
4218         which they refer.         above.
4219    
4220           Like recursive subpatterns, a "subroutine" call is always treated as an
4221           atomic group. That is, once it has matched some of the subject  string,
4222           it  is  never  re-entered, even if it contains untried alternatives and
4223           there is a subsequent matching failure.
4224    
4225           When a subpattern is used as a subroutine, processing options  such  as
4226           case-independence are fixed when the subpattern is defined. They cannot
4227           be changed for different calls. For example, consider this pattern:
4228    
4229             (abc)(?i:(?1))
4230    
4231           It matches "abcabc". It does not match "abcABC" because the  change  of
4232           processing option does not affect the called subpattern.
4233    
4234    
4235  CALLOUTS  CALLOUTS
# Line 3747  CALLOUTS Line 4266  CALLOUTS
4266         gether. A complete description of the interface to the callout function         gether. A complete description of the interface to the callout function
4267         is given in the pcrecallout documentation.         is given in the pcrecallout documentation.
4268    
4269  Last updated: 28 February 2005  
4270  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
4271    
4272           pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).
4273    
4274