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

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

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

revision 123 by ph10, Mon Mar 12 15:19:06 2007 UTC revision 261 by ph10, Fri Sep 21 08:37:48 2007 UTC
# Line 45  INTRODUCTION Line 45  INTRODUCTION
45    
46         Details of exactly which Perl regular expression features are  and  are         Details of exactly which Perl regular expression features are  and  are
47         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
48         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
49           page.
50    
51         Some features of PCRE can be included, excluded, or  changed  when  the         Some  features  of  PCRE can be included, excluded, or changed when the
52         library  is  built.  The pcre_config() function makes it possible for a         library is built. The pcre_config() function makes it  possible  for  a
53         client to discover which features are  available.  The  features  them-         client  to  discover  which  features are available. The features them-
54         selves  are described in the pcrebuild page. Documentation about build-         selves are described in the pcrebuild page. Documentation about  build-
55         ing PCRE for various operating systems can be found in the README  file         ing  PCRE for various operating systems can be found in the README file
56         in the source distribution.         in the source distribution.
57    
58         The  library  contains  a number of undocumented internal functions and         The library contains a number of undocumented  internal  functions  and
59         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
60         functions,  but  which  are  not  intended for use by external callers.         functions, but which are not intended  for  use  by  external  callers.
61         Their names all begin with "_pcre_", which hopefully will  not  provoke         Their  names  all begin with "_pcre_", which hopefully will not provoke
62         any name clashes. In some environments, it is possible to control which         any name clashes. In some environments, it is possible to control which
63         external symbols are exported when a shared library is  built,  and  in         external  symbols  are  exported when a shared library is built, and in
64         these cases the undocumented symbols are not exported.         these cases the undocumented symbols are not exported.
65    
66    
67  USER DOCUMENTATION  USER DOCUMENTATION
68    
69         The  user  documentation  for PCRE comprises a number of different sec-         The user documentation for PCRE comprises a number  of  different  sec-
70         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
71         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.
72         In the plain text format, all the sections are concatenated,  for  ease         In  the  plain text format, all the sections are concatenated, for ease
73         of searching. The sections are as follows:         of searching. The sections are as follows:
74    
75           pcre              this document           pcre              this document
76             pcre-config       show PCRE installation configuration information
77           pcreapi           details of PCRE's native C API           pcreapi           details of PCRE's native C API
78           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
79           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
# Line 82  USER DOCUMENTATION Line 84  USER DOCUMENTATION
84           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
85           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
86                               regular expressions                               regular expressions
87             pcresyntax        quick syntax reference
88           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
89           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
90           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
# Line 89  USER DOCUMENTATION Line 92  USER DOCUMENTATION
92           pcrestack         discussion of stack usage           pcrestack         discussion of stack usage
93           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
94    
95         In addition, in the "man" and HTML formats, there is a short  page  for         In  addition,  in the "man" and HTML formats, there is a short page for
96         each C library function, listing its arguments and results.         each C library function, listing its arguments and results.
97    
98    
99  LIMITATIONS  LIMITATIONS
100    
101         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
102         never in practice be relevant.         never in practice be relevant.
103    
104         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
105         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
106         process regular expressions that are truly enormous,  you  can  compile         process  regular  expressions  that are truly enormous, you can compile
107         PCRE  with  an  internal linkage size of 3 or 4 (see the README file in         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
108         the source distribution and the pcrebuild documentation  for  details).         the  source  distribution and the pcrebuild documentation for details).
109         In  these  cases the limit is substantially larger.  However, the speed         In these cases the limit is substantially larger.  However,  the  speed
110         of execution is slower.         of execution is slower.
111    
112         All values in repeating quantifiers must be less than 65536. The  maxi-         All values in repeating quantifiers must be less than 65536.
        mum  compiled  length  of  subpattern  with an explicit repeat count is  
        30000 bytes. The maximum number of capturing subpatterns is 65535.  
113    
114         There is no limit to the number of parenthesized subpatterns, but there         There is no limit to the number of parenthesized subpatterns, but there
115         can be no more than 65535 capturing subpatterns.         can be no more than 65535 capturing subpatterns.
# Line 116  LIMITATIONS Line 117  LIMITATIONS
117         The maximum length of name for a named subpattern is 32 characters, and         The maximum length of name for a named subpattern is 32 characters, and
118         the maximum number of named subpatterns is 10000.         the maximum number of named subpatterns is 10000.
119    
120         The maximum length of a subject string is the largest  positive  number         The  maximum  length of a subject string is the largest positive number
121         that  an integer variable can hold. However, when using the traditional         that an integer variable can hold. However, when using the  traditional
122         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
123         inite  repetition.  This means that the available stack space may limit         inite repetition.  This means that the available stack space may  limit
124         the size of a subject string that can be processed by certain patterns.         the size of a subject string that can be processed by certain patterns.
125         For a discussion of stack issues, see the pcrestack documentation.         For a discussion of stack issues, see the pcrestack documentation.
126    
127    
128  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
129    
130         From  release  3.3,  PCRE  has  had  some support for character strings         From release 3.3, PCRE has  had  some  support  for  character  strings
131         encoded in the UTF-8 format. For release 4.0 this was greatly  extended         encoded  in the UTF-8 format. For release 4.0 this was greatly extended
132         to  cover  most common requirements, and in release 5.0 additional sup-         to cover most common requirements, and in release 5.0  additional  sup-
133         port for Unicode general category properties was added.         port for Unicode general category properties was added.
134    
135         In order process UTF-8 strings, you must build PCRE  to  include  UTF-8         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
136         support  in  the  code,  and, in addition, you must call pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
137         with the PCRE_UTF8 option flag. When you do this, both the pattern  and         with  the PCRE_UTF8 option flag. When you do this, both the pattern and
138         any  subject  strings  that are matched against it are treated as UTF-8         any subject strings that are matched against it are  treated  as  UTF-8
139         strings instead of just strings of bytes.         strings instead of just strings of bytes.
140    
141         If you compile PCRE with UTF-8 support, but do not use it at run  time,         If  you compile PCRE with UTF-8 support, but do not use it at run time,
142         the  library will be a bit bigger, but the additional run time overhead         the library will be a bit bigger, but the additional run time  overhead
143         is limited to testing the PCRE_UTF8 flag occasionally, so should not be         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
144         very big.         very big.
145    
146         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
147         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
148         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
149         general category properties such as Lu for an upper case letter  or  Nd         general  category  properties such as Lu for an upper case letter or Nd
150         for  a  decimal number, the Unicode script names such as Arabic or Han,         for a decimal number, the Unicode script names such as Arabic  or  Han,
151         and the derived properties Any and L&. A full  list  is  given  in  the         and  the  derived  properties  Any  and L&. A full list is given in the
152         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
153         ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-         ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-
154         ter},  is  not  supported.   Furthermore,  in Perl, many properties may         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
155         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
156         does not support this.         does not support this.
157    
158         The following comments apply when PCRE is running in UTF-8 mode:     Validity of UTF-8 strings
159    
160           When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
161           subjects are (by default) checked for validity on entry to the relevant
162           functions. From release 7.3 of PCRE, the check is according  the  rules
163           of  RFC  3629, which are themselves derived from the Unicode specifica-
164           tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
165           allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
166           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
167           to U+DFFF.
168    
169           The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
170           which the Unicode Standard says this: "The Low Surrogate Area does  not
171           contain  any  character  assignments,  consequently  no  character code
172           charts or namelists are provided for this area. Surrogates are reserved
173           for  use  with  UTF-16 and then must be used in pairs." The code points
174           that are encoded by UTF-16 pairs  are  available  as  independent  code
175           points  in  the  UTF-8  encoding.  (In other words, the whole surrogate
176           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
177    
178           If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return
179           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
180           that your strings are valid, and therefore want to skip these checks in
181           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
182           compile time or at run time, PCRE assumes that the pattern  or  subject
183           it  is  given  (respectively)  contains only valid UTF-8 codes. In this
184           case, it does not diagnose an invalid UTF-8 string.
185    
186           If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,
187           what  happens  depends on why the string is invalid. If the string con-
188           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
189           string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,
190           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
191           strings  according  to  the more liberal rules of RFC 2279. However, if
192           the string does not even conform to RFC 2279, the result is  undefined.
193           Your program may crash.
194    
195           If  you  want  to  process  strings  of  values  in the full range 0 to
196           0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can
197           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
198           this situation, you will have to apply your own validity check.
199    
200         1.  When you set the PCRE_UTF8 flag, the strings passed as patterns and     General comments about UTF-8 mode
        subjects are checked for validity on entry to the  relevant  functions.  
        If an invalid UTF-8 string is passed, an error return is given. In some  
        situations, you may already know  that  your  strings  are  valid,  and  
        therefore want to skip these checks in order to improve performance. If  
        you set the PCRE_NO_UTF8_CHECK flag at compile time  or  at  run  time,  
        PCRE  assumes  that  the  pattern or subject it is given (respectively)  
        contains only valid UTF-8 codes. In this case, it does not diagnose  an  
        invalid  UTF-8 string. If you pass an invalid UTF-8 string to PCRE when  
        PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may  
        crash.  
201    
202         2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
203         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
204    
205         3. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8         2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8
206         characters for values greater than \177.         characters for values greater than \177.
207    
208         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-         3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
209         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
210    
211         5. The dot metacharacter matches one UTF-8 character instead of a  sin-         4.  The dot metacharacter matches one UTF-8 character instead of a sin-
212         gle byte.         gle byte.
213    
214         6.  The  escape sequence \C can be used to match a single byte in UTF-8         5. The escape sequence \C can be used to match a single byte  in  UTF-8
215         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
216         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
217    
218         7.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly         6. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly
219         test characters of any code value, but the characters that PCRE  recog-         test  characters of any code value, but the characters that PCRE recog-
220         nizes  as  digits,  spaces,  or  word characters remain the same set as         nizes as digits, spaces, or word characters  remain  the  same  set  as
221         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
222         includes  Unicode  property support, because to do otherwise would slow         includes Unicode property support, because to do otherwise  would  slow
223         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
224         sense  of,  say,  "digit",  you must use Unicode property tests such as         sense of, say, "digit", you must use Unicode  property  tests  such  as
225         \p{Nd}.         \p{Nd}.
226    
227         8. Similarly, characters that match the POSIX named  character  classes         7.  Similarly,  characters that match the POSIX named character classes
228         are all low-valued characters.         are all low-valued characters.
229    
230         9.  Case-insensitive  matching  applies only to characters whose values         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
231         are less than 128, unless PCRE is built with Unicode property  support.         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
232         Even  when  Unicode  property support is available, PCRE still uses its         acters.
233         own character tables when checking the case of  low-valued  characters,  
234         so  as not to degrade performance.  The Unicode property information is         9. Case-insensitive matching applies only to  characters  whose  values
235           are  less than 128, unless PCRE is built with Unicode property support.
236           Even when Unicode property support is available, PCRE  still  uses  its
237           own  character  tables when checking the case of low-valued characters,
238           so as not to degrade performance.  The Unicode property information  is
239         used only for characters with higher values. Even when Unicode property         used only for characters with higher values. Even when Unicode property
240         support is available, PCRE supports case-insensitive matching only when         support is available, PCRE supports case-insensitive matching only when
241         there is a one-to-one mapping between a letter's  cases.  There  are  a         there  is  a  one-to-one  mapping between a letter's cases. There are a
242         small  number  of  many-to-one  mappings in Unicode; these are not sup-         small number of many-to-one mappings in Unicode;  these  are  not  sup-
243         ported by PCRE.         ported by PCRE.
244    
245    
# Line 214  AUTHOR Line 249  AUTHOR
249         University Computing Service         University Computing Service
250         Cambridge CB2 3QH, England.         Cambridge CB2 3QH, England.
251    
252         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,
253         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  two  initials,
254         name, separated by a dot, at the domain ucs.cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
255    
256    
257  REVISION  REVISION
258    
259         Last updated: 06 March 2007         Last updated: 09 August 2007
260         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
261  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
262    
# Line 236  NAME Line 271  NAME
271  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
272    
273         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
274         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
275         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
276         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
277         includes  the  standard  ones such as the selection of the installation         the  same  options  can be selected in both Unix-like and non-Unix-like
278         directory) can be obtained by running         environments using the GUI facility of  CMakeSetup  if  you  are  using
279           CMake instead of configure to build PCRE.
280    
281           The complete list of options for configure (which includes the standard
282           ones such as the  selection  of  the  installation  directory)  can  be
283           obtained by running
284    
285           ./configure --help           ./configure --help
286    
287         The following sections describe certain options whose names begin  with         The  following  sections  include  descriptions  of options whose names
288         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
289         for the configure command. Because of the  way  that  configure  works,         defaults  for  the configure command. Because of the way that configure
290         --enable  and  --disable  always  come  in  pairs, so the complementary         works, --enable and --disable always come in pairs, so  the  complemen-
291         option always exists as well, but as it specifies the  default,  it  is         tary  option always exists as well, but as it specifies the default, it
292         not described.         is not described.
293    
294    
295  C++ SUPPORT  C++ SUPPORT
# Line 269  UTF-8 SUPPORT Line 309  UTF-8 SUPPORT
309    
310           --enable-utf8           --enable-utf8
311    
312         to  the  configure  command.  Of  itself, this does not make PCRE treat         to the configure command. Of itself, this  does  not  make  PCRE  treat
313         strings as UTF-8. As well as compiling PCRE with this option, you  also         strings  as UTF-8. As well as compiling PCRE with this option, you also
314         have  have to set the PCRE_UTF8 option when you call the pcre_compile()         have have to set the PCRE_UTF8 option when you call the  pcre_compile()
315         function.         function.
316    
317    
318  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
319    
320         UTF-8 support allows PCRE to process character values greater than  255         UTF-8  support allows PCRE to process character values greater than 255
321         in  the  strings that it handles. On its own, however, it does not pro-         in the strings that it handles. On its own, however, it does  not  pro-
322         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
323         you  want  to  be able to use the pattern escapes \P, \p, and \X, which         you want to be able to use the pattern escapes \P, \p,  and  \X,  which
324         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
325    
326           --enable-unicode-properties           --enable-unicode-properties
327    
328         to the configure command. This implies UTF-8 support, even if you  have         to  the configure command. This implies UTF-8 support, even if you have
329         not explicitly requested it.         not explicitly requested it.
330    
331         Including  Unicode  property  support  adds around 90K of tables to the         Including Unicode property support adds around 30K  of  tables  to  the
332         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE  library.  Only  the general category properties such as Lu and Nd
333         gory  properties  such as Lu and Nd are supported. Details are given in         are supported. Details are given in the pcrepattern documentation.
        the pcrepattern documentation.  
334    
335    
336  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
# Line 313  CODE VALUE OF NEWLINE Line 352  CODE VALUE OF NEWLINE
352    
353         to the configure command. There is a fourth option, specified by         to the configure command. There is a fourth option, specified by
354    
355             --enable-newline-is-anycrlf
356    
357           which  causes  PCRE  to recognize any of the three sequences CR, LF, or
358           CRLF as indicating a line ending. Finally, a fifth option, specified by
359    
360           --enable-newline-is-any           --enable-newline-is-any
361    
362         which causes PCRE to recognize any Unicode newline sequence.         causes PCRE to recognize any Unicode newline sequence.
363    
364         Whatever  line  ending convention is selected when PCRE is built can be         Whatever  line  ending convention is selected when PCRE is built can be
365         overridden when the library functions are called. At build time  it  is         overridden when the library functions are called. At build time  it  is
366         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
367    
368    
369    WHAT \R MATCHES
370    
371           By  default,  the  sequence \R in a pattern matches any Unicode newline
372           sequence, whatever has been selected as the line  ending  sequence.  If
373           you specify
374    
375             --enable-bsr-anycrlf
376    
377           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
378           ever is selected when PCRE is built can be overridden when the  library
379           functions are called.
380    
381    
382  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
383    
384         The  PCRE building process uses libtool to build both shared and static         The  PCRE building process uses libtool to build both shared and static
# Line 367  HANDLING VERY LARGE PATTERNS Line 424  HANDLING VERY LARGE PATTERNS
424         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
425         additional bytes when handling them.         additional bytes when handling them.
426    
        If  you  build  PCRE with an increased link size, test 2 (and test 5 if  
        you are using UTF-8) will fail. Part of the output of these tests is  a  
        representation  of the compiled pattern, and this changes with the link  
        size.  
   
427    
428  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
429    
430         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
431         ing  by  making recursive calls to an internal function called match().         ing by making recursive calls to an internal function  called  match().
432         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-
433         verely  limit  PCRE's operation. (The Unix environment does not usually         verely limit PCRE's operation. (The Unix environment does  not  usually
434         suffer from this problem, but it may sometimes be necessary to increase         suffer from this problem, but it may sometimes be necessary to increase
435         the  maximum  stack size.  There is a discussion in the pcrestack docu-         the maximum stack size.  There is a discussion in the  pcrestack  docu-
436         mentation.) An alternative approach to recursion that uses memory  from         mentation.)  An alternative approach to recursion that uses memory from
437         the  heap  to remember data, instead of using recursive function calls,         the heap to remember data, instead of using recursive  function  calls,
438         has been implemented to work round the problem of limited  stack  size.         has  been  implemented to work round the problem of limited stack size.
439         If you want to build a version of PCRE that works this way, add         If you want to build a version of PCRE that works this way, add
440    
441           --disable-stack-for-recursion           --disable-stack-for-recursion
442    
443         to  the  configure  command. With this configuration, PCRE will use the         to the configure command. With this configuration, PCRE  will  use  the
444         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
445         ment  functions.  Separate  functions are provided because the usage is         ment functions. By default these point to malloc() and free(), but  you
446         very predictable: the block sizes requested are always  the  same,  and         can replace the pointers so that your own functions are used.
447         the  blocks  are always freed in reverse order. A calling program might  
448         be able to implement optimized functions that perform better  than  the         Separate  functions  are  provided  rather  than  using pcre_malloc and
449         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more         pcre_free because the  usage  is  very  predictable:  the  block  sizes
450         slowly when built in this way. This option affects only the pcre_exec()         requested  are  always  the  same,  and  the blocks are always freed in
451         function; it is not relevant for the the pcre_dfa_exec() function.         reverse order. A calling program might be able to  implement  optimized
452           functions  that  perform  better  than  malloc()  and free(). PCRE runs
453           noticeably more slowly when built in this way. This option affects only
454           the   pcre_exec()   function;   it   is   not   relevant  for  the  the
455           pcre_dfa_exec() function.
456    
457    
458  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
459    
460         Internally,  PCRE has a function called match(), which it calls repeat-         Internally, PCRE has a function called match(), which it calls  repeat-
461         edly  (sometimes  recursively)  when  matching  a  pattern   with   the         edly   (sometimes   recursively)  when  matching  a  pattern  with  the
462         pcre_exec()  function.  By controlling the maximum number of times this         pcre_exec() function. By controlling the maximum number of  times  this
463         function may be called during a single matching operation, a limit  can         function  may be called during a single matching operation, a limit can
464         be  placed  on  the resources used by a single call to pcre_exec(). The         be placed on the resources used by a single call  to  pcre_exec().  The
465         limit can be changed at run time, as described in the pcreapi  documen-         limit  can be changed at run time, as described in the pcreapi documen-
466         tation.  The default is 10 million, but this can be changed by adding a         tation. The default is 10 million, but this can be changed by adding  a
467         setting such as         setting such as
468    
469           --with-match-limit=500000           --with-match-limit=500000
470    
471         to  the  configure  command.  This  setting  has  no  effect   on   the         to   the   configure  command.  This  setting  has  no  effect  on  the
472         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
473    
474         In  some  environments  it is desirable to limit the depth of recursive         In some environments it is desirable to limit the  depth  of  recursive
475         calls of match() more strictly than the total number of calls, in order         calls of match() more strictly than the total number of calls, in order
476         to  restrict  the maximum amount of stack (or heap, if --disable-stack-         to restrict the maximum amount of stack (or heap,  if  --disable-stack-
477         for-recursion is specified) that is used. A second limit controls this;         for-recursion is specified) that is used. A second limit controls this;
478         it  defaults  to  the  value  that is set for --with-match-limit, which         it defaults to the value that  is  set  for  --with-match-limit,  which
479         imposes no additional constraints. However, you can set a  lower  limit         imposes  no  additional constraints. However, you can set a lower limit
480         by adding, for example,         by adding, for example,
481    
482           --with-match-limit-recursion=10000           --with-match-limit-recursion=10000
483    
484         to  the  configure  command.  This  value can also be overridden at run         to the configure command. This value can  also  be  overridden  at  run
485         time.         time.
486    
487    
488    CREATING CHARACTER TABLES AT BUILD TIME
489    
490           PCRE  uses fixed tables for processing characters whose code values are
491           less than 256. By default, PCRE is built with a set of tables that  are
492           distributed  in  the  file pcre_chartables.c.dist. These tables are for
493           ASCII codes only. If you add
494    
495             --enable-rebuild-chartables
496    
497           to the configure command, the distributed tables are  no  longer  used.
498           Instead,  a  program  called dftables is compiled and run. This outputs
499           the source for new set of tables, created in the default locale of your
500           C runtime system. (This method of replacing the tables does not work if
501           you are cross compiling, because dftables is run on the local host.  If
502           you  need  to  create alternative tables when cross compiling, you will
503           have to do so "by hand".)
504    
505    
506  USING EBCDIC CODE  USING EBCDIC CODE
507    
508         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
509         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
510         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by         This is the case for most computer operating systems.  PCRE  can,  how-
511         adding         ever, be compiled to run in an EBCDIC environment by adding
512    
513           --enable-ebcdic           --enable-ebcdic
514    
515         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
516           bles. You should only use it if you know that  you  are  in  an  EBCDIC
517           environment (for example, an IBM mainframe operating system).
518    
519    
520  SEE ALSO  SEE ALSO
# Line 455  AUTHOR Line 531  AUTHOR
531    
532  REVISION  REVISION
533    
534         Last updated: 06 March 2007         Last updated: 21 September 2007
535         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
536  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
537    
# Line 508  REGULAR EXPRESSIONS AS TREES Line 584  REGULAR EXPRESSIONS AS TREES
584    
585  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
586    
587         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
588         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
589         depth-first search of the pattern tree. That is, it  proceeds  along  a         depth-first search of the pattern tree. That is, it  proceeds  along  a
590         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
591         required. When there is a mismatch, the algorithm  tries  any  alterna-         required. When there is a mismatch, the algorithm  tries  any  alterna-
# Line 591  THE ALTERNATIVE MATCHING ALGORITHM Line 667  THE ALTERNATIVE MATCHING ALGORITHM
667         ence  as  the  condition or test for a specific group recursion are not         ence  as  the  condition or test for a specific group recursion are not
668         supported.         supported.
669    
670         5. Callouts are supported, but the value of the  capture_top  field  is         5. Because many paths through the tree may be  active,  the  \K  escape
671           sequence, which resets the start of the match when encountered (but may
672           be on some paths and not on others), is not  supported.  It  causes  an
673           error if encountered.
674    
675           6.  Callouts  are  supported, but the value of the capture_top field is
676         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.
677    
678         6.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
679         single byte, even in UTF-8 mode, is not supported because the  alterna-         single  byte, even in UTF-8 mode, is not supported because the alterna-
680         tive  algorithm  moves  through  the  subject string one character at a         tive algorithm moves through the subject  string  one  character  at  a
681         time, for all active paths through the tree.         time, for all active paths through the tree.
682    
683           8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-
684           ported.
685    
686    
687  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
688    
# Line 645  AUTHOR Line 729  AUTHOR
729    
730  REVISION  REVISION
731    
732         Last updated: 06 March 2007         Last updated: 08 August 2007
733         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
734  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
735    
# Line 828  PCRE API OVERVIEW Line 912  PCRE API OVERVIEW
912    
913  NEWLINES  NEWLINES
914    
915         PCRE  supports four different conventions for indicating line breaks in         PCRE  supports five different conventions for indicating line breaks in
916         strings: a single CR (carriage return) character, a  single  LF  (line-         strings: a single CR (carriage return) character, a  single  LF  (line-
917         feed)  character,  the two-character sequence CRLF, or any Unicode new-         feed) character, the two-character sequence CRLF, any of the three pre-
918         line sequence.  The Unicode newline sequences are the three  just  men-         ceding, or any Unicode newline sequence. The Unicode newline  sequences
919         tioned, plus the single characters VT (vertical tab, U+000B), FF (form-         are  the  three just mentioned, plus the single characters VT (vertical
920         feed, U+000C), NEL (next line, U+0085), LS  (line  separator,  U+2028),         tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
921         and PS (paragraph separator, U+2029).         separator, U+2028), and PS (paragraph separator, U+2029).
922    
923         Each  of  the first three conventions is used by at least one operating         Each  of  the first three conventions is used by at least one operating
924         system as its standard newline sequence. When PCRE is built, a  default         system as its standard newline sequence. When PCRE is built, a  default
# Line 842  NEWLINES Line 926  NEWLINES
926         dard. When PCRE is run, the default can be overridden,  either  when  a         dard. When PCRE is run, the default can be overridden,  either  when  a
927         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
928    
929           At compile time, the newline convention can be specified by the options
930           argument of pcre_compile(), or it can be specified by special  text  at
931           the start of the pattern itself; this overrides any other settings. See
932           the pcrepattern page for details of the special character sequences.
933    
934         In the PCRE documentation the word "newline" is used to mean "the char-         In the PCRE documentation the word "newline" is used to mean "the char-
935         acter or pair of characters that indicate a line break". The choice  of         acter  or pair of characters that indicate a line break". The choice of
936         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
937         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
938         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
939         ment for a non-anchored pattern. The choice of newline convention  does         ment for a non-anchored pattern. There is more detail about this in the
940         not affect the interpretation of the \n or \r escape sequences.         section on pcre_exec() options below.
941    
942           The choice of newline convention does not affect the interpretation  of
943           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
944           which is controlled in a similar way, but by separate options.
945    
946    
947  MULTITHREADING  MULTITHREADING
948    
949         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
950         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
951         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
952         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
953    
954         The  compiled form of a regular expression is not altered during match-         The compiled form of a regular expression is not altered during  match-
955         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
956         at once.         at once.
957    
# Line 866  MULTITHREADING Line 959  MULTITHREADING
959  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
960    
961         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
962         later time, possibly by a different program, and even on a  host  other         later  time,  possibly by a different program, and even on a host other
963         than  the  one  on  which  it  was  compiled.  Details are given in the         than the one on which  it  was  compiled.  Details  are  given  in  the
964         pcreprecompile documentation.         pcreprecompile  documentation.  However, compiling a regular expression
965           with one version of PCRE for use with a different version is not  guar-
966           anteed to work and may cause crashes.
967    
968    
969  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
970    
971         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
972    
973         The function pcre_config() makes it possible for a PCRE client to  dis-         The  function pcre_config() makes it possible for a PCRE client to dis-
974         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
975         The pcrebuild documentation has more details about these optional  fea-         The  pcrebuild documentation has more details about these optional fea-
976         tures.         tures.
977    
978         The  first  argument  for pcre_config() is an integer, specifying which         The first argument for pcre_config() is an  integer,  specifying  which
979         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
980         into  which  the  information  is  placed. The following information is         into which the information is  placed.  The  following  information  is
981         available:         available:
982    
983           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
984    
985         The output is an integer that is set to one if UTF-8 support is  avail-         The  output is an integer that is set to one if UTF-8 support is avail-
986         able; otherwise it is set to zero.         able; otherwise it is set to zero.
987    
988           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
989    
990         The  output  is  an  integer  that is set to one if support for Unicode         The output is an integer that is set to  one  if  support  for  Unicode
991         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
992    
993           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
994    
995         The output is an integer whose value specifies  the  default  character         The  output  is  an integer whose value specifies the default character
996         sequence  that is recognized as meaning "newline". The four values that         sequence that is recognized as meaning "newline". The four values  that
997         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, and -1 for ANY.         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
998         The default should normally be the standard sequence for your operating         and -1 for ANY. The default should normally be  the  standard  sequence
999         system.         for your operating system.
1000    
1001             PCRE_CONFIG_BSR
1002    
1003           The output is an integer whose value indicates what character sequences
1004           the \R escape sequence matches by default. A value of 0 means  that  \R
1005           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1006           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1007           tern is compiled or matched.
1008    
1009           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1010    
1011         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
1012         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1013         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1014         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1015         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1016         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1017    
1018           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1019    
1020         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1021         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1022         given in the pcreposix documentation.         given in the pcreposix documentation.
1023    
1024           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1025    
1026         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
1027         internal matching function calls in a  pcre_exec()  execution.  Further         internal  matching  function  calls in a pcre_exec() execution. Further
1028         details are given with pcre_exec() below.         details are given with pcre_exec() below.
1029    
1030           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1031    
1032         The  output is an integer that gives the default limit for the depth of         The output is an integer that gives the default limit for the depth  of
1033         recursion when calling the internal matching function in a  pcre_exec()         recursion  when calling the internal matching function in a pcre_exec()
1034         execution. Further details are given with pcre_exec() below.         execution. Further details are given with pcre_exec() below.
1035    
1036           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1037    
1038         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
1039         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1040         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
1041         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
1042         on  the  heap  instead  of  recursive  function  calls.  In  this case,         on the  heap  instead  of  recursive  function  calls.  In  this  case,
1043         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
1044         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1045    
1046    
# Line 954  COMPILING A PATTERN Line 1057  COMPILING A PATTERN
1057    
1058         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1059         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1060         the  two interfaces is that pcre_compile2() has an additional argument,         the two interfaces is that pcre_compile2() has an additional  argument,
1061         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
1062    
1063         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
1064         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
1065         obtained via pcre_malloc is returned. This contains the  compiled  code         obtained  via  pcre_malloc is returned. This contains the compiled code
1066         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
1067         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1068         It is up to the caller to free the memory (via pcre_free) when it is no         It is up to the caller to free the memory (via pcre_free) when it is no
1069         longer required.         longer required.
1070    
1071         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
1072         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
1073         fully relocatable, because it may contain a copy of the tableptr  argu-         fully  relocatable, because it may contain a copy of the tableptr argu-
1074         ment, which is an address (see below).         ment, which is an address (see below).
1075    
1076         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1077         pilation. It should be zero if no options are required.  The  available         pilation.  It  should be zero if no options are required. The available
1078         options  are  described  below. Some of them, in particular, those that         options are described below. Some of them, in  particular,  those  that
1079         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
1080         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern (see the detailed description  in  the  pcrepattern  documenta-
1081         tion). For these options, the contents of the options  argument  speci-         tion).  For  these options, the contents of the options argument speci-
1082         fies  their initial settings at the start of compilation and execution.         fies their initial settings at the start of compilation and  execution.
1083         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time
1084         of matching as well as at compile time.         of matching as well as at compile time.
1085    
1086         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1087         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1088         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-
1089         sage. This is a static string that is part of the library. You must not         sage. This is a static string that is part of the library. You must not
1090         try to free it. The offset from the start of the pattern to the charac-         try to free it. The offset from the start of the pattern to the charac-
1091         ter where the error was discovered is placed in the variable pointed to         ter where the error was discovered is placed in the variable pointed to
1092         by  erroffset,  which must not be NULL. If it is, an immediate error is         by erroffset, which must not be NULL. If it is, an immediate  error  is
1093         given.         given.
1094    
1095         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1096         codeptr  argument is not NULL, a non-zero error code number is returned         codeptr argument is not NULL, a non-zero error code number is  returned
1097         via this argument in the event of an error. This is in addition to  the         via  this argument in the event of an error. This is in addition to the
1098         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1099    
1100         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1101         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1102         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1103         result of a call to pcre_maketables(). This value is  stored  with  the         result  of  a  call to pcre_maketables(). This value is stored with the
1104         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1105         pointer is passed to it. For more discussion, see the section on locale         pointer is passed to it. For more discussion, see the section on locale
1106         support below.         support below.
1107    
1108         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1109         pile():         pile():
1110    
1111           pcre *re;           pcre *re;
# Line 1015  COMPILING A PATTERN Line 1118  COMPILING A PATTERN
1118             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1119             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1120    
1121         The following names for option bits are defined in  the  pcre.h  header         The  following  names  for option bits are defined in the pcre.h header
1122         file:         file:
1123    
1124           PCRE_ANCHORED           PCRE_ANCHORED
1125    
1126         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
1127         is constrained to match only at the first matching point in the  string         is  constrained to match only at the first matching point in the string
1128         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1129         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1130         only way to do it in Perl.         only way to do it in Perl.
1131    
1132           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1133    
1134         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1135         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1136         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1137    
1138             PCRE_BSR_ANYCRLF
1139             PCRE_BSR_UNICODE
1140    
1141           These options (which are mutually exclusive) control what the \R escape
1142           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1143           or to match any Unicode newline sequence. The default is specified when
1144           PCRE is built. It can be overridden from within the pattern, or by set-
1145           ting an option when a compiled pattern is matched.
1146    
1147           PCRE_CASELESS           PCRE_CASELESS
1148    
1149         If  this  bit is set, letters in the pattern match both upper and lower         If this bit is set, letters in the pattern match both upper  and  lower
1150         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1151         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1152         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1153         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1154         with higher values, the concept of case is supported if  PCRE  is  com-         with  higher  values,  the concept of case is supported if PCRE is com-
1155         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1156         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1157         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1158         UTF-8 support.         UTF-8 support.
1159    
1160           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1161    
1162         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
1163         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
1164         matches immediately before a newline at the end of the string (but  not         matches  immediately before a newline at the end of the string (but not
1165         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1166         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1167         Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1168    
1169           PCRE_DOTALL           PCRE_DOTALL
1170    
1171         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-
1172         acters, including those that indicate newline. Without it, a  dot  does         acters,  including  those that indicate newline. Without it, a dot does
1173         not  match  when  the  current position is at a newline. This option is         not match when the current position is at a  newline.  This  option  is
1174         equivalent to Perl's /s option, and it can be changed within a  pattern         equivalent  to Perl's /s option, and it can be changed within a pattern
1175         by  a (?s) option setting. A negative class such as [^a] always matches         by a (?s) option setting. A negative class such as [^a] always  matches
1176         newline characters, independent of the setting of this option.         newline characters, independent of the setting of this option.
1177    
1178           PCRE_DUPNAMES           PCRE_DUPNAMES
1179    
1180         If this bit is set, names used to identify capturing  subpatterns  need         If  this  bit is set, names used to identify capturing subpatterns need
1181         not be unique. This can be helpful for certain types of pattern when it         not be unique. This can be helpful for certain types of pattern when it
1182         is known that only one instance of the named  subpattern  can  ever  be         is  known  that  only  one instance of the named subpattern can ever be
1183         matched.  There  are  more details of named subpatterns below; see also         matched. There are more details of named subpatterns  below;  see  also
1184         the pcrepattern documentation.         the pcrepattern documentation.
1185    
1186           PCRE_EXTENDED           PCRE_EXTENDED
1187    
1188         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1189         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1190         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1191         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1192         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1193         option,  and  it  can be changed within a pattern by a (?x) option set-         option, and it can be changed within a pattern by a  (?x)  option  set-
1194         ting.         ting.
1195    
1196         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1197         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1198         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1199         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1200         introduces a conditional subpattern.         introduces a conditional subpattern.
1201    
1202           PCRE_EXTRA           PCRE_EXTRA
1203    
1204         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1205         of  PCRE  that  is  incompatible with Perl, but it is currently of very         of PCRE that is incompatible with Perl, but it  is  currently  of  very
1206         little use. When set, any backslash in a pattern that is followed by  a         little  use. When set, any backslash in a pattern that is followed by a
1207         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1208         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1209         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
1210         literal. (Perl can, however, be persuaded to give a warning for  this.)         literal.  (Perl can, however, be persuaded to give a warning for this.)
1211         There  are  at  present no other features controlled by this option. It         There are at present no other features controlled by  this  option.  It
1212         can also be set by a (?X) option setting within a pattern.         can also be set by a (?X) option setting within a pattern.
1213    
1214           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1215    
1216         If this option is set, an  unanchored  pattern  is  required  to  match         If  this  option  is  set,  an  unanchored pattern is required to match
1217         before  or  at  the  first  newline  in  the subject string, though the         before or at the first  newline  in  the  subject  string,  though  the
1218         matched text may continue over the newline.         matched text may continue over the newline.
1219    
1220           PCRE_MULTILINE           PCRE_MULTILINE
1221    
1222         By default, PCRE treats the subject string as consisting  of  a  single         By  default,  PCRE  treats the subject string as consisting of a single
1223         line  of characters (even if it actually contains newlines). The "start         line of characters (even if it actually contains newlines). The  "start
1224         of line" metacharacter (^) matches only at the  start  of  the  string,         of  line"  metacharacter  (^)  matches only at the start of the string,
1225         while  the  "end  of line" metacharacter ($) matches only at the end of         while the "end of line" metacharacter ($) matches only at  the  end  of
1226         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1227         is set). This is the same as Perl.         is set). This is the same as Perl.
1228    
1229         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"
1230         constructs match immediately following or immediately  before  internal         constructs  match  immediately following or immediately before internal
1231         newlines  in  the  subject string, respectively, as well as at the very         newlines in the subject string, respectively, as well as  at  the  very
1232         start and end. This is equivalent to Perl's /m option, and  it  can  be         start  and  end.  This is equivalent to Perl's /m option, and it can be
1233         changed within a pattern by a (?m) option setting. If there are no new-         changed within a pattern by a (?m) option setting. If there are no new-
1234         lines 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,
1235         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1236    
1237           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1238           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1239           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
1240             PCRE_NEWLINE_ANYCRLF
1241           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1242    
1243         These  options  override the default newline definition that was chosen         These options override the default newline definition that  was  chosen
1244         when PCRE was built. Setting the first or the second specifies  that  a         when  PCRE  was built. Setting the first or the second specifies that a
1245         newline  is  indicated  by a single character (CR or LF, respectively).         newline is indicated by a single character (CR  or  LF,  respectively).
1246         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the         Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1247         two-character  CRLF  sequence.  Setting PCRE_NEWLINE_ANY specifies that         two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1248         any Unicode newline sequence should be recognized. The Unicode  newline         that any of the three preceding sequences should be recognized. Setting
1249         sequences  are  the three just mentioned, plus the single characters VT         PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1250         (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085),         recognized. The Unicode newline sequences are the three just mentioned,
1251         LS  (line separator, U+2028), and PS (paragraph separator, U+2029). The         plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1252         last two are recognized only in UTF-8 mode.         U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1253           (paragraph separator, U+2029). The last  two  are  recognized  only  in
1254         The newline setting in the  options  word  uses  three  bits  that  are         UTF-8 mode.
1255         treated  as  a  number, giving eight possibilities. Currently only five  
1256         are used (default plus the four values above). This means that  if  you         The  newline  setting  in  the  options  word  uses three bits that are
1257         set  more  than  one  newline option, the combination may or may not be         treated as a number, giving eight possibilities. Currently only six are
1258         sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is  equiva-         used  (default  plus the five values above). This means that if you set
1259         lent  to PCRE_NEWLINE_CRLF, but other combinations yield unused numbers         more than one newline option, the combination may or may not be  sensi-
1260         and cause an error.         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1261           PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1262         The only time that a line break is specially recognized when  compiling         cause an error.
1263         a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a  
1264         character class is encountered. This indicates  a  comment  that  lasts         The  only time that a line break is specially recognized when compiling
1265         until  after the next line break sequence. In other circumstances, line         a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1266         break  sequences  are  treated  as  literal  data,   except   that   in         character  class  is  encountered.  This indicates a comment that lasts
1267           until after the next line break sequence. In other circumstances,  line
1268           break   sequences   are   treated  as  literal  data,  except  that  in
1269         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1270         and are therefore ignored.         and are therefore ignored.
1271    
1272         The newline option that is set at compile time becomes the default that         The newline option that is set at compile time becomes the default that
1273         is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.         is used for pcre_exec() and pcre_dfa_exec(), but it can be  overridden.
1274    
1275           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1276    
1277         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-
1278         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1279         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1280         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1281         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1282    
1283           PCRE_UNGREEDY           PCRE_UNGREEDY
1284    
1285         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1286         are  not greedy by default, but become greedy if followed by "?". It is         are not greedy by default, but become greedy if followed by "?". It  is
1287         not compatible with Perl. It can also be set by a (?U)  option  setting         not  compatible  with Perl. It can also be set by a (?U) option setting
1288         within the pattern.         within the pattern.
1289    
1290           PCRE_UTF8           PCRE_UTF8
1291    
1292         This  option  causes PCRE to regard both the pattern and the subject as         This option causes PCRE to regard both the pattern and the  subject  as
1293         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1294         However,  it is available only when PCRE is built to include UTF-8 sup-         However, it is available only when PCRE is built to include UTF-8  sup-
1295         port. If not, the use of this option provokes an error. Details of  how         port.  If not, the use of this option provokes an error. Details of how
1296         this  option  changes the behaviour of PCRE are given in the section on         this option changes the behaviour of PCRE are given in the  section  on
1297         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1298    
1299           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1300    
1301         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1302         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically checked. There is a  discussion  about  the  validity  of
1303         pcre_compile() returns an error. If you already know that your  pattern         UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1304         is  valid, and you want to skip this check for performance reasons, you         bytes is found, pcre_compile() returns an error. If  you  already  know
1305         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of         that your pattern is valid, and you want to skip this check for perfor-
1306         passing an invalid UTF-8 string as a pattern is undefined. It may cause         mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1307         your program to crash.  Note that this option can  also  be  passed  to         set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1308         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-         undefined. It may cause your program to crash. Note  that  this  option
1309         ing of subject strings.         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1310           UTF-8 validity checking of subject strings.
1311    
1312    
1313  COMPILATION ERROR CODES  COMPILATION ERROR CODES
# Line 1230  COMPILATION ERROR CODES Line 1346  COMPILATION ERROR CODES
1346           26  malformed number or name after (?(           26  malformed number or name after (?(
1347           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1348           28  assertion expected after (?(           28  assertion expected after (?(
1349           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1350           30  unknown POSIX class name           30  unknown POSIX class name
1351           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1352           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
# Line 1251  COMPILATION ERROR CODES Line 1367  COMPILATION ERROR CODES
1367           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1368           48  subpattern name is too long (maximum 32 characters)           48  subpattern name is too long (maximum 32 characters)
1369           49  too many named subpatterns (maximum 10,000)           49  too many named subpatterns (maximum 10,000)
1370           50  repeated subpattern is too long           50  [this code is not in use]
1371           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1372           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1373           53   internal  error:  previously-checked  referenced  subpattern not           53   internal  error:  previously-checked  referenced  subpattern not
1374         found         found
1375           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1376           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1377           56  inconsistent NEWLINE options"           56  inconsistent NEWLINE options
1378             57  \g is not followed by a braced name or an optionally braced
1379                   non-zero number
1380             58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
1381    
1382    
1383  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1310  STUDYING A PATTERN Line 1429  STUDYING A PATTERN
1429  LOCALE SUPPORT  LOCALE SUPPORT
1430    
1431         PCRE handles caseless matching, and determines whether  characters  are         PCRE handles caseless matching, and determines whether  characters  are
1432         letters  digits,  or whatever, by reference to a set of tables, indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1433         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
1434         characters  with  codes  less than 128. Higher-valued codes never match         characters  with  codes  less than 128. Higher-valued codes never match
1435         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
1436         with  Unicode  character property support. The use of locales with Uni-         with  Unicode  character property support. The use of locales with Uni-
1437         code is discouraged.         code is discouraged. If you are handling characters with codes  greater
1438           than  128, you should either use UTF-8 and Unicode, or use locales, but
1439         An internal set of tables is created in the default C locale when  PCRE         not try to mix the two.
1440         is  built.  This  is  used when the final argument of pcre_compile() is  
1441         NULL, and is sufficient for many applications. An  alternative  set  of         PCRE contains an internal set of tables that are used  when  the  final
1442         tables  can,  however, be supplied. These may be created in a different         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1443         locale from the default. As more and more applications change to  using         applications.  Normally, the internal tables recognize only ASCII char-
1444         Unicode, the need for this locale support is expected to die away.         acters. However, when PCRE is built, it is possible to cause the inter-
1445           nal tables to be rebuilt in the default "C" locale of the local system,
1446         External  tables  are  built by calling the pcre_maketables() function,         which may cause them to be different.
1447         which has no arguments, in the relevant locale. The result can then  be  
1448         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For         The  internal tables can always be overridden by tables supplied by the
1449         example, to build and use tables that are appropriate  for  the  French         application that calls PCRE. These may be created in a different locale
1450         locale  (where  accented  characters  with  values greater than 128 are         from  the  default.  As more and more applications change to using Uni-
1451           code, the need for this locale support is expected to die away.
1452    
1453           External tables are built by calling  the  pcre_maketables()  function,
1454           which  has no arguments, in the relevant locale. The result can then be
1455           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1456           example,  to  build  and use tables that are appropriate for the French
1457           locale (where accented characters with  values  greater  than  128  are
1458         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1459    
1460           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1461           tables = pcre_maketables();           tables = pcre_maketables();
1462           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1463    
1464           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1465           if you are using Windows, the name for the French locale is "french".
1466    
1467         When pcre_maketables() runs, the tables are built  in  memory  that  is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1468         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1469         that the memory containing the tables remains available for as long  as         that the memory containing the tables remains available for as long  as
# Line 1437  INFORMATION ABOUT A PATTERN Line 1566  INFORMATION ABOUT A PATTERN
1566         returned. The fourth argument should point to an unsigned char *  vari-         returned. The fourth argument should point to an unsigned char *  vari-
1567         able.         able.
1568    
1569             PCRE_INFO_HASCRORLF
1570    
1571           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1572           characters, otherwise 0. The fourth argument should  point  to  an  int
1573           variable.  An explicit match is either a literal CR or LF character, or
1574           \r or \n.
1575    
1576             PCRE_INFO_JCHANGED
1577    
1578           Return 1 if the (?J) option setting is used in the  pattern,  otherwise
1579           0. The fourth argument should point to an int variable. The (?J) inter-
1580           nal option setting changes the local PCRE_DUPNAMES option.
1581    
1582           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1583    
1584         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
1585         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
1586         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1587         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
1588         byte  is  recorded only if it follows something of variable length. For         byte is recorded only if it follows something of variable  length.  For
1589         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
1590         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1591    
# Line 1451  INFORMATION ABOUT A PATTERN Line 1593  INFORMATION ABOUT A PATTERN
1593           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1594           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1595    
1596         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1597         ses. The names are just an additional way of identifying the  parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1598         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1599         pcre_get_named_substring() are provided for  extracting  captured  sub-         pcre_get_named_substring()  are  provided  for extracting captured sub-
1600         strings  by  name. It is also possible to extract the data directly, by         strings by name. It is also possible to extract the data  directly,  by
1601         first converting the name to a number in order to  access  the  correct         first  converting  the  name to a number in order to access the correct
1602         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1603         the conversion, you need  to  use  the  name-to-number  map,  which  is         the  conversion,  you  need  to  use  the  name-to-number map, which is
1604         described by these three values.         described by these three values.
1605    
1606         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
1607         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1608         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
1609         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1610         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
1611         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-
1612         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-
1613         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1614         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1615         theses numbers. For example, consider  the  following  pattern  (assume         theses  numbers.  For  example,  consider the following pattern (assume
1616         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1617         ignored):         ignored):
1618    
1619           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1620           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1621    
1622         There are four named subpatterns, so the table has  four  entries,  and         There  are  four  named subpatterns, so the table has four entries, and
1623         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,
1624         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1625         as ??:         as ??:
1626    
# Line 1487  INFORMATION ABOUT A PATTERN Line 1629  INFORMATION ABOUT A PATTERN
1629           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1630           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1631    
1632         When  writing  code  to  extract  data from named subpatterns using the         When writing code to extract data  from  named  subpatterns  using  the
1633         name-to-number map, remember that the length of the entries  is  likely         name-to-number  map,  remember that the length of the entries is likely
1634         to be different for each compiled pattern.         to be different for each compiled pattern.
1635    
1636             PCRE_INFO_OKPARTIAL
1637    
1638           Return 1 if the pattern can be used for partial matching, otherwise  0.
1639           The  fourth  argument  should point to an int variable. The pcrepartial
1640           documentation lists the restrictions that apply to patterns  when  par-
1641           tial matching is used.
1642    
1643           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1644    
1645         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
1646         fourth argument should point to an unsigned long  int  variable.  These         fourth argument should point to an unsigned long  int  variable.  These
1647         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1648         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1649           other  words,  they are the options that will be in force when matching
1650           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1651           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1652           and PCRE_EXTENDED.
1653    
1654         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
1655         alternatives begin with one of the following:         alternatives begin with one of the following:
# Line 1699  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1852  MATCHING A PATTERN: THE TRADITIONAL FUNC
1852         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
1853         unachored at matching time.         unachored at matching time.
1854    
1855             PCRE_BSR_ANYCRLF
1856             PCRE_BSR_UNICODE
1857    
1858           These options (which are mutually exclusive) control what the \R escape
1859           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1860           or to match any Unicode newline sequence. These  options  override  the
1861           choice that was made or defaulted when the pattern was compiled.
1862    
1863           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1864           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1865           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
1866             PCRE_NEWLINE_ANYCRLF
1867           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1868    
1869         These options override  the  newline  definition  that  was  chosen  or         These  options  override  the  newline  definition  that  was chosen or
1870         defaulted  when the pattern was compiled. For details, see the descrip-         defaulted when the pattern was compiled. For details, see the  descrip-
1871         tion of pcre_compile()  above.  During  matching,  the  newline  choice         tion  of  pcre_compile()  above.  During  matching,  the newline choice
1872         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1873         ters. It may also alter the way the match position is advanced after  a         ters.  It may also alter the way the match position is advanced after a
1874         match  failure  for  an  unanchored  pattern. When PCRE_NEWLINE_CRLF or         match failure for an unanchored pattern.
1875         PCRE_NEWLINE_ANY is set, and a match attempt  fails  when  the  current  
1876         position  is  at a CRLF sequence, the match position is advanced by two         When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
1877         characters instead of one, in other words, to after the CRLF.         set,  and a match attempt for an unanchored pattern fails when the cur-
1878           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1879           explicit  matches  for  CR  or  LF  characters,  the  match position is
1880           advanced by two characters instead of one, in other words, to after the
1881           CRLF.
1882    
1883           The above rule is a compromise that makes the most common cases work as
1884           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1885           option is not set), it does not match the string "\r\nA" because, after
1886           failing at the start, it skips both the CR and the LF before  retrying.
1887           However,  the  pattern  [\r\n]A does match that string, because it con-
1888           tains an explicit CR or LF reference, and so advances only by one char-
1889           acter after the first failure.
1890    
1891           An explicit match for CR of LF is either a literal appearance of one of
1892           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1893           matches  such  as [^X] do not count, nor does \s (which includes CR and
1894           LF in the characters that it matches).
1895    
1896           Notwithstanding the above, anomalous effects may still occur when  CRLF
1897           is a valid newline sequence and explicit \r or \n escapes appear in the
1898           pattern.
1899    
1900           PCRE_NOTBOL           PCRE_NOTBOL
1901    
# Line 1759  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1942  MATCHING A PATTERN: THE TRADITIONAL FUNC
1942         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
1943         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
1944         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
1945         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence         points  to  the start of a UTF-8 character. There is a discussion about
1946         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         the validity of UTF-8 strings in the section on UTF-8  support  in  the
1947         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
1948         returned.         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
1949           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1950         If you already know that your subject is valid, and you  want  to  skip  
1951         these    checks    for   performance   reasons,   you   can   set   the         If  you  already  know that your subject is valid, and you want to skip
1952         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         these   checks   for   performance   reasons,   you   can    set    the
1953         do  this  for the second and subsequent calls to pcre_exec() if you are         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
1954         making repeated calls to find all  the  matches  in  a  single  subject         do this for the second and subsequent calls to pcre_exec() if  you  are
1955         string.  However,  you  should  be  sure  that the value of startoffset         making  repeated  calls  to  find  all  the matches in a single subject
1956         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is         string. However, you should be  sure  that  the  value  of  startoffset
1957         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
1958         value of startoffset that does not point to the start of a UTF-8  char-         set, the effect of passing an invalid UTF-8 string as a subject,  or  a
1959           value  of startoffset that does not point to the start of a UTF-8 char-
1960         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1961    
1962           PCRE_PARTIAL           PCRE_PARTIAL
1963    
1964         This  option  turns  on  the  partial  matching feature. If the subject         This option turns on the  partial  matching  feature.  If  the  subject
1965         string fails to match the pattern, but at some point during the  match-         string  fails to match the pattern, but at some point during the match-
1966         ing  process  the  end of the subject was reached (that is, the subject         ing process the end of the subject was reached (that  is,  the  subject
1967         partially matches the pattern and the failure to  match  occurred  only         partially  matches  the  pattern and the failure to match occurred only
1968         because  there were not enough subject characters), pcre_exec() returns         because there were not enough subject characters), pcre_exec()  returns
1969         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1970         used,  there  are restrictions on what may appear in the pattern. These         used, there are restrictions on what may appear in the  pattern.  These
1971         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1972    
1973     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1974    
1975         The subject string is passed to pcre_exec() as a pointer in subject,  a         The  subject string is passed to pcre_exec() as a pointer in subject, a
1976         length  in  length, and a starting byte offset in startoffset. In UTF-8         length in length, and a starting byte offset in startoffset.  In  UTF-8
1977         mode, the byte offset must point to the start  of  a  UTF-8  character.         mode,  the  byte  offset  must point to the start of a UTF-8 character.
1978         Unlike  the  pattern string, the subject may contain binary zero bytes.         Unlike the pattern string, the subject may contain binary  zero  bytes.
1979         When the starting offset is zero, the search for a match starts at  the         When  the starting offset is zero, the search for a match starts at the
1980         beginning of the subject, and this is by far the most common case.         beginning of the subject, and this is by far the most common case.
1981    
1982         A  non-zero  starting offset is useful when searching for another match         A non-zero starting offset is useful when searching for  another  match
1983         in the same subject by calling pcre_exec() again after a previous  suc-         in  the same subject by calling pcre_exec() again after a previous suc-
1984         cess.   Setting  startoffset differs from just passing over a shortened         cess.  Setting startoffset differs from just passing over  a  shortened
1985         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
1986         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1987    
1988           \Biss\B           \Biss\B
1989    
1990         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
1991         only if the current position in the subject is not  a  word  boundary.)         only  if  the  current position in the subject is not a word boundary.)
1992         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
1993         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
1994         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
1995         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
1996         to  be  a  word  boundary. However, if pcre_exec() is passed the entire         to be a word boundary. However, if pcre_exec()  is  passed  the  entire
1997         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
1998         rence  of "iss" because it is able to look behind the starting point to         rence of "iss" because it is able to look behind the starting point  to
1999         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2000    
2001         If a non-zero starting offset is passed when the pattern  is  anchored,         If  a  non-zero starting offset is passed when the pattern is anchored,
2002         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
2003         if the pattern does not require the match to be at  the  start  of  the         if  the  pattern  does  not require the match to be at the start of the
2004         subject.         subject.
2005    
2006     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2007    
2008         In  general, a pattern matches a certain portion of the subject, and in         In general, a pattern matches a certain portion of the subject, and  in
2009         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2010         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2011         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2012         subpattern"  is  used for a fragment of a pattern that picks out a sub-         subpattern" is used for a fragment of a pattern that picks out  a  sub-
2013         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2014         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2015    
2016         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of  integer
2017         offsets whose address is passed in ovector. The number of  elements  in         offsets  whose  address is passed in ovector. The number of elements in
2018         the  vector is passed in ovecsize, which must be a non-negative number.         the vector is passed in ovecsize, which must be a non-negative  number.
2019         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
2020    
2021         The first two-thirds of the vector is used to pass back  captured  sub-         The  first  two-thirds of the vector is used to pass back captured sub-
2022         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2023         of the vector is used as workspace by pcre_exec() while  matching  cap-         of  the  vector is used as workspace by pcre_exec() while matching cap-
2024         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2025         The length passed in ovecsize should always be a multiple of three.  If         The  length passed in ovecsize should always be a multiple of three. If
2026         it is not, it is rounded down.         it is not, it is rounded down.
2027    
2028         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2029         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2030         and  continuing  up  to two-thirds of its length at the most. The first         and continuing up to two-thirds of its length at the  most.  The  first
2031         element of a pair is set to the offset of the first character in a sub-         element of a pair is set to the offset of the first character in a sub-
2032         string,  and  the  second  is  set to the offset of the first character         string, and the second is set to the  offset  of  the  first  character
2033         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-
2034         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1], identify the portion of  the  subject  string  matched  by  the
2035         entire pattern. The next pair is used for the first  capturing  subpat-         entire  pattern.  The next pair is used for the first capturing subpat-
2036         tern, and so on. The value returned by pcre_exec() is one more than the         tern, and so on. The value returned by pcre_exec() is one more than the
2037         highest numbered pair that has been set. For example, if two substrings         highest numbered pair that has been set. For example, if two substrings
2038         have  been captured, the returned value is 3. If there are no capturing         have been captured, the returned value is 3. If there are no  capturing
2039         subpatterns, the return value from a successful match is 1,  indicating         subpatterns,  the return value from a successful match is 1, indicating
2040         that just the first pair of offsets has been set.         that just the first pair of offsets has been set.
2041    
2042         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2043         of the string that it matched that is returned.         of the string that it matched that is returned.
2044    
2045         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,
2046         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
2047         function returns a value of zero. In particular, if the substring  off-         function  returns a value of zero. In particular, if the substring off-
2048         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
2049         as NULL and ovecsize as zero. However, if  the  pattern  contains  back         as  NULL  and  ovecsize  as zero. However, if the pattern contains back
2050         references  and  the  ovector is not big enough to remember the related         references and the ovector is not big enough to  remember  the  related
2051         substrings, PCRE has to get additional memory for use during  matching.         substrings,  PCRE has to get additional memory for use during matching.
2052         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
2053    
2054         The  pcre_info()  function  can  be used to find out how many capturing         The pcre_info() function can be used to find  out  how  many  capturing
2055         subpatterns there are in a compiled  pattern.  The  smallest  size  for         subpatterns  there  are  in  a  compiled pattern. The smallest size for
2056         ovector  that  will allow for n captured substrings, in addition to the         ovector that will allow for n captured substrings, in addition  to  the
2057         offsets 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.
2058    
2059         It is possible for capturing subpattern number n+1 to match  some  part         It  is  possible for capturing subpattern number n+1 to match some part
2060         of the subject when subpattern n has not been used at all. For example,         of the subject when subpattern n has not been used at all. For example,
2061         if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the         if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
2062         return from the function is 4, and subpatterns 1 and 3 are matched, but         return from the function is 4, and subpatterns 1 and 3 are matched, but
2063         2 is not. When this happens, both values in  the  offset  pairs  corre-         2  is  not.  When  this happens, both values in the offset pairs corre-
2064         sponding to unused subpatterns are set to -1.         sponding to unused subpatterns are set to -1.
2065    
2066         Offset  values  that correspond to unused subpatterns at the end of the         Offset values that correspond to unused subpatterns at the end  of  the
2067         expression are also set to -1. For example,  if  the  string  "abc"  is         expression  are  also  set  to  -1. For example, if the string "abc" is
2068         matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not         matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
2069         matched. The return from the function is 2, because  the  highest  used         matched.  The  return  from the function is 2, because the highest used
2070         capturing subpattern number is 1. However, you can refer to the offsets         capturing subpattern number is 1. However, you can refer to the offsets
2071         for the second and third capturing subpatterns if  you  wish  (assuming         for  the  second  and third capturing subpatterns if you wish (assuming
2072         the vector is large enough, of course).         the vector is large enough, of course).
2073    
2074         Some  convenience  functions  are  provided for extracting the captured         Some convenience functions are provided  for  extracting  the  captured
2075         substrings as separate strings. These are described below.         substrings as separate strings. These are described below.
2076    
2077     Error return values from pcre_exec()     Error return values from pcre_exec()
2078    
2079         If pcre_exec() fails, it returns a negative number. The  following  are         If  pcre_exec()  fails, it returns a negative number. The following are
2080         defined in the header file:         defined in the header file:
2081    
2082           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1901  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2085  MATCHING A PATTERN: THE TRADITIONAL FUNC
2085    
2086           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2087    
2088         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
2089         ovecsize was not zero.         ovecsize was not zero.
2090    
2091           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1910  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2094  MATCHING A PATTERN: THE TRADITIONAL FUNC
2094    
2095           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2096    
2097         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,
2098         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
2099         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
2100         an  environment  with the other endianness. This is the error that PCRE         an environment with the other endianness. This is the error  that  PCRE
2101         gives when the magic number is not present.         gives when the magic number is not present.
2102    
2103           PCRE_ERROR_UNKNOWN_OPCODE (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2104    
2105         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2106         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
2107         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2108    
2109           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2110    
2111         If a pattern contains back references, but the ovector that  is  passed         If  a  pattern contains back references, but the ovector that is passed
2112         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2113         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
2114         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
2115         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2116    
2117           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2118    
2119         This error is used by the pcre_copy_substring(),  pcre_get_substring(),         This  error is used by the pcre_copy_substring(), pcre_get_substring(),
2120         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2121         returned by pcre_exec().         returned by pcre_exec().
2122    
2123           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2124    
2125         The backtracking limit, as specified by  the  match_limit  field  in  a         The  backtracking  limit,  as  specified  by the match_limit field in a
2126         pcre_extra  structure  (or  defaulted) was reached. See the description         pcre_extra structure (or defaulted) was reached.  See  the  description
2127         above.         above.
2128    
2129           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2130    
2131         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
2132         use  by  callout functions that want to yield a distinctive error code.         use by callout functions that want to yield a distinctive  error  code.
2133         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2134    
2135           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2136    
2137         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
2138         subject.         subject.
2139    
2140           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2141    
2142         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
2143         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-
2144         ter.         ter.
2145    
2146           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2147    
2148         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
2149         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2150    
2151           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2152    
2153         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
2154         items  that are not supported for partial matching. See the pcrepartial         items that are not supported for partial matching. See the  pcrepartial
2155         documentation for details of partial matching.         documentation for details of partial matching.
2156    
2157           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2158    
2159         An unexpected internal error has occurred. This error could  be  caused         An  unexpected  internal error has occurred. This error could be caused
2160         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2161    
2162           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2163    
2164         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.
2165    
2166           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2167    
2168         The internal recursion limit, as specified by the match_limit_recursion         The internal recursion limit, as specified by the match_limit_recursion
2169         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2170         description above.         description above.
2171    
          PCRE_ERROR_NULLWSLIMIT    (-22)  
   
        When a group that can match an empty  substring  is  repeated  with  an  
        unbounded  upper  limit, the subject position at the start of the group  
        must be remembered, so that a test for an empty string can be made when  
        the  end  of the group is reached. Some workspace is required for this;  
        if it runs out, this error is given.  
   
2172           PCRE_ERROR_BADNEWLINE     (-23)           PCRE_ERROR_BADNEWLINE     (-23)
2173    
2174         An invalid combination of PCRE_NEWLINE_xxx options was given.         An invalid combination of PCRE_NEWLINE_xxx options was given.
2175    
2176         Error numbers -16 to -20 are not used by pcre_exec().         Error numbers -16 to -20 and -22 are not used by pcre_exec().
2177    
2178    
2179  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 2013  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2189  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2189         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2190              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2191    
2192         Captured substrings can be  accessed  directly  by  using  the  offsets         Captured  substrings  can  be  accessed  directly  by using the offsets
2193         returned  by  pcre_exec()  in  ovector.  For convenience, the functions         returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2194         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2195         string_list()  are  provided for extracting captured substrings as new,         string_list() are provided for extracting captured substrings  as  new,
2196         separate, zero-terminated strings. These functions identify  substrings         separate,  zero-terminated strings. These functions identify substrings
2197         by  number.  The  next section describes functions for extracting named         by number. The next section describes functions  for  extracting  named
2198         substrings.         substrings.
2199    
2200         A substring that contains a binary zero is correctly extracted and  has         A  substring that contains a binary zero is correctly extracted and has
2201         a  further zero added on the end, but the result is not, of course, a C         a further zero added on the end, but the result is not, of course, a  C
2202         string.  However, you can process such a string  by  referring  to  the         string.   However,  you  can  process such a string by referring to the
2203         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2204         string().  Unfortunately, the interface to pcre_get_substring_list() is         string().  Unfortunately, the interface to pcre_get_substring_list() is
2205         not  adequate for handling strings containing binary zeros, because the         not adequate for handling strings containing binary zeros, because  the
2206         end of the final string is not independently indicated.         end of the final string is not independently indicated.
2207    
2208         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-
2209         tions:  subject  is  the subject string that has just been successfully         tions: subject is the subject string that has  just  been  successfully
2210         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
2211         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2212         were captured by the match, including the substring  that  matched  the         were  captured  by  the match, including the substring that matched the
2213         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2214         it is greater than zero. If pcre_exec() returned zero, indicating  that         it  is greater than zero. If pcre_exec() returned zero, indicating that
2215         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
2216         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2217    
2218         The functions pcre_copy_substring() and pcre_get_substring() extract  a         The  functions pcre_copy_substring() and pcre_get_substring() extract a
2219         single  substring,  whose  number  is given as stringnumber. A value of         single substring, whose number is given as  stringnumber.  A  value  of
2220         zero extracts the substring that matched the  entire  pattern,  whereas         zero  extracts  the  substring that matched the entire pattern, whereas
2221         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2222         string(), the string is placed in buffer,  whose  length  is  given  by         string(),  the  string  is  placed  in buffer, whose length is given by
2223         buffersize,  while  for  pcre_get_substring()  a new block of memory is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2224         obtained via pcre_malloc, and its address is  returned  via  stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2225         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
2226         the terminating zero, or one of these error codes:         the terminating zero, or one of these error codes:
2227    
2228           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2229    
2230         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
2231         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2232    
2233           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2234    
2235         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2236    
2237         The  pcre_get_substring_list()  function  extracts  all  available sub-         The pcre_get_substring_list()  function  extracts  all  available  sub-
2238         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
2239         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
2240         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
2241         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
2242         pointer. The yield of the function is zero if all  went  well,  or  the         pointer.  The  yield  of  the function is zero if all went well, or the
2243         error code         error code
2244    
2245           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2246    
2247         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2248    
2249         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2250         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2251         the  subject, but subpattern n has not been used at all, they return an         the subject, but subpattern n has not been used at all, they return  an
2252         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2253         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2254         tive for unset substrings.         tive for unset substrings.
2255    
2256         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2257         string_list()  can  be  used  to free the memory returned by a previous         string_list() can be used to free the memory  returned  by  a  previous
2258         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2259         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2260         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.
2261         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-
2262         cial  interface  to  another  programming  language  that  cannot   use         cial   interface  to  another  programming  language  that  cannot  use
2263         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-
2264         vided.         vided.
2265    
2266    
# Line 2103  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2279  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2279              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2280              const char **stringptr);              const char **stringptr);
2281    
2282         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-
2283         ber.  For example, for this pattern         ber.  For example, for this pattern
2284    
2285           (a+)b(?<xxx>\d+)...           (a+)b(?<xxx>\d+)...
# Line 2112  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2288  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2288         be unique (PCRE_DUPNAMES was not set), you can find the number from the         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2289         name by calling pcre_get_stringnumber(). The first argument is the com-         name by calling pcre_get_stringnumber(). The first argument is the com-
2290         piled pattern, and the second is the name. The yield of the function is         piled pattern, and the second is the name. The yield of the function is
2291         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2292         subpattern of that name.         subpattern of that name.
2293    
2294         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
2295         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2296         are also two functions that do the whole job.         are also two functions that do the whole job.
2297    
2298         Most   of   the   arguments    of    pcre_copy_named_substring()    and         Most    of    the    arguments   of   pcre_copy_named_substring()   and
2299         pcre_get_named_substring()  are  the  same  as  those for the similarly         pcre_get_named_substring() are the same  as  those  for  the  similarly
2300         named functions that extract by number. As these are described  in  the         named  functions  that extract by number. As these are described in the
2301         previous  section,  they  are not re-described here. There are just two         previous section, they are not re-described here. There  are  just  two
2302         differences:         differences:
2303    
2304         First, instead of a substring number, a substring name is  given.  Sec-         First,  instead  of a substring number, a substring name is given. Sec-
2305         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
2306         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
2307         name-to-number translation table.         name-to-number translation table.
2308    
2309         These  functions call pcre_get_stringnumber(), and if it succeeds, they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2310         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2311         ate.         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2312           behaviour may not be what you want (see the next section).
2313    
2314    
2315  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
# Line 2144  DUPLICATE SUBPATTERN NAMES Line 2321  DUPLICATE SUBPATTERN NAMES
2321         subpatterns are not required to  be  unique.  Normally,  patterns  with         subpatterns are not required to  be  unique.  Normally,  patterns  with
2322         duplicate  names  are such that in any one match, only one of the named         duplicate  names  are such that in any one match, only one of the named
2323         subpatterns participates. An example is shown in the pcrepattern  docu-         subpatterns participates. An example is shown in the pcrepattern  docu-
2324         mentation. When duplicates are present, pcre_copy_named_substring() and         mentation.
2325    
2326           When    duplicates   are   present,   pcre_copy_named_substring()   and
2327         pcre_get_named_substring() return the first substring corresponding  to         pcre_get_named_substring() return the first substring corresponding  to
2328         the  given  name  that  is  set.  If  none  are set, an empty string is         the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2329         returned.  The pcre_get_stringnumber() function returns one of the num-         (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2330         bers  that are associated with the name, but it is not defined which it         function  returns one of the numbers that are associated with the name,
2331         is.         but it is not defined which it is.
2332    
2333         If you want to get full details of all captured substrings for a  given         If you want to get full details of all captured substrings for a  given
2334         name,  you  must  use  the pcre_get_stringtable_entries() function. The         name,  you  must  use  the pcre_get_stringtable_entries() function. The
# Line 2351  AUTHOR Line 2530  AUTHOR
2530    
2531  REVISION  REVISION
2532    
2533         Last updated: 06 March 2007         Last updated: 11 September 2007
2534         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2535  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2536    
# Line 2379  PCRE CALLOUTS Line 2558  PCRE CALLOUTS
2558         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2559         points:         points:
2560    
2561           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2562    
2563         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2564         called, PCRE automatically  inserts  callouts,  all  with  number  255,         called, PCRE automatically  inserts  callouts,  all  with  number  255,
# Line 2454  THE CALLOUT INTERFACE Line 2633  THE CALLOUT INTERFACE
2633         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2634         were passed to pcre_exec().         were passed to pcre_exec().
2635    
2636         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
2637         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
2638         callout function may be called several times from the same point in the         sequence \K has been encountered, this value is changed to reflect  the
2639         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2640           function may be called several times from the same point in the pattern
2641           for different starting points in the subject.
2642    
2643         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
2644         the current match pointer.         the current match pointer.
# Line 2520  AUTHOR Line 2701  AUTHOR
2701    
2702  REVISION  REVISION
2703    
2704         Last updated: 06 March 2007         Last updated: 29 May 2007
2705         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2706  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2707    
# Line 2536  DIFFERENCES BETWEEN PCRE AND PERL Line 2717  DIFFERENCES BETWEEN PCRE AND PERL
2717    
2718         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2719         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences described here  are  mainly
2720         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2721         tures that are expected to be in the forthcoming Perl 5.10.         some features that are expected to be in the forthcoming Perl 5.10.
2722    
2723         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2724         of  what  it does have are given in the section on UTF-8 support in the         of  what  it does have are given in the section on UTF-8 support in the
# Line 2602  DIFFERENCES BETWEEN PCRE AND PERL Line 2783  DIFFERENCES BETWEEN PCRE AND PERL
2783         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2784         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2785    
2786         11. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2787           (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2788           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2789           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2790           ture group; this is different to Perl.
2791    
2792           12. PCRE provides some extensions to the Perl regular expression facil-
2793         ities.   Perl  5.10  will  include new features that are not in earlier         ities.   Perl  5.10  will  include new features that are not in earlier
2794         versions, some of which (such as named parentheses) have been  in  PCRE         versions, some of which (such as named parentheses) have been  in  PCRE
2795         for some time. This list is with respect to Perl 5.10:         for some time. This list is with respect to Perl 5.10:
# Line 2615  DIFFERENCES BETWEEN PCRE AND PERL Line 2802  DIFFERENCES BETWEEN PCRE AND PERL
2802         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2803    
2804         (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-
2805         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2806         ignored. (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
2807    
2808         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2809         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 2628  DIFFERENCES BETWEEN PCRE AND PERL Line 2815  DIFFERENCES BETWEEN PCRE AND PERL
2815         (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-
2816         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2817    
2818         (g) The callout facility is PCRE-specific.         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2819           CRLF by the PCRE_BSR_ANYCRLF option.
2820    
2821           (h) The callout facility is PCRE-specific.
2822    
2823         (h) The partial matching facility is PCRE-specific.         (i) The partial matching facility is PCRE-specific.
2824    
2825         (i) Patterns compiled by PCRE can be saved and re-used at a later time,         (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2826         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2827    
2828         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2829         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2830    
2831           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2832           of a pattern that set overall options that cannot be changed within the
2833           pattern.
2834    
2835    
2836  AUTHOR  AUTHOR
2837    
# Line 2648  AUTHOR Line 2842  AUTHOR
2842    
2843  REVISION  REVISION
2844    
2845         Last updated: 06 March 2007         Last updated: 11 September 2007
2846         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2847  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2848    
# Line 2662  NAME Line 2856  NAME
2856    
2857  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2858    
2859         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2860         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2861         documentation  and  in  a  number  of books, some of which have copious         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are
2862         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         described in its own documentation, and regular expressions in  general
2863         by  O'Reilly, covers regular expressions in great detail. This descrip-         are  covered in a number of books, some of which have copious examples.
2864         tion of PCRE's regular expressions is intended as reference material.         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by
2865           O'Reilly,  covers regular expressions in great detail. This description
2866           of PCRE's regular expressions is intended as reference material.
2867    
2868         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2869         However,  there is now also support for UTF-8 character strings. To use         However,  there is now also support for UTF-8 character strings. To use
# Line 2681  PCRE REGULAR EXPRESSION DETAILS Line 2877  PCRE REGULAR EXPRESSION DETAILS
2877         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2878         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
2879         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
2880         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
2881         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2882         the pcrematching page.         alternative function, and how it differs from the normal function,  are
2883           discussed in the pcrematching page.
2884    
2885    
2886    NEWLINE CONVENTIONS
2887    
2888           PCRE  supports five different conventions for indicating line breaks in
2889           strings: a single CR (carriage return) character, a  single  LF  (line-
2890           feed) character, the two-character sequence CRLF, any of the three pre-
2891           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2892           discussion  about newlines, and shows how to set the newline convention
2893           in the options arguments for the compiling and matching functions.
2894    
2895           It is also possible to specify a newline convention by starting a  pat-
2896           tern string with one of the following five sequences:
2897    
2898             (*CR)        carriage return
2899             (*LF)        linefeed
2900             (*CRLF)      carriage return, followed by linefeed
2901             (*ANYCRLF)   any of the three above
2902             (*ANY)       all Unicode newline sequences
2903    
2904           These override the default and the options given to pcre_compile(). For
2905           example, on a Unix system where LF is the default newline sequence, the
2906           pattern
2907    
2908             (*CR)a.b
2909    
2910           changes the convention to CR. That pattern matches "a\nb" because LF is
2911           no longer a newline. Note that these special settings,  which  are  not
2912           Perl-compatible,  are  recognized  only at the very start of a pattern,
2913           and that they must be in upper case.  If  more  than  one  of  them  is
2914           present, the last one is used.
2915    
2916           The  newline  convention  does  not  affect what the \R escape sequence
2917           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2918           compatibility.  However, this can be changed; see the description of \R
2919           in the section entitled "Newline sequences" below. A change of \R  set-
2920           ting can be combined with a change of newline convention.
2921    
2922    
2923  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
2924    
2925         A regular expression is a pattern that is  matched  against  a  subject         A  regular  expression  is  a pattern that is matched against a subject
2926         string  from  left  to right. Most characters stand for themselves in a         string from left to right. Most characters stand for  themselves  in  a
2927         pattern, and match the corresponding characters in the  subject.  As  a         pattern,  and  match  the corresponding characters in the subject. As a
2928         trivial example, the pattern         trivial example, the pattern
2929    
2930           The quick brown fox           The quick brown fox
2931    
2932         matches a portion of a subject string that is identical to itself. When         matches a portion of a subject string that is identical to itself. When
2933         caseless matching is specified (the PCRE_CASELESS option), letters  are         caseless  matching is specified (the PCRE_CASELESS option), letters are
2934         matched  independently  of case. In UTF-8 mode, PCRE always understands         matched independently of case. In UTF-8 mode, PCRE  always  understands
2935         the concept of case for characters whose values are less than  128,  so         the  concept  of case for characters whose values are less than 128, so
2936         caseless  matching  is always possible. For characters with higher val-         caseless matching is always possible. For characters with  higher  val-
2937         ues, the concept of case is supported if PCRE is compiled with  Unicode         ues,  the concept of case is supported if PCRE is compiled with Unicode
2938         property  support,  but  not  otherwise.   If  you want to use caseless         property support, but not otherwise.   If  you  want  to  use  caseless
2939         matching for characters 128 and above, you must  ensure  that  PCRE  is         matching  for  characters  128  and above, you must ensure that PCRE is
2940         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
2941    
2942         The  power  of  regular  expressions  comes from the ability to include         The power of regular expressions comes  from  the  ability  to  include
2943         alternatives and repetitions in the pattern. These are encoded  in  the         alternatives  and  repetitions in the pattern. These are encoded in the
2944         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
2945         but instead are interpreted in some special way.         but instead are interpreted in some special way.
2946    
2947         There are two different sets of metacharacters: those that  are  recog-         There  are  two different sets of metacharacters: those that are recog-
2948         nized  anywhere in the pattern except within square brackets, and those         nized anywhere in the pattern except within square brackets, and  those
2949         that are recognized within square brackets.  Outside  square  brackets,         that  are  recognized  within square brackets. Outside square brackets,
2950         the metacharacters are as follows:         the metacharacters are as follows:
2951    
2952           \      general escape character with several uses           \      general escape character with several uses
# Line 2731  CHARACTERS AND METACHARACTERS Line 2965  CHARACTERS AND METACHARACTERS
2965                  also "possessive quantifier"                  also "possessive quantifier"
2966           {      start min/max quantifier           {      start min/max quantifier
2967    
2968         Part  of  a  pattern  that is in square brackets is called a "character         Part of a pattern that is in square brackets  is  called  a  "character
2969         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
2970    
2971           \      general escape character           \      general escape character
# Line 2741  CHARACTERS AND METACHARACTERS Line 2975  CHARACTERS AND METACHARACTERS
2975                    syntax)                    syntax)
2976           ]      terminates the character class           ]      terminates the character class
2977    
2978         The following sections describe the use of each of the  metacharacters.         The  following sections describe the use of each of the metacharacters.
2979    
2980    
2981  BACKSLASH  BACKSLASH
2982    
2983         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
2984         a non-alphanumeric character, it takes away any  special  meaning  that         a  non-alphanumeric  character,  it takes away any special meaning that
2985         character  may  have.  This  use  of  backslash  as an escape character         character may have. This  use  of  backslash  as  an  escape  character
2986         applies both inside and outside character classes.         applies both inside and outside character classes.
2987    
2988         For example, if you want to match a * character, you write  \*  in  the         For  example,  if  you want to match a * character, you write \* in the
2989         pattern.   This  escaping  action  applies whether or not the following         pattern.  This escaping action applies whether  or  not  the  following
2990         character would otherwise be interpreted as a metacharacter, so  it  is         character  would  otherwise be interpreted as a metacharacter, so it is
2991         always  safe  to  precede  a non-alphanumeric with backslash to specify         always safe to precede a non-alphanumeric  with  backslash  to  specify
2992         that it stands for itself. In particular, if you want to match a  back-         that  it stands for itself. In particular, if you want to match a back-
2993         slash, you write \\.         slash, you write \\.
2994    
2995         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
2996         the pattern (other than in a character class) and characters between  a         the  pattern (other than in a character class) and characters between a
2997         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
2998         ing backslash can be used to include a whitespace  or  #  character  as         ing  backslash  can  be  used to include a whitespace or # character as
2999         part of the pattern.         part of the pattern.
3000    
3001         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-
3002         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-
3003         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E
3004         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
3005         tion. Note the following examples:         tion. Note the following examples:
3006    
3007           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2777  BACKSLASH Line 3011  BACKSLASH
3011           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3012           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3013    
3014         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
3015         classes.         classes.
3016    
3017     Non-printing characters     Non-printing characters
3018    
3019         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
3020         acters  in patterns in a visible manner. There is no restriction on the         acters in patterns in a visible manner. There is no restriction on  the
3021         appearance of non-printing characters, apart from the binary zero  that         appearance  of non-printing characters, apart from the binary zero that
3022         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates a pattern, but when a pattern  is  being  prepared  by  text
3023         editing, it is usually easier  to  use  one  of  the  following  escape         editing,  it  is  usually  easier  to  use  one of the following escape
3024         sequences than the binary character it represents:         sequences than the binary character it represents:
3025    
3026           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3027           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3028           \e        escape (hex 1B)           \e        escape (hex 1B)
3029           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3030           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3031           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3032           \t        tab (hex 09)           \t        tab (hex 09)
3033           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
3034           \xhh      character with hex code hh           \xhh      character with hex code hh
3035           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3036    
3037         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,
3038         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
3039         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;
3040         becomes hex 7B.         becomes hex 7B.
3041    
3042         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
3043         in  upper  or  lower case). Any number of hexadecimal digits may appear         in upper or lower case). Any number of hexadecimal  digits  may  appear
3044         between \x{ and }, but the value of the character  code  must  be  less         between  \x{  and  },  but the value of the character code must be less
3045         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode (that is,         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3046         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger
3047         hexadecimal  digits  appear between \x{ and }, or if there is no termi-         than the largest Unicode code point, which is 10FFFF.
3048         nating }, this form of escape is not recognized.  Instead, the  initial  
3049         \x will be interpreted as a basic hexadecimal escape, with no following         If characters other than hexadecimal digits appear between \x{  and  },
3050         digits, giving a character whose value is zero.         or if there is no terminating }, this form of escape is not recognized.
3051           Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal
3052           escape,  with  no  following  digits, giving a character whose value is
3053           zero.
3054    
3055         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
3056         two  syntaxes  for  \x. There is no difference in the way they are han-         two  syntaxes  for  \x. There is no difference in the way they are han-
# Line 2868  BACKSLASH Line 3105  BACKSLASH
3105    
3106     Absolute and relative back references     Absolute and relative back references
3107    
3108         The sequence \g followed by a positive or negative  number,  optionally         The sequence \g followed by an unsigned or a negative  number,  option-
3109         enclosed  in  braces,  is  an absolute or relative back reference. Back         ally  enclosed  in braces, is an absolute or relative back reference. A
3110         references are discussed later, following the discussion  of  parenthe-         named back reference can be coded as \g{name}. Back references are dis-
3111         sized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3112    
3113     Generic character types     Generic character types
3114    
# Line 2880  BACKSLASH Line 3117  BACKSLASH
3117    
3118           \d     any decimal digit           \d     any decimal digit
3119           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3120             \h     any horizontal whitespace character
3121             \H     any character that is not a horizontal whitespace character
3122           \s     any whitespace character           \s     any whitespace character
3123           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3124             \v     any vertical whitespace character
3125             \V     any character that is not a vertical whitespace character
3126           \w     any "word" character           \w     any "word" character
3127           \W     any "non-word" character           \W     any "non-word" character
3128    
# Line 2896  BACKSLASH Line 3137  BACKSLASH
3137    
3138         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
3139         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
3140         characters  are  HT (9), LF (10), FF (12), CR (13), and space (32). (If         characters  are  HT  (9), LF (10), FF (12), CR (13), and space (32). If
3141         "use locale;" is included in a Perl script, \s may match the VT charac-         "use locale;" is included in a Perl script, \s may match the VT charac-
3142         ter. In PCRE, it never does.)         ter. In PCRE, it never does.
3143    
3144           In  UTF-8 mode, characters with values greater than 128 never match \d,
3145           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3146           code  character  property  support is available. These sequences retain
3147           their original meanings from before UTF-8 support was available, mainly
3148           for efficiency reasons.
3149    
3150           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3151           the other sequences, these do match certain high-valued  codepoints  in
3152           UTF-8 mode.  The horizontal space characters are:
3153    
3154             U+0009     Horizontal tab
3155             U+0020     Space
3156             U+00A0     Non-break space
3157             U+1680     Ogham space mark
3158             U+180E     Mongolian vowel separator
3159             U+2000     En quad
3160             U+2001     Em quad
3161             U+2002     En space
3162             U+2003     Em space
3163             U+2004     Three-per-em space
3164             U+2005     Four-per-em space
3165             U+2006     Six-per-em space
3166             U+2007     Figure space
3167             U+2008     Punctuation space
3168             U+2009     Thin space
3169             U+200A     Hair space
3170             U+202F     Narrow no-break space
3171             U+205F     Medium mathematical space
3172             U+3000     Ideographic space
3173    
3174           The vertical space characters are:
3175    
3176             U+000A     Linefeed
3177             U+000B     Vertical tab
3178             U+000C     Formfeed
3179             U+000D     Carriage return
3180             U+0085     Next line
3181             U+2028     Line separator
3182             U+2029     Paragraph separator
3183    
3184         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
3185         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-
3186         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-
3187         specific matching is taking place (see "Locale support" in the  pcreapi         specific matching is taking place (see "Locale support" in the  pcreapi
3188         page).  For  example,  in  the  "fr_FR" (French) locale, some character         page).  For  example,  in  a French locale such as "fr_FR" in Unix-like
3189         codes greater than 128 are used for accented  letters,  and  these  are         systems, or "french" in Windows, some character codes greater than  128
3190         matched by \w.         are  used for accented letters, and these are matched by \w. The use of
3191           locales with Unicode is discouraged.
        In  UTF-8 mode, characters with values greater than 128 never match \d,  
        \s, or \w, and always match \D, \S, and \W. This is true even when Uni-  
        code  character  property support is available. The use of locales with  
        Unicode is discouraged.  
3192    
3193     Newline sequences     Newline sequences
3194    
3195         Outside a character class, the escape sequence \R matches  any  Unicode         Outside a character class, by default, the escape sequence  \R  matches
3196         newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is         any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3197         equivalent to the following:         mode \R is equivalent to the following:
3198    
3199           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3200    
# Line 2933  BACKSLASH Line 3210  BACKSLASH
3210         rator,  U+2029).   Unicode character property support is not needed for         rator,  U+2029).   Unicode character property support is not needed for
3211         these characters to be recognized.         these characters to be recognized.
3212    
3213           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3214           the  complete  set  of  Unicode  line  endings)  by  setting the option
3215           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3216           (BSR is an abbrevation for "backslash R".) This can be made the default
3217           when PCRE is built; if this is the case, the  other  behaviour  can  be
3218           requested  via  the  PCRE_BSR_UNICODE  option.   It is also possible to
3219           specify these settings by starting a pattern string  with  one  of  the
3220           following sequences:
3221    
3222             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3223             (*BSR_UNICODE)   any Unicode newline sequence
3224    
3225           These override the default and the options given to pcre_compile(), but
3226           they can be overridden by options given to pcre_exec(). Note that these
3227           special settings, which are not Perl-compatible, are recognized only at
3228           the very start of a pattern, and that they must be in  upper  case.  If
3229           more  than  one  of  them is present, the last one is used. They can be
3230           combined with a change of newline convention, for  example,  a  pattern
3231           can start with:
3232    
3233             (*ANY)(*BSR_ANYCRLF)
3234    
3235         Inside a character class, \R matches the letter "R".         Inside a character class, \R matches the letter "R".
3236    
3237     Unicode character properties     Unicode character properties
3238    
3239         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3240         tional  escape  sequences  to  match character properties are available         tional escape sequences that match characters with specific  properties
3241         when UTF-8 mode is selected. They are:         are  available.   When not in UTF-8 mode, these sequences are of course
3242           limited to testing characters whose codepoints are less than  256,  but
3243           they do work in this mode.  The extra escape sequences are:
3244    
3245           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3246           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
3247           \X       an extended Unicode sequence           \X       an extended Unicode sequence
3248    
3249         The property names represented by xx above are limited to  the  Unicode         The  property  names represented by xx above are limited to the Unicode
3250         script names, the general category properties, and "Any", which matches         script names, the general category properties, and "Any", which matches
3251         any character (including newline). Other properties such as "InMusical-         any character (including newline). Other properties such as "InMusical-
3252         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does
3253         not match any characters, so always causes a match failure.         not match any characters, so always causes a match failure.
3254    
3255         Sets of Unicode characters are defined as belonging to certain scripts.         Sets of Unicode characters are defined as belonging to certain scripts.
3256         A  character from one of these sets can be matched using a script name.         A character from one of these sets can be matched using a script  name.
3257         For example:         For example:
3258    
3259           \p{Greek}           \p{Greek}
3260           \P{Han}           \P{Han}
3261    
3262         Those that are not part of an identified script are lumped together  as         Those  that are not part of an identified script are lumped together as
3263         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3264    
3265         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3266         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,         Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,
3267         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3268         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-         Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
3269         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,         gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,
3270         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3271         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,         Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,
3272         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3273         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3274    
3275         Each  character has exactly one general category property, specified by         Each character has exactly one general category property, specified  by
3276         a two-letter abbreviation. For compatibility with Perl, negation can be         a two-letter abbreviation. For compatibility with Perl, negation can be
3277         specified  by  including a circumflex between the opening brace and the         specified by including a circumflex between the opening brace  and  the
3278         property name. For example, \p{^Lu} is the same as \P{Lu}.         property name. For example, \p{^Lu} is the same as \P{Lu}.
3279    
3280         If only one letter is specified with \p or \P, it includes all the gen-         If only one letter is specified with \p or \P, it includes all the gen-
3281         eral  category properties that start with that letter. In this case, in         eral category properties that start with that letter. In this case,  in
3282         the absence of negation, the curly brackets in the escape sequence  are         the  absence of negation, the curly brackets in the escape sequence are
3283         optional; these two examples have the same effect:         optional; these two examples have the same effect:
3284    
3285           \p{L}           \p{L}
# Line 3030  BACKSLASH Line 3331  BACKSLASH
3331           Zp    Paragraph separator           Zp    Paragraph separator
3332           Zs    Space separator           Zs    Space separator
3333    
3334         The  special property L& is also supported: it matches a character that         The special property L& is also supported: it matches a character  that
3335         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not
3336         classified as a modifier or "other".         classified as a modifier or "other".
3337    
3338         The  long  synonyms  for  these  properties that Perl supports (such as         The Cs (Surrogate) property applies only to  characters  in  the  range
3339         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix         U+D800  to  U+DFFF. Such characters are not valid in UTF-8 strings (see
3340           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3341           ing  has  been  turned off (see the discussion of PCRE_NO_UTF8_CHECK in
3342           the pcreapi page).
3343    
3344           The long synonyms for these properties  that  Perl  supports  (such  as
3345           \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix
3346         any of these properties with "Is".         any of these properties with "Is".
3347    
3348         No character that is in the Unicode table has the Cn (unassigned) prop-         No character that is in the Unicode table has the Cn (unassigned) prop-
3349         erty.  Instead, this property is assumed for any code point that is not         erty.  Instead, this property is assumed for any code point that is not
3350         in the Unicode table.         in the Unicode table.
3351    
3352         Specifying  caseless  matching  does not affect these escape sequences.         Specifying caseless matching does not affect  these  escape  sequences.
3353         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3354    
3355         The \X escape matches any number of Unicode  characters  that  form  an         The  \X  escape  matches  any number of Unicode characters that form an
3356         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3357    
3358           (?>\PM\pM*)           (?>\PM\pM*)
3359    
3360         That  is,  it matches a character without the "mark" property, followed         That is, it matches a character without the "mark"  property,  followed
3361         by zero or more characters with the "mark"  property,  and  treats  the         by  zero  or  more  characters with the "mark" property, and treats the
3362         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3363         property are typically accents that affect the preceding character.         property  are  typically  accents  that affect the preceding character.
3364           None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
3365           matches any one character.
3366    
3367         Matching characters by Unicode property is not fast, because  PCRE  has         Matching  characters  by Unicode property is not fast, because PCRE has
3368         to  search  a  structure  that  contains data for over fifteen thousand         to search a structure that contains  data  for  over  fifteen  thousand
3369         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3370         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3371    
3372       Resetting the match start
3373    
3374           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3375           ously  matched  characters  not  to  be  included  in the final matched
3376           sequence. For example, the pattern:
3377    
3378             foo\Kbar
3379    
3380           matches "foobar", but reports that it has matched "bar".  This  feature
3381           is  similar  to  a lookbehind assertion (described below).  However, in
3382           this case, the part of the subject before the real match does not  have
3383           to  be of fixed length, as lookbehind assertions do. The use of \K does
3384           not interfere with the setting of captured  substrings.   For  example,
3385           when the pattern
3386    
3387             (foo)\Kbar
3388    
3389           matches "foobar", the first substring is still set to "foo".
3390    
3391     Simple assertions     Simple assertions
3392    
3393         The  final use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
# Line 3275  SQUARE BRACKETS AND CHARACTER CLASSES Line 3603  SQUARE BRACKETS AND CHARACTER CLASSES
3603         If a range that includes letters is used when caseless matching is set,         If a range that includes letters is used when caseless matching is set,
3604         it matches the letters in either case. For example, [W-c] is equivalent         it matches the letters in either case. For example, [W-c] is equivalent
3605         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3606         character tables for the "fr_FR" locale are in use, [\xc8-\xcb] matches         character tables for a French locale are in  use,  [\xc8-\xcb]  matches
3607         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the
3608         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3609         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 3359  VERTICAL BAR Line 3687  VERTICAL BAR
3687  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3688    
3689         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
3690         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED options (which are Perl-compatible) can be  changed  from
3691         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         within  the  pattern  by  a  sequence  of  Perl option letters enclosed
3692         option letters are         between "(?" and ")".  The option letters are
3693    
3694           i  for PCRE_CASELESS           i  for PCRE_CASELESS
3695           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 3375  INTERNAL OPTION SETTING Line 3703  INTERNAL OPTION SETTING
3703         is also permitted. If a  letter  appears  both  before  and  after  the         is also permitted. If a  letter  appears  both  before  and  after  the
3704         hyphen, the option is unset.         hyphen, the option is unset.
3705    
3706           The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
3707           can be changed in the same way as the Perl-compatible options by  using
3708           the characters J, U and X respectively.
3709    
3710         When  an option change occurs at top level (that is, not inside subpat-         When  an option change occurs at top level (that is, not inside subpat-
3711         tern parentheses), the change applies to the remainder of  the  pattern         tern parentheses), the change applies to the remainder of  the  pattern
3712         that follows.  If the change is placed right at the start of a pattern,         that follows.  If the change is placed right at the start of a pattern,
# Line 3400  INTERNAL OPTION SETTING Line 3732  INTERNAL OPTION SETTING
3732         the  effects  of option settings happen at compile time. There would be         the  effects  of option settings happen at compile time. There would be
3733         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3734    
3735         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         Note: There are other PCRE-specific options that  can  be  set  by  the
3736         can  be changed in the same way as the Perl-compatible options by using         application  when  the  compile  or match functions are called. In some
3737         the characters J, U and X respectively.         cases the pattern can contain special  leading  sequences  to  override
3738           what  the  application  has set or what has been defaulted. Details are
3739           given in the section entitled "Newline sequences" above.
3740    
3741    
3742  SUBPATTERNS  SUBPATTERNS
# Line 3460  SUBPATTERNS Line 3794  SUBPATTERNS
3794         "Saturday".         "Saturday".
3795    
3796    
3797    DUPLICATE SUBPATTERN NUMBERS
3798    
3799           Perl 5.10 introduced a feature whereby each alternative in a subpattern
3800           uses the same numbers for its capturing parentheses. Such a  subpattern
3801           starts  with (?| and is itself a non-capturing subpattern. For example,
3802           consider this pattern:
3803    
3804             (?|(Sat)ur|(Sun))day
3805    
3806           Because the two alternatives are inside a (?| group, both sets of  cap-
3807           turing  parentheses  are  numbered one. Thus, when the pattern matches,
3808           you can look at captured substring number  one,  whichever  alternative
3809           matched.  This  construct  is useful when you want to capture part, but
3810           not all, of one of a number of alternatives. Inside a (?| group, paren-
3811           theses  are  numbered as usual, but the number is reset at the start of
3812           each branch. The numbers of any capturing buffers that follow the  sub-
3813           pattern  start after the highest number used in any branch. The follow-
3814           ing example is taken from the Perl documentation.  The  numbers  under-
3815           neath show in which buffer the captured content will be stored.
3816    
3817             # before  ---------------branch-reset----------- after
3818             / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3819             # 1            2         2  3        2     3     4
3820    
3821           A  backreference  or  a  recursive call to a numbered subpattern always
3822           refers to the first one in the pattern with the given number.
3823    
3824           An alternative approach to using this "branch reset" feature is to  use
3825           duplicate named subpatterns, as described in the next section.
3826    
3827    
3828  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3829    
3830         Identifying  capturing  parentheses  by number is simple, but it can be         Identifying  capturing  parentheses  by number is simple, but it can be
# Line 3499  NAMED SUBPATTERNS Line 3864  NAMED SUBPATTERNS
3864           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
3865    
3866         There  are  five capturing substrings, but only one is ever set after a         There  are  five capturing substrings, but only one is ever set after a
3867         match.  The convenience  function  for  extracting  the  data  by  name         match.  (An alternative way of solving this problem is to use a "branch
3868         returns  the  substring  for  the first (and in this example, the only)         reset" subpattern, as described in the previous section.)
3869         subpattern of that name that matched.  This  saves  searching  to  find  
3870         which  numbered  subpattern  it  was. If you make a reference to a non-         The  convenience  function  for extracting the data by name returns the
3871         unique named subpattern from elsewhere in the  pattern,  the  one  that         substring for the first (and in this example, the only)  subpattern  of
3872         corresponds  to  the  lowest number is used. For further details of the         that  name  that  matched.  This saves searching to find which numbered
3873         interfaces for handling named subpatterns, see the  pcreapi  documenta-         subpattern it was. If you make a reference to a non-unique  named  sub-
3874         tion.         pattern  from elsewhere in the pattern, the one that corresponds to the
3875           lowest number is used. For further details of the interfaces  for  han-
3876           dling named subpatterns, see the pcreapi documentation.
3877    
3878    
3879  REPETITION  REPETITION
# Line 3711  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4078  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4078    
4079           \d++foo           \d++foo
4080    
4081         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Note that a possessive quantifier can be used with an entire group, for
4082           example:
4083    
4084             (abc|xyz){2,3}+
4085    
4086           Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4087         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4088         simpler forms of atomic group. However, there is no difference  in  the         simpler  forms  of atomic group. However, there is no difference in the
4089         meaning  of  a  possessive  quantifier and the equivalent atomic group,         meaning of a possessive quantifier and  the  equivalent  atomic  group,
4090         though there may be a performance  difference;  possessive  quantifiers         though  there  may  be a performance difference; possessive quantifiers
4091         should be slightly faster.         should be slightly faster.
4092    
4093         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-         The possessive quantifier syntax is an extension to the Perl  5.8  syn-
4094         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first         tax.   Jeffrey  Friedl  originated the idea (and the name) in the first
4095         edition of his book. Mike McCloskey liked it, so implemented it when he         edition of his book. Mike McCloskey liked it, so implemented it when he
4096         built Sun's Java package, and PCRE copied it from there. It  ultimately         built  Sun's Java package, and PCRE copied it from there. It ultimately
4097         found its way into Perl at release 5.10.         found its way into Perl at release 5.10.
4098    
4099         PCRE has an optimization that automatically "possessifies" certain sim-         PCRE has an optimization that automatically "possessifies" certain sim-
4100         ple pattern constructs. For example, the sequence  A+B  is  treated  as         ple  pattern  constructs.  For  example, the sequence A+B is treated as
4101         A++B  because  there is no point in backtracking into a sequence of A's         A++B because there is no point in backtracking into a sequence  of  A's
4102         when B must follow.         when B must follow.
4103    
4104         When a pattern contains an unlimited repeat inside  a  subpattern  that         When  a  pattern  contains an unlimited repeat inside a subpattern that
4105         can  itself  be  repeated  an  unlimited number of times, the use of an         can itself be repeated an unlimited number of  times,  the  use  of  an
4106         atomic group is the only way to avoid some  failing  matches  taking  a         atomic  group  is  the  only way to avoid some failing matches taking a
4107         very long time indeed. The pattern         very long time indeed. The pattern
4108    
4109           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
4110    
4111         matches  an  unlimited number of substrings that either consist of non-         matches an unlimited number of substrings that either consist  of  non-
4112         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it
4113         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
4114    
4115           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4116    
4117         it  takes  a  long  time  before reporting failure. This is because the         it takes a long time before reporting  failure.  This  is  because  the
4118         string can be divided between the internal \D+ repeat and the  external         string  can be divided between the internal \D+ repeat and the external
4119         *  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
4120         example uses [!?] rather than a single character at  the  end,  because         example  uses  [!?]  rather than a single character at the end, because
4121         both  PCRE  and  Perl have an optimization that allows for fast failure         both PCRE and Perl have an optimization that allows  for  fast  failure
4122         when a single character is used. They remember the last single  charac-         when  a single character is used. They remember the last single charac-
4123         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
4124         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
4125         group, like this:         group, like this:
4126    
4127           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4128    
4129         sequences  of non-digits cannot be broken, and failure happens quickly.         sequences of non-digits cannot be broken, and failure happens  quickly.
4130    
4131    
4132  BACK REFERENCES  BACK REFERENCES
4133    
4134         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4135         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-
4136         pattern earlier (that is, to its left) in the pattern,  provided  there         pattern  earlier  (that is, to its left) in the pattern, provided there
4137         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4138    
4139         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4140         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
4141         there  are  not that many capturing left parentheses in the entire pat-         there are not that many capturing left parentheses in the  entire  pat-
4142         tern. In other words, the parentheses that are referenced need  not  be         tern.  In  other words, the parentheses that are referenced need not be
4143         to  the left of the reference for numbers less than 10. A "forward back         to the left of the reference for numbers less than 10. A "forward  back
4144         reference" of this type can make sense when a  repetition  is  involved         reference"  of  this  type can make sense when a repetition is involved
4145         and  the  subpattern to the right has participated in an earlier itera-         and the subpattern to the right has participated in an  earlier  itera-
4146         tion.         tion.
4147    
4148         It is not possible to have a numerical "forward back  reference"  to  a         It  is  not  possible to have a numerical "forward back reference" to a
4149         subpattern  whose  number  is  10  or  more using this syntax because a         subpattern whose number is 10 or  more  using  this  syntax  because  a
4150         sequence such as \50 is interpreted as a character  defined  in  octal.         sequence  such  as  \50 is interpreted as a character defined in octal.
4151         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4152         details of the handling of digits following a backslash.  There  is  no         details  of  the  handling of digits following a backslash. There is no
4153         such  problem  when named parentheses are used. A back reference to any         such problem when named parentheses are used. A back reference  to  any
4154         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4155    
4156         Another way of avoiding the ambiguity inherent in  the  use  of  digits         Another  way  of  avoiding  the ambiguity inherent in the use of digits
4157         following a backslash is to use the \g escape sequence, which is a fea-         following a backslash is to use the \g escape sequence, which is a fea-
4158         ture introduced in Perl 5.10. This escape must be followed by  a  posi-         ture  introduced  in  Perl  5.10.  This  escape  must be followed by an
4159         tive  or  a negative number, optionally enclosed in braces. These exam-         unsigned number or a negative number, optionally  enclosed  in  braces.
4160         ples are all identical:         These examples are all identical:
4161    
4162           (ring), \1           (ring), \1
4163           (ring), \g1           (ring), \g1
4164           (ring), \g{1}           (ring), \g{1}
4165    
4166         A positive number specifies an absolute reference without the ambiguity         An  unsigned number specifies an absolute reference without the ambigu-
4167         that  is  present  in  the older syntax. It is also useful when literal         ity that is present in the older syntax. It is also useful when literal
4168         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4169         Consider this example:         Consider this example:
4170    
4171           (abc(def)ghi)\g{-1}           (abc(def)ghi)\g{-1}
4172    
4173         The sequence \g{-1} is a reference to the most recently started captur-         The sequence \g{-1} is a reference to the most recently started captur-
4174         ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,         ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,
4175         \g{-2} would be equivalent to \1. The use of relative references can be         \g{-2} would be equivalent to \1. The use of relative references can be
4176         helpful in long patterns, and also in  patterns  that  are  created  by         helpful  in  long  patterns,  and  also in patterns that are created by
4177         joining together fragments that contain references within themselves.         joining together fragments that contain references within themselves.
4178    
4179         A  back  reference matches whatever actually matched the capturing sub-         A back reference matches whatever actually matched the  capturing  sub-
4180         pattern in the current subject string, rather  than  anything  matching         pattern  in  the  current subject string, rather than anything matching
4181         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
4182         of doing that). So the pattern         of doing that). So the pattern
4183    
4184           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4185    
4186         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4187         not  "sense and responsibility". If caseful matching is in force at the         not "sense and responsibility". If caseful matching is in force at  the
4188         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-
4189         ple,         ple,
4190    
4191           ((?i)rah)\s+\1           ((?i)rah)\s+\1
4192    
4193         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
4194         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4195    
4196         Back references to named subpatterns use the Perl  syntax  \k<name>  or         There  are  several  different ways of writing back references to named
4197         \k'name'  or  the  Python  syntax (?P=name). We could rewrite the above         subpatterns. The .NET syntax \k{name} and the Perl syntax  \k<name>  or
4198         example in either of the following ways:         \k'name'  are supported, as is the Python syntax (?P=name). Perl 5.10's
4199           unified back reference syntax, in which \g can be used for both numeric
4200           and  named  references,  is  also supported. We could rewrite the above
4201           example in any of the following ways:
4202    
4203           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
4204             (?'p1'(?i)rah)\s+\k{p1}
4205           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4206             (?<p1>(?i)rah)\s+\g{p1}
4207    
4208         A subpattern that is referenced by  name  may  appear  in  the  pattern         A subpattern that is referenced by  name  may  appear  in  the  pattern
4209         before or after the reference.         before or after the reference.
# Line 3941  ASSERTIONS Line 4318  ASSERTIONS
4318    
4319           (?<=abc|abde)           (?<=abc|abde)
4320    
4321           In some cases, the Perl 5.10 escape sequence \K (see above) can be used
4322           instead  of  a lookbehind assertion; this is not restricted to a fixed-
4323           length.
4324    
4325         The implementation of lookbehind assertions is, for  each  alternative,         The implementation of lookbehind assertions is, for  each  alternative,
4326         to  temporarily  move the current position back by the fixed length and         to  temporarily  move the current position back by the fixed length and
4327         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
# Line 4034  CONDITIONAL SUBPATTERNS Line 4415  CONDITIONAL SUBPATTERNS
4415    
4416         If  the  text between the parentheses consists of a sequence of digits,         If  the  text between the parentheses consists of a sequence of digits,
4417         the condition is true if the capturing subpattern of  that  number  has         the condition is true if the capturing subpattern of  that  number  has
4418         previously matched.         previously  matched.  An  alternative notation is to precede the digits
4419           with a plus or minus sign. In this case, the subpattern number is rela-
4420           tive rather than absolute.  The most recently opened parentheses can be
4421           referenced by (?(-1), the next most recent by (?(-2),  and  so  on.  In
4422           looping constructs it can also make sense to refer to subsequent groups
4423           with constructs such as (?(+2).
4424    
4425         Consider  the  following  pattern, which contains non-significant white         Consider the following pattern, which  contains  non-significant  white
4426         space to make it more readable (assume the PCRE_EXTENDED option) and to         space to make it more readable (assume the PCRE_EXTENDED option) and to
4427         divide it into three parts for ease of discussion:         divide it into three parts for ease of discussion:
4428    
4429           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4430    
4431         The  first  part  matches  an optional opening parenthesis, and if that         The first part matches an optional opening  parenthesis,  and  if  that
4432         character is present, sets it as the first captured substring. The sec-         character is present, sets it as the first captured substring. The sec-
4433         ond  part  matches one or more characters that are not parentheses. The         ond part matches one or more characters that are not  parentheses.  The
4434         third part is a conditional subpattern that tests whether the first set         third part is a conditional subpattern that tests whether the first set
4435         of parentheses matched or not. If they did, that is, if subject started         of parentheses matched or not. If they did, that is, if subject started
4436         with an opening parenthesis, the condition is true, and so the yes-pat-         with an opening parenthesis, the condition is true, and so the yes-pat-
4437         tern  is  executed  and  a  closing parenthesis is required. Otherwise,         tern is executed and a  closing  parenthesis  is  required.  Otherwise,
4438         since no-pattern is not present, the  subpattern  matches  nothing.  In         since  no-pattern  is  not  present, the subpattern matches nothing. In
4439         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other words,  this  pattern  matches  a  sequence  of  non-parentheses,
4440         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4441    
4442           If  you  were  embedding  this pattern in a larger one, you could use a
4443           relative reference:
4444    
4445             ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4446    
4447           This makes the fragment independent of the parentheses  in  the  larger
4448           pattern.
4449    
4450     Checking for a used subpattern by name     Checking for a used subpattern by name
4451    
4452         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a         Perl  uses  the  syntax  (?(<name>)...) or (?('name')...) to test for a
4453         used  subpattern  by  name.  For compatibility with earlier versions of         used subpattern by name. For compatibility  with  earlier  versions  of
4454         PCRE, which had this facility before Perl, the syntax  (?(name)...)  is         PCRE,  which  had this facility before Perl, the syntax (?(name)...) is
4455         also  recognized. However, there is a possible ambiguity with this syn-         also recognized. However, there is a possible ambiguity with this  syn-
4456         tax, because subpattern names may  consist  entirely  of  digits.  PCRE         tax,  because  subpattern  names  may  consist entirely of digits. PCRE
4457         looks  first for a named subpattern; if it cannot find one and the name         looks first for a named subpattern; if it cannot find one and the  name
4458         consists entirely of digits, PCRE looks for a subpattern of  that  num-         consists  entirely  of digits, PCRE looks for a subpattern of that num-
4459         ber,  which must be greater than zero. Using subpattern names that con-         ber, which must be greater than zero. Using subpattern names that  con-
4460         sist entirely of digits is not recommended.         sist entirely of digits is not recommended.
4461    
4462         Rewriting the above example to use a named subpattern gives this:         Rewriting the above example to use a named subpattern gives this:
# Line 4073  CONDITIONAL SUBPATTERNS Line 4467  CONDITIONAL SUBPATTERNS
4467     Checking for pattern recursion     Checking for pattern recursion
4468    
4469         If the condition is the string (R), and there is no subpattern with the         If the condition is the string (R), and there is no subpattern with the
4470         name  R, the condition is true if a recursive call to the whole pattern         name R, the condition is true if a recursive call to the whole  pattern
4471         or any subpattern has been made. If digits or a name preceded by amper-         or any subpattern has been made. If digits or a name preceded by amper-
4472         sand follow the letter R, for example:         sand follow the letter R, for example:
4473    
4474           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4475    
4476         the  condition is true if the most recent recursion is into the subpat-         the condition is true if the most recent recursion is into the  subpat-
4477         tern whose number or name is given. This condition does not  check  the         tern  whose  number or name is given. This condition does not check the
4478         entire recursion stack.         entire recursion stack.
4479    
4480         At  "top  level", all these recursion test conditions are false. Recur-         At "top level", all these recursion test conditions are  false.  Recur-
4481         sive patterns are described below.         sive patterns are described below.
4482    
4483     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4484    
4485         If the condition is the string (DEFINE), and  there  is  no  subpattern         If  the  condition  is  the string (DEFINE), and there is no subpattern
4486         with  the  name  DEFINE,  the  condition is always false. In this case,         with the name DEFINE, the condition is  always  false.  In  this  case,
4487         there may be only one alternative  in  the  subpattern.  It  is  always         there  may  be  only  one  alternative  in the subpattern. It is always
4488         skipped  if  control  reaches  this  point  in the pattern; the idea of         skipped if control reaches this point  in  the  pattern;  the  idea  of
4489         DEFINE is that it can be used to define "subroutines" that can be  ref-         DEFINE  is that it can be used to define "subroutines" that can be ref-
4490         erenced  from elsewhere. (The use of "subroutines" is described below.)         erenced from elsewhere. (The use of "subroutines" is described  below.)
4491         For example, a pattern to match an IPv4 address could be  written  like         For  example,  a pattern to match an IPv4 address could be written like
4492         this (ignore whitespace and line breaks):         this (ignore whitespace and line breaks):
4493    
4494           (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )           (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
4495           \b (?&byte) (\.(?&byte)){3} \b           \b (?&byte) (\.(?&byte)){3} \b
4496    
4497         The  first part of the pattern is a DEFINE group inside which a another         The first part of the pattern is a DEFINE group inside which a  another
4498         group named "byte" is defined. This matches an individual component  of         group  named "byte" is defined. This matches an individual component of
4499         an  IPv4  address  (a number less than 256). When matching takes place,         an IPv4 address (a number less than 256). When  matching  takes  place,
4500         this part of the pattern is skipped because DEFINE acts  like  a  false         this  part  of  the pattern is skipped because DEFINE acts like a false
4501         condition.         condition.
4502    
4503         The rest of the pattern uses references to the named group to match the         The rest of the pattern uses references to the named group to match the
4504         four dot-separated components of an IPv4 address, insisting on  a  word         four  dot-separated  components of an IPv4 address, insisting on a word
4505         boundary at each end.         boundary at each end.
4506    
4507     Assertion conditions     Assertion conditions
4508    
4509         If  the  condition  is  not  in any of the above formats, it must be an         If the condition is not in any of the above  formats,  it  must  be  an
4510         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.   This may be a positive or negative lookahead or lookbehind
4511         assertion.  Consider  this  pattern,  again  containing non-significant         assertion. Consider  this  pattern,  again  containing  non-significant
4512         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
4513    
4514           (?(?=[^a-z]*[a-z])           (?(?=[^a-z]*[a-z])
4515           \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )           \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )
4516    
4517         The condition  is  a  positive  lookahead  assertion  that  matches  an         The  condition  is  a  positive  lookahead  assertion  that  matches an
4518         optional  sequence of non-letters followed by a letter. In other words,         optional sequence of non-letters followed by a letter. In other  words,
4519         it tests for the presence of at least one letter in the subject.  If  a         it  tests  for the presence of at least one letter in the subject. If a
4520         letter  is found, the subject is matched against the first alternative;         letter is found, the subject is matched against the first  alternative;
4521         otherwise it is  matched  against  the  second.  This  pattern  matches         otherwise  it  is  matched  against  the  second.  This pattern matches
4522         strings  in  one  of the two forms dd-aaa-dd or dd-dd-dd, where aaa are         strings in one of the two forms dd-aaa-dd or dd-dd-dd,  where  aaa  are
4523         letters and dd are digits.         letters and dd are digits.
4524    
4525    
4526  COMMENTS  COMMENTS
4527    
4528         The sequence (?# marks the start of a comment that continues up to  the         The  sequence (?# marks the start of a comment that continues up to the
4529         next  closing  parenthesis.  Nested  parentheses are not permitted. The         next closing parenthesis. Nested parentheses  are  not  permitted.  The
4530         characters that make up a comment play no part in the pattern  matching         characters  that make up a comment play no part in the pattern matching
4531         at all.         at all.
4532    
4533         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If the PCRE_EXTENDED option is set, an unescaped # character outside  a
4534         character class introduces a  comment  that  continues  to  immediately         character  class  introduces  a  comment  that continues to immediately
4535         after the next newline in the pattern.         after the next newline in the pattern.
4536    
4537    
4538  RECURSIVE PATTERNS  RECURSIVE PATTERNS
4539    
4540         Consider  the problem of matching a string in parentheses, allowing for         Consider the problem of matching a string in parentheses, allowing  for
4541         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited  nested  parentheses.  Without the use of recursion, the best
4542         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
4543         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth  of  nesting.  It  is not possible to handle an arbitrary nesting
4544         depth.         depth.
4545    
4546         For some time, Perl has provided a facility that allows regular expres-         For some time, Perl has provided a facility that allows regular expres-
4547         sions to recurse (amongst other things). It does this by  interpolating         sions  to recurse (amongst other things). It does this by interpolating
4548         Perl  code in the expression at run time, and the code can refer to the         Perl code in the expression at run time, and the code can refer to  the
4549         expression itself. A Perl pattern using code interpolation to solve the         expression itself. A Perl pattern using code interpolation to solve the
4550         parentheses problem can be created like this:         parentheses problem can be created like this:
4551    
# Line 4161  RECURSIVE PATTERNS Line 4555  RECURSIVE PATTERNS
4555         refers recursively to the pattern in which it appears.         refers recursively to the pattern in which it appears.
4556    
4557         Obviously, PCRE cannot support the interpolation of Perl code. Instead,         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4558         it  supports  special  syntax  for recursion of the entire pattern, and         it supports special syntax for recursion of  the  entire  pattern,  and
4559         also for individual subpattern recursion.  After  its  introduction  in         also  for  individual  subpattern  recursion. After its introduction in
4560         PCRE  and  Python,  this  kind of recursion was introduced into Perl at         PCRE and Python, this kind of recursion was  introduced  into  Perl  at
4561         release 5.10.         release 5.10.
4562    
4563         A special item that consists of (? followed by a  number  greater  than         A  special  item  that consists of (? followed by a number greater than
4564         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
4565         the given number, provided that it occurs inside that  subpattern.  (If         the  given  number, provided that it occurs inside that subpattern. (If
4566         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-
4567         tion.) The special item (?R) or (?0) is a recursive call of the  entire         tion.)  The special item (?R) or (?0) is a recursive call of the entire
4568         regular expression.         regular expression.
4569    
4570         In  PCRE (like Python, but unlike Perl), a recursive subpattern call is         In PCRE (like Python, but unlike Perl), a recursive subpattern call  is
4571         always treated as an atomic group. That is, once it has matched some of         always treated as an atomic group. That is, once it has matched some of
4572         the subject string, it is never re-entered, even if it contains untried         the subject string, it is never re-entered, even if it contains untried
4573         alternatives and there is a subsequent matching failure.         alternatives and there is a subsequent matching failure.
4574    
4575         This PCRE pattern solves the nested  parentheses  problem  (assume  the         This  PCRE  pattern  solves  the nested parentheses problem (assume the
4576         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4577    
4578           \( ( (?>[^()]+) | (?R) )* \)           \( ( (?>[^()]+) | (?R) )* \)
4579    
4580         First  it matches an opening parenthesis. Then it matches any number of         First it matches an opening parenthesis. Then it matches any number  of
4581         substrings which can either be a  sequence  of  non-parentheses,  or  a         substrings  which  can  either  be  a sequence of non-parentheses, or a
4582         recursive  match  of the pattern itself (that is, a correctly parenthe-         recursive match of the pattern itself (that is, a  correctly  parenthe-
4583         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis.
4584    
4585         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
4586         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4587    
4588           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( (?>[^()]+) | (?1) )* \) )
4589    
4590         We  have  put the pattern into parentheses, and caused the recursion to         We have put the pattern into parentheses, and caused the  recursion  to
4591         refer to them instead of the whole pattern. In a larger pattern,  keep-         refer to them instead of the whole pattern.
4592         ing  track  of parenthesis numbers can be tricky. It may be more conve-  
4593         nient to use named parentheses instead. The Perl  syntax  for  this  is         In  a  larger  pattern,  keeping  track  of  parenthesis numbers can be
4594         (?&name);  PCRE's  earlier syntax (?P>name) is also supported. We could         tricky. This is made easier by the use of relative references. (A  Perl
4595         rewrite the above example as follows:         5.10  feature.)   Instead  of  (?1)  in the pattern above you can write
4596           (?-2) to refer to the second most recently opened parentheses preceding
4597           the  recursion.  In  other  words,  a  negative number counts capturing
4598           parentheses leftwards from the point at which it is encountered.
4599    
4600           It is also possible to refer to  subsequently  opened  parentheses,  by
4601           writing  references  such  as (?+2). However, these cannot be recursive
4602           because the reference is not inside the  parentheses  that  are  refer-
4603           enced.  They  are  always  "subroutine" calls, as described in the next
4604           section.
4605    
4606           An alternative approach is to use named parentheses instead.  The  Perl
4607           syntax  for  this  is (?&name); PCRE's earlier syntax (?P>name) is also
4608           supported. We could rewrite the above example as follows:
4609    
4610           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
4611    
4612         If there is more than one subpattern with the same name,  the  earliest         If there is more than one subpattern with the same name,  the  earliest
4613         one  is used. This particular example pattern contains nested unlimited         one is used.
4614         repeats, and so the use of atomic grouping for matching strings of non-  
4615         parentheses  is  important when applying the pattern to strings that do         This  particular  example pattern that we have been looking at contains
4616         not match. For example, when this pattern is applied to         nested unlimited repeats, and so the use of atomic grouping for  match-
4617           ing  strings  of non-parentheses is important when applying the pattern
4618           to strings that do not match. For example, when this pattern is applied
4619           to
4620    
4621           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
4622    
4623         it yields "no match" quickly. However, if atomic grouping is not  used,         it  yields "no match" quickly. However, if atomic grouping is not used,
4624         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
4625         different ways the + and * repeats can carve up the  subject,  and  all         different  ways  the  + and * repeats can carve up the subject, and all
4626         have to be tested before failure can be reported.         have to be tested before failure can be reported.
4627    
4628         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
4629         those from the outermost level of the recursion at which the subpattern         those from the outermost level of the recursion at which the subpattern
4630         value  is  set.   If  you want to obtain intermediate values, a callout         value is set.  If you want to obtain  intermediate  values,  a  callout
4631         function can be used (see below and the pcrecallout documentation).  If         function  can be used (see below and the pcrecallout documentation). If
4632         the pattern above is matched against         the pattern above is matched against
4633    
4634           (ab(cd)ef)           (ab(cd)ef)
4635    
4636         the  value  for  the  capturing  parentheses is "ef", which is the last         the value for the capturing parentheses is  "ef",  which  is  the  last
4637         value taken on at the top level. If additional parentheses  are  added,         value  taken  on at the top level. If additional parentheses are added,
4638         giving         giving
4639    
4640           \( ( ( (?>[^()]+) | (?R) )* ) \)           \( ( ( (?>[^()]+) | (?R) )* ) \)
4641              ^                        ^              ^                        ^
4642              ^                        ^              ^                        ^
4643    
4644         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
4645         parentheses. If there are more than 15 capturing parentheses in a  pat-         parentheses.  If there are more than 15 capturing parentheses in a pat-
4646         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,
4647         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-
4648         wards.  If  no  memory  can  be  obtained,  the  match  fails  with the         wards. If  no  memory  can  be  obtained,  the  match  fails  with  the
4649         PCRE_ERROR_NOMEMORY error.         PCRE_ERROR_NOMEMORY error.
4650    
4651         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
4652         recursion.   Consider  this pattern, which matches text in angle brack-         recursion.  Consider this pattern, which matches text in  angle  brack-
4653         ets, allowing for arbitrary nesting. Only digits are allowed in  nested         ets,  allowing for arbitrary nesting. Only digits are allowed in nested
4654         brackets  (that is, when recursing), whereas any characters are permit-         brackets (that is, when recursing), whereas any characters are  permit-
4655         ted at the outer level.         ted at the outer level.
4656    
4657           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >
4658    
4659         In this pattern, (?(R) is the start of a conditional  subpattern,  with         In  this  pattern, (?(R) is the start of a conditional subpattern, with
4660         two  different  alternatives for the recursive and non-recursive cases.         two different alternatives for the recursive and  non-recursive  cases.
4661         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
4662    
4663    
4664  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
4665    
4666         If the syntax for a recursive subpattern reference (either by number or         If the syntax for a recursive subpattern reference (either by number or
4667         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-
4668         ates like a subroutine in a programming language. The "called"  subpat-         ates  like a subroutine in a programming language. The "called" subpat-
4669         tern  may  be defined before or after the reference. An earlier example         tern may be defined before or after the reference. A numbered reference
4670         pointed out that the pattern         can be absolute or relative, as in these examples:
4671    
4672             (...(absolute)...)...(?2)...
4673             (...(relative)...)...(?-1)...
4674             (...(?+1)...(relative)...
4675    
4676           An earlier example pointed out that the pattern
4677    
4678           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4679    
4680         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4681         not "sense and responsibility". If instead the pattern         not "sense and responsibility". If instead the pattern
4682    
4683           (sens|respons)e and (?1)ibility           (sens|respons)e and (?1)ibility
4684    
4685         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
4686         two strings. Another example is  given  in  the  discussion  of  DEFINE         two  strings.  Another  example  is  given  in the discussion of DEFINE
4687         above.         above.
4688    
4689         Like recursive subpatterns, a "subroutine" call is always treated as an         Like recursive subpatterns, a "subroutine" call is always treated as an
4690         atomic group. That is, once it has matched some of the subject  string,         atomic  group. That is, once it has matched some of the subject string,
4691         it  is  never  re-entered, even if it contains untried alternatives and         it is never re-entered, even if it contains  untried  alternatives  and
4692         there is a subsequent matching failure.         there is a subsequent matching failure.
4693    
4694         When a subpattern is used as a subroutine, processing options  such  as         When  a  subpattern is used as a subroutine, processing options such as
4695         case-independence are fixed when the subpattern is defined. They cannot         case-independence are fixed when the subpattern is defined. They cannot
4696         be changed for different calls. For example, consider this pattern:         be changed for different calls. For example, consider this pattern:
4697    
4698           (abc)(?i:(?1))           (abc)(?i:(?-1))
4699    
4700         It matches "abcabc". It does not match "abcABC" because the  change  of         It  matches  "abcabc". It does not match "abcABC" because the change of
4701         processing option does not affect the called subpattern.         processing option does not affect the called subpattern.
4702    
4703    
4704  CALLOUTS  CALLOUTS
4705    
4706         Perl has a feature whereby using the sequence (?{...}) causes arbitrary         Perl has a feature whereby using the sequence (?{...}) causes arbitrary
4707         Perl code to be obeyed in the middle of matching a regular  expression.         Perl  code to be obeyed in the middle of matching a regular expression.
4708         This makes it possible, amongst other things, to extract different sub-         This makes it possible, amongst other things, to extract different sub-
4709         strings that match the same pair of parentheses when there is a repeti-         strings that match the same pair of parentheses when there is a repeti-
4710         tion.         tion.
4711    
4712         PCRE provides a similar feature, but of course it cannot obey arbitrary         PCRE provides a similar feature, but of course it cannot obey arbitrary
4713         Perl code. The feature is called "callout". The caller of PCRE provides         Perl code. The feature is called "callout". The caller of PCRE provides
4714         an  external function by putting its entry point in the global variable         an external function by putting its entry point in the global  variable
4715         pcre_callout.  By default, this variable contains NULL, which  disables         pcre_callout.   By default, this variable contains NULL, which disables
4716         all calling out.         all calling out.
4717    
4718         Within  a  regular  expression,  (?C) indicates the points at which the         Within a regular expression, (?C) indicates the  points  at  which  the
4719         external function is to be called. If you want  to  identify  different         external  function  is  to be called. If you want to identify different
4720         callout  points, you can put a number less than 256 after the letter C.         callout points, you can put a number less than 256 after the letter  C.
4721         The default value is zero.  For example, this pattern has  two  callout         The  default  value is zero.  For example, this pattern has two callout
4722         points:         points:
4723    
4724           (?C1)abc(?C2)def           (?C1)abc(?C2)def
4725    
4726         If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are         If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are
4727         automatically installed before each item in the pattern. They  are  all         automatically  installed  before each item in the pattern. They are all
4728         numbered 255.         numbered 255.
4729    
4730         During matching, when PCRE reaches a callout point (and pcre_callout is         During matching, when PCRE reaches a callout point (and pcre_callout is
4731         set), the external function is called. It is provided with  the  number         set),  the  external function is called. It is provided with the number
4732         of  the callout, the position in the pattern, and, optionally, one item         of the callout, the position in the pattern, and, optionally, one  item
4733         of data originally supplied by the caller of pcre_exec().  The  callout         of  data  originally supplied by the caller of pcre_exec(). The callout
4734         function  may cause matching to proceed, to backtrack, or to fail alto-         function may cause matching to proceed, to backtrack, or to fail  alto-
4735         gether. A complete description of the interface to the callout function         gether. A complete description of the interface to the callout function
4736         is given in the pcrecallout documentation.         is given in the pcrecallout documentation.
4737    
4738    
4739    BACKTRACKING CONTROL
4740    
4741           Perl 5.10 introduced a number of "Special Backtracking Control  Verbs",
4742           which are described in the Perl documentation as "experimental and sub-
4743           ject to change or removal in a future version of Perl". It goes  on  to
4744           say:  "Their usage in production code should be noted to avoid problems
4745           during upgrades." The same remarks apply to the PCRE features described
4746           in this section.
4747    
4748           Since these verbs are specifically related to backtracking, they can be
4749           used only when the pattern is to be matched  using  pcre_exec(),  which
4750           uses  a  backtracking  algorithm. They cause an error if encountered by
4751           pcre_dfa_exec().
4752    
4753           The new verbs make use of what was previously invalid syntax: an  open-
4754           ing parenthesis followed by an asterisk. In Perl, they are generally of
4755           the form (*VERB:ARG) but PCRE does not support the use of arguments, so
4756           its  general  form is just (*VERB). Any number of these verbs may occur
4757           in a pattern. There are two kinds:
4758    
4759       Verbs that act immediately
4760    
4761           The following verbs act as soon as they are encountered:
4762    
4763              (*ACCEPT)
4764    
4765           This verb causes the match to end successfully, skipping the  remainder
4766           of  the pattern. When inside a recursion, only the innermost pattern is
4767           ended immediately. PCRE differs  from  Perl  in  what  happens  if  the
4768           (*ACCEPT)  is inside capturing parentheses. In Perl, the data so far is
4769           captured: in PCRE no data is captured. For example:
4770    
4771             A(A|B(*ACCEPT)|C)D
4772    
4773           This matches "AB", "AAD", or "ACD", but when it matches "AB",  no  data
4774           is captured.
4775    
4776             (*FAIL) or (*F)
4777    
4778           This  verb  causes the match to fail, forcing backtracking to occur. It
4779           is equivalent to (?!) but easier to read. The Perl documentation  notes
4780           that  it  is  probably  useful only when combined with (?{}) or (??{}).
4781           Those are, of course, Perl features that are not present in  PCRE.  The
4782           nearest  equivalent is the callout feature, as for example in this pat-
4783           tern:
4784    
4785             a+(?C)(*FAIL)
4786    
4787           A match with the string "aaaa" always fails, but the callout  is  taken
4788           before each backtrack happens (in this example, 10 times).
4789    
4790       Verbs that act after backtracking
4791    
4792           The following verbs do nothing when they are encountered. Matching con-
4793           tinues with what follows, but if there is no subsequent match, a  fail-
4794           ure  is  forced.   The  verbs  differ  in  exactly what kind of failure
4795           occurs.
4796    
4797             (*COMMIT)
4798    
4799           This verb causes the whole match to fail outright if the  rest  of  the
4800           pattern  does  not match. Even if the pattern is unanchored, no further
4801           attempts to find a match by advancing the start point take place.  Once
4802           (*COMMIT)  has been passed, pcre_exec() is committed to finding a match
4803           at the current starting point, or not at all. For example:
4804    
4805             a+(*COMMIT)b
4806    
4807           This matches "xxaab" but not "aacaab". It can be thought of as  a  kind
4808           of dynamic anchor, or "I've started, so I must finish."
4809    
4810             (*PRUNE)
4811    
4812           This  verb causes the match to fail at the current position if the rest
4813           of the pattern does not match. If the pattern is unanchored, the normal
4814           "bumpalong"  advance to the next starting character then happens. Back-
4815           tracking can occur as usual to the left of (*PRUNE), or  when  matching
4816           to  the right of (*PRUNE), but if there is no match to the right, back-
4817           tracking cannot cross (*PRUNE).  In simple cases, the use  of  (*PRUNE)
4818           is just an alternative to an atomic group or possessive quantifier, but
4819           there are some uses of (*PRUNE) that cannot be expressed in  any  other
4820           way.
4821    
4822             (*SKIP)
4823    
4824           This  verb  is like (*PRUNE), except that if the pattern is unanchored,
4825           the "bumpalong" advance is not to the next character, but to the  posi-
4826           tion  in  the  subject where (*SKIP) was encountered. (*SKIP) signifies
4827           that whatever text was matched leading up to it cannot  be  part  of  a
4828           successful match. Consider:
4829    
4830             a+(*SKIP)b
4831    
4832           If  the  subject  is  "aaaac...",  after  the first match attempt fails
4833           (starting at the first character in the  string),  the  starting  point
4834           skips on to start the next attempt at "c". Note that a possessive quan-
4835           tifer does not have the same effect in this example; although it  would
4836           suppress  backtracking  during  the  first  match  attempt,  the second
4837           attempt would start at the second character instead of skipping  on  to
4838           "c".
4839    
4840             (*THEN)
4841    
4842           This verb causes a skip to the next alternation if the rest of the pat-
4843           tern does not match. That is, it cancels pending backtracking, but only
4844           within  the  current  alternation.  Its name comes from the observation
4845           that it can be used for a pattern-based if-then-else block:
4846    
4847             ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
4848    
4849           If the COND1 pattern matches, FOO is tried (and possibly further  items
4850           after  the  end  of  the group if FOO succeeds); on failure the matcher
4851           skips to the second alternative and tries COND2,  without  backtracking
4852           into  COND1.  If  (*THEN)  is  used outside of any alternation, it acts
4853           exactly like (*PRUNE).
4854    
4855    
4856  SEE ALSO  SEE ALSO
4857    
4858         pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).         pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).
# Line 4334  AUTHOR Line 4867  AUTHOR
4867    
4868  REVISION  REVISION
4869    
4870         Last updated: 06 March 2007         Last updated: 17 September 2007
4871           Copyright (c) 1997-2007 University of Cambridge.
4872    ------------------------------------------------------------------------------
4873    
4874    
4875    PCRESYNTAX(3)                                                    PCRESYNTAX(3)
4876    
4877    
4878    NAME
4879           PCRE - Perl-compatible regular expressions
4880    
4881    
4882    PCRE REGULAR EXPRESSION SYNTAX SUMMARY
4883    
4884           The  full syntax and semantics of the regular expressions that are sup-
4885           ported by PCRE are described in  the  pcrepattern  documentation.  This
4886           document contains just a quick-reference summary of the syntax.
4887    
4888    
4889    QUOTING
4890    
4891             \x         where x is non-alphanumeric is a literal x
4892             \Q...\E    treat enclosed characters as literal
4893    
4894    
4895    CHARACTERS
4896    
4897             \a         alarm, that is, the BEL character (hex 07)
4898             \cx        "control-x", where x is any character
4899             \e         escape (hex 1B)
4900             \f         formfeed (hex 0C)
4901             \n         newline (hex 0A)
4902             \r         carriage return (hex 0D)
4903             \t         tab (hex 09)
4904             \ddd       character with octal code ddd, or backreference
4905             \xhh       character with hex code hh
4906             \x{hhh..}  character with hex code hhh..
4907    
4908    
4909    CHARACTER TYPES
4910    
4911             .          any character except newline;
4912                          in dotall mode, any character whatsoever
4913             \C         one byte, even in UTF-8 mode (best avoided)
4914             \d         a decimal digit
4915             \D         a character that is not a decimal digit
4916             \h         a horizontal whitespace character
4917             \H         a character that is not a horizontal whitespace character
4918             \p{xx}     a character with the xx property
4919             \P{xx}     a character without the xx property
4920             \R         a newline sequence
4921             \s         a whitespace character
4922             \S         a character that is not a whitespace character
4923             \v         a vertical whitespace character
4924             \V         a character that is not a vertical whitespace character
4925             \w         a "word" character
4926             \W         a "non-word" character
4927             \X         an extended Unicode sequence
4928    
4929           In PCRE, \d, \D, \s, \S, \w, and \W recognize only ASCII characters.
4930    
4931    
4932    GENERAL CATEGORY PROPERTY CODES FOR \p and \P
4933    
4934             C          Other
4935             Cc         Control
4936             Cf         Format
4937             Cn         Unassigned
4938             Co         Private use
4939             Cs         Surrogate
4940    
4941             L          Letter
4942             Ll         Lower case letter
4943             Lm         Modifier letter
4944             Lo         Other letter
4945             Lt         Title case letter
4946             Lu         Upper case letter
4947             L&         Ll, Lu, or Lt
4948    
4949             M          Mark
4950             Mc         Spacing mark
4951             Me         Enclosing mark
4952             Mn         Non-spacing mark
4953    
4954             N          Number
4955             Nd         Decimal number
4956             Nl         Letter number
4957             No         Other number
4958    
4959             P          Punctuation
4960             Pc         Connector punctuation
4961             Pd         Dash punctuation
4962             Pe         Close punctuation
4963             Pf         Final punctuation
4964             Pi         Initial punctuation
4965             Po         Other punctuation
4966             Ps         Open punctuation
4967    
4968             S          Symbol
4969             Sc         Currency symbol
4970             Sk         Modifier symbol
4971             Sm         Mathematical symbol
4972             So         Other symbol
4973    
4974             Z          Separator
4975             Zl         Line separator
4976             Zp         Paragraph separator
4977             Zs         Space separator
4978    
4979    
4980    SCRIPT NAMES FOR \p AND \P
4981    
4982           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
4983           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
4984           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
4985           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
4986           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
4987           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
4988           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
4989           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
4990           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
4991    
4992    
4993    CHARACTER CLASSES
4994    
4995             [...]       positive character class
4996             [^...]      negative character class
4997             [x-y]       range (can be used for hex characters)
4998             [[:xxx:]]   positive POSIX named set
4999             [[^:xxx:]]  negative POSIX named set
5000    
5001             alnum       alphanumeric
5002             alpha       alphabetic
5003             ascii       0-127
5004             blank       space or tab
5005             cntrl       control character
5006             digit       decimal digit
5007             graph       printing, excluding space
5008             lower       lower case letter
5009             print       printing, including space
5010             punct       printing, excluding alphanumeric
5011             space       whitespace
5012             upper       upper case letter
5013             word        same as \w
5014             xdigit      hexadecimal digit
5015    
5016           In PCRE, POSIX character set names recognize only ASCII characters. You
5017           can use \Q...\E inside a character class.
5018    
5019    
5020    QUANTIFIERS
5021    
5022             ?           0 or 1, greedy
5023             ?+          0 or 1, possessive
5024             ??          0 or 1, lazy
5025             *           0 or more, greedy
5026             *+          0 or more, possessive
5027             *?          0 or more, lazy
5028             +           1 or more, greedy
5029             ++          1 or more, possessive
5030             +?          1 or more, lazy
5031             {n}         exactly n
5032             {n,m}       at least n, no more than m, greedy
5033             {n,m}+      at least n, no more than m, possessive
5034             {n,m}?      at least n, no more than m, lazy
5035             {n,}        n or more, greedy
5036             {n,}+       n or more, possessive
5037             {n,}?       n or more, lazy
5038    
5039    
5040    ANCHORS AND SIMPLE ASSERTIONS
5041    
5042             \b          word boundary
5043             \B          not a word boundary
5044             ^           start of subject
5045                          also after internal newline in multiline mode
5046             \A          start of subject
5047             $           end of subject
5048                          also before newline at end of subject
5049                          also before internal newline in multiline mode
5050             \Z          end of subject
5051                          also before newline at end of subject
5052             \z          end of subject
5053             \G          first matching position in subject
5054    
5055    
5056    MATCH POINT RESET
5057    
5058             \K          reset start of match
5059    
5060    
5061    ALTERNATION
5062    
5063             expr|expr|expr...
5064    
5065    
5066    CAPTURING
5067    
5068             (...)          capturing group
5069             (?<name>...)   named capturing group (Perl)
5070             (?'name'...)   named capturing group (Perl)
5071             (?P<name>...)  named capturing group (Python)
5072             (?:...)        non-capturing group
5073             (?|...)        non-capturing group; reset group numbers for
5074                             capturing groups in each alternative