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# 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    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
521    
522           By default, pcregrep reads all files as plain text. You can build it so
523           that it recognizes files whose names end in .gz or .bz2, and reads them
524           with libz or libbz2, respectively, by adding one or both of
525    
526             --enable-pcregrep-libz
527             --enable-pcregrep-libbz2
528    
529           to the configure command. These options naturally require that the rel-
530           evant libraries are installed on your system. Configuration  will  fail
531           if they are not.
532    
533    
534    PCRETEST OPTION FOR LIBREADLINE SUPPORT
535    
536           If you add
537    
538             --enable-pcretest-libreadline
539    
540           to  the  configure  command,  pcretest  is  linked with the libreadline
541           library, and when its input is from a terminal, it reads it  using  the
542           readline() function. This provides line-editing and history facilities.
543           Note that libreadline is GPL-licenced, so if you distribute a binary of
544           pcretest linked in this way, there may be licensing issues.
545    
546    
547  SEE ALSO  SEE ALSO
# Line 455  AUTHOR Line 558  AUTHOR
558    
559  REVISION  REVISION
560    
561         Last updated: 06 March 2007         Last updated: 18 December 2007
562         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
563  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
564    
# Line 508  REGULAR EXPRESSIONS AS TREES Line 611  REGULAR EXPRESSIONS AS TREES
611    
612  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
613    
614         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
615         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
616         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
617         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
618         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 694  THE ALTERNATIVE MATCHING ALGORITHM
694         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
695         supported.         supported.
696    
697         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
698           sequence, which resets the start of the match when encountered (but may
699           be on some paths and not on others), is not  supported.  It  causes  an
700           error if encountered.
701    
702           6.  Callouts  are  supported, but the value of the capture_top field is
703         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.
704    
705         6.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
706         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-
707         tive  algorithm  moves  through  the  subject string one character at a         tive algorithm moves through the subject  string  one  character  at  a
708         time, for all active paths through the tree.         time, for all active paths through the tree.
709    
710           8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-
711           ported.
712    
713    
714  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
715    
# Line 645  AUTHOR Line 756  AUTHOR
756    
757  REVISION  REVISION
758    
759         Last updated: 06 March 2007         Last updated: 08 August 2007
760         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
761  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
762    
# Line 828  PCRE API OVERVIEW Line 939  PCRE API OVERVIEW
939    
940  NEWLINES  NEWLINES
941    
942         PCRE  supports four different conventions for indicating line breaks in         PCRE  supports five different conventions for indicating line breaks in
943         strings: a single CR (carriage return) character, a  single  LF  (line-         strings: a single CR (carriage return) character, a  single  LF  (line-
944         feed)  character,  the two-character sequence CRLF, or any Unicode new-         feed) character, the two-character sequence CRLF, any of the three pre-
945         line sequence.  The Unicode newline sequences are the three  just  men-         ceding, or any Unicode newline sequence. The Unicode newline  sequences
946         tioned, plus the single characters VT (vertical tab, U+000B), FF (form-         are  the  three just mentioned, plus the single characters VT (vertical
947         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
948         and PS (paragraph separator, U+2029).         separator, U+2028), and PS (paragraph separator, U+2029).
949    
950         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
951         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 953  NEWLINES
953         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
954         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
955    
956           At compile time, the newline convention can be specified by the options
957           argument of pcre_compile(), or it can be specified by special  text  at
958           the start of the pattern itself; this overrides any other settings. See
959           the pcrepattern page for details of the special character sequences.
960    
961         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-
962         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
963         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
964         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
965         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
966         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
967         not affect the interpretation of the \n or \r escape sequences.         section on pcre_exec() options below.
968    
969           The choice of newline convention does not affect the interpretation  of
970           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
971           which is controlled in a similar way, but by separate options.
972    
973    
974  MULTITHREADING  MULTITHREADING
975    
976         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
977         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
978         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
979         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
980    
981         The  compiled form of a regular expression is not altered during match-         The compiled form of a regular expression is not altered during  match-
982         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
983         at once.         at once.
984    
# Line 866  MULTITHREADING Line 986  MULTITHREADING
986  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
987    
988         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
989         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
990         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
991         pcreprecompile documentation.         pcreprecompile  documentation.  However, compiling a regular expression
992           with one version of PCRE for use with a different version is not  guar-
993           anteed to work and may cause crashes.
994    
995    
996  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
997    
998         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
999    
1000         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-
1001         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
1002         The pcrebuild documentation has more details about these optional  fea-         The  pcrebuild documentation has more details about these optional fea-
1003         tures.         tures.
1004    
1005         The  first  argument  for pcre_config() is an integer, specifying which         The first argument for pcre_config() is an  integer,  specifying  which
1006         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
1007         into  which  the  information  is  placed. The following information is         into which the information is  placed.  The  following  information  is
1008         available:         available:
1009    
1010           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
1011    
1012         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-
1013         able; otherwise it is set to zero.         able; otherwise it is set to zero.
1014    
1015           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
1016    
1017         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
1018         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
1019    
1020           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1021    
1022         The output is an integer whose value specifies  the  default  character         The  output  is  an integer whose value specifies the default character
1023         sequence  that is recognized as meaning "newline". The four values that         sequence that is recognized as meaning "newline". The four values  that
1024         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,
1025         The default should normally be the standard sequence for your operating         and -1 for ANY. The default should normally be  the  standard  sequence
1026         system.         for your operating system.
1027    
1028             PCRE_CONFIG_BSR
1029    
1030           The output is an integer whose value indicates what character sequences
1031           the \R escape sequence matches by default. A value of 0 means  that  \R
1032           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1033           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1034           tern is compiled or matched.
1035    
1036           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1037    
1038         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
1039         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1040         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1041         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1042         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1043         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1044    
1045           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1046    
1047         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1048         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1049         given in the pcreposix documentation.         given in the pcreposix documentation.
1050    
1051           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1052    
1053         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
1054         internal matching function calls in a  pcre_exec()  execution.  Further         internal  matching  function  calls in a pcre_exec() execution. Further
1055         details are given with pcre_exec() below.         details are given with pcre_exec() below.
1056    
1057           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1058    
1059         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
1060         recursion when calling the internal matching function in a  pcre_exec()         recursion  when calling the internal matching function in a pcre_exec()
1061         execution. Further details are given with pcre_exec() below.         execution. Further details are given with pcre_exec() below.
1062    
1063           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1064    
1065         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
1066         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1067         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
1068         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
1069         on  the  heap  instead  of  recursive  function  calls.  In  this case,         on the  heap  instead  of  recursive  function  calls.  In  this  case,
1070         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
1071         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1072    
1073    
# Line 954  COMPILING A PATTERN Line 1084  COMPILING A PATTERN
1084    
1085         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1086         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1087         the  two interfaces is that pcre_compile2() has an additional argument,         the two interfaces is that pcre_compile2() has an additional  argument,
1088         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
1089    
1090         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
1091         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
1092         obtained via pcre_malloc is returned. This contains the  compiled  code         obtained  via  pcre_malloc is returned. This contains the compiled code
1093         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
1094         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1095         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
1096         longer required.         longer required.
1097    
1098         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
1099         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
1100         fully relocatable, because it may contain a copy of the tableptr  argu-         fully  relocatable, because it may contain a copy of the tableptr argu-
1101         ment, which is an address (see below).         ment, which is an address (see below).
1102    
1103         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1104         pilation. It should be zero if no options are required.  The  available         pilation.  It  should be zero if no options are required. The available
1105         options  are  described  below. Some of them, in particular, those that         options are described below. Some of them, in  particular,  those  that
1106         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
1107         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern (see the detailed description  in  the  pcrepattern  documenta-
1108         tion). For these options, the contents of the options  argument  speci-         tion).  For  these options, the contents of the options argument speci-
1109         fies  their initial settings at the start of compilation and execution.         fies their initial settings at the start of compilation and  execution.
1110         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
1111         of matching as well as at compile time.         of matching as well as at compile time.
1112    
1113         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1114         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1115         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-
1116         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
1117         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-
1118         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
1119         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
1120         given.         given.
1121    
1122         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1123         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
1124         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
1125         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1126    
1127         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
1128         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1129         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1130         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
1131         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1132         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
1133         support below.         support below.
1134    
1135         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1136         pile():         pile():
1137    
1138           pcre *re;           pcre *re;
# Line 1015  COMPILING A PATTERN Line 1145  COMPILING A PATTERN
1145             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1146             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1147    
1148         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
1149         file:         file:
1150    
1151           PCRE_ANCHORED           PCRE_ANCHORED
1152    
1153         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
1154         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
1155         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1156         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1157         only way to do it in Perl.         only way to do it in Perl.
1158    
1159           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1160    
1161         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1162         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1163         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1164    
1165             PCRE_BSR_ANYCRLF
1166             PCRE_BSR_UNICODE
1167    
1168           These options (which are mutually exclusive) control what the \R escape
1169           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1170           or to match any Unicode newline sequence. The default is specified when
1171           PCRE is built. It can be overridden from within the pattern, or by set-
1172           ting an option when a compiled pattern is matched.
1173    
1174           PCRE_CASELESS           PCRE_CASELESS
1175    
1176         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
1177         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
1178         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
1179         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1180         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1181         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-
1182         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1183         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1184         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1185         UTF-8 support.         UTF-8 support.
1186    
1187           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1188    
1189         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
1190         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
1191         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
1192         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1193         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
1194         Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1195    
1196           PCRE_DOTALL           PCRE_DOTALL
1197    
1198         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-
1199         acters, including those that indicate newline. Without it, a  dot  does         acters,  including  those that indicate newline. Without it, a dot does
1200         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
1201         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
1202         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
1203         newline characters, independent of the setting of this option.         newline characters, independent of the setting of this option.
1204    
1205           PCRE_DUPNAMES           PCRE_DUPNAMES
1206    
1207         If this bit is set, names used to identify capturing  subpatterns  need         If  this  bit is set, names used to identify capturing subpatterns need
1208         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
1209         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
1210         matched.  There  are  more details of named subpatterns below; see also         matched. There are more details of named subpatterns  below;  see  also
1211         the pcrepattern documentation.         the pcrepattern documentation.
1212    
1213           PCRE_EXTENDED           PCRE_EXTENDED
1214    
1215         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1216         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1217         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1218         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1219         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1220         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-
1221         ting.         ting.
1222    
1223         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1224         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1225         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1226         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1227         introduces a conditional subpattern.         introduces a conditional subpattern.
1228    
1229           PCRE_EXTRA           PCRE_EXTRA
1230    
1231         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1232         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
1233         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
1234         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1235         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1236         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
1237         literal. (Perl can, however, be persuaded to give a warning for  this.)         literal.  (Perl can, however, be persuaded to give a warning for this.)
1238         There  are  at  present no other features controlled by this option. It         There are at present no other features controlled by  this  option.  It
1239         can also be set by a (?X) option setting within a pattern.         can also be set by a (?X) option setting within a pattern.
1240    
1241           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1242    
1243         If this option is set, an  unanchored  pattern  is  required  to  match         If  this  option  is  set,  an  unanchored pattern is required to match
1244         before  or  at  the  first  newline  in  the subject string, though the         before or at the first  newline  in  the  subject  string,  though  the
1245         matched text may continue over the newline.         matched text may continue over the newline.
1246    
1247           PCRE_MULTILINE           PCRE_MULTILINE
1248    
1249         By default, PCRE treats the subject string as consisting  of  a  single         By  default,  PCRE  treats the subject string as consisting of a single
1250         line  of characters (even if it actually contains newlines). The "start         line of characters (even if it actually contains newlines). The  "start
1251         of line" metacharacter (^) matches only at the  start  of  the  string,         of  line"  metacharacter  (^)  matches only at the start of the string,
1252         while  the  "end  of line" metacharacter ($) matches only at the end of         while the "end of line" metacharacter ($) matches only at  the  end  of
1253         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1254         is set). This is the same as Perl.         is set). This is the same as Perl.
1255    
1256         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"
1257         constructs match immediately following or immediately  before  internal         constructs  match  immediately following or immediately before internal
1258         newlines  in  the  subject string, respectively, as well as at the very         newlines in the subject string, respectively, as well as  at  the  very
1259         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
1260         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-
1261         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,
1262         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1263    
1264           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1265           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1266           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
1267             PCRE_NEWLINE_ANYCRLF
1268           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1269    
1270         These  options  override the default newline definition that was chosen         These options override the default newline definition that  was  chosen
1271         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
1272         newline  is  indicated  by a single character (CR or LF, respectively).         newline is indicated by a single character (CR  or  LF,  respectively).
1273         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the         Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1274         two-character  CRLF  sequence.  Setting PCRE_NEWLINE_ANY specifies that         two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1275         any Unicode newline sequence should be recognized. The Unicode  newline         that any of the three preceding sequences should be recognized. Setting
1276         sequences  are  the three just mentioned, plus the single characters VT         PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1277         (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085),         recognized. The Unicode newline sequences are the three just mentioned,
1278         LS  (line separator, U+2028), and PS (paragraph separator, U+2029). The         plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1279         last two are recognized only in UTF-8 mode.         U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1280           (paragraph separator, U+2029). The last  two  are  recognized  only  in
1281         The newline setting in the  options  word  uses  three  bits  that  are         UTF-8 mode.
1282         treated  as  a  number, giving eight possibilities. Currently only five  
1283         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
1284         set  more  than  one  newline option, the combination may or may not be         treated as a number, giving eight possibilities. Currently only six are
1285         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
1286         lent  to PCRE_NEWLINE_CRLF, but other combinations yield unused numbers         more than one newline option, the combination may or may not be  sensi-
1287         and cause an error.         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1288           PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1289         The only time that a line break is specially recognized when  compiling         cause an error.
1290         a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a  
1291         character class is encountered. This indicates  a  comment  that  lasts         The  only time that a line break is specially recognized when compiling
1292         until  after the next line break sequence. In other circumstances, line         a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1293         break  sequences  are  treated  as  literal  data,   except   that   in         character  class  is  encountered.  This indicates a comment that lasts
1294           until after the next line break sequence. In other circumstances,  line
1295           break   sequences   are   treated  as  literal  data,  except  that  in
1296         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1297         and are therefore ignored.         and are therefore ignored.
1298    
1299         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
1300         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.
1301    
1302           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1303    
1304         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-
1305         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1306         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1307         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1308         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1309    
1310           PCRE_UNGREEDY           PCRE_UNGREEDY
1311    
1312         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1313         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
1314         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
1315         within the pattern.         within the pattern.
1316    
1317           PCRE_UTF8           PCRE_UTF8
1318    
1319         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
1320         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1321         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-
1322         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
1323         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
1324         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1325    
1326           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1327    
1328         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
1329         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically checked. There is a  discussion  about  the  validity  of
1330         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
1331         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
1332         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-
1333         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
1334         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
1335         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
1336         ing of subject strings.         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1337           UTF-8 validity checking of subject strings.
1338    
1339    
1340  COMPILATION ERROR CODES  COMPILATION ERROR CODES
# Line 1230  COMPILATION ERROR CODES Line 1373  COMPILATION ERROR CODES
1373           26  malformed number or name after (?(           26  malformed number or name after (?(
1374           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1375           28  assertion expected after (?(           28  assertion expected after (?(
1376           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1377           30  unknown POSIX class name           30  unknown POSIX class name
1378           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1379           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 1394  COMPILATION ERROR CODES
1394           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1395           48  subpattern name is too long (maximum 32 characters)           48  subpattern name is too long (maximum 32 characters)
1396           49  too many named subpatterns (maximum 10,000)           49  too many named subpatterns (maximum 10,000)
1397           50  repeated subpattern is too long           50  [this code is not in use]
1398           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1399           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1400           53   internal  error:  previously-checked  referenced  subpattern not           53   internal  error:  previously-checked  referenced  subpattern not
1401         found         found
1402           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1403           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1404           56  inconsistent NEWLINE options"           56  inconsistent NEWLINE options
1405             57  \g is not followed by a braced name or an optionally braced
1406                   non-zero number
1407             58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
1408    
1409    
1410  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1310  STUDYING A PATTERN Line 1456  STUDYING A PATTERN
1456  LOCALE SUPPORT  LOCALE SUPPORT
1457    
1458         PCRE handles caseless matching, and determines whether  characters  are         PCRE handles caseless matching, and determines whether  characters  are
1459         letters  digits,  or whatever, by reference to a set of tables, indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1460         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
1461         characters  with  codes  less than 128. Higher-valued codes never match         characters  with  codes  less than 128. Higher-valued codes never match
1462         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
1463         with  Unicode  character property support. The use of locales with Uni-         with  Unicode  character property support. The use of locales with Uni-
1464         code is discouraged.         code is discouraged. If you are handling characters with codes  greater
1465           than  128, you should either use UTF-8 and Unicode, or use locales, but
1466         An internal set of tables is created in the default C locale when  PCRE         not try to mix the two.
1467         is  built.  This  is  used when the final argument of pcre_compile() is  
1468         NULL, and is sufficient for many applications. An  alternative  set  of         PCRE contains an internal set of tables that are used  when  the  final
1469         tables  can,  however, be supplied. These may be created in a different         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1470         locale from the default. As more and more applications change to  using         applications.  Normally, the internal tables recognize only ASCII char-
1471         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-
1472           nal tables to be rebuilt in the default "C" locale of the local system,
1473         External  tables  are  built by calling the pcre_maketables() function,         which may cause them to be different.
1474         which has no arguments, in the relevant locale. The result can then  be  
1475         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For         The  internal tables can always be overridden by tables supplied by the
1476         example, to build and use tables that are appropriate  for  the  French         application that calls PCRE. These may be created in a different locale
1477         locale  (where  accented  characters  with  values greater than 128 are         from  the  default.  As more and more applications change to using Uni-
1478           code, the need for this locale support is expected to die away.
1479    
1480           External tables are built by calling  the  pcre_maketables()  function,
1481           which  has no arguments, in the relevant locale. The result can then be
1482           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1483           example,  to  build  and use tables that are appropriate for the French
1484           locale (where accented characters with  values  greater  than  128  are
1485         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1486    
1487           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1488           tables = pcre_maketables();           tables = pcre_maketables();
1489           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1490    
1491           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1492           if you are using Windows, the name for the French locale is "french".
1493    
1494         When pcre_maketables() runs, the tables are built  in  memory  that  is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1495         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1496         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 1593  INFORMATION ABOUT A PATTERN
1593         returned. The fourth argument should point to an unsigned char *  vari-         returned. The fourth argument should point to an unsigned char *  vari-
1594         able.         able.
1595    
1596             PCRE_INFO_HASCRORLF
1597    
1598           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1599           characters, otherwise 0. The fourth argument should  point  to  an  int
1600           variable.  An explicit match is either a literal CR or LF character, or
1601           \r or \n.
1602    
1603             PCRE_INFO_JCHANGED
1604    
1605           Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1606           otherwise  0. The fourth argument should point to an int variable. (?J)
1607           and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1608    
1609           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1610    
1611         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
1612         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
1613         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1614         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
1615         byte  is  recorded only if it follows something of variable length. For         byte is recorded only if it follows something of variable  length.  For
1616         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
1617         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1618    
# Line 1451  INFORMATION ABOUT A PATTERN Line 1620  INFORMATION ABOUT A PATTERN
1620           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1621           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1622    
1623         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1624         ses. The names are just an additional way of identifying the  parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1625         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1626         pcre_get_named_substring() are provided for  extracting  captured  sub-         pcre_get_named_substring()  are  provided  for extracting captured sub-
1627         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
1628         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
1629         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1630         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
1631         described by these three values.         described by these three values.
1632    
1633         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
1634         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1635         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
1636         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1637         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
1638         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-
1639         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-
1640         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1641         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-
1642         theses numbers. For example, consider  the  following  pattern  (assume         theses  numbers.  For  example,  consider the following pattern (assume
1643         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1644         ignored):         ignored):
1645    
1646           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1647           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1648    
1649         There are four named subpatterns, so the table has  four  entries,  and         There  are  four  named subpatterns, so the table has four entries, and
1650         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,
1651         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1652         as ??:         as ??:
1653    
# Line 1487  INFORMATION ABOUT A PATTERN Line 1656  INFORMATION ABOUT A PATTERN
1656           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1657           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1658    
1659         When  writing  code  to  extract  data from named subpatterns using the         When writing code to extract data  from  named  subpatterns  using  the
1660         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
1661         to be different for each compiled pattern.         to be different for each compiled pattern.
1662    
1663             PCRE_INFO_OKPARTIAL
1664    
1665           Return 1 if the pattern can be used for partial matching, otherwise  0.
1666           The  fourth  argument  should point to an int variable. The pcrepartial
1667           documentation lists the restrictions that apply to patterns  when  par-
1668           tial matching is used.
1669    
1670           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1671    
1672         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
1673         fourth argument should point to an unsigned long  int  variable.  These         fourth argument should point to an unsigned long  int  variable.  These
1674         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1675         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1676           other  words,  they are the options that will be in force when matching
1677           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1678           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1679           and PCRE_EXTENDED.
1680    
1681         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
1682         alternatives begin with one of the following:         alternatives begin with one of the following:
# Line 1699  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1879  MATCHING A PATTERN: THE TRADITIONAL FUNC
1879         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
1880         unachored at matching time.         unachored at matching time.
1881    
1882             PCRE_BSR_ANYCRLF
1883             PCRE_BSR_UNICODE
1884    
1885           These options (which are mutually exclusive) control what the \R escape
1886           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1887           or to match any Unicode newline sequence. These  options  override  the
1888           choice that was made or defaulted when the pattern was compiled.
1889    
1890           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1891           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1892           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
1893             PCRE_NEWLINE_ANYCRLF
1894           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1895    
1896         These options override  the  newline  definition  that  was  chosen  or         These  options  override  the  newline  definition  that  was chosen or
1897         defaulted  when the pattern was compiled. For details, see the descrip-         defaulted when the pattern was compiled. For details, see the  descrip-
1898         tion of pcre_compile()  above.  During  matching,  the  newline  choice         tion  of  pcre_compile()  above.  During  matching,  the newline choice
1899         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1900         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
1901         match  failure  for  an  unanchored  pattern. When PCRE_NEWLINE_CRLF or         match failure for an unanchored pattern.
1902         PCRE_NEWLINE_ANY is set, and a match attempt  fails  when  the  current  
1903         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
1904         characters instead of one, in other words, to after the CRLF.         set,  and a match attempt for an unanchored pattern fails when the cur-
1905           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1906           explicit  matches  for  CR  or  LF  characters,  the  match position is
1907           advanced by two characters instead of one, in other words, to after the
1908           CRLF.
1909    
1910           The above rule is a compromise that makes the most common cases work as
1911           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1912           option is not set), it does not match the string "\r\nA" because, after
1913           failing at the start, it skips both the CR and the LF before  retrying.
1914           However,  the  pattern  [\r\n]A does match that string, because it con-
1915           tains an explicit CR or LF reference, and so advances only by one char-
1916           acter after the first failure.
1917    
1918           An explicit match for CR of LF is either a literal appearance of one of
1919           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1920           matches  such  as [^X] do not count, nor does \s (which includes CR and
1921           LF in the characters that it matches).
1922    
1923           Notwithstanding the above, anomalous effects may still occur when  CRLF
1924           is a valid newline sequence and explicit \r or \n escapes appear in the
1925           pattern.
1926    
1927           PCRE_NOTBOL           PCRE_NOTBOL
1928    
# Line 1759  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1969  MATCHING A PATTERN: THE TRADITIONAL FUNC
1969         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
1970         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
1971         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
1972         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
1973         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
1974         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
1975         returned.         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
1976           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1977         If you already know that your subject is valid, and you  want  to  skip  
1978         these    checks    for   performance   reasons,   you   can   set   the         If  you  already  know that your subject is valid, and you want to skip
1979         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         these   checks   for   performance   reasons,   you   can    set    the
1980         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
1981         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
1982         string.  However,  you  should  be  sure  that the value of startoffset         making  repeated  calls  to  find  all  the matches in a single subject
1983         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
1984         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
1985         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
1986           value  of startoffset that does not point to the start of a UTF-8 char-
1987         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1988    
1989           PCRE_PARTIAL           PCRE_PARTIAL
1990    
1991         This  option  turns  on  the  partial  matching feature. If the subject         This option turns on the  partial  matching  feature.  If  the  subject
1992         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-
1993         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
1994         partially matches the pattern and the failure to  match  occurred  only         partially  matches  the  pattern and the failure to match occurred only
1995         because  there were not enough subject characters), pcre_exec() returns         because there were not enough subject characters), pcre_exec()  returns
1996         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1997         used,  there  are restrictions on what may appear in the pattern. These         used, there are restrictions on what may appear in the  pattern.  These
1998         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1999    
2000     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2001    
2002         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
2003         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
2004         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.
2005         Unlike  the  pattern string, the subject may contain binary zero bytes.         Unlike the pattern string, the subject may contain binary  zero  bytes.
2006         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
2007         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.
2008    
2009         A  non-zero  starting offset is useful when searching for another match         A non-zero starting offset is useful when searching for  another  match
2010         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-
2011         cess.   Setting  startoffset differs from just passing over a shortened         cess.  Setting startoffset differs from just passing over  a  shortened
2012         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
2013         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2014    
2015           \Biss\B           \Biss\B
2016    
2017         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
2018         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.)
2019         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
2020         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
2021         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
2022         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
2023         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
2024         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-
2025         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
2026         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2027    
2028         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,
2029         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
2030         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
2031         subject.         subject.
2032    
2033     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2034    
2035         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
2036         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2037         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2038         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2039         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-
2040         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2041         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2042    
2043         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of  integer
2044         offsets whose address is passed in ovector. The number of  elements  in         offsets  whose  address is passed in ovector. The number of elements in
2045         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.
2046         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
2047    
2048         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-
2049         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2050         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-
2051         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2052         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
2053         it is not, it is rounded down.         it is not, it is rounded down.
2054    
2055         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2056         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2057         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
2058         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-
2059         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
2060         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-
2061         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1], identify the portion of  the  subject  string  matched  by  the
2062         entire pattern. The next pair is used for the first  capturing  subpat-         entire  pattern.  The next pair is used for the first capturing subpat-
2063         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
2064         highest numbered pair that has been set. For example, if two substrings         highest numbered pair that has been set. For example, if two substrings
2065         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
2066         subpatterns, the return value from a successful match is 1,  indicating         subpatterns,  the return value from a successful match is 1, indicating
2067         that just the first pair of offsets has been set.         that just the first pair of offsets has been set.
2068    
2069         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2070         of the string that it matched that is returned.         of the string that it matched that is returned.
2071    
2072         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,
2073         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
2074         function returns a value of zero. In particular, if the substring  off-         function  returns a value of zero. In particular, if the substring off-
2075         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
2076         as NULL and ovecsize as zero. However, if  the  pattern  contains  back         as  NULL  and  ovecsize  as zero. However, if the pattern contains back
2077         references  and  the  ovector is not big enough to remember the related         references and the ovector is not big enough to  remember  the  related
2078         substrings, PCRE has to get additional memory for use during  matching.         substrings,  PCRE has to get additional memory for use during matching.
2079         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
2080    
2081         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
2082         subpatterns there are in a compiled  pattern.  The  smallest  size  for         subpatterns  there  are  in  a  compiled pattern. The smallest size for
2083         ovector  that  will allow for n captured substrings, in addition to the         ovector that will allow for n captured substrings, in addition  to  the
2084         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.
2085    
2086         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
2087         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,
2088         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
2089         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
2090         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-
2091         sponding to unused subpatterns are set to -1.         sponding to unused subpatterns are set to -1.
2092    
2093         Offset  values  that correspond to unused subpatterns at the end of the         Offset values that correspond to unused subpatterns at the end  of  the
2094         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
2095         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
2096         matched. The return from the function is 2, because  the  highest  used         matched.  The  return  from the function is 2, because the highest used
2097         capturing subpattern number is 1. However, you can refer to the offsets         capturing subpattern number is 1. However, you can refer to the offsets
2098         for the second and third capturing subpatterns if  you  wish  (assuming         for  the  second  and third capturing subpatterns if you wish (assuming
2099         the vector is large enough, of course).         the vector is large enough, of course).
2100    
2101         Some  convenience  functions  are  provided for extracting the captured         Some convenience functions are provided  for  extracting  the  captured
2102         substrings as separate strings. These are described below.         substrings as separate strings. These are described below.
2103    
2104     Error return values from pcre_exec()     Error return values from pcre_exec()
2105    
2106         If pcre_exec() fails, it returns a negative number. The  following  are         If  pcre_exec()  fails, it returns a negative number. The following are
2107         defined in the header file:         defined in the header file:
2108    
2109           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1901  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2112  MATCHING A PATTERN: THE TRADITIONAL FUNC
2112    
2113           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2114    
2115         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
2116         ovecsize was not zero.         ovecsize was not zero.
2117    
2118           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1910  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2121  MATCHING A PATTERN: THE TRADITIONAL FUNC
2121    
2122           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2123    
2124         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,
2125         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
2126         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
2127         an  environment  with the other endianness. This is the error that PCRE         an environment with the other endianness. This is the error  that  PCRE
2128         gives when the magic number is not present.         gives when the magic number is not present.
2129    
2130           PCRE_ERROR_UNKNOWN_OPCODE (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2131    
2132         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2133         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
2134         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2135    
2136           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2137    
2138         If a pattern contains back references, but the ovector that  is  passed         If  a  pattern contains back references, but the ovector that is passed
2139         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2140         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
2141         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
2142         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2143    
2144           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2145    
2146         This error is used by the pcre_copy_substring(),  pcre_get_substring(),         This  error is used by the pcre_copy_substring(), pcre_get_substring(),
2147         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2148         returned by pcre_exec().         returned by pcre_exec().
2149    
2150           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2151    
2152         The backtracking limit, as specified by  the  match_limit  field  in  a         The  backtracking  limit,  as  specified  by the match_limit field in a
2153         pcre_extra  structure  (or  defaulted) was reached. See the description         pcre_extra structure (or defaulted) was reached.  See  the  description
2154         above.         above.
2155    
2156           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2157    
2158         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
2159         use  by  callout functions that want to yield a distinctive error code.         use by callout functions that want to yield a distinctive  error  code.
2160         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2161    
2162           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2163    
2164         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
2165         subject.         subject.
2166    
2167           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2168    
2169         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
2170         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-
2171         ter.         ter.
2172    
2173           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2174    
2175         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
2176         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2177    
2178           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2179    
2180         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
2181         items  that are not supported for partial matching. See the pcrepartial         items that are not supported for partial matching. See the  pcrepartial
2182         documentation for details of partial matching.         documentation for details of partial matching.
2183    
2184           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2185    
2186         An unexpected internal error has occurred. This error could  be  caused         An  unexpected  internal error has occurred. This error could be caused
2187         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2188    
2189           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2190    
2191         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.
2192    
2193           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2194    
2195         The internal recursion limit, as specified by the match_limit_recursion         The internal recursion limit, as specified by the match_limit_recursion
2196         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2197         description above.         description above.
2198    
          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.  
   
2199           PCRE_ERROR_BADNEWLINE     (-23)           PCRE_ERROR_BADNEWLINE     (-23)
2200    
2201         An invalid combination of PCRE_NEWLINE_xxx options was given.         An invalid combination of PCRE_NEWLINE_xxx options was given.
2202    
2203         Error numbers -16 to -20 are not used by pcre_exec().         Error numbers -16 to -20 and -22 are not used by pcre_exec().
2204    
2205    
2206  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 2013  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2216  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2216         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2217              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2218    
2219         Captured substrings can be  accessed  directly  by  using  the  offsets         Captured  substrings  can  be  accessed  directly  by using the offsets
2220         returned  by  pcre_exec()  in  ovector.  For convenience, the functions         returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2221         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2222         string_list()  are  provided for extracting captured substrings as new,         string_list() are provided for extracting captured substrings  as  new,
2223         separate, zero-terminated strings. These functions identify  substrings         separate,  zero-terminated strings. These functions identify substrings
2224         by  number.  The  next section describes functions for extracting named         by number. The next section describes functions  for  extracting  named
2225         substrings.         substrings.
2226    
2227         A substring that contains a binary zero is correctly extracted and  has         A  substring that contains a binary zero is correctly extracted and has
2228         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
2229         string.  However, you can process such a string  by  referring  to  the         string.   However,  you  can  process such a string by referring to the
2230         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2231         string().  Unfortunately, the interface to pcre_get_substring_list() is         string().  Unfortunately, the interface to pcre_get_substring_list() is
2232         not  adequate for handling strings containing binary zeros, because the         not adequate for handling strings containing binary zeros, because  the
2233         end of the final string is not independently indicated.         end of the final string is not independently indicated.
2234    
2235         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-
2236         tions:  subject  is  the subject string that has just been successfully         tions: subject is the subject string that has  just  been  successfully
2237         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
2238         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2239         were captured by the match, including the substring  that  matched  the         were  captured  by  the match, including the substring that matched the
2240         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2241         it is greater than zero. If pcre_exec() returned zero, indicating  that         it  is greater than zero. If pcre_exec() returned zero, indicating that
2242         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
2243         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2244    
2245         The functions pcre_copy_substring() and pcre_get_substring() extract  a         The  functions pcre_copy_substring() and pcre_get_substring() extract a
2246         single  substring,  whose  number  is given as stringnumber. A value of         single substring, whose number is given as  stringnumber.  A  value  of
2247         zero extracts the substring that matched the  entire  pattern,  whereas         zero  extracts  the  substring that matched the entire pattern, whereas
2248         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2249         string(), the string is placed in buffer,  whose  length  is  given  by         string(),  the  string  is  placed  in buffer, whose length is given by
2250         buffersize,  while  for  pcre_get_substring()  a new block of memory is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2251         obtained via pcre_malloc, and its address is  returned  via  stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2252         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
2253         the terminating zero, or one of these error codes:         the terminating zero, or one of these error codes:
2254    
2255           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2256    
2257         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
2258         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2259    
2260           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2261    
2262         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2263    
2264         The  pcre_get_substring_list()  function  extracts  all  available sub-         The pcre_get_substring_list()  function  extracts  all  available  sub-
2265         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
2266         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
2267         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
2268         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
2269         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
2270         error code         error code
2271    
2272           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2273    
2274         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2275    
2276         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2277         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2278         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
2279         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2280         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2281         tive for unset substrings.         tive for unset substrings.
2282    
2283         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2284         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
2285         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2286         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2287         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.
2288         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-
2289         cial  interface  to  another  programming  language  that  cannot   use         cial   interface  to  another  programming  language  that  cannot  use
2290         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-
2291         vided.         vided.
2292    
2293    
# Line 2103  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2306  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2306              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2307              const char **stringptr);              const char **stringptr);
2308    
2309         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-
2310         ber.  For example, for this pattern         ber.  For example, for this pattern
2311    
2312           (a+)b(?<xxx>\d+)...           (a+)b(?<xxx>\d+)...
# Line 2112  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2315  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2315         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
2316         name by calling pcre_get_stringnumber(). The first argument is the com-         name by calling pcre_get_stringnumber(). The first argument is the com-
2317         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
2318         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2319         subpattern of that name.         subpattern of that name.
2320    
2321         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
2322         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2323         are also two functions that do the whole job.         are also two functions that do the whole job.
2324    
2325         Most   of   the   arguments    of    pcre_copy_named_substring()    and         Most    of    the    arguments   of   pcre_copy_named_substring()   and
2326         pcre_get_named_substring()  are  the  same  as  those for the similarly         pcre_get_named_substring() are the same  as  those  for  the  similarly
2327         named functions that extract by number. As these are described  in  the         named  functions  that extract by number. As these are described in the
2328         previous  section,  they  are not re-described here. There are just two         previous section, they are not re-described here. There  are  just  two
2329         differences:         differences:
2330    
2331         First, instead of a substring number, a substring name is  given.  Sec-         First,  instead  of a substring number, a substring name is given. Sec-
2332         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
2333         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
2334         name-to-number translation table.         name-to-number translation table.
2335    
2336         These  functions call pcre_get_stringnumber(), and if it succeeds, they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2337         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2338         ate.         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2339           behaviour may not be what you want (see the next section).
2340    
2341    
2342  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
# Line 2144  DUPLICATE SUBPATTERN NAMES Line 2348  DUPLICATE SUBPATTERN NAMES
2348         subpatterns are not required to  be  unique.  Normally,  patterns  with         subpatterns are not required to  be  unique.  Normally,  patterns  with
2349         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
2350         subpatterns participates. An example is shown in the pcrepattern  docu-         subpatterns participates. An example is shown in the pcrepattern  docu-
2351         mentation. When duplicates are present, pcre_copy_named_substring() and         mentation.
2352    
2353           When    duplicates   are   present,   pcre_copy_named_substring()   and
2354         pcre_get_named_substring() return the first substring corresponding  to         pcre_get_named_substring() return the first substring corresponding  to
2355         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
2356         returned.  The pcre_get_stringnumber() function returns one of the num-         (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2357         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,
2358         is.         but it is not defined which it is.
2359    
2360         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
2361         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 2557  AUTHOR
2557    
2558  REVISION  REVISION
2559    
2560         Last updated: 06 March 2007         Last updated: 27 November 2007
2561         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2562  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2563    
# Line 2379  PCRE CALLOUTS Line 2585  PCRE CALLOUTS
2585         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2586         points:         points:
2587    
2588           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2589    
2590         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
2591         called, PCRE automatically  inserts  callouts,  all  with  number  255,         called, PCRE automatically  inserts  callouts,  all  with  number  255,
# Line 2454  THE CALLOUT INTERFACE Line 2660  THE CALLOUT INTERFACE
2660         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2661         were passed to pcre_exec().         were passed to pcre_exec().
2662    
2663         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
2664         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
2665         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
2666         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2667           function may be called several times from the same point in the pattern
2668           for different starting points in the subject.
2669    
2670         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
2671         the current match pointer.         the current match pointer.
# Line 2520  AUTHOR Line 2728  AUTHOR
2728    
2729  REVISION  REVISION
2730    
2731         Last updated: 06 March 2007         Last updated: 29 May 2007
2732         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2733  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2734    
# Line 2536  DIFFERENCES BETWEEN PCRE AND PERL Line 2744  DIFFERENCES BETWEEN PCRE AND PERL
2744    
2745         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2746         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences described here  are  mainly
2747         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
2748         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.
2749    
2750         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
2751         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 2810  DIFFERENCES BETWEEN PCRE AND PERL
2810         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2811         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2812    
2813         11. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2814           (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2815           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2816           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2817           ture group; this is different to Perl.
2818    
2819           12. PCRE provides some extensions to the Perl regular expression facil-
2820         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
2821         versions, some of which (such as named parentheses) have been  in  PCRE         versions, some of which (such as named parentheses) have been  in  PCRE
2822         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 2829  DIFFERENCES BETWEEN PCRE AND PERL
2829         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2830    
2831         (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-
2832         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2833         ignored. (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
2834    
2835         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2836         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 2842  DIFFERENCES BETWEEN PCRE AND PERL
2842         (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-
2843         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2844    
2845         (g) The callout facility is PCRE-specific.         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2846           CRLF by the PCRE_BSR_ANYCRLF option.
2847    
2848           (h) The callout facility is PCRE-specific.
2849    
2850         (h) The partial matching facility is PCRE-specific.         (i) The partial matching facility is PCRE-specific.
2851    
2852         (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,
2853         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2854    
2855         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2856         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2857    
2858           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2859           of a pattern that set overall options that cannot be changed within the
2860           pattern.
2861    
2862    
2863  AUTHOR  AUTHOR
2864    
# Line 2648  AUTHOR Line 2869  AUTHOR
2869    
2870  REVISION  REVISION
2871    
2872         Last updated: 06 March 2007         Last updated: 11 September 2007
2873         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2874  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2875    
# Line 2662  NAME Line 2883  NAME
2883    
2884  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2885    
2886         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2887         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2888         documentation  and  in  a  number  of books, some of which have copious         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are
2889         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         described in its own documentation, and regular expressions in  general
2890         by  O'Reilly, covers regular expressions in great detail. This descrip-         are  covered in a number of books, some of which have copious examples.
2891         tion of PCRE's regular expressions is intended as reference material.         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by
2892           O'Reilly,  covers regular expressions in great detail. This description
2893           of PCRE's regular expressions is intended as reference material.
2894    
2895         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2896         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 2904  PCRE REGULAR EXPRESSION DETAILS
2904         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2905         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
2906         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
2907         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
2908         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2909         the pcrematching page.         alternative function, and how it differs from the normal function,  are
2910           discussed in the pcrematching page.
2911    
2912    
2913    NEWLINE CONVENTIONS
2914    
2915           PCRE  supports five different conventions for indicating line breaks in
2916           strings: a single CR (carriage return) character, a  single  LF  (line-
2917           feed) character, the two-character sequence CRLF, any of the three pre-
2918           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2919           discussion  about newlines, and shows how to set the newline convention
2920           in the options arguments for the compiling and matching functions.
2921    
2922           It is also possible to specify a newline convention by starting a  pat-
2923           tern string with one of the following five sequences:
2924    
2925             (*CR)        carriage return
2926             (*LF)        linefeed
2927             (*CRLF)      carriage return, followed by linefeed
2928             (*ANYCRLF)   any of the three above
2929             (*ANY)       all Unicode newline sequences
2930    
2931           These override the default and the options given to pcre_compile(). For
2932           example, on a Unix system where LF is the default newline sequence, the
2933           pattern
2934    
2935             (*CR)a.b
2936    
2937           changes the convention to CR. That pattern matches "a\nb" because LF is
2938           no longer a newline. Note that these special settings,  which  are  not
2939           Perl-compatible,  are  recognized  only at the very start of a pattern,
2940           and that they must be in upper case.  If  more  than  one  of  them  is
2941           present, the last one is used.
2942    
2943           The  newline  convention  does  not  affect what the \R escape sequence
2944           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2945           compatibility.  However, this can be changed; see the description of \R
2946           in the section entitled "Newline sequences" below. A change of \R  set-
2947           ting can be combined with a change of newline convention.
2948    
2949    
2950  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
2951    
2952         A regular expression is a pattern that is  matched  against  a  subject         A  regular  expression  is  a pattern that is matched against a subject
2953         string  from  left  to right. Most characters stand for themselves in a         string from left to right. Most characters stand for  themselves  in  a
2954         pattern, and match the corresponding characters in the  subject.  As  a         pattern,  and  match  the corresponding characters in the subject. As a
2955         trivial example, the pattern         trivial example, the pattern
2956    
2957           The quick brown fox           The quick brown fox
2958    
2959         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
2960         caseless matching is specified (the PCRE_CASELESS option), letters  are         caseless  matching is specified (the PCRE_CASELESS option), letters are
2961         matched  independently  of case. In UTF-8 mode, PCRE always understands         matched independently of case. In UTF-8 mode, PCRE  always  understands
2962         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
2963         caseless  matching  is always possible. For characters with higher val-         caseless matching is always possible. For characters with  higher  val-
2964         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
2965         property  support,  but  not  otherwise.   If  you want to use caseless         property support, but not otherwise.   If  you  want  to  use  caseless
2966         matching for characters 128 and above, you must  ensure  that  PCRE  is         matching  for  characters  128  and above, you must ensure that PCRE is
2967         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
2968    
2969         The  power  of  regular  expressions  comes from the ability to include         The power of regular expressions comes  from  the  ability  to  include
2970         alternatives and repetitions in the pattern. These are encoded  in  the         alternatives  and  repetitions in the pattern. These are encoded in the
2971         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
2972         but instead are interpreted in some special way.         but instead are interpreted in some special way.
2973    
2974         There are two different sets of metacharacters: those that  are  recog-         There  are  two different sets of metacharacters: those that are recog-
2975         nized  anywhere in the pattern except within square brackets, and those         nized anywhere in the pattern except within square brackets, and  those
2976         that are recognized within square brackets.  Outside  square  brackets,         that  are  recognized  within square brackets. Outside square brackets,
2977         the metacharacters are as follows:         the metacharacters are as follows:
2978    
2979           \      general escape character with several uses           \      general escape character with several uses
# Line 2731  CHARACTERS AND METACHARACTERS Line 2992  CHARACTERS AND METACHARACTERS
2992                  also "possessive quantifier"                  also "possessive quantifier"
2993           {      start min/max quantifier           {      start min/max quantifier
2994    
2995         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
2996         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
2997    
2998           \      general escape character           \      general escape character
# Line 2741  CHARACTERS AND METACHARACTERS Line 3002  CHARACTERS AND METACHARACTERS
3002                    syntax)                    syntax)
3003           ]      terminates the character class           ]      terminates the character class
3004    
3005         The following sections describe the use of each of the  metacharacters.         The  following sections describe the use of each of the metacharacters.
3006    
3007    
3008  BACKSLASH  BACKSLASH
3009    
3010         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
3011         a non-alphanumeric character, it takes away any  special  meaning  that         a  non-alphanumeric  character,  it takes away any special meaning that
3012         character  may  have.  This  use  of  backslash  as an escape character         character may have. This  use  of  backslash  as  an  escape  character
3013         applies both inside and outside character classes.         applies both inside and outside character classes.
3014    
3015         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
3016         pattern.   This  escaping  action  applies whether or not the following         pattern.  This escaping action applies whether  or  not  the  following
3017         character would otherwise be interpreted as a metacharacter, so  it  is         character  would  otherwise be interpreted as a metacharacter, so it is
3018         always  safe  to  precede  a non-alphanumeric with backslash to specify         always safe to precede a non-alphanumeric  with  backslash  to  specify
3019         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-
3020         slash, you write \\.         slash, you write \\.
3021    
3022         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
3023         the pattern (other than in a character class) and characters between  a         the  pattern (other than in a character class) and characters between a
3024         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
3025         ing backslash can be used to include a whitespace  or  #  character  as         ing  backslash  can  be  used to include a whitespace or # character as
3026         part of the pattern.         part of the pattern.
3027    
3028         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-
3029         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-
3030         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
3031         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
3032         tion. Note the following examples:         tion. Note the following examples:
3033    
3034           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2777  BACKSLASH Line 3038  BACKSLASH
3038           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3039           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3040    
3041         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
3042         classes.         classes.
3043    
3044     Non-printing characters     Non-printing characters
3045    
3046         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-
3047         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
3048         appearance of non-printing characters, apart from the binary zero  that         appearance  of non-printing characters, apart from the binary zero that
3049         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates a pattern, but when a pattern  is  being  prepared  by  text
3050         editing, it is usually easier  to  use  one  of  the  following  escape         editing,  it  is  usually  easier  to  use  one of the following escape
3051         sequences than the binary character it represents:         sequences than the binary character it represents:
3052    
3053           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3054           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3055           \e        escape (hex 1B)           \e        escape (hex 1B)
3056           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3057           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3058           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3059           \t        tab (hex 09)           \t        tab (hex 09)
3060           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
3061           \xhh      character with hex code hh           \xhh      character with hex code hh
3062           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3063    
3064         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,
3065         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
3066         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;
3067         becomes hex 7B.         becomes hex 7B.
3068    
3069         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
3070         in  upper  or  lower case). Any number of hexadecimal digits may appear         in upper or lower case). Any number of hexadecimal  digits  may  appear
3071         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
3072         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,
3073         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger
3074         hexadecimal  digits  appear between \x{ and }, or if there is no termi-         than the largest Unicode code point, which is 10FFFF.
3075         nating }, this form of escape is not recognized.  Instead, the  initial  
3076         \x will be interpreted as a basic hexadecimal escape, with no following         If characters other than hexadecimal digits appear between \x{  and  },
3077         digits, giving a character whose value is zero.         or if there is no terminating }, this form of escape is not recognized.
3078           Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal
3079           escape,  with  no  following  digits, giving a character whose value is
3080           zero.
3081    
3082         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
3083         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 3132  BACKSLASH
3132    
3133     Absolute and relative back references     Absolute and relative back references
3134    
3135         The sequence \g followed by a positive or negative  number,  optionally         The sequence \g followed by an unsigned or a negative  number,  option-
3136         enclosed  in  braces,  is  an absolute or relative back reference. Back         ally  enclosed  in braces, is an absolute or relative back reference. A
3137         references are discussed later, following the discussion  of  parenthe-         named back reference can be coded as \g{name}. Back references are dis-
3138         sized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3139    
3140     Generic character types     Generic character types
3141    
# Line 2880  BACKSLASH Line 3144  BACKSLASH
3144    
3145           \d     any decimal digit           \d     any decimal digit
3146           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3147             \h     any horizontal whitespace character
3148             \H     any character that is not a horizontal whitespace character
3149           \s     any whitespace character           \s     any whitespace character
3150           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3151             \v     any vertical whitespace character
3152             \V     any character that is not a vertical whitespace character
3153           \w     any "word" character           \w     any "word" character
3154           \W     any "non-word" character           \W     any "non-word" character
3155    
# Line 2896  BACKSLASH Line 3164  BACKSLASH
3164    
3165         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
3166         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
3167         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
3168         "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-
3169         ter. In PCRE, it never does.)         ter. In PCRE, it never does.
3170    
3171           In  UTF-8 mode, characters with values greater than 128 never match \d,
3172           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3173           code  character  property  support is available. These sequences retain
3174           their original meanings from before UTF-8 support was available, mainly
3175           for efficiency reasons.
3176    
3177           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3178           the other sequences, these do match certain high-valued  codepoints  in
3179           UTF-8 mode.  The horizontal space characters are:
3180    
3181             U+0009     Horizontal tab
3182             U+0020     Space
3183             U+00A0     Non-break space
3184             U+1680     Ogham space mark
3185             U+180E     Mongolian vowel separator
3186             U+2000     En quad
3187             U+2001     Em quad
3188             U+2002     En space
3189             U+2003     Em space
3190             U+2004     Three-per-em space
3191             U+2005     Four-per-em space
3192             U+2006     Six-per-em space
3193             U+2007     Figure space
3194             U+2008     Punctuation space
3195             U+2009     Thin space
3196             U+200A     Hair space
3197             U+202F     Narrow no-break space
3198             U+205F     Medium mathematical space
3199             U+3000     Ideographic space
3200    
3201           The vertical space characters are:
3202    
3203             U+000A     Linefeed
3204             U+000B     Vertical tab
3205             U+000C     Formfeed
3206             U+000D     Carriage return
3207             U+0085     Next line
3208             U+2028     Line separator
3209             U+2029     Paragraph separator
3210    
3211         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
3212         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-
3213         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-
3214         specific matching is taking place (see "Locale support" in the  pcreapi         specific matching is taking place (see "Locale support" in the  pcreapi
3215         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
3216         codes greater than 128 are used for accented  letters,  and  these  are         systems, or "french" in Windows, some character codes greater than  128
3217         matched by \w.         are  used for accented letters, and these are matched by \w. The use of
3218           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.  
3219    
3220     Newline sequences     Newline sequences
3221    
3222         Outside a character class, the escape sequence \R matches  any  Unicode         Outside a character class, by default, the escape sequence  \R  matches
3223         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
3224         equivalent to the following:         mode \R is equivalent to the following:
3225    
3226           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3227    
# Line 2933  BACKSLASH Line 3237  BACKSLASH
3237         rator,  U+2029).   Unicode character property support is not needed for         rator,  U+2029).   Unicode character property support is not needed for
3238         these characters to be recognized.         these characters to be recognized.
3239    
3240           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3241           the  complete  set  of  Unicode  line  endings)  by  setting the option
3242           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3243           (BSR is an abbrevation for "backslash R".) This can be made the default
3244           when PCRE is built; if this is the case, the  other  behaviour  can  be
3245           requested  via  the  PCRE_BSR_UNICODE  option.   It is also possible to
3246           specify these settings by starting a pattern string  with  one  of  the
3247           following sequences:
3248    
3249             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3250             (*BSR_UNICODE)   any Unicode newline sequence
3251    
3252           These override the default and the options given to pcre_compile(), but
3253           they can be overridden by options given to pcre_exec(). Note that these
3254           special settings, which are not Perl-compatible, are recognized only at
3255           the very start of a pattern, and that they must be in  upper  case.  If
3256           more  than  one  of  them is present, the last one is used. They can be
3257           combined with a change of newline convention, for  example,  a  pattern
3258           can start with:
3259    
3260             (*ANY)(*BSR_ANYCRLF)
3261    
3262         Inside a character class, \R matches the letter "R".         Inside a character class, \R matches the letter "R".
3263    
3264     Unicode character properties     Unicode character properties
3265    
3266         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3267         tional  escape  sequences  to  match character properties are available         tional escape sequences that match characters with specific  properties
3268         when UTF-8 mode is selected. They are:         are  available.   When not in UTF-8 mode, these sequences are of course
3269           limited to testing characters whose codepoints are less than  256,  but
3270           they do work in this mode.  The extra escape sequences are:
3271    
3272           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3273           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
3274           \X       an extended Unicode sequence           \X       an extended Unicode sequence
3275    
3276         The property names represented by xx above are limited to  the  Unicode         The  property  names represented by xx above are limited to the Unicode
3277         script names, the general category properties, and "Any", which matches         script names, the general category properties, and "Any", which matches
3278         any character (including newline). Other properties such as "InMusical-         any character (including newline). Other properties such as "InMusical-
3279         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does
3280         not match any characters, so always causes a match failure.         not match any characters, so always causes a match failure.
3281    
3282         Sets of Unicode characters are defined as belonging to certain scripts.         Sets of Unicode characters are defined as belonging to certain scripts.
3283         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.
3284         For example:         For example:
3285    
3286           \p{Greek}           \p{Greek}
3287           \P{Han}           \P{Han}
3288    
3289         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
3290         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3291    
3292         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3293         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,         Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,
3294         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3295         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-         Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
3296         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,         gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,
3297         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3298         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,         Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,
3299         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3300         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3301    
3302         Each  character has exactly one general category property, specified by         Each character has exactly one general category property, specified  by
3303         a two-letter abbreviation. For compatibility with Perl, negation can be         a two-letter abbreviation. For compatibility with Perl, negation can be
3304         specified  by  including a circumflex between the opening brace and the         specified by including a circumflex between the opening brace  and  the
3305         property name. For example, \p{^Lu} is the same as \P{Lu}.         property name. For example, \p{^Lu} is the same as \P{Lu}.
3306    
3307         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-
3308         eral  category properties that start with that letter. In this case, in         eral category properties that start with that letter. In this case,  in
3309         the absence of negation, the curly brackets in the escape sequence  are         the  absence of negation, the curly brackets in the escape sequence are
3310         optional; these two examples have the same effect:         optional; these two examples have the same effect:
3311    
3312           \p{L}           \p{L}
# Line 3030  BACKSLASH Line 3358  BACKSLASH
3358           Zp    Paragraph separator           Zp    Paragraph separator
3359           Zs    Space separator           Zs    Space separator
3360    
3361         The  special property L& is also supported: it matches a character that         The special property L& is also supported: it matches a character  that
3362         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
3363         classified as a modifier or "other".         classified as a modifier or "other".
3364    
3365         The  long  synonyms  for  these  properties that Perl supports (such as         The Cs (Surrogate) property applies only to  characters  in  the  range
3366         \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
3367           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3368           ing  has  been  turned off (see the discussion of PCRE_NO_UTF8_CHECK in
3369           the pcreapi page).
3370    
3371           The long synonyms for these properties  that  Perl  supports  (such  as
3372           \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix
3373         any of these properties with "Is".         any of these properties with "Is".
3374    
3375         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-
3376         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
3377         in the Unicode table.         in the Unicode table.
3378    
3379         Specifying  caseless  matching  does not affect these escape sequences.         Specifying caseless matching does not affect  these  escape  sequences.
3380         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3381    
3382         The \X escape matches any number of Unicode  characters  that  form  an         The  \X  escape  matches  any number of Unicode characters that form an
3383         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3384    
3385           (?>\PM\pM*)           (?>\PM\pM*)
3386    
3387         That  is,  it matches a character without the "mark" property, followed         That is, it matches a character without the "mark"  property,  followed
3388         by zero or more characters with the "mark"  property,  and  treats  the         by  zero  or  more  characters with the "mark" property, and treats the
3389         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3390         property are typically accents that affect the preceding character.         property  are  typically  accents  that affect the preceding character.
3391           None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
3392           matches any one character.
3393    
3394         Matching characters by Unicode property is not fast, because  PCRE  has         Matching  characters  by Unicode property is not fast, because PCRE has
3395         to  search  a  structure  that  contains data for over fifteen thousand         to search a structure that contains  data  for  over  fifteen  thousand
3396         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3397         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3398    
3399       Resetting the match start
3400    
3401           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3402           ously  matched  characters  not  to  be  included  in the final matched
3403           sequence. For example, the pattern:
3404    
3405             foo\Kbar
3406    
3407           matches "foobar", but reports that it has matched "bar".  This  feature
3408           is  similar  to  a lookbehind assertion (described below).  However, in
3409           this case, the part of the subject before the real match does not  have
3410           to  be of fixed length, as lookbehind assertions do. The use of \K does
3411           not interfere with the setting of captured  substrings.   For  example,
3412           when the pattern
3413    
3414             (foo)\Kbar
3415    
3416           matches "foobar", the first substring is still set to "foo".
3417    
3418     Simple assertions     Simple assertions
3419    
3420         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 3630  SQUARE BRACKETS AND CHARACTER CLASSES
3630         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,
3631         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
3632         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3633         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
3634         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
3635         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3636         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 3359  VERTICAL BAR Line 3714  VERTICAL BAR
3714  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3715    
3716         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
3717         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED options (which are Perl-compatible) can be  changed  from
3718         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         within  the  pattern  by  a  sequence  of  Perl option letters enclosed
3719         option letters are         between "(?" and ")".  The option letters are
3720    
3721           i  for PCRE_CASELESS           i  for PCRE_CASELESS
3722           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 3375  INTERNAL OPTION SETTING Line 3730  INTERNAL OPTION SETTING
3730         is also permitted. If a  letter  appears  both  before  and  after  the         is also permitted. If a  letter  appears  both  before  and  after  the
3731         hyphen, the option is unset.         hyphen, the option is unset.
3732    
3733           The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
3734           can be changed in the same way as the Perl-compatible options by  using
3735           the characters J, U and X respectively.
3736    
3737         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-
3738         tern parentheses), the change applies to the remainder of  the  pattern         tern parentheses), the change applies to the remainder of  the  pattern
3739         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 3759  INTERNAL OPTION SETTING
3759         the  effects  of option settings happen at compile time. There would be         the  effects  of option settings happen at compile time. There would be
3760         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3761    
3762         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         Note: There are other PCRE-specific options that  can  be  set  by  the
3763         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
3764         the characters J, U and X respectively.         cases the pattern can contain special  leading  sequences  to  override
3765           what  the  application  has set or what has been defaulted. Details are
3766           given in the section entitled "Newline sequences" above.
3767    
3768    
3769  SUBPATTERNS  SUBPATTERNS
# Line 3460  SUBPATTERNS Line 3821  SUBPATTERNS
3821         "Saturday".         "Saturday".
3822    
3823    
3824    DUPLICATE SUBPATTERN NUMBERS
3825    
3826           Perl 5.10 introduced a feature whereby each alternative in a subpattern
3827           uses the same numbers for its capturing parentheses. Such a  subpattern
3828           starts  with (?| and is itself a non-capturing subpattern. For example,
3829           consider this pattern:
3830    
3831             (?|(Sat)ur|(Sun))day
3832    
3833           Because the two alternatives are inside a (?| group, both sets of  cap-
3834           turing  parentheses  are  numbered one. Thus, when the pattern matches,
3835           you can look at captured substring number  one,  whichever  alternative
3836           matched.  This  construct  is useful when you want to capture part, but
3837           not all, of one of a number of alternatives. Inside a (?| group, paren-
3838           theses  are  numbered as usual, but the number is reset at the start of
3839           each branch. The numbers of any capturing buffers that follow the  sub-
3840           pattern  start after the highest number used in any branch. The follow-
3841           ing example is taken from the Perl documentation.  The  numbers  under-
3842           neath show in which buffer the captured content will be stored.
3843    
3844             # before  ---------------branch-reset----------- after
3845             / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3846             # 1            2         2  3        2     3     4
3847    
3848           A  backreference  or  a  recursive call to a numbered subpattern always
3849           refers to the first one in the pattern with the given number.
3850    
3851           An alternative approach to using this "branch reset" feature is to  use
3852           duplicate named subpatterns, as described in the next section.
3853    
3854    
3855  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3856    
3857         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 3891  NAMED SUBPATTERNS
3891           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
3892    
3893         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
3894         match.  The convenience  function  for  extracting  the  data  by  name         match.  (An alternative way of solving this problem is to use a "branch
3895         returns  the  substring  for  the first (and in this example, the only)         reset" subpattern, as described in the previous section.)
3896         subpattern of that name that matched.  This  saves  searching  to  find  
3897         which  numbered  subpattern  it  was. If you make a reference to a non-         The  convenience  function  for extracting the data by name returns the
3898         unique named subpattern from elsewhere in the  pattern,  the  one  that         substring for the first (and in this example, the only)  subpattern  of
3899         corresponds  to  the  lowest number is used. For further details of the         that  name  that  matched.  This saves searching to find which numbered
3900         interfaces for handling named subpatterns, see the  pcreapi  documenta-         subpattern it was. If you make a reference to a non-unique  named  sub-
3901         tion.         pattern  from elsewhere in the pattern, the one that corresponds to the
3902           lowest number is used. For further details of the interfaces  for  han-
3903           dling named subpatterns, see the pcreapi documentation.
3904    
3905    
3906  REPETITION  REPETITION
# Line 3711  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4105  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4105    
4106           \d++foo           \d++foo
4107    
4108         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Note that a possessive quantifier can be used with an entire group, for
4109           example:
4110    
4111             (abc|xyz){2,3}+
4112    
4113           Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4114         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4115         simpler forms of atomic group. However, there is no difference  in  the         simpler  forms  of atomic group. However, there is no difference in the
4116         meaning  of  a  possessive  quantifier and the equivalent atomic group,         meaning of a possessive quantifier and  the  equivalent  atomic  group,
4117         though there may be a performance  difference;  possessive  quantifiers         though  there  may  be a performance difference; possessive quantifiers
4118         should be slightly faster.         should be slightly faster.
4119    
4120         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-
4121         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first         tax.   Jeffrey  Friedl  originated the idea (and the name) in the first
4122         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
4123         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
4124         found its way into Perl at release 5.10.         found its way into Perl at release 5.10.
4125    
4126         PCRE has an optimization that automatically "possessifies" certain sim-         PCRE has an optimization that automatically "possessifies" certain sim-
4127         ple pattern constructs. For example, the sequence  A+B  is  treated  as         ple  pattern  constructs.  For  example, the sequence A+B is treated as
4128         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
4129         when B must follow.         when B must follow.
4130    
4131         When a pattern contains an unlimited repeat inside  a  subpattern  that         When  a  pattern  contains an unlimited repeat inside a subpattern that
4132         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
4133         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
4134         very long time indeed. The pattern         very long time indeed. The pattern
4135    
4136           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
4137    
4138         matches  an  unlimited number of substrings that either consist of non-         matches an unlimited number of substrings that either consist  of  non-
4139         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it
4140         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
4141    
4142           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4143    
4144         it  takes  a  long  time  before reporting failure. This is because the         it takes a long time before reporting  failure.  This  is  because  the
4145         string can be divided between the internal \D+ repeat and the  external         string  can be divided between the internal \D+ repeat and the external
4146         *  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
4147         example uses [!?] rather than a single character at  the  end,  because         example  uses  [!?]  rather than a single character at the end, because
4148         both  PCRE  and  Perl have an optimization that allows for fast failure         both PCRE and Perl have an optimization that allows  for  fast  failure
4149         when a single character is used. They remember the last single  charac-         when  a single character is used. They remember the last single charac-
4150         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
4151         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
4152         group, like this:         group, like this:
4153    
4154           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4155    
4156         sequences  of non-digits cannot be broken, and failure happens quickly.         sequences of non-digits cannot be broken, and failure happens  quickly.
4157    
4158    
4159  BACK REFERENCES  BACK REFERENCES
4160    
4161         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4162         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-
4163         pattern earlier (that is, to its left) in the pattern,  provided  there         pattern  earlier  (that is, to its left) in the pattern, provided there
4164         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4165    
4166         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4167         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
4168         there  are  not that many capturing left parentheses in the entire pat-         there are not that many capturing left parentheses in the  entire  pat-
4169         tern. In other words, the parentheses that are referenced need  not  be         tern.  In  other words, the parentheses that are referenced need not be
4170         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
4171         reference" of this type can make sense when a  repetition  is  involved         reference"  of  this  type can make sense when a repetition is involved
4172         and  the  subpattern to the right has participated in an earlier itera-         and the subpattern to the right has participated in an  earlier  itera-
4173         tion.         tion.
4174    
4175         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
4176         subpattern  whose  number  is  10  or  more using this syntax because a         subpattern whose number is 10 or  more  using  this  syntax  because  a
4177         sequence such as \50 is interpreted as a character  defined  in  octal.         sequence  such  as  \50 is interpreted as a character defined in octal.
4178         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4179         details of the handling of digits following a backslash.  There  is  no         details  of  the  handling of digits following a backslash. There is no
4180         such  problem  when named parentheses are used. A back reference to any         such problem when named parentheses are used. A back reference  to  any
4181         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4182    
4183         Another way of avoiding the ambiguity inherent in  the  use  of  digits         Another  way  of  avoiding  the ambiguity inherent in the use of digits
4184         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-
4185         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
4186         tive  or  a negative number, optionally enclosed in braces. These exam-         unsigned number or a negative number, optionally  enclosed  in  braces.
4187         ples are all identical:         These examples are all identical:
4188    
4189           (ring), \1           (ring), \1
4190           (ring), \g1           (ring), \g1
4191           (ring), \g{1}           (ring), \g{1}
4192    
4193         A positive number specifies an absolute reference without the ambiguity         An  unsigned number specifies an absolute reference without the ambigu-
4194         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
4195         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4196         Consider this example:         Consider this example:
4197    
4198           (abc(def)ghi)\g{-1}           (abc(def)ghi)\g{-1}
4199    
4200         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-
4201         ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,         ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,
4202         \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
4203         helpful in long patterns, and also in  patterns  that  are  created  by         helpful  in  long  patterns,  and  also in patterns that are created by
4204         joining together fragments that contain references within themselves.         joining together fragments that contain references within themselves.
4205    
4206         A  back  reference matches whatever actually matched the capturing sub-         A back reference matches whatever actually matched the  capturing  sub-
4207         pattern in the current subject string, rather  than  anything  matching         pattern  in  the  current subject string, rather than anything matching
4208         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
4209         of doing that). So the pattern         of doing that). So the pattern
4210    
4211           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4212    
4213         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4214         not  "sense and responsibility". If caseful matching is in force at the         not "sense and responsibility". If caseful matching is in force at  the
4215         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-
4216         ple,         ple,
4217    
4218           ((?i)rah)\s+\1           ((?i)rah)\s+\1
4219    
4220         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
4221         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4222    
4223         Back references to named subpatterns use the Perl  syntax  \k<name>  or         There  are  several  different ways of writing back references to named
4224         \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
4225         example in either of the following ways:         \k'name'  are supported, as is the Python syntax (?P=name). Perl 5.10's
4226           unified back reference syntax, in which \g can be used for both numeric
4227           and  named  references,  is  also supported. We could rewrite the above
4228           example in any of the following ways:
4229    
4230           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
4231             (?'p1'(?i)rah)\s+\k{p1}
4232           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4233             (?<p1>(?i)rah)\s+\g{p1}
4234    
4235         A subpattern that is referenced by  name  may  appear  in  the  pattern         A subpattern that is referenced by  name  may  appear  in  the  pattern
4236         before or after the reference.         before or after the reference.
# Line 3941  ASSERTIONS Line 4345  ASSERTIONS
4345    
4346           (?<=abc|abde)           (?<=abc|abde)
4347    
4348           In some cases, the Perl 5.10 escape sequence \K (see above) can be used
4349           instead  of  a lookbehind assertion; this is not restricted to a fixed-
4350           length.
4351    
4352         The implementation of lookbehind assertions is, for  each  alternative,         The implementation of lookbehind assertions is, for  each  alternative,
4353         to  temporarily  move the current position back by the fixed length and         to  temporarily  move the current position back by the fixed length and
4354         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 4442  CONDITIONAL SUBPATTERNS
4442    
4443         If  the  text between the parentheses consists of a sequence of digits,         If  the  text between the parentheses consists of a sequence of digits,
4444         the condition is true if the capturing subpattern of  that  number  has         the condition is true if the capturing subpattern of  that  number  has
4445         previously matched.         previously  matched.  An  alternative notation is to precede the digits
4446           with a plus or minus sign. In this case, the subpattern number is rela-
4447           tive rather than absolute.  The most recently opened parentheses can be
4448           referenced by (?(-1), the next most recent by (?(-2),  and  so  on.  In
4449           looping constructs it can also make sense to refer to subsequent groups
4450           with constructs such as (?(+2).
4451    
4452         Consider  the  following  pattern, which contains non-significant white         Consider the following pattern, which  contains  non-significant  white
4453         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
4454         divide it into three parts for ease of discussion:         divide it into three parts for ease of discussion:
4455    
4456           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4457    
4458         The  first  part  matches  an optional opening parenthesis, and if that         The first part matches an optional opening  parenthesis,  and  if  that
4459         character is present, sets it as the first captured substring. The sec-         character is present, sets it as the first captured substring. The sec-
4460         ond  part  matches one or more characters that are not parentheses. The         ond part matches one or more characters that are not  parentheses.  The
4461         third part is a conditional subpattern that tests whether the first set         third part is a conditional subpattern that tests whether the first set
4462         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
4463         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-
4464         tern  is  executed  and  a  closing parenthesis is required. Otherwise,         tern is executed and a  closing  parenthesis  is  required.  Otherwise,
4465         since no-pattern is not present, the  subpattern  matches  nothing.  In         since  no-pattern  is  not  present, the subpattern matches nothing. In
4466         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other words,  this  pattern  matches  a  sequence  of  non-parentheses,
4467         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4468    
4469           If  you  were  embedding  this pattern in a larger one, you could use a
4470           relative reference:
4471    
4472             ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4473    
4474           This makes the fragment independent of the parentheses  in  the  larger
4475           pattern.
4476    
4477     Checking for a used subpattern by name     Checking for a used subpattern by name
4478    
4479         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a         Perl  uses  the  syntax  (?(<name>)...) or (?('name')...) to test for a
4480         used  subpattern  by  name.  For compatibility with earlier versions of         used subpattern by name. For compatibility  with  earlier  versions  of
4481         PCRE, which had this facility before Perl, the syntax  (?(name)...)  is         PCRE,  which  had this facility before Perl, the syntax (?(name)...) is
4482         also  recognized. However, there is a possible ambiguity with this syn-         also recognized. However, there is a possible ambiguity with this  syn-
4483         tax, because subpattern names may  consist  entirely  of  digits.  PCRE         tax,  because  subpattern  names  may  consist entirely of digits. PCRE
4484         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
4485         consists entirely of digits, PCRE looks for a subpattern of  that  num-         consists  entirely  of digits, PCRE looks for a subpattern of that num-
4486         ber,  which must be greater than zero. Using subpattern names that con-         ber, which must be greater than zero. Using subpattern names that  con-
4487         sist entirely of digits is not recommended.         sist entirely of digits is not recommended.
4488    
4489         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 4494  CONDITIONAL SUBPATTERNS
4494     Checking for pattern recursion     Checking for pattern recursion
4495    
4496         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
4497         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
4498         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-
4499         sand follow the letter R, for example:         sand follow the letter R, for example:
4500    
4501           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4502    
4503         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-
4504         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
4505         entire recursion stack.         entire recursion stack.
4506    
4507         At  "top  level", all these recursion test conditions are false. Recur-         At "top level", all these recursion test conditions are  false.  Recur-
4508         sive patterns are described below.         sive patterns are described below.
4509    
4510     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4511    
4512         If the condition is the string (DEFINE), and  there  is  no  subpattern         If  the  condition  is  the string (DEFINE), and there is no subpattern
4513         with  the  name  DEFINE,  the  condition is always false. In this case,         with the name DEFINE, the condition is  always  false.  In  this  case,
4514         there may be only one alternative  in  the  subpattern.  It  is  always         there  may  be  only  one  alternative  in the subpattern. It is always
4515         skipped  if  control  reaches  this  point  in the pattern; the idea of         skipped if control reaches this point  in  the  pattern;  the  idea  of
4516         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-
4517         erenced  from elsewhere. (The use of "subroutines" is described below.)         erenced from elsewhere. (The use of "subroutines" is described  below.)
4518         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
4519         this (ignore whitespace and line breaks):         this (ignore whitespace and line breaks):
4520    
4521           (?(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) )
4522           \b (?&byte) (\.(?&byte)){3} \b           \b (?&byte) (\.(?&byte)){3} \b
4523    
4524         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
4525         group named "byte" is defined. This matches an individual component  of         group  named "byte" is defined. This matches an individual component of
4526         an  IPv4  address  (a number less than 256). When matching takes place,         an IPv4 address (a number less than 256). When  matching  takes  place,
4527         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
4528         condition.         condition.
4529    
4530         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
4531         four dot-separated components of an IPv4 address, insisting on  a  word         four  dot-separated  components of an IPv4 address, insisting on a word
4532         boundary at each end.         boundary at each end.
4533    
4534     Assertion conditions     Assertion conditions
4535    
4536         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
4537         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.   This may be a positive or negative lookahead or lookbehind
4538         assertion.  Consider  this  pattern,  again  containing non-significant         assertion. Consider  this  pattern,  again  containing  non-significant
4539         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
4540    
4541           (?(?=[^a-z]*[a-z])           (?(?=[^a-z]*[a-z])
4542           \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} )
4543    
4544         The condition  is  a  positive  lookahead  assertion  that  matches  an         The  condition  is  a  positive  lookahead  assertion  that  matches an
4545         optional  sequence of non-letters followed by a letter. In other words,         optional sequence of non-letters followed by a letter. In other  words,
4546         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
4547         letter  is found, the subject is matched against the first alternative;         letter is found, the subject is matched against the first  alternative;
4548         otherwise it is  matched  against  the  second.  This  pattern  matches         otherwise  it  is  matched  against  the  second.  This pattern matches
4549         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
4550         letters and dd are digits.         letters and dd are digits.
4551    
4552    
4553  COMMENTS  COMMENTS
4554    
4555         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
4556         next  closing  parenthesis.  Nested  parentheses are not permitted. The         next closing parenthesis. Nested parentheses  are  not  permitted.  The
4557         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
4558         at all.         at all.
4559    
4560         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If the PCRE_EXTENDED option is set, an unescaped # character outside  a
4561         character class introduces a  comment  that  continues  to  immediately         character  class  introduces  a  comment  that continues to immediately
4562         after the next newline in the pattern.         after the next newline in the pattern.
4563    
4564    
4565  RECURSIVE PATTERNS  RECURSIVE PATTERNS
4566    
4567         Consider  the problem of matching a string in parentheses, allowing for         Consider the problem of matching a string in parentheses, allowing  for
4568         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited  nested  parentheses.  Without the use of recursion, the best
4569         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
4570         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth  of  nesting.  It  is not possible to handle an arbitrary nesting
4571         depth.         depth.
4572    
4573         For some time, Perl has provided a facility that allows regular expres-         For some time, Perl has provided a facility that allows regular expres-
4574         sions to recurse (amongst other things). It does this by  interpolating         sions  to recurse (amongst other things). It does this by interpolating
4575         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
4576         expression itself. A Perl pattern using code interpolation to solve the         expression itself. A Perl pattern using code interpolation to solve the
4577         parentheses problem can be created like this:         parentheses problem can be created like this:
4578    
# Line 4161  RECURSIVE PATTERNS Line 4582  RECURSIVE PATTERNS
4582         refers recursively to the pattern in which it appears.         refers recursively to the pattern in which it appears.
4583    
4584         Obviously, PCRE cannot support the interpolation of Perl code. Instead,         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4585         it  supports  special  syntax  for recursion of the entire pattern, and         it supports special syntax for recursion of  the  entire  pattern,  and
4586         also for individual subpattern recursion.  After  its  introduction  in         also  for  individual  subpattern  recursion. After its introduction in
4587         PCRE  and  Python,  this  kind of recursion was introduced into Perl at         PCRE and Python, this kind of recursion was  introduced  into  Perl  at
4588         release 5.10.         release 5.10.
4589    
4590         A special item that consists of (? followed by a  number  greater  than         A  special  item  that consists of (? followed by a number greater than
4591         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
4592         the given number, provided that it occurs inside that  subpattern.  (If         the  given  number, provided that it occurs inside that subpattern. (If
4593         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-
4594         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
4595         regular expression.         regular expression.
4596    
4597         In  PCRE (like Python, but unlike Perl), a recursive subpattern call is         In PCRE (like Python, but unlike Perl), a recursive subpattern call  is
4598         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
4599         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
4600         alternatives and there is a subsequent matching failure.         alternatives and there is a subsequent matching failure.
4601    
4602         This PCRE pattern solves the nested  parentheses  problem  (assume  the         This  PCRE  pattern  solves  the nested parentheses problem (assume the
4603         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4604    
4605           \( ( (?>[^()]+) | (?R) )* \)           \( ( (?>[^()]+) | (?R) )* \)
4606    
4607         First  it matches an opening parenthesis. Then it matches any number of         First it matches an opening parenthesis. Then it matches any number  of
4608         substrings which can either be a  sequence  of  non-parentheses,  or  a         substrings  which  can  either  be  a sequence of non-parentheses, or a
4609         recursive  match  of the pattern itself (that is, a correctly parenthe-         recursive match of the pattern itself (that is, a  correctly  parenthe-
4610         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis.
4611    
4612         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
4613         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4614    
4615           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( (?>[^()]+) | (?1) )* \) )
4616    
4617         We  have  put the pattern into parentheses, and caused the recursion to         We have put the pattern into parentheses, and caused the  recursion  to
4618         refer to them instead of the whole pattern. In a larger pattern,  keep-         refer to them instead of the whole pattern.
4619         ing  track  of parenthesis numbers can be tricky. It may be more conve-  
4620         nient to use named parentheses instead. The Perl  syntax  for  this  is         In  a  larger  pattern,  keeping  track  of  parenthesis numbers can be
4621         (?&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
4622         rewrite the above example as follows:         5.10  feature.)   Instead  of  (?1)  in the pattern above you can write
4623           (?-2) to refer to the second most recently opened parentheses preceding
4624           the  recursion.  In  other  words,  a  negative number counts capturing
4625           parentheses leftwards from the point at which it is encountered.
4626    
4627           It is also possible to refer to  subsequently  opened  parentheses,  by
4628           writing  references  such  as (?+2). However, these cannot be recursive
4629           because the reference is not inside the  parentheses  that  are  refer-
4630           enced.  They  are  always  "subroutine" calls, as described in the next
4631           section.
4632    
4633           An alternative approach is to use named parentheses instead.  The  Perl
4634           syntax  for  this  is (?&name); PCRE's earlier syntax (?P>name) is also
4635           supported. We could rewrite the above example as follows:
4636    
4637           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
4638    
4639         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
4640         one  is used. This particular example pattern contains nested unlimited         one is used.
4641         repeats, and so the use of atomic grouping for matching strings of non-  
4642         parentheses  is  important when applying the pattern to strings that do         This  particular  example pattern that we have been looking at contains
4643         not match. For example, when this pattern is applied to         nested unlimited repeats, and so the use of atomic grouping for  match-
4644           ing  strings  of non-parentheses is important when applying the pattern
4645           to strings that do not match. For example, when this pattern is applied
4646           to
4647    
4648           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
4649    
4650         it yields "no match" quickly. However, if atomic grouping is not  used,         it  yields "no match" quickly. However, if atomic grouping is not used,
4651         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
4652         different ways the + and * repeats can carve up the  subject,  and  all         different  ways  the  + and * repeats can carve up the subject, and all
4653         have to be tested before failure can be reported.         have to be tested before failure can be reported.
4654    
4655         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
4656         those from the outermost level of the recursion at which the subpattern         those from the outermost level of the recursion at which the subpattern
4657         value  is  set.   If  you want to obtain intermediate values, a callout         value is set.  If you want to obtain  intermediate  values,  a  callout
4658         function can be used (see below and the pcrecallout documentation).  If         function  can be used (see below and the pcrecallout documentation). If
4659         the pattern above is matched against         the pattern above is matched against
4660    
4661           (ab(cd)ef)           (ab(cd)ef)
4662    
4663         the  value  for  the  capturing  parentheses is "ef", which is the last         the value for the capturing parentheses is  "ef",  which  is  the  last
4664         value taken on at the top level. If additional parentheses  are  added,         value  taken  on at the top level. If additional parentheses are added,
4665         giving         giving
4666    
4667           \( ( ( (?>[^()]+) | (?R) )* ) \)           \( ( ( (?>[^()]+) | (?R) )* ) \)
4668              ^                        ^              ^                        ^
4669              ^                        ^              ^                        ^
4670    
4671         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
4672         parentheses. If there are more than 15 capturing parentheses in a  pat-         parentheses.  If there are more than 15 capturing parentheses in a pat-
4673         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,
4674         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-
4675         wards.  If  no  memory  can  be  obtained,  the  match  fails  with the         wards. If  no  memory  can  be  obtained,  the  match  fails  with  the
4676         PCRE_ERROR_NOMEMORY error.         PCRE_ERROR_NOMEMORY error.
4677    
4678         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
4679         recursion.   Consider  this pattern, which matches text in angle brack-         recursion.  Consider this pattern, which matches text in  angle  brack-
4680         ets, allowing for arbitrary nesting. Only digits are allowed in  nested         ets,  allowing for arbitrary nesting. Only digits are allowed in nested
4681         brackets  (that is, when recursing), whereas any characters are permit-         brackets (that is, when recursing), whereas any characters are  permit-
4682         ted at the outer level.         ted at the outer level.
4683    
4684           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >
4685    
4686         In this pattern, (?(R) is the start of a conditional  subpattern,  with         In  this  pattern, (?(R) is the start of a conditional subpattern, with
4687         two  different  alternatives for the recursive and non-recursive cases.         two different alternatives for the recursive and  non-recursive  cases.
4688         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
4689    
4690    
4691  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
4692    
4693         If the syntax for a recursive subpattern reference (either by number or         If the syntax for a recursive subpattern reference (either by number or
4694         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-
4695         ates like a subroutine in a programming language. The "called"  subpat-         ates  like a subroutine in a programming language. The "called" subpat-
4696         tern  may  be defined before or after the reference. An earlier example         tern may be defined before or after the reference. A numbered reference
4697         pointed out that the pattern         can be absolute or relative, as in these examples:
4698    
4699             (...(absolute)...)...(?2)...
4700             (...(relative)...)...(?-1)...
4701             (...(?+1)...(relative)...
4702    
4703           An earlier example pointed out that the pattern
4704    
4705           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4706    
4707         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4708         not "sense and responsibility". If instead the pattern         not "sense and responsibility". If instead the pattern
4709    
4710           (sens|respons)e and (?1)ibility           (sens|respons)e and (?1)ibility
4711    
4712         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
4713         two strings. Another example is  given  in  the  discussion  of  DEFINE         two  strings.  Another  example  is  given  in the discussion of DEFINE
4714         above.         above.
4715    
4716         Like recursive subpatterns, a "subroutine" call is always treated as an         Like recursive subpatterns, a "subroutine" call is always treated as an
4717         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,
4718         it  is  never  re-entered, even if it contains untried alternatives and         it is never re-entered, even if it contains  untried  alternatives  and
4719         there is a subsequent matching failure.         there is a subsequent matching failure.
4720    
4721         When a subpattern is used as a subroutine, processing options  such  as         When  a  subpattern is used as a subroutine, processing options such as
4722         case-independence are fixed when the subpattern is defined. They cannot         case-independence are fixed when the subpattern is defined. They cannot
4723         be changed for different calls. For example, consider this pattern:         be changed for different calls. For example, consider this pattern:
4724    
4725           (abc)(?i:(?1))           (abc)(?i:(?-1))
4726    
4727         It matches "abcabc". It does not match "abcABC" because the  change  of         It  matches  "abcabc". It does not match "abcABC" because the change of
4728         processing option does not affect the called subpattern.         processing option does not affect the called subpattern.
4729    
4730    
4731  CALLOUTS  CALLOUTS
4732    
4733         Perl has a feature whereby using the sequence (?{...}) causes arbitrary         Perl has a feature whereby using the sequence (?{...}) causes arbitrary
4734         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.
4735         This makes it possible, amongst other things, to extract different sub-         This makes it possible, amongst other things, to extract different sub-
4736         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-
4737         tion.         tion.
4738    
4739         PCRE provides a similar feature, but of course it cannot obey arbitrary         PCRE provides a similar feature, but of course it cannot obey arbitrary
4740         Perl code. The feature is called "callout". The caller of PCRE provides         Perl code. The feature is called "callout". The caller of PCRE provides
4741         an  external function by putting its entry point in the global variable         an external function by putting its entry point in the global  variable
4742         pcre_callout.  By default, this variable contains NULL, which  disables         pcre_callout.   By default, this variable contains NULL, which disables
4743         all calling out.         all calling out.
4744    
4745         Within  a  regular  expression,  (?C) indicates the points at which the         Within a regular expression, (?C) indicates the  points  at  which  the
4746         external function is to be called. If you want  to  identify  different         external  function  is  to be called. If you want to identify different
4747         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.
4748         The default value is zero.  For example, this pattern has  two  callout         The  default  value is zero.  For example, this pattern has two callout
4749         points:         points:
4750    
4751           (?C1)abc(?C2)def           (?C1)abc(?C2)def
4752    
4753         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
4754         automatically installed before each item in the pattern. They  are  all         automatically  installed  before each item in the pattern. They are all
4755         numbered 255.         numbered 255.
4756    
4757         During matching, when PCRE reaches a callout point (and pcre_callout is         During matching, when PCRE reaches a callout point (and pcre_callout is
4758         set), the external function is called. It is provided with  the  number         set),  the  external function is called. It is provided with the number
4759         of  the callout, the position in the pattern, and, optionally, one item         of the callout, the position in the pattern, and, optionally, one  item
4760         of data originally supplied by the caller of pcre_exec().  The  callout         of  data  originally supplied by the caller of pcre_exec(). The callout
4761         function  may cause matching to proceed, to backtrack, or to fail alto-         function may cause matching to proceed, to backtrack, or to fail  alto-
4762         gether. A complete description of the interface to the callout function         gether. A complete description of the interface to the callout function
4763         is given in the pcrecallout documentation.         is given in the pcrecallout documentation.
4764    
4765    
4766    BACKTRACKING CONTROL
4767    
4768           Perl 5.10 introduced a number of "Special Backtracking Control  Verbs",
4769           which are described in the Perl documentation as "experimental and sub-
4770           ject to change or removal in a future version of Perl". It goes  on  to
4771           say:  "Their usage in production code should be noted to avoid problems
4772           during upgrades." The same remarks apply to the PCRE features described
4773           in this section.
4774    
4775           Since these verbs are specifically related to backtracking, they can be
4776           used only when the pattern is to be matched  using  pcre_exec(),  which
4777           uses  a  backtracking  algorithm. They cause an error if encountered by
4778           pcre_dfa_exec().
4779    
4780           The new verbs make use of what was previously invalid syntax: an  open-
4781           ing parenthesis followed by an asterisk. In Perl, they are generally of
4782           the form (*VERB:ARG) but PCRE does not support the use of arguments, so
4783           its  general  form is just (*VERB). Any number of these verbs may occur
4784           in a pattern. There are two kinds:
4785    
4786       Verbs that act immediately
4787    
4788           The following verbs act as soon as they are encountered:
4789    
4790              (*ACCEPT)
4791    
4792           This verb causes the match to end successfully, skipping the  remainder
4793           of  the pattern. When inside a recursion, only the innermost pattern is
4794           ended immediately. PCRE differs  from  Perl  in  what  happens  if  the
4795           (*ACCEPT)  is inside capturing parentheses. In Perl, the data so far is
4796           captured: in PCRE no data is captured. For example:
4797    
4798             A(A|B(*ACCEPT)|C)D
4799    
4800           This matches "AB", "AAD", or "ACD", but when it matches "AB",  no  data
4801           is captured.
4802    
4803             (*FAIL) or (*F)
4804    
4805           This  verb  causes the match to fail, forcing backtracking to occur. It
4806           is equivalent to (?!) but easier to read. The Perl documentation  notes
4807           that  it  is  probably  useful only when combined with (?{}) or (??{}).
4808           Those are, of course, Perl features that are not present in  PCRE.  The
4809           nearest  equivalent is the callout feature, as for example in this pat-
4810           tern:
4811    
4812             a+(?C)(*FAIL)
4813    
4814           A match with the string "aaaa" always fails, but the callout  is  taken
4815           before each backtrack happens (in this example, 10 times).
4816    
4817       Verbs that act after backtracking
4818    
4819           The following verbs do nothing when they are encountered. Matching con-
4820           tinues with what follows, but if there is no subsequent match, a  fail-
4821           ure  is  forced.   The  verbs  differ  in  exactly what kind of failure
4822           occurs.
4823    
4824             (*COMMIT)
4825    
4826           This verb causes the whole match to fail outright if the  rest  of  the
4827           pattern  does  not match. Even if the pattern is unanchored, no further
4828           attempts to find a match by advancing the start point take place.  Once
4829           (*COMMIT)  has been passed, pcre_exec() is committed to finding a match
4830           at the current starting point, or not at all. For example:
4831    
4832             a+(*COMMIT)b
4833    
4834           This matches "xxaab" but not "aacaab". It can be thought of as  a  kind
4835           of dynamic anchor, or "I've started, so I must finish."
4836    
4837             (*PRUNE)
4838    
4839           This  verb causes the match to fail at the current position if the rest
4840           of the pattern does not match. If the pattern is unanchored, the normal
4841           "bumpalong"  advance to the next starting character then happens. Back-
4842           tracking can occur as usual to the left of (*PRUNE), or  when  matching
4843           to  the right of (*PRUNE), but if there is no match to the right, back-
4844           tracking cannot cross (*PRUNE).  In simple cases, the use  of  (*PRUNE)
4845           is just an alternative to an atomic group or possessive quantifier, but
4846           there are some uses of (*PRUNE) that cannot be expressed in  any  other
4847           way.
4848    
4849             (*SKIP)
4850    
4851           This  verb  is like (*PRUNE), except that if the pattern is unanchored,
4852           the "bumpalong" advance is not to the next character, but to the  posi-
4853           tion  in  the  subject where (*SKIP) was encountered. (*SKIP) signifies
4854           that whatever text was matched leading up to it cannot  be  part  of  a
4855           successful match. Consider:
4856    
4857             a+(*SKIP)b
4858    
4859           If  the  subject  is  "aaaac...",  after  the first match attempt fails
4860           (starting at the first character in the  string),  the  starting  point
4861           skips on to start the next attempt at "c". Note that a possessive quan-
4862           tifer does not have the same effect in this example; although it  would
4863           suppress  backtracking  during  the  first  match  attempt,  the second
4864           attempt would start at the second character instead of skipping  on  to
4865           "c".
4866    
4867             (*THEN)
4868    
4869           This verb causes a skip to the next alternation if the rest of the pat-
4870           tern does not match. That is, it cancels pending backtracking, but only
4871           within  the  current  alternation.  Its name comes from the observation
4872           that it can be used for a pattern-based if-then-else block:
4873    
4874             ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
4875    
4876           If the COND1 pattern matches, FOO is tried (and possibly further  items
4877           after  the  end  of  the group if FOO succeeds); on failure the matcher
4878           skips to the second alternative and tries COND2,  without  backtracking
4879           into  COND1.  If  (*THEN)  is  used outside of any alternation, it acts
4880           exactly like (*PRUNE).
4881    
4882    
4883  SEE ALSO  SEE ALSO
4884    
4885         pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).         pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).
# Line 4334  AUTHOR Line 4894  AUTHOR
4894    
4895  REVISION  REVISION
4896    
4897         Last updated: 06 March 2007         Last updated: 17 September 2007
4898           Copyright (c) 1997-2007 University of Cambridge.
4899    ------------------------------------------------------------------------------
4900    
4901    
4902    PCRESYNTAX(3)                                                    PCRESYNTAX(3)
4903    
4904    
4905    NAME
4906           PCRE - Perl-compatible regular expressions
4907    
4908    
4909    PCRE REGULAR EXPRESSION SYNTAX SUMMARY
4910    
4911           The  full syntax and semantics of the regular expressions that are sup-
4912           ported by PCRE are described in  the  pcrepattern  documentation.  This
4913           document contains just a quick-reference summary of the syntax.
4914    
4915    
4916    QUOTING
4917    
4918             \x         where x is non-alphanumeric is a literal x
4919             \Q...\E    treat enclosed characters as literal
4920    
4921    
4922    CHARACTERS
4923    
4924             \a         alarm, that is, the BEL character (hex 07)
4925             \cx        "control-x", where x is any character
4926             \e         escape (hex 1B)
4927             \f         formfeed (hex 0C)
4928             \n         newline (hex 0A)
4929             \r         carriage return (hex 0D)
4930             \t         tab (hex 09)
4931             \ddd       character with octal code ddd, or backreference
4932             \xhh       character with hex code hh
4933             \x{hhh..}  character with hex code hhh..
4934    
4935    
4936    CHARACTER TYPES
4937    
4938             .          any character except newline;
4939                          in dotall mode, any character whatsoever
4940             \C         one byte, even in UTF-8 mode (best avoided)
4941             \d         a decimal digit
4942             \D         a character that is not a decimal digit
4943             \h         a horizontal whitespace character
4944             \H         a character that is not a horizontal whitespace character
4945             \p{xx}     a character with the xx property
4946             \P{xx}     a character without the xx property
4947             \R         a newline sequence
4948             \s         a whitespace character
4949             \S         a character that is not a whitespace character
4950             \v         a vertical whitespace character
4951             \V         a character that is not a vertical whitespace character
4952             \w         a "word" character
4953             \W         a "non-word" character
4954             \X         an extended Unicode sequence
4955    
4956           In PCRE, \d, \D, \s, \S, \w, and \W recognize only ASCII characters.
4957    
4958    
4959    GENERAL CATEGORY PROPERTY CODES FOR \p and \P
4960    
4961             C          Other
4962             Cc         Control
4963             Cf         Format
4964             Cn         Unassigned
4965             Co         Private use
4966             Cs         Surrogate
4967    
4968             L          Letter
4969             Ll         Lower case letter
4970             Lm         Modifier letter
4971             Lo         Other letter
4972             Lt         Title case letter
4973             Lu         Upper case letter
4974             L&         Ll, Lu, or Lt
4975    
4976             M          Mark
4977             Mc         Spacing mark
4978             Me         Enclosing mark
4979             Mn         Non-spacing mark
4980    
4981             N          Number
4982             Nd         Decimal number
4983             Nl         Letter number
4984             No         Other number
4985    
4986             P          Punctuation
4987             Pc         Connector punctuation
4988             Pd         Dash punctuation
4989             Pe         Close punctuation
4990             Pf         Final punctuation
4991             Pi         Initial punctuation
4992             Po         Other punctuation
4993             Ps         Open punctuation
4994    
4995             S          Symbol
4996             Sc         Currency symbol
4997             Sk         Modifier symbol
4998             Sm         Mathematical symbol
4999             So         Other symbol
5000    
5001             Z          Separator
5002             Zl         Line separator
5003             Zp         Paragraph separator
5004             Zs         Space separator
5005    
5006    
5007    SCRIPT NAMES FOR \p AND \P
5008    
5009           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
5010           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
5011           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
5012           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
5013           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
5014           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
5015           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
5016           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
5017           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
5018    
5019    
5020    CHARACTER CLASSES
5021    
5022             [...]       positive character class
5023             [^...]      negative character class
5024             [x-y]       range (can be used for hex characters)
5025             [[:xxx:]]   positive POSIX named set
5026             [[:^xxx:]]  negative POSIX named set
5027    
5028             alnum       alphanumeric
5029             alpha       alphabetic
5030             ascii       0-127
5031             blank       space or tab
5032             cntrl       control character
5033             digit       decimal digit
5034             graph       printing, excluding space
5035             lower       lower case letter
5036             print       printing, including space
5037             punct       printing, excluding alphanumeric
5038             space       whitespace
5039             upper       upper case letter
5040             word        same as \w
5041             xdigit      hexadecimal digit
5042    
5043           In PCRE, POSIX character set names recognize only ASCII characters. You
5044           can use \Q...\E inside a character class.
5045    
5046    
5047    QUANTIFIERS
5048    
5049             ?           0 or 1, greedy
5050             ?+          0 or 1, possessive
5051             ??          0 or 1, lazy
5052             *           0 or more, greedy
5053             *+          0 or more, possessive
5054             *?          0 or more, lazy
5055             +           1 or more, greedy
5056             ++          1 or more, possessive
5057             +?          1 or more, lazy
5058             {n}         exactly n
5059             {n,m}       at least n, no more than m, greedy
5060             {n,m}+      at least n, no more than m, possessive
5061             {n,m}?      at least n, no more than m, lazy
5062             {n,}        n or more, greedy
5063             {n,}+       n or more, possessive
5064             {n,}?       n or more, lazy
5065    
5066    
5067    ANCHORS AND SIMPLE ASSERTIONS
5068    
5069             \b          word boundary
5070             \B          not a word boundary
5071             ^           start of subject
5072                          also after internal newline in multiline mode
5073             \A          start of subject
5074             $           end of subject
5075