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revision 211 by ph10, Thu Aug 9 09:52:43 2007 UTC revision 548 by ph10, Fri Jun 25 14:42:00 2010 UTC
# Line 2  Line 2 
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
5  synopses of each function in the library have not been included. There are  synopses of each function in the library have not been included. Neither has
6  separate text files for the pcregrep and pcretest commands.  the pcredemo program. There are separate text files for the pcregrep and
7    pcretest commands.
8  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
9    
10    
# Line 18  INTRODUCTION Line 19  INTRODUCTION
19    
20         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
21         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
22         just  a  few differences. (Certain features that appeared in Python and         just  a few differences. Some features that appeared in Python and PCRE
23         PCRE before they appeared in Perl are also available using  the  Python         before they appeared in Perl are also available using the  Python  syn-
24         syntax.)         tax,  there  is  some  support for one or two .NET and Oniguruma syntax
25           items, and there is an option for requesting some  minor  changes  that
26         The  current  implementation of PCRE (release 7.x) corresponds approxi-         give better JavaScript compatibility.
27         mately with Perl 5.10, including support for UTF-8 encoded strings  and  
28         Unicode general category properties. However, UTF-8 and Unicode support         The  current implementation of PCRE corresponds approximately with Perl
29         has to be explicitly enabled; it is not the default. The Unicode tables         5.10/5.11, including support for UTF-8 encoded strings and Unicode gen-
30         correspond to Unicode release 5.0.0.         eral  category properties. However, UTF-8 and Unicode support has to be
31           explicitly enabled; it is not the default. The  Unicode  tables  corre-
32           spond to Unicode release 5.2.0.
33    
34         In  addition to the Perl-compatible matching function, PCRE contains an         In  addition to the Perl-compatible matching function, PCRE contains an
35         alternative matching function that matches the same  compiled  patterns         alternative function that matches the same compiled patterns in a  dif-
36         in  a different way. In certain circumstances, the alternative function         ferent way. In certain circumstances, the alternative function has some
37         has some advantages. For a discussion of the two  matching  algorithms,         advantages.  For a discussion of the two matching algorithms,  see  the
38         see the pcrematching page.         pcrematching page.
39    
40         PCRE  is  written  in C and released as a C library. A number of people         PCRE  is  written  in C and released as a C library. A number of people
41         have written wrappers and interfaces of various kinds.  In  particular,         have written wrappers and interfaces of various kinds.  In  particular,
# Line 52  INTRODUCTION Line 55  INTRODUCTION
55         library is built. The pcre_config() function makes it  possible  for  a         library is built. The pcre_config() function makes it  possible  for  a
56         client  to  discover  which  features are available. The features them-         client  to  discover  which  features are available. The features them-
57         selves are described in the pcrebuild page. Documentation about  build-         selves are described in the pcrebuild page. Documentation about  build-
58         ing  PCRE for various operating systems can be found in the README file         ing  PCRE  for various operating systems can be found in the README and
59         in the source distribution.         NON-UNIX-USE files in the source distribution.
60    
61         The library contains a number of undocumented  internal  functions  and         The library contains a number of undocumented  internal  functions  and
62         data  tables  that  are  used by more than one of the exported external         data  tables  that  are  used by more than one of the exported external
# Line 69  USER DOCUMENTATION Line 72  USER DOCUMENTATION
72         The user documentation for PCRE comprises a number  of  different  sec-         The user documentation for PCRE comprises a number  of  different  sec-
73         tions.  In the "man" format, each of these is a separate "man page". In         tions.  In the "man" format, each of these is a separate "man page". In
74         the HTML format, each is a separate page, linked from the  index  page.         the HTML format, each is a separate page, linked from the  index  page.
75         In  the  plain text format, all the sections are concatenated, for ease         In  the  plain  text format, all the sections, except the pcredemo sec-
76         of searching. The sections are as follows:         tion, are concatenated, for ease of searching. The sections are as fol-
77           lows:
78    
79           pcre              this document           pcre              this document
80           pcre-config       show PCRE installation configuration information           pcre-config       show PCRE installation configuration information
# Line 79  USER DOCUMENTATION Line 83  USER DOCUMENTATION
83           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
84           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
85           pcrecpp           details of the C++ wrapper           pcrecpp           details of the C++ wrapper
86             pcredemo          a demonstration C program that uses PCRE
87           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
88           pcrematching      discussion of the two matching algorithms           pcrematching      discussion of the two matching algorithms
89           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
90           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
91                               regular expressions                               regular expressions
          pcresyntax        quick syntax reference  
92           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
93           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
94           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
95           pcresample        discussion of the sample program           pcresample        discussion of the pcredemo program
96           pcrestack         discussion of stack usage           pcrestack         discussion of stack usage
97             pcresyntax        quick syntax reference
98           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
99    
100         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 134  UTF-8 AND UNICODE PROPERTY SUPPORT Line 139  UTF-8 AND UNICODE PROPERTY SUPPORT
139    
140         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
141         support in the code, and, in addition,  you  must  call  pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
142         with  the PCRE_UTF8 option flag. When you do this, both the pattern and         with  the  PCRE_UTF8  option  flag,  or the pattern must start with the
143         any subject strings that are matched against it are  treated  as  UTF-8         sequence (*UTF8). When either of these is the case,  both  the  pattern
144         strings instead of just strings of bytes.         and  any  subject  strings  that  are matched against it are treated as
145           UTF-8 strings instead of strings of 1-byte characters.
146    
147         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,
148         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
149         is limited to testing the PCRE_UTF8 flag occasionally, so should not be         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
150         very big.         very big.
151    
152         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
153         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
154         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
155         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
156         for a decimal number, the Unicode script names such as Arabic  or  Han,         for  a  decimal number, the Unicode script names such as Arabic or Han,
157         and  the  derived  properties  Any  and L&. A full list is given in the         and the derived properties Any and L&. A full  list  is  given  in  the
158         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
159         ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-         ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
160         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may         ter},  is  not  supported.   Furthermore,  in Perl, many properties may
161         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
162         does not support this.         does not support this.
163    
164     Validity of UTF-8 strings     Validity of UTF-8 strings
165    
166         When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and         When  you  set  the  PCRE_UTF8 flag, the strings passed as patterns and
167         subjects are (by default) checked for validity on entry to the relevant         subjects are (by default) checked for validity on entry to the relevant
168         functions. From release 7.3 of PCRE, the check is according  the  rules         functions.  From  release 7.3 of PCRE, the check is according the rules
169         of  RFC  3629, which are themselves derived from the Unicode specifica-         of RFC 3629, which are themselves derived from the  Unicode  specifica-
170         tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which         tion.  Earlier  releases  of PCRE followed the rules of RFC 2279, which
171         allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current         allows the full range of 31-bit values (0 to 0x7FFFFFFF).  The  current
172         check allows only values in the range U+0 to U+10FFFF, excluding U+D800         check allows only values in the range U+0 to U+10FFFF, excluding U+D800
173         to U+DFFF.         to U+DFFF.
174    
175         The  excluded  code  points are the "Low Surrogate Area" of Unicode, of         The excluded code points are the "Low Surrogate Area"  of  Unicode,  of
176         which the Unicode Standard says this: "The Low Surrogate Area does  not         which  the Unicode Standard says this: "The Low Surrogate Area does not
177         contain  any  character  assignments,  consequently  no  character code         contain any  character  assignments,  consequently  no  character  code
178         charts or namelists are provided for this area. Surrogates are reserved         charts or namelists are provided for this area. Surrogates are reserved
179         for  use  with  UTF-16 and then must be used in pairs." The code points         for use with UTF-16 and then must be used in pairs."  The  code  points
180         that are encoded by UTF-16 pairs  are  available  as  independent  code         that  are  encoded  by  UTF-16  pairs are available as independent code
181         points  in  the  UTF-8  encoding.  (In other words, the whole surrogate         points in the UTF-8 encoding. (In  other  words,  the  whole  surrogate
182         thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)         thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
183    
184         If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return         If  an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error return
185         (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know         (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
186         that your strings are valid, and therefore want to skip these checks in         that your strings are valid, and therefore want to skip these checks in
187         order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at         order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
188         compile time or at run time, PCRE assumes that the pattern  or  subject         compile  time  or at run time, PCRE assumes that the pattern or subject
189         it  is  given  (respectively)  contains only valid UTF-8 codes. In this         it is given (respectively) contains only valid  UTF-8  codes.  In  this
190         case, it does not diagnose an invalid UTF-8 string.         case, it does not diagnose an invalid UTF-8 string.
191    
192         If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,         If  you  pass  an  invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,
193         what  happens  depends on why the string is invalid. If the string con-         what happens depends on why the string is invalid. If the  string  con-
194         forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a         forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
195         string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,         string of characters in the range 0  to  0x7FFFFFFF.  In  other  words,
196         apart from the initial validity test, PCRE (when in UTF-8 mode) handles         apart from the initial validity test, PCRE (when in UTF-8 mode) handles
197         strings  according  to  the more liberal rules of RFC 2279. However, if         strings according to the more liberal rules of RFC  2279.  However,  if
198         the string does not even conform to RFC 2279, the result is  undefined.         the  string does not even conform to RFC 2279, the result is undefined.
199         Your program may crash.         Your program may crash.
200    
201         If  you  want  to  process  strings  of  values  in the full range 0 to         If you want to process strings  of  values  in  the  full  range  0  to
202         0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can         0x7FFFFFFF,  encoded in a UTF-8-like manner as per the old RFC, you can
203         set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in         set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
204         this situation, you will have to apply your own validity check.         this situation, you will have to apply your own validity check.
205    
206     General comments about UTF-8 mode     General comments about UTF-8 mode
207    
208         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a         1.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
209         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
210    
211         2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8         2. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
212         characters for values greater than \177.         characters for values greater than \177.
213    
214         3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         3.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
215         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
216    
217         4.  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-
218         gle byte.         gle byte.
219    
220         5. 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
221         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
222         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
223    
224         6. 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
225         test  characters of any code value, but the characters that PCRE recog-         test characters of any code value, but, by default, the characters that
226         nizes as digits, spaces, or word characters  remain  the  same  set  as         PCRE  recognizes  as digits, spaces, or word characters remain the same
227         before, all with values less than 256. This remains true even when PCRE         set as before, all with values less than 256. This  remains  true  even
228         includes Unicode property support, because to do otherwise  would  slow         when  PCRE  is built to include Unicode property support, because to do
229         down  PCRE in many common cases. If you really want to test for a wider         otherwise would slow down PCRE in many common  cases.  Note  that  this
230         sense of, say, "digit", you must use Unicode  property  tests  such  as         also applies to \b, because it is defined in terms of \w and \W. If you
231         \p{Nd}.         really want to test for a wider sense of, say,  "digit",  you  can  use
232           explicit  Unicode property tests such as \p{Nd}.  Alternatively, if you
233           set the PCRE_UCP option, the way that the  character  escapes  work  is
234           changed  so that Unicode properties are used to determine which charac-
235           ters match. There are more details in the section on generic  character
236           types in the pcrepattern documentation.
237    
238         7.  Similarly,  characters that match the POSIX named character classes         7.  Similarly,  characters that match the POSIX named character classes
239         are all low-valued characters.         are all low-valued characters, unless the PCRE_UCP option is set.
240    
241         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
242         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
243         acters.         acters, whether or not PCRE_UCP is set.
244    
245         9. Case-insensitive matching applies only to  characters  whose  values         9. Case-insensitive matching applies only to  characters  whose  values
246         are  less than 128, unless PCRE is built with Unicode property support.         are  less than 128, unless PCRE is built with Unicode property support.
# Line 256  AUTHOR Line 267  AUTHOR
267    
268  REVISION  REVISION
269    
270         Last updated: 09 August 2007         Last updated: 12 May 2010
271         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
272  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
273    
274    
# Line 271  NAME Line 282  NAME
282  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
283    
284         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
285         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
286         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
287         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
288         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
289         directory) can be obtained by running         environments using the GUI facility of cmake-gui if you are using CMake
290           instead of configure to build PCRE.
291    
292           There  is  a  lot more information about building PCRE in non-Unix-like
293           environments in the file called NON_UNIX_USE, which is part of the PCRE
294           distribution.  You  should consult this file as well as the README file
295           if you are building in a non-Unix-like environment.
296    
297           The complete list of options for configure (which includes the standard
298           ones  such  as  the  selection  of  the  installation directory) can be
299           obtained by running
300    
301           ./configure --help           ./configure --help
302    
# Line 300  C++ SUPPORT Line 321  C++ SUPPORT
321    
322  UTF-8 SUPPORT  UTF-8 SUPPORT
323    
324         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
325    
326           --enable-utf8           --enable-utf8
327    
328         to  the  configure  command.  Of  itself, this does not make PCRE treat         to  the  configure  command.  Of  itself, this does not make PCRE treat
329         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
330         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()
331         function.         or pcre_compile2() functions.
332    
333           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
334           expects its input to be either ASCII or UTF-8 (depending on the runtime
335           option). It is not possible to support both EBCDIC and UTF-8  codes  in
336           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
337           --enable-ebcdic are mutually exclusive.
338    
339    
340  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
# Line 330  UNICODE CHARACTER PROPERTY SUPPORT Line 357  UNICODE CHARACTER PROPERTY SUPPORT
357    
358  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
359    
360         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating         By  default,  PCRE interprets the linefeed (LF) character as indicating
361         the end of a line. This is the normal newline  character  on  Unix-like         the end of a line. This is the normal newline  character  on  Unix-like
362         systems. You can compile PCRE to use character 13 (carriage return, CR)         systems.  You  can compile PCRE to use carriage return (CR) instead, by
363         instead, by adding         adding
364    
365           --enable-newline-is-cr           --enable-newline-is-cr
366    
# Line 356  CODE VALUE OF NEWLINE Line 383  CODE VALUE OF NEWLINE
383    
384         causes PCRE to recognize any Unicode newline sequence.         causes PCRE to recognize any Unicode newline sequence.
385    
386         Whatever line ending convention is selected when PCRE is built  can  be         Whatever  line  ending convention is selected when PCRE is built can be
387         overridden  when  the library functions are called. At build time it is         overridden when the library functions are called. At build time  it  is
388         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
389    
390    
391    WHAT \R MATCHES
392    
393           By  default,  the  sequence \R in a pattern matches any Unicode newline
394           sequence, whatever has been selected as the line  ending  sequence.  If
395           you specify
396    
397             --enable-bsr-anycrlf
398    
399           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
400           ever is selected when PCRE is built can be overridden when the  library
401           functions are called.
402    
403    
404  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
405    
406         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
407         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
408         of         of
409    
410           --disable-shared           --disable-shared
# Line 376  BUILDING SHARED AND STATIC LIBRARIES Line 416  BUILDING SHARED AND STATIC LIBRARIES
416  POSIX MALLOC USAGE  POSIX MALLOC USAGE
417    
418         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
419         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
420         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
421         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
422         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
423         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.
424         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 391  POSIX MALLOC USAGE Line 431  POSIX MALLOC USAGE
431    
432  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
433    
434         Within  a  compiled  pattern,  offset values are used to point from one         Within a compiled pattern, offset values are used  to  point  from  one
435         part to another (for example, from an opening parenthesis to an  alter-         part  to another (for example, from an opening parenthesis to an alter-
436         nation  metacharacter).  By default, two-byte values are used for these         nation metacharacter). By default, two-byte values are used  for  these
437         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets,  leading  to  a  maximum size for a compiled pattern of around
438         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
439         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless,  some  people do want to process truyl enormous patterns,
440         is  possible  to compile PCRE to use three-byte or four-byte offsets by         so it is possible to compile PCRE to use three-byte or  four-byte  off-
441         adding a setting such as         sets by adding a setting such as
442    
443           --with-link-size=3           --with-link-size=3
444    
445         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
446         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
447         additional bytes when handling them.         additional bytes when handling them.
448    
449    
450  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
451    
452         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
453         ing  by  making recursive calls to an internal function called match().         ing by making recursive calls to an internal function  called  match().
454         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-
455         verely  limit  PCRE's operation. (The Unix environment does not usually         verely limit PCRE's operation. (The Unix environment does  not  usually
456         suffer from this problem, but it may sometimes be necessary to increase         suffer from this problem, but it may sometimes be necessary to increase
457         the  maximum  stack size.  There is a discussion in the pcrestack docu-         the maximum stack size.  There is a discussion in the  pcrestack  docu-
458         mentation.) An alternative approach to recursion that uses memory  from         mentation.)  An alternative approach to recursion that uses memory from
459         the  heap  to remember data, instead of using recursive function calls,         the heap to remember data, instead of using recursive  function  calls,
460         has been implemented to work round the problem of limited  stack  size.         has  been  implemented to work round the problem of limited stack size.
461         If you want to build a version of PCRE that works this way, add         If you want to build a version of PCRE that works this way, add
462    
463           --disable-stack-for-recursion           --disable-stack-for-recursion
464    
465         to  the  configure  command. With this configuration, PCRE will use the         to the configure command. With this configuration, PCRE  will  use  the
466         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
467         ment  functions. By default these point to malloc() and free(), but you         ment functions. By default these point to malloc() and free(), but  you
468         can replace the pointers so that your own functions are used.         can replace the pointers so that your own functions are used instead.
469    
470         Separate functions are  provided  rather  than  using  pcre_malloc  and         Separate  functions  are  provided  rather  than  using pcre_malloc and
471         pcre_free  because  the  usage  is  very  predictable:  the block sizes         pcre_free because the  usage  is  very  predictable:  the  block  sizes
472         requested are always the same, and  the  blocks  are  always  freed  in         requested  are  always  the  same,  and  the blocks are always freed in
473         reverse  order.  A calling program might be able to implement optimized         reverse order. A calling program might be able to  implement  optimized
474         functions that perform better  than  malloc()  and  free().  PCRE  runs         functions  that  perform  better  than  malloc()  and free(). PCRE runs
475         noticeably more slowly when built in this way. This option affects only         noticeably more slowly when built in this way. This option affects only
476         the  pcre_exec()  function;  it   is   not   relevant   for   the   the         the pcre_exec() function; it is not relevant for pcre_dfa_exec().
        pcre_dfa_exec() function.  
477    
478    
479  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
# Line 496  USING EBCDIC CODE Line 535  USING EBCDIC CODE
535    
536         to the configure command. This setting implies --enable-rebuild-charta-         to the configure command. This setting implies --enable-rebuild-charta-
537         bles.  You  should  only  use  it if you know that you are in an EBCDIC         bles.  You  should  only  use  it if you know that you are in an EBCDIC
538         environment (for example, an IBM mainframe operating system).         environment (for example,  an  IBM  mainframe  operating  system).  The
539           --enable-ebcdic option is incompatible with --enable-utf8.
540    
541    
542    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
543    
544           By default, pcregrep reads all files as plain text. You can build it so
545           that it recognizes files whose names end in .gz or .bz2, and reads them
546           with libz or libbz2, respectively, by adding one or both of
547    
548             --enable-pcregrep-libz
549             --enable-pcregrep-libbz2
550    
551           to the configure command. These options naturally require that the rel-
552           evant libraries are installed on your system. Configuration  will  fail
553           if they are not.
554    
555    
556    PCRETEST OPTION FOR LIBREADLINE SUPPORT
557    
558           If you add
559    
560             --enable-pcretest-libreadline
561    
562           to  the  configure  command,  pcretest  is  linked with the libreadline
563           library, and when its input is from a terminal, it reads it  using  the
564           readline() function. This provides line-editing and history facilities.
565           Note that libreadline is GPL-licensed, so if you distribute a binary of
566           pcretest linked in this way, there may be licensing issues.
567    
568           Setting  this  option  causes  the -lreadline option to be added to the
569           pcretest build. In many operating environments with  a  sytem-installed
570           libreadline this is sufficient. However, in some environments (e.g.  if
571           an unmodified distribution version of readline is in use),  some  extra
572           configuration  may  be necessary. The INSTALL file for libreadline says
573           this:
574    
575             "Readline uses the termcap functions, but does not link with the
576             termcap or curses library itself, allowing applications which link
577             with readline the to choose an appropriate library."
578    
579           If your environment has not been set up so that an appropriate  library
580           is automatically included, you may need to add something like
581    
582             LIBS="-ncurses"
583    
584           immediately before the configure command.
585    
586    
587  SEE ALSO  SEE ALSO
# Line 513  AUTHOR Line 598  AUTHOR
598    
599  REVISION  REVISION
600    
601         Last updated: 30 July 2007         Last updated: 29 September 2009
602         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
603  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
604    
605    
# Line 601  THE ALTERNATIVE MATCHING ALGORITHM Line 686  THE ALTERNATIVE MATCHING ALGORITHM
686         though  it is not implemented as a traditional finite state machine (it         though  it is not implemented as a traditional finite state machine (it
687         keeps multiple states active simultaneously).         keeps multiple states active simultaneously).
688    
689           Although the general principle of this matching algorithm  is  that  it
690           scans  the subject string only once, without backtracking, there is one
691           exception: when a lookaround assertion is encountered,  the  characters
692           following  or  preceding  the  current  point  have to be independently
693           inspected.
694    
695         The scan continues until either the end of the subject is  reached,  or         The scan continues until either the end of the subject is  reached,  or
696         there  are  no more unterminated paths. At this point, terminated paths         there  are  no more unterminated paths. At this point, terminated paths
697         represent the different matching possibilities (if there are none,  the         represent the different matching possibilities (if there are none,  the
698         match  has  failed).   Thus,  if there is more than one possible match,         match  has  failed).   Thus,  if there is more than one possible match,
699         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-
700         est.  In PCRE, there is an option to stop the algorithm after the first         est.  There  is  an  option to stop the algorithm after the first match
701         match (which is necessarily the shortest) has been found.         (which is necessarily the shortest) is found.
702    
703         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
704         subject. If the pattern         subject. If the pattern
# Line 662  THE ALTERNATIVE MATCHING ALGORITHM Line 753  THE ALTERNATIVE MATCHING ALGORITHM
753         tive algorithm moves through the subject  string  one  character  at  a         tive algorithm moves through the subject  string  one  character  at  a
754         time, for all active paths through the tree.         time, for all active paths through the tree.
755    
756         8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-         8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
757         ported.         are not supported. (*FAIL) is supported, and  behaves  like  a  failing
758           negative assertion.
759    
760    
761  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
762    
763         Using the alternative matching algorithm provides the following  advan-         Using  the alternative matching algorithm provides the following advan-
764         tages:         tages:
765    
766         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-
767         ically found, and in particular, the longest match is  found.  To  find         ically  found,  and  in particular, the longest match is found. To find
768         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
769         things with callouts.         things with callouts.
770    
771         2. There is much better support for partial matching. The  restrictions         2.  Because  the  alternative  algorithm  scans the subject string just
772         on  the content of the pattern that apply when using the standard algo-         once, and never needs to backtrack, it is possible to  pass  very  long
773         rithm for partial matching do not apply to the  alternative  algorithm.         subject  strings  to  the matching function in several pieces, checking
774         For  non-anchored patterns, the starting position of a partial match is         for partial matching each time.  The  pcrepartial  documentation  gives
775         available.         details of partial matching.
   
        3. Because the alternative algorithm  scans  the  subject  string  just  
        once,  and  never  needs to backtrack, it is possible to pass very long  
        subject strings to the matching function in  several  pieces,  checking  
        for partial matching each time.  
776    
777    
778  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
# Line 711  AUTHOR Line 798  AUTHOR
798    
799  REVISION  REVISION
800    
801         Last updated: 08 August 2007         Last updated: 29 September 2009
802         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
803  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
804    
805    
# Line 819  PCRE API OVERVIEW Line 906  PCRE API OVERVIEW
906         bers for the library.  Applications can use these  to  include  support         bers for the library.  Applications can use these  to  include  support
907         for different releases of PCRE.         for different releases of PCRE.
908    
909           In a Windows environment, if you want to statically link an application
910           program against a non-dll pcre.a  file,  you  must  define  PCRE_STATIC
911           before  including  pcre.h or pcrecpp.h, because otherwise the pcre_mal-
912           loc()   and   pcre_free()   exported   functions   will   be   declared
913           __declspec(dllimport), with unwanted results.
914    
915         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
916         pcre_exec() are used for compiling and matching regular expressions  in         pcre_exec() are used for compiling and matching regular expressions  in
917         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
918         plest way of using them is provided in the file  called  pcredemo.c  in         plest way of using them is provided in the file  called  pcredemo.c  in
919         the  source distribution. The pcresample documentation describes how to         the PCRE source distribution. A listing of this program is given in the
920         run it.         pcredemo documentation, and the pcresample documentation describes  how
921           to compile and run it.
922    
923         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
924         ble,  is  also provided. This uses a different algorithm for the match-         ble, is also provided. This uses a different algorithm for  the  match-
925         ing. The alternative algorithm finds all possible matches (at  a  given         ing.  The  alternative algorithm finds all possible matches (at a given
926         point  in  the subject), and scans the subject just once. However, this         point in the subject), and scans the subject just  once  (unless  there
927         algorithm does not return captured substrings. A description of the two         are  lookbehind  assertions).  However,  this algorithm does not return
928         matching  algorithms and their advantages and disadvantages is given in         captured substrings. A description of the two matching  algorithms  and
929         the pcrematching documentation.         their  advantages  and disadvantages is given in the pcrematching docu-
930           mentation.
931    
932         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
933         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 908  NEWLINES Line 1003  NEWLINES
1003         dard. When PCRE is run, the default can be overridden,  either  when  a         dard. When PCRE is run, the default can be overridden,  either  when  a
1004         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
1005    
1006           At compile time, the newline convention can be specified by the options
1007           argument of pcre_compile(), or it can be specified by special  text  at
1008           the start of the pattern itself; this overrides any other settings. See
1009           the pcrepattern page for details of the special character sequences.
1010    
1011         In the PCRE documentation the word "newline" is used to mean "the char-         In the PCRE documentation the word "newline" is used to mean "the char-
1012         acter or pair of characters that indicate a line break". The choice  of         acter  or pair of characters that indicate a line break". The choice of
1013         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
1014         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
1015         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
1016         ment for a non-anchored pattern. The choice of newline convention  does         ment for a non-anchored pattern. There is more detail about this in the
1017         not affect the interpretation of the \n or \r escape sequences.         section on pcre_exec() options below.
1018    
1019           The choice of newline convention does not affect the interpretation  of
1020           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1021           which is controlled in a similar way, but by separate options.
1022    
1023    
1024  MULTITHREADING  MULTITHREADING
1025    
1026         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
1027         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
1028         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
1029         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
# Line 968  CHECKING BUILD-TIME OPTIONS Line 1072  CHECKING BUILD-TIME OPTIONS
1072         The output is an integer whose value specifies  the  default  character         The output is an integer whose value specifies  the  default  character
1073         sequence  that is recognized as meaning "newline". The four values that         sequence  that is recognized as meaning "newline". The four values that
1074         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1075         and  -1  for  ANY. The default should normally be the standard sequence         and  -1  for  ANY.  Though they are derived from ASCII, the same values
1076         for your operating system.         are returned in EBCDIC environments. The default should normally corre-
1077           spond to the standard sequence for your operating system.
1078    
1079             PCRE_CONFIG_BSR
1080    
1081           The output is an integer whose value indicates what character sequences
1082           the \R escape sequence matches by default. A value of 0 means  that  \R
1083           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1084           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1085           tern is compiled or matched.
1086    
1087           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1088    
1089         The output is an integer that contains the number  of  bytes  used  for         The  output  is  an  integer that contains the number of bytes used for
1090         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1091         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1092         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1093         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1094         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1095    
1096           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1097    
1098         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1099         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1100         given in the pcreposix documentation.         given in the pcreposix documentation.
1101    
1102           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1103    
1104         The output is an integer that gives the default limit for the number of         The output is a long integer that gives the default limit for the  num-
1105         internal matching function calls in a  pcre_exec()  execution.  Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1106         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1107    
1108           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1109    
1110         The  output is an integer that gives the default limit for the depth of         The output is a long integer that gives the default limit for the depth
1111         recursion when calling the internal matching function in a  pcre_exec()         of   recursion  when  calling  the  internal  matching  function  in  a
1112         execution. Further details are given with pcre_exec() below.         pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1113           below.
1114    
1115           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1116    
# Line 1023  COMPILING A PATTERN Line 1137  COMPILING A PATTERN
1137         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1138         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1139         the  two interfaces is that pcre_compile2() has an additional argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1140         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1141           avoid  too  much repetition, we refer just to pcre_compile() below, but
1142           the information applies equally to pcre_compile2().
1143    
1144         The pattern is a C string terminated by a binary zero, and is passed in         The pattern is a C string terminated by a binary zero, and is passed in
1145         the  pattern  argument.  A  pointer to a single block of memory that is         the  pattern  argument.  A  pointer to a single block of memory that is
# Line 1040  COMPILING A PATTERN Line 1156  COMPILING A PATTERN
1156    
1157         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1158         pilation. It should be zero if no options are required.  The  available         pilation. It should be zero if no options are required.  The  available
1159         options  are  described  below. Some of them, in particular, those that         options  are  described  below. Some of them (in particular, those that
1160         are compatible with Perl, can also be set and  unset  from  within  the         are compatible with Perl, but some others as well) can also be set  and
1161         pattern  (see  the  detailed  description in the pcrepattern documenta-         unset  from  within  the  pattern  (see the detailed description in the
1162         tion). For these options, the contents of the options  argument  speci-         pcrepattern documentation). For those options that can be different  in
1163         fies  their initial settings at the start of compilation and execution.         different  parts  of  the pattern, the contents of the options argument
1164         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time         specifies their settings at the start of compilation and execution. The
1165         of matching as well as at compile time.         PCRE_ANCHORED, PCRE_BSR_xxx, and PCRE_NEWLINE_xxx options can be set at
1166           the time of matching as well as at compile time.
1167    
1168         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1169         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1170         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-
1171         sage. This is a static string that is part of the library. You must not         sage. This is a static string that is part of the library. You must not
1172         try to free it. The offset from the start of the pattern to the charac-         try to free it. The byte offset from the start of the  pattern  to  the
1173         ter where the error was discovered is placed in the variable pointed to         character  that  was  being  processed when the error was discovered is
1174         by  erroffset,  which must not be NULL. If it is, an immediate error is         placed in the variable pointed to by erroffset, which must not be NULL.
1175         given.         If  it  is,  an  immediate error is given. Some errors are not detected
1176           until checks are carried out when the whole pattern has  been  scanned;
1177         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         in this case the offset is set to the end of the pattern.
1178         codeptr  argument is not NULL, a non-zero error code number is returned  
1179         via this argument in the event of an error. This is in addition to  the         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1180           codeptr argument is not NULL, a non-zero error code number is  returned
1181           via  this argument in the event of an error. This is in addition to the
1182         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1183    
1184         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
1185         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1186         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1187         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
1188         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1189         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
1190         support below.         support below.
1191    
1192         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1193         pile():         pile():
1194    
1195           pcre *re;           pcre *re;
# Line 1083  COMPILING A PATTERN Line 1202  COMPILING A PATTERN
1202             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1203             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1204    
1205         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
1206         file:         file:
1207    
1208           PCRE_ANCHORED           PCRE_ANCHORED
1209    
1210         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
1211         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
1212         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1213         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1214         only way to do it in Perl.         only way to do it in Perl.
1215    
1216           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1217    
1218         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1219         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1220         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1221    
1222             PCRE_BSR_ANYCRLF
1223             PCRE_BSR_UNICODE
1224    
1225           These options (which are mutually exclusive) control what the \R escape
1226           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1227           or to match any Unicode newline sequence. The default is specified when
1228           PCRE is built. It can be overridden from within the pattern, or by set-
1229           ting an option when a compiled pattern is matched.
1230    
1231           PCRE_CASELESS           PCRE_CASELESS
1232    
1233         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
1234         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
1235         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
1236         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1237         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1238         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-
1239         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1240         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1241         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1242         UTF-8 support.         UTF-8 support.
1243    
1244           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1245    
1246         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
1247         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
1248         matches immediately before a newline at the end of the string (but  not         matches  immediately before a newline at the end of the string (but not
1249         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1250         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1251         Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1252    
1253           PCRE_DOTALL           PCRE_DOTALL
1254    
1255         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-
1256         acters, including those that indicate newline. Without it, a  dot  does         acters,  including  those that indicate newline. Without it, a dot does
1257         not  match  when  the  current position is at a newline. This option is         not match when the current position is at a  newline.  This  option  is
1258         equivalent to Perl's /s option, and it can be changed within a  pattern         equivalent  to Perl's /s option, and it can be changed within a pattern
1259         by  a (?s) option setting. A negative class such as [^a] always matches         by a (?s) option setting. A negative class such as [^a] always  matches
1260         newline characters, independent of the setting of this option.         newline characters, independent of the setting of this option.
1261    
1262           PCRE_DUPNAMES           PCRE_DUPNAMES
1263    
1264         If this bit is set, names used to identify capturing  subpatterns  need         If  this  bit is set, names used to identify capturing subpatterns need
1265         not be unique. This can be helpful for certain types of pattern when it         not be unique. This can be helpful for certain types of pattern when it
1266         is known that only one instance of the named  subpattern  can  ever  be         is  known  that  only  one instance of the named subpattern can ever be
1267         matched.  There  are  more details of named subpatterns below; see also         matched. There are more details of named subpatterns  below;  see  also
1268         the pcrepattern documentation.         the pcrepattern documentation.
1269    
1270           PCRE_EXTENDED           PCRE_EXTENDED
1271    
1272         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1273         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1274         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1275         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1276         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1277         option,  and  it  can be changed within a pattern by a (?x) option set-         option, and it can be changed within a pattern by a  (?x)  option  set-
1278         ting.         ting.
1279    
1280         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1281         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1282         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1283         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1284         introduces a conditional subpattern.         introduces a conditional subpattern.
1285    
1286           PCRE_EXTRA           PCRE_EXTRA
1287    
1288         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1289         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
1290         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
1291         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1292         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1293         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
1294         literal. (Perl can, however, be persuaded to give a warning for  this.)         literal. (Perl can, however, be persuaded to give an error for this, by
1295         There  are  at  present no other features controlled by this option. It         running it with the -w option.) There are at present no other  features
1296         can also be set by a (?X) option setting within a pattern.         controlled  by this option. It can also be set by a (?X) option setting
1297           within a pattern.
1298    
1299           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1300    
# Line 1173  COMPILING A PATTERN Line 1302  COMPILING A PATTERN
1302         before  or  at  the  first  newline  in  the subject string, though the         before  or  at  the  first  newline  in  the subject string, though the
1303         matched text may continue over the newline.         matched text may continue over the newline.
1304    
1305             PCRE_JAVASCRIPT_COMPAT
1306    
1307           If this option is set, PCRE's behaviour is changed in some ways so that
1308           it  is  compatible with JavaScript rather than Perl. The changes are as
1309           follows:
1310    
1311           (1) A lone closing square bracket in a pattern  causes  a  compile-time
1312           error,  because this is illegal in JavaScript (by default it is treated
1313           as a data character). Thus, the pattern AB]CD becomes illegal when this
1314           option is set.
1315    
1316           (2)  At run time, a back reference to an unset subpattern group matches
1317           an empty string (by default this causes the current  matching  alterna-
1318           tive  to  fail). A pattern such as (\1)(a) succeeds when this option is
1319           set (assuming it can find an "a" in the subject), whereas it  fails  by
1320           default, for Perl compatibility.
1321    
1322           PCRE_MULTILINE           PCRE_MULTILINE
1323    
1324         By default, PCRE treats the subject string as consisting  of  a  single         By  default,  PCRE  treats the subject string as consisting of a single
1325         line  of characters (even if it actually contains newlines). The "start         line of characters (even if it actually contains newlines). The  "start
1326         of line" metacharacter (^) matches only at the  start  of  the  string,         of  line"  metacharacter  (^)  matches only at the start of the string,
1327         while  the  "end  of line" metacharacter ($) matches only at the end of         while the "end of line" metacharacter ($) matches only at  the  end  of
1328         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1329         is set). This is the same as Perl.         is set). This is the same as Perl.
1330    
1331         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"
1332         constructs match immediately following or immediately  before  internal         constructs  match  immediately following or immediately before internal
1333         newlines  in  the  subject string, respectively, as well as at the very         newlines in the subject string, respectively, as well as  at  the  very
1334         start and end. This is equivalent to Perl's /m option, and  it  can  be         start  and  end.  This is equivalent to Perl's /m option, and it can be
1335         changed within a pattern by a (?m) option setting. If there are no new-         changed within a pattern by a (?m) option setting. If there are no new-
1336         lines in a subject string, or no occurrences of ^ or $  in  a  pattern,         lines  in  a  subject string, or no occurrences of ^ or $ in a pattern,
1337         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1338    
1339           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
# Line 1196  COMPILING A PATTERN Line 1342  COMPILING A PATTERN
1342           PCRE_NEWLINE_ANYCRLF           PCRE_NEWLINE_ANYCRLF
1343           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1344    
1345         These  options  override the default newline definition that was chosen         These options override the default newline definition that  was  chosen
1346         when PCRE was built. Setting the first or the second specifies  that  a         when  PCRE  was built. Setting the first or the second specifies that a
1347         newline  is  indicated  by a single character (CR or LF, respectively).         newline is indicated by a single character (CR  or  LF,  respectively).
1348         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the         Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1349         two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies         two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1350         that any of the three preceding sequences should be recognized. Setting         that any of the three preceding sequences should be recognized. Setting
1351         PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be         PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1352         recognized. The Unicode newline sequences are the three just mentioned,         recognized. The Unicode newline sequences are the three just mentioned,
1353         plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,         plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1354         U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS         U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1355         (paragraph  separator,  U+2029).  The  last  two are recognized only in         (paragraph separator, U+2029). The last  two  are  recognized  only  in
1356         UTF-8 mode.         UTF-8 mode.
1357    
1358         The newline setting in the  options  word  uses  three  bits  that  are         The  newline  setting  in  the  options  word  uses three bits that are
1359         treated as a number, giving eight possibilities. Currently only six are         treated as a number, giving eight possibilities. Currently only six are
1360         used (default plus the five values above). This means that if  you  set         used  (default  plus the five values above). This means that if you set
1361         more  than one newline option, the combination may or may not be sensi-         more than one newline option, the combination may or may not be  sensi-
1362         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1363         PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and         PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1364         cause an error.         cause an error.
1365    
1366         The only time that a line break is specially recognized when  compiling         The  only time that a line break is specially recognized when compiling
1367         a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a         a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1368         character class is encountered. This indicates  a  comment  that  lasts         character  class  is  encountered.  This indicates a comment that lasts
1369         until  after the next line break sequence. In other circumstances, line         until after the next line break sequence. In other circumstances,  line
1370         break  sequences  are  treated  as  literal  data,   except   that   in         break   sequences   are   treated  as  literal  data,  except  that  in
1371         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1372         and are therefore ignored.         and are therefore ignored.
1373    
1374         The newline option that is set at compile time becomes the default that         The newline option that is set at compile time becomes the default that
1375         is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.         is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1376    
1377           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1378    
# Line 1236  COMPILING A PATTERN Line 1382  COMPILING A PATTERN
1382         be  used  for  capturing  (and  they acquire numbers in the usual way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1383         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1384    
1385             PCRE_UCP
1386    
1387           This option changes the way PCRE processes \b, \d, \s, \w, and some  of
1388           the POSIX character classes. By default, only ASCII characters are rec-
1389           ognized, but if PCRE_UCP is set, Unicode properties are used instead to
1390           classify  characters.  More details are given in the section on generic
1391           character types in the pcrepattern page. If you set PCRE_UCP,  matching
1392           one  of the items it affects takes much longer. The option is available
1393           only if PCRE has been compiled with Unicode property support.
1394    
1395           PCRE_UNGREEDY           PCRE_UNGREEDY
1396    
1397         This option inverts the "greediness" of the quantifiers  so  that  they         This option inverts the "greediness" of the quantifiers  so  that  they
# Line 1285  COMPILATION ERROR CODES Line 1441  COMPILATION ERROR CODES
1441            9  nothing to repeat            9  nothing to repeat
1442           10  [this code is not in use]           10  [this code is not in use]
1443           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1444           12  unrecognized character after (?           12  unrecognized character after (? or (?-
1445           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
1446           14  missing )           14  missing )
1447           15  reference to non-existent subpattern           15  reference to non-existent subpattern
# Line 1293  COMPILATION ERROR CODES Line 1449  COMPILATION ERROR CODES
1449           17  unknown option bit(s) set           17  unknown option bit(s) set
1450           18  missing ) after comment           18  missing ) after comment
1451           19  [this code is not in use]           19  [this code is not in use]
1452           20  regular expression too large           20  regular expression is too large
1453           21  failed to get memory           21  failed to get memory
1454           22  unmatched parentheses           22  unmatched parentheses
1455           23  internal error: code overflow           23  internal error: code overflow
# Line 1322  COMPILATION ERROR CODES Line 1478  COMPILATION ERROR CODES
1478           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1479           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1480           48  subpattern name is too long (maximum 32 characters)           48  subpattern name is too long (maximum 32 characters)
1481           49  too many named subpatterns (maximum 10,000)           49  too many named subpatterns (maximum 10000)
1482           50  [this code is not in use]           50  [this code is not in use]
1483           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1484           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1485           53  internal  error:  previously-checked  referenced  subpattern  not           53  internal error: previously-checked referenced subpattern
1486         found                 not found
1487           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1488           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1489           56  inconsistent NEWLINE options"           56  inconsistent NEWLINE options
1490           57  \g is not followed by a braced name or an optionally braced           57  \g is not followed by a braced, angle-bracketed, or quoted
1491                 non-zero number                 name/number or by a plain number
1492           58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number           58  a numbered reference must not be zero
1493             59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1494             60  (*VERB) not recognized
1495             61  number is too big
1496             62  subpattern name expected
1497             63  digit expected after (?+
1498             64  ] is an invalid data character in JavaScript compatibility mode
1499             65  different names for subpatterns of the same number are
1500                   not allowed
1501             66  (*MARK) must have an argument
1502             67  this version of PCRE is not compiled with PCRE_UCP support
1503    
1504           The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1505           values may be used if the limits were changed when PCRE was built.
1506    
1507    
1508  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1350  STUDYING A PATTERN Line 1519  STUDYING A PATTERN
1519         the results of the study.         the results of the study.
1520    
1521         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1522         pcre_exec(). However, a pcre_extra block  also  contains  other  fields         pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block  also  con-
1523         that  can  be  set  by the caller before the block is passed; these are         tains  other  fields  that can be set by the caller before the block is
1524         described below in the section on matching a pattern.         passed; these are described below in the section on matching a pattern.
1525    
1526         If studying the pattern does not  produce  any  additional  information         If studying the  pattern  does  not  produce  any  useful  information,
1527         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1528         wants to pass any of the other fields to pcre_exec(), it  must  set  up         wants  to  pass  any  of   the   other   fields   to   pcre_exec()   or
1529         its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1530    
1531         The  second  argument of pcre_study() contains option bits. At present,         The  second  argument of pcre_study() contains option bits. At present,
1532         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
# Line 1377  STUDYING A PATTERN Line 1546  STUDYING A PATTERN
1546             0,              /* no options exist */             0,              /* no options exist */
1547             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1548    
1549         At present, studying a pattern is useful only for non-anchored patterns         Studying a pattern does two things: first, a lower bound for the length
1550         that do not have a single fixed starting character. A bitmap of  possi-         of subject string that is needed to match the pattern is computed. This
1551         ble starting bytes is created.         does not mean that there are any strings of that length that match, but
1552           it does guarantee that no shorter strings match. The value is  used  by
1553           pcre_exec()  and  pcre_dfa_exec()  to  avoid  wasting time by trying to
1554           match strings that are shorter than the lower bound. You can  find  out
1555           the value in a calling program via the pcre_fullinfo() function.
1556    
1557           Studying a pattern is also useful for non-anchored patterns that do not
1558           have a single fixed starting character. A bitmap of  possible  starting
1559           bytes  is  created. This speeds up finding a position in the subject at
1560           which to start matching.
1561    
1562           The two optimizations just described can be  disabled  by  setting  the
1563           PCRE_NO_START_OPTIMIZE    option    when    calling    pcre_exec()   or
1564           pcre_dfa_exec(). You might want to do this  if  your  pattern  contains
1565           callouts,  or  make  use of (*MARK), and you make use of these in cases
1566           where matching fails.  See  the  discussion  of  PCRE_NO_START_OPTIMIZE
1567           below.
1568    
1569    
1570  LOCALE SUPPORT  LOCALE SUPPORT
# Line 1387  LOCALE SUPPORT Line 1572  LOCALE SUPPORT
1572         PCRE  handles  caseless matching, and determines whether characters are         PCRE  handles  caseless matching, and determines whether characters are
1573         letters, digits, or whatever, by reference to a set of tables,  indexed         letters, digits, or whatever, by reference to a set of tables,  indexed
1574         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
1575         characters with codes less than 128. Higher-valued  codes  never  match         characters with codes less than 128. By  default,  higher-valued  codes
1576         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built         never match escapes such as \w or \d, but they can be tested with \p if
1577         with Unicode character property support. The use of locales  with  Uni-         PCRE is built with Unicode character property  support.  Alternatively,
1578         code  is discouraged. If you are handling characters with codes greater         the  PCRE_UCP  option  can  be  set at compile time; this causes \w and
1579         than 128, you should either use UTF-8 and Unicode, or use locales,  but         friends to use Unicode property support instead of built-in tables. The
1580         not try to mix the two.         use of locales with Unicode is discouraged. If you are handling charac-
1581           ters with codes greater than 128, you should either use UTF-8 and  Uni-
1582           code, or use locales, but not try to mix the two.
1583    
1584         PCRE  contains  an  internal set of tables that are used when the final         PCRE  contains  an  internal set of tables that are used when the final
1585         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
# Line 1522  INFORMATION ABOUT A PATTERN Line 1709  INFORMATION ABOUT A PATTERN
1709         returned.  The fourth argument should point to an unsigned char * vari-         returned.  The fourth argument should point to an unsigned char * vari-
1710         able.         able.
1711    
1712             PCRE_INFO_HASCRORLF
1713    
1714           Return 1 if the pattern contains any explicit  matches  for  CR  or  LF
1715           characters,  otherwise  0.  The  fourth argument should point to an int
1716           variable. An explicit match is either a literal CR or LF character,  or
1717           \r or \n.
1718    
1719           PCRE_INFO_JCHANGED           PCRE_INFO_JCHANGED
1720    
1721         Return 1 if the (?J) option setting is used in the  pattern,  otherwise         Return  1  if  the (?J) or (?-J) option setting is used in the pattern,
1722         0. The fourth argument should point to an int variable. The (?J) inter-         otherwise 0. The fourth argument should point to an int variable.  (?J)
1723         nal option setting changes the local PCRE_DUPNAMES option.         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1724    
1725           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1726    
1727         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
1728         matched  string,  other  than  at  its  start,  if such a byte has been         matched string, other than at its  start,  if  such  a  byte  has  been
1729         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1730         is  no such byte, -1 is returned. For anchored patterns, a last literal         is no such byte, -1 is returned. For anchored patterns, a last  literal
1731         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1732         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1733         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1734    
1735             PCRE_INFO_MINLENGTH
1736    
1737           If  the  pattern  was studied and a minimum length for matching subject
1738           strings was computed, its value is  returned.  Otherwise  the  returned
1739           value  is  -1. The value is a number of characters, not bytes (this may
1740           be relevant in UTF-8 mode). The fourth argument should point to an  int
1741           variable.  A  non-negative  value is a lower bound to the length of any
1742           matching string. There may not be any strings of that  length  that  do
1743           actually match, but every string that does match is at least that long.
1744    
1745           PCRE_INFO_NAMECOUNT           PCRE_INFO_NAMECOUNT
1746           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1747           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1748    
1749         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1750         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1751         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1752         pcre_get_named_substring()  are  provided  for extracting captured sub-         pcre_get_named_substring() are provided for  extracting  captured  sub-
1753         strings by name. It is also possible to extract the data  directly,  by         strings  by  name. It is also possible to extract the data directly, by
1754         first  converting  the  name to a number in order to access the correct         first converting the name to a number in order to  access  the  correct
1755         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1756         the  conversion,  you  need  to  use  the  name-to-number map, which is         the conversion, you need  to  use  the  name-to-number  map,  which  is
1757         described by these three values.         described by these three values.
1758    
1759         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
1760         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1761         of each entry; both of these  return  an  int  value.  The  entry  size         of  each  entry;  both  of  these  return  an int value. The entry size
1762         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1763         a pointer to the first entry of the table  (a  pointer  to  char).  The         a  pointer  to  the  first  entry of the table (a pointer to char). The
1764         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-
1765         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-
1766         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated.
1767         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-  
1768         theses  numbers.  For  example,  consider the following pattern (assume         The names are in alphabetical order. Duplicate names may appear if  (?|
1769         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is         is used to create multiple groups with the same number, as described in
1770         ignored):         the section on duplicate subpattern numbers in  the  pcrepattern  page.
1771           Duplicate  names  for  subpatterns with different numbers are permitted
1772           only if PCRE_DUPNAMES is set. In all cases  of  duplicate  names,  they
1773           appear  in  the table in the order in which they were found in the pat-
1774           tern. In the absence of (?| this is the  order  of  increasing  number;
1775           when (?| is used this is not necessarily the case because later subpat-
1776           terns may have lower numbers.
1777    
1778           As a simple example of the name/number table,  consider  the  following
1779           pattern  (assume  PCRE_EXTENDED is set, so white space - including new-
1780           lines - is ignored):
1781    
1782           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1783           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1784    
1785         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1786         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,
1787         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1788         as ??:         as ??:
1789    
# Line 1578  INFORMATION ABOUT A PATTERN Line 1792  INFORMATION ABOUT A PATTERN
1792           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1793           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1794    
1795         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1796         name-to-number  map,  remember that the length of the entries is likely         name-to-number map, remember that the length of the entries  is  likely
1797         to be different for each compiled pattern.         to be different for each compiled pattern.
1798    
1799           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1800    
1801         Return 1 if the pattern can be used for partial matching, otherwise  0.         Return  1  if  the  pattern  can  be  used  for  partial  matching with
1802         The  fourth  argument  should point to an int variable. The pcrepartial         pcre_exec(), otherwise 0. The fourth argument should point  to  an  int
1803         documentation lists the restrictions that apply to patterns  when  par-         variable.  From  release  8.00,  this  always  returns  1,  because the
1804         tial matching is used.         restrictions that previously applied  to  partial  matching  have  been
1805           lifted.  The  pcrepartial documentation gives details of partial match-
1806           ing.
1807    
1808           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1809    
1810         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
1811         fourth argument should point to an unsigned long  int  variable.  These         fourth  argument  should  point to an unsigned long int variable. These
1812         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1813         by any top-level option settings at the start of the pattern itself. In         by any top-level option settings at the start of the pattern itself. In
1814         other  words,  they are the options that will be in force when matching         other words, they are the options that will be in force  when  matching
1815         starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with         starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
1816         the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,         the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1817         and PCRE_EXTENDED.         and PCRE_EXTENDED.
1818    
1819         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
1820         alternatives begin with one of the following:         alternatives begin with one of the following:
1821    
1822           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1614  INFORMATION ABOUT A PATTERN Line 1830  INFORMATION ABOUT A PATTERN
1830    
1831           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1832    
1833         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
1834         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
1835         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
1836         size_t variable.         size_t variable.
# Line 1622  INFORMATION ABOUT A PATTERN Line 1838  INFORMATION ABOUT A PATTERN
1838           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1839    
1840         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
1841         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
1842         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
1843         created by pcre_study(). The fourth argument should point to  a  size_t         created  by  pcre_study().  If pcre_extra is NULL, or there is no study
1844           data, zero is returned. The fourth argument should point  to  a  size_t
1845         variable.         variable.
1846    
1847    
# Line 1678  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1895  MATCHING A PATTERN: THE TRADITIONAL FUNC
1895              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1896              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1897    
1898         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
1899         compiled pattern, which is passed in the code argument. If the  pattern         compiled  pattern, which is passed in the code argument. If the pattern
1900         has been studied, the result of the study should be passed in the extra         was studied, the result of the study should  be  passed  in  the  extra
1901         argument. This function is the main matching facility of  the  library,         argument.  This  function is the main matching facility of the library,
1902         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
1903         an alternative matching function, which is described below in the  sec-         an  alternative matching function, which is described below in the sec-
1904         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1905    
1906         In  most applications, the pattern will have been compiled (and option-         In most applications, the pattern will have been compiled (and  option-
1907         ally studied) in the same process that calls pcre_exec().  However,  it         ally  studied)  in the same process that calls pcre_exec(). However, it
1908         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
1909         later in different processes, possibly even on different hosts.  For  a         later  in  different processes, possibly even on different hosts. For a
1910         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1911    
1912         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1708  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1925  MATCHING A PATTERN: THE TRADITIONAL FUNC
1925    
1926     Extra data for pcre_exec()     Extra data for pcre_exec()
1927    
1928         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
1929         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
1930         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-
1931         tional information in it. The pcre_extra block contains  the  following         tional  information  in it. The pcre_extra block contains the following
1932         fields (not necessarily in this order):         fields (not necessarily in this order):
1933    
1934           unsigned long int flags;           unsigned long int flags;
# Line 1720  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1937  MATCHING A PATTERN: THE TRADITIONAL FUNC
1937           unsigned long int match_limit_recursion;           unsigned long int match_limit_recursion;
1938           void *callout_data;           void *callout_data;
1939           const unsigned char *tables;           const unsigned char *tables;
1940             unsigned char **mark;
1941    
1942         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
1943         are set. The flag bits are:         are set. The flag bits are:
1944    
1945           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
# Line 1729  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1947  MATCHING A PATTERN: THE TRADITIONAL FUNC
1947           PCRE_EXTRA_MATCH_LIMIT_RECURSION           PCRE_EXTRA_MATCH_LIMIT_RECURSION
1948           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1949           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1950             PCRE_EXTRA_MARK
1951    
1952         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
1953         the  pcre_extra  block  that is returned by pcre_study(), together with         the pcre_extra block that is returned by  pcre_study(),  together  with
1954         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
1955         add  to  the  block by setting the other fields and their corresponding         add to the block by setting the other fields  and  their  corresponding
1956         flag bits.         flag bits.
1957    
1958         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
1959         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
1960         match, but which have a very large number  of  possibilities  in  their         match,  but  which  have  a very large number of possibilities in their
1961         search  trees.  The  classic  example  is  the  use of nested unlimited         search trees. The classic example is a pattern that uses nested  unlim-
1962         repeats.         ited repeats.
1963    
1964         Internally, PCRE uses a function called match() which it calls  repeat-         Internally,  PCRE uses a function called match() which it calls repeat-
1965         edly  (sometimes  recursively). The limit set by match_limit is imposed         edly (sometimes recursively). The limit set by match_limit  is  imposed
1966         on the number of times this function is called during  a  match,  which         on  the  number  of times this function is called during a match, which
1967         has  the  effect  of  limiting the amount of backtracking that can take         has the effect of limiting the amount of  backtracking  that  can  take
1968         place. For patterns that are not anchored, the count restarts from zero         place. For patterns that are not anchored, the count restarts from zero
1969         for each position in the subject string.         for each position in the subject string.
1970    
1971         The  default  value  for  the  limit can be set when PCRE is built; the         The default value for the limit can be set  when  PCRE  is  built;  the
1972         default default is 10 million, which handles all but the  most  extreme         default  default  is 10 million, which handles all but the most extreme
1973         cases.  You  can  override  the  default by suppling pcre_exec() with a         cases. You can override the default  by  suppling  pcre_exec()  with  a
1974         pcre_extra    block    in    which    match_limit    is    set,     and         pcre_extra     block    in    which    match_limit    is    set,    and
1975         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
1976         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1977    
1978         The match_limit_recursion field is similar to match_limit, but  instead         The  match_limit_recursion field is similar to match_limit, but instead
1979         of limiting the total number of times that match() is called, it limits         of limiting the total number of times that match() is called, it limits
1980         the depth of recursion. The recursion depth is a  smaller  number  than         the  depth  of  recursion. The recursion depth is a smaller number than
1981         the  total number of calls, because not all calls to match() are recur-         the total number of calls, because not all calls to match() are  recur-
1982         sive.  This limit is of use only if it is set smaller than match_limit.         sive.  This limit is of use only if it is set smaller than match_limit.
1983    
1984         Limiting  the  recursion  depth  limits the amount of stack that can be         Limiting  the  recursion  depth  limits the amount of stack that can be
# Line 1773  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1992  MATCHING A PATTERN: THE TRADITIONAL FUNC
1992         PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the         PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1993         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1994    
1995         The pcre_callout field is used in conjunction with the  "callout"  fea-         The callout_data field is used in conjunction with the  "callout"  fea-
1996         ture, which is described in the pcrecallout documentation.         ture, and is described in the pcrecallout documentation.
1997    
1998         The  tables  field  is  used  to  pass  a  character  tables pointer to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1999         pcre_exec(); this overrides the value that is stored with the  compiled         pcre_exec(); this overrides the value that is stored with the  compiled
# Line 1787  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2006  MATCHING A PATTERN: THE TRADITIONAL FUNC
2006         address  when  pcre_exec() is called. See the pcreprecompile documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
2007         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
2008    
2009           If PCRE_EXTRA_MARK is set in the flags field, the mark  field  must  be
2010           set  to  point  to a char * variable. If the pattern contains any back-
2011           tracking control verbs such as (*MARK:NAME), and the execution ends  up
2012           with  a  name  to  pass back, a pointer to the name string (zero termi-
2013           nated) is placed in the variable pointed to  by  the  mark  field.  The
2014           names  are  within  the  compiled pattern; if you wish to retain such a
2015           name you must copy it before freeing the memory of a compiled  pattern.
2016           If  there  is no name to pass back, the variable pointed to by the mark
2017           field set to NULL. For details of the backtracking control  verbs,  see
2018           the section entitled "Backtracking control" in the pcrepattern documen-
2019           tation.
2020    
2021     Option bits for pcre_exec()     Option bits for pcre_exec()
2022    
2023         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.
2024         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
2025         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,   PCRE_NOTEOL,    PCRE_NOTEMPTY,    PCRE_NOTEMPTY_ATSTART,
2026         PCRE_PARTIAL.         PCRE_NO_START_OPTIMIZE,   PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,  and
2027           PCRE_PARTIAL_HARD.
2028    
2029           PCRE_ANCHORED           PCRE_ANCHORED
2030    
2031         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
2032         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
2033         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
2034         unachored at matching time.         unachored at matching time.
2035    
2036             PCRE_BSR_ANYCRLF
2037             PCRE_BSR_UNICODE
2038    
2039           These options (which are mutually exclusive) control what the \R escape
2040           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
2041           or  to  match  any Unicode newline sequence. These options override the
2042           choice that was made or defaulted when the pattern was compiled.
2043    
2044           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
2045           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
2046           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
# Line 1812  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2052  MATCHING A PATTERN: THE TRADITIONAL FUNC
2052         tion of pcre_compile()  above.  During  matching,  the  newline  choice         tion of pcre_compile()  above.  During  matching,  the  newline  choice
2053         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
2054         ters. It may also alter the way the match position is advanced after  a         ters. It may also alter the way the match position is advanced after  a
2055         match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,         match failure for an unanchored pattern.
2056         PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a  match  attempt  
2057         fails  when the current position is at a CRLF sequence, the match posi-         When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or PCRE_NEWLINE_ANY is
2058         tion is advanced by two characters instead of one, in other  words,  to         set, and a match attempt for an unanchored pattern fails when the  cur-
2059         after the CRLF.         rent  position  is  at  a  CRLF  sequence,  and the pattern contains no
2060           explicit matches for  CR  or  LF  characters,  the  match  position  is
2061           advanced by two characters instead of one, in other words, to after the
2062           CRLF.
2063    
2064           The above rule is a compromise that makes the most common cases work as
2065           expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL
2066           option is not set), it does not match the string "\r\nA" because, after
2067           failing  at the start, it skips both the CR and the LF before retrying.
2068           However, the pattern [\r\n]A does match that string,  because  it  con-
2069           tains an explicit CR or LF reference, and so advances only by one char-
2070           acter after the first failure.
2071    
2072           An explicit match for CR of LF is either a literal appearance of one of
2073           those  characters,  or  one  of the \r or \n escape sequences. Implicit
2074           matches such as [^X] do not count, nor does \s (which includes  CR  and
2075           LF in the characters that it matches).
2076    
2077           Notwithstanding  the above, anomalous effects may still occur when CRLF
2078           is a valid newline sequence and explicit \r or \n escapes appear in the
2079           pattern.
2080    
2081           PCRE_NOTBOL           PCRE_NOTBOL
2082    
# Line 1844  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2104  MATCHING A PATTERN: THE TRADITIONAL FUNC
2104    
2105           a?b?           a?b?
2106    
2107         is  applied  to  a string not beginning with "a" or "b", it matches the         is  applied  to  a  string not beginning with "a" or "b", it matches an
2108         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
2109         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
2110         rences of "a" or "b".         rences of "a" or "b".
2111    
2112         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-           PCRE_NOTEMPTY_ATSTART
2113         cial  case  of  a  pattern match of the empty string within its split()  
2114         function, and when using the /g modifier. It  is  possible  to  emulate         This is like PCRE_NOTEMPTY, except that an empty string match  that  is
2115         Perl's behaviour after matching a null string by first trying the match         not  at  the  start  of  the  subject  is  permitted. If the pattern is
2116         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         anchored, such a match can occur only if the pattern contains \K.
2117         if  that  fails by advancing the starting offset (see below) and trying  
2118         an ordinary match again. There is some code that demonstrates how to do         Perl    has    no    direct    equivalent    of    PCRE_NOTEMPTY     or
2119         this in the pcredemo.c sample program.         PCRE_NOTEMPTY_ATSTART,  but  it  does  make a special case of a pattern
2120           match of the empty string within its split() function, and  when  using
2121           the  /g  modifier.  It  is  possible  to emulate Perl's behaviour after
2122           matching a null string by first trying the match again at the same off-
2123           set  with  PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED,  and then if that
2124           fails, by advancing the starting offset (see below) and trying an ordi-
2125           nary  match  again. There is some code that demonstrates how to do this
2126           in the pcredemo sample program.
2127    
2128             PCRE_NO_START_OPTIMIZE
2129    
2130           There are a number of optimizations that pcre_exec() uses at the  start
2131           of  a  match,  in  order to speed up the process. For example, if it is
2132           known that an unanchored match must start with a specific character, it
2133           searches  the  subject  for that character, and fails immediately if it
2134           cannot find it, without actually running the  main  matching  function.
2135           This means that a special item such as (*COMMIT) at the start of a pat-
2136           tern is not considered until after a suitable starting  point  for  the
2137           match  has been found. When callouts or (*MARK) items are in use, these
2138           "start-up" optimizations can cause them to be skipped if the pattern is
2139           never  actually  used.  The start-up optimizations are in effect a pre-
2140           scan of the subject that takes place before the pattern is run.
2141    
2142           The PCRE_NO_START_OPTIMIZE option disables the start-up  optimizations,
2143           possibly  causing  performance  to  suffer,  but ensuring that in cases
2144           where the result is "no match", the callouts do occur, and  that  items
2145           such as (*COMMIT) and (*MARK) are considered at every possible starting
2146           position in the subject  string.   Setting  PCRE_NO_START_OPTIMIZE  can
2147           change the outcome of a matching operation.  Consider the pattern
2148    
2149             (*COMMIT)ABC
2150    
2151           When  this  is  compiled, PCRE records the fact that a match must start
2152           with the character "A". Suppose the subject  string  is  "DEFABC".  The
2153           start-up  optimization  scans along the subject, finds "A" and runs the
2154           first match attempt from there. The (*COMMIT) item means that the  pat-
2155           tern  must  match the current starting position, which in this case, it
2156           does. However, if the same match  is  run  with  PCRE_NO_START_OPTIMIZE
2157           set,  the  initial  scan  along the subject string does not happen. The
2158           first match attempt is run starting  from  "D"  and  when  this  fails,
2159           (*COMMIT)  prevents  any  further  matches  being tried, so the overall
2160           result is "no match". If the pattern is studied,  more  start-up  opti-
2161           mizations  may  be  used. For example, a minimum length for the subject
2162           may be recorded. Consider the pattern
2163    
2164             (*MARK:A)(X|Y)
2165    
2166           The minimum length for a match is one  character.  If  the  subject  is
2167           "ABC",  there  will  be  attempts  to  match "ABC", "BC", "C", and then
2168           finally an empty string.  If the pattern is studied, the final  attempt
2169           does  not take place, because PCRE knows that the subject is too short,
2170           and so the (*MARK) is never encountered.  In this  case,  studying  the
2171           pattern  does  not  affect the overall match result, which is still "no
2172           match", but it does affect the auxiliary information that is returned.
2173    
2174           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2175    
2176         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
2177         UTF-8 string is automatically checked when pcre_exec() is  subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
2178         called.   The  value  of  startoffset is also checked to ensure that it         called.  The value of startoffset is also checked  to  ensure  that  it
2179         points to the start of a UTF-8 character. There is a  discussion  about         points  to  the start of a UTF-8 character. There is a discussion about
2180         the  validity  of  UTF-8 strings in the section on UTF-8 support in the         the validity of UTF-8 strings in the section on UTF-8  support  in  the
2181         main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2182         pcre_exec()  returns  the error PCRE_ERROR_BADUTF8. If startoffset con-         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2183         tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.         tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2184    
2185         If you already know that your subject is valid, and you  want  to  skip         If  you  already  know that your subject is valid, and you want to skip
2186         these    checks    for   performance   reasons,   you   can   set   the         these   checks   for   performance   reasons,   you   can    set    the
2187         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
2188         do  this  for the second and subsequent calls to pcre_exec() if you are         do this for the second and subsequent calls to pcre_exec() if  you  are
2189         making repeated calls to find all  the  matches  in  a  single  subject         making  repeated  calls  to  find  all  the matches in a single subject
2190         string.  However,  you  should  be  sure  that the value of startoffset         string. However, you should be  sure  that  the  value  of  startoffset
2191         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
2192         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         set, the effect of passing an invalid UTF-8 string as a subject,  or  a
2193         value of startoffset that does not point to the start of a UTF-8  char-         value  of startoffset that does not point to the start of a UTF-8 char-
2194         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
2195    
2196           PCRE_PARTIAL           PCRE_PARTIAL_HARD
2197             PCRE_PARTIAL_SOFT
2198    
2199         This  option  turns  on  the  partial  matching feature. If the subject         These options turn on the partial matching feature. For backwards  com-
2200         string fails to match the pattern, but at some point during the  match-         patibility,  PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
2201         ing  process  the  end of the subject was reached (that is, the subject         match occurs if the end of the subject string is reached  successfully,
2202         partially matches the pattern and the failure to  match  occurred  only         but  there  are not enough subject characters to complete the match. If
2203         because  there were not enough subject characters), pcre_exec() returns         this happens when PCRE_PARTIAL_HARD  is  set,  pcre_exec()  immediately
2204         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         returns  PCRE_ERROR_PARTIAL.  Otherwise,  if  PCRE_PARTIAL_SOFT is set,
2205         used,  there  are restrictions on what may appear in the pattern. These         matching continues by testing any other alternatives. Only if they  all
2206         are discussed in the pcrepartial documentation.         fail  is  PCRE_ERROR_PARTIAL  returned (instead of PCRE_ERROR_NOMATCH).
2207           The portion of the string that was inspected when the partial match was
2208           found  is  set  as  the first matching string. There is a more detailed
2209           discussion in the pcrepartial documentation.
2210    
2211     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2212    
2213         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
2214         length  in  length, and a starting byte offset in startoffset. In UTF-8         length (in bytes) in length, and a starting byte offset in startoffset.
2215         mode, the byte offset must point to the start  of  a  UTF-8  character.         In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-
2216         Unlike  the  pattern string, the subject may contain binary zero bytes.         acter.  Unlike  the pattern string, the subject may contain binary zero
2217         When the starting offset is zero, the search for a match starts at  the         bytes. When the starting offset is zero, the search for a match  starts
2218         beginning of the subject, and this is by far the most common case.         at  the  beginning  of  the subject, and this is by far the most common
2219           case.
2220         A  non-zero  starting offset is useful when searching for another match  
2221         in the same subject by calling pcre_exec() again after a previous  suc-         A non-zero starting offset is useful when searching for  another  match
2222         cess.   Setting  startoffset differs from just passing over a shortened         in  the same subject by calling pcre_exec() again after a previous suc-
2223         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         cess.  Setting startoffset differs from just passing over  a  shortened
2224           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2225         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2226    
2227           \Biss\B           \Biss\B
2228    
2229         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
2230         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.)
2231         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
2232         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
2233         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
2234         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
2235         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
2236         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-
2237         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
2238         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2239    
2240         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,
2241         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
2242         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
2243         subject.         subject.
2244    
2245     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2246    
2247         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
2248         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2249         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2250         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2251         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-
2252         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2253         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2254    
2255         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of integers
2256         offsets whose address is passed in ovector. The number of  elements  in         whose  address is passed in ovector. The number of elements in the vec-
2257         the  vector is passed in ovecsize, which must be a non-negative number.         tor is passed in ovecsize, which must be a non-negative  number.  Note:
2258         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2259    
2260         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-
2261         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2262         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-
2263         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2264         The length passed in ovecsize should always be a multiple of three.  If         The  number passed in ovecsize should always be a multiple of three. If
2265         it is not, it is rounded down.         it is not, it is rounded down.
2266    
2267         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2268         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2269         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
2270         element of a pair is set to the offset of the first character in a sub-         element  of  each pair is set to the byte offset of the first character
2271         string,  and  the  second  is  set to the offset of the first character         in a substring, and the second is set to the byte offset of  the  first
2272         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-         character  after  the end of a substring. Note: these values are always
2273         tor[1],  identify  the  portion  of  the  subject string matched by the         byte offsets, even in UTF-8 mode. They are not character counts.
2274         entire pattern. The next pair is used for the first  capturing  subpat-  
2275         tern, and so on. The value returned by pcre_exec() is one more than the         The first pair of integers, ovector[0]  and  ovector[1],  identify  the
2276         highest numbered pair that has been set. For example, if two substrings         portion  of  the subject string matched by the entire pattern. The next
2277         have  been captured, the returned value is 3. If there are no capturing         pair is used for the first capturing subpattern, and so on.  The  value
2278         subpatterns, the return value from a successful match is 1,  indicating         returned by pcre_exec() is one more than the highest numbered pair that
2279         that just the first pair of offsets has been set.         has been set.  For example, if two substrings have been  captured,  the
2280           returned  value is 3. If there are no capturing subpatterns, the return
2281           value from a successful match is 1, indicating that just the first pair
2282           of offsets has been set.
2283    
2284         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2285         of the string that it matched that is returned.         of the string that it matched that is returned.
2286    
2287         If the vector is too small to hold all the captured substring  offsets,         If the vector is too small to hold all the captured substring  offsets,
2288         it is used as far as possible (up to two-thirds of its length), and the         it is used as far as possible (up to two-thirds of its length), and the
2289         function returns a value of zero. In particular, if the substring  off-         function returns a value of zero. If the substring offsets are  not  of
2290         sets are not of interest, pcre_exec() may be called with ovector passed         interest,  pcre_exec()  may  be  called with ovector passed as NULL and
2291         as NULL and ovecsize as zero. However, if  the  pattern  contains  back         ovecsize as zero. However, if the pattern contains back references  and
2292         references  and  the  ovector is not big enough to remember the related         the  ovector is not big enough to remember the related substrings, PCRE
2293         substrings, PCRE has to get additional memory for use during  matching.         has to get additional memory for use during matching. Thus it  is  usu-
2294         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2295    
2296         The  pcre_info()  function  can  be used to find out how many capturing         The pcre_fullinfo() function can be used to find out how many capturing
2297         subpatterns there are in a compiled  pattern.  The  smallest  size  for         subpatterns there are in a compiled  pattern.  The  smallest  size  for
2298         ovector  that  will allow for n captured substrings, in addition to the         ovector  that  will allow for n captured substrings, in addition to the
2299         offsets of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
# Line 2035  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2356  MATCHING A PATTERN: THE TRADITIONAL FUNC
2356         purpose.  If the call via pcre_malloc() fails, this error is given. The         purpose.  If the call via pcre_malloc() fails, this error is given. The
2357         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2358    
2359           This error is also given if pcre_stack_malloc() fails  in  pcre_exec().
2360           This  can happen only when PCRE has been compiled with --disable-stack-
2361           for-recursion.
2362    
2363           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2364    
2365         This error is used by the pcre_copy_substring(),  pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
# Line 2071  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2396  MATCHING A PATTERN: THE TRADITIONAL FUNC
2396    
2397           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2398    
2399         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         This code is no longer in  use.  It  was  formerly  returned  when  the
2400         items  that are not supported for partial matching. See the pcrepartial         PCRE_PARTIAL  option  was used with a compiled pattern containing items
2401         documentation for details of partial matching.         that were  not  supported  for  partial  matching.  From  release  8.00
2402           onwards, there are no restrictions on partial matching.
2403    
2404           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2405    
2406         An unexpected internal error has occurred. This error could  be  caused         An  unexpected  internal error has occurred. This error could be caused
2407         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2408    
2409           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2410    
2411         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.
2412    
2413           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2414    
# Line 2232  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2558  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2558         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2559         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2560    
2561           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2562           terns  with  the  same number, as described in the section on duplicate
2563           subpattern numbers in the pcrepattern page, you  cannot  use  names  to
2564           distinguish  the  different subpatterns, because names are not included
2565           in the compiled code. The matching process uses only numbers. For  this
2566           reason,  the  use of different names for subpatterns of the same number
2567           causes an error at compile time.
2568    
2569    
2570  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
2571    
# Line 2239  DUPLICATE SUBPATTERN NAMES Line 2573  DUPLICATE SUBPATTERN NAMES
2573              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2574    
2575         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2576         subpatterns  are  not  required  to  be unique. Normally, patterns with         subpatterns  are not required to be unique. (Duplicate names are always
2577         duplicate names are such that in any one match, only one of  the  named         allowed for subpatterns with the same number, created by using the  (?|
2578         subpatterns  participates. An example is shown in the pcrepattern docu-         feature.  Indeed,  if  such subpatterns are named, they are required to
2579         mentation.         use the same names.)
2580    
2581           Normally, patterns with duplicate names are such that in any one match,
2582           only  one of the named subpatterns participates. An example is shown in
2583           the pcrepattern documentation.
2584    
2585         When   duplicates   are   present,   pcre_copy_named_substring()    and         When   duplicates   are   present,   pcre_copy_named_substring()    and
2586         pcre_get_named_substring()  return the first substring corresponding to         pcre_get_named_substring()  return the first substring corresponding to
# Line 2295  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2633  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2633         characteristics  to  the  normal  algorithm, and is not compatible with         characteristics  to  the  normal  algorithm, and is not compatible with
2634         Perl. Some of the features of PCRE patterns are not  supported.  Never-         Perl. Some of the features of PCRE patterns are not  supported.  Never-
2635         theless,  there are times when this kind of matching can be useful. For         theless,  there are times when this kind of matching can be useful. For
2636         a discussion of the two matching algorithms, see the pcrematching docu-         a discussion of the two matching algorithms, and  a  list  of  features
2637         mentation.         that  pcre_dfa_exec() does not support, see the pcrematching documenta-
2638           tion.
2639    
2640         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
2641         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-
2642         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2643         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
2644         repeated here.         repeated here.
2645    
2646         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2647         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2648         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2649         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2650         lot of potential matches.         lot of potential matches.
2651    
2652         Here is an example of a simple call to pcre_dfa_exec():         Here is an example of a simple call to pcre_dfa_exec():
# Line 2329  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2668  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2668    
2669     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2670    
2671         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
2672         zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-         zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2673         LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2674         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last         PCRE_NOTEMPTY_ATSTART,       PCRE_NO_UTF8_CHECK,      PCRE_BSR_ANYCRLF,
2675         three of these are the same as for pcre_exec(), so their description is         PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD,  PCRE_PAR-
2676         not repeated here.         TIAL_SOFT,  PCRE_DFA_SHORTEST,  and PCRE_DFA_RESTART.  All but the last
2677           four of these are  exactly  the  same  as  for  pcre_exec(),  so  their
2678           PCRE_PARTIAL         description is not repeated here.
2679    
2680         This has the same general effect as it does for  pcre_exec(),  but  the           PCRE_PARTIAL_HARD
2681         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for           PCRE_PARTIAL_SOFT
2682         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into  
2683         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have         These  have the same general effect as they do for pcre_exec(), but the
2684         been no complete matches, but there is still at least one matching pos-         details are slightly  different.  When  PCRE_PARTIAL_HARD  is  set  for
2685         sibility.  The portion of the string that provided the partial match is         pcre_dfa_exec(),  it  returns PCRE_ERROR_PARTIAL if the end of the sub-
2686         set as the first matching string.         ject is reached and there is still at least  one  matching  possibility
2687           that requires additional characters. This happens even if some complete
2688           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2689           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2690           of the subject is reached, there have been  no  complete  matches,  but
2691           there  is  still  at least one matching possibility. The portion of the
2692           string that was inspected when the longest partial match was  found  is
2693           set as the first matching string in both cases.
2694    
2695           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2696    
2697         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2698         stop as soon as it has found one match. Because of the way the alterna-         stop as soon as it has found one match. Because of the way the alterna-
2699         tive algorithm works, this is necessarily the shortest  possible  match         tive  algorithm  works, this is necessarily the shortest possible match
2700         at the first possible matching point in the subject string.         at the first possible matching point in the subject string.
2701    
2702           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2703    
2704         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec() returns a partial match, it is possible to call it
2705         returns a partial match, it is possible to call it  again,  with  addi-         again,  with  additional  subject characters, and have it continue with
2706         tional  subject  characters,  and have it continue with the same match.         the same match. The PCRE_DFA_RESTART option requests this action;  when
2707         The PCRE_DFA_RESTART option requests this action; when it is  set,  the         it  is  set,  the workspace and wscount options must reference the same
2708         workspace  and wscount options must reference the same vector as before         vector as before because data about the match so far is  left  in  them
2709         because data about the match so far is left in  them  after  a  partial         after a partial match. There is more discussion of this facility in the
2710         match.  There  is  more  discussion of this facility in the pcrepartial         pcrepartial documentation.
        documentation.  
2711    
2712     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2713    
# Line 2439  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2784  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2784  SEE ALSO  SEE ALSO
2785    
2786         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2787         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2788    
2789    
2790  AUTHOR  AUTHOR
# Line 2451  AUTHOR Line 2796  AUTHOR
2796    
2797  REVISION  REVISION
2798    
2799         Last updated: 09 August 2007         Last updated: 21 June 2010
2800         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
2801  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2802    
2803    
# Line 2481  PCRE CALLOUTS Line 2826  PCRE CALLOUTS
2826    
2827           (?C1)abc(?C2)def           (?C1)abc(?C2)def
2828    
2829         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() or
2830         called, PCRE automatically  inserts  callouts,  all  with  number  255,         pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
2831         before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is         with  number  255,  before  each  item  in the pattern. For example, if
2832         used with the pattern         PCRE_AUTO_CALLOUT is used with the pattern
2833    
2834           A(\d{2}|--)           A(\d{2}|--)
2835    
# Line 2503  PCRE CALLOUTS Line 2848  PCRE CALLOUTS
2848  MISSING CALLOUTS  MISSING CALLOUTS
2849    
2850         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
2851         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
2852         pattern is         example, if the pattern is
2853    
2854           ab(?C4)cd           ab(?C4)cd
2855    
# Line 2513  MISSING CALLOUTS Line 2858  MISSING CALLOUTS
2858         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2859         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2860    
2861           If the pattern is studied, PCRE knows the minimum length of a  matching
2862           string,  and will immediately give a "no match" return without actually
2863           running a match if the subject is not long enough, or,  for  unanchored
2864           patterns, if it has been scanned far enough.
2865    
2866           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
2867           MIZE option to pcre_exec() or  pcre_dfa_exec().  This  slows  down  the
2868           matching  process,  but  does  ensure that callouts such as the example
2869           above are obeyed.
2870    
2871    
2872  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2873    
# Line 2540  THE CALLOUT INTERFACE Line 2895  THE CALLOUT INTERFACE
2895         version number will change again in future  if  additional  fields  are         version number will change again in future  if  additional  fields  are
2896         added, but the intention is never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2897    
2898         The callout_number field contains the number of the  callout,  as  com-         The  callout_number  field  contains the number of the callout, as com-
2899         piled  into  the pattern (that is, the number after ?C for manual call-         piled into the pattern (that is, the number after ?C for  manual  call-
2900         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2901    
2902         The offset_vector field is a pointer to the vector of offsets that  was         The  offset_vector field is a pointer to the vector of offsets that was
2903         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When         passed  by  the  caller  to  pcre_exec()   or   pcre_dfa_exec().   When
2904         pcre_exec() is used, the contents can be inspected in order to  extract         pcre_exec()  is used, the contents can be inspected in order to extract
2905         substrings  that  have  been  matched  so  far,  in the same way as for         substrings that have been matched so  far,  in  the  same  way  as  for
2906         extracting substrings after a match has completed. For  pcre_dfa_exec()         extracting  substrings after a match has completed. For pcre_dfa_exec()
2907         this field is not useful.         this field is not useful.
2908    
2909         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2910         were passed to pcre_exec().         were passed to pcre_exec().
2911    
2912         The start_match field normally contains the offset within  the  subject         The  start_match  field normally contains the offset within the subject
2913         at  which  the  current  match  attempt started. However, if the escape         at which the current match attempt  started.  However,  if  the  escape
2914         sequence \K has been encountered, this value is changed to reflect  the         sequence  \K has been encountered, this value is changed to reflect the
2915         modified  starting  point.  If the pattern is not anchored, the callout         modified starting point. If the pattern is not  anchored,  the  callout
2916         function may be called several times from the same point in the pattern         function may be called several times from the same point in the pattern
2917         for different starting points in the subject.         for different starting points in the subject.
2918    
2919         The  current_position  field  contains the offset within the subject of         The current_position field contains the offset within  the  subject  of
2920         the current match pointer.         the current match pointer.
2921    
2922         When the pcre_exec() function is used, the capture_top  field  contains         When  the  pcre_exec() function is used, the capture_top field contains
2923         one  more than the number of the highest numbered captured substring so         one more than the number of the highest numbered captured substring  so
2924         far. If no substrings have been captured, the value of  capture_top  is         far.  If  no substrings have been captured, the value of capture_top is
2925         one.  This  is always the case when pcre_dfa_exec() is used, because it         one. This is always the case when pcre_dfa_exec() is used,  because  it
2926         does not support captured substrings.         does not support captured substrings.
2927    
2928         The capture_last field contains the number of the  most  recently  cap-         The  capture_last  field  contains the number of the most recently cap-
2929         tured  substring. If no substrings have been captured, its value is -1.         tured substring. If no substrings have been captured, its value is  -1.
2930         This is always the case when pcre_dfa_exec() is used.         This is always the case when pcre_dfa_exec() is used.
2931    
2932         The callout_data field contains a value that is passed  to  pcre_exec()         The  callout_data  field contains a value that is passed to pcre_exec()
2933         or  pcre_dfa_exec() specifically so that it can be passed back in call-         or pcre_dfa_exec() specifically so that it can be passed back in  call-
2934         outs. It is passed in the pcre_callout field  of  the  pcre_extra  data         outs.  It  is  passed  in the pcre_callout field of the pcre_extra data
2935         structure.  If  no such data was passed, the value of callout_data in a         structure. If no such data was passed, the value of callout_data  in  a
2936         pcre_callout block is NULL. There is a description  of  the  pcre_extra         pcre_callout  block  is  NULL. There is a description of the pcre_extra
2937         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2938    
2939         The  pattern_position field is present from version 1 of the pcre_call-         The pattern_position field is present from version 1 of the  pcre_call-
2940         out structure. It contains the offset to the next item to be matched in         out structure. It contains the offset to the next item to be matched in
2941         the pattern string.         the pattern string.
2942    
2943         The  next_item_length field is present from version 1 of the pcre_call-         The next_item_length field is present from version 1 of the  pcre_call-
2944         out structure. It contains the length of the next item to be matched in         out structure. It contains the length of the next item to be matched in
2945         the  pattern  string. When the callout immediately precedes an alterna-         the pattern string. When the callout immediately precedes  an  alterna-
2946         tion bar, a closing parenthesis, or the end of the pattern, the  length         tion  bar, a closing parenthesis, or the end of the pattern, the length
2947         is  zero.  When the callout precedes an opening parenthesis, the length         is zero. When the callout precedes an opening parenthesis,  the  length
2948         is that of the entire subpattern.         is that of the entire subpattern.
2949    
2950         The pattern_position and next_item_length fields are intended  to  help         The  pattern_position  and next_item_length fields are intended to help
2951         in  distinguishing between different automatic callouts, which all have         in distinguishing between different automatic callouts, which all  have
2952         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
2953    
2954    
2955  RETURN VALUES  RETURN VALUES
2956    
2957         The external callout function returns an integer to PCRE. If the  value         The  external callout function returns an integer to PCRE. If the value
2958         is  zero,  matching  proceeds  as  normal. If the value is greater than         is zero, matching proceeds as normal. If  the  value  is  greater  than
2959         zero, matching fails at the current point, but  the  testing  of  other         zero,  matching  fails  at  the current point, but the testing of other
2960         matching possibilities goes ahead, just as if a lookahead assertion had         matching possibilities goes ahead, just as if a lookahead assertion had
2961         failed. If the value is less than zero, the  match  is  abandoned,  and         failed.  If  the  value  is less than zero, the match is abandoned, and
2962         pcre_exec() (or pcre_dfa_exec()) returns the negative value.         pcre_exec() or pcre_dfa_exec() returns the negative value.
2963    
2964         Negative   values   should   normally   be   chosen  from  the  set  of         Negative  values  should  normally  be   chosen   from   the   set   of
2965         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2966         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is
2967         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
2968         itself.         itself.
2969    
2970    
# Line 2622  AUTHOR Line 2977  AUTHOR
2977    
2978  REVISION  REVISION
2979    
2980         Last updated: 29 May 2007         Last updated: 29 September 2009
2981         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2982  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2983    
2984    
# Line 2637  NAME Line 2992  NAME
2992  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2993    
2994         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2995         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences  described  here  are  with
2996         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain         respect to Perl 5.10/5.11.
        some features that are expected to be in the forthcoming Perl 5.10.  
2997    
2998         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details         1.  PCRE has only a subset of Perl's UTF-8 and Unicode support. Details
2999         of  what  it does have are given in the section on UTF-8 support in the         of what it does have are given in the section on UTF-8 support  in  the
3000         main pcre page.         main pcre page.
3001    
3002         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
3003         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,
3004         (?!a){3} does not assert that the next three characters are not "a". It         (?!a){3} does not assert that the next three characters are not "a". It
3005         just asserts that the next character is not "a" three times.         just asserts that the next character is not "a" three times.
3006    
3007         3.  Capturing  subpatterns  that occur inside negative lookahead asser-         3. Capturing subpatterns that occur inside  negative  lookahead  asser-
3008         tions are counted, but their entries in the offsets  vector  are  never         tions  are  counted,  but their entries in the offsets vector are never
3009         set.  Perl sets its numerical variables from any such patterns that are         set. Perl sets its numerical variables from any such patterns that  are
3010         matched before the assertion fails to match something (thereby succeed-         matched before the assertion fails to match something (thereby succeed-
3011         ing),  but  only  if the negative lookahead assertion contains just one         ing), but only if the negative lookahead assertion  contains  just  one
3012         branch.         branch.
3013    
3014         4. Though binary zero characters are supported in the  subject  string,         4.  Though  binary zero characters are supported in the subject string,
3015         they are not allowed in a pattern string because it is passed as a nor-         they are not allowed in a pattern string because it is passed as a nor-
3016         mal C string, terminated by zero. The escape sequence \0 can be used in         mal C string, terminated by zero. The escape sequence \0 can be used in
3017         the pattern to represent a binary zero.         the pattern to represent a binary zero.
3018    
3019         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5. The following Perl escape sequences are not supported: \l,  \u,  \L,
3020         \U, and \N. In fact these are implemented by Perl's general string-han-         \U, and \N. In fact these are implemented by Perl's general string-han-
3021         dling  and are not part of its pattern matching engine. If any of these         dling and are not part of its pattern matching engine. If any of  these
3022         are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
3023    
3024         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
3025         is  built  with Unicode character property support. The properties that         is built with Unicode character property support. The  properties  that
3026         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-
3027         erties  such  as  Lu and Nd, script names such as Greek or Han, and the         erties such as Lu and Nd, script names such as Greek or  Han,  and  the
3028         derived properties Any and L&.         derived  properties  Any  and  L&. PCRE does support the Cs (surrogate)
3029           property, which Perl does not; the  Perl  documentation  says  "Because
3030           Perl hides the need for the user to understand the internal representa-
3031           tion of Unicode characters, there is no need to implement the  somewhat
3032           messy concept of surrogates."
3033    
3034         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
3035         ters  in  between  are  treated as literals. This is slightly different         ters in between are treated as literals.  This  is  slightly  different
3036         from Perl in that $ and @ are  also  handled  as  literals  inside  the         from  Perl  in  that  $  and  @ are also handled as literals inside the
3037         quotes.  In Perl, they cause variable interpolation (but of course PCRE         quotes. In Perl, they cause variable interpolation (but of course  PCRE
3038         does not have variables). Note the following examples:         does not have variables). Note the following examples:
3039    
3040             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2686  DIFFERENCES BETWEEN PCRE AND PERL Line 3044  DIFFERENCES BETWEEN PCRE AND PERL
3044             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
3045             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
3046    
3047         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3048         classes.         classes.
3049    
3050         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
3051         constructions. However, there is support for recursive  patterns.  This         constructions.  However,  there is support for recursive patterns. This
3052         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE         is not available in Perl 5.8, but it is in Perl 5.10.  Also,  the  PCRE
3053         "callout" feature allows an external function to be called during  pat-         "callout"  feature allows an external function to be called during pat-
3054         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
3055    
3056         9.  Subpatterns  that  are  called  recursively or as "subroutines" are         9. Subpatterns that are called  recursively  or  as  "subroutines"  are
3057         always treated as atomic groups in  PCRE.  This  is  like  Python,  but         always  treated  as  atomic  groups  in  PCRE. This is like Python, but
3058         unlike Perl.         unlike Perl. There is a discussion of an example that explains this  in
3059           more  detail  in  the section on recursion differences from Perl in the
3060         10.  There are some differences that are concerned with the settings of         pcrepattern page.
3061         captured strings when part of  a  pattern  is  repeated.  For  example,  
3062         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         10. There are some differences that are concerned with the settings  of
3063           captured  strings  when  part  of  a  pattern is repeated. For example,
3064           matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
3065         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
3066    
3067         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),         11.  PCRE's handling of duplicate subpattern numbers and duplicate sub-
3068         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in         pattern names is not as general as Perl's. This is a consequence of the
3069         the forms without an  argument.  PCRE  does  not  support  (*MARK).  If         fact the PCRE works internally just with numbers, using an external ta-
3070         (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-         ble to translate between numbers and names. In  particular,  a  pattern
3071         ture group; this is different to Perl.         such  as  (?|(?<a>A)|(?<b)B),  where the two capturing parentheses have
3072           the same number but different names, is not supported,  and  causes  an
3073           error  at compile time. If it were allowed, it would not be possible to
3074           distinguish which parentheses matched, because both names map  to  cap-
3075           turing subpattern number 1. To avoid this confusing situation, an error
3076           is given at compile time.
3077    
3078         12. PCRE provides some extensions to the Perl regular expression facil-         12. PCRE provides some extensions to the Perl regular expression facil-
3079         ities.   Perl  5.10  will  include new features that are not in earlier         ities.   Perl  5.10  includes new features that are not in earlier ver-
3080         versions, some of which (such as named parentheses) have been  in  PCRE         sions of Perl, some of which (such as named parentheses) have  been  in
3081         for some time. This list is with respect to Perl 5.10:         PCRE for some time. This list is with respect to Perl 5.10:
3082    
3083         (a)  Although  lookbehind  assertions  must match fixed length strings,         (a)  Although  lookbehind  assertions  in  PCRE must match fixed length
3084         each alternative branch of a lookbehind assertion can match a different         strings, each alternative branch of a lookbehind assertion can match  a
3085         length of string. Perl requires them all to have the same length.         different  length  of  string.  Perl requires them all to have the same
3086           length.
3087    
3088         (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  $
3089         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
3090    
3091         (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-
3092         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
3093         ignored.  (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
3094    
3095         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-
3096         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-
3097         lowed by a question mark they are.         lowed by a question mark they are.
3098    
3099         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
3100         tried only at the first matching position in the subject string.         tried only at the first matching position in the subject string.
3101    
3102         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3103         TURE options for pcre_exec() have no Perl equivalents.         and  PCRE_NO_AUTO_CAPTURE  options for pcre_exec() have no Perl equiva-
3104           lents.
3105    
3106         (g) The callout facility is PCRE-specific.         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
3107           CRLF by the PCRE_BSR_ANYCRLF option.
3108    
3109         (h) The partial matching facility is PCRE-specific.         (h) The callout facility is PCRE-specific.
3110    
3111         (i) Patterns compiled by PCRE can be saved and re-used at a later time,         (i) The partial matching facility is PCRE-specific.
3112    
3113           (j) Patterns compiled by PCRE can be saved and re-used at a later time,
3114         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
3115    
3116         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
3117         different way and is not Perl-compatible.         different way and is not Perl-compatible.
3118    
3119           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
3120           of a pattern that set overall options that cannot be changed within the
3121           pattern.
3122    
3123    
3124  AUTHOR  AUTHOR
3125    
# Line 2756  AUTHOR Line 3130  AUTHOR
3130    
3131  REVISION  REVISION
3132    
3133         Last updated: 08 August 2007         Last updated: 12 May 2010
3134         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
3135  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3136    
3137    
# Line 2772  PCRE REGULAR EXPRESSION DETAILS Line 3146  PCRE REGULAR EXPRESSION DETAILS
3146    
3147         The  syntax and semantics of the regular expressions that are supported         The  syntax and semantics of the regular expressions that are supported
3148         by PCRE are described in detail below. There is a quick-reference  syn-         by PCRE are described in detail below. There is a quick-reference  syn-
3149         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are         tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
3150         described in its own documentation, and regular expressions in  general         semantics as closely as it can. PCRE  also  supports  some  alternative
3151         are  covered in a number of books, some of which have copious examples.         regular  expression  syntax (which does not conflict with the Perl syn-
3152         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by         tax) in order to provide some compatibility with regular expressions in
3153         O'Reilly,  covers regular expressions in great detail. This description         Python, .NET, and Oniguruma.
3154         of PCRE's regular expressions is intended as reference material.  
3155           Perl's  regular expressions are described in its own documentation, and
3156           regular expressions in general are covered in a number of  books,  some
3157           of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
3158           Expressions", published by  O'Reilly,  covers  regular  expressions  in
3159           great  detail.  This  description  of  PCRE's  regular  expressions  is
3160           intended as reference material.
3161    
3162         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
3163         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
3164         this, you must build PCRE to  include  UTF-8  support,  and  then  call         this, PCRE must be built to include UTF-8 support, and  you  must  call
3165         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern         pcre_compile()  or  pcre_compile2() with the PCRE_UTF8 option. There is
3166         matching is mentioned in several places below. There is also a  summary         also a special sequence that can be given at the start of a pattern:
3167         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre  
3168         page.           (*UTF8)
3169    
3170           Starting a pattern with this sequence  is  equivalent  to  setting  the
3171           PCRE_UTF8  option.  This  feature  is  not Perl-compatible. How setting
3172           UTF-8 mode affects pattern matching  is  mentioned  in  several  places
3173           below.  There  is  also  a  summary of UTF-8 features in the section on
3174           UTF-8 support in the main pcre page.
3175    
3176           Another special sequence that may appear at the start of a  pattern  or
3177           in combination with (*UTF8) is:
3178    
3179             (*UCP)
3180    
3181           This  has  the  same  effect  as setting the PCRE_UCP option: it causes
3182           sequences such as \d and \w to  use  Unicode  properties  to  determine
3183           character types, instead of recognizing only characters with codes less
3184           than 128 via a lookup table.
3185    
3186         The remainder of this document discusses the  patterns  that  are  sup-         The remainder of this document discusses the  patterns  that  are  sup-
3187         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
# Line 2797  PCRE REGULAR EXPRESSION DETAILS Line 3193  PCRE REGULAR EXPRESSION DETAILS
3193         discussed in the pcrematching page.         discussed in the pcrematching page.
3194    
3195    
3196    NEWLINE CONVENTIONS
3197    
3198           PCRE  supports five different conventions for indicating line breaks in
3199           strings: a single CR (carriage return) character, a  single  LF  (line-
3200           feed) character, the two-character sequence CRLF, any of the three pre-
3201           ceding, or any Unicode newline sequence. The pcreapi page  has  further
3202           discussion  about newlines, and shows how to set the newline convention
3203           in the options arguments for the compiling and matching functions.
3204    
3205           It is also possible to specify a newline convention by starting a  pat-
3206           tern string with one of the following five sequences:
3207    
3208             (*CR)        carriage return
3209             (*LF)        linefeed
3210             (*CRLF)      carriage return, followed by linefeed
3211             (*ANYCRLF)   any of the three above
3212             (*ANY)       all Unicode newline sequences
3213    
3214           These  override  the default and the options given to pcre_compile() or
3215           pcre_compile2(). For example, on a Unix system where LF is the  default
3216           newline sequence, the pattern
3217    
3218             (*CR)a.b
3219    
3220           changes the convention to CR. That pattern matches "a\nb" because LF is
3221           no longer a newline. Note that these special settings,  which  are  not
3222           Perl-compatible,  are  recognized  only at the very start of a pattern,
3223           and that they must be in upper case.  If  more  than  one  of  them  is
3224           present, the last one is used.
3225    
3226           The  newline convention affects the interpretation of the dot metachar-
3227           acter when PCRE_DOTALL is not set, and also the behaviour of  \N.  How-
3228           ever,  it  does  not  affect  what  the  \R escape sequence matches. By
3229           default, this is any Unicode newline sequence, for Perl  compatibility.
3230           However,  this can be changed; see the description of \R in the section
3231           entitled "Newline sequences" below. A change of \R setting can be  com-
3232           bined with a change of newline convention.
3233    
3234    
3235  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
3236    
3237         A  regular  expression  is  a pattern that is matched against a subject         A  regular  expression  is  a pattern that is matched against a subject
# Line 2852  CHARACTERS AND METACHARACTERS Line 3287  CHARACTERS AND METACHARACTERS
3287                    syntax)                    syntax)
3288           ]      terminates the character class           ]      terminates the character class
3289    
3290         The  following sections describe the use of each of the metacharacters.         The following sections describe the use of each of the metacharacters.
3291    
3292    
3293  BACKSLASH  BACKSLASH
3294    
3295         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
3296         a  non-alphanumeric  character,  it takes away any special meaning that         a non-alphanumeric character, it takes away any  special  meaning  that
3297         character may have. This  use  of  backslash  as  an  escape  character         character  may  have.  This  use  of  backslash  as an escape character
3298         applies both inside and outside character classes.         applies both inside and outside character classes.
3299    
3300         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
3301         pattern.  This escaping action applies whether  or  not  the  following         pattern.   This  escaping  action  applies whether or not the following
3302         character  would  otherwise be interpreted as a metacharacter, so it is         character would otherwise be interpreted as a metacharacter, so  it  is
3303         always safe to precede a non-alphanumeric  with  backslash  to  specify         always  safe  to  precede  a non-alphanumeric with backslash to specify
3304         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-
3305         slash, you write \\.         slash, you write \\.
3306    
3307         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
3308         the  pattern (other than in a character class) and characters between a         the pattern (other than in a character class) and characters between  a
3309         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
3310         ing  backslash  can  be  used to include a whitespace or # character as         ing backslash can be used to include a whitespace  or  #  character  as
3311         part of the pattern.         part of the pattern.
3312    
3313         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-
3314         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-
3315         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
3316         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
3317         tion. Note the following examples:         tion. Note the following examples:
3318    
3319           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2888  BACKSLASH Line 3323  BACKSLASH
3323           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3324           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3325    
3326         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3327         classes.         classes.
3328    
3329     Non-printing characters     Non-printing characters
3330    
3331         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-
3332         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
3333         appearance  of non-printing characters, apart from the binary zero that         appearance of non-printing characters, apart from the binary zero  that
3334         terminates a pattern, but when a pattern  is  being  prepared  by  text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3335         editing,  it  is  usually  easier  to  use  one of the following escape         editing, it is  often  easier  to  use  one  of  the  following  escape
3336         sequences than the binary character it represents:         sequences than the binary character it represents:
3337    
3338           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3339           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3340           \e        escape (hex 1B)           \e        escape (hex 1B)
3341           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3342           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3343           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3344           \t        tab (hex 09)           \t        tab (hex 09)
3345           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or back reference
3346           \xhh      character with hex code hh           \xhh      character with hex code hh
3347           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3348    
3349         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,
3350         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
3351         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;
3352         becomes hex 7B.         becomes hex 7B.
3353    
3354         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
3355         in upper or lower case). Any number of hexadecimal  digits  may  appear         in  upper  or  lower case). Any number of hexadecimal digits may appear
3356         between  \x{  and  },  but the value of the character code must be less         between \x{ and }, but the value of the character  code  must  be  less
3357         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3358         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3359         than the largest Unicode code point, which is 10FFFF.         than the largest Unicode code point, which is 10FFFF.
3360    
3361         If characters other than hexadecimal digits appear between \x{  and  },         If  characters  other than hexadecimal digits appear between \x{ and },
3362         or if there is no terminating }, this form of escape is not recognized.         or if there is no terminating }, this form of escape is not recognized.
3363         Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal         Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3364         escape,  with  no  following  digits, giving a character whose value is         escape, with no following digits, giving a  character  whose  value  is
3365         zero.         zero.
3366    
3367         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
3368         two  syntaxes  for  \x. There is no difference in the way they are han-         two syntaxes for \x. There is no difference in the way  they  are  han-
3369         dled. For example, \xdc is exactly the same as \x{dc}.         dled. For example, \xdc is exactly the same as \x{dc}.
3370    
3371         After \0 up to two further octal digits are read. If  there  are  fewer         After  \0  up  to two further octal digits are read. If there are fewer
3372         than  two  digits,  just  those  that  are  present  are used. Thus the         than two digits, just  those  that  are  present  are  used.  Thus  the
3373         sequence \0\x\07 specifies two binary zeros followed by a BEL character         sequence \0\x\07 specifies two binary zeros followed by a BEL character
3374         (code  value 7). Make sure you supply two digits after the initial zero         (code value 7). Make sure you supply two digits after the initial  zero
3375         if the pattern character that follows is itself an octal digit.         if the pattern character that follows is itself an octal digit.
3376    
3377         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-
3378         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3379         its as a decimal number. If the number is less than  10,  or  if  there         its  as  a  decimal  number. If the number is less than 10, or if there
3380         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3381         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
3382         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
3383         of parenthesized subpatterns.         of parenthesized subpatterns.
3384    
3385         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
3386         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
3387         up to three octal digits following the backslash, and uses them to gen-         up to three octal digits following the backslash, and uses them to gen-
3388         erate  a data character. Any subsequent digits stand for themselves. In         erate a data character. Any subsequent digits stand for themselves.  In
3389         non-UTF-8 mode, the value of a character specified  in  octal  must  be         non-UTF-8  mode,  the  value  of a character specified in octal must be
3390         less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For         less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
3391         example:         example:
3392    
3393           \040   is another way of writing a space           \040   is another way of writing a space
# Line 2970  BACKSLASH Line 3405  BACKSLASH
3405           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3406                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3407    
3408         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
3409         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3410    
3411         All the sequences that define a single character value can be used both         All the sequences that define a single character value can be used both
3412         inside and outside character classes. In addition, inside  a  character         inside  and  outside character classes. In addition, inside a character
3413         class,  the  sequence \b is interpreted as the backspace character (hex         class, the sequence \b is interpreted as the backspace  character  (hex
3414         08), and the sequences \R and \X are interpreted as the characters  "R"         08).  The sequences \B, \N, \R, and \X are not special inside a charac-
3415         and  "X", respectively. Outside a character class, these sequences have         ter class. Like any  other  unrecognized  escape  sequences,  they  are
3416         different meanings (see below).         treated  as  the  literal characters "B", "N", "R", and "X" by default,
3417           but cause an error if the PCRE_EXTRA option is set. Outside a character
3418           class, these sequences have different meanings.
3419    
3420     Absolute and relative back references     Absolute and relative back references
3421    
3422         The sequence \g followed by an unsigned or a negative  number,  option-         The  sequence  \g followed by an unsigned or a negative number, option-
3423         ally  enclosed  in braces, is an absolute or relative back reference. A         ally enclosed in braces, is an absolute or relative back  reference.  A
3424         named back reference can be coded as \g{name}. Back references are dis-         named back reference can be coded as \g{name}. Back references are dis-
3425         cussed later, following the discussion of parenthesized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3426    
3427       Absolute and relative subroutine calls
3428    
3429           For compatibility with Oniguruma, the non-Perl syntax \g followed by  a
3430           name or a number enclosed either in angle brackets or single quotes, is
3431           an alternative syntax for referencing a subpattern as  a  "subroutine".
3432           Details  are  discussed  later.   Note  that  \g{...} (Perl syntax) and
3433           \g<...> (Oniguruma syntax) are not synonymous. The  former  is  a  back
3434           reference; the latter is a subroutine call.
3435    
3436     Generic character types     Generic character types
3437    
3438         Another use of backslash is for specifying generic character types. The         Another use of backslash is for specifying generic character types:
        following are always recognized:  
3439    
3440           \d     any decimal digit           \d     any decimal digit
3441           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 3003  BACKSLASH Line 3448  BACKSLASH
3448           \w     any "word" character           \w     any "word" character
3449           \W     any "non-word" character           \W     any "non-word" character
3450    
3451         Each pair of escape sequences partitions the complete set of characters         There is also the single sequence \N, which matches a non-newline char-
3452         into  two disjoint sets. Any given character matches one, and only one,         acter.  This is the same as the "." metacharacter when  PCRE_DOTALL  is
3453         of each pair.         not set.
3454    
3455         These character type sequences can appear both inside and outside char-         Each  pair of lower and upper case escape sequences partitions the com-
3456         acter  classes.  They each match one character of the appropriate type.         plete set of characters into two disjoint  sets.  Any  given  character
3457         If the current matching point is at the end of the subject string,  all         matches  one, and only one, of each pair. The sequences can appear both
3458         of them fail, since there is no character to match.         inside and outside character classes. They each match one character  of
3459           the  appropriate  type.  If the current matching point is at the end of
3460           the subject string, all of them fail, because there is no character  to
3461           match.
3462    
3463         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
3464         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
# Line 3018  BACKSLASH Line 3466  BACKSLASH
3466         "use locale;" is included in a Perl script, \s may match the VT charac-         "use locale;" is included in a Perl script, \s may match the VT charac-
3467         ter. In PCRE, it never does.         ter. In PCRE, it never does.
3468    
3469         In  UTF-8 mode, characters with values greater than 128 never match \d,         A  "word"  character is an underscore or any character that is a letter
3470         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         or digit.  By default, the definition of letters  and  digits  is  con-
3471         code  character  property  support is available. These sequences retain         trolled  by PCRE's low-valued character tables, and may vary if locale-
3472         their original meanings from before UTF-8 support was available, mainly         specific matching is taking place (see "Locale support" in the  pcreapi
3473         for efficiency reasons.         page).  For  example,  in  a French locale such as "fr_FR" in Unix-like
3474           systems, or "french" in Windows, some character codes greater than  128
3475           are  used  for  accented letters, and these are then matched by \w. The
3476           use of locales with Unicode is discouraged.
3477    
3478           By default, in UTF-8 mode, characters  with  values  greater  than  128
3479           never  match  \d,  \s,  or  \w,  and always match \D, \S, and \W. These
3480           sequences retain their original meanings from before UTF-8 support  was
3481           available,  mainly for efficiency reasons. However, if PCRE is compiled
3482           with Unicode property support, and the PCRE_UCP option is set, the  be-
3483           haviour  is  changed  so  that Unicode properties are used to determine
3484           character types, as follows:
3485    
3486             \d  any character that \p{Nd} matches (decimal digit)
3487             \s  any character that \p{Z} matches, plus HT, LF, FF, CR
3488             \w  any character that \p{L} or \p{N} matches, plus underscore
3489    
3490           The upper case escapes match the inverse sets of characters. Note  that
3491           \d  matches  only decimal digits, whereas \w matches any Unicode digit,
3492           as well as any Unicode letter, and underscore. Note also that  PCRE_UCP
3493           affects  \b,  and  \B  because  they are defined in terms of \w and \W.
3494           Matching these sequences is noticeably slower when PCRE_UCP is set.
3495    
3496         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3497         the other sequences, these do match certain high-valued  codepoints  in         the  other  sequences,  which  match  only ASCII characters by default,
3498         UTF-8 mode.  The horizontal space characters are:         these always  match  certain  high-valued  codepoints  in  UTF-8  mode,
3499           whether or not PCRE_UCP is set. The horizontal space characters are:
3500    
3501           U+0009     Horizontal tab           U+0009     Horizontal tab
3502           U+0020     Space           U+0020     Space
# Line 3058  BACKSLASH Line 3528  BACKSLASH
3528           U+2028     Line separator           U+2028     Line separator
3529           U+2029     Paragraph separator           U+2029     Paragraph separator
3530    
        A "word" character is an underscore or any character less than 256 that  
        is a letter or digit. The definition of  letters  and  digits  is  con-  
        trolled  by PCRE's low-valued character tables, and may vary if locale-  
        specific matching is taking place (see "Locale support" in the  pcreapi  
        page).  For  example,  in  a French locale such as "fr_FR" in Unix-like  
        systems, or "french" in Windows, some character codes greater than  128  
        are  used for accented letters, and these are matched by \w. The use of  
        locales with Unicode is discouraged.  
   
3531     Newline sequences     Newline sequences
3532    
3533         Outside a character class, the escape sequence \R matches  any  Unicode         Outside  a  character class, by default, the escape sequence \R matches
3534         newline  sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \R is         any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3535         equivalent to the following:         mode \R is equivalent to the following:
3536    
3537           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3538    
3539         This is an example of an "atomic group", details  of  which  are  given         This  is  an  example  of an "atomic group", details of which are given
3540         below.  This particular group matches either the two-character sequence         below.  This particular group matches either the two-character sequence
3541         CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,         CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
3542         U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage         U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3543         return, U+000D), or NEL (next line, U+0085). The two-character sequence         return, U+000D), or NEL (next line, U+0085). The two-character sequence
3544         is treated as a single unit that cannot be split.         is treated as a single unit that cannot be split.
3545    
3546         In  UTF-8  mode, two additional characters whose codepoints are greater         In UTF-8 mode, two additional characters whose codepoints  are  greater
3547         than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-         than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3548         rator,  U+2029).   Unicode character property support is not needed for         rator, U+2029).  Unicode character property support is not  needed  for
3549         these characters to be recognized.         these characters to be recognized.
3550    
3551         Inside a character class, \R matches the letter "R".         It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3552           the complete set  of  Unicode  line  endings)  by  setting  the  option
3553           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3554           (BSR is an abbrevation for "backslash R".) This can be made the default
3555           when  PCRE  is  built;  if this is the case, the other behaviour can be
3556           requested via the PCRE_BSR_UNICODE option.   It  is  also  possible  to
3557           specify  these  settings  by  starting a pattern string with one of the
3558           following sequences:
3559    
3560             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3561             (*BSR_UNICODE)   any Unicode newline sequence
3562    
3563           These override the default and the options given to  pcre_compile()  or
3564           pcre_compile2(),  but  they  can  be  overridden  by  options  given to
3565           pcre_exec() or pcre_dfa_exec(). Note that these special settings, which
3566           are  not  Perl-compatible,  are  recognized only at the very start of a
3567           pattern, and that they must be in upper case. If more than one of  them
3568           is present, the last one is used. They can be combined with a change of
3569           newline convention; for example, a pattern can start with:
3570    
3571             (*ANY)(*BSR_ANYCRLF)
3572    
3573           They can also be combined with the (*UTF8) or (*UCP) special sequences.
3574           Inside  a  character  class,  \R  is  treated as an unrecognized escape
3575           sequence, and so matches the letter "R" by default, but causes an error
3576           if PCRE_EXTRA is set.
3577    
3578     Unicode character properties     Unicode character properties
3579    
3580         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3581         tional  escape sequences that match characters with specific properties         tional escape sequences that match characters with specific  properties
3582         are available.  When not in UTF-8 mode, these sequences are  of  course         are  available.   When not in UTF-8 mode, these sequences are of course
3583         limited  to  testing characters whose codepoints are less than 256, but         limited to testing characters whose codepoints are less than  256,  but
3584         they do work in this mode.  The extra escape sequences are:         they do work in this mode.  The extra escape sequences are:
3585    
3586           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3587           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
3588           \X       an extended Unicode sequence           \X       an extended Unicode sequence
3589    
3590         The property names represented by xx above are limited to  the  Unicode         The  property  names represented by xx above are limited to the Unicode
3591         script names, the general category properties, and "Any", which matches         script names, the general category properties, "Any", which matches any
3592         any character (including newline). Other properties such as "InMusical-         character   (including  newline),  and  some  special  PCRE  properties
3593         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does         (described in the next section).  Other Perl properties such as  "InMu-
3594         not match any characters, so always causes a match failure.         sicalSymbols"  are  not  currently supported by PCRE. Note that \P{Any}
3595           does not match any characters, so always causes a match failure.
3596    
3597         Sets of Unicode characters are defined as belonging to certain scripts.         Sets of Unicode characters are defined as belonging to certain scripts.
3598         A  character from one of these sets can be matched using a script name.         A  character from one of these sets can be matched using a script name.
# Line 3117  BACKSLASH Line 3604  BACKSLASH
3604         Those that are not part of an identified script are lumped together  as         Those that are not part of an identified script are lumped together  as
3605         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3606    
3607         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille,
3608         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,         Buginese, Buhid, Canadian_Aboriginal, Carian, Cham,  Cherokee,  Common,
3609         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Coptic,   Cuneiform,  Cypriot,  Cyrillic,  Deseret,  Devanagari,  Egyp-
3610         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-         tian_Hieroglyphs,  Ethiopic,  Georgian,  Glagolitic,   Gothic,   Greek,
3611         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,         Gujarati,  Gurmukhi,  Han,  Hangul,  Hanunoo,  Hebrew,  Hiragana, Impe-
3612         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian,
3613         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,         Javanese,  Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao,
3614         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Latin,  Lepcha,  Limbu,  Linear_B,  Lisu,  Lycian,  Lydian,  Malayalam,
3615         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Meetei_Mayek,  Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic,
3616           Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki,  Oriya,  Osmanya,
3617         Each  character has exactly one general category property, specified by         Phags_Pa,  Phoenician,  Rejang,  Runic, Samaritan, Saurashtra, Shavian,
3618         a two-letter abbreviation. For compatibility with Perl, negation can be         Sinhala, Sundanese, Syloti_Nagri, Syriac,  Tagalog,  Tagbanwa,  Tai_Le,
3619         specified  by  including a circumflex between the opening brace and the         Tai_Tham,  Tai_Viet,  Tamil,  Telugu,  Thaana, Thai, Tibetan, Tifinagh,
3620         property name. For example, \p{^Lu} is the same as \P{Lu}.         Ugaritic, Vai, Yi.
3621    
3622           Each character has exactly one Unicode general category property, spec-
3623           ified  by a two-letter abbreviation. For compatibility with Perl, nega-
3624           tion can be specified by including a  circumflex  between  the  opening
3625           brace  and  the  property  name.  For  example,  \p{^Lu} is the same as
3626           \P{Lu}.
3627    
3628         If only one letter is specified with \p or \P, it includes all the gen-         If only one letter is specified with \p or \P, it includes all the gen-
3629         eral  category properties that start with that letter. In this case, in         eral  category properties that start with that letter. In this case, in
# Line 3194  BACKSLASH Line 3687  BACKSLASH
3687         U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see         U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see
3688         RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-         RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3689         ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in         ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in
3690         the pcreapi page).         the pcreapi page). Perl does not support the Cs property.
3691    
3692         The  long  synonyms  for  these  properties that Perl supports (such as         The  long  synonyms  for  property  names  that  Perl supports (such as
3693         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3694         any of these properties with "Is".         any of these properties with "Is".
3695    
# Line 3222  BACKSLASH Line 3715  BACKSLASH
3715         Matching characters by Unicode property is not fast, because  PCRE  has         Matching characters by Unicode property is not fast, because  PCRE  has
3716         to  search  a  structure  that  contains data for over fifteen thousand         to  search  a  structure  that  contains data for over fifteen thousand
3717         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3718         \w do not use Unicode properties in PCRE.         \w  do  not  use  Unicode properties in PCRE by default, though you can
3719           make them do so by setting the PCRE_UCP option for pcre_compile() or by
3720           starting the pattern with (*UCP).
3721    
3722       PCRE's additional properties
3723    
3724           As  well  as  the standard Unicode properties described in the previous
3725           section, PCRE supports four more that make it possible to convert  tra-
3726           ditional escape sequences such as \w and \s and POSIX character classes
3727           to use Unicode properties. PCRE uses these non-standard, non-Perl prop-
3728           erties internally when PCRE_UCP is set. They are:
3729    
3730             Xan   Any alphanumeric character
3731             Xps   Any POSIX space character
3732             Xsp   Any Perl space character
3733             Xwd   Any Perl "word" character
3734    
3735           Xan  matches  characters that have either the L (letter) or the N (num-
3736           ber) property. Xps matches the characters tab, linefeed, vertical  tab,
3737           formfeed,  or  carriage  return, and any other character that has the Z
3738           (separator) property.  Xsp is the same as Xps, except that vertical tab
3739           is excluded. Xwd matches the same characters as Xan, plus underscore.
3740    
3741     Resetting the match start     Resetting the match start
3742    
# Line 3243  BACKSLASH Line 3757  BACKSLASH
3757    
3758         matches "foobar", the first substring is still set to "foo".         matches "foobar", the first substring is still set to "foo".
3759    
3760           Perl documents that the use  of  \K  within  assertions  is  "not  well
3761           defined".  In  PCRE,  \K  is  acted upon when it occurs inside positive
3762           assertions, but is ignored in negative assertions.
3763    
3764     Simple assertions     Simple assertions
3765    
3766         The final use of backslash is for certain simple assertions. An  asser-         The final use of backslash is for certain simple assertions. An  asser-
# Line 3259  BACKSLASH Line 3777  BACKSLASH
3777           \z     matches only at the end of the subject           \z     matches only at the end of the subject
3778           \G     matches at the first matching position in the subject           \G     matches at the first matching position in the subject
3779    
3780         These assertions may not appear in character classes (but note that  \b         Inside a character class, \b has a different meaning;  it  matches  the
3781         has a different meaning, namely the backspace character, inside a char-         backspace  character.  If  any  other  of these assertions appears in a
3782         acter class).         character class, by default it matches the corresponding literal  char-
3783           acter  (for  example,  \B  matches  the  letter  B).  However,  if  the
3784         A word boundary is a position in the subject string where  the  current         PCRE_EXTRA option is set, an "invalid escape sequence" error is  gener-
3785         character  and  the previous character do not both match \w or \W (i.e.         ated instead.
3786         one matches \w and the other matches \W), or the start or  end  of  the  
3787         string if the first or last character matches \w, respectively.         A  word  boundary is a position in the subject string where the current
3788           character and the previous character do not both match \w or  \W  (i.e.
3789           one  matches  \w  and the other matches \W), or the start or end of the
3790           string if the first or last  character  matches  \w,  respectively.  In
3791           UTF-8  mode,  the  meanings  of \w and \W can be changed by setting the
3792           PCRE_UCP option. When this is done, it also affects \b and \B.  Neither
3793           PCRE  nor  Perl has a separate "start of word" or "end of word" metase-
3794           quence. However, whatever follows \b normally determines which  it  is.
3795           For example, the fragment \ba matches "a" at the start of a word.
3796    
3797         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3798         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
# Line 3349  CIRCUMFLEX AND DOLLAR Line 3875  CIRCUMFLEX AND DOLLAR
3875         set.         set.
3876    
3877    
3878  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT) AND \N
3879    
3880         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-
3881         ter  in  the subject string except (by default) a character that signi-         ter  in  the subject string except (by default) a character that signi-
# Line 3372  FULL STOP (PERIOD, DOT) Line 3898  FULL STOP (PERIOD, DOT)
3898         flex and dollar, the only relationship being  that  they  both  involve         flex and dollar, the only relationship being  that  they  both  involve
3899         newlines. Dot has no special meaning in a character class.         newlines. Dot has no special meaning in a character class.
3900    
3901           The escape sequence \N always behaves as a dot does when PCRE_DOTALL is
3902           not set. In other words, it matches any one character except  one  that
3903           signifies the end of a line.
3904    
3905    
3906  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3907    
# Line 3392  SQUARE BRACKETS AND CHARACTER CLASSES Line 3922  SQUARE BRACKETS AND CHARACTER CLASSES
3922    
3923         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3924         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3925         cial. If a closing square bracket is required as a member of the class,         cial by default.  However, if the PCRE_JAVASCRIPT_COMPAT option is set,
3926         it should be the first data character in the class  (after  an  initial         a lone closing square bracket causes a compile-time error. If a closing
3927         circumflex, if present) or escaped with a backslash.         square  bracket  is required as a member of the class, it should be the
3928           first data character in the class  (after  an  initial  circumflex,  if
3929           present) or escaped with a backslash.
3930    
3931         A  character  class matches a single character in the subject. In UTF-8         A  character  class matches a single character in the subject. In UTF-8
3932         mode, the character may occupy more than one byte. A matched  character         mode, the character may be more than one byte long. A matched character
3933         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3934         character in the class definition is a circumflex, in  which  case  the         character in the class definition is a circumflex, in  which  case  the
3935         subject  character  must  not  be in the set defined by the class. If a         subject  character  must  not  be in the set defined by the class. If a
# Line 3408  SQUARE BRACKETS AND CHARACTER CLASSES Line 3940  SQUARE BRACKETS AND CHARACTER CLASSES
3940         while [^aeiou] matches any character that is not a  lower  case  vowel.         while [^aeiou] matches any character that is not a  lower  case  vowel.
3941         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3942         characters that are in the class by enumerating those that are  not.  A         characters that are in the class by enumerating those that are  not.  A
3943         class  that starts with a circumflex is not an assertion: it still con-         class  that starts with a circumflex is not an assertion; it still con-
3944         sumes a character from the subject string, and therefore  it  fails  if         sumes a character from the subject string, and therefore  it  fails  if
3945         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3946    
# Line 3424  SQUARE BRACKETS AND CHARACTER CLASSES Line 3956  SQUARE BRACKETS AND CHARACTER CLASSES
3956         than 128, so caseless matching is always possible. For characters  with         than 128, so caseless matching is always possible. For characters  with
3957         higher  values,  the  concept  of case is supported if PCRE is compiled         higher  values,  the  concept  of case is supported if PCRE is compiled
3958         with Unicode property support, but not otherwise.  If you want  to  use         with Unicode property support, but not otherwise.  If you want  to  use
3959         caseless  matching  for  characters 128 and above, you must ensure that         caseless  matching  in UTF8-mode for characters 128 and above, you must
3960         PCRE is compiled with Unicode property support as well  as  with  UTF-8         ensure that PCRE is compiled with Unicode property support as  well  as
3961         support.         with UTF-8 support.
3962    
3963         Characters  that  might  indicate  line breaks are never treated in any         Characters  that  might  indicate  line breaks are never treated in any
3964         special way  when  matching  character  classes,  whatever  line-ending         special way  when  matching  character  classes,  whatever  line-ending
# Line 3463  SQUARE BRACKETS AND CHARACTER CLASSES Line 3995  SQUARE BRACKETS AND CHARACTER CLASSES
3995         concept  of  case for characters with values greater than 128 only when         concept  of  case for characters with values greater than 128 only when
3996         it is compiled with Unicode property support.         it is compiled with Unicode property support.
3997    
3998         The character types \d, \D, \p, \P, \s, \S, \w, and \W may also  appear         The character types \d, \D, \h, \H, \p, \P, \s, \S, \v, \V, \w, and  \W
3999         in  a  character  class,  and add the characters that they match to the         may  also appear in a character class, and add the characters that they
4000         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         match to the class. For example,  [\dABCDEF]  matches  any  hexadecimal
4001         flex  can  conveniently  be used with the upper case character types to         digit.  A circumflex can conveniently be used with the upper case char-
4002         specify a more restricted set of characters  than  the  matching  lower         acter types to specify a more restricted set  of  characters  than  the
4003         case  type.  For example, the class [^\W_] matches any letter or digit,         matching  lower  case  type.  For example, the class [^\W_] matches any
4004         but not underscore.         letter or digit, but not underscore.
4005    
4006         The only metacharacters that are recognized in  character  classes  are         The only metacharacters that are recognized in  character  classes  are
4007         backslash,  hyphen  (only  where  it can be interpreted as specifying a         backslash,  hyphen  (only  where  it can be interpreted as specifying a
# Line 3488  POSIX CHARACTER CLASSES Line 4020  POSIX CHARACTER CLASSES
4020           [01[:alpha:]%]           [01[:alpha:]%]
4021    
4022         matches "0", "1", any alphabetic character, or "%". The supported class         matches "0", "1", any alphabetic character, or "%". The supported class
4023         names are         names are:
4024    
4025           alnum    letters and digits           alnum    letters and digits
4026           alpha    letters           alpha    letters
# Line 3499  POSIX CHARACTER CLASSES Line 4031  POSIX CHARACTER CLASSES
4031           graph    printing characters, excluding space           graph    printing characters, excluding space
4032           lower    lower case letters           lower    lower case letters
4033           print    printing characters, including space           print    printing characters, including space
4034           punct    printing characters, excluding letters and digits           punct    printing characters, excluding letters and digits and space
4035           space    white space (not quite the same as \s)           space    white space (not quite the same as \s)
4036           upper    upper case letters           upper    upper case letters
4037           word     "word" characters (same as \w)           word     "word" characters (same as \w)
# Line 3520  POSIX CHARACTER CLASSES Line 4052  POSIX CHARACTER CLASSES
4052         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
4053         these are not supported, and an error is given if they are encountered.         these are not supported, and an error is given if they are encountered.
4054    
4055         In UTF-8 mode, characters with values greater than 128 do not match any         By  default,  in UTF-8 mode, characters with values greater than 128 do
4056         of the POSIX character classes.         not match any of the POSIX character classes. However, if the  PCRE_UCP
4057           option  is passed to pcre_compile(), some of the classes are changed so
4058           that Unicode character properties are used. This is achieved by replac-
4059           ing the POSIX classes by other sequences, as follows:
4060    
4061             [:alnum:]  becomes  \p{Xan}
4062             [:alpha:]  becomes  \p{L}
4063             [:blank:]  becomes  \h
4064             [:digit:]  becomes  \p{Nd}
4065             [:lower:]  becomes  \p{Ll}
4066             [:space:]  becomes  \p{Xps}
4067             [:upper:]  becomes  \p{Lu}
4068             [:word:]   becomes  \p{Xwd}
4069    
4070           Negated  versions,  such  as [:^alpha:] use \P instead of \p. The other
4071           POSIX classes are unchanged, and match only characters with code points
4072           less than 128.
4073    
4074    
4075  VERTICAL BAR  VERTICAL BAR
# Line 3536  VERTICAL BAR Line 4084  VERTICAL BAR
4084         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
4085         to  right, and the first one that succeeds is used. If the alternatives         to  right, and the first one that succeeds is used. If the alternatives
4086         are within a subpattern (defined below), "succeeds" means matching  the         are within a subpattern (defined below), "succeeds" means matching  the
4087         rest  of the main pattern as well as the alternative in the subpattern.         rest of the main pattern as well as the alternative in the subpattern.
4088    
4089    
4090  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
4091    
4092         The settings of the  PCRE_CASELESS,  PCRE_MULTILINE,  PCRE_DOTALL,  and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
4093         PCRE_EXTENDED  options  can  be  changed  from  within the pattern by a         PCRE_EXTENDED options (which are Perl-compatible) can be  changed  from
4094         sequence of Perl option letters enclosed  between  "(?"  and  ")".  The         within  the  pattern  by  a  sequence  of  Perl option letters enclosed
4095         option letters are         between "(?" and ")".  The option letters are
4096    
4097           i  for PCRE_CASELESS           i  for PCRE_CASELESS
4098           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 3553  INTERNAL OPTION SETTING Line 4101  INTERNAL OPTION SETTING
4101    
4102         For example, (?im) sets caseless, multiline matching. It is also possi-         For example, (?im) sets caseless, multiline matching. It is also possi-
4103         ble to unset these options by preceding the letter with a hyphen, and a         ble to unset these options by preceding the letter with a hyphen, and a
4104         combined  setting and unsetting such as (?im-sx), which sets PCRE_CASE-         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-
4105         LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and  PCRE_EXTENDED,         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
4106         is  also  permitted.  If  a  letter  appears  both before and after the         is also permitted. If a  letter  appears  both  before  and  after  the
4107         hyphen, the option is unset.         hyphen, the option is unset.
4108    
4109         When an option change occurs at top level (that is, not inside  subpat-         The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
4110         tern  parentheses),  the change applies to the remainder of the pattern         can be changed in the same way as the Perl-compatible options by  using
4111         that follows.  If the change is placed right at the start of a pattern,         the characters J, U and X respectively.
4112         PCRE extracts it into the global options (and it will therefore show up  
4113         in data extracted by the pcre_fullinfo() function).         When  one  of  these  option  changes occurs at top level (that is, not
4114           inside subpattern parentheses), the change applies to the remainder  of
4115           the pattern that follows. If the change is placed right at the start of
4116           a pattern, PCRE extracts it into the global options (and it will there-
4117           fore show up in data extracted by the pcre_fullinfo() function).
4118    
4119         An option change within a subpattern (see below for  a  description  of         An  option  change  within a subpattern (see below for a description of
4120         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the current pattern that follows
4121         it, so         it, so
4122    
4123           (a(?i)b)c           (a(?i)b)c
4124    
4125         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
4126         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
4127         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
4128         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
4129         example,         example,
4130    
4131           (a(?i)b|c)           (a(?i)b|c)
4132    
4133         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
4134         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
4135         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
4136         some very weird behaviour otherwise.         some very weird behaviour otherwise.
4137    
4138         The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA         Note: There are other PCRE-specific options that  can  be  set  by  the
4139         can be changed in the same way as the Perl-compatible options by  using         application  when  the  compile  or match functions are called. In some
4140         the characters J, U and X respectively.         cases the pattern can contain special leading sequences such as (*CRLF)
4141           to  override  what  the application has set or what has been defaulted.
4142           Details are given in the section entitled  "Newline  sequences"  above.
4143           There  are  also  the  (*UTF8) and (*UCP) leading sequences that can be
4144           used to set UTF-8 and Unicode property modes; they  are  equivalent  to
4145           setting the PCRE_UTF8 and the PCRE_UCP options, respectively.
4146    
4147    
4148  SUBPATTERNS  SUBPATTERNS
# Line 3667  DUPLICATE SUBPATTERN NUMBERS Line 4224  DUPLICATE SUBPATTERN NUMBERS
4224           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
4225           # 1            2         2  3        2     3     4           # 1            2         2  3        2     3     4
4226    
4227         A backreference or a recursive call to  a  numbered  subpattern  always         A back reference to a numbered subpattern uses the  most  recent  value
4228         refers to the first one in the pattern with the given number.         that  is  set  for that number by any subpattern. The following pattern
4229           matches "abcabc" or "defdef":
4230    
4231         An  alternative approach to using this "branch reset" feature is to use           /(?|(abc)|(def))\1/
4232    
4233           In contrast, a recursive or "subroutine" call to a numbered  subpattern
4234           always  refers  to  the first one in the pattern with the given number.
4235           The following pattern matches "abcabc" or "defabc":
4236    
4237             /(?|(abc)|(def))(?1)/
4238    
4239           If a condition test for a subpattern's having matched refers to a  non-
4240           unique  number, the test is true if any of the subpatterns of that num-
4241           ber have matched.
4242    
4243           An alternative approach to using this "branch reset" feature is to  use
4244         duplicate named subpatterns, as described in the next section.         duplicate named subpatterns, as described in the next section.
4245    
4246    
4247  NAMED SUBPATTERNS  NAMED SUBPATTERNS
4248    
4249         Identifying capturing parentheses by number is simple, but  it  can  be         Identifying  capturing  parentheses  by number is simple, but it can be
4250         very  hard  to keep track of the numbers in complicated regular expres-         very hard to keep track of the numbers in complicated  regular  expres-
4251         sions. Furthermore, if an  expression  is  modified,  the  numbers  may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
4252         change.  To help with this difficulty, PCRE supports the naming of sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
4253         patterns. This feature was not added to Perl until release 5.10. Python         patterns. This feature was not added to Perl until release 5.10. Python
4254         had  the  feature earlier, and PCRE introduced it at release 4.0, using         had the feature earlier, and PCRE introduced it at release  4.0,  using
4255         the Python syntax. PCRE now supports both the Perl and the Python  syn-         the  Python syntax. PCRE now supports both the Perl and the Python syn-
4256         tax.         tax. Perl allows identically numbered  subpatterns  to  have  different
4257           names, but PCRE does not.
4258    
4259         In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)         In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)
4260         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References
4261         to capturing parentheses from other parts of the pattern, such as back-         to  capturing parentheses from other parts of the pattern, such as back
4262         references, recursion, and conditions, can be made by name as  well  as         references, recursion, and conditions, can be made by name as  well  as
4263         by number.         by number.
4264    
# Line 3700  NAMED SUBPATTERNS Line 4271  NAMED SUBPATTERNS
4271    
4272         By default, a name must be unique within a pattern, but it is  possible         By default, a name must be unique within a pattern, but it is  possible
4273         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
4274         time. This can be useful for patterns where only one  instance  of  the         time. (Duplicate names are also always permitted for  subpatterns  with
4275           the  same  number, set up as described in the previous section.) Dupli-
4276           cate names can be useful for patterns where only one  instance  of  the
4277         named  parentheses  can  match. Suppose you want to match the name of a         named  parentheses  can  match. Suppose you want to match the name of a
4278         weekday, either as a 3-letter abbreviation or as the full name, and  in         weekday, either as a 3-letter abbreviation or as the full name, and  in
4279         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
# Line 3719  NAMED SUBPATTERNS Line 4292  NAMED SUBPATTERNS
4292         The convenience function for extracting the data by  name  returns  the         The convenience function for extracting the data by  name  returns  the
4293         substring  for  the first (and in this example, the only) subpattern of         substring  for  the first (and in this example, the only) subpattern of
4294         that name that matched. This saves searching  to  find  which  numbered         that name that matched. This saves searching  to  find  which  numbered
4295         subpattern  it  was. If you make a reference to a non-unique named sub-         subpattern it was.
4296         pattern from elsewhere in the pattern, the one that corresponds to  the  
4297         lowest  number  is used. For further details of the interfaces for han-         If  you  make  a  back  reference to a non-unique named subpattern from
4298         dling named subpatterns, see the pcreapi documentation.         elsewhere in the pattern, the one that corresponds to the first  occur-
4299           rence of the name is used. In the absence of duplicate numbers (see the
4300           previous section) this is the one with the lowest number. If you use  a
4301           named  reference  in a condition test (see the section about conditions
4302           below), either to check whether a subpattern has matched, or  to  check
4303           for  recursion,  all  subpatterns with the same name are tested. If the
4304           condition is true for any one of them, the overall condition  is  true.
4305           This is the same behaviour as testing by number. For further details of
4306           the interfaces for handling named subpatterns, see the pcreapi documen-
4307           tation.
4308    
4309           Warning: You cannot use different names to distinguish between two sub-
4310           patterns with the same number because PCRE uses only the  numbers  when
4311           matching. For this reason, an error is given at compile time if differ-
4312           ent names are given to subpatterns with the same number.  However,  you
4313           can  give  the same name to subpatterns with the same number, even when
4314           PCRE_DUPNAMES is not set.
4315    
4316    
4317  REPETITION  REPETITION
# Line 3739  REPETITION Line 4328  REPETITION
4328           a character class           a character class
4329           a back reference (see next section)           a back reference (see next section)
4330           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
4331             a recursive or "subroutine" call to a subpattern
4332    
4333         The  general repetition quantifier specifies a minimum and maximum num-         The  general repetition quantifier specifies a minimum and maximum num-
4334         ber of permitted matches, by giving the two numbers in  curly  brackets         ber of permitted matches, by giving the two numbers in  curly  brackets
# Line 3764  REPETITION Line 4354  REPETITION
4354         the syntax of a quantifier, is taken as a literal character. For  exam-         the syntax of a quantifier, is taken as a literal character. For  exam-
4355         ple, {,6} is not a quantifier, but a literal string of four characters.         ple, {,6} is not a quantifier, but a literal string of four characters.
4356    
4357         In UTF-8 mode, quantifiers apply to UTF-8  characters  rather  than  to         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to
4358         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-
4359         acters, each of which is represented by a two-byte sequence. Similarly,         acters, each of which is represented by a two-byte sequence. Similarly,
4360         when Unicode property support is available, \X{3} matches three Unicode         when Unicode property support is available, \X{3} matches three Unicode
4361         extended sequences, each of which may be several bytes long  (and  they         extended  sequences,  each of which may be several bytes long (and they
4362         may be of different lengths).         may be of different lengths).
4363    
4364         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
4365         the previous item and the quantifier were not present.         the previous item and the quantifier were not present. This may be use-
4366           ful for subpatterns that are referenced as subroutines  from  elsewhere
4367           in the pattern. Items other than subpatterns that have a {0} quantifier
4368           are omitted from the compiled pattern.
4369    
4370         For convenience, the three most common quantifiers have  single-charac-         For convenience, the three most common quantifiers have  single-charac-
4371         ter abbreviations:         ter abbreviations:
# Line 3850  REPETITION Line 4443  REPETITION
4443         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
4444    
4445         However,  there is one situation where the optimization cannot be used.         However,  there is one situation where the optimization cannot be used.
4446         When .*  is inside capturing parentheses that  are  the  subject  of  a         When .*  is inside capturing parentheses that are the subject of a back
4447         backreference  elsewhere  in the pattern, a match at the start may fail         reference elsewhere in the pattern, a match at the start may fail where
4448         where a later one succeeds. Consider, for example:         a later one succeeds. Consider, for example:
4449    
4450           (.*)abc\1           (.*)abc\1
4451    
# Line 3902  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4495  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4495    
4496           (?>\d+)foo           (?>\d+)foo
4497    
4498         This kind of parenthesis "locks up" the  part of the  pattern  it  con-         This  kind  of  parenthesis "locks up" the  part of the pattern it con-
4499         tains  once  it  has matched, and a failure further into the pattern is         tains once it has matched, and a failure further into  the  pattern  is
4500         prevented from backtracking into it. Backtracking past it  to  previous         prevented  from  backtracking into it. Backtracking past it to previous
4501         items, however, works as normal.         items, however, works as normal.
4502    
4503         An  alternative  description  is that a subpattern of this type matches         An alternative description is that a subpattern of  this  type  matches
4504         the string of characters that an  identical  standalone  pattern  would         the  string  of  characters  that an identical standalone pattern would
4505         match, if anchored at the current point in the subject string.         match, if anchored at the current point in the subject string.
4506    
4507         Atomic grouping subpatterns are not capturing subpatterns. Simple cases         Atomic grouping subpatterns are not capturing subpatterns. Simple cases
4508         such as the above example can be thought of as a maximizing repeat that         such as the above example can be thought of as a maximizing repeat that
4509         must  swallow  everything  it can. So, while both \d+ and \d+? are pre-         must swallow everything it can. So, while both \d+ and  \d+?  are  pre-
4510         pared to adjust the number of digits they match in order  to  make  the         pared  to  adjust  the number of digits they match in order to make the
4511         rest of the pattern match, (?>\d+) can only match an entire sequence of         rest of the pattern match, (?>\d+) can only match an entire sequence of
4512         digits.         digits.
4513    
4514         Atomic groups in general can of course contain arbitrarily  complicated         Atomic  groups in general can of course contain arbitrarily complicated
4515         subpatterns,  and  can  be  nested. However, when the subpattern for an         subpatterns, and can be nested. However, when  the  subpattern  for  an
4516         atomic group is just a single repeated item, as in the example above, a         atomic group is just a single repeated item, as in the example above, a
4517         simpler  notation,  called  a "possessive quantifier" can be used. This         simpler notation, called a "possessive quantifier" can  be  used.  This
4518         consists of an additional + character  following  a  quantifier.  Using         consists  of  an  additional  + character following a quantifier. Using
4519         this notation, the previous example can be rewritten as         this notation, the previous example can be rewritten as
4520    
4521           \d++foo           \d++foo
# Line 3932  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4525  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4525    
4526           (abc|xyz){2,3}+           (abc|xyz){2,3}+
4527    
4528         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4529         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4530         simpler forms of atomic group. However, there is no difference  in  the         simpler  forms  of atomic group. However, there is no difference in the
4531         meaning  of  a  possessive  quantifier and the equivalent atomic group,         meaning of a possessive quantifier and  the  equivalent  atomic  group,
4532         though there may be a performance  difference;  possessive  quantifiers         though  there  may  be a performance difference; possessive quantifiers
4533         should be slightly faster.         should be slightly faster.
4534    
4535         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-         The possessive quantifier syntax is an extension to the Perl  5.8  syn-
4536         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first         tax.   Jeffrey  Friedl  originated the idea (and the name) in the first
4537         edition of his book. Mike McCloskey liked it, so implemented it when he         edition of his book. Mike McCloskey liked it, so implemented it when he
4538         built Sun's Java package, and PCRE copied it from there. It  ultimately         built  Sun's Java package, and PCRE copied it from there. It ultimately
4539         found its way into Perl at release 5.10.         found its way into Perl at release 5.10.
4540    
4541         PCRE has an optimization that automatically "possessifies" certain sim-         PCRE has an optimization that automatically "possessifies" certain sim-
4542         ple pattern constructs. For example, the sequence  A+B  is  treated  as         ple  pattern  constructs.  For  example, the sequence A+B is treated as
4543         A++B  because  there is no point in backtracking into a sequence of A's         A++B because there is no point in backtracking into a sequence  of  A's
4544         when B must follow.         when B must follow.
4545    
4546         When a pattern contains an unlimited repeat inside  a  subpattern  that         When  a  pattern  contains an unlimited repeat inside a subpattern that
4547         can  itself  be  repeated  an  unlimited number of times, the use of an         can itself be repeated an unlimited number of  times,  the  use  of  an
4548         atomic group is the only way to avoid some  failing  matches  taking  a         atomic  group  is  the  only way to avoid some failing matches taking a
4549         very long time indeed. The pattern         very long time indeed. The pattern
4550    
4551           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
4552    
4553         matches  an  unlimited number of substrings that either consist of non-         matches an unlimited number of substrings that either consist  of  non-
4554         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it
4555         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
4556    
4557           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4558    
4559         it  takes  a  long  time  before reporting failure. This is because the         it takes a long time before reporting  failure.  This  is  because  the
4560         string can be divided between the internal \D+ repeat and the  external         string  can be divided between the internal \D+ repeat and the external
4561         *  repeat  in  a  large  number of ways, and all have to be tried. (The         * repeat in a large number of ways, and all  have  to  be  tried.  (The
4562         example uses [!?] rather than a single character at  the  end,  because         example  uses  [!?]  rather than a single character at the end, because
4563         both  PCRE  and  Perl have an optimization that allows for fast failure         both PCRE and Perl have an optimization that allows  for  fast  failure
4564         when a single character is used. They remember the last single  charac-         when  a single character is used. They remember the last single charac-
4565         ter  that  is required for a match, and fail early if it is not present         ter that is required for a match, and fail early if it is  not  present
4566         in the string.) If the pattern is changed so that  it  uses  an  atomic         in  the  string.)  If  the pattern is changed so that it uses an atomic
4567         group, like this:         group, like this:
4568    
4569           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4570    
4571         sequences  of non-digits cannot be broken, and failure happens quickly.         sequences of non-digits cannot be broken, and failure happens quickly.
4572    
4573    
4574  BACK REFERENCES  BACK REFERENCES
# Line 4059  BACK REFERENCES Line 4652  BACK REFERENCES
4652    
4653         There may be more than one back reference to the same subpattern. If  a         There may be more than one back reference to the same subpattern. If  a
4654         subpattern  has  not actually been used in a particular match, any back         subpattern  has  not actually been used in a particular match, any back
4655         references to it always fail. For example, the pattern         references to it always fail by default. For example, the pattern
4656    
4657           (a|(bc))\2           (a|(bc))\2
4658    
4659         always fails if it starts to match "a" rather than "bc". Because  there         always fails if it starts to match "a" rather than  "bc".  However,  if
4660         may  be  many  capturing parentheses in a pattern, all digits following         the PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back refer-
4661         the backslash are taken as part of a potential back  reference  number.         ence to an unset value matches an empty string.
4662         If the pattern continues with a digit character, some delimiter must be  
4663         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         Because there may be many capturing parentheses in a pattern, all  dig-
4664         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         its  following a backslash are taken as part of a potential back refer-
4665         ments" below) can be used.         ence number.  If the pattern continues with  a  digit  character,  some
4666           delimiter  must  be  used  to  terminate  the  back  reference.  If the
4667         A back reference that occurs inside the parentheses to which it  refers         PCRE_EXTENDED option is set, this can be whitespace. Otherwise, the \g{
4668         fails  when  the subpattern is first used, so, for example, (a\1) never         syntax or an empty comment (see "Comments" below) can be used.
4669         matches.  However, such references can be useful inside  repeated  sub-  
4670       Recursive back references
4671    
4672           A  back reference that occurs inside the parentheses to which it refers
4673           fails when the subpattern is first used, so, for example,  (a\1)  never
4674           matches.   However,  such references can be useful inside repeated sub-
4675         patterns. For example, the pattern         patterns. For example, the pattern
4676    
4677           (a|b\1)+           (a|b\1)+
4678    
4679         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-
4680         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
4681         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
4682         work, the pattern must be such that the first iteration does  not  need         work,  the  pattern must be such that the first iteration does not need
4683         to  match the back reference. This can be done using alternation, as in         to match the back reference. This can be done using alternation, as  in
4684         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
4685    
4686           Back  references of this type cause the group that they reference to be
4687           treated as an atomic group.  Once the whole group has been  matched,  a
4688           subsequent  matching  failure cannot cause backtracking into the middle
4689           of the group.
4690    
4691    
4692  ASSERTIONS  ASSERTIONS
4693    
# Line 4132  ASSERTIONS Line 4735  ASSERTIONS
4735         If you want to force a matching failure at some point in a pattern, the         If you want to force a matching failure at some point in a pattern, the
4736         most convenient way to do it is  with  (?!)  because  an  empty  string         most convenient way to do it is  with  (?!)  because  an  empty  string
4737         always  matches, so an assertion that requires there not to be an empty         always  matches, so an assertion that requires there not to be an empty
4738         string must always fail.         string must always fail.   The  Perl  5.10  backtracking  control  verb
4739           (*FAIL) or (*F) is essentially a synonym for (?!).
4740    
4741     Lookbehind assertions     Lookbehind assertions
4742    
4743         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
4744         for negative assertions. For example,         for negative assertions. For example,
4745    
4746           (?<!foo)bar           (?<!foo)bar
4747    
4748         does  find  an  occurrence  of "bar" that is not preceded by "foo". The         does find an occurrence of "bar" that is not  preceded  by  "foo".  The
4749         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
4750         strings it matches must have a fixed length. However, if there are sev-         strings it matches must have a fixed length. However, if there are sev-
4751         eral top-level alternatives, they do not all  have  to  have  the  same         eral  top-level  alternatives,  they  do  not all have to have the same
4752         fixed length. Thus         fixed length. Thus
4753    
4754           (?<=bullock|donkey)           (?<=bullock|donkey)
# Line 4153  ASSERTIONS Line 4757  ASSERTIONS
4757    
4758           (?<!dogs?|cats?)           (?<!dogs?|cats?)
4759    
4760         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
4761         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
4762         This  is  an  extension  compared  with  Perl (at least for 5.8), which         This is an extension compared with Perl (5.8 and 5.10), which  requires
4763         requires all branches to match the same length of string. An  assertion         all branches to match the same length of string. An assertion such as
        such as  
4764    
4765           (?<=ab(c|de))           (?<=ab(c|de))
4766    
4767         is  not  permitted,  because  its single top-level branch can match two         is  not  permitted,  because  its single top-level branch can match two
4768         different lengths, but it is acceptable if rewritten to  use  two  top-         different lengths, but it is acceptable to PCRE if rewritten to use two
4769         level branches:         top-level branches:
4770    
4771           (?<=abc|abde)           (?<=abc|abde)
4772    
4773         In some cases, the Perl 5.10 escape sequence \K (see above) can be used         In some cases, the Perl 5.10 escape sequence \K (see above) can be used
4774         instead of a lookbehind assertion; this is not restricted to  a  fixed-         instead of  a  lookbehind  assertion  to  get  round  the  fixed-length
4775         length.         restriction.
4776    
4777         The  implementation  of lookbehind assertions is, for each alternative,         The  implementation  of lookbehind assertions is, for each alternative,
4778         to temporarily move the current position back by the fixed  length  and         to temporarily move the current position back by the fixed  length  and
# Line 4181  ASSERTIONS Line 4784  ASSERTIONS
4784         ble to calculate the length of the lookbehind. The \X and  \R  escapes,         ble to calculate the length of the lookbehind. The \X and  \R  escapes,
4785         which can match different numbers of bytes, are also not permitted.         which can match different numbers of bytes, are also not permitted.
4786    
4787           "Subroutine"  calls  (see below) such as (?2) or (?&X) are permitted in
4788           lookbehinds, as long as the subpattern matches a  fixed-length  string.
4789           Recursion, however, is not supported.
4790    
4791         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind
4792         assertions to specify efficient matching at  the  end  of  the  subject         assertions to specify efficient matching of fixed-length strings at the
4793         string. Consider a simple pattern such as         end of subject strings. Consider a simple pattern such as
4794    
4795           abcd$           abcd$
4796    
# Line 4246  CONDITIONAL SUBPATTERNS Line 4853  CONDITIONAL SUBPATTERNS
4853    
4854         It  is possible to cause the matching process to obey a subpattern con-         It  is possible to cause the matching process to obey a subpattern con-
4855         ditionally or to choose between two alternative subpatterns,  depending         ditionally or to choose between two alternative subpatterns,  depending
4856         on  the result of an assertion, or whether a previous capturing subpat-         on  the result of an assertion, or whether a specific capturing subpat-
4857         tern matched or not. The two possible forms of  conditional  subpattern         tern has already been matched. The two possible  forms  of  conditional
4858         are         subpattern are:
4859    
4860           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4861           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
# Line 4263  CONDITIONAL SUBPATTERNS Line 4870  CONDITIONAL SUBPATTERNS
4870     Checking for a used subpattern by number     Checking for a used subpattern by number
4871    
4872         If the text between the parentheses consists of a sequence  of  digits,         If the text between the parentheses consists of a sequence  of  digits,
4873         the  condition  is  true if the capturing subpattern of that number has         the condition is true if a capturing subpattern of that number has pre-
4874         previously matched. An alternative notation is to  precede  the  digits         viously matched. If there is more than one  capturing  subpattern  with
4875         with a plus or minus sign. In this case, the subpattern number is rela-         the  same  number  (see  the earlier section about duplicate subpattern
4876         tive rather than absolute.  The most recently opened parentheses can be         numbers), the condition is true if any of them have been set. An alter-
4877         referenced  by  (?(-1),  the  next most recent by (?(-2), and so on. In         native  notation is to precede the digits with a plus or minus sign. In
4878         looping constructs it can also make sense to refer to subsequent groups         this case, the subpattern number is relative rather than absolute.  The
4879         with constructs such as (?(+2).         most  recently opened parentheses can be referenced by (?(-1), the next
4880           most recent by (?(-2), and so on. In looping  constructs  it  can  also
4881           make  sense  to  refer  to  subsequent  groups  with constructs such as
4882