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# Line 18  INTRODUCTION Line 18  INTRODUCTION
18    
19         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
20         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
21         just  a  few differences. (Certain features that appeared in Python and         just  a  few  differences. Certain features that appeared in Python and
22         PCRE before they appeared in Perl are also available using  the  Python         PCRE before they appeared in Perl are also available using  the  Python
23         syntax.)         syntax.  There is also some support for certain .NET and Oniguruma syn-
24           tax items, and there is an option for  requesting  some  minor  changes
25           that give better JavaScript compatibility.
26    
27         The  current  implementation of PCRE (release 7.x) corresponds approxi-         The  current  implementation of PCRE (release 7.x) corresponds approxi-
28         mately with Perl 5.10, including support for UTF-8 encoded strings  and         mately with Perl 5.10, including support for UTF-8 encoded strings  and
# Line 45  INTRODUCTION Line 47  INTRODUCTION
47    
48         Details of exactly which Perl regular expression features are  and  are         Details of exactly which Perl regular expression features are  and  are
49         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
50         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
51           page.
52    
53         Some features of PCRE can be included, excluded, or  changed  when  the         Some  features  of  PCRE can be included, excluded, or changed when the
54         library  is  built.  The pcre_config() function makes it possible for a         library is built. The pcre_config() function makes it  possible  for  a
55         client to discover which features are  available.  The  features  them-         client  to  discover  which  features are available. The features them-
56         selves  are described in the pcrebuild page. Documentation about build-         selves are described in the pcrebuild page. Documentation about  build-
57         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
58         in the source distribution.         in the source distribution.
59    
60         The  library  contains  a number of undocumented internal functions and         The library contains a number of undocumented  internal  functions  and
61         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
62         functions,  but  which  are  not  intended for use by external callers.         functions, but which are not intended  for  use  by  external  callers.
63         Their names all begin with "_pcre_", which hopefully will  not  provoke         Their  names  all begin with "_pcre_", which hopefully will not provoke
64         any name clashes. In some environments, it is possible to control which         any name clashes. In some environments, it is possible to control which
65         external symbols are exported when a shared library is  built,  and  in         external  symbols  are  exported when a shared library is built, and in
66         these cases the undocumented symbols are not exported.         these cases the undocumented symbols are not exported.
67    
68    
69  USER DOCUMENTATION  USER DOCUMENTATION
70    
71         The  user  documentation  for PCRE comprises a number of different sec-         The user documentation for PCRE comprises a number  of  different  sec-
72         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
73         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.
74         In the plain text format, all the sections are concatenated,  for  ease         In  the  plain text format, all the sections are concatenated, for ease
75         of searching. The sections are as follows:         of searching. The sections are as follows:
76    
77           pcre              this document           pcre              this document
78             pcre-config       show PCRE installation configuration information
79           pcreapi           details of PCRE's native C API           pcreapi           details of PCRE's native C API
80           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
81           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
# Line 82  USER DOCUMENTATION Line 86  USER DOCUMENTATION
86           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
87           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
88                               regular expressions                               regular expressions
89             pcresyntax        quick syntax reference
90           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
91           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
92           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
# Line 89  USER DOCUMENTATION Line 94  USER DOCUMENTATION
94           pcrestack         discussion of stack usage           pcrestack         discussion of stack usage
95           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
96    
97         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
98         each C library function, listing its arguments and results.         each C library function, listing its arguments and results.
99    
100    
101  LIMITATIONS  LIMITATIONS
102    
103         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
104         never in practice be relevant.         never in practice be relevant.
105    
106         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
107         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
108         process regular expressions that are truly enormous,  you  can  compile         process  regular  expressions  that are truly enormous, you can compile
109         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
110         the source distribution and the pcrebuild documentation  for  details).         the  source  distribution and the pcrebuild documentation for details).
111         In  these  cases the limit is substantially larger.  However, the speed         In these cases the limit is substantially larger.  However,  the  speed
112         of execution is slower.         of execution is slower.
113    
114         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.  
115    
116         There is no limit to the number of parenthesized subpatterns, but there         There is no limit to the number of parenthesized subpatterns, but there
117         can be no more than 65535 capturing subpatterns.         can be no more than 65535 capturing subpatterns.
# Line 116  LIMITATIONS Line 119  LIMITATIONS
119         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
120         the maximum number of named subpatterns is 10000.         the maximum number of named subpatterns is 10000.
121    
122         The maximum length of a subject string is the largest  positive  number         The  maximum  length of a subject string is the largest positive number
123         that  an integer variable can hold. However, when using the traditional         that an integer variable can hold. However, when using the  traditional
124         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
125         inite  repetition.  This means that the available stack space may limit         inite repetition.  This means that the available stack space may  limit
126         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.
127         For a discussion of stack issues, see the pcrestack documentation.         For a discussion of stack issues, see the pcrestack documentation.
128    
129    
130  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
131    
132         From  release  3.3,  PCRE  has  had  some support for character strings         From release 3.3, PCRE has  had  some  support  for  character  strings
133         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
134         to  cover  most common requirements, and in release 5.0 additional sup-         to cover most common requirements, and in release 5.0  additional  sup-
135         port for Unicode general category properties was added.         port for Unicode general category properties was added.
136    
137         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
138         support  in  the  code,  and, in addition, you must call pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
139         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
140         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
141         strings instead of just strings of bytes.         strings instead of just strings of bytes.
142    
143         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,
144         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
145         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
146         very big.         very big.
147    
148         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
149         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
150         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
151         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
152         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,
153         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
154         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
155         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-
156         ter},  is  not  supported.   Furthermore,  in Perl, many properties may         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
157         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
158         does not support this.         does not support this.
159    
160         The following comments apply when PCRE is running in UTF-8 mode:     Validity of UTF-8 strings
161    
162           When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
163           subjects are (by default) checked for validity on entry to the relevant
164           functions. From release 7.3 of PCRE, the check is according  the  rules
165           of  RFC  3629, which are themselves derived from the Unicode specifica-
166           tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
167           allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
168           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
169           to U+DFFF.
170    
171           The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
172           which the Unicode Standard says this: "The Low Surrogate Area does  not
173           contain  any  character  assignments,  consequently  no  character code
174           charts or namelists are provided for this area. Surrogates are reserved
175           for  use  with  UTF-16 and then must be used in pairs." The code points
176           that are encoded by UTF-16 pairs  are  available  as  independent  code
177           points  in  the  UTF-8  encoding.  (In other words, the whole surrogate
178           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
179    
180           If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return
181           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
182           that your strings are valid, and therefore want to skip these checks in
183           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
184           compile time or at run time, PCRE assumes that the pattern  or  subject
185           it  is  given  (respectively)  contains only valid UTF-8 codes. In this
186           case, it does not diagnose an invalid UTF-8 string.
187    
188           If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,
189           what  happens  depends on why the string is invalid. If the string con-
190           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
191           string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,
192           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
193           strings  according  to  the more liberal rules of RFC 2279. However, if
194           the string does not even conform to RFC 2279, the result is  undefined.
195           Your program may crash.
196    
197           If  you  want  to  process  strings  of  values  in the full range 0 to
198           0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can
199           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
200           this situation, you will have to apply your own validity check.
201    
202         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.  
203    
204         2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
205         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
206    
207         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
208         characters for values greater than \177.         characters for values greater than \177.
209    
210         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-         3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
211         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
212    
213         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-
214         gle byte.         gle byte.
215    
216         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
217         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
218         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
219    
220         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
221         test characters of any code value, but the characters that PCRE  recog-         test  characters of any code value, but the characters that PCRE recog-
222         nizes  as  digits,  spaces,  or  word characters remain the same set as         nizes as digits, spaces, or word characters  remain  the  same  set  as
223         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
224         includes  Unicode  property support, because to do otherwise would slow         includes Unicode property support, because to do otherwise  would  slow
225         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
226         sense  of,  say,  "digit",  you must use Unicode property tests such as         sense of, say, "digit", you must use Unicode  property  tests  such  as
227         \p{Nd}.         \p{Nd}.
228    
229         8. Similarly, characters that match the POSIX named  character  classes         7.  Similarly,  characters that match the POSIX named character classes
230         are all low-valued characters.         are all low-valued characters.
231    
232         9.  Case-insensitive  matching  applies only to characters whose values         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
233         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-
234         Even  when  Unicode  property support is available, PCRE still uses its         acters.
235         own character tables when checking the case of  low-valued  characters,  
236         so  as not to degrade performance.  The Unicode property information is         9. Case-insensitive matching applies only to  characters  whose  values
237           are  less than 128, unless PCRE is built with Unicode property support.
238           Even when Unicode property support is available, PCRE  still  uses  its
239           own  character  tables when checking the case of low-valued characters,
240           so as not to degrade performance.  The Unicode property information  is
241         used only for characters with higher values. Even when Unicode property         used only for characters with higher values. Even when Unicode property
242         support is available, PCRE supports case-insensitive matching only when         support is available, PCRE supports case-insensitive matching only when
243         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
244         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-
245         ported by PCRE.         ported by PCRE.
246    
247    
248  AUTHOR  AUTHOR
249    
250         Philip Hazel         Philip Hazel
251         University Computing Service,         University Computing Service
252         Cambridge CB2 3QH, England.         Cambridge CB2 3QH, England.
253    
254         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,
255         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,
256         name, separated by a dot, at the domain ucs.cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
257    
258    
259  Last updated: 23 November 2006  REVISION
260  Copyright (c) 1997-2006 University of Cambridge.  
261           Last updated: 12 April 2008
262           Copyright (c) 1997-2008 University of Cambridge.
263  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
264    
265    
# Line 233  NAME Line 273  NAME
273  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
274    
275         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
276         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
277         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
278         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
279         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
280         directory) can be obtained by running         environments using the GUI facility of  CMakeSetup  if  you  are  using
281           CMake instead of configure to build PCRE.
282    
283           The complete list of options for configure (which includes the standard
284           ones such as the  selection  of  the  installation  directory)  can  be
285           obtained by running
286    
287           ./configure --help           ./configure --help
288    
289         The following sections describe certain options whose names begin  with         The  following  sections  include  descriptions  of options whose names
290         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
291         for the configure command. Because of the  way  that  configure  works,         defaults  for  the configure command. Because of the way that configure
292         --enable  and  --disable  always  come  in  pairs, so the complementary         works, --enable and --disable always come in pairs, so  the  complemen-
293         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
294         not described.         is not described.
295    
296    
297  C++ SUPPORT  C++ SUPPORT
# Line 266  UTF-8 SUPPORT Line 311  UTF-8 SUPPORT
311    
312           --enable-utf8           --enable-utf8
313    
314         to  the  configure  command.  Of  itself, this does not make PCRE treat         to the configure command. Of itself, this  does  not  make  PCRE  treat
315         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
316         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()
317         function.         function.
318    
319    
320  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
321    
322         UTF-8 support allows PCRE to process character values greater than  255         UTF-8  support allows PCRE to process character values greater than 255
323         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-
324         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
325         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
326         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
327    
328           --enable-unicode-properties           --enable-unicode-properties
329    
330         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
331         not explicitly requested it.         not explicitly requested it.
332    
333         Including  Unicode  property  support  adds around 90K of tables to the         Including Unicode property support adds around 30K  of  tables  to  the
334         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE  library.  Only  the general category properties such as Lu and Nd
335         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.  
336    
337    
338  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
# Line 310  CODE VALUE OF NEWLINE Line 354  CODE VALUE OF NEWLINE
354    
355         to the configure command. There is a fourth option, specified by         to the configure command. There is a fourth option, specified by
356    
357             --enable-newline-is-anycrlf
358    
359           which  causes  PCRE  to recognize any of the three sequences CR, LF, or
360           CRLF as indicating a line ending. Finally, a fifth option, specified by
361    
362           --enable-newline-is-any           --enable-newline-is-any
363    
364         which causes PCRE to recognize any Unicode newline sequence.         causes PCRE to recognize any Unicode newline sequence.
365    
366         Whatever  line  ending convention is selected when PCRE is built can be         Whatever  line  ending convention is selected when PCRE is built can be
367         overridden when the library functions are called. At build time  it  is         overridden when the library functions are called. At build time  it  is
368         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
369    
370    
371    WHAT \R MATCHES
372    
373           By  default,  the  sequence \R in a pattern matches any Unicode newline
374           sequence, whatever has been selected as the line  ending  sequence.  If
375           you specify
376    
377             --enable-bsr-anycrlf
378    
379           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
380           ever is selected when PCRE is built can be overridden when the  library
381           functions are called.
382    
383    
384  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
385    
386         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 364  HANDLING VERY LARGE PATTERNS Line 426  HANDLING VERY LARGE PATTERNS
426         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
427         additional bytes when handling them.         additional bytes when handling them.
428    
        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.  
   
429    
430  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
431    
432         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
433         ing  by  making recursive calls to an internal function called match().         ing by making recursive calls to an internal function  called  match().
434         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-
435         verely  limit  PCRE's operation. (The Unix environment does not usually         verely limit PCRE's operation. (The Unix environment does  not  usually
436         suffer from this problem, but it may sometimes be necessary to increase         suffer from this problem, but it may sometimes be necessary to increase
437         the  maximum  stack size.  There is a discussion in the pcrestack docu-         the maximum stack size.  There is a discussion in the  pcrestack  docu-
438         mentation.) An alternative approach to recursion that uses memory  from         mentation.)  An alternative approach to recursion that uses memory from
439         the  heap  to remember data, instead of using recursive function calls,         the heap to remember data, instead of using recursive  function  calls,
440         has been implemented to work round the problem of limited  stack  size.         has  been  implemented to work round the problem of limited stack size.
441         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
442    
443           --disable-stack-for-recursion           --disable-stack-for-recursion
444    
445         to  the  configure  command. With this configuration, PCRE will use the         to the configure command. With this configuration, PCRE  will  use  the
446         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
447         ment  functions.  Separate  functions are provided because the usage is         ment functions. By default these point to malloc() and free(), but  you
448         very predictable: the block sizes requested are always  the  same,  and         can replace the pointers so that your own functions are used.
449         the  blocks  are always freed in reverse order. A calling program might  
450         be able to implement optimized functions that perform better  than  the         Separate  functions  are  provided  rather  than  using pcre_malloc and
451         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more         pcre_free because the  usage  is  very  predictable:  the  block  sizes
452         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
453         function; it is not relevant for the the pcre_dfa_exec() function.         reverse order. A calling program might be able to  implement  optimized
454           functions  that  perform  better  than  malloc()  and free(). PCRE runs
455           noticeably more slowly when built in this way. This option affects only
456           the   pcre_exec()   function;   it   is   not   relevant  for  the  the
457           pcre_dfa_exec() function.
458    
459    
460  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
461    
462         Internally,  PCRE has a function called match(), which it calls repeat-         Internally, PCRE has a function called match(), which it calls  repeat-
463         edly  (sometimes  recursively)  when  matching  a  pattern   with   the         edly   (sometimes   recursively)  when  matching  a  pattern  with  the
464         pcre_exec()  function.  By controlling the maximum number of times this         pcre_exec() function. By controlling the maximum number of  times  this
465         function may be called during a single matching operation, a limit  can         function  may be called during a single matching operation, a limit can
466         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
467         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-
468         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
469         setting such as         setting such as
470    
471           --with-match-limit=500000           --with-match-limit=500000
472    
473         to  the  configure  command.  This  setting  has  no  effect   on   the         to   the   configure  command.  This  setting  has  no  effect  on  the
474         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
475    
476         In  some  environments  it is desirable to limit the depth of recursive         In some environments it is desirable to limit the  depth  of  recursive
477         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
478         to  restrict  the maximum amount of stack (or heap, if --disable-stack-         to restrict the maximum amount of stack (or heap,  if  --disable-stack-
479         for-recursion is specified) that is used. A second limit controls this;         for-recursion is specified) that is used. A second limit controls this;
480         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
481         imposes no additional constraints. However, you can set a  lower  limit         imposes  no  additional constraints. However, you can set a lower limit
482         by adding, for example,         by adding, for example,
483    
484           --with-match-limit-recursion=10000           --with-match-limit-recursion=10000
485    
486         to  the  configure  command.  This  value can also be overridden at run         to the configure command. This value can  also  be  overridden  at  run
487         time.         time.
488    
489    
490    CREATING CHARACTER TABLES AT BUILD TIME
491    
492           PCRE  uses fixed tables for processing characters whose code values are
493           less than 256. By default, PCRE is built with a set of tables that  are
494           distributed  in  the  file pcre_chartables.c.dist. These tables are for
495           ASCII codes only. If you add
496    
497             --enable-rebuild-chartables
498    
499           to the configure command, the distributed tables are  no  longer  used.
500           Instead,  a  program  called dftables is compiled and run. This outputs
501           the source for new set of tables, created in the default locale of your
502           C runtime system. (This method of replacing the tables does not work if
503           you are cross compiling, because dftables is run on the local host.  If
504           you  need  to  create alternative tables when cross compiling, you will
505           have to do so "by hand".)
506    
507    
508  USING EBCDIC CODE  USING EBCDIC CODE
509    
510         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
511         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
512         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by         This is the case for most computer operating systems.  PCRE  can,  how-
513         adding         ever, be compiled to run in an EBCDIC environment by adding
514    
515           --enable-ebcdic           --enable-ebcdic
516    
517         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
518           bles. You should only use it if you know that  you  are  in  an  EBCDIC
519           environment (for example, an IBM mainframe operating system).
520    
521    
522    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
523    
524           By default, pcregrep reads all files as plain text. You can build it so
525           that it recognizes files whose names end in .gz or .bz2, and reads them
526           with libz or libbz2, respectively, by adding one or both of
527    
528             --enable-pcregrep-libz
529             --enable-pcregrep-libbz2
530    
531           to the configure command. These options naturally require that the rel-
532           evant libraries are installed on your system. Configuration  will  fail
533           if they are not.
534    
535    
536    PCRETEST OPTION FOR LIBREADLINE SUPPORT
537    
538           If you add
539    
540             --enable-pcretest-libreadline
541    
542           to  the  configure  command,  pcretest  is  linked with the libreadline
543           library, and when its input is from a terminal, it reads it  using  the
544           readline() function. This provides line-editing and history facilities.
545           Note that libreadline is GPL-licenced, so if you distribute a binary of
546           pcretest linked in this way, there may be licensing issues.
547    
548           Setting  this  option  causes  the -lreadline option to be added to the
549           pcretest build. In many operating environments with  a  sytem-installed
550           libreadline this is sufficient. However, in some environments (e.g.  if
551           an unmodified distribution version of readline is in use),  some  extra
552           configuration  may  be necessary. The INSTALL file for libreadline says
553           this:
554    
555             "Readline uses the termcap functions, but does not link with the
556             termcap or curses library itself, allowing applications which link
557             with readline the to choose an appropriate library."
558    
559           If your environment has not been set up so that an appropriate  library
560           is automatically included, you may need to add something like
561    
562             LIBS="-ncurses"
563    
564           immediately before the configure command.
565    
566    
567  SEE ALSO  SEE ALSO
568    
569         pcreapi(3), pcre_config(3).         pcreapi(3), pcre_config(3).
570    
571  Last updated: 30 November 2006  
572  Copyright (c) 1997-2006 University of Cambridge.  AUTHOR
573    
574           Philip Hazel
575           University Computing Service
576           Cambridge CB2 3QH, England.
577    
578    
579    REVISION
580    
581           Last updated: 13 April 2008
582           Copyright (c) 1997-2008 University of Cambridge.
583  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
584    
585    
# Line 495  REGULAR EXPRESSIONS AS TREES Line 631  REGULAR EXPRESSIONS AS TREES
631    
632  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
633    
634         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
635         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
636         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
637         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
638         required. When there is a mismatch, the algorithm  tries  any  alterna-         required. When there is a mismatch, the algorithm  tries  any  alterna-
# Line 578  THE ALTERNATIVE MATCHING ALGORITHM Line 714  THE ALTERNATIVE MATCHING ALGORITHM
714         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
715         supported.         supported.
716    
717         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
718           sequence, which resets the start of the match when encountered (but may
719           be on some paths and not on others), is not  supported.  It  causes  an
720           error if encountered.
721    
722           6.  Callouts  are  supported, but the value of the capture_top field is
723         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.
724    
725         6.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
726         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-
727         tive  algorithm  moves  through  the  subject string one character at a         tive algorithm moves through the subject  string  one  character  at  a
728         time, for all active paths through the tree.         time, for all active paths through the tree.
729    
730           8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
731           are not supported. (*FAIL) is supported, and  behaves  like  a  failing
732           negative assertion.
733    
734    
735  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
736    
737         Using the alternative matching algorithm provides the following  advan-         Using  the alternative matching algorithm provides the following advan-
738         tages:         tages:
739    
740         1. All possible matches (at a single point in the subject) are automat-         1. All possible matches (at a single point in the subject) are automat-
741         ically found, and in particular, the longest match is  found.  To  find         ically  found,  and  in particular, the longest match is found. To find
742         more than one match using the standard algorithm, you have to do kludgy         more than one match using the standard algorithm, you have to do kludgy
743         things with callouts.         things with callouts.
744    
745         2. There is much better support for partial matching. The  restrictions         2.  There is much better support for partial matching. The restrictions
746         on  the content of the pattern that apply when using the standard algo-         on the content of the pattern that apply when using the standard  algo-
747         rithm for partial matching do not apply to the  alternative  algorithm.         rithm  for  partial matching do not apply to the alternative algorithm.
748         For  non-anchored patterns, the starting position of a partial match is         For non-anchored patterns, the starting position of a partial match  is
749         available.         available.
750    
751         3. Because the alternative algorithm  scans  the  subject  string  just         3.  Because  the  alternative  algorithm  scans the subject string just
752         once,  and  never  needs to backtrack, it is possible to pass very long         once, and never needs to backtrack, it is possible to  pass  very  long
753         subject strings to the matching function in  several  pieces,  checking         subject  strings  to  the matching function in several pieces, checking
754         for partial matching each time.         for partial matching each time.
755    
756    
# Line 613  DISADVANTAGES OF THE ALTERNATIVE ALGORIT Line 758  DISADVANTAGES OF THE ALTERNATIVE ALGORIT
758    
759         The alternative algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
760    
761         1.  It  is  substantially  slower  than the standard algorithm. This is         1. It is substantially slower than  the  standard  algorithm.  This  is
762         partly because it has to search for all possible matches, but  is  also         partly  because  it has to search for all possible matches, but is also
763         because it is less susceptible to optimization.         because it is less susceptible to optimization.
764    
765         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
# Line 622  DISADVANTAGES OF THE ALTERNATIVE ALGORIT Line 767  DISADVANTAGES OF THE ALTERNATIVE ALGORIT
767         3. Although atomic groups are supported, their use does not provide the         3. Although atomic groups are supported, their use does not provide the
768         performance advantage that it does for the standard algorithm.         performance advantage that it does for the standard algorithm.
769    
770  Last updated: 24 November 2006  
771  Copyright (c) 1997-2006 University of Cambridge.  AUTHOR
772    
773           Philip Hazel
774           University Computing Service
775           Cambridge CB2 3QH, England.
776    
777    
778    REVISION
779    
780           Last updated: 19 April 2008
781           Copyright (c) 1997-2008 University of Cambridge.
782  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
783    
784    
# Line 735  PCRE API OVERVIEW Line 890  PCRE API OVERVIEW
890         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
891         plest way of using them is provided in the file  called  pcredemo.c  in         plest way of using them is provided in the file  called  pcredemo.c  in
892         the  source distribution. The pcresample documentation describes how to         the  source distribution. The pcresample documentation describes how to
893         run it.         compile and run it.
894    
895         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
896         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
# Line 805  PCRE API OVERVIEW Line 960  PCRE API OVERVIEW
960    
961  NEWLINES  NEWLINES
962    
963         PCRE  supports four different conventions for indicating line breaks in         PCRE  supports five different conventions for indicating line breaks in
964         strings: a single CR (carriage return) character, a  single  LF  (line-         strings: a single CR (carriage return) character, a  single  LF  (line-
965         feed)  character,  the two-character sequence CRLF, or any Unicode new-         feed) character, the two-character sequence CRLF, any of the three pre-
966         line sequence.  The Unicode newline sequences are the three  just  men-         ceding, or any Unicode newline sequence. The Unicode newline  sequences
967         tioned, plus the single characters VT (vertical tab, U+000B), FF (form-         are  the  three just mentioned, plus the single characters VT (vertical
968         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
969         and PS (paragraph separator, U+2029).         separator, U+2028), and PS (paragraph separator, U+2029).
970    
971         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
972         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 819  NEWLINES Line 974  NEWLINES
974         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
975         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
976    
977           At compile time, the newline convention can be specified by the options
978           argument of pcre_compile(), or it can be specified by special  text  at
979           the start of the pattern itself; this overrides any other settings. See
980           the pcrepattern page for details of the special character sequences.
981    
982         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-
983         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
984         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
985         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
986         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
987         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
988         not affect the interpretation of the \n or \r escape sequences.         section on pcre_exec() options below.
989    
990           The choice of newline convention does not affect the interpretation  of
991           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
992           which is controlled in a similar way, but by separate options.
993    
994    
995  MULTITHREADING  MULTITHREADING
996    
997         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
998         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
999         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
1000         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
1001    
1002         The  compiled form of a regular expression is not altered during match-         The compiled form of a regular expression is not altered during  match-
1003         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
1004         at once.         at once.
1005    
# Line 843  MULTITHREADING Line 1007  MULTITHREADING
1007  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
1008    
1009         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
1010         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
1011         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
1012         pcreprecompile documentation.         pcreprecompile  documentation.  However, compiling a regular expression
1013           with one version of PCRE for use with a different version is not  guar-
1014           anteed to work and may cause crashes.
1015    
1016    
1017  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
1018    
1019         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
1020    
1021         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-
1022         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
1023         The pcrebuild documentation has more details about these optional  fea-         The  pcrebuild documentation has more details about these optional fea-
1024         tures.         tures.
1025    
1026         The  first  argument  for pcre_config() is an integer, specifying which         The first argument for pcre_config() is an  integer,  specifying  which
1027         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
1028         into  which  the  information  is  placed. The following information is         into which the information is  placed.  The  following  information  is
1029         available:         available:
1030    
1031           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
1032    
1033         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-
1034         able; otherwise it is set to zero.         able; otherwise it is set to zero.
1035    
1036           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
1037    
1038         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
1039         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
1040    
1041           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1042    
1043         The output is an integer whose value specifies  the  default  character         The  output  is  an integer whose value specifies the default character
1044         sequence  that is recognized as meaning "newline". The four values that         sequence that is recognized as meaning "newline". The four values  that
1045         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,
1046         The default should normally be the standard sequence for your operating         and -1 for ANY. The default should normally be  the  standard  sequence
1047         system.         for your operating system.
1048    
1049             PCRE_CONFIG_BSR
1050    
1051           The output is an integer whose value indicates what character sequences
1052           the \R escape sequence matches by default. A value of 0 means  that  \R
1053           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1054           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1055           tern is compiled or matched.
1056    
1057           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1058    
1059         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
1060         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1061         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1062         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1063         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1064         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1065    
1066           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1067    
1068         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1069         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1070         given in the pcreposix documentation.         given in the pcreposix documentation.
1071    
1072           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1073    
1074         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
1075         internal matching function calls in a  pcre_exec()  execution.  Further         internal  matching  function  calls in a pcre_exec() execution. Further
1076         details are given with pcre_exec() below.         details are given with pcre_exec() below.
1077    
1078           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1079    
1080         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
1081         recursion when calling the internal matching function in a  pcre_exec()         recursion  when calling the internal matching function in a pcre_exec()
1082         execution. Further details are given with pcre_exec() below.         execution. Further details are given with pcre_exec() below.
1083    
1084           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1085    
1086         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
1087         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1088         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
1089         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
1090         on  the  heap  instead  of  recursive  function  calls.  In  this case,         on the  heap  instead  of  recursive  function  calls.  In  this  case,
1091         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
1092         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1093    
1094    
# Line 931  COMPILING A PATTERN Line 1105  COMPILING A PATTERN
1105    
1106         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1107         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1108         the  two interfaces is that pcre_compile2() has an additional argument,         the two interfaces is that pcre_compile2() has an additional  argument,
1109         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
1110    
1111         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
1112         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
1113         obtained via pcre_malloc is returned. This contains the  compiled  code         obtained  via  pcre_malloc is returned. This contains the compiled code
1114         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
1115         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1116         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
1117         longer required.         longer required.
1118    
1119         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
1120         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
1121         fully relocatable, because it may contain a copy of the tableptr  argu-         fully  relocatable, because it may contain a copy of the tableptr argu-
1122         ment, which is an address (see below).         ment, which is an address (see below).
1123    
1124         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1125         pilation. It should be zero if no options are required.  The  available         pilation.  It  should be zero if no options are required. The available
1126         options  are  described  below. Some of them, in particular, those that         options are described below. Some of them, in  particular,  those  that
1127         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
1128         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern (see the detailed description  in  the  pcrepattern  documenta-
1129         tion). For these options, the contents of the options  argument  speci-         tion).  For  these options, the contents of the options argument speci-
1130         fies  their initial settings at the start of compilation and execution.         fies their initial settings at the start of compilation and  execution.
1131         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
1132         of matching as well as at compile time.         of matching as well as at compile time.
1133    
1134         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1135         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1136         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-
1137         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
1138         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-
1139         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
1140         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
1141         given.         given.
1142    
1143         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1144         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
1145         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
1146         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1147    
1148         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
1149         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1150         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1151         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
1152         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1153         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
1154         support below.         support below.
1155    
1156         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1157         pile():         pile():
1158    
1159           pcre *re;           pcre *re;
# Line 992  COMPILING A PATTERN Line 1166  COMPILING A PATTERN
1166             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1167             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1168    
1169         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
1170         file:         file:
1171    
1172           PCRE_ANCHORED           PCRE_ANCHORED
1173    
1174         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
1175         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
1176         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1177         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1178         only way to do it in Perl.         only way to do it in Perl.
1179    
1180           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1181    
1182         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1183         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1184         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1185    
1186             PCRE_BSR_ANYCRLF
1187             PCRE_BSR_UNICODE
1188    
1189           These options (which are mutually exclusive) control what the \R escape
1190           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1191           or to match any Unicode newline sequence. The default is specified when
1192           PCRE is built. It can be overridden from within the pattern, or by set-
1193           ting an option when a compiled pattern is matched.
1194    
1195           PCRE_CASELESS           PCRE_CASELESS
1196    
1197         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
1198         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
1199         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
1200         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1201         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1202         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-
1203         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1204         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1205         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1206         UTF-8 support.         UTF-8 support.
1207    
1208           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1209    
1210         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
1211         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
1212         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
1213         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1214         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
1215         Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1216    
1217           PCRE_DOTALL           PCRE_DOTALL
1218    
1219         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-
1220         acters, including those that indicate newline. Without it, a  dot  does         acters,  including  those that indicate newline. Without it, a dot does
1221         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
1222         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
1223         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
1224         newline characters, independent of the setting of this option.         newline characters, independent of the setting of this option.
1225    
1226           PCRE_DUPNAMES           PCRE_DUPNAMES
1227    
1228         If this bit is set, names used to identify capturing  subpatterns  need         If  this  bit is set, names used to identify capturing subpatterns need
1229         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
1230         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
1231         matched.  There  are  more details of named subpatterns below; see also         matched. There are more details of named subpatterns  below;  see  also
1232         the pcrepattern documentation.         the pcrepattern documentation.
1233    
1234           PCRE_EXTENDED           PCRE_EXTENDED
1235    
1236         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1237         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1238         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1239         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1240         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1241         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-
1242         ting.         ting.
1243    
1244         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1245         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1246         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1247         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1248         introduces a conditional subpattern.         introduces a conditional subpattern.
1249    
1250           PCRE_EXTRA           PCRE_EXTRA
1251    
1252         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1253         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
1254         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
1255         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1256         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1257         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
1258         literal. (Perl can, however, be persuaded to give a warning for  this.)         literal.  (Perl can, however, be persuaded to give a warning for this.)
1259         There  are  at  present no other features controlled by this option. It         There are at present no other features controlled by  this  option.  It
1260         can also be set by a (?X) option setting within a pattern.         can also be set by a (?X) option setting within a pattern.
1261    
1262           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1263    
1264         If this option is set, an  unanchored  pattern  is  required  to  match         If  this  option  is  set,  an  unanchored pattern is required to match
1265         before  or  at  the  first  newline  in  the subject string, though the         before or at the first  newline  in  the  subject  string,  though  the
1266         matched text may continue over the newline.         matched text may continue over the newline.
1267    
1268             PCRE_JAVASCRIPT_COMPAT
1269    
1270           If this option is set, PCRE's behaviour is changed in some ways so that
1271           it is compatible with JavaScript rather than Perl. The changes  are  as
1272           follows:
1273    
1274           (1)  A  lone  closing square bracket in a pattern causes a compile-time
1275           error, because this is illegal in JavaScript (by default it is  treated
1276           as a data character). Thus, the pattern AB]CD becomes illegal when this
1277           option is set.
1278    
1279           (2) At run time, a back reference to an unset subpattern group  matches
1280           an  empty  string (by default this causes the current matching alterna-
1281           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1282           set  (assuming  it can find an "a" in the subject), whereas it fails by
1283           default, for Perl compatibility.
1284    
1285           PCRE_MULTILINE           PCRE_MULTILINE
1286    
1287         By default, PCRE treats the subject string as consisting  of  a  single         By default, PCRE treats the subject string as consisting  of  a  single
# Line 1102  COMPILING A PATTERN Line 1302  COMPILING A PATTERN
1302           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1303           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1304           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
1305             PCRE_NEWLINE_ANYCRLF
1306           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1307    
1308         These  options  override the default newline definition that was chosen         These  options  override the default newline definition that was chosen
1309         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
1310         newline  is  indicated  by a single character (CR or LF, respectively).         newline  is  indicated  by a single character (CR or LF, respectively).
1311         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1312         two-character  CRLF  sequence.  Setting PCRE_NEWLINE_ANY specifies that         two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1313         any Unicode newline sequence should be recognized. The Unicode  newline         that any of the three preceding sequences should be recognized. Setting
1314         sequences  are  the three just mentioned, plus the single characters VT         PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1315         (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085),         recognized. The Unicode newline sequences are the three just mentioned,
1316         LS  (line separator, U+2028), and PS (paragraph separator, U+2029). The         plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1317         last two are recognized only in UTF-8 mode.         U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1318           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1319           UTF-8 mode.
1320    
1321         The newline setting in the  options  word  uses  three  bits  that  are         The newline setting in the  options  word  uses  three  bits  that  are
1322         treated  as  a  number, giving eight possibilities. Currently only five         treated as a number, giving eight possibilities. Currently only six are
1323         are used (default plus the four values above). This means that  if  you         used (default plus the five values above). This means that if  you  set
1324         set  more  than  one  newline option, the combination may or may not be         more  than one newline option, the combination may or may not be sensi-
1325         sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is  equiva-         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1326         lent  to PCRE_NEWLINE_CRLF, but other combinations yield unused numbers         PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1327         and cause an error.         cause an error.
1328    
1329         The only time that a line break is specially recognized when  compiling         The only time that a line break is specially recognized when  compiling
1330         a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a         a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
# Line 1161  COMPILING A PATTERN Line 1364  COMPILING A PATTERN
1364           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1365    
1366         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
1367         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically  checked.  There  is  a  discussion about the validity of
1368         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
1369         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
1370         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-
1371         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
1372         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
1373         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
1374         ing of subject strings.         can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1375           UTF-8 validity checking of subject strings.
1376    
1377    
1378  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1379    
1380         The following table lists the error  codes  than  may  be  returned  by         The  following  table  lists  the  error  codes than may be returned by
1381         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(), along with the error messages that may be returned  by
1382         both compiling functions. As PCRE has developed, some error codes  have         both  compiling functions. As PCRE has developed, some error codes have
1383         fallen out of use. To avoid confusion, they have not been re-used.         fallen out of use. To avoid confusion, they have not been re-used.
1384    
1385            0  no error            0  no error
# Line 1190  COMPILATION ERROR CODES Line 1394  COMPILATION ERROR CODES
1394            9  nothing to repeat            9  nothing to repeat
1395           10  [this code is not in use]           10  [this code is not in use]
1396           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1397           12  unrecognized character after (?           12  unrecognized character after (? or (?-
1398           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
1399           14  missing )           14  missing )
1400           15  reference to non-existent subpattern           15  reference to non-existent subpattern
# Line 1198  COMPILATION ERROR CODES Line 1402  COMPILATION ERROR CODES
1402           17  unknown option bit(s) set           17  unknown option bit(s) set
1403           18  missing ) after comment           18  missing ) after comment
1404           19  [this code is not in use]           19  [this code is not in use]
1405           20  regular expression too large           20  regular expression is too large
1406           21  failed to get memory           21  failed to get memory
1407           22  unmatched parentheses           22  unmatched parentheses
1408           23  internal error: code overflow           23  internal error: code overflow
# Line 1207  COMPILATION ERROR CODES Line 1411  COMPILATION ERROR CODES
1411           26  malformed number or name after (?(           26  malformed number or name after (?(
1412           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1413           28  assertion expected after (?(           28  assertion expected after (?(
1414           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1415           30  unknown POSIX class name           30  unknown POSIX class name
1416           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1417           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 1227  COMPILATION ERROR CODES Line 1431  COMPILATION ERROR CODES
1431           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1432           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1433           48  subpattern name is too long (maximum 32 characters)           48  subpattern name is too long (maximum 32 characters)
1434           49  too many named subpatterns (maximum 10,000)           49  too many named subpatterns (maximum 10000)
1435           50  repeated subpattern is too long           50  [this code is not in use]
1436           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1437           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1438           53   internal  error:  previously-checked  referenced  subpattern not           53  internal  error:  previously-checked  referenced  subpattern  not
1439         found         found
1440           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1441           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1442           56  inconsistent NEWLINE options"           56  inconsistent NEWLINE options
1443             57  \g is not followed by a braced, angle-bracketed, or quoted
1444                   name/number or by a plain number
1445             58  a numbered reference must not be zero
1446             59  (*VERB) with an argument is not supported
1447             60  (*VERB) not recognized
1448             61  number is too big
1449             62  subpattern name expected
1450             63  digit expected after (?+
1451             64  ] is an invalid data character in JavaScript compatibility mode
1452    
1453           The  numbers  32  and 10000 in errors 48 and 49 are defaults; different
1454           values may be used if the limits were changed when PCRE was built.
1455    
1456    
1457  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1287  STUDYING A PATTERN Line 1503  STUDYING A PATTERN
1503  LOCALE SUPPORT  LOCALE SUPPORT
1504    
1505         PCRE handles caseless matching, and determines whether  characters  are         PCRE handles caseless matching, and determines whether  characters  are
1506         letters  digits,  or whatever, by reference to a set of tables, indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1507         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
1508         characters  with  codes  less than 128. Higher-valued codes never match         characters  with  codes  less than 128. Higher-valued codes never match
1509         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
1510         with  Unicode  character property support. The use of locales with Uni-         with  Unicode  character property support. The use of locales with Uni-
1511         code is discouraged.         code is discouraged. If you are handling characters with codes  greater
1512           than  128, you should either use UTF-8 and Unicode, or use locales, but
1513         An internal set of tables is created in the default C locale when  PCRE         not try to mix the two.
1514         is  built.  This  is  used when the final argument of pcre_compile() is  
1515         NULL, and is sufficient for many applications. An  alternative  set  of         PCRE contains an internal set of tables that are used  when  the  final
1516         tables  can,  however, be supplied. These may be created in a different         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1517         locale from the default. As more and more applications change to  using         applications.  Normally, the internal tables recognize only ASCII char-
1518         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-
1519           nal tables to be rebuilt in the default "C" locale of the local system,
1520         External  tables  are  built by calling the pcre_maketables() function,         which may cause them to be different.
1521         which has no arguments, in the relevant locale. The result can then  be  
1522         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For         The  internal tables can always be overridden by tables supplied by the
1523         example, to build and use tables that are appropriate  for  the  French         application that calls PCRE. These may be created in a different locale
1524         locale  (where  accented  characters  with  values greater than 128 are         from  the  default.  As more and more applications change to using Uni-
1525           code, the need for this locale support is expected to die away.
1526    
1527           External tables are built by calling  the  pcre_maketables()  function,
1528           which  has no arguments, in the relevant locale. The result can then be
1529           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1530           example,  to  build  and use tables that are appropriate for the French
1531           locale (where accented characters with  values  greater  than  128  are
1532         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1533    
1534           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1535           tables = pcre_maketables();           tables = pcre_maketables();
1536           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1537    
1538           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1539           if you are using Windows, the name for the French locale is "french".
1540    
1541         When pcre_maketables() runs, the tables are built  in  memory  that  is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1542         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1543         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 1414  INFORMATION ABOUT A PATTERN Line 1640  INFORMATION ABOUT A PATTERN
1640         returned. The fourth argument should point to an unsigned char *  vari-         returned. The fourth argument should point to an unsigned char *  vari-
1641         able.         able.
1642    
1643             PCRE_INFO_HASCRORLF
1644    
1645           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1646           characters, otherwise 0. The fourth argument should  point  to  an  int
1647           variable.  An explicit match is either a literal CR or LF character, or
1648           \r or \n.
1649    
1650             PCRE_INFO_JCHANGED
1651    
1652           Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1653           otherwise  0. The fourth argument should point to an int variable. (?J)
1654           and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1655    
1656           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1657    
1658         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
1659         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
1660         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1661         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
1662         byte  is  recorded only if it follows something of variable length. For         byte is recorded only if it follows something of variable  length.  For
1663         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
1664         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1665    
# Line 1428  INFORMATION ABOUT A PATTERN Line 1667  INFORMATION ABOUT A PATTERN
1667           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1668           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1669    
1670         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1671         ses. The names are just an additional way of identifying the  parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1672         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1673         pcre_get_named_substring() are provided for  extracting  captured  sub-         pcre_get_named_substring()  are  provided  for extracting captured sub-
1674         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
1675         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
1676         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1677         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
1678         described by these three values.         described by these three values.
1679    
1680         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
1681         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1682         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
1683         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1684         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
1685         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-
1686         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-
1687         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1688         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-
1689         theses numbers. For example, consider  the  following  pattern  (assume         theses  numbers.  For  example,  consider the following pattern (assume
1690         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1691         ignored):         ignored):
1692    
1693           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1694           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1695    
1696         There are four named subpatterns, so the table has  four  entries,  and         There  are  four  named subpatterns, so the table has four entries, and
1697         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,
1698         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1699         as ??:         as ??:
1700    
# Line 1464  INFORMATION ABOUT A PATTERN Line 1703  INFORMATION ABOUT A PATTERN
1703           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1704           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1705    
1706         When  writing  code  to  extract  data from named subpatterns using the         When writing code to extract data  from  named  subpatterns  using  the
1707         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
1708         to be different for each compiled pattern.         to be different for each compiled pattern.
1709    
1710             PCRE_INFO_OKPARTIAL
1711    
1712           Return 1 if the pattern can be used for partial matching, otherwise  0.
1713           The  fourth  argument  should point to an int variable. The pcrepartial
1714           documentation lists the restrictions that apply to patterns  when  par-
1715           tial matching is used.
1716    
1717           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1718    
1719         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
1720         fourth argument should point to an unsigned long  int  variable.  These         fourth argument should point to an unsigned long  int  variable.  These
1721         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1722         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1723           other  words,  they are the options that will be in force when matching
1724           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1725           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1726           and PCRE_EXTENDED.
1727    
1728         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
1729         alternatives begin with one of the following:         alternatives begin with one of the following:
# Line 1676  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1926  MATCHING A PATTERN: THE TRADITIONAL FUNC
1926         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
1927         unachored at matching time.         unachored at matching time.
1928    
1929             PCRE_BSR_ANYCRLF
1930             PCRE_BSR_UNICODE
1931    
1932           These options (which are mutually exclusive) control what the \R escape
1933           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1934           or to match any Unicode newline sequence. These  options  override  the
1935           choice that was made or defaulted when the pattern was compiled.
1936    
1937           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1938           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1939           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
1940             PCRE_NEWLINE_ANYCRLF
1941           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1942    
1943         These options override  the  newline  definition  that  was  chosen  or         These  options  override  the  newline  definition  that  was chosen or
1944         defaulted  when the pattern was compiled. For details, see the descrip-         defaulted when the pattern was compiled. For details, see the  descrip-
1945         tion of pcre_compile()  above.  During  matching,  the  newline  choice         tion  of  pcre_compile()  above.  During  matching,  the newline choice
1946         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1947         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
1948         match  failure  for  an  unanchored  pattern. When PCRE_NEWLINE_CRLF or         match failure for an unanchored pattern.
1949         PCRE_NEWLINE_ANY is set, and a match attempt  fails  when  the  current  
1950         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
1951         characters instead of one, in other words, to after the CRLF.         set,  and a match attempt for an unanchored pattern fails when the cur-
1952           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1953           explicit  matches  for  CR  or  LF  characters,  the  match position is
1954           advanced by two characters instead of one, in other words, to after the
1955           CRLF.
1956    
1957           The above rule is a compromise that makes the most common cases work as
1958           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1959           option is not set), it does not match the string "\r\nA" because, after
1960           failing at the start, it skips both the CR and the LF before  retrying.
1961           However,  the  pattern  [\r\n]A does match that string, because it con-
1962           tains an explicit CR or LF reference, and so advances only by one char-
1963           acter after the first failure.
1964    
1965           An explicit match for CR of LF is either a literal appearance of one of
1966           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1967           matches  such  as [^X] do not count, nor does \s (which includes CR and
1968           LF in the characters that it matches).
1969    
1970           Notwithstanding the above, anomalous effects may still occur when  CRLF
1971           is a valid newline sequence and explicit \r or \n escapes appear in the
1972           pattern.
1973    
1974           PCRE_NOTBOL           PCRE_NOTBOL
1975    
# Line 1736  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2016  MATCHING A PATTERN: THE TRADITIONAL FUNC
2016         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
2017         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
2018         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
2019         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
2020         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
2021         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2022         returned.         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2023           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2024         If you already know that your subject is valid, and you  want  to  skip  
2025         these    checks    for   performance   reasons,   you   can   set   the         If  you  already  know that your subject is valid, and you want to skip
2026         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         these   checks   for   performance   reasons,   you   can    set    the
2027         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
2028         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
2029         string.  However,  you  should  be  sure  that the value of startoffset         making  repeated  calls  to  find  all  the matches in a single subject
2030         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
2031         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
2032         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
2033           value  of startoffset that does not point to the start of a UTF-8 char-
2034         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
2035    
2036           PCRE_PARTIAL           PCRE_PARTIAL
2037    
2038         This  option  turns  on  the  partial  matching feature. If the subject         This option turns on the  partial  matching  feature.  If  the  subject
2039         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-
2040         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
2041         partially matches the pattern and the failure to  match  occurred  only         partially  matches  the  pattern and the failure to match occurred only
2042         because  there were not enough subject characters), pcre_exec() returns         because there were not enough subject characters), pcre_exec()  returns
2043         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
2044         used,  there  are restrictions on what may appear in the pattern. These         used, there are restrictions on what may appear in the  pattern.  These
2045         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
2046    
2047     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2048    
2049         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
2050         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
2051         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.
2052         Unlike  the  pattern string, the subject may contain binary zero bytes.         Unlike the pattern string, the subject may contain binary  zero  bytes.
2053         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
2054         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.
2055    
2056         A  non-zero  starting offset is useful when searching for another match         A non-zero starting offset is useful when searching for  another  match
2057         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-
2058         cess.   Setting  startoffset differs from just passing over a shortened         cess.  Setting startoffset differs from just passing over  a  shortened
2059         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
2060         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2061    
2062           \Biss\B           \Biss\B
2063    
2064         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
2065         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.)
2066         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
2067         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
2068         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
2069         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
2070         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
2071         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-
2072         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
2073         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2074    
2075         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,
2076         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
2077         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
2078         subject.         subject.
2079    
2080     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2081    
2082         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
2083         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2084         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2085         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2086         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-
2087         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2088         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2089    
2090         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of  integer
2091         offsets whose address is passed in ovector. The number of  elements  in         offsets  whose  address is passed in ovector. The number of elements in
2092         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.
2093         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
2094    
2095         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-
2096         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2097         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-
2098         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2099         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
2100         it is not, it is rounded down.         it is not, it is rounded down.
2101    
2102         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2103         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2104         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
2105         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-
2106         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
2107         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-
2108         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1], identify the portion of  the  subject  string  matched  by  the
2109         entire pattern. The next pair is used for the first  capturing  subpat-         entire  pattern.  The next pair is used for the first capturing subpat-
2110         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
2111         highest numbered pair that has been set. For example, if two substrings         highest numbered pair that has been set. For example, if two substrings
2112         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
2113         subpatterns, the return value from a successful match is 1,  indicating         subpatterns,  the return value from a successful match is 1, indicating
2114         that just the first pair of offsets has been set.         that just the first pair of offsets has been set.
2115    
2116         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2117         of the string that it matched that is returned.         of the string that it matched that is returned.
2118    
2119         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,
2120         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
2121         function returns a value of zero. In particular, if the substring  off-         function  returns a value of zero. In particular, if the substring off-
2122         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
2123         as NULL and ovecsize as zero. However, if  the  pattern  contains  back         as  NULL  and  ovecsize  as zero. However, if the pattern contains back
2124         references  and  the  ovector is not big enough to remember the related         references and the ovector is not big enough to  remember  the  related
2125         substrings, PCRE has to get additional memory for use during  matching.         substrings,  PCRE has to get additional memory for use during matching.
2126         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
2127    
2128         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
2129         subpatterns there are in a compiled  pattern.  The  smallest  size  for         subpatterns  there  are  in  a  compiled pattern. The smallest size for
2130         ovector  that  will allow for n captured substrings, in addition to the         ovector that will allow for n captured substrings, in addition  to  the
2131         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.
2132    
2133         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
2134         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,
2135         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
2136         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
2137         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-
2138         sponding to unused subpatterns are set to -1.         sponding to unused subpatterns are set to -1.
2139    
2140         Offset  values  that correspond to unused subpatterns at the end of the         Offset values that correspond to unused subpatterns at the end  of  the
2141         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
2142         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
2143         matched. The return from the function is 2, because  the  highest  used         matched.  The  return  from the function is 2, because the highest used
2144         capturing subpattern number is 1. However, you can refer to the offsets         capturing subpattern number is 1. However, you can refer to the offsets
2145         for the second and third capturing subpatterns if  you  wish  (assuming         for  the  second  and third capturing subpatterns if you wish (assuming
2146         the vector is large enough, of course).         the vector is large enough, of course).
2147    
2148         Some  convenience  functions  are  provided for extracting the captured         Some convenience functions are provided  for  extracting  the  captured
2149         substrings as separate strings. These are described below.         substrings as separate strings. These are described below.
2150    
2151     Error return values from pcre_exec()     Error return values from pcre_exec()
2152    
2153         If pcre_exec() fails, it returns a negative number. The  following  are         If  pcre_exec()  fails, it returns a negative number. The following are
2154         defined in the header file:         defined in the header file:
2155    
2156           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1878  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2159  MATCHING A PATTERN: THE TRADITIONAL FUNC
2159    
2160           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2161    
2162         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
2163         ovecsize was not zero.         ovecsize was not zero.
2164    
2165           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1887  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2168  MATCHING A PATTERN: THE TRADITIONAL FUNC
2168    
2169           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2170    
2171         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,
2172         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
2173         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
2174         an  environment  with the other endianness. This is the error that PCRE         an environment with the other endianness. This is the error  that  PCRE
2175         gives when the magic number is not present.         gives when the magic number is not present.
2176    
2177           PCRE_ERROR_UNKNOWN_OPCODE (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2178    
2179         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2180         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
2181         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2182    
2183           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2184    
2185         If a pattern contains back references, but the ovector that  is  passed         If  a  pattern contains back references, but the ovector that is passed
2186         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2187         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
2188         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
2189         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2190    
2191           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2192    
2193         This error is used by the pcre_copy_substring(),  pcre_get_substring(),         This  error is used by the pcre_copy_substring(), pcre_get_substring(),
2194         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2195         returned by pcre_exec().         returned by pcre_exec().
2196    
2197           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2198    
2199         The backtracking limit, as specified by  the  match_limit  field  in  a         The  backtracking  limit,  as  specified  by the match_limit field in a
2200         pcre_extra  structure  (or  defaulted) was reached. See the description         pcre_extra structure (or defaulted) was reached.  See  the  description
2201         above.         above.
2202    
2203           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2204    
2205         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
2206         use  by  callout functions that want to yield a distinctive error code.         use by callout functions that want to yield a distinctive  error  code.
2207         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2208    
2209           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2210    
2211         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
2212         subject.         subject.
2213    
2214           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2215    
2216         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
2217         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-
2218         ter.         ter.
2219    
2220           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2221    
2222         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
2223         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2224    
2225           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2226    
2227         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
2228         items  that are not supported for partial matching. See the pcrepartial         items that are not supported for partial matching. See the  pcrepartial
2229         documentation for details of partial matching.         documentation for details of partial matching.
2230    
2231           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2232    
2233         An unexpected internal error has occurred. This error could  be  caused         An  unexpected  internal error has occurred. This error could be caused
2234         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2235    
2236           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2237    
2238         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.
2239    
2240           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2241    
2242         The internal recursion limit, as specified by the match_limit_recursion         The internal recursion limit, as specified by the match_limit_recursion
2243         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2244         description above.         description above.
2245    
          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.  
   
2246           PCRE_ERROR_BADNEWLINE     (-23)           PCRE_ERROR_BADNEWLINE     (-23)
2247    
2248         An invalid combination of PCRE_NEWLINE_xxx options was given.         An invalid combination of PCRE_NEWLINE_xxx options was given.
2249    
2250         Error numbers -16 to -20 are not used by pcre_exec().         Error numbers -16 to -20 and -22 are not used by pcre_exec().
2251    
2252    
2253  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 1990  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2263  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2263         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2264              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2265    
2266         Captured substrings can be  accessed  directly  by  using  the  offsets         Captured  substrings  can  be  accessed  directly  by using the offsets
2267         returned  by  pcre_exec()  in  ovector.  For convenience, the functions         returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2268         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2269         string_list()  are  provided for extracting captured substrings as new,         string_list() are provided for extracting captured substrings  as  new,
2270         separate, zero-terminated strings. These functions identify  substrings         separate,  zero-terminated strings. These functions identify substrings
2271         by  number.  The  next section describes functions for extracting named         by number. The next section describes functions  for  extracting  named
2272         substrings.         substrings.
2273    
2274         A substring that contains a binary zero is correctly extracted and  has         A  substring that contains a binary zero is correctly extracted and has
2275         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
2276         string.  However, you can process such a string  by  referring  to  the         string.   However,  you  can  process such a string by referring to the
2277         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2278         string().  Unfortunately, the interface to pcre_get_substring_list() is         string().  Unfortunately, the interface to pcre_get_substring_list() is
2279         not  adequate for handling strings containing binary zeros, because the         not adequate for handling strings containing binary zeros, because  the
2280         end of the final string is not independently indicated.         end of the final string is not independently indicated.
2281    
2282         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-
2283         tions:  subject  is  the subject string that has just been successfully         tions: subject is the subject string that has  just  been  successfully
2284         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
2285         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2286         were captured by the match, including the substring  that  matched  the         were  captured  by  the match, including the substring that matched the
2287         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2288         it is greater than zero. If pcre_exec() returned zero, indicating  that         it  is greater than zero. If pcre_exec() returned zero, indicating that
2289         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
2290         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2291    
2292         The functions pcre_copy_substring() and pcre_get_substring() extract  a         The  functions pcre_copy_substring() and pcre_get_substring() extract a
2293         single  substring,  whose  number  is given as stringnumber. A value of         single substring, whose number is given as  stringnumber.  A  value  of
2294         zero extracts the substring that matched the  entire  pattern,  whereas         zero  extracts  the  substring that matched the entire pattern, whereas
2295         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2296         string(), the string is placed in buffer,  whose  length  is  given  by         string(),  the  string  is  placed  in buffer, whose length is given by
2297         buffersize,  while  for  pcre_get_substring()  a new block of memory is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2298         obtained via pcre_malloc, and its address is  returned  via  stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2299         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
2300         the terminating zero, or one of these error codes:         the terminating zero, or one of these error codes:
2301    
2302           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2303    
2304         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
2305         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2306    
2307           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2308    
2309         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2310    
2311         The  pcre_get_substring_list()  function  extracts  all  available sub-         The pcre_get_substring_list()  function  extracts  all  available  sub-
2312         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
2313         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
2314         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
2315         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
2316         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
2317         error code         error code
2318    
2319           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2320    
2321         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2322    
2323         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2324         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2325         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
2326         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2327         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2328         tive for unset substrings.         tive for unset substrings.
2329    
2330         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2331         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
2332         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2333         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2334         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.
2335         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-
2336         cial  interface  to  another  programming  language  that  cannot   use         cial   interface  to  another  programming  language  that  cannot  use
2337         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-
2338         vided.         vided.
2339    
2340    
# Line 2080  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2353  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2353              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2354              const char **stringptr);              const char **stringptr);
2355    
2356         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-
2357         ber.  For example, for this pattern         ber.  For example, for this pattern
2358    
2359           (a+)b(?<xxx>\d+)...           (a+)b(?<xxx>\d+)...
# Line 2089  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2362  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2362         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
2363         name by calling pcre_get_stringnumber(). The first argument is the com-         name by calling pcre_get_stringnumber(). The first argument is the com-
2364         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
2365         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2366         subpattern of that name.         subpattern of that name.
2367    
2368         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
2369         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2370         are also two functions that do the whole job.         are also two functions that do the whole job.
2371    
2372         Most   of   the   arguments    of    pcre_copy_named_substring()    and         Most    of    the    arguments   of   pcre_copy_named_substring()   and
2373         pcre_get_named_substring()  are  the  same  as  those for the similarly         pcre_get_named_substring() are the same  as  those  for  the  similarly
2374         named functions that extract by number. As these are described  in  the         named  functions  that extract by number. As these are described in the
2375         previous  section,  they  are not re-described here. There are just two         previous section, they are not re-described here. There  are  just  two
2376         differences:         differences:
2377    
2378         First, instead of a substring number, a substring name is  given.  Sec-         First,  instead  of a substring number, a substring name is given. Sec-
2379         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
2380         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
2381         name-to-number translation table.         name-to-number translation table.
2382    
2383         These  functions call pcre_get_stringnumber(), and if it succeeds, they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2384         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2385         ate.         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2386           behaviour may not be what you want (see the next section).
2387    
2388    
2389  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
# Line 2121  DUPLICATE SUBPATTERN NAMES Line 2395  DUPLICATE SUBPATTERN NAMES
2395         subpatterns are not required to  be  unique.  Normally,  patterns  with         subpatterns are not required to  be  unique.  Normally,  patterns  with
2396         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
2397         subpatterns participates. An example is shown in the pcrepattern  docu-         subpatterns participates. An example is shown in the pcrepattern  docu-
2398         mentation. When duplicates are present, pcre_copy_named_substring() and         mentation.
2399    
2400           When    duplicates   are   present,   pcre_copy_named_substring()   and
2401         pcre_get_named_substring() return the first substring corresponding  to         pcre_get_named_substring() return the first substring corresponding  to
2402         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
2403         returned.  The pcre_get_stringnumber() function returns one of the num-         (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2404         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,
2405         is.         but it is not defined which it is.
2406    
2407         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
2408         name,  you  must  use  the pcre_get_stringtable_entries() function. The         name,  you  must  use  the pcre_get_stringtable_entries() function. The
# Line 2318  SEE ALSO Line 2594  SEE ALSO
2594         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2595         tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).         tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2596    
2597  Last updated: 30 November 2006  
2598  Copyright (c) 1997-2006 University of Cambridge.  AUTHOR
2599    
2600           Philip Hazel
2601           University Computing Service
2602           Cambridge CB2 3QH, England.
2603    
2604    
2605    REVISION
2606    
2607           Last updated: 12 April 2008
2608           Copyright (c) 1997-2008 University of Cambridge.
2609  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2610    
2611    
# Line 2346  PCRE CALLOUTS Line 2632  PCRE CALLOUTS
2632         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2633         points:         points:
2634    
2635           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2636    
2637         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
2638         called, PCRE automatically  inserts  callouts,  all  with  number  255,         called, PCRE automatically  inserts  callouts,  all  with  number  255,
# Line 2421  THE CALLOUT INTERFACE Line 2707  THE CALLOUT INTERFACE
2707         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2708         were passed to pcre_exec().         were passed to pcre_exec().
2709    
2710         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
2711         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
2712         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
2713         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2714           function may be called several times from the same point in the pattern
2715           for different starting points in the subject.
2716    
2717         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
2718         the current match pointer.         the current match pointer.
# Line 2477  RETURN VALUES Line 2765  RETURN VALUES
2765         reserved for use by callout functions; it will never be  used  by  PCRE         reserved for use by callout functions; it will never be  used  by  PCRE
2766         itself.         itself.
2767    
2768  Last updated: 28 February 2005  
2769  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2770    
2771           Philip Hazel
2772           University Computing Service
2773           Cambridge CB2 3QH, England.
2774    
2775    
2776    REVISION
2777    
2778           Last updated: 29 May 2007
2779           Copyright (c) 1997-2007 University of Cambridge.
2780  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2781    
2782    
# Line 2493  DIFFERENCES BETWEEN PCRE AND PERL Line 2791  DIFFERENCES BETWEEN PCRE AND PERL
2791    
2792         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2793         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences described here  are  mainly
2794         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
2795         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.
2796    
2797         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
2798         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 2559  DIFFERENCES BETWEEN PCRE AND PERL Line 2857  DIFFERENCES BETWEEN PCRE AND PERL
2857         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2858         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2859    
2860         11. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2861           (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2862           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2863           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2864           ture group; this is different to Perl.
2865    
2866           12. PCRE provides some extensions to the Perl regular expression facil-
2867         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
2868         versions, some of which (such as named parentheses) have been  in  PCRE         versions, some of which (such as named parentheses) have been  in  PCRE
2869         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 2572  DIFFERENCES BETWEEN PCRE AND PERL Line 2876  DIFFERENCES BETWEEN PCRE AND PERL
2876         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2877    
2878         (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-
2879         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2880         ignored. (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
2881    
2882         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2883         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 2585  DIFFERENCES BETWEEN PCRE AND PERL Line 2889  DIFFERENCES BETWEEN PCRE AND PERL
2889         (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-
2890         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2891    
2892         (g) The callout facility is PCRE-specific.         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2893           CRLF by the PCRE_BSR_ANYCRLF option.
2894    
2895           (h) The callout facility is PCRE-specific.
2896    
2897         (h) The partial matching facility is PCRE-specific.         (i) The partial matching facility is PCRE-specific.
2898    
2899         (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,
2900         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2901    
2902         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2903         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2904    
2905  Last updated: 28 November 2006         (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2906  Copyright (c) 1997-2006 University of Cambridge.         of a pattern that set overall options that cannot be changed within the
2907           pattern.
2908    
2909    
2910    AUTHOR
2911    
2912           Philip Hazel
2913           University Computing Service
2914           Cambridge CB2 3QH, England.
2915    
2916    
2917    REVISION
2918    
2919           Last updated: 11 September 2007
2920           Copyright (c) 1997-2007 University of Cambridge.
2921  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2922    
2923    
# Line 2609  NAME Line 2930  NAME
2930    
2931  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2932    
2933         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2934         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2935         documentation  and  in  a  number  of books, some of which have copious         tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
2936         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         semantics as closely as it can. PCRE  also  supports  some  alternative
2937         by  O'Reilly, covers regular expressions in great detail. This descrip-         regular  expression  syntax (which does not conflict with the Perl syn-
2938         tion of PCRE's regular expressions is intended as reference material.         tax) in order to provide some compatibility with regular expressions in
2939           Python, .NET, and Oniguruma.
2940    
2941           Perl's  regular expressions are described in its own documentation, and
2942           regular expressions in general are covered in a number of  books,  some
2943           of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
2944           Expressions", published by  O'Reilly,  covers  regular  expressions  in
2945           great  detail.  This  description  of  PCRE's  regular  expressions  is
2946           intended as reference material.
2947    
2948         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2949         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 2628  PCRE REGULAR EXPRESSION DETAILS Line 2957  PCRE REGULAR EXPRESSION DETAILS
2957         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2958         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
2959         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
2960         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
2961         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2962         the pcrematching page.         alternative function, and how it differs from the normal function,  are
2963           discussed in the pcrematching page.
2964    
2965    
2966    NEWLINE CONVENTIONS
2967    
2968           PCRE  supports five different conventions for indicating line breaks in
2969           strings: a single CR (carriage return) character, a  single  LF  (line-
2970           feed) character, the two-character sequence CRLF, any of the three pre-
2971           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2972           discussion  about newlines, and shows how to set the newline convention
2973           in the options arguments for the compiling and matching functions.
2974    
2975           It is also possible to specify a newline convention by starting a  pat-
2976           tern string with one of the following five sequences:
2977    
2978             (*CR)        carriage return
2979             (*LF)        linefeed
2980             (*CRLF)      carriage return, followed by linefeed
2981             (*ANYCRLF)   any of the three above
2982             (*ANY)       all Unicode newline sequences
2983    
2984           These override the default and the options given to pcre_compile(). For
2985           example, on a Unix system where LF is the default newline sequence, the
2986           pattern
2987    
2988             (*CR)a.b
2989    
2990           changes the convention to CR. That pattern matches "a\nb" because LF is
2991           no longer a newline. Note that these special settings,  which  are  not
2992           Perl-compatible,  are  recognized  only at the very start of a pattern,
2993           and that they must be in upper case.  If  more  than  one  of  them  is
2994           present, the last one is used.
2995    
2996           The  newline  convention  does  not  affect what the \R escape sequence
2997           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2998           compatibility.  However, this can be changed; see the description of \R
2999           in the section entitled "Newline sequences" below. A change of \R  set-
3000           ting can be combined with a change of newline convention.
3001    
3002    
3003  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
3004    
3005         A regular expression is a pattern that is  matched  against  a  subject         A  regular  expression  is  a pattern that is matched against a subject
3006         string  from  left  to right. Most characters stand for themselves in a         string from left to right. Most characters stand for  themselves  in  a
3007         pattern, and match the corresponding characters in the  subject.  As  a         pattern,  and  match  the corresponding characters in the subject. As a
3008         trivial example, the pattern         trivial example, the pattern
3009    
3010           The quick brown fox           The quick brown fox
3011    
3012         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
3013         caseless matching is specified (the PCRE_CASELESS option), letters  are         caseless  matching is specified (the PCRE_CASELESS option), letters are
3014         matched  independently  of case. In UTF-8 mode, PCRE always understands         matched independently of case. In UTF-8 mode, PCRE  always  understands
3015         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
3016         caseless  matching  is always possible. For characters with higher val-         caseless matching is always possible. For characters with  higher  val-
3017         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
3018         property  support,  but  not  otherwise.   If  you want to use caseless         property support, but not otherwise.   If  you  want  to  use  caseless
3019         matching for characters 128 and above, you must  ensure  that  PCRE  is         matching  for  characters  128  and above, you must ensure that PCRE is
3020         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
3021    
3022         The  power  of  regular  expressions  comes from the ability to include         The power of regular expressions comes  from  the  ability  to  include
3023         alternatives and repetitions in the pattern. These are encoded  in  the         alternatives  and  repetitions in the pattern. These are encoded in the
3024         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
3025         but instead are interpreted in some special way.         but instead are interpreted in some special way.
3026    
3027         There are two different sets of metacharacters: those that  are  recog-         There  are  two different sets of metacharacters: those that are recog-
3028         nized  anywhere in the pattern except within square brackets, and those         nized anywhere in the pattern except within square brackets, and  those
3029         that are recognized within square brackets.  Outside  square  brackets,         that  are  recognized  within square brackets. Outside square brackets,
3030         the metacharacters are as follows:         the metacharacters are as follows:
3031    
3032           \      general escape character with several uses           \      general escape character with several uses
# Line 2678  CHARACTERS AND METACHARACTERS Line 3045  CHARACTERS AND METACHARACTERS
3045                  also "possessive quantifier"                  also "possessive quantifier"
3046           {      start min/max quantifier           {      start min/max quantifier
3047    
3048         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
3049         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
3050    
3051           \      general escape character           \      general escape character
# Line 2688  CHARACTERS AND METACHARACTERS Line 3055  CHARACTERS AND METACHARACTERS
3055                    syntax)                    syntax)
3056           ]      terminates the character class           ]      terminates the character class
3057    
3058         The following sections describe the use of each of the  metacharacters.         The  following sections describe the use of each of the metacharacters.
3059    
3060    
3061  BACKSLASH  BACKSLASH
3062    
3063         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
3064         a non-alphanumeric character, it takes away any  special  meaning  that         a  non-alphanumeric  character,  it takes away any special meaning that
3065         character  may  have.  This  use  of  backslash  as an escape character         character may have. This  use  of  backslash  as  an  escape  character
3066         applies both inside and outside character classes.         applies both inside and outside character classes.
3067    
3068         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
3069         pattern.   This  escaping  action  applies whether or not the following         pattern.  This escaping action applies whether  or  not  the  following
3070         character would otherwise be interpreted as a metacharacter, so  it  is         character  would  otherwise be interpreted as a metacharacter, so it is
3071         always  safe  to  precede  a non-alphanumeric with backslash to specify         always safe to precede a non-alphanumeric  with  backslash  to  specify
3072         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-
3073         slash, you write \\.         slash, you write \\.
3074    
3075         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
3076         the pattern (other than in a character class) and characters between  a         the  pattern (other than in a character class) and characters between a
3077         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
3078         ing backslash can be used to include a whitespace  or  #  character  as         ing  backslash  can  be  used to include a whitespace or # character as
3079         part of the pattern.         part of the pattern.
3080    
3081         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-
3082         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-
3083         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
3084         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
3085         tion. Note the following examples:         tion. Note the following examples:
3086    
3087           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2724  BACKSLASH Line 3091  BACKSLASH
3091           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3092           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3093    
3094         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
3095         classes.         classes.
3096    
3097     Non-printing characters     Non-printing characters
3098    
3099         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-
3100         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
3101         appearance of non-printing characters, apart from the binary zero  that         appearance  of non-printing characters, apart from the binary zero that
3102         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates a pattern, but when a pattern  is  being  prepared  by  text
3103         editing, it is usually easier  to  use  one  of  the  following  escape         editing,  it  is  usually  easier  to  use  one of the following escape
3104         sequences than the binary character it represents:         sequences than the binary character it represents:
3105    
3106           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3107           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3108           \e        escape (hex 1B)           \e        escape (hex 1B)
3109           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3110           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3111           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3112           \t        tab (hex 09)           \t        tab (hex 09)
3113           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
3114           \xhh      character with hex code hh           \xhh      character with hex code hh
3115           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3116    
3117         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,
3118         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
3119         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;
3120         becomes hex 7B.         becomes hex 7B.
3121    
3122         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
3123         in  upper  or  lower case). Any number of hexadecimal digits may appear         in upper or lower case). Any number of hexadecimal  digits  may  appear
3124         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
3125         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,
3126         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger
3127         hexadecimal  digits  appear between \x{ and }, or if there is no termi-         than the largest Unicode code point, which is 10FFFF.
3128         nating }, this form of escape is not recognized.  Instead, the  initial  
3129         \x will be interpreted as a basic hexadecimal escape, with no following         If characters other than hexadecimal digits appear between \x{  and  },
3130         digits, giving a character whose value is zero.         or if there is no terminating }, this form of escape is not recognized.
3131           Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal
3132           escape,  with  no  following  digits, giving a character whose value is
3133           zero.
3134    
3135         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
3136         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 2815  BACKSLASH Line 3185  BACKSLASH
3185    
3186     Absolute and relative back references     Absolute and relative back references
3187    
3188         The sequence \g followed by a positive or negative  number,  optionally         The sequence \g followed by an unsigned or a negative  number,  option-
3189         enclosed  in  braces,  is  an absolute or relative back reference. Back         ally  enclosed  in braces, is an absolute or relative back reference. A
3190         references are discussed later, following the discussion  of  parenthe-         named back reference can be coded as \g{name}. Back references are dis-
3191         sized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3192    
3193       Absolute and relative subroutine calls
3194    
3195           For  compatibility with Oniguruma, the non-Perl syntax \g followed by a
3196           name or a number enclosed either in angle brackets or single quotes, is
3197           an  alternative  syntax for referencing a subpattern as a "subroutine".
3198           Details are discussed later.   Note  that  \g{...}  (Perl  syntax)  and
3199           \g<...>  (Oniguruma  syntax)  are  not synonymous. The former is a back
3200           reference; the latter is a subroutine call.
3201    
3202     Generic character types     Generic character types
3203    
# Line 2827  BACKSLASH Line 3206  BACKSLASH
3206    
3207           \d     any decimal digit           \d     any decimal digit
3208           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3209             \h     any horizontal whitespace character
3210             \H     any character that is not a horizontal whitespace character
3211           \s     any whitespace character           \s     any whitespace character
3212           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3213             \v     any vertical whitespace character
3214             \V     any character that is not a vertical whitespace character
3215           \w     any "word" character           \w     any "word" character
3216           \W     any "non-word" character           \W     any "non-word" character
3217    
3218         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
3219         into  two disjoint sets. Any given character matches one, and only one,         into two disjoint sets. Any given character matches one, and only  one,
3220         of each pair.         of each pair.
3221    
3222         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
3223         acter  classes.  They each match one character of the appropriate type.         acter classes. They each match one character of the  appropriate  type.
3224         If the current matching point is at the end of the subject string,  all         If  the current matching point is at the end of the subject string, all
3225         of them fail, since there is no character to match.         of them fail, since there is no character to match.
3226    
3227         For  compatibility  with Perl, \s does not match the VT character (code         For compatibility with Perl, \s does not match the VT  character  (code
3228         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
3229         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
3230         "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-
3231         ter. In PCRE, it never does.)         ter. In PCRE, it never does.
3232    
3233         A "word" character is an underscore or any character less than 256 that         In UTF-8 mode, characters with values greater than 128 never match  \d,
        is a letter or digit. The definition of  letters  and  digits  is  con-  
        trolled  by PCRE's low-valued character tables, and may vary if locale-  
        specific matching is taking place (see "Locale support" in the  pcreapi  
        page).  For  example,  in  the  "fr_FR" (French) locale, some character  
        codes greater than 128 are used for accented  letters,  and  these  are  
        matched by \w.  
   
        In  UTF-8 mode, characters with values greater than 128 never match \d,  
3234         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3235         code  character  property support is available. The use of locales with         code character property support is available.  These  sequences  retain
3236         Unicode is discouraged.         their original meanings from before UTF-8 support was available, mainly
3237           for efficiency reasons.
3238    
3239           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3240           the  other  sequences, these do match certain high-valued codepoints in
3241           UTF-8 mode.  The horizontal space characters are:
3242    
3243             U+0009     Horizontal tab
3244             U+0020     Space
3245             U+00A0     Non-break space
3246             U+1680     Ogham space mark
3247             U+180E     Mongolian vowel separator
3248             U+2000     En quad
3249             U+2001     Em quad
3250             U+2002     En space
3251             U+2003     Em space
3252             U+2004     Three-per-em space
3253             U+2005     Four-per-em space
3254             U+2006     Six-per-em space
3255             U+2007     Figure space
3256             U+2008     Punctuation space
3257             U+2009     Thin space
3258             U+200A     Hair space
3259             U+202F     Narrow no-break space
3260             U+205F     Medium mathematical space
3261             U+3000     Ideographic space
3262    
3263           The vertical space characters are:
3264    
3265             U+000A     Linefeed
3266             U+000B     Vertical tab
3267             U+000C     Formfeed
3268             U+000D     Carriage return
3269             U+0085     Next line
3270             U+2028     Line separator
3271             U+2029     Paragraph separator
3272    
3273           A "word" character is an underscore or any character less than 256 that
3274           is  a  letter  or  digit.  The definition of letters and digits is con-
3275           trolled by PCRE's low-valued character tables, and may vary if  locale-
3276           specific  matching is taking place (see "Locale support" in the pcreapi
3277           page). For example, in a French locale such  as  "fr_FR"  in  Unix-like
3278           systems,  or "french" in Windows, some character codes greater than 128
3279           are used for accented letters, and these are matched by \w. The use  of
3280           locales with Unicode is discouraged.
3281    
3282     Newline sequences     Newline sequences
3283    
3284         Outside a character class, the escape sequence \R matches  any  Unicode         Outside  a  character class, by default, the escape sequence \R matches
3285         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
3286         equivalent to the following:         mode \R is equivalent to the following:
3287    
3288           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3289    
3290         This is an example of an "atomic group", details  of  which  are  given         This  is  an  example  of an "atomic group", details of which are given
3291         below.  This particular group matches either the two-character sequence         below.  This particular group matches either the two-character sequence
3292         CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,         CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
3293         U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage         U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3294         return, U+000D), or NEL (next line, U+0085). The two-character sequence         return, U+000D), or NEL (next line, U+0085). The two-character sequence
3295         is treated as a single unit that cannot be split.         is treated as a single unit that cannot be split.
3296    
3297         In  UTF-8  mode, two additional characters whose codepoints are greater         In UTF-8 mode, two additional characters whose codepoints  are  greater
3298         than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-         than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3299         rator,  U+2029).   Unicode character property support is not needed for         rator, U+2029).  Unicode character property support is not  needed  for
3300         these characters to be recognized.         these characters to be recognized.
3301    
3302           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3303           the complete set  of  Unicode  line  endings)  by  setting  the  option
3304           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3305           (BSR is an abbrevation for "backslash R".) This can be made the default
3306           when  PCRE  is  built;  if this is the case, the other behaviour can be
3307           requested via the PCRE_BSR_UNICODE option.   It  is  also  possible  to
3308           specify  these  settings  by  starting a pattern string with one of the
3309           following sequences:
3310    
3311             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3312             (*BSR_UNICODE)   any Unicode newline sequence
3313    
3314           These override the default and the options given to pcre_compile(), but
3315           they can be overridden by options given to pcre_exec(). Note that these
3316           special settings, which are not Perl-compatible, are recognized only at
3317           the  very  start  of a pattern, and that they must be in upper case. If
3318           more than one of them is present, the last one is  used.  They  can  be
3319           combined  with  a  change of newline convention, for example, a pattern
3320           can start with:
3321    
3322             (*ANY)(*BSR_ANYCRLF)
3323    
3324         Inside a character class, \R matches the letter "R".         Inside a character class, \R matches the letter "R".
3325    
3326     Unicode character properties     Unicode character properties
3327    
3328         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3329         tional  escape  sequences  to  match character properties are available         tional  escape sequences that match characters with specific properties
3330         when UTF-8 mode is selected. They are:         are available.  When not in UTF-8 mode, these sequences are  of  course
3331           limited  to  testing characters whose codepoints are less than 256, but
3332           they do work in this mode.  The extra escape sequences are:
3333    
3334           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3335           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
# Line 2981  BACKSLASH Line 3424  BACKSLASH
3424         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
3425         classified as a modifier or "other".         classified as a modifier or "other".
3426    
3427           The  Cs  (Surrogate)  property  applies only to characters in the range
3428           U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see
3429           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3430           ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in
3431           the pcreapi page).
3432    
3433         The  long  synonyms  for  these  properties that Perl supports (such as         The  long  synonyms  for  these  properties that Perl supports (such as
3434         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3435         any of these properties with "Is".         any of these properties with "Is".
# Line 3000  BACKSLASH Line 3449  BACKSLASH
3449         That  is,  it matches a character without the "mark" property, followed         That  is,  it matches a character without the "mark" property, followed
3450         by zero or more characters with the "mark"  property,  and  treats  the         by zero or more characters with the "mark"  property,  and  treats  the
3451         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence  as  an  atomic group (see below).  Characters with the "mark"
3452         property are typically accents that affect the preceding character.         property are typically accents that  affect  the  preceding  character.
3453           None  of  them  have  codepoints less than 256, so in non-UTF-8 mode \X
3454           matches any one character.
3455    
3456         Matching characters by Unicode property is not fast, because  PCRE  has         Matching characters by Unicode property is not fast, because  PCRE  has
3457         to  search  a  structure  that  contains data for over fifteen thousand         to  search  a  structure  that  contains data for over fifteen thousand
3458         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3459         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3460    
3461       Resetting the match start
3462    
3463           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3464           ously matched characters not  to  be  included  in  the  final  matched
3465           sequence. For example, the pattern:
3466    
3467             foo\Kbar
3468    
3469           matches  "foobar",  but reports that it has matched "bar". This feature
3470           is similar to a lookbehind assertion (described  below).   However,  in
3471           this  case, the part of the subject before the real match does not have
3472           to be of fixed length, as lookbehind assertions do. The use of \K  does
3473           not  interfere  with  the setting of captured substrings.  For example,
3474           when the pattern
3475    
3476             (foo)\Kbar
3477    
3478           matches "foobar", the first substring is still set to "foo".
3479    
3480     Simple assertions     Simple assertions
3481    
3482         The  final use of backslash is for certain simple assertions. An asser-         The final use of backslash is for certain simple assertions. An  asser-
3483         tion specifies a condition that has to be met at a particular point  in         tion  specifies a condition that has to be met at a particular point in
3484         a  match, without consuming any characters from the subject string. The         a match, without consuming any characters from the subject string.  The
3485         use of subpatterns for more complicated assertions is described  below.         use  of subpatterns for more complicated assertions is described below.
3486         The backslashed assertions are:         The backslashed assertions are:
3487    
3488           \b     matches at a word boundary           \b     matches at a word boundary
# Line 3023  BACKSLASH Line 3493  BACKSLASH
3493           \z     matches only at the end of the subject           \z     matches only at the end of the subject
3494           \G     matches at the first matching position in the subject           \G     matches at the first matching position in the subject
3495    
3496         These  assertions may not appear in character classes (but note that \b         These assertions may not appear in character classes (but note that  \b
3497         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3498         acter class).         acter class).
3499    
3500         A  word  boundary is a position in the subject string where the current         A word boundary is a position in the subject string where  the  current
3501         character and the previous character do not both match \w or  \W  (i.e.         character  and  the previous character do not both match \w or \W (i.e.
3502         one  matches  \w  and the other matches \W), or the start or end of the         one matches \w and the other matches \W), or the start or  end  of  the
3503         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
3504    
3505         The \A, \Z, and \z assertions differ from  the  traditional  circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3506         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
3507         at the very start and end of the subject string, whatever  options  are         at  the  very start and end of the subject string, whatever options are
3508         set.  Thus,  they are independent of multiline mode. These three asser-         set. Thus, they are independent of multiline mode. These  three  asser-
3509         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3510         affect  only the behaviour of the circumflex and dollar metacharacters.         affect only the behaviour of the circumflex and dollar  metacharacters.
3511         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However,  if the startoffset argument of pcre_exec() is non-zero, indi-
3512         cating that matching is to start at a point other than the beginning of         cating that matching is to start at a point other than the beginning of
3513         the subject, \A can never match. The difference between \Z  and  \z  is         the  subject,  \A  can never match. The difference between \Z and \z is
3514         that \Z matches before a newline at the end of the string as well as at         that \Z matches before a newline at the end of the string as well as at
3515         the very end, whereas \z matches only at the end.         the very end, whereas \z matches only at the end.
3516    
3517         The \G assertion is true only when the current matching position is  at         The  \G assertion is true only when the current matching position is at
3518         the  start point of the match, as specified by the startoffset argument         the start point of the match, as specified by the startoffset  argument
3519         of pcre_exec(). It differs from \A when the  value  of  startoffset  is         of  pcre_exec().  It  differs  from \A when the value of startoffset is
3520         non-zero.  By calling pcre_exec() multiple times with appropriate argu-         non-zero. By calling pcre_exec() multiple times with appropriate  argu-
3521         ments, you can mimic Perl's /g option, and it is in this kind of imple-         ments, you can mimic Perl's /g option, and it is in this kind of imple-
3522         mentation where \G can be useful.         mentation where \G can be useful.
3523    
3524         Note,  however,  that  PCRE's interpretation of \G, as the start of the         Note, however, that PCRE's interpretation of \G, as the  start  of  the
3525         current match, is subtly different from Perl's, which defines it as the         current match, is subtly different from Perl's, which defines it as the
3526         end  of  the  previous  match. In Perl, these can be different when the         end of the previous match. In Perl, these can  be  different  when  the
3527         previously matched string was empty. Because PCRE does just  one  match         previously  matched  string was empty. Because PCRE does just one match
3528         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3529    
3530         If  all  the alternatives of a pattern begin with \G, the expression is         If all the alternatives of a pattern begin with \G, the  expression  is
3531         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3532         in the compiled regular expression.         in the compiled regular expression.
3533    
# Line 3065  BACKSLASH Line 3535  BACKSLASH
3535  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3536    
3537         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3538         character is an assertion that is true only  if  the  current  matching         character  is  an  assertion  that is true only if the current matching
3539         point  is  at the start of the subject string. If the startoffset argu-         point is at the start of the subject string. If the  startoffset  argu-
3540         ment of pcre_exec() is non-zero, circumflex  can  never  match  if  the         ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the
3541         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex
3542         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3543    
3544         Circumflex need not be the first character of the pattern if  a  number         Circumflex  need  not be the first character of the pattern if a number
3545         of  alternatives are involved, but it should be the first thing in each         of alternatives are involved, but it should be the first thing in  each
3546         alternative in which it appears if the pattern is ever  to  match  that         alternative  in  which  it appears if the pattern is ever to match that
3547         branch.  If all possible alternatives start with a circumflex, that is,         branch. If all possible alternatives start with a circumflex, that  is,
3548         if the pattern is constrained to match only at the start  of  the  sub-         if  the  pattern  is constrained to match only at the start of the sub-
3549         ject,  it  is  said  to be an "anchored" pattern. (There are also other         ject, it is said to be an "anchored" pattern.  (There  are  also  other
3550         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3551    
3552         A dollar character is an assertion that is true  only  if  the  current         A  dollar  character  is  an assertion that is true only if the current
3553         matching  point  is  at  the  end of the subject string, or immediately         matching point is at the end of  the  subject  string,  or  immediately
3554         before a newline at the end of the string (by default). Dollar need not         before a newline at the end of the string (by default). Dollar need not
3555         be  the  last  character of the pattern if a number of alternatives are         be the last character of the pattern if a number  of  alternatives  are
3556         involved, but it should be the last item in  any  branch  in  which  it         involved,  but  it  should  be  the last item in any branch in which it
3557         appears. Dollar has no special meaning in a character class.         appears. Dollar has no special meaning in a character class.
3558    
3559         The  meaning  of  dollar  can be changed so that it matches only at the         The meaning of dollar can be changed so that it  matches  only  at  the
3560         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at         very  end  of  the string, by setting the PCRE_DOLLAR_ENDONLY option at
3561         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3562    
3563         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3564         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex         PCRE_MULTILINE  option  is  set.  When  this  is the case, a circumflex
3565         matches  immediately after internal newlines as well as at the start of         matches immediately after internal newlines as well as at the start  of
3566         the subject string. It does not match after a  newline  that  ends  the         the  subject  string.  It  does not match after a newline that ends the
3567         string.  A dollar matches before any newlines in the string, as well as         string. A dollar matches before any newlines in the string, as well  as
3568         at the very end, when PCRE_MULTILINE is set. When newline is  specified         at  the very end, when PCRE_MULTILINE is set. When newline is specified
3569         as  the  two-character  sequence CRLF, isolated CR and LF characters do         as the two-character sequence CRLF, isolated CR and  LF  characters  do
3570         not indicate newlines.         not indicate newlines.
3571    
3572         For example, the pattern /^abc$/ matches the subject string  "def\nabc"         For  example, the pattern /^abc$/ matches the subject string "def\nabc"
3573         (where  \n  represents a newline) in multiline mode, but not otherwise.         (where \n represents a newline) in multiline mode, but  not  otherwise.
3574         Consequently, patterns that are anchored in single  line  mode  because         Consequently,  patterns  that  are anchored in single line mode because
3575         all  branches  start  with  ^ are not anchored in multiline mode, and a         all branches start with ^ are not anchored in  multiline  mode,  and  a
3576         match for circumflex is  possible  when  the  startoffset  argument  of         match  for  circumflex  is  possible  when  the startoffset argument of
3577         pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if         pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is  ignored  if
3578         PCRE_MULTILINE is set.         PCRE_MULTILINE is set.
3579    
3580         Note that the sequences \A, \Z, and \z can be used to match  the  start         Note  that  the sequences \A, \Z, and \z can be used to match the start
3581         and  end of the subject in both modes, and if all branches of a pattern         and end of the subject in both modes, and if all branches of a  pattern
3582         start with \A it is always anchored, whether or not  PCRE_MULTILINE  is         start  with  \A it is always anchored, whether or not PCRE_MULTILINE is
3583         set.         set.
3584    
3585    
3586  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3587    
3588         Outside a character class, a dot in the pattern matches any one charac-         Outside a character class, a dot in the pattern matches any one charac-
3589         ter in the subject string except (by default) a character  that  signi-         ter  in  the subject string except (by default) a character that signi-
3590         fies  the  end  of  a line. In UTF-8 mode, the matched character may be         fies the end of a line. In UTF-8 mode, the  matched  character  may  be
3591         more than one byte long.         more than one byte long.
3592    
3593         When a line ending is defined as a single character, dot never  matches         When  a line ending is defined as a single character, dot never matches
3594         that  character; when the two-character sequence CRLF is used, dot does         that character; when the two-character sequence CRLF is used, dot  does
3595         not match CR if it is immediately followed  by  LF,  but  otherwise  it         not  match  CR  if  it  is immediately followed by LF, but otherwise it
3596         matches  all characters (including isolated CRs and LFs). When any Uni-         matches all characters (including isolated CRs and LFs). When any  Uni-
3597         code line endings are being recognized, dot does not match CR or LF  or         code  line endings are being recognized, dot does not match CR or LF or
3598         any of the other line ending characters.         any of the other line ending characters.
3599    
3600         The  behaviour  of  dot  with regard to newlines can be changed. If the         The behaviour of dot with regard to newlines can  be  changed.  If  the
3601         PCRE_DOTALL option is set, a dot matches  any  one  character,  without         PCRE_DOTALL  option  is  set,  a dot matches any one character, without
3602         exception. If the two-character sequence CRLF is present in the subject         exception. If the two-character sequence CRLF is present in the subject
3603         string, it takes two dots to match it.         string, it takes two dots to match it.
3604    
3605         The handling of dot is entirely independent of the handling of  circum-         The  handling of dot is entirely independent of the handling of circum-
3606         flex  and  dollar,  the  only relationship being that they both involve         flex and dollar, the only relationship being  that  they  both  involve
3607         newlines. Dot has no special meaning in a character class.         newlines. Dot has no special meaning in a character class.
3608    
3609    
3610  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3611    
3612         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3613         both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any         both in and out of UTF-8 mode. Unlike a  dot,  it  always  matches  any
3614         line-ending characters. The feature is provided in  Perl  in  order  to         line-ending  characters.  The  feature  is provided in Perl in order to
3615         match  individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-         match individual bytes in UTF-8 mode. Because it breaks up UTF-8  char-
3616         acters into individual bytes, what remains in the string may be a  mal-         acters  into individual bytes, what remains in the string may be a mal-
3617         formed  UTF-8  string.  For this reason, the \C escape sequence is best         formed UTF-8 string. For this reason, the \C escape  sequence  is  best
3618         avoided.         avoided.
3619    
3620         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE  does  not  allow \C to appear in lookbehind assertions (described
3621         below),  because  in UTF-8 mode this would make it impossible to calcu-         below), because in UTF-8 mode this would make it impossible  to  calcu-
3622         late the length of the lookbehind.         late the length of the lookbehind.
3623    
3624    
# Line 3157  SQUARE BRACKETS AND CHARACTER CLASSES Line 3627  SQUARE BRACKETS AND CHARACTER CLASSES
3627         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3628         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3629         cial. If a closing square bracket is required as a member of the class,         cial. If a closing square bracket is required as a member of the class,
3630         it  should  be  the first data character in the class (after an initial         it should be the first data character in the class  (after  an  initial
3631         circumflex, if present) or escaped with a backslash.         circumflex, if present) or escaped with a backslash.
3632    
3633         A character class matches a single character in the subject.  In  UTF-8         A  character  class matches a single character in the subject. In UTF-8
3634         mode,  the character may occupy more than one byte. A matched character         mode, the character may occupy more than one byte. A matched  character
3635         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3636         character  in  the  class definition is a circumflex, in which case the         character in the class definition is a circumflex, in  which  case  the
3637         subject character must not be in the set defined by  the  class.  If  a         subject  character  must  not  be in the set defined by the class. If a
3638         circumflex  is actually required as a member of the class, ensure it is         circumflex is actually required as a member of the class, ensure it  is
3639         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3640    
3641         For example, the character class [aeiou] matches any lower case  vowel,         For  example, the character class [aeiou] matches any lower case vowel,
3642         while  [^aeiou]  matches  any character that is not a lower case vowel.         while [^aeiou] matches any character that is not a  lower  case  vowel.
3643         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3644         characters  that  are in the class by enumerating those that are not. A         characters that are in the class by enumerating those that are  not.  A
3645         class that starts with a circumflex is not an assertion: it still  con-         class  that starts with a circumflex is not an assertion: it still con-
3646         sumes  a  character  from the subject string, and therefore it fails if         sumes a character from the subject string, and therefore  it  fails  if
3647         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3648    
3649         In UTF-8 mode, characters with values greater than 255 can be  included         In  UTF-8 mode, characters with values greater than 255 can be included
3650         in  a  class as a literal string of bytes, or by using the \x{ escaping         in a class as a literal string of bytes, or by using the  \x{  escaping
3651         mechanism.         mechanism.
3652    
3653         When caseless matching is set, any letters in a  class  represent  both         When  caseless  matching  is set, any letters in a class represent both
3654         their  upper  case  and lower case versions, so for example, a caseless         their upper case and lower case versions, so for  example,  a  caseless
3655         [aeiou] matches "A" as well as "a", and a caseless  [^aeiou]  does  not         [aeiou]  matches  "A"  as well as "a", and a caseless [^aeiou] does not
3656         match  "A", whereas a caseful version would. In UTF-8 mode, PCRE always         match "A", whereas a caseful version would. In UTF-8 mode, PCRE  always
3657         understands the concept of case for characters whose  values  are  less         understands  the  concept  of case for characters whose values are less
3658         than  128, so caseless matching is always possible. For characters with         than 128, so caseless matching is always possible. For characters  with
3659         higher values, the concept of case is supported  if  PCRE  is  compiled         higher  values,  the  concept  of case is supported if PCRE is compiled
3660         with  Unicode  property support, but not otherwise.  If you want to use         with Unicode property support, but not otherwise.  If you want  to  use
3661         caseless matching for characters 128 and above, you  must  ensure  that         caseless  matching  for  characters 128 and above, you must ensure that
3662         PCRE  is  compiled  with Unicode property support as well as with UTF-8         PCRE is compiled with Unicode property support as well  as  with  UTF-8
3663         support.         support.
3664    
3665         Characters that might indicate line breaks are  never  treated  in  any         Characters  that  might  indicate  line breaks are never treated in any
3666         special  way  when  matching  character  classes,  whatever line-ending         special way  when  matching  character  classes,  whatever  line-ending
3667         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and         sequence  is  in  use,  and  whatever  setting  of  the PCRE_DOTALL and
3668         PCRE_MULTILINE options is used. A class such as [^a] always matches one         PCRE_MULTILINE options is used. A class such as [^a] always matches one
3669         of these characters.         of these characters.
3670    
3671         The minus (hyphen) character can be used to specify a range of  charac-         The  minus (hyphen) character can be used to specify a range of charac-
3672         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters in a character  class.  For  example,  [d-m]  matches  any  letter
3673         between d and m, inclusive. If a  minus  character  is  required  in  a         between  d  and  m,  inclusive.  If  a minus character is required in a
3674         class,  it  must  be  escaped  with a backslash or appear in a position         class, it must be escaped with a backslash  or  appear  in  a  position
3675         where it cannot be interpreted as indicating a range, typically as  the         where  it cannot be interpreted as indicating a range, typically as the
3676         first or last character in the class.         first or last character in the class.
3677    
3678         It is not possible to have the literal character "]" as the end charac-         It is not possible to have the literal character "]" as the end charac-
3679         ter of a range. A pattern such as [W-]46] is interpreted as a class  of         ter  of a range. A pattern such as [W-]46] is interpreted as a class of
3680         two  characters ("W" and "-") followed by a literal string "46]", so it         two characters ("W" and "-") followed by a literal string "46]", so  it
3681         would match "W46]" or "-46]". However, if the "]"  is  escaped  with  a         would  match  "W46]"  or  "-46]". However, if the "]" is escaped with a
3682         backslash  it is interpreted as the end of range, so [W-\]46] is inter-         backslash it is interpreted as the end of range, so [W-\]46] is  inter-
3683         preted as a class containing a range followed by two other  characters.         preted  as a class containing a range followed by two other characters.
3684         The  octal or hexadecimal representation of "]" can also be used to end         The octal or hexadecimal representation of "]" can also be used to  end
3685         a range.         a range.
3686    
3687         Ranges operate in the collating sequence of character values. They  can         Ranges  operate in the collating sequence of character values. They can
3688         also   be  used  for  characters  specified  numerically,  for  example         also  be  used  for  characters  specified  numerically,  for   example
3689         [\000-\037]. In UTF-8 mode, ranges can include characters whose  values         [\000-\037].  In UTF-8 mode, ranges can include characters whose values
3690         are greater than 255, for example [\x{100}-\x{2ff}].         are greater than 255, for example [\x{100}-\x{2ff}].
3691    
3692         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,
3693         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
3694         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to [][\\^_`wxyzabc], matched caselessly,  and  in  non-UTF-8  mode,  if
3695         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
3696         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
3697         concept of case for characters with values greater than 128  only  when         concept  of  case for characters with values greater than 128 only when
3698         it is compiled with Unicode property support.         it is compiled with Unicode property support.
3699    
3700         The  character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear         The character types \d, \D, \p, \P, \s, \S, \w, and \W may also  appear
3701         in a character class, and add the characters that  they  match  to  the         in  a  character  class,  and add the characters that they match to the
3702         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
3703         flex can conveniently be used with the upper case  character  types  to         flex  can  conveniently  be used with the upper case character types to
3704         specify  a  more  restricted  set of characters than the matching lower         specify a more restricted set of characters  than  the  matching  lower
3705         case type. For example, the class [^\W_] matches any letter  or  digit,         case  type.  For example, the class [^\W_] matches any letter or digit,
3706         but not underscore.         but not underscore.
3707    
3708         The  only  metacharacters  that are recognized in character classes are         The only metacharacters that are recognized in  character  classes  are
3709         backslash, hyphen (only where it can be  interpreted  as  specifying  a         backslash,  hyphen  (only  where  it can be interpreted as specifying a
3710         range),  circumflex  (only  at the start), opening square bracket (only         range), circumflex (only at the start), opening  square  bracket  (only
3711         when it can be interpreted as introducing a POSIX class name - see  the         when  it can be interpreted as introducing a POSIX class name - see the
3712         next  section),  and  the  terminating closing square bracket. However,         next section), and the terminating  closing  square  bracket.  However,
3713         escaping other non-alphanumeric characters does no harm.         escaping other non-alphanumeric characters does no harm.
3714    
3715    
3716  POSIX CHARACTER CLASSES  POSIX CHARACTER CLASSES
3717    
3718         Perl supports the POSIX notation for character classes. This uses names         Perl supports the POSIX notation for character classes. This uses names
3719         enclosed  by  [: and :] within the enclosing square brackets. PCRE also         enclosed by [: and :] within the enclosing square brackets.  PCRE  also
3720         supports this notation. For example,         supports this notation. For example,
3721    
3722           [01[:alpha:]%]           [01[:alpha:]%]
# Line 3269  POSIX CHARACTER CLASSES Line 3739  POSIX CHARACTER CLASSES
3739           word     "word" characters (same as \w)           word     "word" characters (same as \w)
3740           xdigit   hexadecimal digits           xdigit   hexadecimal digits
3741    
3742         The  "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),         The "space" characters are HT (9), LF (10), VT (11), FF (12), CR  (13),
3743         and space (32). Notice that this list includes the VT  character  (code         and  space  (32). Notice that this list includes the VT character (code
3744         11). This makes "space" different to \s, which does not include VT (for         11). This makes "space" different to \s, which does not include VT (for
3745         Perl compatibility).         Perl compatibility).
3746    
3747         The name "word" is a Perl extension, and "blank"  is  a  GNU  extension         The  name  "word"  is  a Perl extension, and "blank" is a GNU extension
3748         from  Perl  5.8. Another Perl extension is negation, which is indicated         from Perl 5.8. Another Perl extension is negation, which  is  indicated
3749         by a ^ character after the colon. For example,         by a ^ character after the colon. For example,
3750    
3751           [12[:^digit:]]           [12[:^digit:]]
3752    
3753         matches "1", "2", or any non-digit. PCRE (and Perl) also recognize  the         matches  "1", "2", or any non-digit. PCRE (and Perl) also recognize the
3754         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
3755         these are not supported, and an error is given if they are encountered.         these are not supported, and an error is given if they are encountered.
3756    
# Line 3290  POSIX CHARACTER CLASSES Line 3760  POSIX CHARACTER CLASSES
3760    
3761  VERTICAL BAR  VERTICAL BAR
3762    
3763         Vertical bar characters are used to separate alternative patterns.  For         Vertical  bar characters are used to separate alternative patterns. For
3764         example, the pattern         example, the pattern
3765    
3766           gilbert|sullivan           gilbert|sullivan
3767    
3768         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches either "gilbert" or "sullivan". Any number of alternatives  may
3769         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear,  and  an  empty  alternative  is  permitted (matching the empty
3770         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
3771         to right, and the first one that succeeds is used. If the  alternatives         to  right, and the first one that succeeds is used. If the alternatives
3772         are  within a subpattern (defined below), "succeeds" means matching the         are within a subpattern (defined below), "succeeds" means matching  the
3773         rest of the main pattern as well as the alternative in the  subpattern.         rest  of the main pattern as well as the alternative in the subpattern.
3774    
3775    
3776  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3777    
3778         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The settings of the  PCRE_CASELESS,  PCRE_MULTILINE,  PCRE_DOTALL,  and
3779         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED  options  (which are Perl-compatible) can be changed from
3780         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         within the pattern by  a  sequence  of  Perl  option  letters  enclosed
3781         option letters are         between "(?" and ")".  The option letters are
3782    
3783           i  for PCRE_CASELESS           i  for PCRE_CASELESS
3784           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 3317  INTERNAL OPTION SETTING Line 3787  INTERNAL OPTION SETTING
3787    
3788         For example, (?im) sets caseless, multiline matching. It is also possi-         For example, (?im) sets caseless, multiline matching. It is also possi-
3789         ble to unset these options by preceding the letter with a hyphen, and a         ble to unset these options by preceding the letter with a hyphen, and a
3790         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-         combined  setting and unsetting such as (?im-sx), which sets PCRE_CASE-
3791         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,         LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and  PCRE_EXTENDED,
3792         is also permitted. If a  letter  appears  both  before  and  after  the         is  also  permitted.  If  a  letter  appears  both before and after the
3793         hyphen, the option is unset.         hyphen, the option is unset.
3794    
3795         When  an option change occurs at top level (that is, not inside subpat-         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3796         tern parentheses), the change applies to the remainder of  the  pattern         can  be changed in the same way as the Perl-compatible options by using
3797           the characters J, U and X respectively.
3798    
3799           When an option change occurs at top level (that is, not inside  subpat-
3800           tern  parentheses),  the change applies to the remainder of the pattern
3801         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,
3802         PCRE extracts it into the global options (and it will therefore show up         PCRE extracts it into the global options (and it will therefore show up
3803         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3804    
3805         An  option  change  within a subpattern (see below for a description of         An option change within a subpattern (see below for  a  description  of
3806         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the current pattern that follows
3807         it, so         it, so
3808    
3809           (a(?i)b)c           (a(?i)b)c
3810    
3811         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
3812         used).  By this means, options can be made to have  different  settings         used).   By  this means, options can be made to have different settings
3813         in  different parts of the pattern. Any changes made in one alternative         in different parts of the pattern. Any changes made in one  alternative
3814         do carry on into subsequent branches within the  same  subpattern.  For         do  carry  on  into subsequent branches within the same subpattern. For
3815         example,         example,
3816    
3817           (a(?i)b|c)           (a(?i)b|c)
3818    
3819         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the
3820         first branch is abandoned before the option setting.  This  is  because         first  branch  is  abandoned before the option setting. This is because
3821         the  effects  of option settings happen at compile time. There would be         the effects of option settings happen at compile time. There  would  be
3822         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3823    
3824         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         Note:  There  are  other  PCRE-specific  options that can be set by the
3825         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
3826         the characters J, U and X respectively.         cases  the  pattern  can  contain special leading sequences to override
3827           what the application has set or what has been  defaulted.  Details  are
3828           given in the section entitled "Newline sequences" above.
3829    
3830    
3831  SUBPATTERNS  SUBPATTERNS
# Line 3361  SUBPATTERNS Line 3837  SUBPATTERNS
3837    
3838           cat(aract|erpillar|)           cat(aract|erpillar|)
3839    
3840         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches one of the words "cat", "cataract", or  "caterpillar".  Without
3841         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty         the  parentheses,  it  would  match  "cataract", "erpillar" or an empty
3842         string.         string.
3843    
3844         2.  It  sets  up  the  subpattern as a capturing subpattern. This means         2. It sets up the subpattern as  a  capturing  subpattern.  This  means
3845         that, when the whole pattern  matches,  that  portion  of  the  subject         that,  when  the  whole  pattern  matches,  that portion of the subject
3846         string that matched the subpattern is passed back to the caller via the         string that matched the subpattern is passed back to the caller via the
3847         ovector argument of pcre_exec(). Opening parentheses are  counted  from         ovector  argument  of pcre_exec(). Opening parentheses are counted from
3848         left  to  right  (starting  from 1) to obtain numbers for the capturing         left to right (starting from 1) to obtain  numbers  for  the  capturing
3849         subpatterns.         subpatterns.
3850    
3851         For example, if the string "the red king" is matched against  the  pat-         For  example,  if the string "the red king" is matched against the pat-
3852         tern         tern
3853    
3854           the ((red|white) (king|queen))           the ((red|white) (king|queen))
# Line 3380  SUBPATTERNS Line 3856  SUBPATTERNS
3856         the captured substrings are "red king", "red", and "king", and are num-         the captured substrings are "red king", "red", and "king", and are num-
3857         bered 1, 2, and 3, respectively.         bered 1, 2, and 3, respectively.
3858    
3859         The fact that plain parentheses fulfil  two  functions  is  not  always         The  fact  that  plain  parentheses  fulfil two functions is not always
3860         helpful.   There are often times when a grouping subpattern is required         helpful.  There are often times when a grouping subpattern is  required
3861         without a capturing requirement. If an opening parenthesis is  followed         without  a capturing requirement. If an opening parenthesis is followed
3862         by  a question mark and a colon, the subpattern does not do any captur-         by a question mark and a colon, the subpattern does not do any  captur-
3863         ing, and is not counted when computing the  number  of  any  subsequent         ing,  and  is  not  counted when computing the number of any subsequent
3864         capturing  subpatterns. For example, if the string "the white queen" is         capturing subpatterns. For example, if the string "the white queen"  is
3865         matched against the pattern         matched against the pattern
3866    
3867           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
# Line 3393  SUBPATTERNS Line 3869  SUBPATTERNS
3869         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3870         1 and 2. The maximum number of capturing subpatterns is 65535.         1 and 2. The maximum number of capturing subpatterns is 65535.
3871    
3872         As  a  convenient shorthand, if any option settings are required at the         As a convenient shorthand, if any option settings are required  at  the
3873         start of a non-capturing subpattern,  the  option  letters  may  appear         start  of  a  non-capturing  subpattern,  the option letters may appear
3874         between the "?" and the ":". Thus the two patterns         between the "?" and the ":". Thus the two patterns
3875    
3876           (?i:saturday|sunday)           (?i:saturday|sunday)
3877           (?:(?i)saturday|sunday)           (?:(?i)saturday|sunday)
3878    
3879         match exactly the same set of strings. Because alternative branches are         match exactly the same set of strings. Because alternative branches are
3880         tried from left to right, and options are not reset until  the  end  of         tried  from  left  to right, and options are not reset until the end of
3881         the  subpattern is reached, an option setting in one branch does affect         the subpattern is reached, an option setting in one branch does  affect
3882         subsequent branches, so the above patterns match "SUNDAY"  as  well  as         subsequent  branches,  so  the above patterns match "SUNDAY" as well as
3883         "Saturday".         "Saturday".
3884    
3885    
3886    DUPLICATE SUBPATTERN NUMBERS
3887    
3888           Perl 5.10 introduced a feature whereby each alternative in a subpattern
3889           uses  the same numbers for its capturing parentheses. Such a subpattern
3890           starts with (?| and is itself a non-capturing subpattern. For  example,
3891           consider this pattern:
3892    
3893             (?|(Sat)ur|(Sun))day
3894    
3895           Because  the two alternatives are inside a (?| group, both sets of cap-
3896           turing parentheses are numbered one. Thus, when  the  pattern  matches,
3897           you  can  look  at captured substring number one, whichever alternative
3898           matched. This construct is useful when you want to  capture  part,  but
3899           not all, of one of a number of alternatives. Inside a (?| group, paren-
3900           theses are numbered as usual, but the number is reset at the  start  of
3901           each  branch. The numbers of any capturing buffers that follow the sub-
3902           pattern start after the highest number used in any branch. The  follow-
3903           ing  example  is taken from the Perl documentation.  The numbers under-
3904           neath show in which buffer the captured content will be stored.
3905    
3906             # before  ---------------branch-reset----------- after
3907             / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3908             # 1            2         2  3        2     3     4
3909    
3910           A backreference or a recursive call to  a  numbered  subpattern  always
3911           refers to the first one in the pattern with the given number.
3912    
3913           An  alternative approach to using this "branch reset" feature is to use
3914           duplicate named subpatterns, as described in the next section.
3915    
3916    
3917  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3918    
3919         Identifying  capturing  parentheses  by number is simple, but it can be         Identifying capturing parentheses by number is simple, but  it  can  be
3920         very hard to keep track of the numbers in complicated  regular  expres-         very  hard  to keep track of the numbers in complicated regular expres-
3921         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions. Furthermore, if an  expression  is  modified,  the  numbers  may
3922         change. To help with this difficulty, PCRE supports the naming of  sub-         change.  To help with this difficulty, PCRE supports the naming of sub-
3923         patterns. This feature was not added to Perl until release 5.10. Python         patterns. This feature was not added to Perl until release 5.10. Python
3924         had the feature earlier, and PCRE introduced it at release  4.0,  using         had  the  feature earlier, and PCRE introduced it at release 4.0, using
3925         the  Python syntax. PCRE now supports both the Perl and the Python syn-         the Python syntax. PCRE now supports both the Perl and the Python  syn-
3926         tax.         tax.
3927    
3928         In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)         In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)
3929         or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References
3930         to capturing parentheses from other parts of the pattern, such as back-         to capturing parentheses from other parts of the pattern, such as back-
3931         references,  recursion,  and conditions, can be made by name as well as         references, recursion, and conditions, can be made by name as  well  as
3932         by number.         by number.
3933    
3934         Names consist of up to  32  alphanumeric  characters  and  underscores.         Names  consist  of  up  to  32 alphanumeric characters and underscores.
3935         Named  capturing  parentheses  are  still  allocated numbers as well as         Named capturing parentheses are still  allocated  numbers  as  well  as
3936         names, exactly as if the names were not present. The PCRE API  provides         names,  exactly as if the names were not present. The PCRE API provides
3937         function calls for extracting the name-to-number translation table from         function calls for extracting the name-to-number translation table from
3938         a compiled pattern. There is also a convenience function for extracting         a compiled pattern. There is also a convenience function for extracting
3939         a captured substring by name.         a captured substring by name.
3940    
3941         By  default, a name must be unique within a pattern, but it is possible         By default, a name must be unique within a pattern, but it is  possible
3942         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
3943         time.  This  can  be useful for patterns where only one instance of the         time. This can be useful for patterns where only one  instance  of  the
3944         named parentheses can match. Suppose you want to match the  name  of  a         named  parentheses  can  match. Suppose you want to match the name of a
3945         weekday,  either as a 3-letter abbreviation or as the full name, and in         weekday, either as a 3-letter abbreviation or as the full name, and  in
3946         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
3947         the line breaks) does the job:         the line breaks) does the job:
3948    
# Line 3445  NAMED SUBPATTERNS Line 3952  NAMED SUBPATTERNS
3952           (?<DN>Thu)(?:rsday)?|           (?<DN>Thu)(?:rsday)?|
3953           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
3954    
3955         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
3956         match.  The convenience  function  for  extracting  the  data  by  name         match.  (An alternative way of solving this problem is to use a "branch
3957         returns  the  substring  for  the first (and in this example, the only)         reset" subpattern, as described in the previous section.)
3958         subpattern of that name that matched.  This  saves  searching  to  find  
3959         which  numbered  subpattern  it  was. If you make a reference to a non-         The convenience function for extracting the data by  name  returns  the
3960         unique named subpattern from elsewhere in the  pattern,  the  one  that         substring  for  the first (and in this example, the only) subpattern of
3961         corresponds  to  the  lowest number is used. For further details of the         that name that matched. This saves searching  to  find  which  numbered
3962         interfaces for handling named subpatterns, see the  pcreapi  documenta-         subpattern  it  was. If you make a reference to a non-unique named sub-
3963         tion.         pattern from elsewhere in the pattern, the one that corresponds to  the
3964           lowest  number  is used. For further details of the interfaces for han-
3965           dling named subpatterns, see the pcreapi documentation.
3966    
3967    
3968  REPETITION  REPETITION
3969    
3970         Repetition  is  specified  by  quantifiers, which can follow any of the         Repetition is specified by quantifiers, which can  follow  any  of  the
3971         following items:         following items:
3972    
3973           a literal data character           a literal data character
# Line 3471  REPETITION Line 3980  REPETITION
3980           a back reference (see next section)           a back reference (see next section)
3981           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
3982    
3983         The general repetition quantifier specifies a minimum and maximum  num-         The  general repetition quantifier specifies a minimum and maximum num-
3984         ber  of  permitted matches, by giving the two numbers in curly brackets         ber of permitted matches, by giving the two numbers in  curly  brackets
3985         (braces), separated by a comma. The numbers must be  less  than  65536,         (braces),  separated  by  a comma. The numbers must be less than 65536,
3986         and the first must be less than or equal to the second. For example:         and the first must be less than or equal to the second. For example:
3987    
3988           z{2,4}           z{2,4}
3989    
3990         matches  "zz",  "zzz",  or  "zzzz". A closing brace on its own is not a         matches "zz", "zzz", or "zzzz". A closing brace on its  own  is  not  a
3991         special character. If the second number is omitted, but  the  comma  is         special  character.  If  the second number is omitted, but the comma is
3992         present,  there  is  no upper limit; if the second number and the comma         present, there is no upper limit; if the second number  and  the  comma
3993         are both omitted, the quantifier specifies an exact number of  required         are  both omitted, the quantifier specifies an exact number of required
3994         matches. Thus         matches. Thus
3995    
3996           [aeiou]{3,}           [aeiou]{3,}
# Line 3490  REPETITION Line 3999  REPETITION
3999    
4000           \d{8}           \d{8}
4001    
4002         matches  exactly  8  digits. An opening curly bracket that appears in a         matches exactly 8 digits. An opening curly bracket that  appears  in  a
4003         position where a quantifier is not allowed, or one that does not  match         position  where a quantifier is not allowed, or one that does not match
4004         the  syntax of a quantifier, is taken as a literal character. For exam-         the syntax of a quantifier, is taken as a literal character. For  exam-
4005         ple, {,6} is not a quantifier, but a literal string of four characters.         ple, {,6} is not a quantifier, but a literal string of four characters.
4006    
4007         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to         In UTF-8 mode, quantifiers apply to UTF-8  characters  rather  than  to
4008         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-
4009         acters, each of which is represented by a two-byte sequence. Similarly,         acters, each of which is represented by a two-byte sequence. Similarly,
4010         when Unicode property support is available, \X{3} matches three Unicode         when Unicode property support is available, \X{3} matches three Unicode
4011         extended  sequences,  each of which may be several bytes long (and they         extended sequences, each of which may be several bytes long  (and  they
4012         may be of different lengths).         may be of different lengths).
4013    
4014         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
4015         the previous item and the quantifier were not present.         the previous item and the quantifier were not present. This may be use-
4016           ful  for  subpatterns that are referenced as subroutines from elsewhere
4017           in the pattern. Items other than subpatterns that have a {0} quantifier
4018           are omitted from the compiled pattern.
4019    
4020         For  convenience, the three most common quantifiers have single-charac-         For  convenience, the three most common quantifiers have single-charac-
4021         ter abbreviations:         ter abbreviations:
# Line 3658  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4170  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4170    
4171           \d++foo           \d++foo
4172    
4173         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Note that a possessive quantifier can be used with an entire group, for
4174           example:
4175    
4176             (abc|xyz){2,3}+
4177    
4178           Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4179         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4180         simpler forms of atomic group. However, there is no difference  in  the         simpler  forms  of atomic group. However, there is no difference in the
4181         meaning  of  a  possessive  quantifier and the equivalent atomic group,         meaning of a possessive quantifier and  the  equivalent  atomic  group,
4182         though there may be a performance  difference;  possessive  quantifiers         though  there  may  be a performance difference; possessive quantifiers
4183         should be slightly faster.         should be slightly faster.
4184    
4185         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-
4186         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first         tax.   Jeffrey  Friedl  originated the idea (and the name) in the first
4187         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
4188         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
4189         found its way into Perl at release 5.10.         found its way into Perl at release 5.10.
4190    
4191         PCRE has an optimization that automatically "possessifies" certain sim-         PCRE has an optimization that automatically "possessifies" certain sim-
4192         ple pattern constructs. For example, the sequence  A+B  is  treated  as         ple  pattern  constructs.  For  example, the sequence A+B is treated as
4193         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
4194         when B must follow.         when B must follow.
4195    
4196         When a pattern contains an unlimited repeat inside  a  subpattern  that         When  a  pattern  contains an unlimited repeat inside a subpattern that
4197         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
4198         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
4199         very long time indeed. The pattern         very long time indeed. The pattern
4200    
4201           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
4202    
4203         matches  an  unlimited number of substrings that either consist of non-         matches an unlimited number of substrings that either consist  of  non-
4204         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it
4205         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
4206    
4207           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4208    
4209         it  takes  a  long  time  before reporting failure. This is because the         it takes a long time before reporting  failure.  This  is  because  the
4210         string can be divided between the internal \D+ repeat and the  external         string  can be divided between the internal \D+ repeat and the external
4211         *  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
4212         example uses [!?] rather than a single character at  the  end,  because         example  uses  [!?]  rather than a single character at the end, because
4213         both  PCRE  and  Perl have an optimization that allows for fast failure         both PCRE and Perl have an optimization that allows  for  fast  failure
4214         when a single character is used. They remember the last single  charac-         when  a single character is used. They remember the last single charac-
4215         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
4216         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
4217         group, like this:         group, like this:
4218    
4219           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4220    
4221         sequences  of non-digits cannot be broken, and failure happens quickly.         sequences of non-digits cannot be broken, and failure happens  quickly.
4222    
4223    
4224  BACK REFERENCES  BACK REFERENCES
4225    
4226         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4227         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-
4228         pattern earlier (that is, to its left) in the pattern,  provided  there         pattern  earlier  (that is, to its left) in the pattern, provided there
4229         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4230    
4231         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4232         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
4233         there  are  not that many capturing left parentheses in the entire pat-         there are not that many capturing left parentheses in the  entire  pat-
4234         tern. In other words, the parentheses that are referenced need  not  be         tern.  In  other words, the parentheses that are referenced need not be
4235         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
4236         reference" of this type can make sense when a  repetition  is  involved         reference"  of  this  type can make sense when a repetition is involved
4237         and  the  subpattern to the right has participated in an earlier itera-         and the subpattern to the right has participated in an  earlier  itera-
4238         tion.         tion.
4239    
4240         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
4241         subpattern  whose  number  is  10  or  more using this syntax because a         subpattern whose number is 10 or  more  using  this  syntax  because  a
4242         sequence such as \50 is interpreted as a character  defined  in  octal.         sequence  such  as  \50 is interpreted as a character defined in octal.
4243         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4244         details of the handling of digits following a backslash.  There  is  no         details  of  the  handling of digits following a backslash. There is no
4245         such  problem  when named parentheses are used. A back reference to any         such problem when named parentheses are used. A back reference  to  any
4246         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4247    
4248         Another way of avoiding the ambiguity inherent in  the  use  of  digits         Another  way  of  avoiding  the ambiguity inherent in the use of digits
4249         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-
4250         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
4251         tive  or  a negative number, optionally enclosed in braces. These exam-         unsigned number or a negative number, optionally  enclosed  in  braces.
4252         ples are all identical:         These examples are all identical:
4253    
4254           (ring), \1           (ring), \1
4255           (ring), \g1           (ring), \g1
4256           (ring), \g{1}           (ring), \g{1}
4257    
4258         A positive number specifies an absolute reference without the ambiguity         An  unsigned number specifies an absolute reference without the ambigu-
4259         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
4260         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4261         Consider this example:         Consider this example:
4262    
4263           (abc(def)ghi)\g{-1}           (abc(def)ghi)\g{-1}
4264    
4265         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-
4266         ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,         ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,
4267         \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
4268         helpful in long patterns, and also in  patterns  that  are  created  by         helpful  in  long  patterns,  and  also in patterns that are created by
4269         joining together fragments that contain references within themselves.         joining together fragments that contain references within themselves.
4270    
4271         A  back  reference matches whatever actually matched the capturing sub-         A back reference matches whatever actually matched the  capturing  sub-
4272         pattern in the current subject string, rather  than  anything  matching         pattern  in  the  current subject string, rather than anything matching
4273         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
4274         of doing that). So the pattern         of doing that). So the pattern
4275    
4276           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4277    
4278         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4279         not  "sense and responsibility". If caseful matching is in force at the         not "sense and responsibility". If caseful matching is in force at  the
4280         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-
4281         ple,         ple,
4282    
4283           ((?i)rah)\s+\1           ((?i)rah)\s+\1
4284    
4285         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
4286         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4287    
4288         Back references to named subpatterns use the Perl  syntax  \k<name>  or         There  are  several  different ways of writing back references to named
4289         \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
4290         example in either of the following ways:         \k'name'  are supported, as is the Python syntax (?P=name). Perl 5.10's
4291           unified back reference syntax, in which \g can be used for both numeric
4292           and  named  references,  is  also supported. We could rewrite the above
4293           example in any of the following ways:
4294    
4295           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
4296             (?'p1'(?i)rah)\s+\k{p1}
4297           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4298             (?<p1>(?i)rah)\s+\g{p1}
4299    
4300         A subpattern that is referenced by  name  may  appear  in  the  pattern         A subpattern that is referenced by  name  may  appear  in  the  pattern
4301         before or after the reference.         before or after the reference.
# Line 3888  ASSERTIONS Line 4410  ASSERTIONS
4410    
4411           (?<=abc|abde)           (?<=abc|abde)
4412    
4413           In some cases, the Perl 5.10 escape sequence \K (see above) can be used
4414           instead  of  a lookbehind assertion; this is not restricted to a fixed-
4415           length.
4416    
4417         The implementation of lookbehind assertions is, for  each  alternative,         The implementation of lookbehind assertions is, for  each  alternative,
4418         to  temporarily  move the current position back by the fixed length and         to  temporarily  move the current position back by the fixed length and
4419         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 3981  CONDITIONAL SUBPATTERNS Line 4507  CONDITIONAL SUBPATTERNS
4507    
4508         If  the  text between the parentheses consists of a sequence of digits,         If  the  text between the parentheses consists of a sequence of digits,
4509         the condition is true if the capturing subpattern of  that  number  has         the condition is true if the capturing subpattern of  that  number  has
4510         previously matched.         previously  matched.  An  alternative notation is to precede the digits
4511           with a plus or minus sign. In this case, the subpattern number is rela-
4512           tive rather than absolute.  The most recently opened parentheses can be
4513           referenced by (?(-1), the next most recent by (?(-2),  and  so  on.  In
4514           looping constructs it can also make sense to refer to subsequent groups
4515           with constructs such as (?(+2).
4516    
4517         Consider  the  following  pattern, which contains non-significant white         Consider the following pattern, which  contains  non-significant  white
4518         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
4519         divide it into three parts for ease of discussion:         divide it into three parts for ease of discussion:
4520    
4521           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4522    
4523         The  first  part  matches  an optional opening parenthesis, and if that         The first part matches an optional opening  parenthesis,  and  if  that
4524         character is present, sets it as the first captured substring. The sec-         character is present, sets it as the first captured substring. The sec-
4525         ond  part  matches one or more characters that are not parentheses. The         ond part matches one or more characters that are not  parentheses.  The
4526         third part is a conditional subpattern that tests whether the first set         third part is a conditional subpattern that tests whether the first set
4527         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
4528         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-
4529         tern  is  executed  and  a  closing parenthesis is required. Otherwise,         tern is executed and a  closing  parenthesis  is  required.  Otherwise,
4530         since no-pattern is not present, the  subpattern  matches  nothing.  In         since  no-pattern  is  not  present, the subpattern matches nothing. In
4531         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other words,  this  pattern  matches  a  sequence  of  non-parentheses,
4532         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4533    
4534           If  you  were  embedding  this pattern in a larger one, you could use a
4535           relative reference:
4536    
4537             ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4538    
4539           This makes the fragment independent of the parentheses  in  the  larger
4540           pattern.
4541    
4542     Checking for a used subpattern by name     Checking for a used subpattern by name
4543    
4544         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a         Perl  uses  the  syntax  (?(<name>)...) or (?('name')...) to test for a
4545         used  subpattern  by  name.  For compatibility with earlier versions of         used subpattern by name. For compatibility  with  earlier  versions  of
4546         PCRE, which had this facility before Perl, the syntax  (?(name)...)  is         PCRE,  which  had this facility before Perl, the syntax (?(name)...) is
4547         also  recognized. However, there is a possible ambiguity with this syn-         also recognized. However, there is a possible ambiguity with this  syn-
4548         tax, because subpattern names may  consist  entirely  of  digits.  PCRE         tax,  because  subpattern  names  may  consist entirely of digits. PCRE
4549         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
4550         consists entirely of digits, PCRE looks for a subpattern of  that  num-         consists  entirely  of digits, PCRE looks for a subpattern of that num-
4551         ber,  which must be greater than zero. Using subpattern names that con-         ber, which must be greater than zero. Using subpattern names that  con-
4552         sist entirely of digits is not recommended.         sist entirely of digits is not recommended.
4553    
4554         Rewriting the above example to use a named subpattern gives this:         Rewriting the above example to use a named subpattern gives this:
# Line 4020  CONDITIONAL SUBPATTERNS Line 4559  CONDITIONAL SUBPATTERNS
4559     Checking for pattern recursion     Checking for pattern recursion
4560    
4561         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
4562         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
4563         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-
4564         sand follow the letter R, for example:         sand follow the letter R, for example:
4565