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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.  The current implementation of PCRE (release         just  a  few differences. (Certain features that appeared in Python and
22         6.x) corresponds approximately with Perl  5.8,  including  support  for         PCRE before they appeared in Perl are also available using  the  Python
23         UTF-8 encoded strings and Unicode general category properties. However,         syntax.)
24         this support has to be explicitly enabled; it is not the default.  
25           The  current  implementation of PCRE (release 7.x) corresponds approxi-
26         In addition to the Perl-compatible matching function,  PCRE  also  con-         mately with Perl 5.10, including support for UTF-8 encoded strings  and
27         tains  an  alternative matching function that matches the same compiled         Unicode general category properties. However, UTF-8 and Unicode support
28         patterns in a different way. In certain circumstances, the  alternative         has to be explicitly enabled; it is not the default. The Unicode tables
29         function  has  some  advantages.  For  a discussion of the two matching         correspond to Unicode release 5.0.0.
30         algorithms, see the pcrematching page.  
31           In  addition to the Perl-compatible matching function, PCRE contains an
32         PCRE is written in C and released as a C library. A  number  of  people         alternative matching function that matches the same  compiled  patterns
33         have  written  wrappers and interfaces of various kinds. In particular,         in  a different way. In certain circumstances, the alternative function
34         Google Inc.  have provided a comprehensive C++  wrapper.  This  is  now         has some advantages. For a discussion of the two  matching  algorithms,
35           see the pcrematching page.
36    
37           PCRE  is  written  in C and released as a C library. A number of people
38           have written wrappers and interfaces of various kinds.  In  particular,
39           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
40         included as part of the PCRE distribution. The pcrecpp page has details         included as part of the PCRE distribution. The pcrecpp page has details
41         of this interface. Other people's contributions can  be  found  in  the         of  this  interface.  Other  people's contributions can be found in the
42         Contrib directory at the primary FTP site, which is:         Contrib directory at the primary FTP site, which is:
43    
44         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
45    
46         Details  of  exactly which Perl regular expression features are and are         Details of exactly which Perl regular expression features are  and  are
47         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
48         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
49           page.
50    
51         Some  features  of  PCRE can be included, excluded, or changed when the         Some  features  of  PCRE can be included, excluded, or changed when the
52         library is built. The pcre_config() function makes it  possible  for  a         library is built. The pcre_config() function makes it  possible  for  a
# Line 67  USER DOCUMENTATION Line 73  USER DOCUMENTATION
73         of searching. The sections are as follows:         of searching. The sections are as follows:
74    
75           pcre              this document           pcre              this document
76             pcre-config       show PCRE installation configuration information
77           pcreapi           details of PCRE's native C API           pcreapi           details of PCRE's native C API
78           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
79           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
# Line 77  USER DOCUMENTATION Line 84  USER DOCUMENTATION
84           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
85           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
86                               regular expressions                               regular expressions
87             pcresyntax        quick syntax reference
88           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
89           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
90           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
91           pcresample        discussion of the sample program           pcresample        discussion of the sample program
92             pcrestack         discussion of stack usage
93           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
94    
95         In  addition,  in the "man" and HTML formats, there is a short page for         In  addition,  in the "man" and HTML formats, there is a short page for
# Line 98  LIMITATIONS Line 107  LIMITATIONS
107         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
108         the  source  distribution and the pcrebuild documentation for details).         the  source  distribution and the pcrebuild documentation for details).
109         In these cases the limit is substantially larger.  However,  the  speed         In these cases the limit is substantially larger.  However,  the  speed
110         of execution will be slower.         of execution is slower.
111    
112           All values in repeating quantifiers must be less than 65536.
113    
114         All values in repeating quantifiers must be less than 65536.  The maxi-         There is no limit to the number of parenthesized subpatterns, but there
115         mum number of capturing subpatterns is 65535.         can be no more than 65535 capturing subpatterns.
116    
117         There is no limit to the number of non-capturing subpatterns,  but  the         The maximum length of name for a named subpattern is 32 characters, and
118         maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,         the maximum number of named subpatterns is 10000.
        including capturing subpatterns, assertions, and other types of subpat-  
        tern, is 200.  
119    
120         The  maximum  length of a subject string is the largest positive number         The  maximum  length of a subject string is the largest positive number
121         that an integer variable can hold. However, when using the  traditional         that an integer variable can hold. However, when using the  traditional
122         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
123         inite repetition.  This means that the available stack space may  limit         inite repetition.  This means that the available stack space may  limit
124         the size of a subject string that can be processed by certain patterns.         the size of a subject string that can be processed by certain patterns.
125           For a discussion of stack issues, see the pcrestack documentation.
126    
127    
128  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
# Line 130  UTF-8 AND UNICODE PROPERTY SUPPORT Line 140  UTF-8 AND UNICODE PROPERTY SUPPORT
140    
141         If  you compile PCRE with UTF-8 support, but do not use it at run time,         If  you compile PCRE with UTF-8 support, but do not use it at run time,
142         the library will be a bit bigger, but the additional run time  overhead         the library will be a bit bigger, but the additional run time  overhead
143         is  limited  to testing the PCRE_UTF8 flag in several places, so should         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
144         not be very large.         very big.
145    
146         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
147         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
148         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
149         general  category  properties such as Lu for an upper case letter or Nd         general  category  properties such as Lu for an upper case letter or Nd
150         for a decimal number. A full list is given in the pcrepattern  documen-         for a decimal number, the Unicode script names such as Arabic  or  Han,
151         tation. The PCRE library is increased in size by about 90K when Unicode         and  the  derived  properties  Any  and L&. A full list is given in the
152         property support is included.         pcrepattern documentation. Only the short names for properties are sup-
153           ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-
154         The following comments apply when PCRE is running in UTF-8 mode:         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
155           optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
156         1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and         does not support this.
157         subjects  are  checked for validity on entry to the relevant functions.  
158         If an invalid UTF-8 string is passed, an error return is given. In some     Validity of UTF-8 strings
159         situations,  you  may  already  know  that  your strings are valid, and  
160         therefore want to skip these checks in order to improve performance. If         When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
161         you  set  the  PCRE_NO_UTF8_CHECK  flag at compile time or at run time,         subjects are (by default) checked for validity on entry to the relevant
162         PCRE assumes that the pattern or subject  it  is  given  (respectively)         functions. From release 7.3 of PCRE, the check is according  the  rules
163         contains  only valid UTF-8 codes. In this case, it does not diagnose an         of  RFC  3629, which are themselves derived from the Unicode specifica-
164         invalid UTF-8 string. If you pass an invalid UTF-8 string to PCRE  when         tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
165         PCRE_NO_UTF8_CHECK  is set, the results are undefined. Your program may         allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
166         crash.         check allows only values in the range U+0 to U+10FFFF, excluding U+D800
167           to U+DFFF.
168         2. In a pattern, the escape sequence \x{...}, where the contents of the  
169         braces  is  a  string  of hexadecimal digits, is interpreted as a UTF-8         The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
170         character whose code number is the given hexadecimal number, for  exam-         which the Unicode Standard says this: "The Low Surrogate Area does  not
171         ple:  \x{1234}.  If a non-hexadecimal digit appears between the braces,         contain  any  character  assignments,  consequently  no  character code
172         the item is not recognized.  This escape sequence can be used either as         charts or namelists are provided for this area. Surrogates are reserved
173         a literal, or within a character class.         for  use  with  UTF-16 and then must be used in pairs." The code points
174           that are encoded by UTF-16 pairs  are  available  as  independent  code
175           points  in  the  UTF-8  encoding.  (In other words, the whole surrogate
176           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
177    
178           If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return
179           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
180           that your strings are valid, and therefore want to skip these checks in
181           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
182           compile time or at run time, PCRE assumes that the pattern  or  subject
183           it  is  given  (respectively)  contains only valid UTF-8 codes. In this
184           case, it does not diagnose an invalid UTF-8 string.
185    
186           If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,
187           what  happens  depends on why the string is invalid. If the string con-
188           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
189           string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,
190           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
191           strings  according  to  the more liberal rules of RFC 2279. However, if
192           the string does not even conform to RFC 2279, the result is  undefined.
193           Your program may crash.
194    
195           If  you  want  to  process  strings  of  values  in the full range 0 to
196           0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can
197           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
198           this situation, you will have to apply your own validity check.
199    
200       General comments about UTF-8 mode
201    
202         3.  The  original hexadecimal escape sequence, \xhh, matches a two-byte         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
203         UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
204    
205         4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8
206           characters for values greater than \177.
207    
208           3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
209         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
210    
211         5.  The dot metacharacter matches one UTF-8 character instead of a sin-         4.  The dot metacharacter matches one UTF-8 character instead of a sin-
212         gle byte.         gle byte.
213    
214         6. The escape sequence \C can be used to match a single byte  in  UTF-8         5. The escape sequence \C can be used to match a single byte  in  UTF-8
215         mode,  but  its  use can lead to some strange effects. This facility is         mode,  but  its  use can lead to some strange effects. This facility is
216         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
217    
218         7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly         6. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly
219         test  characters of any code value, but the characters that PCRE recog-         test  characters of any code value, but the characters that PCRE recog-
220         nizes as digits, spaces, or word characters  remain  the  same  set  as         nizes as digits, spaces, or word characters  remain  the  same  set  as
221         before, all with values less than 256. This remains true even when PCRE         before, all with values less than 256. This remains true even when PCRE
# Line 184  UTF-8 AND UNICODE PROPERTY SUPPORT Line 224  UTF-8 AND UNICODE PROPERTY SUPPORT
224         sense of, say, "digit", you must use Unicode  property  tests  such  as         sense of, say, "digit", you must use Unicode  property  tests  such  as
225         \p{Nd}.         \p{Nd}.
226    
227         8.  Similarly,  characters that match the POSIX named character classes         7.  Similarly,  characters that match the POSIX named character classes
228         are all low-valued characters.         are all low-valued characters.
229    
230           8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
231           escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
232           acters.
233    
234         9. Case-insensitive matching applies only to  characters  whose  values         9. Case-insensitive matching applies only to  characters  whose  values
235         are  less than 128, unless PCRE is built with Unicode property support.         are  less than 128, unless PCRE is built with Unicode property support.
236         Even when Unicode property support is available, PCRE  still  uses  its         Even when Unicode property support is available, PCRE  still  uses  its
237         own  character  tables when checking the case of low-valued characters,         own  character  tables when checking the case of low-valued characters,
238         so as not to degrade performance.  The Unicode property information  is         so as not to degrade performance.  The Unicode property information  is
239         used only for characters with higher values.         used only for characters with higher values. Even when Unicode property
240           support is available, PCRE supports case-insensitive matching only when
241           there  is  a  one-to-one  mapping between a letter's cases. There are a
242           small number of many-to-one mappings in Unicode;  these  are  not  sup-
243           ported by PCRE.
244    
245    
246  AUTHOR  AUTHOR
247    
248         Philip Hazel         Philip Hazel
249         University Computing Service,         University Computing Service
250         Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
251    
252         Putting  an actual email address here seems to have been a spam magnet,         Putting  an actual email address here seems to have been a spam magnet,
253         so I've taken it away. If you want to email me, use my initial and sur-         so I've taken it away. If you want to email me, use  my  two  initials,
254         name, separated by a dot, at the domain ucs.cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
255    
256    
257    REVISION
258    
259  Last updated: 07 March 2005         Last updated: 09 August 2007
260  Copyright (c) 1997-2005 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
261  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
262    
263    
# Line 220  NAME Line 271  NAME
271  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
272    
273         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
274         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
275         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
276         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
277         includes  the  standard  ones such as the selection of the installation         the  same  options  can be selected in both Unix-like and non-Unix-like
278         directory) can be obtained by running         environments using the GUI facility of  CMakeSetup  if  you  are  using
279           CMake instead of configure to build PCRE.
280    
281           The complete list of options for configure (which includes the standard
282           ones such as the  selection  of  the  installation  directory)  can  be
283           obtained by running
284    
285           ./configure --help           ./configure --help
286    
287         The following sections describe certain options whose names begin  with         The  following  sections  include  descriptions  of options whose names
288         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
289         for the configure command. Because of the  way  that  configure  works,         defaults  for  the configure command. Because of the way that configure
290         --enable  and  --disable  always  come  in  pairs, so the complementary         works, --enable and --disable always come in pairs, so  the  complemen-
291         option always exists as well, but as it specifies the  default,  it  is         tary  option always exists as well, but as it specifies the default, it
292         not described.         is not described.
293    
294    
295  C++ SUPPORT  C++ SUPPORT
# Line 253  UTF-8 SUPPORT Line 309  UTF-8 SUPPORT
309    
310           --enable-utf8           --enable-utf8
311    
312         to  the  configure  command.  Of  itself, this does not make PCRE treat         to the configure command. Of itself, this  does  not  make  PCRE  treat
313         strings as UTF-8. As well as compiling PCRE with this option, you  also         strings  as UTF-8. As well as compiling PCRE with this option, you also
314         have  have to set the PCRE_UTF8 option when you call the pcre_compile()         have have to set the PCRE_UTF8 option when you call the  pcre_compile()
315         function.         function.
316    
317    
318  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
319    
320         UTF-8 support allows PCRE to process character values greater than  255         UTF-8  support allows PCRE to process character values greater than 255
321         in  the  strings that it handles. On its own, however, it does not pro-         in the strings that it handles. On its own, however, it does  not  pro-
322         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
323         you  want  to  be able to use the pattern escapes \P, \p, and \X, which         you want to be able to use the pattern escapes \P, \p,  and  \X,  which
324         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
325    
326           --enable-unicode-properties           --enable-unicode-properties
327    
328         to the configure command. This implies UTF-8 support, even if you  have         to  the configure command. This implies UTF-8 support, even if you have
329         not explicitly requested it.         not explicitly requested it.
330    
331         Including  Unicode  property  support  adds around 90K of tables to the         Including Unicode property support adds around 30K  of  tables  to  the
332         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE  library.  Only  the general category properties such as Lu and Nd
333         gory  properties  such as Lu and Nd are supported. Details are given in         are supported. Details are given in the pcrepattern documentation.
        the pcrepattern documentation.  
334    
335    
336  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
337    
338         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating
339         ter. This is the normal newline character on Unix-like systems. You can         the  end  of  a line. This is the normal newline character on Unix-like
340         compile PCRE to use character 13 (carriage return) instead by adding         systems. You can compile PCRE to use character 13 (carriage return, CR)
341           instead, by adding
342    
343           --enable-newline-is-cr           --enable-newline-is-cr
344    
345         to the configure command. For completeness there is  also  a  --enable-         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
346         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
347         line character.  
348           Alternatively, you can specify that line endings are to be indicated by
349           the two character sequence CRLF. If you want this, add
350    
351             --enable-newline-is-crlf
352    
353           to the configure command. There is a fourth option, specified by
354    
355             --enable-newline-is-anycrlf
356    
357           which  causes  PCRE  to recognize any of the three sequences CR, LF, or
358           CRLF as indicating a line ending. Finally, a fifth option, specified by
359    
360             --enable-newline-is-any
361    
362           causes PCRE to recognize any Unicode newline sequence.
363    
364           Whatever  line  ending convention is selected when PCRE is built can be
365           overridden when the library functions are called. At build time  it  is
366           conventional to use the standard for your operating system.
367    
368    
369    WHAT \R MATCHES
370    
371           By  default,  the  sequence \R in a pattern matches any Unicode newline
372           sequence, whatever has been selected as the line  ending  sequence.  If
373           you specify
374    
375             --enable-bsr-anycrlf
376    
377           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
378           ever is selected when PCRE is built can be overridden when the  library
379           functions are called.
380    
381    
382  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
383    
384         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
385         Unix  libraries by default. You can suppress one of these by adding one         Unix libraries by default. You can suppress one of these by adding  one
386         of         of
387    
388           --disable-shared           --disable-shared
# Line 306  BUILDING SHARED AND STATIC LIBRARIES Line 394  BUILDING SHARED AND STATIC LIBRARIES
394  POSIX MALLOC USAGE  POSIX MALLOC USAGE
395    
396         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
397         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
398         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
399         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
400         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
401         on the stack, because this is faster than using malloc() for each call.         on the stack, because this is faster than using malloc() for each call.
402         The default threshold above which the stack is no longer used is 10; it         The default threshold above which the stack is no longer used is 10; it
# Line 319  POSIX MALLOC USAGE Line 407  POSIX MALLOC USAGE
407         to the configure command.         to the configure command.
408    
409    
 LIMITING PCRE RESOURCE USAGE  
   
        Internally,  PCRE has a function called match(), which it calls repeat-  
        edly  (possibly  recursively)  when  matching  a   pattern   with   the  
        pcre_exec()  function.  By controlling the maximum number of times this  
        function may be called during a single matching operation, a limit  can  
        be  placed  on  the resources used by a single call to pcre_exec(). The  
        limit can be changed at run time, as described in the pcreapi  documen-  
        tation.  The default is 10 million, but this can be changed by adding a  
        setting such as  
   
          --with-match-limit=500000  
   
        to  the  configure  command.  This  setting  has  no  effect   on   the  
        pcre_dfa_exec() matching function.  
   
   
410  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
411    
412         Within  a  compiled  pattern,  offset values are used to point from one         Within a compiled pattern, offset values are used  to  point  from  one
413         part to another (for example, from an opening parenthesis to an  alter-         part  to another (for example, from an opening parenthesis to an alter-
414         nation  metacharacter).  By default, two-byte values are used for these         nation metacharacter). By default, two-byte values are used  for  these
415         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets,  leading  to  a  maximum size for a compiled pattern of around
416         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
417         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless,  some  people do want to process enormous patterns, so it
418         is  possible  to compile PCRE to use three-byte or four-byte offsets by         is possible to compile PCRE to use three-byte or four-byte  offsets  by
419         adding a setting such as         adding a setting such as
420    
421           --with-link-size=3           --with-link-size=3
422    
423         to the configure command. The value given must be 2,  3,  or  4.  Using         to  the  configure  command.  The value given must be 2, 3, or 4. Using
424         longer  offsets slows down the operation of PCRE because it has to load         longer offsets slows down the operation of PCRE because it has to  load
425         additional bytes when handling them.         additional bytes when handling them.
426    
        If you build PCRE with an increased link size, test 2 (and  test  5  if  
        you  are using UTF-8) will fail. Part of the output of these tests is a  
        representation of the compiled pattern, and this changes with the  link  
        size.  
   
427    
428  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
429    
# Line 365  AVOIDING EXCESSIVE STACK USAGE Line 431  AVOIDING EXCESSIVE STACK USAGE
431         ing by making recursive calls to an internal function  called  match().         ing by making recursive calls to an internal function  called  match().
432         In  environments  where  the size of the stack is limited, this can se-         In  environments  where  the size of the stack is limited, this can se-
433         verely limit PCRE's operation. (The Unix environment does  not  usually         verely limit PCRE's operation. (The Unix environment does  not  usually
434         suffer  from  this  problem.)  An alternative approach that uses memory         suffer from this problem, but it may sometimes be necessary to increase
435         from the heap to remember data, instead  of  using  recursive  function         the maximum stack size.  There is a discussion in the  pcrestack  docu-
436         calls,  has been implemented to work round this problem. If you want to         mentation.)  An alternative approach to recursion that uses memory from
437         build a version of PCRE that works this way, add         the heap to remember data, instead of using recursive  function  calls,
438           has  been  implemented to work round the problem of limited stack size.
439           If you want to build a version of PCRE that works this way, add
440    
441           --disable-stack-for-recursion           --disable-stack-for-recursion
442    
443         to the configure command. With this configuration, PCRE  will  use  the         to the configure command. With this configuration, PCRE  will  use  the
444         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
445         ment functions. Separate functions are provided because  the  usage  is         ment functions. By default these point to malloc() and free(), but  you
446         very  predictable:  the  block sizes requested are always the same, and         can replace the pointers so that your own functions are used.
447         the blocks are always freed in reverse order. A calling  program  might  
448         be  able  to implement optimized functions that perform better than the         Separate  functions  are  provided  rather  than  using pcre_malloc and
449         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         pcre_free because the  usage  is  very  predictable:  the  block  sizes
450         slowly when built in this way. This option affects only the pcre_exec()         requested  are  always  the  same,  and  the blocks are always freed in
451         function; it is not relevant for the the pcre_dfa_exec() function.         reverse order. A calling program might be able to  implement  optimized
452           functions  that  perform  better  than  malloc()  and free(). PCRE runs
453           noticeably more slowly when built in this way. This option affects only
454           the   pcre_exec()   function;   it   is   not   relevant  for  the  the
455           pcre_dfa_exec() function.
456    
457    
458    LIMITING PCRE RESOURCE USAGE
459    
460           Internally, PCRE has a function called match(), which it calls  repeat-
461           edly   (sometimes   recursively)  when  matching  a  pattern  with  the
462           pcre_exec() function. By controlling the maximum number of  times  this
463           function  may be called during a single matching operation, a limit can
464           be placed on the resources used by a single call  to  pcre_exec().  The
465           limit  can be changed at run time, as described in the pcreapi documen-
466           tation. The default is 10 million, but this can be changed by adding  a
467           setting such as
468    
469             --with-match-limit=500000
470    
471           to   the   configure  command.  This  setting  has  no  effect  on  the
472           pcre_dfa_exec() matching function.
473    
474           In some environments it is desirable to limit the  depth  of  recursive
475           calls of match() more strictly than the total number of calls, in order
476           to restrict the maximum amount of stack (or heap,  if  --disable-stack-
477           for-recursion is specified) that is used. A second limit controls this;
478           it defaults to the value that  is  set  for  --with-match-limit,  which
479           imposes  no  additional constraints. However, you can set a lower limit
480           by adding, for example,
481    
482             --with-match-limit-recursion=10000
483    
484           to the configure command. This value can  also  be  overridden  at  run
485           time.
486    
487    
488    CREATING CHARACTER TABLES AT BUILD TIME
489    
490           PCRE  uses fixed tables for processing characters whose code values are
491           less than 256. By default, PCRE is built with a set of tables that  are
492           distributed  in  the  file pcre_chartables.c.dist. These tables are for
493           ASCII codes only. If you add
494    
495             --enable-rebuild-chartables
496    
497           to the configure command, the distributed tables are  no  longer  used.
498           Instead,  a  program  called dftables is compiled and run. This outputs
499           the source for new set of tables, created in the default locale of your
500           C runtime system. (This method of replacing the tables does not work if
501           you are cross compiling, because dftables is run on the local host.  If
502           you  need  to  create alternative tables when cross compiling, you will
503           have to do so "by hand".)
504    
505    
506  USING EBCDIC CODE  USING EBCDIC CODE
507    
508         PCRE assumes by default that it will run in an  environment  where  the         PCRE assumes by default that it will run in an  environment  where  the
509         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
510         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by         This is the case for most computer operating systems.  PCRE  can,  how-
511         adding         ever, be compiled to run in an EBCDIC environment by adding
512    
513           --enable-ebcdic           --enable-ebcdic
514    
515         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
516           bles. You should only use it if you know that  you  are  in  an  EBCDIC
517           environment (for example, an IBM mainframe operating system).
518    
519    
520    SEE ALSO
521    
522  Last updated: 15 August 2005         pcreapi(3), pcre_config(3).
523  Copyright (c) 1997-2005 University of Cambridge.  
524    
525    AUTHOR
526    
527           Philip Hazel
528           University Computing Service
529           Cambridge CB2 3QH, England.
530    
531    
532    REVISION
533    
534           Last updated: 21 September 2007
535           Copyright (c) 1997-2007 University of Cambridge.
536  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
537    
538    
# Line 431  PCRE MATCHING ALGORITHMS Line 568  PCRE MATCHING ALGORITHMS
568           <something> <something else> <something further>           <something> <something else> <something further>
569    
570         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
571         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
572    
573    
574  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 440  REGULAR EXPRESSIONS AS TREES Line 577  REGULAR EXPRESSIONS AS TREES
577         resented  as  a  tree structure. An unlimited repetition in the pattern         resented  as  a  tree structure. An unlimited repetition in the pattern
578         makes the tree of infinite size, but it is still a tree.  Matching  the         makes the tree of infinite size, but it is still a tree.  Matching  the
579         pattern  to a given subject string (from a given starting point) can be         pattern  to a given subject string (from a given starting point) can be
580         thought of as a search of the tree.  There are  two  standard  ways  to         thought of as a search of the tree.  There are two  ways  to  search  a
581         search  a  tree: depth-first and breadth-first, and these correspond to         tree:  depth-first  and  breadth-first, and these correspond to the two
582         the two matching algorithms provided by PCRE.         matching algorithms provided by PCRE.
583    
584    
585  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
586    
587         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
588         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
589         depth-first search of the pattern tree. That is, it  proceeds  along  a         depth-first search of the pattern tree. That is, it  proceeds  along  a
590         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
591         required. When there is a mismatch, the algorithm  tries  any  alterna-         required. When there is a mismatch, the algorithm  tries  any  alterna-
# Line 472  THE STANDARD MATCHING ALGORITHM Line 609  THE STANDARD MATCHING ALGORITHM
609         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
610    
611    
612  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
613    
614         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
615         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
616         first search of the tree. Starting from the first matching point in the         string from left to right, once, character by character, and as it does
617         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
618         ter by character, and as it does  this,  it  remembers  all  the  paths         matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
619         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
620           keeps multiple states active simultaneously).
621         The  scan  continues until either the end of the subject is reached, or  
622         there are no more unterminated paths. At this point,  terminated  paths         The scan continues until either the end of the subject is  reached,  or
623         represent  the different matching possibilities (if there are none, the         there  are  no more unterminated paths. At this point, terminated paths
624         match has failed).  Thus, if there is more  than  one  possible  match,         represent the different matching possibilities (if there are none,  the
625           match  has  failed).   Thus,  if there is more than one possible match,
626         this algorithm finds all of them, and in particular, it finds the long-         this algorithm finds all of them, and in particular, it finds the long-
627         est. In PCRE, there is an option to stop the algorithm after the  first         est.  In PCRE, there is an option to stop the algorithm after the first
628         match (which is necessarily the shortest) has been found.         match (which is necessarily the shortest) has been found.
629    
630         Note that all the matches that are found start at the same point in the         Note that all the matches that are found start at the same point in the
# Line 494  THE DFA MATCHING ALGORITHM Line 632  THE DFA MATCHING ALGORITHM
632    
633           cat(er(pillar)?)           cat(er(pillar)?)
634    
635         is matched against the string "the caterpillar catchment",  the  result         is  matched  against the string "the caterpillar catchment", the result
636         will  be the three strings "cat", "cater", and "caterpillar" that start         will be the three strings "cat", "cater", and "caterpillar" that  start
637         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
638         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
639    
640         There are a number of features of PCRE regular expressions that are not         There are a number of features of PCRE regular expressions that are not
641         supported by the DFA matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
642    
643         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1.  Because  the  algorithm  finds  all possible matches, the greedy or
644         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
645         ungreedy quantifiers are treated in exactly the same way.         ungreedy quantifiers are treated in exactly the same way. However, pos-
646           sessive quantifiers can make a difference when what follows could  also
647           match what is quantified, for example in a pattern like this:
648    
649             ^a++\w!
650    
651           This  pattern matches "aaab!" but not "aaa!", which would be matched by
652           a non-possessive quantifier. Similarly, if an atomic group is  present,
653           it  is matched as if it were a standalone pattern at the current point,
654           and the longest match is then "locked in" for the rest of  the  overall
655           pattern.
656    
657         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
658         is  not  straightforward  to  keep track of captured substrings for the         is not straightforward to keep track of  captured  substrings  for  the
659         different matching possibilities, and  PCRE's  implementation  of  this         different  matching  possibilities,  and  PCRE's implementation of this
660         algorithm does not attempt to do this. This means that no captured sub-         algorithm does not attempt to do this. This means that no captured sub-
661         strings are available.         strings are available.
662    
663         3. Because no substrings are captured, back references within the  pat-         3.  Because no substrings are captured, back references within the pat-
664         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
665    
666         4.  For  the same reason, conditional expressions that use a backrefer-         4. For the same reason, conditional expressions that use  a  backrefer-
667         ence as the condition are not supported.         ence  as  the  condition or test for a specific group recursion are not
668           supported.
669    
670           5. Because many paths through the tree may be  active,  the  \K  escape
671           sequence, which resets the start of the match when encountered (but may
672           be on some paths and not on others), is not  supported.  It  causes  an
673           error if encountered.
674    
675         5. Callouts are supported, but the value of the  capture_top  field  is         6.  Callouts  are  supported, but the value of the capture_top field is
676         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
677    
678         6.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
679         single byte, even in UTF-8 mode, is not supported because the DFA algo-         single  byte, even in UTF-8 mode, is not supported because the alterna-
680         rithm moves through the subject string one character at a time, for all         tive algorithm moves through the subject  string  one  character  at  a
681         active paths through the tree.         time, for all active paths through the tree.
682    
683           8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-
684           ported.
685    
 ADVANTAGES OF THE DFA ALGORITHM  
686    
687         Using the DFA matching algorithm provides the following advantages:  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
688    
689           Using the alternative matching algorithm provides the following  advan-
690           tages:
691    
692         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-
693         ically  found,  and  in particular, the longest match is found. To find         ically found, and in particular, the longest match is  found.  To  find
694         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
695         things with callouts.         things with callouts.
696    
697         2.  There is much better support for partial matching. The restrictions         2. There is much better support for partial matching. The  restrictions
698         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-
699         rithm  for partial matching do not apply to the DFA algorithm. For non-         rithm for partial matching do not apply to the  alternative  algorithm.
700         anchored patterns, the starting position of a partial match  is  avail-         For  non-anchored patterns, the starting position of a partial match is
701         able.         available.
702    
703         3.  Because  the  DFA algorithm scans the subject string just once, and         3. Because the alternative algorithm  scans  the  subject  string  just
704         never needs to backtrack, it is possible  to  pass  very  long  subject         once,  and  never  needs to backtrack, it is possible to pass very long
705         strings  to  the matching function in several pieces, checking for par-         subject strings to the matching function in  several  pieces,  checking
706         tial matching each time.         for partial matching each time.
707    
708    
709  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
710    
711         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
712    
713         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
714         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
715         because it is less susceptible to optimization.         because it is less susceptible to optimization.
716    
717         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
718    
719         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
720         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
721         rithm.  
722    
723    AUTHOR
724    
725           Philip Hazel
726           University Computing Service
727           Cambridge CB2 3QH, England.
728    
729    
730    REVISION
731    
732  Last updated: 28 February 2005         Last updated: 08 August 2007
733  Copyright (c) 1997-2005 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
734  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
735    
736    
# Line 616  PCRE NATIVE API Line 783  PCRE NATIVE API
783         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
784              const char *name);              const char *name);
785    
786           int pcre_get_stringtable_entries(const pcre *code,
787                const char *name, char **first, char **last);
788    
789         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
790              int stringcount, int stringnumber,              int stringcount, int stringnumber,
791              const char **stringptr);              const char **stringptr);
# Line 654  PCRE NATIVE API Line 824  PCRE NATIVE API
824  PCRE API OVERVIEW  PCRE API OVERVIEW
825    
826         PCRE has its own native API, which is described in this document. There         PCRE has its own native API, which is described in this document. There
827         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
828         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
829         Both of these APIs define a set of C function calls. A C++  wrapper  is         Both of these APIs define a set of C function calls. A C++  wrapper  is
830         distributed with PCRE. It is documented in the pcrecpp page.         distributed with PCRE. It is documented in the pcrecpp page.
# Line 676  PCRE API OVERVIEW Line 846  PCRE API OVERVIEW
846    
847         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
848         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
849         ing. This allows it to find all possible matches (at a given  point  in         ing. The alternative algorithm finds all possible matches (at  a  given
850         the  subject),  not  just  one. However, this algorithm does not return         point  in  the subject), and scans the subject just once. However, this
851         captured substrings. A description of the two matching  algorithms  and         algorithm does not return captured substrings. A description of the two
852         their  advantages  and disadvantages is given in the pcrematching docu-         matching  algorithms and their advantages and disadvantages is given in
853         mentation.         the pcrematching documentation.
854    
855         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
856         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 692  PCRE API OVERVIEW Line 862  PCRE API OVERVIEW
862           pcre_get_named_substring()           pcre_get_named_substring()
863           pcre_get_substring_list()           pcre_get_substring_list()
864           pcre_get_stringnumber()           pcre_get_stringnumber()
865             pcre_get_stringtable_entries()
866    
867         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
868         to free the memory used for extracted strings.         to free the memory used for extracted strings.
# Line 723  PCRE API OVERVIEW Line 894  PCRE API OVERVIEW
894         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
895         are used only when PCRE is compiled to use  the  heap  for  remembering         are used only when PCRE is compiled to use  the  heap  for  remembering
896         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
897         function. This is a non-standard way of building PCRE, for use in envi-         function. See the pcrebuild documentation for  details  of  how  to  do
898         ronments that have limited stacks. Because of the greater use of memory         this.  It  is  a non-standard way of building PCRE, for use in environ-
899         management, it runs more slowly.  Separate functions  are  provided  so         ments that have limited stacks. Because of the greater  use  of  memory
900         that  special-purpose  external  code  can  be used for this case. When         management,  it  runs  more  slowly. Separate functions are provided so
901         used, these functions are always called in a  stack-like  manner  (last         that special-purpose external code can be  used  for  this  case.  When
902         obtained,  first freed), and always for memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
903           obtained, first freed), and always for memory blocks of the same  size.
904           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
905           mentation.
906    
907         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
908         by  the  caller  to  a "callout" function, which PCRE will then call at         by  the  caller  to  a "callout" function, which PCRE will then call at
# Line 736  PCRE API OVERVIEW Line 910  PCRE API OVERVIEW
910         pcrecallout documentation.         pcrecallout documentation.
911    
912    
913    NEWLINES
914    
915           PCRE  supports five different conventions for indicating line breaks in
916           strings: a single CR (carriage return) character, a  single  LF  (line-
917           feed) character, the two-character sequence CRLF, any of the three pre-
918           ceding, or any Unicode newline sequence. The Unicode newline  sequences
919           are  the  three just mentioned, plus the single characters VT (vertical
920           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
921           separator, U+2028), and PS (paragraph separator, U+2029).
922    
923           Each  of  the first three conventions is used by at least one operating
924           system as its standard newline sequence. When PCRE is built, a  default
925           can  be  specified.  The default default is LF, which is the Unix stan-
926           dard. When PCRE is run, the default can be overridden,  either  when  a
927           pattern is compiled, or when it is matched.
928    
929           At compile time, the newline convention can be specified by the options
930           argument of pcre_compile(), or it can be specified by special  text  at
931           the start of the pattern itself; this overrides any other settings. See
932           the pcrepattern page for details of the special character sequences.
933    
934           In the PCRE documentation the word "newline" is used to mean "the char-
935           acter  or pair of characters that indicate a line break". The choice of
936           newline convention affects the handling of  the  dot,  circumflex,  and
937           dollar metacharacters, the handling of #-comments in /x mode, and, when
938           CRLF is a recognized line ending sequence, the match position  advance-
939           ment for a non-anchored pattern. There is more detail about this in the
940           section on pcre_exec() options below.
941    
942           The choice of newline convention does not affect the interpretation  of
943           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
944           which is controlled in a similar way, but by separate options.
945    
946    
947  MULTITHREADING  MULTITHREADING
948    
949         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
950         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
951         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
952         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
953    
954         The  compiled form of a regular expression is not altered during match-         The compiled form of a regular expression is not altered during  match-
955         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
956         at once.         at once.
957    
# Line 751  MULTITHREADING Line 959  MULTITHREADING
959  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
960    
961         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
962         later time, possibly by a different program, and even on a  host  other         later  time,  possibly by a different program, and even on a host other
963         than  the  one  on  which  it  was  compiled.  Details are given in the         than the one on which  it  was  compiled.  Details  are  given  in  the
964         pcreprecompile documentation.         pcreprecompile  documentation.  However, compiling a regular expression
965           with one version of PCRE for use with a different version is not  guar-
966           anteed to work and may cause crashes.
967    
968    
969  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
970    
971         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
972    
973         The function pcre_config() makes it possible for a PCRE client to  dis-         The  function pcre_config() makes it possible for a PCRE client to dis-
974         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
975         The pcrebuild documentation has more details about these optional  fea-         The  pcrebuild documentation has more details about these optional fea-
976         tures.         tures.
977    
978         The  first  argument  for pcre_config() is an integer, specifying which         The first argument for pcre_config() is an  integer,  specifying  which
979         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
980         into  which  the  information  is  placed. The following information is         into which the information is  placed.  The  following  information  is
981         available:         available:
982    
983           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
984    
985         The output is an integer that is set to one if UTF-8 support is  avail-         The  output is an integer that is set to one if UTF-8 support is avail-
986         able; otherwise it is set to zero.         able; otherwise it is set to zero.
987    
988           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
989    
990         The  output  is  an  integer  that is set to one if support for Unicode         The output is an integer that is set to  one  if  support  for  Unicode
991         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
992    
993           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
994    
995         The output is an integer that is set to the value of the code  that  is         The  output  is  an integer whose value specifies the default character
996         used  for the newline character. It is either linefeed (10) or carriage         sequence that is recognized as meaning "newline". The four values  that
997         return (13), and should normally be the  standard  character  for  your         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
998         operating system.         and -1 for ANY. The default should normally be  the  standard  sequence
999           for your operating system.
1000    
1001             PCRE_CONFIG_BSR
1002    
1003           The output is an integer whose value indicates what character sequences
1004           the \R escape sequence matches by default. A value of 0 means  that  \R
1005           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1006           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1007           tern is compiled or matched.
1008    
1009           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1010    
# Line 808  CHECKING BUILD-TIME OPTIONS Line 1027  CHECKING BUILD-TIME OPTIONS
1027         internal  matching  function  calls in a pcre_exec() execution. Further         internal  matching  function  calls in a pcre_exec() execution. Further
1028         details are given with pcre_exec() below.         details are given with pcre_exec() below.
1029    
1030             PCRE_CONFIG_MATCH_LIMIT_RECURSION
1031    
1032           The output is an integer that gives the default limit for the depth  of
1033           recursion  when calling the internal matching function in a pcre_exec()
1034           execution. Further details are given with pcre_exec() below.
1035    
1036           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1037    
1038         The output is an integer that is set to one if internal recursion  when         The output is an integer that is set to one if internal recursion  when
# Line 840  COMPILING A PATTERN Line 1065  COMPILING A PATTERN
1065         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained  via  pcre_malloc is returned. This contains the compiled code
1066         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
1067         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1068         It is up to the caller  to  free  the  memory  when  it  is  no  longer         It is up to the caller to free the memory (via pcre_free) when it is no
1069         required.         longer required.
1070    
1071         Although  the compiled code of a PCRE regex is relocatable, that is, it         Although  the compiled code of a PCRE regex is relocatable, that is, it
1072         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
1073         fully  relocatable, because it may contain a copy of the tableptr argu-         fully  relocatable, because it may contain a copy of the tableptr argu-
1074         ment, which is an address (see below).         ment, which is an address (see below).
1075    
1076         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
1077         tion.  It  should  be  zero  if  no options are required. The available         pilation.  It  should be zero if no options are required. The available
1078         options are described below. Some of them, in  particular,  those  that         options are described below. Some of them, in  particular,  those  that
1079         are  compatible  with  Perl,  can also be set and unset from within the         are  compatible  with  Perl,  can also be set and unset from within the
1080         pattern (see the detailed description  in  the  pcrepattern  documenta-         pattern (see the detailed description  in  the  pcrepattern  documenta-
1081         tion).  For  these options, the contents of the options argument speci-         tion).  For  these options, the contents of the options argument speci-
1082         fies their initial settings at the start of compilation and  execution.         fies their initial settings at the start of compilation and  execution.
1083         The  PCRE_ANCHORED option can be set at the time of matching as well as         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time
1084         at compile time.         of matching as well as at compile time.
1085    
1086         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1087         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1088         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
1089         sage.  The  offset from the start of the pattern to the character where         sage. This is a static string that is part of the library. You must not
1090         the error was discovered is  placed  in  the  variable  pointed  to  by         try to free it. The offset from the start of the pattern to the charac-
1091         erroffset,  which  must  not  be  NULL. If it is, an immediate error is         ter where the error was discovered is placed in the variable pointed to
1092           by erroffset, which must not be NULL. If it is, an immediate  error  is
1093         given.         given.
1094    
1095         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1096         codeptr  argument is not NULL, a non-zero error code number is returned         codeptr argument is not NULL, a non-zero error code number is  returned
1097         via this argument in the event of an error. This is in addition to  the         via  this argument in the event of an error. This is in addition to the
1098         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1099    
1100         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1101         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1102         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1103         result of a call to pcre_maketables(). This value is  stored  with  the         result  of  a  call to pcre_maketables(). This value is stored with the
1104         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1105         pointer is passed to it. For more discussion, see the section on locale         pointer is passed to it. For more discussion, see the section on locale
1106         support below.         support below.
1107    
1108         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1109         pile():         pile():
1110    
1111           pcre *re;           pcre *re;
# Line 892  COMPILING A PATTERN Line 1118  COMPILING A PATTERN
1118             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1119             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1120    
1121         The following names for option bits are defined in  the  pcre.h  header         The  following  names  for option bits are defined in the pcre.h header
1122         file:         file:
1123    
1124           PCRE_ANCHORED           PCRE_ANCHORED
1125    
1126         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
1127         is constrained to match only at the first matching point in the  string         is  constrained to match only at the first matching point in the string
1128         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1129         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1130         only way to do it in Perl.         only way to do it in Perl.
1131    
1132           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1133    
1134         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1135         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1136         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1137    
1138             PCRE_BSR_ANYCRLF
1139             PCRE_BSR_UNICODE
1140    
1141           These options (which are mutually exclusive) control what the \R escape
1142           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1143           or to match any Unicode newline sequence. The default is specified when
1144           PCRE is built. It can be overridden from within the pattern, or by set-
1145           ting an option when a compiled pattern is matched.
1146    
1147           PCRE_CASELESS           PCRE_CASELESS
1148    
1149         If  this  bit is set, letters in the pattern match both upper and lower         If this bit is set, letters in the pattern match both upper  and  lower
1150         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1151         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1152         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1153         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1154         with higher values, the concept of case is supported if  PCRE  is  com-         with  higher  values,  the concept of case is supported if PCRE is com-
1155         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1156         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1157         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1158         UTF-8 support.         UTF-8 support.
1159    
1160           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1161    
1162         If this bit is set, a dollar metacharacter in the pattern matches  only         If  this bit is set, a dollar metacharacter in the pattern matches only
1163         at  the  end  of the subject string. Without this option, a dollar also         at the end of the subject string. Without this option,  a  dollar  also
1164         matches immediately before the final character if it is a newline  (but         matches  immediately before a newline at the end of the string (but not
1165         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1166         ignored if PCRE_MULTILINE is set. There is no equivalent to this option         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1167         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1168    
1169           PCRE_DOTALL           PCRE_DOTALL
1170    
1171         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharater in the pattern matches all char-
1172         acters, including newlines. Without it,  newlines  are  excluded.  This         acters,  including  those that indicate newline. Without it, a dot does
1173         option  is equivalent to Perl's /s option, and it can be changed within         not match when the current position is at a  newline.  This  option  is
1174         a pattern by a (?s) option setting.  A  negative  class  such  as  [^a]         equivalent  to Perl's /s option, and it can be changed within a pattern
1175         always  matches a newline character, independent of the setting of this         by a (?s) option setting. A negative class such as [^a] always  matches
1176         option.         newline characters, independent of the setting of this option.
1177    
1178             PCRE_DUPNAMES
1179    
1180           If  this  bit is set, names used to identify capturing subpatterns need
1181           not be unique. This can be helpful for certain types of pattern when it
1182           is  known  that  only  one instance of the named subpattern can ever be
1183           matched. There are more details of named subpatterns  below;  see  also
1184           the pcrepattern documentation.
1185    
1186           PCRE_EXTENDED           PCRE_EXTENDED
1187    
1188         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1189         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1190         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1191         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1192         line character, inclusive, are also  ignored.  This  is  equivalent  to         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1193         Perl's  /x  option,  and  it  can be changed within a pattern by a (?x)         option, and it can be changed within a pattern by a  (?x)  option  set-
1194         option setting.         ting.
1195    
1196         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1197         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1198         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1199         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1200         introduces a conditional subpattern.         introduces a conditional subpattern.
1201    
1202           PCRE_EXTRA           PCRE_EXTRA
1203    
1204         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1205         of  PCRE  that  is  incompatible with Perl, but it is currently of very         of PCRE that is incompatible with Perl, but it  is  currently  of  very
1206         little use. When set, any backslash in a pattern that is followed by  a         little  use. When set, any backslash in a pattern that is followed by a
1207         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1208         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1209         backslash  followed by a letter with no special meaning is treated as a         backslash followed by a letter with no special meaning is treated as  a
1210         literal. There are at present no  other  features  controlled  by  this         literal.  (Perl can, however, be persuaded to give a warning for this.)
1211         option. It can also be set by a (?X) option setting within a pattern.         There are at present no other features controlled by  this  option.  It
1212           can also be set by a (?X) option setting within a pattern.
1213    
1214           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1215    
1216         If  this  option  is  set,  an  unanchored pattern is required to match         If  this  option  is  set,  an  unanchored pattern is required to match
1217         before or at the first newline character in the subject string,  though         before or at the first  newline  in  the  subject  string,  though  the
1218         the matched text may continue over the newline.         matched text may continue over the newline.
1219    
1220           PCRE_MULTILINE           PCRE_MULTILINE
1221    
# Line 983  COMPILING A PATTERN Line 1227  COMPILING A PATTERN
1227         is set). This is the same as Perl.         is set). This is the same as Perl.
1228    
1229         When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"         When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"
1230         constructs  match  immediately following or immediately before any new-         constructs  match  immediately following or immediately before internal
1231         line in the subject string, respectively, as well as at the very  start         newlines in the subject string, respectively, as well as  at  the  very
1232         and  end. This is equivalent to Perl's /m option, and it can be changed         start  and  end.  This is equivalent to Perl's /m option, and it can be
1233         within a pattern by a (?m) option setting. If there are no "\n" charac-         changed within a pattern by a (?m) option setting. If there are no new-
1234         ters  in  a  subject  string, or no occurrences of ^ or $ in a pattern,         lines  in  a  subject string, or no occurrences of ^ or $ in a pattern,
1235         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1236    
1237             PCRE_NEWLINE_CR
1238             PCRE_NEWLINE_LF
1239             PCRE_NEWLINE_CRLF
1240             PCRE_NEWLINE_ANYCRLF
1241             PCRE_NEWLINE_ANY
1242    
1243           These options override the default newline definition that  was  chosen
1244           when  PCRE  was built. Setting the first or the second specifies that a
1245           newline is indicated by a single character (CR  or  LF,  respectively).
1246           Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1247           two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1248           that any of the three preceding sequences should be recognized. Setting
1249           PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1250           recognized. The Unicode newline sequences are the three just mentioned,
1251           plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1252           U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1253           (paragraph separator, U+2029). The last  two  are  recognized  only  in
1254           UTF-8 mode.
1255    
1256           The  newline  setting  in  the  options  word  uses three bits that are
1257           treated as a number, giving eight possibilities. Currently only six are
1258           used  (default  plus the five values above). This means that if you set
1259           more than one newline option, the combination may or may not be  sensi-
1260           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1261           PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1262           cause an error.
1263    
1264           The  only time that a line break is specially recognized when compiling
1265           a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1266           character  class  is  encountered.  This indicates a comment that lasts
1267           until after the next line break sequence. In other circumstances,  line
1268           break   sequences   are   treated  as  literal  data,  except  that  in
1269           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1270           and are therefore ignored.
1271    
1272           The newline option that is set at compile time becomes the default that
1273           is used for pcre_exec() and pcre_dfa_exec(), but it can be  overridden.
1274    
1275           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1276    
1277         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
1278         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1279         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1280         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1281         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1282    
1283           PCRE_UNGREEDY           PCRE_UNGREEDY
1284    
1285         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1286         are  not greedy by default, but become greedy if followed by "?". It is         are not greedy by default, but become greedy if followed by "?". It  is
1287         not compatible with Perl. It can also be set by a (?U)  option  setting         not  compatible  with Perl. It can also be set by a (?U) option setting
1288         within the pattern.         within the pattern.
1289    
1290           PCRE_UTF8           PCRE_UTF8
1291    
1292         This  option  causes PCRE to regard both the pattern and the subject as         This option causes PCRE to regard both the pattern and the  subject  as
1293         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1294         However,  it is available only when PCRE is built to include UTF-8 sup-         However, it is available only when PCRE is built to include UTF-8  sup-
1295         port. If not, the use of this option provokes an error. Details of  how         port.  If not, the use of this option provokes an error. Details of how
1296         this  option  changes the behaviour of PCRE are given in the section on         this option changes the behaviour of PCRE are given in the  section  on
1297         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1298    
1299           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1300    
1301         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1302         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically checked. There is a  discussion  about  the  validity  of
1303         pcre_compile() returns an error. If you already know that your  pattern         UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1304         is  valid, and you want to skip this check for performance reasons, you         bytes is found, pcre_compile() returns an error. If  you  already  know
1305         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of         that your pattern is valid, and you want to skip this check for perfor-
1306         passing an invalid UTF-8 string as a pattern is undefined. It may cause         mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1307         your program to crash.  Note that this option can  also  be  passed  to         set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1308         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-         undefined. It may cause your program to crash. Note  that  this  option
1309         ing of subject strings.         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1310           UTF-8 validity checking of subject strings.
1311    
1312    
1313  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1314    
1315         The following table lists the error  codes  than  may  be  returned  by         The following table lists the error  codes  than  may  be  returned  by
1316         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(),  along with the error messages that may be returned by
1317         both compiling functions.         both compiling functions. As PCRE has developed, some error codes  have
1318           fallen out of use. To avoid confusion, they have not been re-used.
1319    
1320            0  no error            0  no error
1321            1  \ at end of pattern            1  \ at end of pattern
# Line 1043  COMPILATION ERROR CODES Line 1327  COMPILATION ERROR CODES
1327            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1328            8  range out of order in character class            8  range out of order in character class
1329            9  nothing to repeat            9  nothing to repeat
1330           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1331           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1332           12  unrecognized character after (?           12  unrecognized character after (?
1333           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
# Line 1052  COMPILATION ERROR CODES Line 1336  COMPILATION ERROR CODES
1336           16  erroffset passed as NULL           16  erroffset passed as NULL
1337           17  unknown option bit(s) set           17  unknown option bit(s) set
1338           18  missing ) after comment           18  missing ) after comment
1339           19  parentheses nested too deeply           19  [this code is not in use]
1340           20  regular expression too large           20  regular expression too large
1341           21  failed to get memory           21  failed to get memory
1342           22  unmatched parentheses           22  unmatched parentheses
1343           23  internal error: code overflow           23  internal error: code overflow
1344           24  unrecognized character after (?<           24  unrecognized character after (?<
1345           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1346           26  malformed number after (?(           26  malformed number or name after (?(
1347           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1348           28  assertion expected after (?(           28  assertion expected after (?(
1349           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1350           30  unknown POSIX class name           30  unknown POSIX class name
1351           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1352           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1353           33  spare error           33  [this code is not in use]
1354           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1355           35  invalid condition (?(0)           35  invalid condition (?(0)
1356           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1075  COMPILATION ERROR CODES Line 1359  COMPILATION ERROR CODES
1359           39  closing ) for (?C expected           39  closing ) for (?C expected
1360           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1361           41  unrecognized character after (?P           41  unrecognized character after (?P
1362           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1363           43  two named groups have the same name           43  two named subpatterns have the same name
1364           44  invalid UTF-8 string           44  invalid UTF-8 string
1365           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1366           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1367           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1368             48  subpattern name is too long (maximum 32 characters)
1369             49  too many named subpatterns (maximum 10,000)
1370             50  [this code is not in use]
1371             51  octal value is greater than \377 (not in UTF-8 mode)
1372             52  internal error: overran compiling workspace
1373             53   internal  error:  previously-checked  referenced  subpattern not
1374           found
1375             54  DEFINE group contains more than one branch
1376             55  repeating a DEFINE group is not allowed
1377             56  inconsistent NEWLINE options
1378             57  \g is not followed by a braced name or an optionally braced
1379                   non-zero number
1380             58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
1381    
1382    
1383  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1111  STUDYING A PATTERN Line 1408  STUDYING A PATTERN
1408    
1409         The  third argument for pcre_study() is a pointer for an error message.         The  third argument for pcre_study() is a pointer for an error message.
1410         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1411         points  to  is set to NULL. Otherwise it points to a textual error mes-         points  to  is  set  to NULL. Otherwise it is set to point to a textual
1412         sage. You should therefore test the error pointer for NULL after  call-         error message. This is a static string that is part of the library. You
1413         ing pcre_study(), to be sure that it has run successfully.         must  not  try  to  free it. You should test the error pointer for NULL
1414           after calling pcre_study(), to be sure that it has run successfully.
1415    
1416         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1417    
# Line 1124  STUDYING A PATTERN Line 1422  STUDYING A PATTERN
1422             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1423    
1424         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1425         that do not have a single fixed starting character. A bitmap of  possi-         that  do not have a single fixed starting character. A bitmap of possi-
1426         ble starting bytes is created.         ble starting bytes is created.
1427    
1428    
1429  LOCALE SUPPORT  LOCALE SUPPORT
1430    
1431         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1432         letters digits, or whatever, by reference to a set of  tables,  indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1433         by  character  value.  When running in UTF-8 mode, this applies only to         by character value. When running in UTF-8 mode, this  applies  only  to
1434         characters with codes less than 128. Higher-valued  codes  never  match         characters  with  codes  less than 128. Higher-valued codes never match
1435         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
1436         with Unicode character property support.         with  Unicode  character property support. The use of locales with Uni-
1437           code is discouraged. If you are handling characters with codes  greater
1438         An internal set of tables is created in the default C locale when  PCRE         than  128, you should either use UTF-8 and Unicode, or use locales, but
1439         is  built.  This  is  used when the final argument of pcre_compile() is         not try to mix the two.
1440         NULL, and is sufficient for many applications. An  alternative  set  of  
1441         tables  can,  however, be supplied. These may be created in a different         PCRE contains an internal set of tables that are used  when  the  final
1442         locale from the default. As more and more applications change to  using         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1443         Unicode, the need for this locale support is expected to die away.         applications.  Normally, the internal tables recognize only ASCII char-
1444           acters. However, when PCRE is built, it is possible to cause the inter-
1445         External  tables  are  built by calling the pcre_maketables() function,         nal tables to be rebuilt in the default "C" locale of the local system,
1446         which has no arguments, in the relevant locale. The result can then  be         which may cause them to be different.
1447         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For  
1448         example, to build and use tables that are appropriate  for  the  French         The  internal tables can always be overridden by tables supplied by the
1449         locale  (where  accented  characters  with  values greater than 128 are         application that calls PCRE. These may be created in a different locale
1450           from  the  default.  As more and more applications change to using Uni-
1451           code, the need for this locale support is expected to die away.
1452    
1453           External tables are built by calling  the  pcre_maketables()  function,
1454           which  has no arguments, in the relevant locale. The result can then be
1455           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1456           example,  to  build  and use tables that are appropriate for the French
1457           locale (where accented characters with  values  greater  than  128  are
1458         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1459    
1460           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1461           tables = pcre_maketables();           tables = pcre_maketables();
1462           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1463    
1464           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1465           if you are using Windows, the name for the French locale is "french".
1466    
1467         When pcre_maketables() runs, the tables are built  in  memory  that  is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1468         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1469         that the memory containing the tables remains available for as long  as         that the memory containing the tables remains available for as long  as
# Line 1200  INFORMATION ABOUT A PATTERN Line 1509  INFORMATION ABOUT A PATTERN
1509         pattern:         pattern:
1510    
1511           int rc;           int rc;
1512           unsigned long int length;           size_t length;
1513           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1514             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1515             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
# Line 1232  INFORMATION ABOUT A PATTERN Line 1541  INFORMATION ABOUT A PATTERN
1541           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1542    
1543         Return  information  about  the first byte of any matched string, for a         Return  information  about  the first byte of any matched string, for a
1544         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored pattern. The fourth argument should point to an int  vari-
1545         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1546         compatibility.)         is still recognized for backwards compatibility.)
1547    
1548         If there is a fixed first byte, for example, from  a  pattern  such  as         If there is a fixed first byte, for example, from  a  pattern  such  as
1549         (cat|cow|coyote),  it  is  returned in the integer pointed to by where.         (cat|cow|coyote), its value is returned. Otherwise, if either
        Otherwise, if either  
1550    
1551         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1552         branch starts with "^", or         branch starts with "^", or
1553    
1554         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1555         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1556    
1557         -1 is returned, indicating that the pattern matches only at  the  start         -1  is  returned, indicating that the pattern matches only at the start
1558         of  a  subject string or after any newline within the string. Otherwise         of a subject string or after any newline within the  string.  Otherwise
1559         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1560    
1561           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1562    
1563         If the pattern was studied, and this resulted in the construction of  a         If  the pattern was studied, and this resulted in the construction of a
1564         256-bit table indicating a fixed set of bytes for the first byte in any         256-bit table indicating a fixed set of bytes for the first byte in any
1565         matching string, a pointer to the table is returned. Otherwise NULL  is         matching  string, a pointer to the table is returned. Otherwise NULL is
1566         returned.  The fourth argument should point to an unsigned char * vari-         returned. The fourth argument should point to an unsigned char *  vari-
1567         able.         able.
1568    
1569             PCRE_INFO_HASCRORLF
1570    
1571           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1572           characters, otherwise 0. The fourth argument should  point  to  an  int
1573           variable.  An explicit match is either a literal CR or LF character, or
1574           \r or \n.
1575    
1576             PCRE_INFO_JCHANGED
1577    
1578           Return 1 if the (?J) option setting is used in the  pattern,  otherwise
1579           0. The fourth argument should point to an int variable. The (?J) inter-
1580           nal option setting changes the local PCRE_DUPNAMES option.
1581    
1582           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1583    
1584         Return the value of the rightmost literal byte that must exist  in  any         Return the value of the rightmost literal byte that must exist  in  any
# Line 1274  INFORMATION ABOUT A PATTERN Line 1595  INFORMATION ABOUT A PATTERN
1595    
1596         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1597         ses.  The names are just an additional way of identifying the parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1598         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1599         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring()  are  provided  for extracting captured sub-
1600         captured substring by name. It is also possible  to  extract  the  data         strings by name. It is also possible to extract the data  directly,  by
1601         directly,  by  first converting the name to a number in order to access         first  converting  the  name to a number in order to access the correct
1602         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1603         below).  To  do the conversion, you need to use the name-to-number map,         the  conversion,  you  need  to  use  the  name-to-number map, which is
1604         which is described by these three values.         described by these three values.
1605    
1606         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1607         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
# Line 1290  INFORMATION ABOUT A PATTERN Line 1611  INFORMATION ABOUT A PATTERN
1611         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1612         sis, most significant byte first. The rest of the entry is  the  corre-         sis, most significant byte first. The rest of the entry is  the  corre-
1613         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1614         For example, consider the following pattern  (assume  PCRE_EXTENDED  is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1615         set, so white space - including newlines - is ignored):         theses  numbers.  For  example,  consider the following pattern (assume
1616           PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1617           ignored):
1618    
1619           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1620           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1621    
1622         There  are  four  named subpatterns, so the table has four entries, and         There  are  four  named subpatterns, so the table has four entries, and
1623         each entry in the table is eight bytes long. The table is  as  follows,         each entry in the table is eight bytes long. The table is  as  follows,
# Line 1307  INFORMATION ABOUT A PATTERN Line 1630  INFORMATION ABOUT A PATTERN
1630           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1631    
1632         When writing code to extract data  from  named  subpatterns  using  the         When writing code to extract data  from  named  subpatterns  using  the
1633         name-to-number map, remember that the length of each entry is likely to         name-to-number  map,  remember that the length of the entries is likely
1634         be different for each compiled pattern.         to be different for each compiled pattern.
1635    
1636             PCRE_INFO_OKPARTIAL
1637    
1638           Return 1 if the pattern can be used for partial matching, otherwise  0.
1639           The  fourth  argument  should point to an int variable. The pcrepartial
1640           documentation lists the restrictions that apply to patterns  when  par-
1641           tial matching is used.
1642    
1643           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1644    
1645         Return a copy of the options with which the pattern was  compiled.  The         Return  a  copy of the options with which the pattern was compiled. The
1646         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1647         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1648         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1649           other  words,  they are the options that will be in force when matching
1650           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1651           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1652           and PCRE_EXTENDED.
1653    
1654         A  pattern  is  automatically  anchored by PCRE if all of its top-level         A pattern is automatically anchored by PCRE if  all  of  its  top-level
1655         alternatives begin with one of the following:         alternatives begin with one of the following:
1656    
1657           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1331  INFORMATION ABOUT A PATTERN Line 1665  INFORMATION ABOUT A PATTERN
1665    
1666           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1667    
1668         Return  the  size  of the compiled pattern, that is, the value that was         Return the size of the compiled pattern, that is, the  value  that  was
1669         passed as the argument to pcre_malloc() when PCRE was getting memory in         passed as the argument to pcre_malloc() when PCRE was getting memory in
1670         which to place the compiled data. The fourth argument should point to a         which to place the compiled data. The fourth argument should point to a
1671         size_t variable.         size_t variable.
# Line 1339  INFORMATION ABOUT A PATTERN Line 1673  INFORMATION ABOUT A PATTERN
1673           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1674    
1675         Return the size of the data block pointed to by the study_data field in         Return the size of the data block pointed to by the study_data field in
1676         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to         a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1677         pcre_malloc() when PCRE was getting memory into which to place the data         pcre_malloc() when PCRE was getting memory into which to place the data
1678         created  by  pcre_study(). The fourth argument should point to a size_t         created by pcre_study(). The fourth argument should point to  a  size_t
1679         variable.         variable.
1680    
1681    
# Line 1349  OBSOLETE INFO FUNCTION Line 1683  OBSOLETE INFO FUNCTION
1683    
1684         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1685    
1686         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1687         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1688         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1689         pcre_info()  is the number of capturing subpatterns, or one of the fol-         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1690         lowing negative numbers:         lowing negative numbers:
1691    
1692           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1693           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1694    
1695         If the optptr argument is not NULL, a copy of the  options  with  which         If  the  optptr  argument is not NULL, a copy of the options with which
1696         the  pattern  was  compiled  is placed in the integer it points to (see         the pattern was compiled is placed in the integer  it  points  to  (see
1697         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1698    
1699         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1700         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1701         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1702    
1703    
# Line 1371  REFERENCE COUNTS Line 1705  REFERENCE COUNTS
1705    
1706         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1707    
1708         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1709         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1710         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1711         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1712         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1713    
1714         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1715         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1716         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1717         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1718         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1719         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1720    
1721         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1722         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1723         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1724    
1725    
# Line 1395  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1729  MATCHING A PATTERN: THE TRADITIONAL FUNC
1729              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1730              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1731    
1732         The function pcre_exec() is called to match a subject string against  a         The  function pcre_exec() is called to match a subject string against a
1733         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1734         has been studied, the result of the study should be passed in the extra         has been studied, the result of the study should be passed in the extra
1735         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1736         and it operates in a Perl-like manner. For specialist use there is also         and it operates in a Perl-like manner. For specialist use there is also
1737         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1738         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1739    
1740         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1741         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1742         is possible to save compiled patterns and study data, and then use them         is possible to save compiled patterns and study data, and then use them
1743         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1744         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1745    
1746         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1425  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1759  MATCHING A PATTERN: THE TRADITIONAL FUNC
1759    
1760     Extra data for pcre_exec()     Extra data for pcre_exec()
1761    
1762         If the extra argument is not NULL, it must point to a  pcre_extra  data         If  the  extra argument is not NULL, it must point to a pcre_extra data
1763         block.  The pcre_study() function returns such a block (when it doesn't         block. The pcre_study() function returns such a block (when it  doesn't
1764         return NULL), but you can also create one for yourself, and pass  addi-         return  NULL), but you can also create one for yourself, and pass addi-
1765         tional  information in it. The fields in a pcre_extra block are as fol-         tional information in it. The pcre_extra block contains  the  following
1766         lows:         fields (not necessarily in this order):
1767    
1768           unsigned long int flags;           unsigned long int flags;
1769           void *study_data;           void *study_data;
1770           unsigned long int match_limit;           unsigned long int match_limit;
1771             unsigned long int match_limit_recursion;
1772           void *callout_data;           void *callout_data;
1773           const unsigned char *tables;           const unsigned char *tables;
1774    
1775         The flags field is a bitmap that specifies which of  the  other  fields         The  flags  field  is a bitmap that specifies which of the other fields
1776         are set. The flag bits are:         are set. The flag bits are:
1777    
1778           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1779           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1780             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1781           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1782           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1783    
1784         Other  flag  bits should be set to zero. The study_data field is set in         Other flag bits should be set to zero. The study_data field is  set  in
1785         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1786         the appropriate flag bit. You should not set this yourself, but you may         the appropriate flag bit. You should not set this yourself, but you may
1787         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1788         flag bits.         flag bits.
1789    
1790         The match_limit field provides a means of preventing PCRE from using up         The match_limit field provides a means of preventing PCRE from using up
1791         a vast amount of resources when running patterns that are not going  to         a  vast amount of resources when running patterns that are not going to
1792         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1793         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1794         repeats.         repeats.
1795    
1796         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1797         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly  (sometimes  recursively). The limit set by match_limit is imposed
1798         times  this  function is called during a match, which has the effect of         on the number of times this function is called during  a  match,  which
1799         limiting the amount of recursion and backtracking that can take  place.         has  the  effect  of  limiting the amount of backtracking that can take
1800         For patterns that are not anchored, the count starts from zero for each         place. For patterns that are not anchored, the count restarts from zero
1801         position in the subject string.         for each position in the subject string.
1802    
1803         The default limit for the library can be set when PCRE  is  built;  the         The  default  value  for  the  limit can be set when PCRE is built; the
1804         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1805         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1806         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra    block    in    which    match_limit    is    set,     and
1807         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is         PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1808         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1809    
1810         The  pcre_callout  field is used in conjunction with the "callout" fea-         The match_limit_recursion field is similar to match_limit, but  instead
1811           of limiting the total number of times that match() is called, it limits
1812           the depth of recursion. The recursion depth is a  smaller  number  than
1813           the  total number of calls, because not all calls to match() are recur-
1814           sive.  This limit is of use only if it is set smaller than match_limit.
1815    
1816           Limiting  the  recursion  depth  limits the amount of stack that can be
1817           used, or, when PCRE has been compiled to use memory on the heap instead
1818           of the stack, the amount of heap memory that can be used.
1819    
1820           The  default  value  for  match_limit_recursion can be set when PCRE is
1821           built; the default default  is  the  same  value  as  the  default  for
1822           match_limit.  You can override the default by suppling pcre_exec() with
1823           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1824           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1825           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1826    
1827           The pcre_callout field is used in conjunction with the  "callout"  fea-
1828         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1829    
1830         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1831         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
1832         pattern. A non-NULL value is stored with the compiled pattern  only  if         pattern.  A  non-NULL value is stored with the compiled pattern only if
1833         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1834         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1835         PCRE's  internal  tables  to be used. This facility is helpful when re-         PCRE's internal tables to be used. This facility is  helpful  when  re-
1836         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
1837         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
1838         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1839         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1840    
1841     Option bits for pcre_exec()     Option bits for pcre_exec()
1842    
1843         The  unused  bits of the options argument for pcre_exec() must be zero.         The unused bits of the options argument for pcre_exec() must  be  zero.
1844         The  only  bits  that  may  be  set  are  PCRE_ANCHORED,   PCRE_NOTBOL,         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1845         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1846           PCRE_PARTIAL.
1847    
1848           PCRE_ANCHORED           PCRE_ANCHORED
1849    
# Line 1498  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1852  MATCHING A PATTERN: THE TRADITIONAL FUNC
1852         turned  out to be anchored by virtue of its contents, it cannot be made         turned  out to be anchored by virtue of its contents, it cannot be made
1853         unachored at matching time.         unachored at matching time.
1854    
1855             PCRE_BSR_ANYCRLF
1856             PCRE_BSR_UNICODE
1857    
1858           These options (which are mutually exclusive) control what the \R escape
1859           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1860           or to match any Unicode newline sequence. These  options  override  the
1861           choice that was made or defaulted when the pattern was compiled.
1862    
1863             PCRE_NEWLINE_CR
1864             PCRE_NEWLINE_LF
1865             PCRE_NEWLINE_CRLF
1866             PCRE_NEWLINE_ANYCRLF
1867             PCRE_NEWLINE_ANY
1868    
1869           These  options  override  the  newline  definition  that  was chosen or
1870           defaulted when the pattern was compiled. For details, see the  descrip-
1871           tion  of  pcre_compile()  above.  During  matching,  the newline choice
1872           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1873           ters.  It may also alter the way the match position is advanced after a
1874           match failure for an unanchored pattern.
1875    
1876           When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
1877           set,  and a match attempt for an unanchored pattern fails when the cur-
1878           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1879           explicit  matches  for  CR  or  LF  characters,  the  match position is
1880           advanced by two characters instead of one, in other words, to after the
1881           CRLF.
1882    
1883           The above rule is a compromise that makes the most common cases work as
1884           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1885           option is not set), it does not match the string "\r\nA" because, after
1886           failing at the start, it skips both the CR and the LF before  retrying.
1887           However,  the  pattern  [\r\n]A does match that string, because it con-
1888           tains an explicit CR or LF reference, and so advances only by one char-
1889           acter after the first failure.
1890    
1891           An explicit match for CR of LF is either a literal appearance of one of
1892           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1893           matches  such  as [^X] do not count, nor does \s (which includes CR and
1894           LF in the characters that it matches).
1895    
1896           Notwithstanding the above, anomalous effects may still occur when  CRLF
1897           is a valid newline sequence and explicit \r or \n escapes appear in the
1898           pattern.
1899    
1900           PCRE_NOTBOL           PCRE_NOTBOL
1901    
1902         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
# Line 1543  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1942  MATCHING A PATTERN: THE TRADITIONAL FUNC
1942         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
1943         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
1944         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
1945         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence         points  to  the start of a UTF-8 character. There is a discussion about
1946         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         the validity of UTF-8 strings in the section on UTF-8  support  in  the
1947         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
1948         returned.         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
1949           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1950         If you already know that your subject is valid, and you  want  to  skip  
1951         these    checks    for   performance   reasons,   you   can   set   the         If  you  already  know that your subject is valid, and you want to skip
1952         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         these   checks   for   performance   reasons,   you   can    set    the
1953         do  this  for the second and subsequent calls to pcre_exec() if you are         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
1954         making repeated calls to find all  the  matches  in  a  single  subject         do this for the second and subsequent calls to pcre_exec() if  you  are
1955         string.  However,  you  should  be  sure  that the value of startoffset         making  repeated  calls  to  find  all  the matches in a single subject
1956         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is         string. However, you should be  sure  that  the  value  of  startoffset
1957         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
1958         value of startoffset that does not point to the start of a UTF-8  char-         set, the effect of passing an invalid UTF-8 string as a subject,  or  a
1959           value  of startoffset that does not point to the start of a UTF-8 char-
1960         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1961    
1962           PCRE_PARTIAL           PCRE_PARTIAL
1963    
1964         This  option  turns  on  the  partial  matching feature. If the subject         This option turns on the  partial  matching  feature.  If  the  subject
1965         string fails to match the pattern, but at some point during the  match-         string  fails to match the pattern, but at some point during the match-
1966         ing  process  the  end of the subject was reached (that is, the subject         ing process the end of the subject was reached (that  is,  the  subject
1967         partially matches the pattern and the failure to  match  occurred  only         partially  matches  the  pattern and the failure to match occurred only
1968         because  there were not enough subject characters), pcre_exec() returns         because there were not enough subject characters), pcre_exec()  returns
1969         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1970         used,  there  are restrictions on what may appear in the pattern. These         used, there are restrictions on what may appear in the  pattern.  These
1971         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1972    
1973     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1974    
1975         The subject string is passed to pcre_exec() as a pointer in subject,  a         The  subject string is passed to pcre_exec() as a pointer in subject, a
1976         length  in  length, and a starting byte offset in startoffset. In UTF-8         length in length, and a starting byte offset in startoffset.  In  UTF-8
1977         mode, the byte offset must point to the start  of  a  UTF-8  character.         mode,  the  byte  offset  must point to the start of a UTF-8 character.
1978         Unlike  the  pattern string, the subject may contain binary zero bytes.         Unlike the pattern string, the subject may contain binary  zero  bytes.
1979         When the starting offset is zero, the search for a match starts at  the         When  the starting offset is zero, the search for a match starts at the
1980         beginning of the subject, and this is by far the most common case.         beginning of the subject, and this is by far the most common case.
1981    
1982         A  non-zero  starting offset is useful when searching for another match         A non-zero starting offset is useful when searching for  another  match
1983         in the same subject by calling pcre_exec() again after a previous  suc-         in  the same subject by calling pcre_exec() again after a previous suc-
1984         cess.   Setting  startoffset differs from just passing over a shortened         cess.  Setting startoffset differs from just passing over  a  shortened
1985         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
1986         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1987    
1988           \Biss\B           \Biss\B
1989    
1990         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
1991         only if the current position in the subject is not  a  word  boundary.)         only  if  the  current position in the subject is not a word boundary.)
1992         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
1993         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
1994         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
1995         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
1996         to  be  a  word  boundary. However, if pcre_exec() is passed the entire         to be a word boundary. However, if pcre_exec()  is  passed  the  entire
1997         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
1998         rence  of "iss" because it is able to look behind the starting point to         rence of "iss" because it is able to look behind the starting point  to
1999         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2000    
2001         If a non-zero starting offset is passed when the pattern  is  anchored,         If  a  non-zero starting offset is passed when the pattern is anchored,
2002         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
2003         if the pattern does not require the match to be at  the  start  of  the         if  the  pattern  does  not require the match to be at the start of the
2004         subject.         subject.
2005    
2006     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2007    
2008         In  general, a pattern matches a certain portion of the subject, and in         In general, a pattern matches a certain portion of the subject, and  in
2009         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2010         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2011         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2012         subpattern"  is  used for a fragment of a pattern that picks out a sub-         subpattern" is used for a fragment of a pattern that picks out  a  sub-
2013         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2014         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2015    
2016         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of  integer
2017         offsets whose address is passed in ovector. The number of  elements  in         offsets  whose  address is passed in ovector. The number of elements in
2018         the  vector is passed in ovecsize, which must be a non-negative number.         the vector is passed in ovecsize, which must be a non-negative  number.
2019         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
2020    
2021         The first two-thirds of the vector is used to pass back  captured  sub-         The  first  two-thirds of the vector is used to pass back captured sub-
2022         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2023         of the vector is used as workspace by pcre_exec() while  matching  cap-         of  the  vector is used as workspace by pcre_exec() while matching cap-
2024         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2025         The length passed in ovecsize should always be a multiple of three.  If         The  length passed in ovecsize should always be a multiple of three. If
2026         it is not, it is rounded down.         it is not, it is rounded down.
2027    
2028         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2029         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2030         and  continuing  up  to two-thirds of its length at the most. The first         and continuing up to two-thirds of its length at the  most.  The  first
2031         element of a pair is set to the offset of the first character in a sub-         element of a pair is set to the offset of the first character in a sub-
2032         string,  and  the  second  is  set to the offset of the first character         string, and the second is set to the  offset  of  the  first  character
2033         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-         after  the  end  of  a  substring. The first pair, ovector[0] and ovec-
2034         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1], identify the portion of  the  subject  string  matched  by  the
2035         entire pattern. The next pair is used for the first  capturing  subpat-         entire  pattern.  The next pair is used for the first capturing subpat-
2036         tern,  and  so  on.  The value returned by pcre_exec() is the number of         tern, and so on. The value returned by pcre_exec() is one more than the
2037         pairs that have been set. If there are no  capturing  subpatterns,  the         highest numbered pair that has been set. For example, if two substrings
2038         return  value  from  a  successful match is 1, indicating that just the         have been captured, the returned value is 3. If there are no  capturing
2039         first pair of offsets has been set.         subpatterns,  the return value from a successful match is 1, indicating
2040           that just the first pair of offsets has been set.
        Some convenience functions are provided  for  extracting  the  captured  
        substrings  as  separate  strings. These are described in the following  
        section.  
   
        It is possible for an capturing subpattern number  n+1  to  match  some  
        part  of  the  subject  when subpattern n has not been used at all. For  
        example, if the string "abc" is matched against the pattern (a|(z))(bc)  
        subpatterns  1 and 3 are matched, but 2 is not. When this happens, both  
        offset values corresponding to the unused subpattern are set to -1.  
2041    
2042         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2043         of the string that it matched that is returned.         of the string that it matched that is returned.
# Line 1660  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2051  MATCHING A PATTERN: THE TRADITIONAL FUNC
2051         substrings,  PCRE has to get additional memory for use during matching.         substrings,  PCRE has to get additional memory for use during matching.
2052         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
2053    
2054         Note that pcre_info() can be used to find out how many  capturing  sub-         The pcre_info() function can be used to find  out  how  many  capturing
2055         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns  there  are  in  a  compiled pattern. The smallest size for
2056         that will allow for n captured substrings, in addition to  the  offsets         ovector that will allow for n captured substrings, in addition  to  the
2057         of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
2058    
2059           It  is  possible for capturing subpattern number n+1 to match some part
2060           of the subject when subpattern n has not been used at all. For example,
2061           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
2062           return from the function is 4, and subpatterns 1 and 3 are matched, but
2063           2  is  not.  When  this happens, both values in the offset pairs corre-
2064           sponding to unused subpatterns are set to -1.
2065    
2066           Offset values that correspond to unused subpatterns at the end  of  the
2067           expression  are  also  set  to  -1. For example, if the string "abc" is
2068           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
2069           matched.  The  return  from the function is 2, because the highest used
2070           capturing subpattern number is 1. However, you can refer to the offsets
2071           for  the  second  and third capturing subpatterns if you wish (assuming
2072           the vector is large enough, of course).
2073    
2074           Some convenience functions are provided  for  extracting  the  captured
2075           substrings as separate strings. These are described below.
2076    
2077     Return values from pcre_exec()     Error return values from pcre_exec()
2078    
2079         If  pcre_exec()  fails, it returns a negative number. The following are         If  pcre_exec()  fails, it returns a negative number. The following are
2080         defined in the header file:         defined in the header file:
# Line 1691  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2100  MATCHING A PATTERN: THE TRADITIONAL FUNC
2100         an environment with the other endianness. This is the error  that  PCRE         an environment with the other endianness. This is the error  that  PCRE
2101         gives when the magic number is not present.         gives when the magic number is not present.
2102    
2103           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2104    
2105         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2106         compiled pattern. This error could be caused by a bug  in  PCRE  or  by         compiled pattern. This error could be caused by a bug  in  PCRE  or  by
# Line 1713  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2122  MATCHING A PATTERN: THE TRADITIONAL FUNC
2122    
2123           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2124    
2125         The  recursion  and backtracking limit, as specified by the match_limit         The  backtracking  limit,  as  specified  by the match_limit field in a
2126         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra structure (or defaulted) was reached.  See  the  description
2127         description above.         above.
2128    
2129           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2130    
# Line 1754  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2163  MATCHING A PATTERN: THE TRADITIONAL FUNC
2163    
2164         This error is given if the value of the ovecsize argument is  negative.         This error is given if the value of the ovecsize argument is  negative.
2165    
2166             PCRE_ERROR_RECURSIONLIMIT (-21)
2167    
2168           The internal recursion limit, as specified by the match_limit_recursion
2169           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2170           description above.
2171    
2172             PCRE_ERROR_BADNEWLINE     (-23)
2173    
2174           An invalid combination of PCRE_NEWLINE_xxx options was given.
2175    
2176           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2177    
2178    
2179  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2180    
# Line 1774  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2195  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2195         string_list() are provided for extracting captured substrings  as  new,         string_list() are provided for extracting captured substrings  as  new,
2196         separate,  zero-terminated strings. These functions identify substrings         separate,  zero-terminated strings. These functions identify substrings
2197         by number. The next section describes functions  for  extracting  named         by number. The next section describes functions  for  extracting  named
2198         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2199         extracted and has a further zero added on the end, but  the  result  is  
2200         not, of course, a C string.         A  substring that contains a binary zero is correctly extracted and has
2201           a further zero added on the end, but the result is not, of course, a  C
2202           string.   However,  you  can  process such a string by referring to the
2203           length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2204           string().  Unfortunately, the interface to pcre_get_substring_list() is
2205           not adequate for handling strings containing binary zeros, because  the
2206           end of the final string is not independently indicated.
2207    
2208         The  first  three  arguments  are the same for all three of these func-         The  first  three  arguments  are the same for all three of these func-
2209         tions: subject is the subject string that has  just  been  successfully         tions: subject is the subject string that has  just  been  successfully
# Line 1796  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2223  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2223         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2224         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2225         The yield of the function is the length of the  string,  not  including         The yield of the function is the length of the  string,  not  including
2226         the terminating zero, or one of         the terminating zero, or one of these error codes:
2227    
2228           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2229    
# Line 1812  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2239  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2239         single block of memory that is obtained via pcre_malloc. The address of         single block of memory that is obtained via pcre_malloc. The address of
2240         the  memory  block  is returned via listptr, which is also the start of         the  memory  block  is returned via listptr, which is also the start of
2241         the list of string pointers. The end of the list is marked  by  a  NULL         the list of string pointers. The end of the list is marked  by  a  NULL
2242         pointer. The yield of the function is zero if all went well, or         pointer.  The  yield  of  the function is zero if all went well, or the
2243           error code
2244    
2245           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2246    
2247         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2248    
2249         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2250         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2251         the  subject, but subpattern n has not been used at all, they return an         the subject, but subpattern n has not been used at all, they return  an
2252         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2253         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2254         tive for unset substrings.         tive for unset substrings.
2255    
2256         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2257         string_list()  can  be  used  to free the memory returned by a previous         string_list() can be used to free the memory  returned  by  a  previous
2258         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2259         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2260         pcre_free, which of course could be called directly from a  C  program.         pcre_free,  which  of course could be called directly from a C program.
2261         However,  PCRE is used in some situations where it is linked via a spe-         However, PCRE is used in some situations where it is linked via a  spe-
2262         cial  interface  to  another  programming  language  which  cannot  use         cial   interface  to  another  programming  language  that  cannot  use
2263         pcre_free  directly;  it is for these cases that the functions are pro-         pcre_free directly; it is for these cases that the functions  are  pro-
2264         vided.         vided.
2265    
2266    
# Line 1851  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2279  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2279              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2280              const char **stringptr);              const char **stringptr);
2281    
2282         To extract a substring by name, you first have to find associated  num-         To  extract a substring by name, you first have to find associated num-
2283         ber.  For example, for this pattern         ber.  For example, for this pattern
2284    
2285           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2286    
2287         the number of the subpattern called "xxx" is 2. You can find the number         the number of the subpattern called "xxx" is 2. If the name is known to
2288         from the name by calling pcre_get_stringnumber(). The first argument is         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2289         the  compiled  pattern,  and  the  second is the name. The yield of the         name by calling pcre_get_stringnumber(). The first argument is the com-
2290         function is the subpattern number, or  PCRE_ERROR_NOSUBSTRING  (-7)  if         piled pattern, and the second is the name. The yield of the function is
2291         there is no subpattern of that name.         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2292           subpattern of that name.
2293    
2294         Given the number, you can extract the substring directly, or use one of         Given the number, you can extract the substring directly, or use one of
2295         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
# Line 1879  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2308  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2308    
2309         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2310         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2311         ate.         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2312           behaviour may not be what you want (see the next section).
2313    
2314    
2315    DUPLICATE SUBPATTERN NAMES
2316    
2317           int pcre_get_stringtable_entries(const pcre *code,
2318                const char *name, char **first, char **last);
2319    
2320           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2321           subpatterns are not required to  be  unique.  Normally,  patterns  with
2322           duplicate  names  are such that in any one match, only one of the named
2323           subpatterns participates. An example is shown in the pcrepattern  docu-
2324           mentation.
2325    
2326           When    duplicates   are   present,   pcre_copy_named_substring()   and
2327           pcre_get_named_substring() return the first substring corresponding  to
2328           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2329           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2330           function  returns one of the numbers that are associated with the name,
2331           but it is not defined which it is.
2332    
2333           If you want to get full details of all captured substrings for a  given
2334           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2335           first argument is the compiled pattern, and the second is the name. The
2336           third  and  fourth  are  pointers to variables which are updated by the
2337           function. After it has run, they point to the first and last entries in
2338           the  name-to-number  table  for  the  given  name.  The function itself
2339           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2340           there  are none. The format of the table is described above in the sec-
2341           tion entitled Information about a  pattern.   Given  all  the  relevant
2342           entries  for the name, you can extract each of their numbers, and hence
2343           the captured data, if any.
2344    
2345    
2346  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
# Line 1908  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2369  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2369              int *workspace, int wscount);              int *workspace, int wscount);
2370    
2371         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2372         against a compiled pattern, using a "DFA" matching algorithm. This  has         against a compiled pattern, using a matching algorithm that  scans  the
2373         different  characteristics to the normal algorithm, and is not compati-         subject  string  just  once, and does not backtrack. This has different
2374         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics to the normal algorithm, and  is  not  compatible  with
2375         Nevertheless, there are times when this kind of matching can be useful.         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2376         For a discussion of the two matching algorithms, see  the  pcrematching         theless, there are times when this kind of matching can be useful.  For
2377         documentation.         a discussion of the two matching algorithms, see the pcrematching docu-
2378           mentation.
2379    
2380         The  arguments  for  the  pcre_dfa_exec()  function are the same as for         The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2381         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
2382         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2383         used in the same way as for pcre_exec(), so their  description  is  not         used  in  the  same way as for pcre_exec(), so their description is not
2384         repeated here.         repeated here.
2385    
2386         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2387         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2388         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2389         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2390         lot of possible matches.         lot of potential matches.
2391    
2392         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2393    
2394           int rc;           int rc;
2395           int ovector[10];           int ovector[10];
2396           int wspace[20];           int wspace[20];
2397           rc = pcre_exec(           rc = pcre_dfa_exec(
2398             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2399             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2400             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1946  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2408  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2408    
2409     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2410    
2411         The  unused  bits  of  the options argument for pcre_dfa_exec() must be         The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2412         zero. The only bits that may be  set  are  PCRE_ANCHORED,  PCRE_NOTBOL,         zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2413         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2414         PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last  three  of         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2415         these  are  the  same  as  for pcre_exec(), so their description is not         three of these are the same as for pcre_exec(), so their description is
2416         repeated here.         not repeated here.
2417    
2418           PCRE_PARTIAL           PCRE_PARTIAL
2419    
2420         This has the same general effect as it does for  pcre_exec(),  but  the         This  has  the  same general effect as it does for pcre_exec(), but the
2421         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2422         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2423         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have         PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2424         been no complete matches, but there is still at least one matching pos-         been no complete matches, but there is still at least one matching pos-
2425         sibility.  The portion of the string that provided the partial match is         sibility. The portion of the string that provided the partial match  is
2426         set as the first matching string.         set as the first matching string.
2427    
2428           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2429    
2430         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2431         stop  as  soon  as  it  has found one match. Because of the way the DFA         stop as soon as it has found one match. Because of the way the alterna-
2432         algorithm works, this is necessarily the shortest possible match at the         tive  algorithm  works, this is necessarily the shortest possible match
2433         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2434    
2435           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2436    
2437         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2438         returns a partial match, it is possible to call it  again,  with  addi-         returns  a  partial  match, it is possible to call it again, with addi-
2439         tional  subject  characters,  and have it continue with the same match.         tional subject characters, and have it continue with  the  same  match.
2440         The PCRE_DFA_RESTART option requests this action; when it is  set,  the         The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2441         workspace  and wscount options must reference the same vector as before         workspace and wscount options must reference the same vector as  before
2442         because data about the match so far is left in  them  after  a  partial         because  data  about  the  match so far is left in them after a partial
2443         match.  There  is  more  discussion of this facility in the pcrepartial         match. There is more discussion of this  facility  in  the  pcrepartial
2444         documentation.         documentation.
2445    
2446     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2447    
2448         When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-         When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2449         string in the subject. Note, however, that all the matches from one run         string in the subject. Note, however, that all the matches from one run
2450         of the function start at the same point in  the  subject.  The  shorter         of  the  function  start  at the same point in the subject. The shorter
2451         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2452         if the pattern         if the pattern
2453    
2454           <.*>           <.*>
# Line 2001  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2463  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2463           <something> <something else>           <something> <something else>
2464           <something> <something else> <something further>           <something> <something else> <something further>
2465    
2466         On success, the yield of the function is a number  greater  than  zero,         On  success,  the  yield of the function is a number greater than zero,
2467         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2468         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2469         the  offset  to the start, and the second is the offset to the end. All         the offset to the start, and the second is the offset to  the  end.  In
2470         the strings have the same start offset. (Space could have been saved by         fact,  all  the  strings  have the same start offset. (Space could have
2471         giving  this only once, but it was decided to retain some compatibility         been saved by giving this only once, but it was decided to retain  some
2472         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility  with  the  way pcre_exec() returns data, even though the
2473         strings is different.)         meaning of the strings is different.)
2474    
2475         The strings are returned in reverse order of length; that is, the long-         The strings are returned in reverse order of length; that is, the long-
2476         est matching string is given first. If there were too many  matches  to         est  matching  string is given first. If there were too many matches to
2477         fit  into ovector, the yield of the function is zero, and the vector is         fit into ovector, the yield of the function is zero, and the vector  is
2478         filled with the longest matches.         filled with the longest matches.
2479    
2480     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2481    
2482         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2483         Many  of  the  errors  are  the  same as for pcre_exec(), and these are         Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2484         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2485         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2486    
2487           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2488    
2489         This  return is given if pcre_dfa_exec() encounters an item in the pat-         This return is given if pcre_dfa_exec() encounters an item in the  pat-
2490         tern that it does not support, for instance, the use of \C  or  a  back         tern  that  it  does not support, for instance, the use of \C or a back
2491         reference.         reference.
2492    
2493           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2494    
2495         This  return is given if pcre_dfa_exec() encounters a condition item in         This return is given if pcre_dfa_exec()  encounters  a  condition  item
2496         a pattern that uses a back reference for the  condition.  This  is  not         that  uses  a back reference for the condition, or a test for recursion
2497         supported.         in a specific group. These are not supported.
2498    
2499           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2500    
2501         This  return  is given if pcre_dfa_exec() is called with an extra block         This return is given if pcre_dfa_exec() is called with an  extra  block
2502         that contains a setting of the match_limit field. This is not supported         that contains a setting of the match_limit field. This is not supported
2503         (it is meaningless).         (it is meaningless).
2504    
2505           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2506    
2507         This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the         This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2508         workspace vector.         workspace vector.
2509    
2510           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2511    
2512         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2513         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2514         This error is given if the output vector  is  not  large  enough.  This         This  error  is  given  if  the output vector is not large enough. This
2515         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2516    
2517  Last updated: 16 May 2005  
2518  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2519    
2520           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2521           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2522    
2523    
2524    AUTHOR
2525    
2526           Philip Hazel
2527           University Computing Service
2528           Cambridge CB2 3QH, England.
2529    
2530    
2531    REVISION
2532    
2533           Last updated: 11 September 2007
2534           Copyright (c) 1997-2007 University of Cambridge.
2535  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2536    
2537    
# Line 2080  PCRE CALLOUTS Line 2558  PCRE CALLOUTS
2558         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2559         points:         points:
2560    
2561           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2562    
2563         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2564         called, PCRE automatically  inserts  callouts,  all  with  number  255,         called, PCRE automatically  inserts  callouts,  all  with  number  255,
# Line 2155  THE CALLOUT INTERFACE Line 2633  THE CALLOUT INTERFACE
2633         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2634         were passed to pcre_exec().         were passed to pcre_exec().
2635    
2636         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
2637         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
2638         callout function may be called several times from the same point in the         sequence \K has been encountered, this value is changed to reflect  the
2639         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2640           function may be called several times from the same point in the pattern
2641           for different starting points in the subject.
2642    
2643         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
2644         the current match pointer.         the current match pointer.
# Line 2211  RETURN VALUES Line 2691  RETURN VALUES
2691         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
2692         itself.         itself.
2693    
2694  Last updated: 28 February 2005  
2695  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2696    
2697           Philip Hazel
2698           University Computing Service
2699           Cambridge CB2 3QH, England.
2700    
2701    
2702    REVISION
2703    
2704           Last updated: 29 May 2007
2705           Copyright (c) 1997-2007 University of Cambridge.
2706  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2707    
2708    
# Line 2226  NAME Line 2716  NAME
2716  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2717    
2718         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2719         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2720         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2721           some features that are expected to be in the forthcoming Perl 5.10.
2722         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2723         are given in the section on UTF-8 support in the main pcre page.         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2724           of  what  it does have are given in the section on UTF-8 support in the
2725           main pcre page.
2726    
2727         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2728         permits  them,  but they do not mean what you might think. For example,         permits  them,  but they do not mean what you might think. For example,
# Line 2257  DIFFERENCES BETWEEN PCRE AND PERL Line 2749  DIFFERENCES BETWEEN PCRE AND PERL
2749         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2750         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2751         can be tested with \p and \P are limited to the general category  prop-         can be tested with \p and \P are limited to the general category  prop-
2752         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2753           derived properties Any and L&.
2754    
2755         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2756         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2757         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2758         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2759         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2760    
2761             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2272  DIFFERENCES BETWEEN PCRE AND PERL Line 2765  DIFFERENCES BETWEEN PCRE AND PERL
2765             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2766             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2767    
2768         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2769         classes.         classes.
2770    
2771         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2772         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2773         the non-Perl items (?R),  (?number),  and  (?P>name).  Also,  the  PCRE         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2774         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2775         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2776    
2777         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2778         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2779         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2780    
2781           10.  There are some differences that are concerned with the settings of
2782           captured strings when part of  a  pattern  is  repeated.  For  example,
2783           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2784         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2785    
2786         10. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2787         ities:         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2788           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2789           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2790           ture group; this is different to Perl.
2791    
2792           12. PCRE provides some extensions to the Perl regular expression facil-
2793           ities.   Perl  5.10  will  include new features that are not in earlier
2794           versions, some of which (such as named parentheses) have been  in  PCRE
2795           for some time. This list is with respect to Perl 5.10:
2796    
2797         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2798         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2799         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2800    
2801         (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
2802         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2803    
2804         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2805         cial meaning is faulted.         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2806           ignored.  (Perl can be made to issue a warning.)
2807    
2808         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2809         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
# Line 2309  DIFFERENCES BETWEEN PCRE AND PERL Line 2815  DIFFERENCES BETWEEN PCRE AND PERL
2815         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2816         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2817    
2818         (g) The (?R), (?number), and (?P>name) constructs allows for  recursive         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2819         pattern  matching  (Perl  can  do  this using the (?p{code}) construct,         CRLF by the PCRE_BSR_ANYCRLF option.
        which PCRE cannot support.)  
2820    
2821         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The callout facility is PCRE-specific.
2822    
2823         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) The partial matching facility is PCRE-specific.
        Sun's Java package.  
2824    
2825         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2826           even on different hosts that have the other endianness.
2827    
2828         (k) The callout facility is PCRE-specific.         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2829           different way and is not Perl-compatible.
2830    
2831         (l) The partial matching facility is PCRE-specific.         (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2832           of a pattern that set overall options that cannot be changed within the
2833           pattern.
2834    
        (m) Patterns compiled by PCRE can be saved and re-used at a later time,  
        even on different hosts that have the other endianness.  
2835    
2836         (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  AUTHOR
        different way and is not Perl-compatible.  
2837    
2838  Last updated: 28 February 2005         Philip Hazel
2839  Copyright (c) 1997-2005 University of Cambridge.         University Computing Service
2840           Cambridge CB2 3QH, England.
2841    
2842    
2843    REVISION
2844    
2845           Last updated: 11 September 2007
2846           Copyright (c) 1997-2007 University of Cambridge.
2847  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2848    
2849    
# Line 2344  NAME Line 2856  NAME
2856    
2857  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2858    
2859         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2860         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2861         documentation  and  in  a  number  of books, some of which have copious         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are
2862         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         described in its own documentation, and regular expressions in  general
2863         by  O'Reilly, covers regular expressions in great detail. This descrip-         are  covered in a number of books, some of which have copious examples.
2864         tion of PCRE's regular expressions is intended as reference material.         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by
2865           O'Reilly,  covers regular expressions in great detail. This description
2866           of PCRE's regular expressions is intended as reference material.
2867    
2868         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2869         However,  there is now also support for UTF-8 character strings. To use         However,  there is now also support for UTF-8 character strings. To use
# Line 2363  PCRE REGULAR EXPRESSION DETAILS Line 2877  PCRE REGULAR EXPRESSION DETAILS
2877         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2878         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
2879         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
2880         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
2881         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2882         the pcrematching page.         alternative function, and how it differs from the normal function,  are
2883           discussed in the pcrematching page.
2884         A regular expression is a pattern that is  matched  against  a  subject  
2885         string  from  left  to right. Most characters stand for themselves in a  
2886         pattern, and match the corresponding characters in the  subject.  As  a  NEWLINE CONVENTIONS
2887    
2888           PCRE  supports five different conventions for indicating line breaks in
2889           strings: a single CR (carriage return) character, a  single  LF  (line-
2890           feed) character, the two-character sequence CRLF, any of the three pre-
2891           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2892           discussion  about newlines, and shows how to set the newline convention
2893           in the options arguments for the compiling and matching functions.
2894    
2895           It is also possible to specify a newline convention by starting a  pat-
2896           tern string with one of the following five sequences:
2897    
2898             (*CR)        carriage return
2899             (*LF)        linefeed
2900             (*CRLF)      carriage return, followed by linefeed
2901             (*ANYCRLF)   any of the three above
2902             (*ANY)       all Unicode newline sequences
2903    
2904           These override the default and the options given to pcre_compile(). For
2905           example, on a Unix system where LF is the default newline sequence, the
2906           pattern
2907    
2908             (*CR)a.b
2909    
2910           changes the convention to CR. That pattern matches "a\nb" because LF is
2911           no longer a newline. Note that these special settings,  which  are  not
2912           Perl-compatible,  are  recognized  only at the very start of a pattern,
2913           and that they must be in upper case.  If  more  than  one  of  them  is
2914           present, the last one is used.
2915    
2916           The  newline  convention  does  not  affect what the \R escape sequence
2917           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2918           compatibility.  However, this can be changed; see the description of \R
2919           in the section entitled "Newline sequences" below. A change of \R  set-
2920           ting can be combined with a change of newline convention.
2921    
2922    
2923    CHARACTERS AND METACHARACTERS
2924    
2925           A  regular  expression  is  a pattern that is matched against a subject
2926           string from left to right. Most characters stand for  themselves  in  a
2927           pattern,  and  match  the corresponding characters in the subject. As a
2928         trivial example, the pattern         trivial example, the pattern
2929    
2930           The quick brown fox           The quick brown fox
2931    
2932         matches a portion of a subject string that is identical to itself. When         matches a portion of a subject string that is identical to itself. When
2933         caseless matching is specified (the PCRE_CASELESS option), letters  are         caseless  matching is specified (the PCRE_CASELESS option), letters are
2934         matched  independently  of case. In UTF-8 mode, PCRE always understands         matched independently of case. In UTF-8 mode, PCRE  always  understands
2935         the concept of case for characters whose values are less than  128,  so         the  concept  of case for characters whose values are less than 128, so
2936         caseless  matching  is always possible. For characters with higher val-         caseless matching is always possible. For characters with  higher  val-
2937         ues, the concept of case is supported if PCRE is compiled with  Unicode         ues,  the concept of case is supported if PCRE is compiled with Unicode
2938         property  support,  but  not  otherwise.   If  you want to use caseless         property support, but not otherwise.   If  you  want  to  use  caseless
2939         matching for characters 128 and above, you must  ensure  that  PCRE  is         matching  for  characters  128  and above, you must ensure that PCRE is
2940         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
2941    
2942         The  power  of  regular  expressions  comes from the ability to include         The power of regular expressions comes  from  the  ability  to  include
2943         alternatives and repetitions in the pattern. These are encoded  in  the         alternatives  and  repetitions in the pattern. These are encoded in the
2944         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
2945         but instead are interpreted in some special way.         but instead are interpreted in some special way.
2946    
2947         There are two different sets of metacharacters: those that  are  recog-         There  are  two different sets of metacharacters: those that are recog-
2948         nized  anywhere in the pattern except within square brackets, and those         nized anywhere in the pattern except within square brackets, and  those
2949         that are recognized in square brackets. Outside  square  brackets,  the         that  are  recognized  within square brackets. Outside square brackets,
2950         metacharacters are as follows:         the metacharacters are as follows:
2951    
2952           \      general escape character with several uses           \      general escape character with several uses
2953           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2410  PCRE REGULAR EXPRESSION DETAILS Line 2965  PCRE REGULAR EXPRESSION DETAILS
2965                  also "possessive quantifier"                  also "possessive quantifier"
2966           {      start min/max quantifier           {      start min/max quantifier
2967    
2968         Part  of  a  pattern  that is in square brackets is called a "character         Part of a pattern that is in square brackets  is  called  a  "character
2969         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
2970    
2971           \      general escape character           \      general escape character
# Line 2420  PCRE REGULAR EXPRESSION DETAILS Line 2975  PCRE REGULAR EXPRESSION DETAILS
2975                    syntax)                    syntax)
2976           ]      terminates the character class           ]      terminates the character class
2977    
2978         The following sections describe the use of each of the  metacharacters.         The  following sections describe the use of each of the metacharacters.
2979    
2980    
2981  BACKSLASH  BACKSLASH
2982    
2983         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
2984         a non-alphanumeric character, it takes away any  special  meaning  that         a  non-alphanumeric  character,  it takes away any special meaning that
2985         character  may  have.  This  use  of  backslash  as an escape character         character may have. This  use  of  backslash  as  an  escape  character
2986         applies both inside and outside character classes.         applies both inside and outside character classes.
2987    
2988         For example, if you want to match a * character, you write  \*  in  the         For  example,  if  you want to match a * character, you write \* in the
2989         pattern.   This  escaping  action  applies whether or not the following         pattern.  This escaping action applies whether  or  not  the  following
2990         character would otherwise be interpreted as a metacharacter, so  it  is         character  would  otherwise be interpreted as a metacharacter, so it is
2991         always  safe  to  precede  a non-alphanumeric with backslash to specify         always safe to precede a non-alphanumeric  with  backslash  to  specify
2992         that it stands for itself. In particular, if you want to match a  back-         that  it stands for itself. In particular, if you want to match a back-
2993         slash, you write \\.         slash, you write \\.
2994    
2995         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
2996         the pattern (other than in a character class) and characters between  a         the  pattern (other than in a character class) and characters between a
2997         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2998         An escaping backslash can be used to include a whitespace or #  charac-         ing  backslash  can  be  used to include a whitespace or # character as
2999         ter as part of the pattern.         part of the pattern.
3000    
3001         If  you  want  to remove the special meaning from a sequence of charac-         If you want to remove the special meaning from a  sequence  of  charac-
3002         ters, you can do so by putting them between \Q and \E. This is  differ-         ters,  you can do so by putting them between \Q and \E. This is differ-
3003         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E
3004         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
3005         tion. Note the following examples:         tion. Note the following examples:
3006    
3007           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2456  BACKSLASH Line 3011  BACKSLASH
3011           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3012           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3013    
3014         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
3015         classes.         classes.
3016    
3017     Non-printing characters     Non-printing characters
3018    
3019         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
3020         acters  in patterns in a visible manner. There is no restriction on the         acters in patterns in a visible manner. There is no restriction on  the
3021         appearance of non-printing characters, apart from the binary zero  that         appearance  of non-printing characters, apart from the binary zero that
3022         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates a pattern, but when a pattern  is  being  prepared  by  text
3023         editing, it is usually easier  to  use  one  of  the  following  escape         editing,  it  is  usually  easier  to  use  one of the following escape
3024         sequences than the binary character it represents:         sequences than the binary character it represents:
3025    
3026           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3027           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3028           \e        escape (hex 1B)           \e        escape (hex 1B)
3029           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3030           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3031           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3032           \t        tab (hex 09)           \t        tab (hex 09)
3033           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
3034           \xhh      character with hex code hh           \xhh      character with hex code hh
3035           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
3036    
3037         The  precise  effect of \cx is as follows: if x is a lower case letter,         The precise effect of \cx is as follows: if x is a lower  case  letter,
3038         it is converted to upper case. Then bit 6 of the character (hex 40)  is         it  is converted to upper case. Then bit 6 of the character (hex 40) is
3039         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;
3040         becomes hex 7B.         becomes hex 7B.
3041    
3042         After \x, from zero to two hexadecimal digits are read (letters can  be         After  \x, from zero to two hexadecimal digits are read (letters can be
3043         in  upper or lower case). In UTF-8 mode, any number of hexadecimal dig-         in upper or lower case). Any number of hexadecimal  digits  may  appear
3044         its may appear between \x{ and }, but the value of the  character  code         between  \x{  and  },  but the value of the character code must be less
3045         must  be  less  than  2**31  (that is, the maximum hexadecimal value is         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3046         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger
3047         \x{  and }, or if there is no terminating }, this form of escape is not         than the largest Unicode code point, which is 10FFFF.
3048         recognized. Instead, the initial \x will  be  interpreted  as  a  basic  
3049         hexadecimal  escape, with no following digits, giving a character whose         If characters other than hexadecimal digits appear between \x{  and  },
3050         value is zero.         or if there is no terminating }, this form of escape is not recognized.
3051           Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal
3052           escape,  with  no  following  digits, giving a character whose value is
3053           zero.
3054    
3055         Characters whose value is less than 256 can be defined by either of the         Characters whose value is less than 256 can be defined by either of the
3056         two  syntaxes for \x when PCRE is in UTF-8 mode. There is no difference         two  syntaxes  for  \x. There is no difference in the way they are han-
3057         in the way they are handled. For example, \xdc is exactly the  same  as         dled. For example, \xdc is exactly the same as \x{dc}.
3058         \x{dc}.  
3059           After \0 up to two further octal digits are read. If  there  are  fewer
3060         After  \0  up  to  two further octal digits are read. In both cases, if         than  two  digits,  just  those  that  are  present  are used. Thus the
3061         there are fewer than two digits, just those that are present are  used.         sequence \0\x\07 specifies two binary zeros followed by a BEL character
3062         Thus  the sequence \0\x\07 specifies two binary zeros followed by a BEL         (code  value 7). Make sure you supply two digits after the initial zero
3063         character (code value 7). Make sure you supply  two  digits  after  the         if the pattern character that follows is itself an octal digit.
        initial  zero  if the pattern character that follows is itself an octal  
        digit.  
3064    
3065         The handling of a backslash followed by a digit other than 0 is compli-         The handling of a backslash followed by a digit other than 0 is compli-
3066         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
# Line 2516  BACKSLASH Line 3072  BACKSLASH
3072    
3073         Inside a character class, or if the decimal number is  greater  than  9         Inside a character class, or if the decimal number is  greater  than  9
3074         and  there have not been that many capturing subpatterns, PCRE re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
3075         up to three octal digits following the backslash, and generates a  sin-         up to three octal digits following the backslash, and uses them to gen-
3076         gle byte from the least significant 8 bits of the value. Any subsequent         erate  a data character. Any subsequent digits stand for themselves. In
3077         digits stand for themselves.  For example:         non-UTF-8 mode, the value of a character specified  in  octal  must  be
3078           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
3079           example:
3080    
3081           \040   is another way of writing a space           \040   is another way of writing a space
3082           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2538  BACKSLASH Line 3096  BACKSLASH
3096         Note that octal values of 100 or greater must not be  introduced  by  a         Note that octal values of 100 or greater must not be  introduced  by  a
3097         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3098    
3099         All  the  sequences  that  define a single byte value or a single UTF-8         All the sequences that define a single character value can be used both
3100         character (in UTF-8 mode) can be used both inside and outside character         inside and outside character classes. In addition, inside  a  character
3101         classes.  In  addition,  inside  a  character class, the sequence \b is         class,  the  sequence \b is interpreted as the backspace character (hex
3102         interpreted as the backspace character (hex 08), and the sequence \X is         08), and the sequences \R and \X are interpreted as the characters  "R"
3103         interpreted  as  the  character  "X".  Outside a character class, these         and  "X", respectively. Outside a character class, these sequences have
3104         sequences have different meanings (see below).         different meanings (see below).
3105    
3106       Absolute and relative back references
3107    
3108           The sequence \g followed by an unsigned or a negative  number,  option-
3109           ally  enclosed  in braces, is an absolute or relative back reference. A
3110           named back reference can be coded as \g{name}. Back references are dis-
3111           cussed later, following the discussion of parenthesized subpatterns.
3112    
3113     Generic character types     Generic character types
3114    
3115         The third use of backslash is for specifying generic  character  types.         Another use of backslash is for specifying generic character types. The
3116         The following are always recognized:         following are always recognized:
3117    
3118           \d     any decimal digit           \d     any decimal digit
3119           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3120             \h     any horizontal whitespace character
3121             \H     any character that is not a horizontal whitespace character
3122           \s     any whitespace character           \s     any whitespace character
3123           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3124             \v     any vertical whitespace character
3125             \V     any character that is not a vertical whitespace character
3126           \w     any "word" character           \w     any "word" character
3127           \W     any "non-word" character           \W     any "non-word" character
3128    
3129         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
3130         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
3131         of each pair.         of each pair.
3132    
3133         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
3134         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
3135         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
3136         of them fail, since there is no character to match.         of them fail, since there is no character to match.
3137    
3138         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
3139         11).   This makes it different from the the POSIX "space" class. The \s         11).  This makes it different from the the POSIX "space" class. The  \s
3140         characters are HT (9), LF (10), FF (12), CR (13), and space (32).         characters  are  HT  (9), LF (10), FF (12), CR (13), and space (32). If
3141           "use locale;" is included in a Perl script, \s may match the VT charac-
3142           ter. In PCRE, it never does.
3143    
3144           In  UTF-8 mode, characters with values greater than 128 never match \d,
3145           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3146           code  character  property  support is available. These sequences retain
3147           their original meanings from before UTF-8 support was available, mainly
3148           for efficiency reasons.
3149    
3150           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3151           the other sequences, these do match certain high-valued  codepoints  in
3152           UTF-8 mode.  The horizontal space characters are:
3153    
3154             U+0009     Horizontal tab
3155             U+0020     Space
3156             U+00A0     Non-break space
3157             U+1680     Ogham space mark
3158             U+180E     Mongolian vowel separator
3159             U+2000     En quad
3160             U+2001     Em quad
3161             U+2002     En space
3162             U+2003     Em space
3163             U+2004     Three-per-em space
3164             U+2005     Four-per-em space
3165             U+2006     Six-per-em space
3166             U+2007     Figure space
3167             U+2008     Punctuation space
3168             U+2009     Thin space
3169             U+200A     Hair space
3170             U+202F     Narrow no-break space
3171             U+205F     Medium mathematical space
3172             U+3000     Ideographic space
3173    
3174           The vertical space characters are:
3175    
3176             U+000A     Linefeed
3177             U+000B     Vertical tab
3178             U+000C     Formfeed
3179             U+000D     Carriage return
3180             U+0085     Next line
3181             U+2028     Line separator
3182             U+2029     Paragraph separator
3183    
3184         A "word" character is an underscore or any character less than 256 that         A "word" character is an underscore or any character less than 256 that
3185         is  a  letter  or  digit.  The definition of letters and digits is con-         is a letter or digit. The definition of  letters  and  digits  is  con-
3186         trolled by PCRE's low-valued character tables, and may vary if  locale-         trolled  by PCRE's low-valued character tables, and may vary if locale-
3187         specific  matching is taking place (see "Locale support" in the pcreapi         specific matching is taking place (see "Locale support" in the  pcreapi
3188         page). For example, in the  "fr_FR"  (French)  locale,  some  character         page).  For  example,  in  a French locale such as "fr_FR" in Unix-like
3189         codes  greater  than  128  are used for accented letters, and these are         systems, or "french" in Windows, some character codes greater than  128
3190         matched by \w.         are  used for accented letters, and these are matched by \w. The use of
3191           locales with Unicode is discouraged.
3192    
3193       Newline sequences
3194    
3195           Outside a character class, by default, the escape sequence  \R  matches
3196           any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3197           mode \R is equivalent to the following:
3198    
3199             (?>\r\n|\n|\x0b|\f|\r|\x85)
3200    
3201           This is an example of an "atomic group", details  of  which  are  given
3202           below.  This particular group matches either the two-character sequence
3203           CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
3204           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3205           return, U+000D), or NEL (next line, U+0085). The two-character sequence
3206           is treated as a single unit that cannot be split.
3207    
3208           In  UTF-8  mode, two additional characters whose codepoints are greater
3209           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3210           rator,  U+2029).   Unicode character property support is not needed for
3211           these characters to be recognized.
3212    
3213           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3214           the  complete  set  of  Unicode  line  endings)  by  setting the option
3215           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3216           (BSR is an abbrevation for "backslash R".) This can be made the default
3217           when PCRE is built; if this is the case, the  other  behaviour  can  be
3218           requested  via  the  PCRE_BSR_UNICODE  option.   It is also possible to
3219           specify these settings by starting a pattern string  with  one  of  the
3220           following sequences:
3221    
3222             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3223             (*BSR_UNICODE)   any Unicode newline sequence
3224    
3225           These override the default and the options given to pcre_compile(), but
3226           they can be overridden by options given to pcre_exec(). Note that these
3227           special settings, which are not Perl-compatible, are recognized only at
3228           the very start of a pattern, and that they must be in  upper  case.  If
3229           more  than  one  of  them is present, the last one is used. They can be
3230           combined with a change of newline convention, for  example,  a  pattern
3231           can start with:
3232    
3233         In UTF-8 mode, characters with values greater than 128 never match  \d,           (*ANY)(*BSR_ANYCRLF)
3234         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-  
3235         code character property support is available.         Inside a character class, \R matches the letter "R".
3236    
3237     Unicode character properties     Unicode character properties
3238    
3239         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3240         tional  escape sequences to match generic character types are available         tional escape sequences that match characters with specific  properties
3241         when UTF-8 mode is selected. They are:         are  available.   When not in UTF-8 mode, these sequences are of course
3242           limited to testing characters whose codepoints are less than  256,  but
3243          \p{xx}   a character with the xx property         they do work in this mode.  The extra escape sequences are:
3244          \P{xx}   a character without the xx property  
3245          \X       an extended Unicode sequence           \p{xx}   a character with the xx property
3246             \P{xx}   a character without the xx property
3247         The property names represented by xx above are limited to  the  Unicode           \X       an extended Unicode sequence
3248         general  category properties. Each character has exactly one such prop-  
3249         erty, specified by a two-letter abbreviation.  For  compatibility  with         The  property  names represented by xx above are limited to the Unicode
3250         Perl,  negation  can be specified by including a circumflex between the         script names, the general category properties, and "Any", which matches
3251         opening brace and the property name. For example, \p{^Lu} is  the  same         any character (including newline). Other properties such as "InMusical-
3252         as \P{Lu}.         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does
3253           not match any characters, so always causes a match failure.
3254         If  only  one  letter  is  specified with \p or \P, it includes all the  
3255         properties that start with that letter. In this case, in the absence of         Sets of Unicode characters are defined as belonging to certain scripts.
3256         negation, the curly brackets in the escape sequence are optional; these         A character from one of these sets can be matched using a script  name.
3257         two examples have the same effect:         For example:
3258    
3259             \p{Greek}
3260             \P{Han}
3261    
3262           Those  that are not part of an identified script are lumped together as
3263           "Common". The current list of scripts is:
3264    
3265           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3266           Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,
3267           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3268           Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
3269           gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,
3270           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3271           Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,
3272           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3273           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3274    
3275           Each character has exactly one general category property, specified  by
3276           a two-letter abbreviation. For compatibility with Perl, negation can be
3277           specified by including a circumflex between the opening brace  and  the
3278           property name. For example, \p{^Lu} is the same as \P{Lu}.
3279    
3280           If only one letter is specified with \p or \P, it includes all the gen-
3281           eral category properties that start with that letter. In this case,  in
3282           the  absence of negation, the curly brackets in the escape sequence are
3283           optional; these two examples have the same effect:
3284    
3285           \p{L}           \p{L}
3286           \pL           \pL
3287    
3288         The following property codes are supported:         The following general category property codes are supported:
3289    
3290           C     Other           C     Other
3291           Cc    Control           Cc    Control
# Line 2653  BACKSLASH Line 3331  BACKSLASH
3331           Zp    Paragraph separator           Zp    Paragraph separator
3332           Zs    Space separator           Zs    Space separator
3333    
3334         Extended properties such as "Greek" or "InMusicalSymbols" are not  sup-         The special property L& is also supported: it matches a character  that
3335         ported by PCRE.         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not
3336           classified as a modifier or "other".
3337    
3338           The Cs (Surrogate) property applies only to  characters  in  the  range
3339           U+D800  to  U+DFFF. Such characters are not valid in UTF-8 strings (see
3340           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3341           ing  has  been  turned off (see the discussion of PCRE_NO_UTF8_CHECK in
3342           the pcreapi page).
3343    
3344           The long synonyms for these properties  that  Perl  supports  (such  as
3345           \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix
3346           any of these properties with "Is".
3347    
3348           No character that is in the Unicode table has the Cn (unassigned) prop-
3349           erty.  Instead, this property is assumed for any code point that is not
3350           in the Unicode table.
3351    
3352         Specifying  caseless  matching  does not affect these escape sequences.         Specifying caseless matching does not affect  these  escape  sequences.
3353         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3354    
3355         The \X escape matches any number of Unicode  characters  that  form  an         The  \X  escape  matches  any number of Unicode characters that form an
3356         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3357    
3358           (?>\PM\pM*)           (?>\PM\pM*)
3359    
3360         That  is,  it matches a character without the "mark" property, followed         That is, it matches a character without the "mark"  property,  followed
3361         by zero or more characters with the "mark"  property,  and  treats  the         by  zero  or  more  characters with the "mark" property, and treats the
3362         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3363         property are typically accents that affect the preceding character.         property  are  typically  accents  that affect the preceding character.
3364           None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
3365           matches any one character.
3366    
3367         Matching characters by Unicode property is not fast, because  PCRE  has         Matching  characters  by Unicode property is not fast, because PCRE has
3368         to  search  a  structure  that  contains data for over fifteen thousand         to search a structure that contains  data  for  over  fifteen  thousand
3369         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3370         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3371    
3372       Resetting the match start
3373    
3374           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3375           ously  matched  characters  not  to  be  included  in the final matched
3376           sequence. For example, the pattern:
3377    
3378             foo\Kbar
3379    
3380           matches "foobar", but reports that it has matched "bar".  This  feature
3381           is  similar  to  a lookbehind assertion (described below).  However, in
3382           this case, the part of the subject before the real match does not  have
3383           to  be of fixed length, as lookbehind assertions do. The use of \K does
3384           not interfere with the setting of captured  substrings.   For  example,
3385           when the pattern
3386    
3387             (foo)\Kbar
3388    
3389           matches "foobar", the first substring is still set to "foo".
3390    
3391     Simple assertions     Simple assertions
3392    
3393         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3394         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
3395         a  match, without consuming any characters from the subject string. The         a  match, without consuming any characters from the subject string. The
3396         use of subpatterns for more complicated assertions is described  below.         use of subpatterns for more complicated assertions is described  below.
# Line 2684  BACKSLASH Line 3398  BACKSLASH
3398    
3399           \b     matches at a word boundary           \b     matches at a word boundary
3400           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3401           \A     matches at start of subject           \A     matches at the start of the subject
3402           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3403           \z     matches at end of subject                   also matches before a newline at the end of the subject
3404           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3405             \G     matches at the first matching position in the subject
3406    
3407         These  assertions may not appear in character classes (but note that \b         These  assertions may not appear in character classes (but note that \b
3408         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
# Line 2707  BACKSLASH Line 3422  BACKSLASH
3422         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3423         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
3424         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
3425         that  \Z  matches  before  a  newline that is the last character of the         that \Z matches before a newline at the end of the string as well as at
3426         string as well as at the end of the string, whereas \z matches only  at         the very end, whereas \z matches only at the end.
3427         the end.  
3428           The \G assertion is true only when the current matching position is  at
3429         The  \G assertion is true only when the current matching position is at         the  start point of the match, as specified by the startoffset argument
3430         the start point of the match, as specified by the startoffset  argument         of pcre_exec(). It differs from \A when the  value  of  startoffset  is
3431         of  pcre_exec().  It  differs  from \A when the value of startoffset is         non-zero.  By calling pcre_exec() multiple times with appropriate argu-
        non-zero. By calling pcre_exec() multiple times with appropriate  argu-  
3432         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-
3433         mentation where \G can be useful.         mentation where \G can be useful.
3434    
3435         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
3436         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
3437         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
3438         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3439         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3440    
3441         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
3442         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3443         in the compiled regular expression.         in the compiled regular expression.
3444    
# Line 2732  BACKSLASH Line 3446  BACKSLASH
3446  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3447    
3448         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3449         character  is  an  assertion  that is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3450         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-
3451         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
3452         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3453         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3454    
3455         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
3456         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
3457         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
3458         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3459         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-
3460         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
3461         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3462    
3463         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
3464         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3465         before a newline character that is the last character in the string (by         before a newline at the end of the string (by default). Dollar need not
3466         default). Dollar need not be the last character of  the  pattern  if  a         be  the  last  character of the pattern if a number of alternatives are
3467         number  of alternatives are involved, but it should be the last item in         involved, but it should be the last item in  any  branch  in  which  it
3468         any branch in which it appears.  Dollar has no  special  meaning  in  a         appears. Dollar has no special meaning in a character class.
        character class.  
3469    
3470         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
3471         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
3472         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3473    
3474         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3475         PCRE_MULTILINE option is set. When this is the case, they match immedi-         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex
3476         ately  after  and  immediately  before  an  internal newline character,         matches  immediately after internal newlines as well as at the start of
3477         respectively, in addition to matching at the start and end of the  sub-         the subject string. It does not match after a  newline  that  ends  the
3478         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         string.  A dollar matches before any newlines in the string, as well as
3479         string "def\nabc" (where \n represents a newline character)  in  multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3480         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3481         in single line mode because all branches start with ^ are not  anchored         not indicate newlines.
3482         in  multiline  mode,  and  a  match for circumflex is possible when the  
3483         startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3484         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3485           Consequently, patterns that are anchored in single  line  mode  because
3486         Note  that  the sequences \A, \Z, and \z can be used to match the start         all  branches  start  with  ^ are not anchored in multiline mode, and a
3487         and end of the subject in both modes, and if all branches of a  pattern         match for circumflex is  possible  when  the  startoffset  argument  of
3488         start  with  \A it is always anchored, whether PCRE_MULTILINE is set or         pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
3489         not.         PCRE_MULTILINE is set.
3490    
3491           Note that the sequences \A, \Z, and \z can be used to match  the  start
3492           and  end of the subject in both modes, and if all branches of a pattern
3493           start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3494           set.
3495    
3496    
3497  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3498    
3499         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-
3500         ter  in  the  subject,  including a non-printing character, but not (by         ter in the subject string except (by default) a character  that  signi-
3501         default) newline.  In UTF-8 mode, a dot matches  any  UTF-8  character,         fies  the  end  of  a line. In UTF-8 mode, the matched character may be
3502         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3503         the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-  
3504         dling  of dot is entirely independent of the handling of circumflex and         When a line ending is defined as a single character, dot never  matches
3505         dollar, the only relationship being  that  they  both  involve  newline         that  character; when the two-character sequence CRLF is used, dot does
3506         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3507           matches  all characters (including isolated CRs and LFs). When any Uni-
3508           code line endings are being recognized, dot does not match CR or LF  or
3509           any of the other line ending characters.
3510    
3511           The  behaviour  of  dot  with regard to newlines can be changed. If the
3512           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3513           exception. If the two-character sequence CRLF is present in the subject
3514           string, it takes two dots to match it.
3515    
3516           The handling of dot is entirely independent of the handling of  circum-
3517           flex  and  dollar,  the  only relationship being that they both involve
3518           newlines. Dot has no special meaning in a character class.
3519    
3520    
3521  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3522    
3523         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3524         both in and out of UTF-8 mode. Unlike a dot, it can  match  a  newline.         both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any
3525         The  feature  is provided in Perl in order to match individual bytes in         line-ending characters. The feature is provided in  Perl  in  order  to
3526         UTF-8 mode. Because it  breaks  up  UTF-8  characters  into  individual         match  individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-
3527         bytes,  what remains in the string may be a malformed UTF-8 string. For         acters into individual bytes, what remains in the string may be a  mal-
3528         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3529           avoided.
3530    
3531         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3532         below),  because  in UTF-8 mode this would make it impossible to calcu-         below),  because  in UTF-8 mode this would make it impossible to calcu-
# Line 2842  SQUARE BRACKETS AND CHARACTER CLASSES Line 3573  SQUARE BRACKETS AND CHARACTER CLASSES
3573         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
3574         support.         support.
3575    
3576         The newline character is never treated in any special way in  character         Characters that might indicate line breaks are  never  treated  in  any
3577         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         special  way  when  matching  character  classes,  whatever line-ending
3578         options is. A class such as [^a] will always match a newline.         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3579           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3580           of these characters.
3581    
3582         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-
3583         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters  in  a  character  class.  For  example,  [d-m] matches any letter
# Line 2870  SQUARE BRACKETS AND CHARACTER CLASSES Line 3603  SQUARE BRACKETS AND CHARACTER CLASSES
3603         If a range that includes letters is used when caseless matching is set,         If a range that includes letters is used when caseless matching is set,
3604         it matches the letters in either case. For example, [W-c] is equivalent         it matches the letters in either case. For example, [W-c] is equivalent
3605         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3606         character tables for the "fr_FR" locale are in use, [\xc8-\xcb] matches         character tables for a French locale are in  use,  [\xc8-\xcb]  matches
3607         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the
3608         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3609         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 2945  VERTICAL BAR Line 3678  VERTICAL BAR
3678    
3679         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3680         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3681         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3682         left to right, and the first one that succeeds is used. If the alterna-         to right, and the first one that succeeds is used. If the  alternatives
3683         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3684         ing the rest of the main pattern as well as the alternative in the sub-         rest of the main pattern as well as the alternative in the  subpattern.
        pattern.  
3685    
3686    
3687  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3688    
3689         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
3690         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED options (which are Perl-compatible) can be  changed  from
3691         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         within  the  pattern  by  a  sequence  of  Perl option letters enclosed
3692         option letters are         between "(?" and ")".  The option letters are
3693    
3694           i  for PCRE_CASELESS           i  for PCRE_CASELESS
3695           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 2971  INTERNAL OPTION SETTING Line 3703  INTERNAL OPTION SETTING
3703         is also permitted. If a  letter  appears  both  before  and  after  the         is also permitted. If a  letter  appears  both  before  and  after  the
3704         hyphen, the option is unset.         hyphen, the option is unset.
3705    
3706           The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
3707           can be changed in the same way as the Perl-compatible options by  using
3708           the characters J, U and X respectively.
3709    
3710         When  an option change occurs at top level (that is, not inside subpat-         When  an option change occurs at top level (that is, not inside subpat-
3711         tern parentheses), the change applies to the remainder of  the  pattern         tern parentheses), the change applies to the remainder of  the  pattern
3712         that follows.  If the change is placed right at the start of a pattern,         that follows.  If the change is placed right at the start of a pattern,
3713         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
3714         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3715    
3716         An option change within a subpattern affects only that part of the cur-         An  option  change  within a subpattern (see below for a description of
3717         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3718           it, so
3719    
3720           (a(?i)b)c           (a(?i)b)c
3721    
3722         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
3723         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3724         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3725         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3726         example,         example,
3727    
3728           (a(?i)b|c)           (a(?i)b|c)
3729    
3730         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3731         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3732         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3733         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3734    
3735         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed         Note: There are other PCRE-specific options that  can  be  set  by  the
3736         in the same way as the Perl-compatible options by using the  characters         application  when  the  compile  or match functions are called. In some
3737         U  and X respectively. The (?X) flag setting is special in that it must         cases the pattern can contain special  leading  sequences  to  override
3738         always occur earlier in the pattern than any of the additional features         what  the  application  has set or what has been defaulted. Details are
3739         it  turns on, even when it is at top level. It is best to put it at the         given in the section entitled "Newline sequences" above.
        start.  
3740    
3741    
3742  SUBPATTERNS  SUBPATTERNS
# Line 3013  SUBPATTERNS Line 3749  SUBPATTERNS
3749           cat(aract|erpillar|)           cat(aract|erpillar|)
3750    
3751         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3752         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3753         string.         string.
3754    
3755         2.  It  sets  up  the  subpattern as a capturing subpattern. This means         2.  It  sets  up  the  subpattern as a capturing subpattern. This means
# Line 3042  SUBPATTERNS Line 3778  SUBPATTERNS
3778           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3779    
3780         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3781         1  and 2. The maximum number of capturing subpatterns is 65535, and the         1 and 2. The maximum number of capturing subpatterns is 65535.
        maximum depth of nesting of all subpatterns, both  capturing  and  non-  
        capturing, is 200.  
3782    
3783         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3784         start of a non-capturing subpattern,  the  option  letters  may  appear         start of a non-capturing subpattern,  the  option  letters  may  appear
# Line 3060  SUBPATTERNS Line 3794  SUBPATTERNS
3794         "Saturday".         "Saturday".
3795    
3796    
3797    DUPLICATE SUBPATTERN NUMBERS
3798    
3799           Perl 5.10 introduced a feature whereby each alternative in a subpattern
3800           uses the same numbers for its capturing parentheses. Such a  subpattern
3801           starts  with (?| and is itself a non-capturing subpattern. For example,
3802           consider this pattern:
3803    
3804             (?|(Sat)ur|(Sun))day
3805    
3806           Because the two alternatives are inside a (?| group, both sets of  cap-
3807           turing  parentheses  are  numbered one. Thus, when the pattern matches,
3808           you can look at captured substring number  one,  whichever  alternative
3809           matched.  This  construct  is useful when you want to capture part, but
3810           not all, of one of a number of alternatives. Inside a (?| group, paren-
3811           theses  are  numbered as usual, but the number is reset at the start of
3812           each branch. The numbers of any capturing buffers that follow the  sub-
3813           pattern  start after the highest number used in any branch. The follow-
3814           ing example is taken from the Perl documentation.  The  numbers  under-
3815           neath show in which buffer the captured content will be stored.
3816    
3817             # before  ---------------branch-reset----------- after
3818             / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3819             # 1            2         2  3        2     3     4
3820    
3821           A  backreference  or  a  recursive call to a numbered subpattern always
3822           refers to the first one in the pattern with the given number.
3823    
3824           An alternative approach to using this "branch reset" feature is to  use
3825           duplicate named subpatterns, as described in the next section.
3826    
3827    
3828  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3829    
3830         Identifying  capturing  parentheses  by number is simple, but it can be         Identifying  capturing  parentheses  by number is simple, but it can be
3831         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3832         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3833         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3834         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3835         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3836         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3837           tax.
3838    
3839           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3840           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3841           to capturing parentheses from other parts of the pattern, such as back-
3842           references,  recursion,  and conditions, can be made by name as well as