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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.  The current implementation of PCRE (release         just  a few differences. Some features that appeared in Python and PCRE
23         6.x) corresponds approximately with Perl  5.8,  including  support  for         before they appeared in Perl are also available using the  Python  syn-
24         UTF-8 encoded strings and Unicode general category properties. However,         tax,  there  is  some  support for one or two .NET and Oniguruma syntax
25         this support has to be explicitly enabled; it is not the default.         items, and there is an option for requesting some  minor  changes  that
26           give better JavaScript compatibility.
27         In addition to the Perl-compatible matching function,  PCRE  also  con-  
28         tains  an  alternative matching function that matches the same compiled         The  current implementation of PCRE corresponds approximately with Perl
29         patterns in a different way. In certain circumstances, the  alternative         5.12, including support for UTF-8 encoded strings and  Unicode  general
30         function  has  some  advantages.  For  a discussion of the two matching         category  properties.  However,  UTF-8  and  Unicode  support has to be
31         algorithms, see the pcrematching page.         explicitly enabled; it is not the default. The  Unicode  tables  corre-
32           spond to Unicode release 6.0.0.
33         PCRE is written in C and released as a C library. A  number  of  people  
34         have  written  wrappers and interfaces of various kinds. In particular,         In  addition to the Perl-compatible matching function, PCRE contains an
35         Google Inc.  have provided a comprehensive C++  wrapper.  This  is  now         alternative function that matches the same compiled patterns in a  dif-
36           ferent way. In certain circumstances, the alternative function has some
37           advantages.  For a discussion of the two matching algorithms,  see  the
38           pcrematching page.
39    
40           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,
42           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
43         included as part of the PCRE distribution. The pcrecpp page has details         included as part of the PCRE distribution. The pcrecpp page has details
44         of this interface. Other people's contributions can  be  found  in  the         of  this  interface.  Other  people's contributions can be found in the
45         Contrib directory at the primary FTP site, which is:         Contrib directory at the primary FTP site, which is:
46    
47         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
48    
49         Details  of  exactly which Perl regular expression features are and are         Details of exactly which Perl regular expression features are  and  are
50         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
51         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
52           page.
53    
54         Some  features  of  PCRE can be included, excluded, or changed when the         Some  features  of  PCRE can be included, excluded, or changed when the
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 63  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
81           pcreapi           details of PCRE's native C API           pcreapi           details of PCRE's native C API
82           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
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             pcrejit           discussion of the just-in-time optimization support
89             pcrelimits        details of size and other limits
90           pcrematching      discussion of the two matching algorithms           pcrematching      discussion of the two matching algorithms
91           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
92           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
# Line 80  USER DOCUMENTATION Line 94  USER DOCUMENTATION
94           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
95           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
96           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
97           pcresample        discussion of the sample program           pcresample        discussion of the pcredemo program
98             pcrestack         discussion of stack usage
99             pcresyntax        quick syntax reference
100           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
101             pcreunicode       discussion of Unicode and UTF-8 support
102    
103         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
104         each C library function, listing its arguments and results.         each C library function, listing its arguments and results.
105    
106    
 LIMITATIONS  
   
        There are some size limitations in PCRE but it is hoped that they  will  
        never in practice be relevant.  
   
        The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE  
        is compiled with the default internal linkage size of 2. If you want to  
        process  regular  expressions  that are truly enormous, you can compile  
        PCRE with an internal linkage size of 3 or 4 (see the  README  file  in  
        the  source  distribution and the pcrebuild documentation for details).  
        In these cases the limit is substantially larger.  However,  the  speed  
        of execution will be slower.  
   
        All values in repeating quantifiers must be less than 65536.  The maxi-  
        mum number of capturing subpatterns is 65535.  
   
        There is no limit to the number of non-capturing subpatterns,  but  the  
        maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,  
        including capturing subpatterns, assertions, and other types of subpat-  
        tern, is 200.  
   
        The  maximum  length of a subject string is the largest positive number  
        that an integer variable can hold. However, when using the  traditional  
        matching function, PCRE uses recursion to handle subpatterns and indef-  
        inite repetition.  This means that the available stack space may  limit  
        the size of a subject string that can be processed by certain patterns.  
   
   
 UTF-8 AND UNICODE PROPERTY SUPPORT  
   
        From release 3.3, PCRE has  had  some  support  for  character  strings  
        encoded  in the UTF-8 format. For release 4.0 this was greatly extended  
        to cover most common requirements, and in release 5.0  additional  sup-  
        port for Unicode general category properties was added.  
   
        In  order  process  UTF-8 strings, you must build PCRE to include UTF-8  
        support in the code, and, in addition,  you  must  call  pcre_compile()  
        with  the PCRE_UTF8 option flag. When you do this, both the pattern and  
        any subject strings that are matched against it are  treated  as  UTF-8  
        strings instead of just strings of bytes.  
   
        If  you compile PCRE with UTF-8 support, but do not use it at run time,  
        the library will be a bit bigger, but the additional run time  overhead  
        is  limited  to testing the PCRE_UTF8 flag in several places, so should  
        not be very large.  
   
        If PCRE is built with Unicode character property support (which implies  
        UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-  
        ported.  The available properties that can be tested are limited to the  
        general  category  properties such as Lu for an upper case letter or Nd  
        for a decimal number. A full list is given in the pcrepattern  documen-  
        tation. The PCRE library is increased in size by about 90K when Unicode  
        property support is included.  
   
        The following comments apply when PCRE is running in UTF-8 mode:  
   
        1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and  
        subjects  are  checked for validity on entry to the relevant functions.  
        If an invalid UTF-8 string is passed, an error return is given. In some  
        situations,  you  may  already  know  that  your strings are valid, and  
        therefore want to skip these checks in order to improve performance. If  
        you  set  the  PCRE_NO_UTF8_CHECK  flag at compile time or at run time,  
        PCRE assumes that the pattern or subject  it  is  given  (respectively)  
        contains  only valid UTF-8 codes. In this case, it does not diagnose an  
        invalid UTF-8 string. If you pass an invalid UTF-8 string to PCRE  when  
        PCRE_NO_UTF8_CHECK  is set, the results are undefined. Your program may  
        crash.  
   
        2. In a pattern, the escape sequence \x{...}, where the contents of the  
        braces  is  a  string  of hexadecimal digits, is interpreted as a UTF-8  
        character whose code number is the given hexadecimal number, for  exam-  
        ple:  \x{1234}.  If a non-hexadecimal digit appears between the braces,  
        the item is not recognized.  This escape sequence can be used either as  
        a literal, or within a character class.  
   
        3.  The  original hexadecimal escape sequence, \xhh, matches a two-byte  
        UTF-8 character if the value is greater than 127.  
   
        4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-  
        vidual bytes, for example: \x{100}{3}.  
   
        5.  The dot metacharacter matches one UTF-8 character instead of a sin-  
        gle byte.  
   
        6. The escape sequence \C can be used to match a single byte  in  UTF-8  
        mode,  but  its  use can lead to some strange effects. This facility is  
        not available in the alternative matching function, pcre_dfa_exec().  
   
        7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly  
        test  characters of any code value, but the characters that PCRE recog-  
        nizes as digits, spaces, or word characters  remain  the  same  set  as  
        before, all with values less than 256. This remains true even when PCRE  
        includes Unicode property support, because to do otherwise  would  slow  
        down  PCRE in many common cases. If you really want to test for a wider  
        sense of, say, "digit", you must use Unicode  property  tests  such  as  
        \p{Nd}.  
   
        8.  Similarly,  characters that match the POSIX named character classes  
        are all low-valued characters.  
   
        9. Case-insensitive matching applies only to  characters  whose  values  
        are  less than 128, unless PCRE is built with Unicode property support.  
        Even when Unicode property support is available, PCRE  still  uses  its  
        own  character  tables when checking the case of low-valued characters,  
        so as not to degrade performance.  The Unicode property information  is  
        used only for characters with higher values.  
   
   
107  AUTHOR  AUTHOR
108    
109         Philip Hazel         Philip Hazel
110         University Computing Service,         University Computing Service
111         Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
112    
113           Putting an actual email address here seems to have been a spam  magnet,
114           so  I've  taken  it away. If you want to email me, use my two initials,
115           followed by the two digits 10, at the domain cam.ac.uk.
116    
        Putting  an actual email address here seems to have been a spam magnet,  
        so I've taken it away. If you want to email me, use my initial and sur-  
        name, separated by a dot, at the domain ucs.cam.ac.uk.  
117    
118  Last updated: 07 March 2005  REVISION
119  Copyright (c) 1997-2005 University of Cambridge.  
120           Last updated: 24 August 2011
121           Copyright (c) 1997-2011 University of Cambridge.
122  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
123    
124    
# Line 220  NAME Line 132  NAME
132  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
133    
134         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
135         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
136         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
137         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
138         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
139         directory) can be obtained by running         environments using the GUI facility of cmake-gui if you are using CMake
140           instead of configure to build PCRE.
141    
142           There  is  a  lot more information about building PCRE in non-Unix-like
143           environments in the file called NON_UNIX_USE, which is part of the PCRE
144           distribution.  You  should consult this file as well as the README file
145           if you are building in a non-Unix-like environment.
146    
147           The complete list of options for configure (which includes the standard
148           ones  such  as  the  selection  of  the  installation directory) can be
149           obtained by running
150    
151           ./configure --help           ./configure --help
152    
153         The following sections describe certain options whose names begin  with         The following sections include  descriptions  of  options  whose  names
154         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
155         for the configure command. Because of the  way  that  configure  works,         defaults for the configure command. Because of the way  that  configure
156         --enable  and  --disable  always  come  in  pairs, so the complementary         works,  --enable  and --disable always come in pairs, so the complemen-
157         option always exists as well, but as it specifies the  default,  it  is         tary option always exists as well, but as it specifies the default,  it
158         not described.         is not described.
159    
160    
161    BUILDING SHARED AND STATIC LIBRARIES
162    
163           The  PCRE building process uses libtool to build both shared and static
164           Unix libraries by default. You can suppress one of these by adding  one
165           of
166    
167             --disable-shared
168             --disable-static
169    
170           to the configure command, as required.
171    
172    
173  C++ SUPPORT  C++ SUPPORT
# Line 249  C++ SUPPORT Line 183  C++ SUPPORT
183    
184  UTF-8 SUPPORT  UTF-8 SUPPORT
185    
186         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
187    
188           --enable-utf8           --enable-utf8
189    
190         to  the  configure  command.  Of  itself, this does not make PCRE treat         to  the  configure  command.  Of  itself, this does not make PCRE treat
191         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
192         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()
193         function.         or pcre_compile2() functions.
194    
195           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
196           expects its input to be either ASCII or UTF-8 (depending on the runtime
197           option). It is not possible to support both EBCDIC and UTF-8  codes  in
198           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
199           --enable-ebcdic are mutually exclusive.
200    
201    
202  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
# Line 272  UNICODE CHARACTER PROPERTY SUPPORT Line 212  UNICODE CHARACTER PROPERTY SUPPORT
212         to the configure command. This implies UTF-8 support, even if you  have         to the configure command. This implies UTF-8 support, even if you  have
213         not explicitly requested it.         not explicitly requested it.
214    
215         Including  Unicode  property  support  adds around 90K of tables to the         Including  Unicode  property  support  adds around 30K of tables to the
216         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE library. Only the general category properties such as  Lu  and  Nd
217         gory  properties  such as Lu and Nd are supported. Details are given in         are supported. Details are given in the pcrepattern documentation.
218         the pcrepattern documentation.  
219    
220    JUST-IN-TIME COMPILER SUPPORT
221    
222           Just-in-time compiler support is included in the build by specifying
223    
224             --enable-jit
225    
226           This  support  is available only for certain hardware architectures. If
227           this option is set for an  unsupported  architecture,  a  compile  time
228           error  occurs.   See  the pcrejit documentation for a discussion of JIT
229           usage. When JIT support is enabled, pcregrep automatically makes use of
230           it, unless you add
231    
232             --disable-pcregrep-jit
233    
234           to the "configure" command.
235    
236    
237  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
238    
239         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By  default,  PCRE interprets the linefeed (LF) character as indicating
240         ter. This is the normal newline character on Unix-like systems. You can         the end of a line. This is the normal newline  character  on  Unix-like
241         compile PCRE to use character 13 (carriage return) instead by adding         systems.  You  can compile PCRE to use carriage return (CR) instead, by
242           adding
243    
244           --enable-newline-is-cr           --enable-newline-is-cr
245    
246         to the configure command. For completeness there is  also  a  --enable-         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
247         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
        line character.  
248    
249           Alternatively, you can specify that line endings are to be indicated by
250           the two character sequence CRLF. If you want this, add
251    
252  BUILDING SHARED AND STATIC LIBRARIES           --enable-newline-is-crlf
253    
254         The PCRE building process uses libtool to build both shared and  static         to the configure command. There is a fourth option, specified by
        Unix  libraries by default. You can suppress one of these by adding one  
        of  
255    
256           --disable-shared           --enable-newline-is-anycrlf
          --disable-static  
257    
258         to the configure command, as required.         which causes PCRE to recognize any of the three sequences  CR,  LF,  or
259           CRLF as indicating a line ending. Finally, a fifth option, specified by
260    
261             --enable-newline-is-any
262    
263           causes PCRE to recognize any Unicode newline sequence.
264    
265           Whatever  line  ending convention is selected when PCRE is built can be
266           overridden when the library functions are called. At build time  it  is
267           conventional to use the standard for your operating system.
268    
269    
270    WHAT \R MATCHES
271    
272           By  default,  the  sequence \R in a pattern matches any Unicode newline
273           sequence, whatever has been selected as the line  ending  sequence.  If
274           you specify
275    
276             --enable-bsr-anycrlf
277    
278           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
279           ever is selected when PCRE is built can be overridden when the  library
280           functions are called.
281    
282    
283  POSIX MALLOC USAGE  POSIX MALLOC USAGE
284    
285         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
286         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
287         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
288         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
289         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
290         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.
291         The default threshold above which the stack is no longer used is 10; it         The default threshold above which the stack is no longer used is 10; it
# Line 319  POSIX MALLOC USAGE Line 296  POSIX MALLOC USAGE
296         to the configure command.         to the configure command.
297    
298    
299    HANDLING VERY LARGE PATTERNS
300    
301           Within a compiled pattern, offset values are used  to  point  from  one
302           part  to another (for example, from an opening parenthesis to an alter-
303           nation metacharacter). By default, two-byte values are used  for  these
304           offsets,  leading  to  a  maximum size for a compiled pattern of around
305           64K. This is sufficient to handle all but the most  gigantic  patterns.
306           Nevertheless,  some  people do want to process truyl enormous patterns,
307           so it is possible to compile PCRE to use three-byte or  four-byte  off-
308           sets by adding a setting such as
309    
310             --with-link-size=3
311    
312           to  the  configure  command.  The value given must be 2, 3, or 4. Using
313           longer offsets slows down the operation of PCRE because it has to  load
314           additional bytes when handling them.
315    
316    
317    AVOIDING EXCESSIVE STACK USAGE
318    
319           When matching with the pcre_exec() function, PCRE implements backtrack-
320           ing by making recursive calls to an internal function  called  match().
321           In  environments  where  the size of the stack is limited, this can se-
322           verely limit PCRE's operation. (The Unix environment does  not  usually
323           suffer from this problem, but it may sometimes be necessary to increase
324           the maximum stack size.  There is a discussion in the  pcrestack  docu-
325           mentation.)  An alternative approach to recursion that uses memory from
326           the heap to remember data, instead of using recursive  function  calls,
327           has  been  implemented to work round the problem of limited stack size.
328           If you want to build a version of PCRE that works this way, add
329    
330             --disable-stack-for-recursion
331    
332           to the configure command. With this configuration, PCRE  will  use  the
333           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
334           ment functions. By default these point to malloc() and free(), but  you
335           can replace the pointers so that your own functions are used instead.
336    
337           Separate  functions  are  provided  rather  than  using pcre_malloc and
338           pcre_free because the  usage  is  very  predictable:  the  block  sizes
339           requested  are  always  the  same,  and  the blocks are always freed in
340           reverse order. A calling program might be able to  implement  optimized
341           functions  that  perform  better  than  malloc()  and free(). PCRE runs
342           noticeably more slowly when built in this way. This option affects only
343           the pcre_exec() function; it is not relevant for pcre_dfa_exec().
344    
345    
346  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
347    
348         Internally,  PCRE has a function called match(), which it calls repeat-         Internally,  PCRE has a function called match(), which it calls repeat-
349         edly  (possibly  recursively)  when  matching  a   pattern   with   the         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
350         pcre_exec()  function.  By controlling the maximum number of times this         pcre_exec()  function.  By controlling the maximum number of times this
351         function may be called during a single matching operation, a limit  can         function may be called during a single matching operation, a limit  can
352         be  placed  on  the resources used by a single call to pcre_exec(). The         be  placed  on  the resources used by a single call to pcre_exec(). The
# Line 335  LIMITING PCRE RESOURCE USAGE Line 359  LIMITING PCRE RESOURCE USAGE
359         to  the  configure  command.  This  setting  has  no  effect   on   the         to  the  configure  command.  This  setting  has  no  effect   on   the
360         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
361    
362           In  some  environments  it is desirable to limit the depth of recursive
363           calls of match() more strictly than the total number of calls, in order
364           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
365           for-recursion is specified) that is used. A second limit controls this;
366           it  defaults  to  the  value  that is set for --with-match-limit, which
367           imposes no additional constraints. However, you can set a  lower  limit
368           by adding, for example,
369    
370             --with-match-limit-recursion=10000
371    
372           to  the  configure  command.  This  value can also be overridden at run
373           time.
374    
375    
376    CREATING CHARACTER TABLES AT BUILD TIME
377    
378           PCRE uses fixed tables for processing characters whose code values  are
379           less  than 256. By default, PCRE is built with a set of tables that are
380           distributed in the file pcre_chartables.c.dist. These  tables  are  for
381           ASCII codes only. If you add
382    
383             --enable-rebuild-chartables
384    
385           to  the  configure  command, the distributed tables are no longer used.
386           Instead, a program called dftables is compiled and  run.  This  outputs
387           the source for new set of tables, created in the default locale of your
388           C runtime system. (This method of replacing the tables does not work if
389           you  are cross compiling, because dftables is run on the local host. If
390           you need to create alternative tables when cross  compiling,  you  will
391           have to do so "by hand".)
392    
 HANDLING VERY LARGE PATTERNS  
393    
394         Within  a  compiled  pattern,  offset values are used to point from one  USING EBCDIC CODE
        part to another (for example, from an opening parenthesis to an  alter-  
        nation  metacharacter).  By default, two-byte values are used for these  
        offsets, leading to a maximum size for a  compiled  pattern  of  around  
        64K.  This  is sufficient to handle all but the most gigantic patterns.  
        Nevertheless, some people do want to process enormous patterns,  so  it  
        is  possible  to compile PCRE to use three-byte or four-byte offsets by  
        adding a setting such as  
395    
396           --with-link-size=3         PCRE  assumes  by  default that it will run in an environment where the
397           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
398           This  is  the  case for most computer operating systems. PCRE can, how-
399           ever, be compiled to run in an EBCDIC environment by adding
400    
401         to the configure command. The value given must be 2,  3,  or  4.  Using           --enable-ebcdic
        longer  offsets slows down the operation of PCRE because it has to load  
        additional bytes when handling them.  
402    
403         If you build PCRE with an increased link size, test 2 (and  test  5  if         to the configure command. This setting implies --enable-rebuild-charta-
404         you  are using UTF-8) will fail. Part of the output of these tests is a         bles.  You  should  only  use  it if you know that you are in an EBCDIC
405         representation of the compiled pattern, and this changes with the  link         environment (for example,  an  IBM  mainframe  operating  system).  The
406         size.         --enable-ebcdic option is incompatible with --enable-utf8.
407    
408    
409  AVOIDING EXCESSIVE STACK USAGE  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
410    
411         When matching with the pcre_exec() function, PCRE implements backtrack-         By default, pcregrep reads all files as plain text. You can build it so
412         ing by making recursive calls to an internal function  called  match().         that it recognizes files whose names end in .gz or .bz2, and reads them
413         In  environments  where  the size of the stack is limited, this can se-         with libz or libbz2, respectively, by adding one or both of
        verely limit PCRE's operation. (The Unix environment does  not  usually  
        suffer  from  this  problem.)  An alternative approach that uses memory  
        from the heap to remember data, instead  of  using  recursive  function  
        calls,  has been implemented to work round this problem. If you want to  
        build a version of PCRE that works this way, add  
414    
415           --disable-stack-for-recursion           --enable-pcregrep-libz
416             --enable-pcregrep-libbz2
417    
418         to the configure command. With this configuration, PCRE  will  use  the         to the configure command. These options naturally require that the rel-
419         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         evant libraries are installed on your system. Configuration  will  fail
420         ment functions. Separate functions are provided because  the  usage  is         if they are not.
        very  predictable:  the  block sizes requested are always the same, and  
        the blocks are always freed in reverse order. A calling  program  might  
        be  able  to implement optimized functions that perform better than the  
        standard malloc() and  free()  functions.  PCRE  runs  noticeably  more  
        slowly when built in this way. This option affects only the pcre_exec()  
        function; it is not relevant for the the pcre_dfa_exec() function.  
421    
422    
423  USING EBCDIC CODE  PCREGREP BUFFER SIZE
424    
425         PCRE assumes by default that it will run in an  environment  where  the         pcregrep  uses  an internal buffer to hold a "window" on the file it is
426         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         scanning, in order to be able to output "before" and "after" lines when
427         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by         it  finds  a match. The size of the buffer is controlled by a parameter
428         adding         whose default value is 20K. The buffer itself is three times this size,
429           but because of the way it is used for holding "before" lines, the long-
430           est line that is guaranteed to be processable is  the  parameter  size.
431           You can change the default parameter value by adding, for example,
432    
433           --enable-ebcdic           --with-pcregrep-bufsize=50K
434    
435           to the configure command. The caller of pcregrep can, however, override
436           this value by specifying a run-time option.
437    
438    
439    PCRETEST OPTION FOR LIBREADLINE SUPPORT
440    
441           If you add
442    
443             --enable-pcretest-libreadline
444    
445           to the configure command,  pcretest  is  linked  with  the  libreadline
446           library,  and  when its input is from a terminal, it reads it using the
447           readline() function. This provides line-editing and history facilities.
448           Note that libreadline is GPL-licensed, so if you distribute a binary of
449           pcretest linked in this way, there may be licensing issues.
450    
451           Setting this option causes the -lreadline option to  be  added  to  the
452           pcretest  build.  In many operating environments with a sytem-installed
453           libreadline this is sufficient. However, in some environments (e.g.  if
454           an  unmodified  distribution version of readline is in use), some extra
455           configuration may be necessary. The INSTALL file for  libreadline  says
456           this:
457    
458             "Readline uses the termcap functions, but does not link with the
459             termcap or curses library itself, allowing applications which link
460             with readline the to choose an appropriate library."
461    
462           If  your environment has not been set up so that an appropriate library
463           is automatically included, you may need to add something like
464    
465             LIBS="-ncurses"
466    
467           immediately before the configure command.
468    
469    
470    SEE ALSO
471    
472           pcreapi(3), pcre_config(3).
473    
        to the configure command.  
474    
475  Last updated: 15 August 2005  AUTHOR
476  Copyright (c) 1997-2005 University of Cambridge.  
477           Philip Hazel
478           University Computing Service
479           Cambridge CB2 3QH, England.
480    
481    
482    REVISION
483    
484           Last updated: 06 September 2011
485           Copyright (c) 1997-2011 University of Cambridge.
486  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
487    
488    
# Line 431  PCRE MATCHING ALGORITHMS Line 518  PCRE MATCHING ALGORITHMS
518           <something> <something else> <something further>           <something> <something else> <something further>
519    
520         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
521         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
522    
523    
524  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 440  REGULAR EXPRESSIONS AS TREES Line 527  REGULAR EXPRESSIONS AS TREES
527         resented  as  a  tree structure. An unlimited repetition in the pattern         resented  as  a  tree structure. An unlimited repetition in the pattern
528         makes the tree of infinite size, but it is still a tree.  Matching  the         makes the tree of infinite size, but it is still a tree.  Matching  the
529         pattern  to a given subject string (from a given starting point) can be         pattern  to a given subject string (from a given starting point) can be
530         thought of as a search of the tree.  There are  two  standard  ways  to         thought of as a search of the tree.  There are two  ways  to  search  a
531         search  a  tree: depth-first and breadth-first, and these correspond to         tree:  depth-first  and  breadth-first, and these correspond to the two
532         the two matching algorithms provided by PCRE.         matching algorithms provided by PCRE.
533    
534    
535  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
536    
537         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
538         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
539         depth-first search of the pattern tree. That is, it  proceeds  along  a         depth-first search of the pattern tree. That is, it  proceeds  along  a
540         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
541         required. When there is a mismatch, the algorithm  tries  any  alterna-         required. When there is a mismatch, the algorithm  tries  any  alterna-
# Line 472  THE STANDARD MATCHING ALGORITHM Line 559  THE STANDARD MATCHING ALGORITHM
559         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
560    
561    
562  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
563    
564         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
565         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
566         first search of the tree. Starting from the first matching point in the         string from left to right, once, character by character, and as it does
567         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
568         ter by character, and as it does  this,  it  remembers  all  the  paths         matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
569         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
570           keeps multiple states active simultaneously).
571         The  scan  continues until either the end of the subject is reached, or  
572         there are no more unterminated paths. At this point,  terminated  paths         Although the general principle of this matching algorithm  is  that  it
573         represent  the different matching possibilities (if there are none, the         scans  the subject string only once, without backtracking, there is one
574         match has failed).  Thus, if there is more  than  one  possible  match,         exception: when a lookaround assertion is encountered,  the  characters
575           following  or  preceding  the  current  point  have to be independently
576           inspected.
577    
578           The scan continues until either the end of the subject is  reached,  or
579           there  are  no more unterminated paths. At this point, terminated paths
580           represent the different matching possibilities (if there are none,  the
581           match  has  failed).   Thus,  if there is more than one possible match,
582         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-
583         est. In PCRE, there is an option to stop the algorithm after the  first         est.  The  matches are returned in decreasing order of length. There is
584         match (which is necessarily the shortest) has been found.         an option to stop the algorithm after the first match (which is  neces-
585           sarily the shortest) is found.
586    
587         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
588         subject. If the pattern         subject. If the pattern
589    
590           cat(er(pillar)?)           cat(er(pillar)?)?
591    
592         is matched against the string "the caterpillar catchment",  the  result         is matched against the string "the caterpillar catchment",  the  result
593         will  be the three strings "cat", "cater", and "caterpillar" that start         will  be the three strings "caterpillar", "cater", and "cat" that start
594         at the fourth character of the subject. The algorithm does not automat-         at the fifth character of the subject. The algorithm does not automati-
595         ically move on to find matches that start at later positions.         cally move on to find matches that start at later positions.
596    
597         There are a number of features of PCRE regular expressions that are not         There are a number of features of PCRE regular expressions that are not
598         supported by the DFA matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
599    
600         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1. Because the algorithm finds all  possible  matches,  the  greedy  or
601         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and
602         ungreedy quantifiers are treated in exactly the same way.         ungreedy quantifiers are treated in exactly the same way. However, pos-
603           sessive  quantifiers can make a difference when what follows could also
604           match what is quantified, for example in a pattern like this:
605    
606             ^a++\w!
607    
608           This pattern matches "aaab!" but not "aaa!", which would be matched  by
609           a  non-possessive quantifier. Similarly, if an atomic group is present,
610           it is matched as if it were a standalone pattern at the current  point,
611           and  the  longest match is then "locked in" for the rest of the overall
612           pattern.
613    
614         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
615         is  not  straightforward  to  keep track of captured substrings for the         is  not  straightforward  to  keep track of captured substrings for the
# Line 516  THE DFA MATCHING ALGORITHM Line 621  THE DFA MATCHING ALGORITHM
621         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
622    
623         4.  For  the same reason, conditional expressions that use a backrefer-         4.  For  the same reason, conditional expressions that use a backrefer-
624         ence as the condition are not supported.         ence as the condition or test for a specific group  recursion  are  not
625           supported.
626    
627         5. Callouts are supported, but the value of the  capture_top  field  is         5.  Because  many  paths  through the tree may be active, the \K escape
628           sequence, which resets the start of the match when encountered (but may
629           be  on  some  paths  and not on others), is not supported. It causes an
630           error if encountered.
631    
632           6. Callouts are supported, but the value of the  capture_top  field  is
633         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
634    
635         6.  The \C escape sequence, which (in the standard algorithm) matches a         7.  The \C escape sequence, which (in the standard algorithm) matches a
636         single byte, even in UTF-8 mode, is not supported because the DFA algo-         single byte, even in UTF-8 mode, is not supported because the  alterna-
637         rithm moves through the subject string one character at a time, for all         tive  algorithm  moves  through  the  subject string one character at a
638         active paths through the tree.         time, for all active paths through the tree.
639    
640           8. Except for (*FAIL), the backtracking control verbs such as  (*PRUNE)
641           are  not  supported.  (*FAIL)  is supported, and behaves like a failing
642           negative assertion.
643    
644    
645  ADVANTAGES OF THE DFA ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
646    
647         Using the DFA matching algorithm provides the following advantages:         Using the alternative matching algorithm provides the following  advan-
648           tages:
649    
650         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-
651         ically  found,  and  in particular, the longest match is found. To find         ically found, and in particular, the longest match is  found.  To  find
652         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
653         things with callouts.         things with callouts.
654    
655         2.  There is much better support for partial matching. The restrictions         2. Because the alternative algorithm  scans  the  subject  string  just
656         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
657         rithm  for partial matching do not apply to the DFA algorithm. For non-         subject strings to the matching function in  several  pieces,  checking
658         anchored patterns, the starting position of a partial match  is  avail-         for  partial  matching  each time. Although it is possible to do multi-
659         able.         segment matching using the standard algorithm (pcre_exec()), by retain-
660           ing  partially matched substrings, it is more complicated. The pcrepar-
661         3.  Because  the  DFA algorithm scans the subject string just once, and         tial documentation gives details  of  partial  matching  and  discusses
662         never needs to backtrack, it is possible  to  pass  very  long  subject         multi-segment matching.
        strings  to  the matching function in several pieces, checking for par-  
        tial matching each time.  
663    
664    
665  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
666    
667         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
668    
669         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
670         partly  because  it has to search for all possible matches, but is also         partly because it has to search for all possible matches, but  is  also
671         because it is less susceptible to optimization.         because it is less susceptible to optimization.
672    
673         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
674    
675         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
676         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
677         rithm.  
678    
679    AUTHOR
680    
681           Philip Hazel
682           University Computing Service
683           Cambridge CB2 3QH, England.
684    
685    
686  Last updated: 28 February 2005  REVISION
687  Copyright (c) 1997-2005 University of Cambridge.  
688           Last updated: 17 November 2010
689           Copyright (c) 1997-2010 University of Cambridge.
690  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
691    
692    
# Line 574  NAME Line 697  NAME
697         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
698    
699    
700  PCRE NATIVE API  PCRE NATIVE API BASIC FUNCTIONS
701    
702         #include <pcre.h>         #include <pcre.h>
703    
# Line 590  PCRE NATIVE API Line 713  PCRE NATIVE API
713         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options,
714              const char **errptr);              const char **errptr);
715    
716           void pcre_free_study(pcre_extra *extra);
717    
718         int pcre_exec(const pcre *code, const pcre_extra *extra,         int pcre_exec(const pcre *code, const pcre_extra *extra,
719              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
720              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
721    
722    
723    PCRE NATIVE API AUXILIARY FUNCTIONS
724    
725           pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);
726    
727           void pcre_jit_stack_free(pcre_jit_stack *stack);
728    
729           void pcre_assign_jit_stack(pcre_extra *extra,
730                pcre_jit_callback callback, void *data);
731    
732         int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,         int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
733              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
734              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
# Line 616  PCRE NATIVE API Line 751  PCRE NATIVE API
751         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
752              const char *name);              const char *name);
753    
754           int pcre_get_stringtable_entries(const pcre *code,
755                const char *name, char **first, char **last);
756    
757         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
758              int stringcount, int stringnumber,              int stringcount, int stringnumber,
759              const char **stringptr);              const char **stringptr);
# Line 640  PCRE NATIVE API Line 778  PCRE NATIVE API
778    
779         char *pcre_version(void);         char *pcre_version(void);
780    
781    
782    PCRE NATIVE API INDIRECTED FUNCTIONS
783    
784         void *(*pcre_malloc)(size_t);         void *(*pcre_malloc)(size_t);
785    
786         void (*pcre_free)(void *);         void (*pcre_free)(void *);
# Line 654  PCRE NATIVE API Line 795  PCRE NATIVE API
795  PCRE API OVERVIEW  PCRE API OVERVIEW
796    
797         PCRE has its own native API, which is described in this document. There         PCRE has its own native API, which is described in this document. There
798         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
799         expression  API.  These  are  described in the pcreposix documentation.         expression  API,  but they do not give access to all the functionality.
800         Both of these APIs define a set of C function calls. A C++  wrapper  is         They are described in the pcreposix documentation. Both of  these  APIs
801         distributed with PCRE. It is documented in the pcrecpp page.         define  a  set  of  C function calls. A C++ wrapper is also distributed
802           with PCRE. It is documented in the pcrecpp page.
803    
804         The  native  API  C  function prototypes are defined in the header file         The native API C function prototypes are defined  in  the  header  file
805         pcre.h, and on Unix systems the library itself is called  libpcre.   It         pcre.h,  and  on Unix systems the library itself is called libpcre.  It
806         can normally be accessed by adding -lpcre to the command for linking an         can normally be accessed by adding -lpcre to the command for linking an
807         application  that  uses  PCRE.  The  header  file  defines  the  macros         application  that  uses  PCRE.  The  header  file  defines  the  macros
808         PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-         PCRE_MAJOR and PCRE_MINOR to contain the major and minor  release  num-
809         bers for the library.  Applications can use these  to  include  support         bers  for  the  library.  Applications can use these to include support
810         for different releases of PCRE.         for different releases of PCRE.
811    
812         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and         In a Windows environment, if you want to statically link an application
813         pcre_exec() are used for compiling and matching regular expressions  in         program  against  a  non-dll  pcre.a  file, you must define PCRE_STATIC
814         a  Perl-compatible  manner. A sample program that demonstrates the sim-         before including pcre.h or pcrecpp.h, because otherwise  the  pcre_mal-
815         plest way of using them is provided in the file  called  pcredemo.c  in         loc()   and   pcre_free()   exported   functions   will   be   declared
816         the  source distribution. The pcresample documentation describes how to         __declspec(dllimport), with unwanted results.
817         run it.  
818           The  functions  pcre_compile(),  pcre_compile2(),   pcre_study(),   and
819           pcre_exec()  are used for compiling and matching regular expressions in
820           a Perl-compatible manner. A sample program that demonstrates  the  sim-
821           plest  way  of  using them is provided in the file called pcredemo.c in
822           the PCRE source distribution. A listing of this program is given in the
823           pcredemo  documentation, and the pcresample documentation describes how
824           to compile and run it.
825    
826           Just-in-time compiler support is an optional feature of PCRE  that  can
827           be built in appropriate hardware environments. It greatly speeds up the
828           matching performance of  many  patterns.  Simple  programs  can  easily
829           request  that  it  be  used  if available, by setting an option that is
830           ignored when it is not relevant. More complicated programs  might  need
831           to     make    use    of    the    functions    pcre_jit_stack_alloc(),
832           pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to  control
833           the  JIT  code's  memory  usage.   These functions are discussed in the
834           pcrejit documentation.
835    
836         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
837         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
838         ing. This allows it to find all possible matches (at a given  point  in         ing. The alternative algorithm finds all possible matches (at  a  given
839         the  subject),  not  just  one. However, this algorithm does not return         point  in  the  subject), and scans the subject just once (unless there
840         captured substrings. A description of the two matching  algorithms  and         are lookbehind assertions). However, this  algorithm  does  not  return
841         their  advantages  and disadvantages is given in the pcrematching docu-         captured  substrings.  A description of the two matching algorithms and
842           their advantages and disadvantages is given in the  pcrematching  docu-
843         mentation.         mentation.
844    
845         In addition to the main compiling and  matching  functions,  there  are         In  addition  to  the  main compiling and matching functions, there are
846         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
847         string that is matched by pcre_exec(). They are:         string that is matched by pcre_exec(). They are:
848    
# Line 692  PCRE API OVERVIEW Line 852  PCRE API OVERVIEW
852           pcre_get_named_substring()           pcre_get_named_substring()
853           pcre_get_substring_list()           pcre_get_substring_list()
854           pcre_get_stringnumber()           pcre_get_stringnumber()
855             pcre_get_stringtable_entries()
856    
857         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
858         to free the memory used for extracted strings.         to free the memory used for extracted strings.
859    
860         The  function  pcre_maketables()  is  used  to build a set of character         The function pcre_maketables() is used to  build  a  set  of  character
861         tables  in  the  current  locale   for   passing   to   pcre_compile(),         tables   in   the   current   locale  for  passing  to  pcre_compile(),
862         pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is         pcre_exec(), or pcre_dfa_exec(). This is an optional facility  that  is
863         provided for specialist use.  Most  commonly,  no  special  tables  are         provided  for  specialist  use.  Most  commonly,  no special tables are
864         passed,  in  which case internal tables that are generated when PCRE is         passed, in which case internal tables that are generated when  PCRE  is
865         built are used.         built are used.
866    
867         The function pcre_fullinfo() is used to find out  information  about  a         The  function  pcre_fullinfo()  is used to find out information about a
868         compiled  pattern; pcre_info() is an obsolete version that returns only         compiled pattern; pcre_info() is an obsolete version that returns  only
869         some of the available information, but is retained for  backwards  com-         some  of  the available information, but is retained for backwards com-
870         patibility.   The function pcre_version() returns a pointer to a string         patibility.  The function pcre_version() returns a pointer to a  string
871         containing the version of PCRE and its date of release.         containing the version of PCRE and its date of release.
872    
873         The function pcre_refcount() maintains a  reference  count  in  a  data         The  function  pcre_refcount()  maintains  a  reference count in a data
874         block  containing  a compiled pattern. This is provided for the benefit         block containing a compiled pattern. This is provided for  the  benefit
875         of object-oriented applications.         of object-oriented applications.
876    
877         The global variables pcre_malloc and pcre_free  initially  contain  the         The  global  variables  pcre_malloc and pcre_free initially contain the
878         entry  points  of  the  standard malloc() and free() functions, respec-         entry points of the standard malloc()  and  free()  functions,  respec-
879         tively. PCRE calls the memory management functions via these variables,         tively. PCRE calls the memory management functions via these variables,
880         so  a  calling  program  can replace them if it wishes to intercept the         so a calling program can replace them if it  wishes  to  intercept  the
881         calls. This should be done before calling any PCRE functions.         calls. This should be done before calling any PCRE functions.
882    
883         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also         The  global  variables  pcre_stack_malloc  and pcre_stack_free are also
884         indirections  to  memory  management functions. These special functions         indirections to memory management functions.  These  special  functions
885         are used only when PCRE is compiled to use  the  heap  for  remembering         are  used  only  when  PCRE is compiled to use the heap for remembering
886         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
887         function. This is a non-standard way of building PCRE, for use in envi-         function.  See  the  pcrebuild  documentation  for details of how to do
888         ronments that have limited stacks. Because of the greater use of memory         this. It is a non-standard way of building PCRE, for  use  in  environ-
889         management, it runs more slowly.  Separate functions  are  provided  so         ments  that  have  limited stacks. Because of the greater use of memory
890           management, it runs more slowly. Separate  functions  are  provided  so
891         that  special-purpose  external  code  can  be used for this case. When         that  special-purpose  external  code  can  be used for this case. When
892         used, these functions are always called in a  stack-like  manner  (last         used, these functions are always called in a  stack-like  manner  (last
893         obtained,  first freed), and always for memory blocks of the same size.         obtained,  first freed), and always for memory blocks of the same size.
894           There is a discussion about PCRE's stack usage in the  pcrestack  docu-
895           mentation.
896    
897         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
898         by  the  caller  to  a "callout" function, which PCRE will then call at         by the caller to a "callout" function, which PCRE  will  then  call  at
899         specified points during a matching operation. Details are given in  the         specified  points during a matching operation. Details are given in the
900         pcrecallout documentation.         pcrecallout documentation.
901    
902    
903    NEWLINES
904    
905           PCRE supports five different conventions for indicating line breaks  in
906           strings:  a  single  CR (carriage return) character, a single LF (line-
907           feed) character, the two-character sequence CRLF, any of the three pre-
908           ceding,  or any Unicode newline sequence. The Unicode newline sequences
909           are the three just mentioned, plus the single characters  VT  (vertical
910           tab,  U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
911           separator, U+2028), and PS (paragraph separator, U+2029).
912    
913           Each of the first three conventions is used by at least  one  operating
914           system  as its standard newline sequence. When PCRE is built, a default
915           can be specified.  The default default is LF, which is the  Unix  stan-
916           dard.  When  PCRE  is run, the default can be overridden, either when a
917           pattern is compiled, or when it is matched.
918    
919           At compile time, the newline convention can be specified by the options
920           argument  of  pcre_compile(), or it can be specified by special text at
921           the start of the pattern itself; this overrides any other settings. See
922           the pcrepattern page for details of the special character sequences.
923    
924           In the PCRE documentation the word "newline" is used to mean "the char-
925           acter or pair of characters that indicate a line break". The choice  of
926           newline  convention  affects  the  handling of the dot, circumflex, and
927           dollar metacharacters, the handling of #-comments in /x mode, and, when
928           CRLF  is a recognized line ending sequence, the match position advance-
929           ment for a non-anchored pattern. There is more detail about this in the
930           section on pcre_exec() options below.
931    
932           The  choice of newline convention does not affect the interpretation of
933           the \n or \r escape sequences, nor does  it  affect  what  \R  matches,
934           which is controlled in a similar way, but by separate options.
935    
936    
937  MULTITHREADING  MULTITHREADING
938    
939         The  PCRE  functions  can be used in multi-threading applications, with         The  PCRE  functions  can be used in multi-threading applications, with
# Line 743  MULTITHREADING Line 941  MULTITHREADING
941         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
942         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
943    
944         The  compiled form of a regular expression is not altered during match-         The compiled form of a regular expression is not altered during  match-
945         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
946         at once.         at once.
947    
948           If the just-in-time optimization feature is being used, it needs  sepa-
949           rate  memory stack areas for each thread. See the pcrejit documentation
950           for more details.
951    
952    
953  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
954    
955         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
956         later time, possibly by a different program, and even on a  host  other         later  time,  possibly by a different program, and even on a host other
957         than  the  one  on  which  it  was  compiled.  Details are given in the         than the one on which  it  was  compiled.  Details  are  given  in  the
958         pcreprecompile documentation.         pcreprecompile  documentation.  However, compiling a regular expression
959           with one version of PCRE for use with a different version is not  guar-
960           anteed to work and may cause crashes.
961    
962    
963  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
964    
965         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
966    
967         The function pcre_config() makes it possible for a PCRE client to  dis-         The  function pcre_config() makes it possible for a PCRE client to dis-
968         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
969         The pcrebuild documentation has more details about these optional  fea-         The  pcrebuild documentation has more details about these optional fea-
970         tures.         tures.
971    
972         The  first  argument  for pcre_config() is an integer, specifying which         The first argument for pcre_config() is an  integer,  specifying  which
973         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
974         into  which  the  information  is  placed. The following information is         into which the information is  placed.  The  following  information  is
975         available:         available:
976    
977           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
978    
979         The output is an integer that is set to one if UTF-8 support is  avail-         The  output is an integer that is set to one if UTF-8 support is avail-
980         able; otherwise it is set to zero.         able; otherwise it is set to zero.
981    
982           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
983    
984         The  output  is  an  integer  that is set to one if support for Unicode         The output is an integer that is set to  one  if  support  for  Unicode
985         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
986    
987             PCRE_CONFIG_JIT
988    
989           The output is an integer that is set to one if support for just-in-time
990           compiling is available; otherwise it is set to zero.
991    
992           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
993    
994         The output is an integer that is set to the value of the code  that  is         The output is an integer whose value specifies  the  default  character
995         used  for the newline character. It is either linefeed (10) or carriage         sequence  that is recognized as meaning "newline". The four values that
996         return (13), and should normally be the  standard  character  for  your         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
997         operating system.         and  -1  for  ANY.  Though they are derived from ASCII, the same values
998           are returned in EBCDIC environments. The default should normally corre-
999           spond to the standard sequence for your operating system.
1000    
1001             PCRE_CONFIG_BSR
1002    
1003           The output is an integer whose value indicates what character sequences
1004           the \R escape sequence matches by default. A value of 0 means  that  \R
1005           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1006           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1007           tern is compiled or matched.
1008    
1009           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1010    
# Line 804  CHECKING BUILD-TIME OPTIONS Line 1023  CHECKING BUILD-TIME OPTIONS
1023    
1024           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1025    
1026         The output is an integer that gives the default limit for the number of         The output is a long integer that gives the default limit for the  num-
1027         internal  matching  function  calls in a pcre_exec() execution. Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1028         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1029    
1030             PCRE_CONFIG_MATCH_LIMIT_RECURSION
1031    
1032           The output is a long integer that gives the default limit for the depth
1033           of   recursion  when  calling  the  internal  matching  function  in  a
1034           pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1035           below.
1036    
1037           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1038    
1039         The output is an integer that is set to one if internal recursion  when         The  output is an integer that is set to one if internal recursion when
1040         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1041         the stack to remember their state. This is the usual way that  PCRE  is         the  stack  to remember their state. This is the usual way that PCRE is
1042         compiled. The output is zero if PCRE was compiled to use blocks of data         compiled. The output is zero if PCRE was compiled to use blocks of data
1043         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
1044         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1045         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1046    
1047    
# Line 832  COMPILING A PATTERN Line 1058  COMPILING A PATTERN
1058    
1059         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1060         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1061         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1062         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1063           avoid  too  much repetition, we refer just to pcre_compile() below, but
1064           the information applies equally to pcre_compile2().
1065    
1066         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
1067         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
1068         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
1069         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
1070         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1071         It is up to the caller  to  free  the  memory  when  it  is  no  longer         It is up to the caller to free the memory (via pcre_free) when it is no
1072         required.         longer required.
1073    
1074         Although  the compiled code of a PCRE regex is relocatable, that is, it         Although the compiled code of a PCRE regex is relocatable, that is,  it
1075         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
1076         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
1077         ment, which is an address (see below).         ment, which is an address (see below).
1078    
1079         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
1080         tion.  It  should  be  zero  if  no options are required. The available         pilation. It should be zero if no options are required.  The  available
1081         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them (in particular, those that
1082         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
1083         pattern (see the detailed description  in  the  pcrepattern  documenta-         unset  from  within  the  pattern  (see the detailed description in the
1084         tion).  For  these options, the contents of the options argument speci-         pcrepattern documentation). For those options that can be different  in
1085         fies their initial settings at the start of compilation and  execution.         different  parts  of  the pattern, the contents of the options argument
1086         The  PCRE_ANCHORED option can be set at the time of matching as well as         specifies their settings at the start of compilation and execution. The
1087           PCRE_ANCHORED,  PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and
1088           PCRE_NO_START_OPT options can be set at the time of matching as well as
1089         at compile time.         at compile time.
1090    
1091         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1092         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1093         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-
1094         sage.  The  offset from the start of the pattern to the character where         sage. This is a static string that is part of the library. You must not
1095         the error was discovered is  placed  in  the  variable  pointed  to  by         try  to  free it. Normally, the offset from the start of the pattern to
1096         erroffset,  which  must  not  be  NULL. If it is, an immediate error is         the byte that was being processed when  the  error  was  discovered  is
1097         given.         placed  in the variable pointed to by erroffset, which must not be NULL
1098           (if it is, an immediate error is given). However, for an invalid  UTF-8
1099         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         string,  the offset is that of the first byte of the failing character.
1100         codeptr  argument is not NULL, a non-zero error code number is returned         Also, some errors are not detected until checks are  carried  out  when
1101         via this argument in the event of an error. This is in addition to  the         the  whole  pattern  has been scanned; in these cases the offset passed
1102           back is the length of the pattern.
1103    
1104           Note that the offset is in bytes, not characters, even in  UTF-8  mode.
1105           It may sometimes point into the middle of a UTF-8 character.
1106    
1107           If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1108           codeptr argument is not NULL, a non-zero error code number is  returned
1109           via  this argument in the event of an error. This is in addition to the
1110         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1111    
1112         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
1113         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1114         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1115         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
1116         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1117         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
1118         support below.         support below.
1119    
1120         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1121         pile():         pile():
1122    
1123           pcre *re;           pcre *re;
# Line 892  COMPILING A PATTERN Line 1130  COMPILING A PATTERN
1130             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1131             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1132    
1133         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
1134         file:         file:
1135    
1136           PCRE_ANCHORED           PCRE_ANCHORED
1137    
1138         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
1139         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
1140         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1141         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1142         only way to do it in Perl.         only way to do it in Perl.
1143    
1144           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1145    
1146         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1147         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1148         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1149    
1150             PCRE_BSR_ANYCRLF
1151             PCRE_BSR_UNICODE
1152    
1153           These options (which are mutually exclusive) control what the \R escape
1154           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1155           or to match any Unicode newline sequence. The default is specified when
1156           PCRE is built. It can be overridden from within the pattern, or by set-
1157           ting an option when a compiled pattern is matched.
1158    
1159           PCRE_CASELESS           PCRE_CASELESS
1160    
1161         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
1162         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
1163         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
1164         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1165         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1166         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-
1167         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1168         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1169         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1170         UTF-8 support.         UTF-8 support.
1171    
1172           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1173    
1174         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
1175         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
1176         matches immediately before the final character if it is a newline  (but         matches  immediately before a newline at the end of the string (but not
1177         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1178         ignored if PCRE_MULTILINE is set. There is no equivalent to this option         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1179         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1180    
1181           PCRE_DOTALL           PCRE_DOTALL
1182    
1183         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharacter in the pattern matches a  char-
1184         acters, including newlines. Without it,  newlines  are  excluded.  This         acter of any value, including one that indicates a newline. However, it
1185         option  is equivalent to Perl's /s option, and it can be changed within         only ever matches one character, even if newlines are  coded  as  CRLF.
1186         a pattern by a (?s) option setting.  A  negative  class  such  as  [^a]         Without  this option, a dot does not match when the current position is
1187         always  matches a newline character, independent of the setting of this         at a newline. This option is equivalent to Perl's /s option, and it can
1188         option.         be  changed within a pattern by a (?s) option setting. A negative class
1189           such as [^a] always matches newline characters, independent of the set-
1190           ting of this option.
1191    
1192             PCRE_DUPNAMES
1193    
1194           If  this  bit is set, names used to identify capturing subpatterns need
1195           not be unique. This can be helpful for certain types of pattern when it
1196           is  known  that  only  one instance of the named subpattern can ever be
1197           matched. There are more details of named subpatterns  below;  see  also
1198           the pcrepattern documentation.
1199    
1200           PCRE_EXTENDED           PCRE_EXTENDED
1201    
1202         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1203         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1204         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1205         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1206         line character, inclusive, are also  ignored.  This  is  equivalent  to         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1207         Perl's  /x  option,  and  it  can be changed within a pattern by a (?x)         option, and it can be changed within a pattern by a  (?x)  option  set-
1208         option setting.         ting.
1209    
1210           Which  characters  are  interpreted  as  newlines  is controlled by the
1211           options passed to pcre_compile() or by a special sequence at the  start
1212           of  the  pattern, as described in the section entitled "Newline conven-
1213           tions" in the pcrepattern documentation. Note that the end of this type
1214           of  comment  is  a  literal  newline  sequence  in  the pattern; escape
1215           sequences that happen to represent a newline do not count.
1216    
1217         This option makes it possible to include  comments  inside  complicated         This option makes it possible to include  comments  inside  complicated
1218         patterns.   Note,  however,  that this applies only to data characters.         patterns.   Note,  however,  that this applies only to data characters.
1219         Whitespace  characters  may  never  appear  within  special   character         Whitespace  characters  may  never  appear  within  special   character
1220         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for example within the sequence (?( that intro-
1221         introduces a conditional subpattern.         duces a conditional subpattern.
1222    
1223           PCRE_EXTRA           PCRE_EXTRA
1224    
# Line 964  COMPILING A PATTERN Line 1228  COMPILING A PATTERN
1228         letter  that  has  no  special  meaning causes an error, thus reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1229         these combinations for future expansion. By  default,  as  in  Perl,  a         these combinations for future expansion. By  default,  as  in  Perl,  a
1230         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
1231         literal. There are at present no  other  features  controlled  by  this         literal. (Perl can, however, be persuaded to give an error for this, by
1232         option. It can also be set by a (?X) option setting within a pattern.         running  it with the -w option.) There are at present no other features
1233           controlled by this option. It can also be set by a (?X) option  setting
1234           within a pattern.
1235    
1236           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1237    
1238         If  this  option  is  set,  an  unanchored pattern is required to match         If  this  option  is  set,  an  unanchored pattern is required to match
1239         before or at the first newline character in the subject string,  though         before or at the first  newline  in  the  subject  string,  though  the
1240         the matched text may continue over the newline.         matched text may continue over the newline.
1241    
1242             PCRE_JAVASCRIPT_COMPAT
1243    
1244           If this option is set, PCRE's behaviour is changed in some ways so that
1245           it is compatible with JavaScript rather than Perl. The changes  are  as
1246           follows:
1247    
1248           (1)  A  lone  closing square bracket in a pattern causes a compile-time
1249           error, because this is illegal in JavaScript (by default it is  treated
1250           as a data character). Thus, the pattern AB]CD becomes illegal when this
1251           option is set.
1252    
1253           (2) At run time, a back reference to an unset subpattern group  matches
1254           an  empty  string (by default this causes the current matching alterna-
1255           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1256           set  (assuming  it can find an "a" in the subject), whereas it fails by
1257           default, for Perl compatibility.
1258    
1259           PCRE_MULTILINE           PCRE_MULTILINE
1260    
1261         By  default,  PCRE  treats the subject string as consisting of a single         By default, PCRE treats the subject string as consisting  of  a  single
1262         line of characters (even if it actually contains newlines). The  "start         line  of characters (even if it actually contains newlines). The "start
1263         of  line"  metacharacter  (^)  matches only at the start of the string,         of line" metacharacter (^) matches only at the  start  of  the  string,
1264         while the "end of line" metacharacter ($) matches only at  the  end  of         while  the  "end  of line" metacharacter ($) matches only at the end of
1265         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1266         is set). This is the same as Perl.         is set). This is the same as Perl.
1267    
1268         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"
1269         constructs  match  immediately following or immediately before any new-         constructs match immediately following or immediately  before  internal
1270         line in the subject string, respectively, as well as at the very  start         newlines  in  the  subject string, respectively, as well as at the very
1271         and  end. This is equivalent to Perl's /m option, and it can be changed         start and end. This is equivalent to Perl's /m option, and  it  can  be
1272         within a pattern by a (?m) option setting. If there are no "\n" charac-         changed within a pattern by a (?m) option setting. If there are no new-
1273         ters  in  a  subject  string, or no occurrences of ^ or $ in a pattern,         lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1274         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1275    
1276             PCRE_NEWLINE_CR
1277             PCRE_NEWLINE_LF
1278             PCRE_NEWLINE_CRLF
1279             PCRE_NEWLINE_ANYCRLF
1280             PCRE_NEWLINE_ANY
1281    
1282           These  options  override the default newline definition that was chosen
1283           when PCRE was built. Setting the first or the second specifies  that  a
1284           newline  is  indicated  by a single character (CR or LF, respectively).
1285           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1286           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1287           that any of the three preceding sequences should be recognized. Setting
1288           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1289           recognized. The Unicode newline sequences are the three just mentioned,
1290           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1291           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1292           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1293           UTF-8 mode.
1294    
1295           The newline setting in the  options  word  uses  three  bits  that  are
1296           treated as a number, giving eight possibilities. Currently only six are
1297           used (default plus the five values above). This means that if  you  set
1298           more  than one newline option, the combination may or may not be sensi-
1299           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1300           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1301           cause an error.
1302    
1303           The only time that a line break in a pattern  is  specially  recognized
1304           when  compiling  is when PCRE_EXTENDED is set. CR and LF are whitespace
1305           characters, and so are ignored in this mode. Also, an unescaped #  out-
1306           side  a  character class indicates a comment that lasts until after the
1307           next line break sequence. In other circumstances, line break  sequences
1308           in patterns are treated as literal data.
1309    
1310           The newline option that is set at compile time becomes the default that
1311           is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1312    
1313           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1314    
1315         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
# Line 998  COMPILING A PATTERN Line 1318  COMPILING A PATTERN
1318         be  used  for  capturing  (and  they acquire numbers in the usual way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1319         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1320    
1321             NO_START_OPTIMIZE
1322    
1323           This is an option that acts at matching time; that is, it is really  an
1324           option  for  pcre_exec()  or  pcre_dfa_exec().  If it is set at compile
1325           time, it is remembered with the compiled pattern and assumed at  match-
1326           ing  time.  For  details  see  the discussion of PCRE_NO_START_OPTIMIZE
1327           below.
1328    
1329             PCRE_UCP
1330    
1331           This option changes the way PCRE processes \B, \b, \D, \d, \S, \s,  \W,
1332           \w,  and  some  of  the POSIX character classes. By default, only ASCII
1333           characters are recognized, but if PCRE_UCP is set,  Unicode  properties
1334           are  used instead to classify characters. More details are given in the
1335           section on generic character types in the pcrepattern page. If you  set
1336           PCRE_UCP,  matching  one of the items it affects takes much longer. The
1337           option is available only if PCRE has been compiled with  Unicode  prop-
1338           erty support.
1339    
1340           PCRE_UNGREEDY           PCRE_UNGREEDY
1341    
1342         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1343         are  not greedy by default, but become greedy if followed by "?". It is         are not greedy by default, but become greedy if followed by "?". It  is
1344         not compatible with Perl. It can also be set by a (?U)  option  setting         not  compatible  with Perl. It can also be set by a (?U) option setting
1345         within the pattern.         within the pattern.
1346    
1347           PCRE_UTF8           PCRE_UTF8
1348    
1349         This  option  causes PCRE to regard both the pattern and the subject as         This option causes PCRE to regard both the pattern and the  subject  as
1350         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1351         However,  it is available only when PCRE is built to include UTF-8 sup-         However, it is available only when PCRE is built to include UTF-8  sup-
1352         port. If not, the use of this option provokes an error. Details of  how         port.  If not, the use of this option provokes an error. Details of how
1353         this  option  changes the behaviour of PCRE are given in the section on         this option changes the behaviour of PCRE are given in the  pcreunicode
1354         UTF-8 support in the main pcre page.         page.
1355    
1356           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1357    
1358         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1359         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically checked. There is a  discussion  about  the  validity  of
1360         pcre_compile() returns an error. If you already know that your  pattern         UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1361         is  valid, and you want to skip this check for performance reasons, you         bytes is found, pcre_compile() returns an error. If  you  already  know
1362         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of         that your pattern is valid, and you want to skip this check for perfor-
1363         passing an invalid UTF-8 string as a pattern is undefined. It may cause         mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1364         your program to crash.  Note that this option can  also  be  passed  to         set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1365         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-         undefined. It may cause your program to crash. Note  that  this  option
1366         ing of subject strings.         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1367           UTF-8 validity checking of subject strings.
1368    
1369    
1370  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1371    
1372         The following table lists the error  codes  than  may  be  returned  by         The following table lists the error  codes  than  may  be  returned  by
1373         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(),  along with the error messages that may be returned by
1374         both compiling functions.         both compiling functions. As PCRE has developed, some error codes  have
1375           fallen out of use. To avoid confusion, they have not been re-used.
1376    
1377            0  no error            0  no error
1378            1  \ at end of pattern            1  \ at end of pattern
# Line 1043  COMPILATION ERROR CODES Line 1384  COMPILATION ERROR CODES
1384            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1385            8  range out of order in character class            8  range out of order in character class
1386            9  nothing to repeat            9  nothing to repeat
1387           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1388           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1389           12  unrecognized character after (?           12  unrecognized character after (? or (?-
1390           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
1391           14  missing )           14  missing )
1392           15  reference to non-existent subpattern           15  reference to non-existent subpattern
1393           16  erroffset passed as NULL           16  erroffset passed as NULL
1394           17  unknown option bit(s) set           17  unknown option bit(s) set
1395           18  missing ) after comment           18  missing ) after comment
1396           19  parentheses nested too deeply           19  [this code is not in use]
1397           20  regular expression too large           20  regular expression is too large
1398           21  failed to get memory           21  failed to get memory
1399           22  unmatched parentheses           22  unmatched parentheses
1400           23  internal error: code overflow           23  internal error: code overflow
1401           24  unrecognized character after (?<           24  unrecognized character after (?<
1402           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1403           26  malformed number after (?(           26  malformed number or name after (?(
1404           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1405           28  assertion expected after (?(           28  assertion expected after (?(
1406           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1407           30  unknown POSIX class name           30  unknown POSIX class name
1408           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1409           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1410           33  spare error           33  [this code is not in use]
1411           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1412           35  invalid condition (?(0)           35  invalid condition (?(0)
1413           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
1414           37  PCRE does not support \L, \l, \N, \U, or \u           37  PCRE does not support \L, \l, \N{name}, \U, or \u
1415           38  number after (?C is > 255           38  number after (?C is > 255
1416           39  closing ) for (?C expected           39  closing ) for (?C expected
1417           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1418           41  unrecognized character after (?P           41  unrecognized character after (?P
1419           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1420           43  two named groups have the same name           43  two named subpatterns have the same name
1421           44  invalid UTF-8 string           44  invalid UTF-8 string
1422           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1423           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1424           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1425             48  subpattern name is too long (maximum 32 characters)
1426             49  too many named subpatterns (maximum 10000)
1427             50  [this code is not in use]
1428             51  octal value is greater than \377 (not in UTF-8 mode)
1429             52  internal error: overran compiling workspace
1430             53  internal error: previously-checked referenced subpattern
1431                   not found
1432             54  DEFINE group contains more than one branch
1433             55  repeating a DEFINE group is not allowed
1434             56  inconsistent NEWLINE options
1435             57  \g is not followed by a braced, angle-bracketed, or quoted
1436                   name/number or by a plain number
1437             58  a numbered reference must not be zero
1438             59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1439             60  (*VERB) not recognized
1440             61  number is too big
1441             62  subpattern name expected
1442             63  digit expected after (?+
1443             64  ] is an invalid data character in JavaScript compatibility mode
1444             65  different names for subpatterns of the same number are
1445                   not allowed
1446             66  (*MARK) must have an argument
1447             67  this version of PCRE is not compiled with PCRE_UCP support
1448             68  \c must be followed by an ASCII character
1449             69  \k is not followed by a braced, angle-bracketed, or quoted name
1450    
1451           The  numbers  32  and 10000 in errors 48 and 49 are defaults; different
1452           values may be used if the limits were changed when PCRE was built.
1453    
1454    
1455  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1097  STUDYING A PATTERN Line 1466  STUDYING A PATTERN
1466         the results of the study.         the results of the study.
1467    
1468         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1469         pcre_exec().  However,  a  pcre_extra  block also contains other fields         pcre_exec()  or  pcre_dfa_exec(). However, a pcre_extra block also con-
1470         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
1471         described below in the section on matching a pattern.         passed; these are described below in the section on matching a pattern.
1472    
1473         If  studying  the  pattern  does not produce any additional information         If  studying  the  pattern  does  not  produce  any useful information,
1474         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1475         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
1476         its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1477    
1478         The second argument of pcre_study() contains option bits.  At  present,         The second argument of pcre_study() contains option bits. There is only
1479         no options are defined, and this argument should always be zero.         one  option:  PCRE_STUDY_JIT_COMPILE.  If this is set, and the just-in-
1480           time compiler is  available,  the  pattern  is  further  compiled  into
1481           machine  code  that  executes much faster than the pcre_exec() matching
1482           function. If the just-in-time compiler is not available, this option is
1483           ignored. All other bits in the options argument must be zero.
1484    
1485           JIT  compilation  is  a heavyweight optimization. It can take some time
1486           for patterns to be analyzed, and for one-off matches  and  simple  pat-
1487           terns  the benefit of faster execution might be offset by a much slower
1488           study time.  Not all patterns can be optimized by the JIT compiler. For
1489           those  that cannot be handled, matching automatically falls back to the
1490           pcre_exec() interpreter. For more details, see the  pcrejit  documenta-
1491           tion.
1492    
1493         The  third argument for pcre_study() is a pointer for an error message.         The  third argument for pcre_study() is a pointer for an error message.
1494         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1495         points  to  is set to NULL. Otherwise it points to a textual error mes-         points  to  is  set  to NULL. Otherwise it is set to point to a textual
1496         sage. You should therefore test the error pointer for NULL after  call-         error message. This is a static string that is part of the library. You
1497         ing pcre_study(), to be sure that it has run successfully.         must  not  try  to  free it. You should test the error pointer for NULL
1498           after calling pcre_study(), to be sure that it has run successfully.
1499    
1500           When you are finished with a pattern, you can free the memory used  for
1501           the study data by calling pcre_free_study(). This function was added to
1502           the API for release 8.20. For earlier versions,  the  memory  could  be
1503           freed  with  pcre_free(), just like the pattern itself. This will still
1504           work in cases where PCRE_STUDY_JIT_COMPILE  is  not  used,  but  it  is
1505           advisable to change to the new function when convenient.
1506    
1507         This is a typical call to pcre_study():         This  is  a typical way in which pcre_study() is used (except that in a
1508           real application there should be tests for errors):
1509    
1510           pcre_extra *pe;           int rc;
1511           pe = pcre_study(           pcre *re;
1512             pcre_extra *sd;
1513             re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
1514             sd = pcre_study(
1515             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
1516             0,              /* no options exist */             0,              /* no options */
1517             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1518             rc = pcre_exec(   /* see below for details of pcre_exec() options */
1519         At present, studying a pattern is useful only for non-anchored patterns             re, sd, "subject", 7, 0, 0, ovector, 30);
1520         that do not have a single fixed starting character. A bitmap of  possi-           ...
1521         ble starting bytes is created.           pcre_free_study(sd);
1522             pcre_free(re);
1523    
1524           Studying a pattern does two things: first, a lower bound for the length
1525           of subject string that is needed to match the pattern is computed. This
1526           does not mean that there are any strings of that length that match, but
1527           it  does  guarantee that no shorter strings match. The value is used by
1528           pcre_exec() and pcre_dfa_exec() to avoid  wasting  time  by  trying  to
1529           match  strings  that are shorter than the lower bound. You can find out
1530           the value in a calling program via the pcre_fullinfo() function.
1531    
1532           Studying a pattern is also useful for non-anchored patterns that do not
1533           have  a  single fixed starting character. A bitmap of possible starting
1534           bytes is created. This speeds up finding a position in the  subject  at
1535           which to start matching.
1536    
1537           These  two optimizations apply to both pcre_exec() and pcre_dfa_exec().
1538           However, they are not used by pcre_exec()  if  pcre_study()  is  called
1539           with  the  PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling is
1540           successful.  The  optimizations  can  be  disabled   by   setting   the
1541           PCRE_NO_START_OPTIMIZE    option    when    calling    pcre_exec()   or
1542           pcre_dfa_exec(). You might want to do this  if  your  pattern  contains
1543           callouts  or (*MARK) (which cannot be handled by the JIT compiler), and
1544           you want to make use of these facilities in cases where matching fails.
1545           See the discussion of PCRE_NO_START_OPTIMIZE below.
1546    
1547    
1548  LOCALE SUPPORT  LOCALE SUPPORT
1549    
1550         PCRE  handles  caseless matching, and determines whether characters are         PCRE  handles  caseless matching, and determines whether characters are
1551         letters digits, or whatever, by reference to a set of  tables,  indexed         letters, digits, or whatever, by reference to a set of tables,  indexed
1552         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
1553         characters with codes less than 128. Higher-valued  codes  never  match         characters with codes less than 128. By  default,  higher-valued  codes
1554         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
1555         with Unicode character property support.         PCRE is built with Unicode character property  support.  Alternatively,
1556           the  PCRE_UCP  option  can  be  set at compile time; this causes \w and
1557         An internal set of tables is created in the default C locale when  PCRE         friends to use Unicode property support instead of built-in tables. The
1558         is  built.  This  is  used when the final argument of pcre_compile() is         use of locales with Unicode is discouraged. If you are handling charac-
1559         NULL, and is sufficient for many applications. An  alternative  set  of         ters with codes greater than 128, you should either use UTF-8 and  Uni-
1560         tables  can,  however, be supplied. These may be created in a different         code, or use locales, but not try to mix the two.
1561         locale from the default. As more and more applications change to  using  
1562         Unicode, the need for this locale support is expected to die away.         PCRE  contains  an  internal set of tables that are used when the final
1563           argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
1564           applications.  Normally, the internal tables recognize only ASCII char-
1565           acters. However, when PCRE is built, it is possible to cause the inter-
1566           nal tables to be rebuilt in the default "C" locale of the local system,
1567           which may cause them to be different.
1568    
1569           The internal tables can always be overridden by tables supplied by  the
1570           application that calls PCRE. These may be created in a different locale
1571           from the default. As more and more applications change  to  using  Uni-
1572           code, the need for this locale support is expected to die away.
1573    
1574         External  tables  are  built by calling the pcre_maketables() function,         External  tables  are  built by calling the pcre_maketables() function,
1575         which has no arguments, in the relevant locale. The result can then  be         which has no arguments, in the relevant locale. The result can then  be
# Line 1155  LOCALE SUPPORT Line 1582  LOCALE SUPPORT
1582           tables = pcre_maketables();           tables = pcre_maketables();
1583           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1584    
1585         When pcre_maketables() runs, the tables are built  in  memory  that  is         The locale name "fr_FR" is used on Linux and other  Unix-like  systems;
1586         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         if you are using Windows, the name for the French locale is "french".
1587         that the memory containing the tables remains available for as long  as  
1588           When  pcre_maketables()  runs,  the  tables are built in memory that is
1589           obtained via pcre_malloc. It is the caller's responsibility  to  ensure
1590           that  the memory containing the tables remains available for as long as
1591         it is needed.         it is needed.
1592    
1593         The pointer that is passed to pcre_compile() is saved with the compiled         The pointer that is passed to pcre_compile() is saved with the compiled
1594         pattern, and the same tables are used via this pointer by  pcre_study()         pattern,  and the same tables are used via this pointer by pcre_study()
1595         and normally also by pcre_exec(). Thus, by default, for any single pat-         and normally also by pcre_exec(). Thus, by default, for any single pat-
1596         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1597         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1598    
1599         It  is  possible to pass a table pointer or NULL (indicating the use of         It is possible to pass a table pointer or NULL (indicating the  use  of
1600         the internal tables) to pcre_exec(). Although  not  intended  for  this         the  internal  tables)  to  pcre_exec(). Although not intended for this
1601         purpose,  this facility could be used to match a pattern in a different         purpose, this facility could be used to match a pattern in a  different
1602         locale from the one in which it was compiled. Passing table pointers at         locale from the one in which it was compiled. Passing table pointers at
1603         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1604    
# Line 1178  INFORMATION ABOUT A PATTERN Line 1608  INFORMATION ABOUT A PATTERN
1608         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1609              int what, void *where);              int what, void *where);
1610    
1611         The  pcre_fullinfo() function returns information about a compiled pat-         The pcre_fullinfo() function returns information about a compiled  pat-
1612         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1613         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1614    
1615         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled
1616         pattern. The second argument is the result of pcre_study(), or NULL  if         pattern.  The second argument is the result of pcre_study(), or NULL if
1617         the  pattern  was not studied. The third argument specifies which piece         the pattern was not studied. The third argument specifies  which  piece
1618         of information is required, and the fourth argument is a pointer  to  a         of  information  is required, and the fourth argument is a pointer to a
1619         variable  to  receive  the  data. The yield of the function is zero for         variable to receive the data. The yield of the  function  is  zero  for
1620         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1621    
1622           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 1194  INFORMATION ABOUT A PATTERN Line 1624  INFORMATION ABOUT A PATTERN
1624           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1625           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1626    
1627         The "magic number" is placed at the start of each compiled  pattern  as         The  "magic  number" is placed at the start of each compiled pattern as
1628         an  simple check against passing an arbitrary memory pointer. Here is a         an simple check against passing an arbitrary memory pointer. Here is  a
1629         typical call of pcre_fullinfo(), to obtain the length of  the  compiled         typical  call  of pcre_fullinfo(), to obtain the length of the compiled
1630         pattern:         pattern:
1631    
1632           int rc;           int rc;
1633           unsigned long int length;           size_t length;
1634           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1635             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1636             pe,               /* result of pcre_study(), or NULL */             sd,               /* result of pcre_study(), or NULL */
1637             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1638             &length);         /* where to put the data */             &length);         /* where to put the data */
1639    
1640         The  possible  values for the third argument are defined in pcre.h, and         The possible values for the third argument are defined in  pcre.h,  and
1641         are as follows:         are as follows:
1642    
1643           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1644    
1645         Return the number of the highest back reference  in  the  pattern.  The         Return  the  number  of  the highest back reference in the pattern. The
1646         fourth  argument  should  point to an int variable. Zero is returned if         fourth argument should point to an int variable. Zero  is  returned  if
1647         there are no back references.         there are no back references.
1648    
1649           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1650    
1651         Return the number of capturing subpatterns in the pattern.  The  fourth         Return  the  number of capturing subpatterns in the pattern. The fourth
1652         argument should point to an int variable.         argument should point to an int variable.
1653    
1654           PCRE_INFO_DEFAULT_TABLES           PCRE_INFO_DEFAULT_TABLES
1655    
1656         Return  a pointer to the internal default character tables within PCRE.         Return a pointer to the internal default character tables within  PCRE.
1657         The fourth argument should point to an unsigned char *  variable.  This         The  fourth  argument should point to an unsigned char * variable. This
1658         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1659         tion. External callers can cause PCRE to use  its  internal  tables  by         tion.  External  callers  can  cause PCRE to use its internal tables by
1660         passing a NULL table pointer.         passing a NULL table pointer.
1661    
1662           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1663    
1664         Return  information  about  the first byte of any matched string, for a         Return information about the first byte of any matched  string,  for  a
1665         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored  pattern. The fourth argument should point to an int vari-
1666         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name
1667         compatibility.)         is still recognized for backwards compatibility.)
1668    
1669         If there is a fixed first byte, for example, from  a  pattern  such  as         If  there  is  a  fixed first byte, for example, from a pattern such as
1670         (cat|cow|coyote),  it  is  returned in the integer pointed to by where.         (cat|cow|coyote), its value is returned. Otherwise, if either
        Otherwise, if either  
1671    
1672         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
1673         branch starts with "^", or         branch starts with "^", or
# Line 1258  INFORMATION ABOUT A PATTERN Line 1687  INFORMATION ABOUT A PATTERN
1687         returned.  The fourth argument should point to an unsigned char * vari-         returned.  The fourth argument should point to an unsigned char * vari-
1688         able.         able.
1689    
1690             PCRE_INFO_HASCRORLF
1691    
1692           Return 1 if the pattern contains any explicit  matches  for  CR  or  LF
1693           characters,  otherwise  0.  The  fourth argument should point to an int
1694           variable. An explicit match is either a literal CR or LF character,  or
1695           \r or \n.
1696    
1697             PCRE_INFO_JCHANGED
1698    
1699           Return  1  if  the (?J) or (?-J) option setting is used in the pattern,
1700           otherwise 0. The fourth argument should point to an int variable.  (?J)
1701           and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1702    
1703             PCRE_INFO_JIT
1704    
1705           Return  1  if  the  pattern was studied with the PCRE_STUDY_JIT_COMPILE
1706           option, and just-in-time compiling was successful. The fourth  argument
1707           should  point  to  an  int variable. A return value of 0 means that JIT
1708           support is not available in this version of PCRE, or that  the  pattern
1709           was not studied with the PCRE_STUDY_JIT_COMPILE option, or that the JIT
1710           compiler could not handle this particular pattern. See the pcrejit doc-
1711           umentation for details of what can and cannot be handled.
1712    
1713           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1714    
1715         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
1716         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
1717         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1718         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
1719         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1720         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
1721         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1722    
1723             PCRE_INFO_MINLENGTH
1724    
1725           If  the  pattern  was studied and a minimum length for matching subject
1726           strings was computed, its value is  returned.  Otherwise  the  returned
1727           value  is  -1. The value is a number of characters, not bytes (this may
1728           be relevant in UTF-8 mode). The fourth argument should point to an  int
1729           variable.  A  non-negative  value is a lower bound to the length of any
1730           matching string. There may not be any strings of that  length  that  do
1731           actually match, but every string that does match is at least that long.
1732    
1733           PCRE_INFO_NAMECOUNT           PCRE_INFO_NAMECOUNT
1734           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1735           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1736    
1737         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1738         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1739         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1740         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1741         captured substring by name. It is also possible  to  extract  the  data         strings  by  name. It is also possible to extract the data directly, by
1742         directly,  by  first converting the name to a number in order to access         first converting the name to a number in order to  access  the  correct
1743         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1744         below).  To  do the conversion, you need to use the name-to-number map,         the conversion, you need  to  use  the  name-to-number  map,  which  is
1745         which is described by these three values.         described by these three values.
1746    
1747         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
1748         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1749         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
1750         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1751         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
1752         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-
1753         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-
1754         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated.
        For example, consider the following pattern  (assume  PCRE_EXTENDED  is  
        set, so white space - including newlines - is ignored):  
1755    
1756           (?P<date> (?P<year>(\d\d)?\d\d) -         The names are in alphabetical order. Duplicate names may appear if  (?|
1757           (?P<month>\d\d) - (?P<day>\d\d) )         is used to create multiple groups with the same number, as described in
1758           the section on duplicate subpattern numbers in  the  pcrepattern  page.
1759           Duplicate  names  for  subpatterns with different numbers are permitted
1760           only if PCRE_DUPNAMES is set. In all cases  of  duplicate  names,  they
1761           appear  in  the table in the order in which they were found in the pat-
1762           tern. In the absence of (?| this is the  order  of  increasing  number;
1763           when (?| is used this is not necessarily the case because later subpat-
1764           terns may have lower numbers.
1765    
1766           As a simple example of the name/number table,  consider  the  following
1767           pattern  (assume  PCRE_EXTENDED is set, so white space - including new-
1768           lines - is ignored):
1769    
1770         There  are  four  named subpatterns, so the table has four entries, and           (?<date> (?<year>(\d\d)?\d\d) -
1771         each entry in the table is eight bytes long. The table is  as  follows,           (?<month>\d\d) - (?<day>\d\d) )
1772    
1773           There are four named subpatterns, so the table has  four  entries,  and
1774           each  entry  in the table is eight bytes long. The table is as follows,
1775         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1776         as ??:         as ??:
1777    
# Line 1306  INFORMATION ABOUT A PATTERN Line 1780  INFORMATION ABOUT A PATTERN
1780           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1781           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1782    
1783         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1784         name-to-number map, remember that the length of each entry is likely to         name-to-number map, remember that the length of the entries  is  likely
1785         be different for each compiled pattern.         to be different for each compiled pattern.
1786    
1787             PCRE_INFO_OKPARTIAL
1788    
1789           Return  1  if  the  pattern  can  be  used  for  partial  matching with
1790           pcre_exec(), otherwise 0. The fourth argument should point  to  an  int
1791           variable.  From  release  8.00,  this  always  returns  1,  because the
1792           restrictions that previously applied  to  partial  matching  have  been
1793           lifted.  The  pcrepartial documentation gives details of partial match-
1794           ing.
1795    
1796           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1797    
1798         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
1799         fourth  argument  should  point to an unsigned long int variable. These         fourth  argument  should  point to an unsigned long int variable. These
1800         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1801         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1802           other words, they are the options that will be in force  when  matching
1803           starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
1804           the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1805           and PCRE_EXTENDED.
1806    
1807         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
1808         alternatives begin with one of the following:         alternatives begin with one of the following:
# Line 1339  INFORMATION ABOUT A PATTERN Line 1826  INFORMATION ABOUT A PATTERN
1826           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1827    
1828         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
1829         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to         a  pcre_extra  block. If pcre_extra is NULL, or there is no study data,
1830         pcre_malloc() when PCRE was getting memory into which to place the data         zero is returned. The fourth argument should point to  a  size_t  vari-
1831         created  by  pcre_study(). The fourth argument should point to a size_t         able.   The  study_data field is set by pcre_study() to record informa-
1832         variable.         tion that will speed up matching (see the section entitled "Studying  a
1833           pattern" above). The format of the study_data block is private, but its
1834           length is made available via this option so that it can  be  saved  and
1835           restored (see the pcreprecompile documentation for details).
1836    
1837    
1838  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1839    
1840         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1841    
1842         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1843         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1844         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1845         pcre_info()  is the number of capturing subpatterns, or one of the fol-         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1846         lowing negative numbers:         lowing negative numbers:
1847    
1848           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1849           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1850    
1851         If the optptr argument is not NULL, a copy of the  options  with  which         If  the  optptr  argument is not NULL, a copy of the options with which
1852         the  pattern  was  compiled  is placed in the integer it points to (see         the pattern was compiled is placed in the integer  it  points  to  (see
1853         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1854    
1855         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1856         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1857         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1858    
1859    
# Line 1371  REFERENCE COUNTS Line 1861  REFERENCE COUNTS
1861    
1862         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1863    
1864         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1865         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1866         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1867         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1868         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1869    
1870         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1871         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1872         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1873         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1874         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1875         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1876    
1877         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1878         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1879         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1880    
1881    
# Line 1397  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1887  MATCHING A PATTERN: THE TRADITIONAL FUNC
1887    
1888         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
1889         compiled  pattern, which is passed in the code argument. If the pattern         compiled  pattern, which is passed in the code argument. If the pattern
1890         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
1891         argument.  This  function is the main matching facility of the library,         argument.  This  function is the main matching facility of the library,
1892         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
1893         an  alternative matching function, which is described below in the sec-         an  alternative matching function, which is described below in the sec-
# Line 1428  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1918  MATCHING A PATTERN: THE TRADITIONAL FUNC
1918         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
1919         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
1920         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-
1921         tional  information in it. The fields in a pcre_extra block are as fol-         tional  information  in it. The pcre_extra block contains the following
1922         lows:         fields (not necessarily in this order):
1923    
1924           unsigned long int flags;           unsigned long int flags;
1925           void *study_data;           void *study_data;
1926             void *executable_jit;
1927           unsigned long int match_limit;           unsigned long int match_limit;
1928             unsigned long int match_limit_recursion;
1929           void *callout_data;           void *callout_data;
1930           const unsigned char *tables;           const unsigned char *tables;
1931             unsigned char **mark;
1932    
1933         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
1934         are set. The flag bits are:         are set. The flag bits are:
1935    
1936           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1937             PCRE_EXTRA_EXECUTABLE_JIT
1938           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1939             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1940           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1941           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1942             PCRE_EXTRA_MARK
1943    
1944         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 and some-
1945         the pcre_extra block that is returned by  pcre_study(),  together  with         times the executable_jit field are set in the pcre_extra block that  is
1946         the appropriate flag bit. You should not set this yourself, but you may         returned  by pcre_study(), together with the appropriate flag bits. You
1947         add to the block by setting the other fields  and  their  corresponding         should not set these yourself, but you may add to the block by  setting
1948         flag bits.         the other fields and their corresponding flag bits.
1949    
1950         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
1951         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
1952         match,  but  which  have  a very large number of possibilities in their         match,  but  which  have  a very large number of possibilities in their
1953         search trees. The classic  example  is  the  use  of  nested  unlimited         search trees. The classic example is a pattern that uses nested  unlim-
1954         repeats.         ited repeats.
1955    
1956         Internally,  PCRE uses a function called match() which it calls repeat-         Internally,  pcre_exec() uses a function called match(), which it calls
1957         edly (sometimes recursively). The limit is imposed  on  the  number  of         repeatedly (sometimes recursively). The limit  set  by  match_limit  is
1958         times  this  function is called during a match, which has the effect of         imposed  on the number of times this function is called during a match,
1959         limiting the amount of recursion and backtracking that can take  place.         which has the effect of limiting the amount of  backtracking  that  can
1960         For patterns that are not anchored, the count starts from zero for each         take place. For patterns that are not anchored, the count restarts from
1961         position in the subject string.         zero for each position in the subject string.
1962    
1963         The default limit for the library can be set when PCRE  is  built;  the         When pcre_exec() is called with a pattern that was successfully studied
1964         default  default  is 10 million, which handles all but the most extreme         with  the  PCRE_STUDY_JIT_COMPILE  option, the way that the matching is
1965         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         executed is entirely different. However, there is still the possibility
1966         pcre_extra  block  in  which match_limit is set to a smaller value, and         of  runaway  matching  that  goes  on  for a very long time, and so the
1967         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is         match_limit value is also used in this case (but in a different way) to
1968           limit how long the matching can continue.
1969    
1970           The  default  value  for  the  limit can be set when PCRE is built; the
1971           default default is 10 million, which handles all but the  most  extreme
1972           cases.  You  can  override  the  default by suppling pcre_exec() with a
1973           pcre_extra    block    in    which    match_limit    is    set,     and
1974           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1975         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1976    
1977         The  pcre_callout  field is used in conjunction with the "callout" fea-         The match_limit_recursion field is similar to match_limit, but  instead
1978         ture, which is described in the pcrecallout documentation.         of limiting the total number of times that match() is called, it limits
1979           the depth of recursion. The recursion depth is a  smaller  number  than
1980           the  total number of calls, because not all calls to match() are recur-
1981           sive.  This limit is of use only if it is set smaller than match_limit.
1982    
1983           Limiting the recursion depth limits the amount of  machine  stack  that
1984           can  be used, or, when PCRE has been compiled to use memory on the heap
1985           instead of the stack, the amount of heap memory that can be used.  This
1986           limit  is not relevant, and is ignored, if the pattern was successfully
1987           studied with PCRE_STUDY_JIT_COMPILE.
1988    
1989           The default value for match_limit_recursion can be  set  when  PCRE  is
1990           built;  the  default  default  is  the  same  value  as the default for
1991           match_limit. You can override the default by suppling pcre_exec()  with
1992           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1993           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1994           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1995    
1996           The  callout_data  field is used in conjunction with the "callout" fea-
1997           ture, and is described in the pcrecallout documentation.
1998    
1999         The tables field  is  used  to  pass  a  character  tables  pointer  to         The tables field  is  used  to  pass  a  character  tables  pointer  to
2000         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 1485  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2007  MATCHING A PATTERN: THE TRADITIONAL FUNC
2007         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address when pcre_exec() is called. See the  pcreprecompile  documenta-
2008         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
2009    
2010           If  PCRE_EXTRA_MARK  is  set in the flags field, the mark field must be
2011           set to point to a char * variable. If the pattern  contains  any  back-
2012           tracking  control verbs such as (*MARK:NAME), and the execution ends up
2013           with a name to pass back, a pointer to the  name  string  (zero  termi-
2014           nated)  is  placed  in  the  variable pointed to by the mark field. The
2015           names are within the compiled pattern; if you wish  to  retain  such  a
2016           name  you must copy it before freeing the memory of a compiled pattern.
2017           If there is no name to pass back, the variable pointed to by  the  mark
2018           field  set  to NULL. For details of the backtracking control verbs, see
2019           the section entitled "Backtracking control" in the pcrepattern documen-
2020           tation.
2021    
2022     Option bits for pcre_exec()     Option bits for pcre_exec()
2023    
2024         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.
2025         The  only  bits  that  may  be  set  are  PCRE_ANCHORED,   PCRE_NOTBOL,         The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
2026         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,    PCRE_NOTEOL,    PCRE_NOTEMPTY,   PCRE_NOTEMPTY_ATSTART,
2027           PCRE_NO_START_OPTIMIZE,  PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,   and
2028           PCRE_PARTIAL_HARD.
2029    
2030           If the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE
2031           option,  the   only   supported   options   for   JIT   execution   are
2032           PCRE_NO_UTF8_CHECK,   PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,  and
2033           PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is  not
2034           supported.  If an unsupported option is used, JIT execution is disabled
2035           and the normal interpretive code in pcre_exec() is run.
2036    
2037           PCRE_ANCHORED           PCRE_ANCHORED
2038    
2039         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
2040         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
2041         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
2042         unachored at matching time.         unachored at matching time.
2043    
2044             PCRE_BSR_ANYCRLF
2045             PCRE_BSR_UNICODE
2046    
2047           These options (which are mutually exclusive) control what the \R escape
2048           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
2049           or  to  match  any Unicode newline sequence. These options override the
2050           choice that was made or defaulted when the pattern was compiled.
2051    
2052             PCRE_NEWLINE_CR
2053             PCRE_NEWLINE_LF
2054             PCRE_NEWLINE_CRLF
2055             PCRE_NEWLINE_ANYCRLF
2056             PCRE_NEWLINE_ANY
2057    
2058           These options override  the  newline  definition  that  was  chosen  or
2059           defaulted  when the pattern was compiled. For details, see the descrip-
2060           tion of pcre_compile()  above.  During  matching,  the  newline  choice
2061           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
2062           ters. It may also alter the way the match position is advanced after  a
2063           match failure for an unanchored pattern.
2064    
2065           When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or PCRE_NEWLINE_ANY is
2066           set, and a match attempt for an unanchored pattern fails when the  cur-
2067           rent  position  is  at  a  CRLF  sequence,  and the pattern contains no
2068           explicit matches for  CR  or  LF  characters,  the  match  position  is
2069           advanced by two characters instead of one, in other words, to after the
2070           CRLF.
2071    
2072           The above rule is a compromise that makes the most common cases work as
2073           expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL
2074           option is not set), it does not match the string "\r\nA" because, after
2075           failing  at the start, it skips both the CR and the LF before retrying.
2076           However, the pattern [\r\n]A does match that string,  because  it  con-
2077           tains an explicit CR or LF reference, and so advances only by one char-
2078           acter after the first failure.
2079    
2080           An explicit match for CR of LF is either a literal appearance of one of
2081           those  characters,  or  one  of the \r or \n escape sequences. Implicit
2082           matches such as [^X] do not count, nor does \s (which includes  CR  and
2083           LF in the characters that it matches).
2084    
2085           Notwithstanding  the above, anomalous effects may still occur when CRLF
2086           is a valid newline sequence and explicit \r or \n escapes appear in the
2087           pattern.
2088    
2089           PCRE_NOTBOL           PCRE_NOTBOL
2090    
2091         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
2092         the  beginning  of  a  line, so the circumflex metacharacter should not         the beginning of a line, so the  circumflex  metacharacter  should  not
2093         match before it. Setting this without PCRE_MULTILINE (at compile  time)         match  before it. Setting this without PCRE_MULTILINE (at compile time)
2094         causes  circumflex  never to match. This option affects only the behav-         causes circumflex never to match. This option affects only  the  behav-
2095         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
2096    
2097           PCRE_NOTEOL           PCRE_NOTEOL
2098    
2099         This option specifies that the end of the subject string is not the end         This option specifies that the end of the subject string is not the end
2100         of  a line, so the dollar metacharacter should not match it nor (except         of a line, so the dollar metacharacter should not match it nor  (except
2101         in multiline mode) a newline immediately before it. Setting this  with-         in  multiline mode) a newline immediately before it. Setting this with-
2102         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
2103         option affects only the behaviour of the dollar metacharacter. It  does         option  affects only the behaviour of the dollar metacharacter. It does
2104         not affect \Z or \z.         not affect \Z or \z.
2105    
2106           PCRE_NOTEMPTY           PCRE_NOTEMPTY
2107    
2108         An empty string is not considered to be a valid match if this option is         An empty string is not considered to be a valid match if this option is
2109         set. If there are alternatives in the pattern, they are tried.  If  all         set.  If  there are alternatives in the pattern, they are tried. If all
2110         the  alternatives  match  the empty string, the entire match fails. For         the alternatives match the empty string, the entire  match  fails.  For
2111         example, if the pattern         example, if the pattern
2112    
2113           a?b?           a?b?
2114    
2115         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
2116         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
2117         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-
2118         rences of "a" or "b".         rences of "a" or "b".
2119    
2120         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-           PCRE_NOTEMPTY_ATSTART
2121         cial case of a pattern match of the empty  string  within  its  split()  
2122         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
2123         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
2124         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.
2125         if that fails by advancing the starting offset (see below)  and  trying  
2126         an ordinary match again. There is some code that demonstrates how to do         Perl    has    no    direct    equivalent    of    PCRE_NOTEMPTY     or
2127         this in the pcredemo.c sample program.         PCRE_NOTEMPTY_ATSTART,  but  it  does  make a special case of a pattern
2128           match of the empty string within its split() function, and  when  using
2129           the  /g  modifier.  It  is  possible  to emulate Perl's behaviour after
2130           matching a null string by first trying the match again at the same off-
2131           set  with  PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED,  and then if that
2132           fails, by advancing the starting offset (see below) and trying an ordi-
2133           nary  match  again. There is some code that demonstrates how to do this
2134           in the pcredemo sample program. In the most general case, you  have  to
2135           check  to  see  if the newline convention recognizes CRLF as a newline,
2136           and if so, and the current character is CR followed by LF, advance  the
2137           starting offset by two characters instead of one.
2138    
2139             PCRE_NO_START_OPTIMIZE
2140    
2141           There  are a number of optimizations that pcre_exec() uses at the start
2142           of a match, in order to speed up the process. For  example,  if  it  is
2143           known that an unanchored match must start with a specific character, it
2144           searches the subject for that character, and fails  immediately  if  it
2145           cannot  find  it,  without actually running the main matching function.
2146           This means that a special item such as (*COMMIT) at the start of a pat-
2147           tern  is  not  considered until after a suitable starting point for the
2148           match has been found. When callouts or (*MARK) items are in use,  these
2149           "start-up" optimizations can cause them to be skipped if the pattern is
2150           never actually used. The start-up optimizations are in  effect  a  pre-
2151           scan of the subject that takes place before the pattern is run.
2152    
2153           The  PCRE_NO_START_OPTIMIZE option disables the start-up optimizations,
2154           possibly causing performance to suffer,  but  ensuring  that  in  cases
2155           where  the  result is "no match", the callouts do occur, and that items
2156           such as (*COMMIT) and (*MARK) are considered at every possible starting
2157           position  in  the  subject  string. If PCRE_NO_START_OPTIMIZE is set at
2158           compile time, it cannot be unset at matching time.
2159    
2160           Setting PCRE_NO_START_OPTIMIZE can change the  outcome  of  a  matching
2161           operation.  Consider the pattern
2162    
2163             (*COMMIT)ABC
2164    
2165           When  this  is  compiled, PCRE records the fact that a match must start
2166           with the character "A". Suppose the subject  string  is  "DEFABC".  The
2167           start-up  optimization  scans along the subject, finds "A" and runs the
2168           first match attempt from there. The (*COMMIT) item means that the  pat-
2169           tern  must  match the current starting position, which in this case, it
2170           does. However, if the same match  is  run  with  PCRE_NO_START_OPTIMIZE
2171           set,  the  initial  scan  along the subject string does not happen. The
2172           first match attempt is run starting  from  "D"  and  when  this  fails,
2173           (*COMMIT)  prevents  any  further  matches  being tried, so the overall
2174           result is "no match". If the pattern is studied,  more  start-up  opti-
2175           mizations  may  be  used. For example, a minimum length for the subject
2176           may be recorded. Consider the pattern
2177    
2178             (*MARK:A)(X|Y)
2179    
2180           The minimum length for a match is one  character.  If  the  subject  is
2181           "ABC",  there  will  be  attempts  to  match "ABC", "BC", "C", and then
2182           finally an empty string.  If the pattern is studied, the final  attempt
2183           does  not take place, because PCRE knows that the subject is too short,
2184           and so the (*MARK) is never encountered.  In this  case,  studying  the
2185           pattern  does  not  affect the overall match result, which is still "no
2186           match", but it does affect the auxiliary information that is returned.
2187    
2188           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2189    
2190         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
2191         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
2192         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
2193         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence         points  to  the start of a UTF-8 character. There is a discussion about
2194         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         the validity of UTF-8 strings in the section on UTF-8  support  in  the
2195         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2196         returned.         pcre_exec() returns  the  error  PCRE_ERROR_BADUTF8  or,  if  PCRE_PAR-
2197           TIAL_HARD  is set and the problem is a truncated UTF-8 character at the
2198         If you already know that your subject is valid, and you  want  to  skip         end of the subject, PCRE_ERROR_SHORTUTF8. In  both  cases,  information
2199         these    checks    for   performance   reasons,   you   can   set   the         about  the  precise  nature  of the error may also be returned (see the
2200         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         descriptions of these errors in the section entitled Error return  val-
2201         do  this  for the second and subsequent calls to pcre_exec() if you are         ues from pcre_exec() below).  If startoffset contains a value that does
2202         making repeated calls to find all  the  matches  in  a  single  subject         not point to the start of a UTF-8 character (or to the end of the  sub-
2203         string.  However,  you  should  be  sure  that the value of startoffset         ject), PCRE_ERROR_BADUTF8_OFFSET is returned.
2204         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is  
2205         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         If  you  already  know that your subject is valid, and you want to skip
2206         value of startoffset that does not point to the start of a UTF-8  char-         these   checks   for   performance   reasons,   you   can    set    the
2207         acter, is undefined. Your program may crash.         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
2208           do this for the second and subsequent calls to pcre_exec() if  you  are
2209           PCRE_PARTIAL         making  repeated  calls  to  find  all  the matches in a single subject
2210           string. However, you should be  sure  that  the  value  of  startoffset
2211         This  option  turns  on  the  partial  matching feature. If the subject         points  to  the start of a UTF-8 character (or the end of the subject).
2212         string fails to match the pattern, but at some point during the  match-         When PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid  UTF-8
2213         ing  process  the  end of the subject was reached (that is, the subject         string  as  a  subject or an invalid value of startoffset is undefined.
2214         partially matches the pattern and the failure to  match  occurred  only         Your program may crash.
2215         because  there were not enough subject characters), pcre_exec() returns  
2216         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is           PCRE_PARTIAL_HARD
2217         used,  there  are restrictions on what may appear in the pattern. These           PCRE_PARTIAL_SOFT
2218         are discussed in the pcrepartial documentation.  
2219           These options turn on the partial matching feature. For backwards  com-
2220           patibility,  PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
2221           match occurs if the end of the subject string is reached  successfully,
2222           but  there  are not enough subject characters to complete the match. If
2223           this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set,
2224           matching  continues  by  testing any remaining alternatives. Only if no
2225           complete match can be found is PCRE_ERROR_PARTIAL returned  instead  of
2226           PCRE_ERROR_NOMATCH.  In  other  words,  PCRE_PARTIAL_SOFT says that the
2227           caller is prepared to handle a partial match, but only if  no  complete
2228           match can be found.
2229    
2230           If  PCRE_PARTIAL_HARD  is  set, it overrides PCRE_PARTIAL_SOFT. In this
2231           case, if a partial match  is  found,  pcre_exec()  immediately  returns
2232           PCRE_ERROR_PARTIAL,  without  considering  any  other  alternatives. In
2233           other words, when PCRE_PARTIAL_HARD is set, a partial match is  consid-
2234           ered to be more important that an alternative complete match.
2235    
2236           In  both  cases,  the portion of the string that was inspected when the
2237           partial match was found is set as the first matching string. There is a
2238           more  detailed  discussion  of partial and multi-segment matching, with
2239           examples, in the pcrepartial documentation.
2240    
2241     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2242    
2243         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
2244         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.
2245         mode, the byte offset must point to the start  of  a  UTF-8  character.         If this is  negative  or  greater  than  the  length  of  the  subject,
2246         Unlike  the  pattern string, the subject may contain binary zero bytes.         pcre_exec()  returns  PCRE_ERROR_BADOFFSET. When the starting offset is
2247         When the starting offset is zero, the search for a match starts at  the         zero, the search for a match starts at the beginning  of  the  subject,
2248         beginning of the subject, and this is by far the most common case.         and this is by far the most common case. In UTF-8 mode, the byte offset
2249           must point to the start of a UTF-8 character (or the end  of  the  sub-
2250         A  non-zero  starting offset is useful when searching for another match         ject).  Unlike  the pattern string, the subject may contain binary zero
2251         in the same subject by calling pcre_exec() again after a previous  suc-         bytes.
2252         cess.   Setting  startoffset differs from just passing over a shortened  
2253         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         A non-zero starting offset is useful when searching for  another  match
2254           in  the same subject by calling pcre_exec() again after a previous suc-
2255           cess.  Setting startoffset differs from just passing over  a  shortened
2256           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2257         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2258    
2259           \Biss\B           \Biss\B
2260    
2261         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
2262         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.)
2263         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
2264         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
2265         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
2266         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
2267         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
2268         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-
2269         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
2270         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2271    
2272           Finding  all  the  matches  in a subject is tricky when the pattern can
2273           match an empty string. It is possible to emulate Perl's /g behaviour by
2274           first   trying   the   match   again  at  the  same  offset,  with  the
2275           PCRE_NOTEMPTY_ATSTART and  PCRE_ANCHORED  options,  and  then  if  that
2276           fails,  advancing  the  starting  offset  and  trying an ordinary match
2277           again. There is some code that demonstrates how to do this in the pcre-
2278           demo sample program. In the most general case, you have to check to see
2279           if the newline convention recognizes CRLF as a newline, and if so,  and
2280           the current character is CR followed by LF, advance the starting offset
2281           by two characters instead of one.
2282    
2283         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,
2284         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
2285         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
# Line 1613  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2295  MATCHING A PATTERN: THE TRADITIONAL FUNC
2295         string. PCRE supports several other kinds of  parenthesized  subpattern         string. PCRE supports several other kinds of  parenthesized  subpattern
2296         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2297    
2298         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of integers
2299         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-
2300         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:
2301         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2302    
2303         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-
2304         strings,  each  substring using a pair of integers. The remaining third         strings,  each  substring using a pair of integers. The remaining third
2305         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-
2306         turing  subpatterns, and is not available for passing back information.         turing  subpatterns, and is not available for passing back information.
2307         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
2308         it is not, it is rounded down.         it is not, it is rounded down.
2309    
2310         When  a  match  is successful, information about captured substrings is         When  a  match  is successful, information about captured substrings is
2311         returned in pairs of integers, starting at the  beginning  of  ovector,         returned in pairs of integers, starting at the  beginning  of  ovector,
2312         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
2313         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
2314         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
2315         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
2316         tor[1],  identify  the  portion  of  the  subject string matched by the         byte offsets, even in UTF-8 mode. They are not character counts.
2317         entire pattern. The next pair is used for the first  capturing  subpat-  
2318         tern,  and  so  on.  The value returned by pcre_exec() is the number of         The  first  pair  of  integers, ovector[0] and ovector[1], identify the
2319         pairs that have been set. If there are no  capturing  subpatterns,  the         portion of the subject string matched by the entire pattern.  The  next
2320         return  value  from  a  successful match is 1, indicating that just the         pair  is  used for the first capturing subpattern, and so on. The value
2321         first pair of offsets has been set.         returned by pcre_exec() is one more than the highest numbered pair that
2322           has  been  set.  For example, if two substrings have been captured, the
2323         Some convenience functions are provided  for  extracting  the  captured         returned value is 3. If there are no capturing subpatterns, the  return
2324         substrings  as  separate  strings. These are described in the following         value from a successful match is 1, indicating that just the first pair
2325         section.         of offsets has been set.
   
        It is possible for an capturing subpattern number  n+1  to  match  some  
        part  of  the  subject  when subpattern n has not been used at all. For  
        example, if the string "abc" is matched against the pattern (a|(z))(bc)  
        subpatterns  1 and 3 are matched, but 2 is not. When this happens, both  
        offset values corresponding to the unused subpattern are set to -1.  
2326    
2327         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2328         of the string that it matched that is returned.         of the string that it matched that is returned.
2329    
2330         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,
2331         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
2332         function  returns a value of zero. In particular, if the substring off-         function  returns a value of zero. If neither the actual string matched
2333         sets are not of interest, pcre_exec() may be called with ovector passed         not any captured substrings are of interest, pcre_exec() may be  called
2334         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         with  ovector passed as NULL and ovecsize as zero. However, if the pat-
2335         references and the ovector is not big enough to  remember  the  related         tern contains back references and the ovector  is  not  big  enough  to
2336         substrings,  PCRE has to get additional memory for use during matching.         remember  the related substrings, PCRE has to get additional memory for
2337         Thus it is usually advisable to supply an ovector.         use during matching. Thus it is usually advisable to supply an  ovector
2338           of reasonable size.
2339         Note that pcre_info() can be used to find out how many  capturing  sub-  
2340         patterns there are in a compiled pattern. The smallest size for ovector         There  are  some  cases where zero is returned (indicating vector over-
2341         that will allow for n captured substrings, in addition to  the  offsets         flow) when in fact the vector is exactly the right size for  the  final
2342         of the substring matched by the whole pattern, is (n+1)*3.         match. For example, consider the pattern
2343    
2344             (a)(?:(b)c|bd)
2345    
2346           If  a  vector of 6 elements (allowing for only 1 captured substring) is
2347           given with subject string "abd", pcre_exec() will try to set the second
2348           captured string, thereby recording a vector overflow, before failing to
2349           match "c" and backing up  to  try  the  second  alternative.  The  zero
2350           return,  however,  does  correctly  indicate that the maximum number of
2351           slots (namely 2) have been filled. In similar cases where there is tem-
2352           porary  overflow,  but  the final number of used slots is actually less
2353           than the maximum, a non-zero value is returned.
2354    
2355           The pcre_fullinfo() function can be used to find out how many capturing
2356           subpatterns  there  are  in  a  compiled pattern. The smallest size for
2357           ovector that will allow for n captured substrings, in addition  to  the
2358           offsets of the substring matched by the whole pattern, is (n+1)*3.
2359    
2360           It  is  possible for capturing subpattern number n+1 to match some part
2361           of the subject when subpattern n has not been used at all. For example,
2362           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
2363           return from the function is 4, and subpatterns 1 and 3 are matched, but
2364           2  is  not.  When  this happens, both values in the offset pairs corre-
2365           sponding to unused subpatterns are set to -1.
2366    
2367           Offset values that correspond to unused subpatterns at the end  of  the
2368           expression  are  also  set  to  -1. For example, if the string "abc" is
2369           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
2370           matched.  The  return  from the function is 2, because the highest used
2371           capturing subpattern number is 1, and the offsets for  for  the  second
2372           and  third  capturing subpatterns (assuming the vector is large enough,
2373           of course) are set to -1.
2374    
2375           Note: Elements in the first two-thirds of ovector that  do  not  corre-
2376           spond  to  capturing parentheses in the pattern are never changed. That
2377           is, if a pattern contains n capturing parentheses, no more  than  ovec-
2378           tor[0]  to ovector[2n+1] are set by pcre_exec(). The other elements (in
2379           the first two-thirds) retain whatever values they previously had.
2380    
2381           Some convenience functions are provided  for  extracting  the  captured
2382           substrings as separate strings. These are described below.
2383    
2384     Return values from pcre_exec()     Error return values from pcre_exec()
2385    
2386         If  pcre_exec()  fails, it returns a negative number. The following are         If  pcre_exec()  fails, it returns a negative number. The following are
2387         defined in the header file:         defined in the header file:
# Line 1691  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2407  MATCHING A PATTERN: THE TRADITIONAL FUNC
2407         an environment with the other endianness. This is the error  that  PCRE         an environment with the other endianness. This is the error  that  PCRE
2408         gives when the magic number is not present.         gives when the magic number is not present.
2409    
2410           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2411    
2412         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2413         compiled pattern. This error could be caused by a bug  in  PCRE  or  by         compiled pattern. This error could be caused by a bug  in  PCRE  or  by
# Line 1705  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2421  MATCHING A PATTERN: THE TRADITIONAL FUNC
2421         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
2422         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2423    
2424           This  error  is also given if pcre_stack_malloc() fails in pcre_exec().
2425           This can happen only when PCRE has been compiled with  --disable-stack-
2426           for-recursion.
2427    
2428           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2429    
2430         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 1713  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2433  MATCHING A PATTERN: THE TRADITIONAL FUNC
2433    
2434           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2435    
2436         The  recursion  and backtracking limit, as specified by the match_limit         The  backtracking  limit,  as  specified  by the match_limit field in a
2437         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra structure (or defaulted) was reached.  See  the  description
2438         description above.         above.
2439    
2440           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2441    
# Line 1726  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2446  MATCHING A PATTERN: THE TRADITIONAL FUNC
2446           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2447    
2448         A  string  that contains an invalid UTF-8 byte sequence was passed as a         A  string  that contains an invalid UTF-8 byte sequence was passed as a
2449         subject.         subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size  of
2450           the  output  vector  (ovecsize)  is  at least 2, the byte offset to the
2451           start of the the invalid UTF-8 character is placed in  the  first  ele-
2452           ment,  and  a  reason  code is placed in the second element. The reason
2453           codes are listed in the following section.  For backward compatibility,
2454           if  PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char-
2455           acter  at  the  end  of  the   subject   (reason   codes   1   to   5),
2456           PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
2457    
2458           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2459    
2460         The UTF-8 byte sequence that was passed as a subject was valid, but the         The  UTF-8  byte  sequence that was passed as a subject was checked and
2461           found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but  the
2462         value  of startoffset did not point to the beginning of a UTF-8 charac-         value  of startoffset did not point to the beginning of a UTF-8 charac-
2463         ter.         ter or the end of the subject.
2464    
2465           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2466    
# Line 1741  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2469  MATCHING A PATTERN: THE TRADITIONAL FUNC
2469    
2470           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2471    
2472         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         This  code  is  no  longer  in  use.  It was formerly returned when the
2473         items that are not supported for partial matching. See the  pcrepartial         PCRE_PARTIAL option was used with a compiled pattern  containing  items
2474         documentation for details of partial matching.         that  were  not  supported  for  partial  matching.  From  release 8.00
2475           onwards, there are no restrictions on partial matching.
2476    
2477           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2478    
2479         An  unexpected  internal error has occurred. This error could be caused         An unexpected internal error has occurred. This error could  be  caused
2480         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2481    
2482           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2483    
2484         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.
2485    
2486             PCRE_ERROR_RECURSIONLIMIT (-21)
2487    
2488           The internal recursion limit, as specified by the match_limit_recursion
2489           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2490           description above.
2491    
2492             PCRE_ERROR_BADNEWLINE     (-23)
2493    
2494           An invalid combination of PCRE_NEWLINE_xxx options was given.
2495    
2496             PCRE_ERROR_BADOFFSET      (-24)
2497    
2498           The value of startoffset was negative or greater than the length of the
2499           subject, that is, the value in length.
2500    
2501             PCRE_ERROR_SHORTUTF8      (-25)
2502    
2503           This error is returned instead of PCRE_ERROR_BADUTF8 when  the  subject
2504           string  ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD
2505           option is set.  Information  about  the  failure  is  returned  as  for
2506           PCRE_ERROR_BADUTF8.  It  is in fact sufficient to detect this case, but
2507           this special error code for PCRE_PARTIAL_HARD precedes the  implementa-
2508           tion  of returned information; it is retained for backwards compatibil-
2509           ity.
2510    
2511             PCRE_ERROR_RECURSELOOP    (-26)
2512    
2513           This error is returned when pcre_exec() detects a recursion loop within
2514           the  pattern. Specifically, it means that either the whole pattern or a
2515           subpattern has been called recursively for the second time at the  same
2516           position in the subject string. Some simple patterns that might do this
2517           are detected and faulted at compile time, but more  complicated  cases,
2518           in particular mutual recursions between two different subpatterns, can-
2519           not be detected until run time.
2520    
2521             PCRE_ERROR_JIT_STACKLIMIT (-27)
2522    
2523           This error is returned when a pattern  that  was  successfully  studied
2524           using  the PCRE_STUDY_JIT_COMPILE option is being matched, but the mem-
2525           ory available for  the  just-in-time  processing  stack  is  not  large
2526           enough. See the pcrejit documentation for more details.
2527    
2528           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2529    
2530       Reason codes for invalid UTF-8 strings
2531    
2532           When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT-
2533           UTF8, and the size of the output vector (ovecsize) is at least  2,  the
2534           offset  of  the  start  of the invalid UTF-8 character is placed in the
2535           first output vector element (ovector[0]) and a reason code is placed in
2536           the  second  element  (ovector[1]). The reason codes are given names in
2537           the pcre.h header file:
2538    
2539             PCRE_UTF8_ERR1
2540             PCRE_UTF8_ERR2
2541             PCRE_UTF8_ERR3
2542             PCRE_UTF8_ERR4
2543             PCRE_UTF8_ERR5
2544    
2545           The string ends with a truncated UTF-8 character;  the  code  specifies
2546           how  many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8
2547           characters to be no longer than 4 bytes, the  encoding  scheme  (origi-
2548           nally  defined  by  RFC  2279)  allows  for  up to 6 bytes, and this is
2549           checked first; hence the possibility of 4 or 5 missing bytes.
2550    
2551             PCRE_UTF8_ERR6
2552             PCRE_UTF8_ERR7
2553             PCRE_UTF8_ERR8
2554             PCRE_UTF8_ERR9
2555             PCRE_UTF8_ERR10
2556    
2557           The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of
2558           the  character  do  not have the binary value 0b10 (that is, either the
2559           most significant bit is 0, or the next bit is 1).
2560    
2561             PCRE_UTF8_ERR11
2562             PCRE_UTF8_ERR12
2563    
2564           A character that is valid by the RFC 2279 rules is either 5 or 6  bytes
2565           long; these code points are excluded by RFC 3629.
2566    
2567             PCRE_UTF8_ERR13
2568    
2569           A  4-byte character has a value greater than 0x10fff; these code points
2570           are excluded by RFC 3629.
2571    
2572             PCRE_UTF8_ERR14
2573    
2574           A 3-byte character has a value in the  range  0xd800  to  0xdfff;  this
2575           range  of code points are reserved by RFC 3629 for use with UTF-16, and
2576           so are excluded from UTF-8.
2577    
2578             PCRE_UTF8_ERR15
2579             PCRE_UTF8_ERR16
2580             PCRE_UTF8_ERR17
2581             PCRE_UTF8_ERR18
2582             PCRE_UTF8_ERR19
2583    
2584           A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it  codes
2585           for  a  value that can be represented by fewer bytes, which is invalid.
2586           For example, the two bytes 0xc0, 0xae give the value 0x2e,  whose  cor-
2587           rect coding uses just one byte.
2588    
2589             PCRE_UTF8_ERR20
2590    
2591           The two most significant bits of the first byte of a character have the
2592           binary value 0b10 (that is, the most significant bit is 1 and the  sec-
2593           ond  is  0). Such a byte can only validly occur as the second or subse-
2594           quent byte of a multi-byte character.
2595    
2596             PCRE_UTF8_ERR21
2597    
2598           The first byte of a character has the value 0xfe or 0xff. These  values
2599           can never occur in a valid UTF-8 string.
2600    
2601    
2602  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 1774  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2618  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2618         string_list() are provided for extracting captured substrings  as  new,         string_list() are provided for extracting captured substrings  as  new,
2619         separate,  zero-terminated strings. These functions identify substrings         separate,  zero-terminated strings. These functions identify substrings
2620         by number. The next section describes functions  for  extracting  named         by number. The next section describes functions  for  extracting  named
2621         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2622         extracted and has a further zero added on the end, but  the  result  is  
2623         not, of course, a C string.         A  substring that contains a binary zero is correctly extracted and has
2624           a further zero added on the end, but the result is not, of course, a  C
2625           string.   However,  you  can  process such a string by referring to the
2626           length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2627           string().  Unfortunately, the interface to pcre_get_substring_list() is
2628           not adequate for handling strings containing binary zeros, because  the
2629           end of the final string is not independently indicated.
2630    
2631         The  first  three  arguments  are the same for all three of these func-         The  first  three  arguments  are the same for all three of these func-
2632         tions: subject is the subject string that has  just  been  successfully         tions: subject is the subject string that has  just  been  successfully
# Line 1796  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2646  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2646         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2647         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2648         The yield of the function is the length of the  string,  not  including         The yield of the function is the length of the  string,  not  including
2649         the terminating zero, or one of         the terminating zero, or one of these error codes:
2650    
2651           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2652    
# Line 1812  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2662  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2662         single block of memory that is obtained via pcre_malloc. The address of         single block of memory that is obtained via pcre_malloc. The address of
2663         the  memory  block  is returned via listptr, which is also the start of         the  memory  block  is returned via listptr, which is also the start of
2664         the list of string pointers. The end of the list is marked  by  a  NULL         the list of string pointers. The end of the list is marked  by  a  NULL
2665         pointer. The yield of the function is zero if all went well, or         pointer.  The  yield  of  the function is zero if all went well, or the
2666           error code
2667    
2668           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2669    
2670         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2671    
2672         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2673         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2674         the  subject, but subpattern n has not been used at all, they return an         the subject, but subpattern n has not been used at all, they return  an
2675         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2676         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2677         tive for unset substrings.         tive for unset substrings.
2678    
2679         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2680         string_list()  can  be  used  to free the memory returned by a previous         string_list() can be used to free the memory  returned  by  a  previous
2681         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2682         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2683         pcre_free, which of course could be called directly from a  C  program.         pcre_free,  which  of course could be called directly from a C program.
2684         However,  PCRE is used in some situations where it is linked via a spe-         However, PCRE is used in some situations where it is linked via a  spe-
2685         cial  interface  to  another  programming  language  which  cannot  use         cial   interface  to  another  programming  language  that  cannot  use
2686         pcre_free  directly;  it is for these cases that the functions are pro-         pcre_free directly; it is for these cases that the functions  are  pro-
2687         vided.         vided.
2688    
2689    
# Line 1851  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2702  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2702              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2703              const char **stringptr);              const char **stringptr);
2704    
2705         To extract a substring by name, you first have to find associated  num-         To  extract a substring by name, you first have to find associated num-
2706         ber.  For example, for this pattern         ber.  For example, for this pattern
2707    
2708           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2709    
2710         the number of the subpattern called "xxx" is 2. You can find the number         the number of the subpattern called "xxx" is 2. If the name is known to
2711         from the name by calling pcre_get_stringnumber(). The first argument is         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2712         the  compiled  pattern,  and  the  second is the name. The yield of the         name by calling pcre_get_stringnumber(). The first argument is the com-
2713         function is the subpattern number, or  PCRE_ERROR_NOSUBSTRING  (-7)  if         piled pattern, and the second is the name. The yield of the function is
2714         there is no subpattern of that name.         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2715           subpattern of that name.
2716    
2717         Given the number, you can extract the substring directly, or use one of         Given the number, you can extract the substring directly, or use one of
2718         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
# Line 1879  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2731  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2731    
2732         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2733         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2734         ate.         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2735           behaviour may not be what you want (see the next section).
2736    
2737           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2738           terns with the same number, as described in the  section  on  duplicate
2739           subpattern  numbers  in  the  pcrepattern page, you cannot use names to
2740           distinguish the different subpatterns, because names are  not  included
2741           in  the compiled code. The matching process uses only numbers. For this
2742           reason, the use of different names for subpatterns of the  same  number
2743           causes an error at compile time.
2744    
2745    
2746    DUPLICATE SUBPATTERN NAMES
2747    
2748           int pcre_get_stringtable_entries(const pcre *code,
2749                const char *name, char **first, char **last);
2750    
2751           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2752           subpatterns are not required to be unique. (Duplicate names are  always
2753           allowed  for subpatterns with the same number, created by using the (?|
2754           feature. Indeed, if such subpatterns are named, they  are  required  to
2755           use the same names.)
2756    
2757           Normally, patterns with duplicate names are such that in any one match,
2758           only one of the named subpatterns participates. An example is shown  in
2759           the pcrepattern documentation.
2760    
2761           When    duplicates   are   present,   pcre_copy_named_substring()   and
2762           pcre_get_named_substring() return the first substring corresponding  to
2763           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2764           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2765           function  returns one of the numbers that are associated with the name,
2766           but it is not defined which it is.
2767    
2768           If you want to get full details of all captured substrings for a  given
2769           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2770           first argument is the compiled pattern, and the second is the name. The
2771           third  and  fourth  are  pointers to variables which are updated by the
2772           function. After it has run, they point to the first and last entries in
2773           the  name-to-number  table  for  the  given  name.  The function itself
2774           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2775           there  are none. The format of the table is described above in the sec-
2776           tion entitled Information about a pattern above.  Given all  the  rele-
2777           vant  entries  for the name, you can extract each of their numbers, and
2778           hence the captured data, if any.
2779    
2780    
2781  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
# Line 1908  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2804  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2804              int *workspace, int wscount);              int *workspace, int wscount);
2805    
2806         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2807         against a compiled pattern, using a "DFA" matching algorithm. This  has         against a compiled pattern, using a matching algorithm that  scans  the
2808         different  characteristics to the normal algorithm, and is not compati-         subject  string  just  once, and does not backtrack. This has different
2809         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics to the normal algorithm, and  is  not  compatible  with
2810         Nevertheless, there are times when this kind of matching can be useful.         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2811         For a discussion of the two matching algorithms, see  the  pcrematching         theless, there are times when this kind of matching can be useful.  For
2812         documentation.         a  discussion  of  the  two matching algorithms, and a list of features
2813           that pcre_dfa_exec() does not support, see the pcrematching  documenta-
2814           tion.
2815    
2816         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
2817         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-
# Line 1925  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2823  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2823         workspace vector should contain at least 20 elements. It  is  used  for         workspace vector should contain at least 20 elements. It  is  used  for
2824         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2825         workspace will be needed for patterns and subjects where  there  are  a         workspace will be needed for patterns and subjects where  there  are  a
2826         lot of possible matches.         lot of potential matches.
2827    
2828         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2829    
2830           int rc;           int rc;
2831           int ovector[10];           int ovector[10];
2832           int wspace[20];           int wspace[20];
2833           rc = pcre_exec(           rc = pcre_dfa_exec(
2834             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2835             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2836             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1947  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2845  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2845     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2846    
2847         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
2848         zero. The only bits that may be  set  are  PCRE_ANCHORED,  PCRE_NOTBOL,         zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2849         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2850         PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last  three  of         PCRE_NOTEMPTY_ATSTART,      PCRE_NO_UTF8_CHECK,       PCRE_BSR_ANYCRLF,
2851         these  are  the  same  as  for pcre_exec(), so their description is not         PCRE_BSR_UNICODE,  PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR-
2852         repeated here.         TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART.  All but  the  last
2853           four  of  these  are  exactly  the  same  as  for pcre_exec(), so their
2854           PCRE_PARTIAL         description is not repeated here.
2855    
2856         This has the same general effect as it does for  pcre_exec(),  but  the           PCRE_PARTIAL_HARD
2857         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for           PCRE_PARTIAL_SOFT
2858         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into  
2859         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
2860         been no complete matches, but there is still at least one matching pos-         details  are  slightly  different.  When  PCRE_PARTIAL_HARD  is set for
2861         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-
2862         set as the first matching string.         ject  is  reached  and there is still at least one matching possibility
2863           that requires additional characters. This happens even if some complete
2864           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2865           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2866           of  the  subject  is  reached, there have been no complete matches, but
2867           there is still at least one matching possibility. The  portion  of  the
2868           string  that  was inspected when the longest partial match was found is
2869           set as the first matching string  in  both  cases.   There  is  a  more
2870           detailed  discussion  of partial and multi-segment matching, with exam-
2871           ples, in the pcrepartial documentation.
2872    
2873           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2874    
2875         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2876         stop  as  soon  as  it  has found one match. Because of the way the DFA         stop as soon as it has found one match. Because of the way the alterna-
2877         algorithm works, this is necessarily the shortest possible match at the         tive algorithm works, this is necessarily the shortest  possible  match
2878         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2879    
2880           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2881    
2882         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
2883         returns a partial match, it is possible to call it  again,  with  addi-         again, with additional subject characters, and have  it  continue  with
2884         tional  subject  characters,  and have it continue with the same match.         the  same match. The PCRE_DFA_RESTART option requests this action; when
2885         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
2886         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
2887         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
2888         match.  There  is  more  discussion of this facility in the pcrepartial         pcrepartial documentation.
        documentation.  
2889    
2890     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2891    
2892         When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-         When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2893         string in the subject. Note, however, that all the matches from one run         string in the subject. Note, however, that all the matches from one run
2894         of the function start at the same point in  the  subject.  The  shorter         of  the  function  start  at the same point in the subject. The shorter
2895         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2896         if the pattern         if the pattern
2897    
2898           <.*>           <.*>
# Line 2001  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2907  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2907           <something> <something else>           <something> <something else>
2908           <something> <something else> <something further>           <something> <something else> <something further>
2909    
2910         On success, the yield of the function is a number  greater  than  zero,         On  success,  the  yield of the function is a number greater than zero,
2911         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2912         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2913         the  offset  to the start, and the second is the offset to the end. All         the offset to the start, and the second is the offset to  the  end.  In
2914         the strings have the same start offset. (Space could have been saved by         fact,  all  the  strings  have the same start offset. (Space could have
2915         giving  this only once, but it was decided to retain some compatibility         been saved by giving this only once, but it was decided to retain  some
2916         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility  with  the  way pcre_exec() returns data, even though the
2917         strings is different.)         meaning of the strings is different.)
2918    
2919         The strings are returned in reverse order of length; that is, the long-         The strings are returned in reverse order of length; that is, the long-
2920         est matching string is given first. If there were too many  matches  to         est  matching  string is given first. If there were too many matches to
2921         fit  into ovector, the yield of the function is zero, and the vector is         fit into ovector, the yield of the function is zero, and the vector  is
2922         filled with the longest matches.         filled  with  the  longest matches. Unlike pcre_exec(), pcre_dfa_exec()
2923           can use the entire ovector for returning matched strings.
2924    
2925     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2926    
# Line 2030  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2937  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2937    
2938           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2939    
2940         This  return is given if pcre_dfa_exec() encounters a condition item in         This  return  is  given  if pcre_dfa_exec() encounters a condition item
2941         a pattern that uses a back reference for the  condition.  This  is  not         that uses a back reference for the condition, or a test  for  recursion
2942         supported.         in a specific group. These are not supported.
2943    
2944           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2945    
2946         This  return  is given if pcre_dfa_exec() is called with an extra block         This  return  is given if pcre_dfa_exec() is called with an extra block
2947         that contains a setting of the match_limit field. This is not supported         that contains a setting of  the  match_limit  or  match_limit_recursion
2948         (it is meaningless).         fields.  This  is  not  supported (these fields are meaningless for DFA
2949           matching).
2950    
2951           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2952    
2953         This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the         This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2954         workspace vector.         workspace vector.
2955    
2956           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2957    
2958         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2959         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2960         This error is given if the output vector  is  not  large  enough.  This         This  error  is  given  if  the output vector is not large enough. This
2961         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2962    
 Last updated: 16 May 2005  
 Copyright (c) 1997-2005 University of Cambridge.  
 ------------------------------------------------------------------------------  
2963    
2964    SEE ALSO
2965    
2966  PCRECALLOUT(3)                                                  PCRECALLOUT(3)         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2967           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2968    
2969    
2970  NAME  AUTHOR
2971         PCRE - Perl-compatible regular expressions  
2972           Philip Hazel
2973           University Computing Service
2974           Cambridge CB2 3QH, England.
2975    
2976    
2977    REVISION
2978    
2979           Last updated: 06 September 2011
2980           Copyright (c) 1997-2011 University of Cambridge.
2981    ------------------------------------------------------------------------------
2982    
2983    
2984    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2985    
2986    
2987    NAME
2988           PCRE - Perl-compatible regular expressions
2989    
2990    
2991  PCRE CALLOUTS  PCRE CALLOUTS
# Line 2080  PCRE CALLOUTS Line 3004  PCRE CALLOUTS
3004         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
3005         points:         points:
3006    
3007           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
3008    
3009         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
3010         called, PCRE automatically  inserts  callouts,  all  with  number  255,         pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
3011         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
3012         used with the pattern         PCRE_AUTO_CALLOUT is used with the pattern
3013    
3014           A(\d{2}|--)           A(\d{2}|--)
3015    
# Line 2100  PCRE CALLOUTS Line 3024  PCRE CALLOUTS
3024         pattern is matched. This is useful information when you are  trying  to         pattern is matched. This is useful information when you are  trying  to
3025         optimize the performance of a particular pattern.         optimize the performance of a particular pattern.
3026    
3027           The  use  of callouts in a pattern makes it ineligible for optimization
3028           by  the  just-in-time  compiler.  Studying  such  a  pattern  with  the
3029           PCRE_STUDY_JIT_COMPILE option always fails.
3030    
3031    
3032  MISSING CALLOUTS  MISSING CALLOUTS
3033    
3034         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
3035         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
3036         pattern is         example, if the pattern is
3037    
3038           ab(?C4)cd           ab(?C4)cd
3039    
# Line 2114  MISSING CALLOUTS Line 3042  MISSING CALLOUTS
3042         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
3043         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
3044    
3045           If the pattern is studied, PCRE knows the minimum length of a  matching
3046           string,  and will immediately give a "no match" return without actually
3047           running a match if the subject is not long enough, or,  for  unanchored
3048           patterns, if it has been scanned far enough.
3049    
3050           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
3051           MIZE option to pcre_compile(), pcre_exec(), or pcre_dfa_exec(),  or  by
3052           starting the pattern with (*NO_START_OPT). This slows down the matching
3053           process, but does ensure that callouts such as the  example  above  are
3054           obeyed.
3055    
3056    
3057  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
3058    
3059         During matching, when PCRE reaches a callout point, the external  func-         During  matching, when PCRE reaches a callout point, the external func-
3060         tion  defined by pcre_callout is called (if it is set). This applies to         tion defined by pcre_callout is called (if it is set). This applies  to
3061         both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The         both  the  pcre_exec()  and the pcre_dfa_exec() matching functions. The
3062         only  argument  to  the callout function is a pointer to a pcre_callout         only argument to the callout function is a pointer  to  a  pcre_callout
3063         block. This structure contains the following fields:         block. This structure contains the following fields:
3064    
3065           int          version;           int         version;
3066           int          callout_number;           int         callout_number;
3067           int         *offset_vector;           int        *offset_vector;
3068           const char  *subject;           const char *subject;
3069           int          subject_length;           int         subject_length;
3070           int          start_match;           int         start_match;
3071           int          current_position;           int         current_position;
3072           int          capture_top;           int         capture_top;
3073           int          capture_last;           int         capture_last;
3074           void        *callout_data;           void       *callout_data;
3075           int          pattern_position;           int         pattern_position;
3076           int          next_item_length;           int         next_item_length;
3077             const unsigned char *mark;
3078         The version field is an integer containing the version  number  of  the  
3079         block  format. The initial version was 0; the current version is 1. The         The  version  field  is an integer containing the version number of the
3080         version number will change again in future  if  additional  fields  are         block format. The initial version was 0; the current version is 2.  The
3081           version  number  will  change  again in future if additional fields are
3082         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.
3083    
3084         The callout_number field contains the number of the  callout,  as  com-         The callout_number field contains the number of the  callout,  as  com-
# Line 2155  THE CALLOUT INTERFACE Line 3095  THE CALLOUT INTERFACE
3095         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
3096         were passed to pcre_exec().         were passed to pcre_exec().
3097    
3098         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
3099         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
3100         callout function may be called several times from the same point in the         sequence \K has been encountered, this value is changed to reflect  the
3101         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
3102           function may be called several times from the same point in the pattern
3103           for different starting points in the subject.
3104    
3105         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
3106         the current match pointer.         the current match pointer.
# Line 2195  THE CALLOUT INTERFACE Line 3137  THE CALLOUT INTERFACE
3137         in  distinguishing between different automatic callouts, which all have         in  distinguishing between different automatic callouts, which all have
3138         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
3139    
3140           The mark field is present from version 2 of the pcre_callout structure.
3141           In  callouts  from pcre_exec() it contains a pointer to the zero-termi-
3142           nated name of the most recently passed (*MARK) item in  the  match,  or
3143           NULL if there are no (*MARK)s in the current matching path. In callouts
3144           from pcre_dfa_exec() this field always contains NULL.
3145    
3146    
3147  RETURN VALUES  RETURN VALUES
3148    
# Line 2203  RETURN VALUES Line 3151  RETURN VALUES
3151         zero, matching fails at the current point, but  the  testing  of  other         zero, matching fails at the current point, but  the  testing  of  other
3152         matching possibilities goes ahead, just as if a lookahead assertion had         matching possibilities goes ahead, just as if a lookahead assertion had
3153         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
3154         pcre_exec() (or pcre_dfa_exec()) returns the negative value.         pcre_exec() or pcre_dfa_exec() returns the negative value.
3155    
3156         Negative   values   should   normally   be   chosen  from  the  set  of         Negative   values   should   normally   be   chosen  from  the  set  of
3157         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
# Line 2211  RETURN VALUES Line 3159  RETURN VALUES
3159         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
3160         itself.         itself.
3161    
3162  Last updated: 28 February 2005  
3163  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
3164    
3165           Philip Hazel
3166           University Computing Service
3167           Cambridge CB2 3QH, England.
3168    
3169    
3170    REVISION
3171    
3172           Last updated: 26 August 2011
3173           Copyright (c) 1997-2011 University of Cambridge.
3174  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3175    
3176    
# Line 2227  DIFFERENCES BETWEEN PCRE AND PERL Line 3185  DIFFERENCES BETWEEN PCRE AND PERL
3185    
3186         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
3187         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences  described  here  are  with
3188         respect to Perl 5.8.         respect to Perl versions 5.10 and above.
3189    
3190         1.  PCRE does not have full UTF-8 support. Details of what it does have         1.  PCRE has only a subset of Perl's UTF-8 and Unicode support. Details
3191         are given in the section on UTF-8 support in the main pcre page.         of what it does have are given in the pcreunicode page.
3192    
3193         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE allows repeat quantifiers only on parenthesized assertions, but
3194         permits  them,  but they do not mean what you might think. For example,         they  do  not mean what you might think. For example, (?!a){3} does not
3195         (?!a){3} does not assert that the next three characters are not "a". It         assert that the next three characters are not "a". It just asserts that
3196         just asserts that the next character is not "a" three times.         the next character is not "a" three times (in principle: PCRE optimizes
3197           this to run the assertion just once). Perl allows repeat quantifiers on
3198           other assertions such as \b, but these do not seem to have any use.
3199    
3200         3.  Capturing  subpatterns  that occur inside negative lookahead asser-         3.  Capturing  subpatterns  that occur inside negative lookahead asser-
3201         tions are counted, but their entries in the offsets  vector  are  never         tions are counted, but their entries in the offsets  vector  are  never
# Line 2250  DIFFERENCES BETWEEN PCRE AND PERL Line 3210  DIFFERENCES BETWEEN PCRE AND PERL
3210         the pattern to represent a binary zero.         the pattern to represent a binary zero.
3211    
3212         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5.  The  following Perl escape sequences are not supported: \l, \u, \L,
3213         \U, and \N. In fact these are implemented by Perl's general string-han-         \U, and \N when followed by a character name or Unicode value.  (\N  on
3214         dling  and are not part of its pattern matching engine. If any of these         its own, matching a non-newline character, is supported.) In fact these
3215         are encountered by PCRE, an error is generated.         are implemented by Perl's general string-handling and are not  part  of
3216           its  pattern  matching engine. If any of these are encountered by PCRE,
3217           an error is generated.
3218    
3219         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
3220         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
3221         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-
3222         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
3223           derived properties Any and L&. PCRE does  support  the  Cs  (surrogate)
3224           property,  which  Perl  does  not; the Perl documentation says "Because
3225           Perl hides the need for the user to understand the internal representa-
3226           tion  of Unicode characters, there is no need to implement the somewhat
3227           messy concept of surrogates."
3228    
3229           7. PCRE implements a simpler version of \X than Perl, which changed  to
3230           make  \X  match what Unicode calls an "extended grapheme cluster". This
3231           is more complicated than an extended Unicode sequence,  which  is  what
3232           PCRE matches.
3233    
3234         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         8. PCRE does support the \Q...\E escape for quoting substrings. Charac-
3235         ters in between are treated as literals.  This  is  slightly  different         ters in between are treated as literals.  This  is  slightly  different
3236         from  Perl  in  that  $  and  @ are also handled as literals inside the         from  Perl  in  that  $  and  @ are also handled as literals inside the
3237         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes. In Perl, they cause variable interpolation (but of course  PCRE
# Line 2275  DIFFERENCES BETWEEN PCRE AND PERL Line 3247  DIFFERENCES BETWEEN PCRE AND PERL
3247         The  \Q...\E  sequence  is recognized both inside and outside character         The  \Q...\E  sequence  is recognized both inside and outside character
3248         classes.         classes.
3249    
3250         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         9. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
3251         constructions.  However,  there is support for recursive patterns using         constructions.  However,  there is support for recursive patterns. This
3252         the non-Perl items (?R),  (?number),  and  (?P>name).  Also,  the  PCRE         is not available in Perl 5.8, but it is in Perl 5.10.  Also,  the  PCRE
3253         "callout"  feature allows an external function to be called during pat-         "callout"  feature allows an external function to be called during pat-
3254         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
3255    
3256         9. There are some differences that are concerned with the  settings  of         10. Subpatterns that are called recursively  or  as  "subroutines"  are
3257           always  treated  as  atomic  groups  in  PCRE. This is like Python, but
3258           unlike Perl. There is a discussion of an example that explains this  in
3259           more  detail  in  the section on recursion differences from Perl in the
3260           pcrepattern page.
3261    
3262           11. There are some differences that are concerned with the settings  of
3263         captured  strings  when  part  of  a  pattern is repeated. For example,         captured  strings  when  part  of  a  pattern is repeated. For example,
3264         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
3265         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
3266    
3267         10. PCRE provides some extensions to the Perl regular expression facil-         12.  PCRE's handling of duplicate subpattern numbers and duplicate sub-
3268         ities:         pattern names is not as general as Perl's. This is a consequence of the
3269           fact the PCRE works internally just with numbers, using an external ta-
3270           ble to translate between numbers and names. In  particular,  a  pattern
3271           such  as  (?|(?<a>A)|(?<b)B),  where the two capturing parentheses have
3272           the same number but different names, is not supported,  and  causes  an
3273           error  at compile time. If it were allowed, it would not be possible to
3274           distinguish which parentheses matched, because both names map  to  cap-
3275           turing subpattern number 1. To avoid this confusing situation, an error
3276           is given at compile time.
3277    
3278           13. Perl recognizes comments in some places that  PCRE  does  not,  for
3279           example,  between  the  ( and ? at the start of a subpattern. If the /x
3280           modifier is set, Perl allows whitespace between ( and ? but PCRE  never
3281           does, even if the PCRE_EXTENDED option is set.
3282    
3283           14. PCRE provides some extensions to the Perl regular expression facil-
3284           ities.  Perl 5.10 includes new features that are not  in  earlier  ver-
3285           sions  of  Perl, some of which (such as named parentheses) have been in
3286           PCRE for some time. This list is with respect to Perl 5.10:
3287    
3288           (a) Although lookbehind assertions in  PCRE  must  match  fixed  length
3289           strings,  each alternative branch of a lookbehind assertion can match a
3290           different length of string. Perl requires them all  to  have  the  same
3291           length.
3292    
3293         (a) Although lookbehind assertions must  match  fixed  length  strings,         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
        each alternative branch of a lookbehind assertion can match a different  
        length of string. Perl requires them all to have the same length.  
   
        (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $