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revision 73 by nigel, Sat Feb 24 21:40:30 2007 UTC revision 358 by ph10, Wed Jul 9 11:03:07 2008 UTC
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1    -----------------------------------------------------------------------------
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
# Line 5  synopses of each function in the library Line 6  synopses of each function in the library
6  separate text files for the pcregrep and pcretest commands.  separate text files for the pcregrep and pcretest commands.
7  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
8    
 PCRE(3)                                                                PCRE(3)  
9    
10    PCRE(3)                                                                PCRE(3)
11    
12    
13  NAME  NAME
14         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
15    
16  DESCRIPTION  
17    INTRODUCTION
18    
19         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
20         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
21         just  a  few  differences.  The current implementation of PCRE (release         just  a  few  differences. Certain features that appeared in Python and
22         4.x) corresponds approximately with Perl  5.8,  including  support  for         PCRE before they appeared in Perl are also available using  the  Python
23         UTF-8  encoded  strings.   However,  this  support has to be explicitly         syntax.  There is also some support for certain .NET and Oniguruma syn-
24         enabled; it is not the default.         tax items, and there is an option for  requesting  some  minor  changes
25           that give better JavaScript compatibility.
26         PCRE is written in C and released as a C library. However, a number  of  
27         people  have  written  wrappers  and interfaces of various kinds. A C++         The  current  implementation of PCRE (release 7.x) corresponds approxi-
28         class is included in these contributions, which can  be  found  in  the         mately with Perl 5.10, including support for UTF-8 encoded strings  and
29           Unicode general category properties. However, UTF-8 and Unicode support
30           has to be explicitly enabled; it is not the default. The Unicode tables
31           correspond to Unicode release 5.0.0.
32    
33           In  addition to the Perl-compatible matching function, PCRE contains an
34           alternative matching function that matches the same  compiled  patterns
35           in  a different way. In certain circumstances, the alternative function
36           has some advantages. For a discussion of the two  matching  algorithms,
37           see the pcrematching page.
38    
39           PCRE  is  written  in C and released as a C library. A number of people
40           have written wrappers and interfaces of various kinds.  In  particular,
41           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
42           included as part of the PCRE distribution. The pcrecpp page has details
43           of  this  interface.  Other  people's contributions can be found in the
44         Contrib directory at the primary FTP site, which is:         Contrib directory at the primary FTP site, which is:
45    
46         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
47    
48         Details  of  exactly which Perl regular expression features are and are         Details of exactly which Perl regular expression features are  and  are
49         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
50         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
51           page.
52    
53         Some  features  of  PCRE can be included, excluded, or changed when the         Some  features  of  PCRE can be included, excluded, or changed when the
54         library is built. The pcre_config() function makes it  possible  for  a         library is built. The pcre_config() function makes it  possible  for  a
55         client  to  discover  which features are available. Documentation about         client  to  discover  which  features are available. The features them-
56         building PCRE for various operating systems can be found in the  README         selves are described in the pcrebuild page. Documentation about  build-
57         file in the source distribution.         ing  PCRE for various operating systems can be found in the README file
58           in the source distribution.
59    
60           The library contains a number of undocumented  internal  functions  and
61           data  tables  that  are  used by more than one of the exported external
62           functions, but which are not intended  for  use  by  external  callers.
63           Their  names  all begin with "_pcre_", which hopefully will not provoke
64           any name clashes. In some environments, it is possible to control which
65           external  symbols  are  exported when a shared library is built, and in
66           these cases the undocumented symbols are not exported.
67    
68    
69  USER DOCUMENTATION  USER DOCUMENTATION
70    
71         The user documentation for PCRE has been split up into a number of dif-         The user documentation for PCRE comprises a number  of  different  sec-
72         ferent sections. In the "man" format, each of these is a separate  "man         tions.  In the "man" format, each of these is a separate "man page". In
73         page".  In  the  HTML  format, each is a separate page, linked from the         the HTML format, each is a separate page, linked from the  index  page.
74         index page. In the plain text format, all  the  sections  are  concate-         In  the  plain text format, all the sections are concatenated, for ease
75         nated, for ease of searching. The sections are as follows:         of searching. The sections are as follows:
76    
77           pcre              this document           pcre              this document
78           pcreapi           details of PCRE's native API           pcre-config       show PCRE installation configuration information
79             pcreapi           details of PCRE's native C API
80           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
81           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
82           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
83             pcrecpp           details of the C++ wrapper
84           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
85             pcrematching      discussion of the two matching algorithms
86             pcrepartial       details of the partial matching facility
87           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
88                               regular expressions                               regular expressions
89             pcresyntax        quick syntax reference
90           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
91           pcreposix         the POSIX-compatible API           pcreposix         the POSIX-compatible C API
92             pcreprecompile    details of saving and re-using precompiled patterns
93           pcresample        discussion of the sample program           pcresample        discussion of the sample program
94           pcretest          the pcretest testing command           pcrestack         discussion of stack usage
95             pcretest          description of the pcretest testing command
96    
97         In  addition,  in the "man" and HTML formats, there is a short page for         In  addition,  in the "man" and HTML formats, there is a short page for
98         each library function, listing its arguments and results.         each C library function, listing its arguments and results.
99    
100    
101  LIMITATIONS  LIMITATIONS
# Line 74  LIMITATIONS Line 108  LIMITATIONS
108         process  regular  expressions  that are truly enormous, you can compile         process  regular  expressions  that are truly enormous, you can compile
109         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
110         the  source  distribution and the pcrebuild documentation for details).         the  source  distribution and the pcrebuild documentation for details).
111         If these cases the limit is substantially larger.  However,  the  speed         In these cases the limit is substantially larger.  However,  the  speed
112         of execution will be slower.         of execution is slower.
113    
114         All values in repeating quantifiers must be less than 65536.  The maxi-         All values in repeating quantifiers must be less than 65536.
        mum number of capturing subpatterns is 65535.  
115    
116         There is no limit to the number of non-capturing subpatterns,  but  the         There is no limit to the number of parenthesized subpatterns, but there
117         maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,         can be no more than 65535 capturing subpatterns.
        including capturing subpatterns, assertions, and other types of subpat-  
        tern, is 200.  
118    
119         The  maximum  length of a subject string is the largest positive number         The maximum length of name for a named subpattern is 32 characters, and
120         that an integer variable can hold. However, PCRE uses recursion to han-         the maximum number of named subpatterns is 10000.
        dle  subpatterns  and indefinite repetition. This means that the avail-  
        able stack space may limit the size of a subject  string  that  can  be  
        processed by certain patterns.  
121    
122           The  maximum  length of a subject string is the largest positive number
123           that an integer variable can hold. However, when using the  traditional
124           matching function, PCRE uses recursion to handle subpatterns and indef-
125           inite repetition.  This means that the available stack space may  limit
126           the size of a subject string that can be processed by certain patterns.
127           For a discussion of stack issues, see the pcrestack documentation.
128    
 UTF-8 SUPPORT  
129    
130         Starting  at  release  3.3,  PCRE  has  had  some support for character  UTF-8 AND UNICODE PROPERTY SUPPORT
131         strings encoded in the UTF-8 format. For  release  4.0  this  has  been  
132         greatly extended to cover most common requirements.         From release 3.3, PCRE has  had  some  support  for  character  strings
133           encoded  in the UTF-8 format. For release 4.0 this was greatly extended
134           to cover most common requirements, and in release 5.0  additional  sup-
135           port for Unicode general category properties was added.
136    
137         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
138         support in the code, and, in addition,  you  must  call  pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
# Line 106  UTF-8 SUPPORT Line 142  UTF-8 SUPPORT
142    
143         If  you compile PCRE with UTF-8 support, but do not use it at run time,         If  you compile PCRE with UTF-8 support, but do not use it at run time,
144         the library will be a bit bigger, but the additional run time  overhead         the library will be a bit bigger, but the additional run time  overhead
145         is  limited  to testing the PCRE_UTF8 flag in several places, so should         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
146         not be very large.         very big.
147    
148         The following comments apply when PCRE is running in UTF-8 mode:         If PCRE is built with Unicode character property support (which implies
149           UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
150           ported.  The available properties that can be tested are limited to the
151           general  category  properties such as Lu for an upper case letter or Nd
152           for a decimal number, the Unicode script names such as Arabic  or  Han,
153           and  the  derived  properties  Any  and L&. A full list is given in the
154           pcrepattern documentation. Only the short names for properties are sup-
155           ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-
156           ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
157           optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
158           does not support this.
159    
160       Validity of UTF-8 strings
161    
162           When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
163           subjects are (by default) checked for validity on entry to the relevant
164           functions. From release 7.3 of PCRE, the check is according  the  rules
165           of  RFC  3629, which are themselves derived from the Unicode specifica-
166           tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
167           allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
168           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
169           to U+DFFF.
170    
171           The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
172           which the Unicode Standard says this: "The Low Surrogate Area does  not
173           contain  any  character  assignments,  consequently  no  character code
174           charts or namelists are provided for this area. Surrogates are reserved
175           for  use  with  UTF-16 and then must be used in pairs." The code points
176           that are encoded by UTF-16 pairs  are  available  as  independent  code
177           points  in  the  UTF-8  encoding.  (In other words, the whole surrogate
178           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
179    
180           If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return
181           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
182           that your strings are valid, and therefore want to skip these checks in
183           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
184           compile time or at run time, PCRE assumes that the pattern  or  subject
185           it  is  given  (respectively)  contains only valid UTF-8 codes. In this
186           case, it does not diagnose an invalid UTF-8 string.
187    
188           If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,
189           what  happens  depends on why the string is invalid. If the string con-
190           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
191           string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,
192           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
193           strings  according  to  the more liberal rules of RFC 2279. However, if
194           the string does not even conform to RFC 2279, the result is  undefined.
195           Your program may crash.
196    
197           If  you  want  to  process  strings  of  values  in the full range 0 to
198           0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can
199           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
200           this situation, you will have to apply your own validity check.
201    
202       General comments about UTF-8 mode
203    
204         1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
205         subjects  are  checked for validity on entry to the relevant functions.         two-byte UTF-8 character if the value is greater than 127.
        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.  
206    
207         3.  The  original hexadecimal escape sequence, \xhh, matches a two-byte         2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8
208         UTF-8 character if the value is greater than 127.         characters for values greater than \177.
209    
210         4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
211         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
212    
213         5.  The  dot  metacharacter  matches  one  UTF-8 character instead of a         4.  The dot metacharacter matches one UTF-8 character instead of a sin-
214         single byte.         gle byte.
215    
216         6. The escape sequence \C can be used to match a single byte  in  UTF-8         5. The escape sequence \C can be used to match a single byte  in  UTF-8
217         mode, but its use can lead to some strange effects.         mode,  but  its  use can lead to some strange effects. This facility is
218           not available in the alternative matching function, pcre_dfa_exec().
219    
220           6. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly
221           test  characters of any code value, but the characters that PCRE recog-
222           nizes as digits, spaces, or word characters  remain  the  same  set  as
223           before, all with values less than 256. This remains true even when PCRE
224           includes Unicode property support, because to do otherwise  would  slow
225           down  PCRE in many common cases. If you really want to test for a wider
226           sense of, say, "digit", you must use Unicode  property  tests  such  as
227           \p{Nd}.
228    
229           7.  Similarly,  characters that match the POSIX named character classes
230           are all low-valued characters.
231    
232           8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
233           escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
234           acters.
235    
236           9. Case-insensitive matching applies only to  characters  whose  values
237           are  less than 128, unless PCRE is built with Unicode property support.
238           Even when Unicode property support is available, PCRE  still  uses  its
239           own  character  tables when checking the case of low-valued characters,
240           so as not to degrade performance.  The Unicode property information  is
241           used only for characters with higher values. Even when Unicode property
242           support is available, PCRE supports case-insensitive matching only when
243           there  is  a  one-to-one  mapping between a letter's cases. There are a
244           small number of many-to-one mappings in Unicode;  these  are  not  sup-
245           ported by PCRE.
246    
        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.  
   
        8. Case-insensitive matching applies only to  characters  whose  values  
        are  less  than  256.  PCRE  does  not support the notion of "case" for  
        higher-valued characters.  
247    
248         9. PCRE does not support the use of Unicode tables  and  properties  or  AUTHOR
        the Perl escapes \p, \P, and \X.  
249    
250           Philip Hazel
251           University Computing Service
252           Cambridge CB2 3QH, England.
253    
254  AUTHOR         Putting  an actual email address here seems to have been a spam magnet,
255           so I've taken it away. If you want to email me, use  my  two  initials,
256           followed by the two digits 10, at the domain cam.ac.uk.
257    
        Philip Hazel <ph10@cam.ac.uk>  
        University Computing Service,  
        Cambridge CB2 3QG, England.  
        Phone: +44 1223 334714  
258    
259  Last updated: 20 August 2003  REVISION
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
260    
261  PCRE(3)                                                                PCRE(3)         Last updated: 12 April 2008
262           Copyright (c) 1997-2008 University of Cambridge.
263    ------------------------------------------------------------------------------
264    
265    
266    PCREBUILD(3)                                                      PCREBUILD(3)
267    
268    
269  NAME  NAME
270         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
271    
272    
273  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
274    
275         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
276         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
277         lected,  by  providing  options  to  the  configure script which is run         script,  where the optional features are selected or deselected by pro-
278         before the make command. The complete list  of  options  for  configure         viding options to configure before running the make  command.  However,
279         (which  includes the standard ones such as the selection of the instal-         the  same  options  can be selected in both Unix-like and non-Unix-like
280         lation directory) can be obtained by running         environments using the GUI facility of  CMakeSetup  if  you  are  using
281           CMake instead of configure to build PCRE.
282    
283           The complete list of options for configure (which includes the standard
284           ones such as the  selection  of  the  installation  directory)  can  be
285           obtained by running
286    
287           ./configure --help           ./configure --help
288    
289         The following sections describe certain options whose names begin  with         The  following  sections  include  descriptions  of options whose names
290         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
291         for the configure command. Because of the  way  that  configure  works,         defaults  for  the configure command. Because of the way that configure
292         --enable  and  --disable  always  come  in  pairs, so the complementary         works, --enable and --disable always come in pairs, so  the  complemen-
293         option always exists as well, but as it specifies the  default,  it  is         tary  option always exists as well, but as it specifies the default, it
294         not described.         is not described.
295    
296    
297    C++ SUPPORT
298    
299           By default, the configure script will search for a C++ compiler and C++
300           header files. If it finds them, it automatically builds the C++ wrapper
301           library for PCRE. You can disable this by adding
302    
303             --disable-cpp
304    
305           to the configure command.
306    
307    
308  UTF-8 SUPPORT  UTF-8 SUPPORT
# Line 198  UTF-8 SUPPORT Line 311  UTF-8 SUPPORT
311    
312           --enable-utf8           --enable-utf8
313    
314         to  the  configure  command.  Of  itself, this does not make PCRE treat         to the configure command. Of itself, this  does  not  make  PCRE  treat
315         strings as UTF-8. As well as compiling PCRE with this option, you  also         strings  as UTF-8. As well as compiling PCRE with this option, you also
316         have  have to set the PCRE_UTF8 option when you call the pcre_compile()         have have to set the PCRE_UTF8 option when you call the  pcre_compile()
317         function.         function.
318    
319    
320    UNICODE CHARACTER PROPERTY SUPPORT
321    
322           UTF-8  support allows PCRE to process character values greater than 255
323           in the strings that it handles. On its own, however, it does  not  pro-
324           vide any facilities for accessing the properties of such characters. If
325           you want to be able to use the pattern escapes \P, \p,  and  \X,  which
326           refer to Unicode character properties, you must add
327    
328             --enable-unicode-properties
329    
330           to  the configure command. This implies UTF-8 support, even if you have
331           not explicitly requested it.
332    
333           Including Unicode property support adds around 30K  of  tables  to  the
334           PCRE  library.  Only  the general category properties such as Lu and Nd
335           are supported. Details are given in the pcrepattern documentation.
336    
337    
338  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
339    
340         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating
341         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
342         compile PCRE to use character 13 (carriage return) instead by adding         systems. You can compile PCRE to use character 13 (carriage return, CR)
343           instead, by adding
344    
345           --enable-newline-is-cr           --enable-newline-is-cr
346    
347         to the configure command. For completeness there is  also  a  --enable-         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
348         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
349         line character.  
350           Alternatively, you can specify that line endings are to be indicated by
351           the two character sequence CRLF. If you want this, add
352    
353             --enable-newline-is-crlf
354    
355           to the configure command. There is a fourth option, specified by
356    
357             --enable-newline-is-anycrlf
358    
359           which  causes  PCRE  to recognize any of the three sequences CR, LF, or
360           CRLF as indicating a line ending. Finally, a fifth option, specified by
361    
362             --enable-newline-is-any
363    
364           causes PCRE to recognize any Unicode newline sequence.
365    
366           Whatever  line  ending convention is selected when PCRE is built can be
367           overridden when the library functions are called. At build time  it  is
368           conventional to use the standard for your operating system.
369    
370    
371    WHAT \R MATCHES
372    
373           By  default,  the  sequence \R in a pattern matches any Unicode newline
374           sequence, whatever has been selected as the line  ending  sequence.  If
375           you specify
376    
377             --enable-bsr-anycrlf
378    
379           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
380           ever is selected when PCRE is built can be overridden when the  library
381           functions are called.
382    
383    
384  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
385    
386         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
387         Unix  libraries by default. You can suppress one of these by adding one         Unix libraries by default. You can suppress one of these by adding  one
388         of         of
389    
390           --disable-shared           --disable-shared
# Line 231  BUILDING SHARED AND STATIC LIBRARIES Line 395  BUILDING SHARED AND STATIC LIBRARIES
395    
396  POSIX MALLOC USAGE  POSIX MALLOC USAGE
397    
398         When PCRE is called through the  POSIX  interface  (see  the  pcreposix         When PCRE is called through the POSIX interface (see the pcreposix doc-
399         documentation),  additional working storage is required for holding the         umentation), additional working storage is  required  for  holding  the
400         pointers to capturing substrings because PCRE requires  three  integers         pointers  to capturing substrings, because PCRE requires three integers
401         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
402         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
403         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.
404         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 245  POSIX MALLOC USAGE Line 409  POSIX MALLOC USAGE
409         to the configure command.         to the configure command.
410    
411    
412    HANDLING VERY LARGE PATTERNS
413    
414           Within a compiled pattern, offset values are used  to  point  from  one
415           part  to another (for example, from an opening parenthesis to an alter-
416           nation metacharacter). By default, two-byte values are used  for  these
417           offsets,  leading  to  a  maximum size for a compiled pattern of around
418           64K. This is sufficient to handle all but the most  gigantic  patterns.
419           Nevertheless,  some  people do want to process enormous patterns, so it
420           is possible to compile PCRE to use three-byte or four-byte  offsets  by
421           adding a setting such as
422    
423             --with-link-size=3
424    
425           to  the  configure  command.  The value given must be 2, 3, or 4. Using
426           longer offsets slows down the operation of PCRE because it has to  load
427           additional bytes when handling them.
428    
429    
430    AVOIDING EXCESSIVE STACK USAGE
431    
432           When matching with the pcre_exec() function, PCRE implements backtrack-
433           ing by making recursive calls to an internal function  called  match().
434           In  environments  where  the size of the stack is limited, this can se-
435           verely limit PCRE's operation. (The Unix environment does  not  usually
436           suffer from this problem, but it may sometimes be necessary to increase
437           the maximum stack size.  There is a discussion in the  pcrestack  docu-
438           mentation.)  An alternative approach to recursion that uses memory from
439           the heap to remember data, instead of using recursive  function  calls,
440           has  been  implemented to work round the problem of limited stack size.
441           If you want to build a version of PCRE that works this way, add
442    
443             --disable-stack-for-recursion
444    
445           to the configure command. With this configuration, PCRE  will  use  the
446           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
447           ment functions. By default these point to malloc() and free(), but  you
448           can replace the pointers so that your own functions are used.
449    
450           Separate  functions  are  provided  rather  than  using pcre_malloc and
451           pcre_free because the  usage  is  very  predictable:  the  block  sizes
452           requested  are  always  the  same,  and  the blocks are always freed in
453           reverse order. A calling program might be able to  implement  optimized
454           functions  that  perform  better  than  malloc()  and free(). PCRE runs
455           noticeably more slowly when built in this way. This option affects only
456           the   pcre_exec()   function;   it   is   not   relevant  for  the  the
457           pcre_dfa_exec() function.
458    
459    
460  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
461    
462         Internally,  PCRE  has a function called match() which it calls repeat-         Internally, PCRE has a function called match(), which it calls  repeat-
463         edly (possibly recursively) when performing a  matching  operation.  By         edly   (sometimes   recursively)  when  matching  a  pattern  with  the
464         limiting  the  number of times this function may be called, a limit can         pcre_exec() function. By controlling the maximum number of  times  this
465           function  may be called during a single matching operation, a limit can
466         be placed on the resources used by a single call  to  pcre_exec().  The         be placed on the resources used by a single call  to  pcre_exec().  The
467         limit  can be changed at run time, as described in the pcreapi documen-         limit  can be changed at run time, as described in the pcreapi documen-
468         tation. The default is 10 million, but this can be changed by adding  a         tation. The default is 10 million, but this can be changed by adding  a
# Line 257  LIMITING PCRE RESOURCE USAGE Line 470  LIMITING PCRE RESOURCE USAGE
470    
471           --with-match-limit=500000           --with-match-limit=500000
472    
473         to the configure command.         to   the   configure  command.  This  setting  has  no  effect  on  the
474           pcre_dfa_exec() matching function.
475    
476           In some environments it is desirable to limit the  depth  of  recursive
477           calls of match() more strictly than the total number of calls, in order
478           to restrict the maximum amount of stack (or heap,  if  --disable-stack-
479           for-recursion is specified) that is used. A second limit controls this;
480           it defaults to the value that  is  set  for  --with-match-limit,  which
481           imposes  no  additional constraints. However, you can set a lower limit
482           by adding, for example,
483    
484             --with-match-limit-recursion=10000
485    
486           to the configure command. This value can  also  be  overridden  at  run
487           time.
488    
489    
490    CREATING CHARACTER TABLES AT BUILD TIME
491    
492           PCRE  uses fixed tables for processing characters whose code values are
493           less than 256. By default, PCRE is built with a set of tables that  are
494           distributed  in  the  file pcre_chartables.c.dist. These tables are for
495           ASCII codes only. If you add
496    
497             --enable-rebuild-chartables
498    
499           to the configure command, the distributed tables are  no  longer  used.
500           Instead,  a  program  called dftables is compiled and run. This outputs
501           the source for new set of tables, created in the default locale of your
502           C runtime system. (This method of replacing the tables does not work if
503           you are cross compiling, because dftables is run on the local host.  If
504           you  need  to  create alternative tables when cross compiling, you will
505           have to do so "by hand".)
506    
 HANDLING VERY LARGE PATTERNS  
507    
508         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  
509    
510           --with-link-size=3         PCRE assumes by default that it will run in an  environment  where  the
511           character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
512           This is the case for most computer operating systems.  PCRE  can,  how-
513           ever, be compiled to run in an EBCDIC environment by adding
514    
515         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.  
516    
517         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-
518         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
519         representation of the compiled pattern, and this changes with the  link         environment (for example, an IBM mainframe operating system).
        size.  
520    
521    
522  AVOIDING EXCESSIVE STACK USAGE  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
523    
524         PCRE  implements  backtracking while matching by making recursive calls         By default, pcregrep reads all files as plain text. You can build it so
525         to an internal function called match(). In environments where the  size         that it recognizes files whose names end in .gz or .bz2, and reads them
526         of the stack is limited, this can severely limit PCRE's operation. (The         with libz or libbz2, respectively, by adding one or both of
        Unix environment does not usually suffer from this problem.) An  alter-  
        native  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  
527    
528           --disable-stack-for-recursion           --enable-pcregrep-libz
529             --enable-pcregrep-libbz2
530    
531         to the configure command. With this configuration, PCRE  will  use  the         to the configure command. These options naturally require that the rel-
532         pcre_stack_malloc   and   pcre_stack_free   variables  to  call  memory         evant libraries are installed on your system. Configuration  will  fail
533         management functions. Separate functions are provided because the usage         if they are not.
        is 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.  
534    
535    
536  USING EBCDIC CODE  PCRETEST OPTION FOR LIBREADLINE SUPPORT
537    
538         PCRE  assumes  by  default that it will run in an environment where the         If you add
        character code is ASCII (or UTF-8, which is a superset of ASCII).  PCRE  
        can, however, be compiled to run in an EBCDIC environment by adding  
539    
540           --enable-ebcdic           --enable-pcretest-libreadline
541    
542         to the configure command.         to  the  configure  command,  pcretest  is  linked with the libreadline
543           library, and when its input is from a terminal, it reads it  using  the
544           readline() function. This provides line-editing and history facilities.
545           Note that libreadline is GPL-licenced, so if you distribute a binary of
546           pcretest linked in this way, there may be licensing issues.
547    
548  Last updated: 09 December 2003         Setting  this  option  causes  the -lreadline option to be added to the
549  Copyright (c) 1997-2003 University of Cambridge.         pcretest build. In many operating environments with  a  sytem-installed
550  -----------------------------------------------------------------------------         libreadline this is sufficient. However, in some environments (e.g.  if
551           an unmodified distribution version of readline is in use),  some  extra
552           configuration  may  be necessary. The INSTALL file for libreadline says
553           this:
554    
555             "Readline uses the termcap functions, but does not link with the
556             termcap or curses library itself, allowing applications which link
557             with readline the to choose an appropriate library."
558    
559           If your environment has not been set up so that an appropriate  library
560           is automatically included, you may need to add something like
561    
562             LIBS="-ncurses"
563    
564           immediately before the configure command.
565    
566    
567    SEE ALSO
568    
569           pcreapi(3), pcre_config(3).
570    
571    
572    AUTHOR
573    
574           Philip Hazel
575           University Computing Service
576           Cambridge CB2 3QH, England.
577    
578    
579    REVISION
580    
581           Last updated: 13 April 2008
582           Copyright (c) 1997-2008 University of Cambridge.
583    ------------------------------------------------------------------------------
584    
585    
586    PCREMATCHING(3)                                                PCREMATCHING(3)
587    
588    
589    NAME
590           PCRE - Perl-compatible regular expressions
591    
592    
593    PCRE MATCHING ALGORITHMS
594    
595           This document describes the two different algorithms that are available
596           in PCRE for matching a compiled regular expression against a given sub-
597           ject  string.  The  "standard"  algorithm  is  the  one provided by the
598           pcre_exec() function.  This works in the same was  as  Perl's  matching
599           function, and provides a Perl-compatible matching operation.
600    
601           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
602           this operates in a different way, and is not  Perl-compatible.  It  has
603           advantages  and disadvantages compared with the standard algorithm, and
604           these are described below.
605    
606           When there is only one possible way in which a given subject string can
607           match  a pattern, the two algorithms give the same answer. A difference
608           arises, however, when there are multiple possibilities. For example, if
609           the pattern
610    
611             ^<.*>
612    
613           is matched against the string
614    
615             <something> <something else> <something further>
616    
617           there are three possible answers. The standard algorithm finds only one
618           of them, whereas the alternative algorithm finds all three.
619    
 PCRE(3)                                                                PCRE(3)  
620    
621    REGULAR EXPRESSIONS AS TREES
622    
623           The set of strings that are matched by a regular expression can be rep-
624           resented  as  a  tree structure. An unlimited repetition in the pattern
625           makes the tree of infinite size, but it is still a tree.  Matching  the
626           pattern  to a given subject string (from a given starting point) can be
627           thought of as a search of the tree.  There are two  ways  to  search  a
628           tree:  depth-first  and  breadth-first, and these correspond to the two
629           matching algorithms provided by PCRE.
630    
631    
632    THE STANDARD MATCHING ALGORITHM
633    
634           In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
635           sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
636           depth-first search of the pattern tree. That is, it  proceeds  along  a
637           single path through the tree, checking that the subject matches what is
638           required. When there is a mismatch, the algorithm  tries  any  alterna-
639           tives  at  the  current point, and if they all fail, it backs up to the
640           previous branch point in the  tree,  and  tries  the  next  alternative
641           branch  at  that  level.  This often involves backing up (moving to the
642           left) in the subject string as well.  The  order  in  which  repetition
643           branches  are  tried  is controlled by the greedy or ungreedy nature of
644           the quantifier.
645    
646           If a leaf node is reached, a matching string has  been  found,  and  at
647           that  point the algorithm stops. Thus, if there is more than one possi-
648           ble match, this algorithm returns the first one that it finds.  Whether
649           this  is the shortest, the longest, or some intermediate length depends
650           on the way the greedy and ungreedy repetition quantifiers are specified
651           in the pattern.
652    
653           Because  it  ends  up  with a single path through the tree, it is rela-
654           tively straightforward for this algorithm to keep  track  of  the  sub-
655           strings  that  are  matched  by portions of the pattern in parentheses.
656           This provides support for capturing parentheses and back references.
657    
658    
659    THE ALTERNATIVE MATCHING ALGORITHM
660    
661           This algorithm conducts a breadth-first search of  the  tree.  Starting
662           from  the  first  matching  point  in the subject, it scans the subject
663           string from left to right, once, character by character, and as it does
664           this,  it remembers all the paths through the tree that represent valid
665           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
666           though  it is not implemented as a traditional finite state machine (it
667           keeps multiple states active simultaneously).
668    
669           The scan continues until either the end of the subject is  reached,  or
670           there  are  no more unterminated paths. At this point, terminated paths
671           represent the different matching possibilities (if there are none,  the
672           match  has  failed).   Thus,  if there is more than one possible match,
673           this algorithm finds all of them, and in particular, it finds the long-
674           est.  In PCRE, there is an option to stop the algorithm after the first
675           match (which is necessarily the shortest) has been found.
676    
677           Note that all the matches that are found start at the same point in the
678           subject. If the pattern
679    
680             cat(er(pillar)?)
681    
682           is  matched  against the string "the caterpillar catchment", the result
683           will be the three strings "cat", "cater", and "caterpillar" that  start
684           at the fourth character of the subject. The algorithm does not automat-
685           ically move on to find matches that start at later positions.
686    
687           There are a number of features of PCRE regular expressions that are not
688           supported by the alternative matching algorithm. They are as follows:
689    
690           1.  Because  the  algorithm  finds  all possible matches, the greedy or
691           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
692           ungreedy quantifiers are treated in exactly the same way. However, pos-
693           sessive quantifiers can make a difference when what follows could  also
694           match what is quantified, for example in a pattern like this:
695    
696             ^a++\w!
697    
698           This  pattern matches "aaab!" but not "aaa!", which would be matched by
699           a non-possessive quantifier. Similarly, if an atomic group is  present,
700           it  is matched as if it were a standalone pattern at the current point,
701           and the longest match is then "locked in" for the rest of  the  overall
702           pattern.
703    
704           2. When dealing with multiple paths through the tree simultaneously, it
705           is not straightforward to keep track of  captured  substrings  for  the
706           different  matching  possibilities,  and  PCRE's implementation of this
707           algorithm does not attempt to do this. This means that no captured sub-
708           strings are available.
709    
710           3.  Because no substrings are captured, back references within the pat-
711           tern are not supported, and cause errors if encountered.
712    
713           4. For the same reason, conditional expressions that use  a  backrefer-
714           ence  as  the  condition or test for a specific group recursion are not
715           supported.
716    
717           5. Because many paths through the tree may be  active,  the  \K  escape
718           sequence, which resets the start of the match when encountered (but may
719           be on some paths and not on others), is not  supported.  It  causes  an
720           error if encountered.
721    
722           6.  Callouts  are  supported, but the value of the capture_top field is
723           always 1, and the value of the capture_last field is always -1.
724    
725           7. The \C escape sequence, which (in the standard algorithm) matches  a
726           single  byte, even in UTF-8 mode, is not supported because the alterna-
727           tive algorithm moves through the subject  string  one  character  at  a
728           time, for all active paths through the tree.
729    
730           8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
731           are not supported. (*FAIL) is supported, and  behaves  like  a  failing
732           negative assertion.
733    
734    
735    ADVANTAGES OF THE ALTERNATIVE ALGORITHM
736    
737           Using  the alternative matching algorithm provides the following advan-
738           tages:
739    
740           1. All possible matches (at a single point in the subject) are automat-
741           ically  found,  and  in particular, the longest match is found. To find
742           more than one match using the standard algorithm, you have to do kludgy
743           things with callouts.
744    
745           2.  There is much better support for partial matching. The restrictions
746           on the content of the pattern that apply when using the standard  algo-
747           rithm  for  partial matching do not apply to the alternative algorithm.
748           For non-anchored patterns, the starting position of a partial match  is
749           available.
750    
751           3.  Because  the  alternative  algorithm  scans the subject string just
752           once, and never needs to backtrack, it is possible to  pass  very  long
753           subject  strings  to  the matching function in several pieces, checking
754           for partial matching each time.
755    
756    
757    DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
758    
759           The alternative algorithm suffers from a number of disadvantages:
760    
761           1. It is substantially slower than  the  standard  algorithm.  This  is
762           partly  because  it has to search for all possible matches, but is also
763           because it is less susceptible to optimization.
764    
765           2. Capturing parentheses and back references are not supported.
766    
767           3. Although atomic groups are supported, their use does not provide the
768           performance advantage that it does for the standard algorithm.
769    
770    
771    AUTHOR
772    
773           Philip Hazel
774           University Computing Service
775           Cambridge CB2 3QH, England.
776    
777    
778    REVISION
779    
780           Last updated: 19 April 2008
781           Copyright (c) 1997-2008 University of Cambridge.
782    ------------------------------------------------------------------------------
783    
784    
785    PCREAPI(3)                                                          PCREAPI(3)
786    
787    
788  NAME  NAME
789         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
790    
791  SYNOPSIS OF PCRE API  
792    PCRE NATIVE API
793    
794         #include <pcre.h>         #include <pcre.h>
795    
# Line 335  SYNOPSIS OF PCRE API Line 797  SYNOPSIS OF PCRE API
797              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
798              const unsigned char *tableptr);              const unsigned char *tableptr);
799    
800           pcre *pcre_compile2(const char *pattern, int options,
801                int *errorcodeptr,
802                const char **errptr, int *erroffset,
803                const unsigned char *tableptr);
804    
805         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options,
806              const char **errptr);              const char **errptr);
807    
# Line 342  SYNOPSIS OF PCRE API Line 809  SYNOPSIS OF PCRE API
809              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
810              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
811    
812           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
813                const char *subject, int length, int startoffset,
814                int options, int *ovector, int ovecsize,
815                int *workspace, int wscount);
816    
817         int pcre_copy_named_substring(const pcre *code,         int pcre_copy_named_substring(const pcre *code,
818              const char *subject, int *ovector,              const char *subject, int *ovector,
819              int stringcount, const char *stringname,              int stringcount, const char *stringname,
# Line 359  SYNOPSIS OF PCRE API Line 831  SYNOPSIS OF PCRE API
831         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
832              const char *name);              const char *name);
833    
834           int pcre_get_stringtable_entries(const pcre *code,
835                const char *name, char **first, char **last);
836    
837         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
838              int stringcount, int stringnumber,              int stringcount, int stringnumber,
839              const char **stringptr);              const char **stringptr);
# Line 377  SYNOPSIS OF PCRE API Line 852  SYNOPSIS OF PCRE API
852    
853         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
854    
855           int pcre_refcount(pcre *code, int adjust);
856    
857         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
858    
859         char *pcre_version(void);         char *pcre_version(void);
# Line 392  SYNOPSIS OF PCRE API Line 869  SYNOPSIS OF PCRE API
869         int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
870    
871    
872  PCRE API  PCRE API OVERVIEW
873    
874         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
875         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
876         expression API.  These are described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
877           Both of these APIs define a set of C function calls. A C++  wrapper  is
878         The  native  API  function  prototypes  are  defined in the header file         distributed with PCRE. It is documented in the pcrecpp page.
879         pcre.h, and on Unix systems the library itself is called libpcre.a,  so  
880         can be accessed by adding -lpcre to the command for linking an applica-         The  native  API  C  function prototypes are defined in the header file
881         tion which calls it. The header file defines the macros PCRE_MAJOR  and         pcre.h, and on Unix systems the library itself is called  libpcre.   It
882         PCRE_MINOR  to  contain  the  major  and  minor release numbers for the         can normally be accessed by adding -lpcre to the command for linking an
883         library. Applications can use these to include  support  for  different         application  that  uses  PCRE.  The  header  file  defines  the  macros
884         releases.         PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
885           bers for the library.  Applications can use these  to  include  support
886         The  functions  pcre_compile(),  pcre_study(), and pcre_exec() are used         for different releases of PCRE.
887         for compiling and matching regular expressions. A sample  program  that  
888         demonstrates  the simplest way of using them is given in the file pcre-         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
889         demo.c. The pcresample documentation describes how to run it.         pcre_exec() are used for compiling and matching regular expressions  in
890           a  Perl-compatible  manner. A sample program that demonstrates the sim-
891         There are convenience functions for extracting captured substrings from         plest way of using them is provided in the file  called  pcredemo.c  in
892         a matched subject string. They are:         the  source distribution. The pcresample documentation describes how to
893           compile and run it.
894    
895           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
896           ble,  is  also provided. This uses a different algorithm for the match-
897           ing. The alternative algorithm finds all possible matches (at  a  given
898           point  in  the subject), and scans the subject just once. However, this
899           algorithm does not return captured substrings. A description of the two
900           matching  algorithms and their advantages and disadvantages is given in
901           the pcrematching documentation.
902    
903           In addition to the main compiling and  matching  functions,  there  are
904           convenience functions for extracting captured substrings from a subject
905           string that is matched by pcre_exec(). They are:
906    
907           pcre_copy_substring()           pcre_copy_substring()
908           pcre_copy_named_substring()           pcre_copy_named_substring()
909           pcre_get_substring()           pcre_get_substring()
910           pcre_get_named_substring()           pcre_get_named_substring()
911           pcre_get_substring_list()           pcre_get_substring_list()
912             pcre_get_stringnumber()
913             pcre_get_stringtable_entries()
914    
915         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
916         to free the memory used for extracted strings.         to free the memory used for extracted strings.
917    
918         The function pcre_maketables() is used (optionally) to build a  set  of         The  function  pcre_maketables()  is  used  to build a set of character
919         character tables in the current locale for passing to pcre_compile().         tables  in  the  current  locale   for   passing   to   pcre_compile(),
920           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
921         The  function  pcre_fullinfo()  is used to find out information about a         provided for specialist use.  Most  commonly,  no  special  tables  are
922         compiled pattern; pcre_info() is an obsolete version which returns only         passed,  in  which case internal tables that are generated when PCRE is
923         some  of  the available information, but is retained for backwards com-         built are used.
924         patibility.  The function pcre_version() returns a pointer to a  string  
925           The function pcre_fullinfo() is used to find out  information  about  a
926           compiled  pattern; pcre_info() is an obsolete version that returns only
927           some of the available information, but is retained for  backwards  com-
928           patibility.   The function pcre_version() returns a pointer to a string
929         containing the version of PCRE and its date of release.         containing the version of PCRE and its date of release.
930    
931         The  global  variables  pcre_malloc and pcre_free initially contain the         The function pcre_refcount() maintains a  reference  count  in  a  data
932         entry points of the standard  malloc()  and  free()  functions  respec-         block  containing  a compiled pattern. This is provided for the benefit
933           of object-oriented applications.
934    
935           The global variables pcre_malloc and pcre_free  initially  contain  the
936           entry  points  of  the  standard malloc() and free() functions, respec-
937         tively. PCRE calls the memory management functions via these variables,         tively. PCRE calls the memory management functions via these variables,
938         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
939         calls. This should be done before calling any PCRE functions.         calls. This should be done before calling any PCRE functions.
940    
941         The  global  variables  pcre_stack_malloc  and pcre_stack_free are also         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
942         indirections to memory management functions.  These  special  functions         indirections  to  memory  management functions. These special functions
943         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
944         data, instead of recursive function calls. This is a  non-standard  way         data, instead of recursive function calls, when running the pcre_exec()
945         of  building  PCRE,  for  use in environments that have limited stacks.         function. See the pcrebuild documentation for  details  of  how  to  do
946         Because of the greater use of memory management, it runs  more  slowly.         this.  It  is  a non-standard way of building PCRE, for use in environ-
947         Separate  functions  are provided so that special-purpose external code         ments that have limited stacks. Because of the greater  use  of  memory
948         can be used for this case. When used, these functions are always called         management,  it  runs  more  slowly. Separate functions are provided so
949         in  a  stack-like  manner  (last obtained, first freed), and always for         that special-purpose external code can be  used  for  this  case.  When
950         memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
951           obtained, first freed), and always for memory blocks of the same  size.
952           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
953           mentation.
954    
955         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
956         by  the  caller  to  a "callout" function, which PCRE will then call at         by  the  caller  to  a "callout" function, which PCRE will then call at
# Line 455  PCRE API Line 958  PCRE API
958         pcrecallout documentation.         pcrecallout documentation.
959    
960    
961    NEWLINES
962    
963           PCRE  supports five different conventions for indicating line breaks in
964           strings: a single CR (carriage return) character, a  single  LF  (line-
965           feed) character, the two-character sequence CRLF, any of the three pre-
966           ceding, or any Unicode newline sequence. The Unicode newline  sequences
967           are  the  three just mentioned, plus the single characters VT (vertical
968           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
969           separator, U+2028), and PS (paragraph separator, U+2029).
970    
971           Each  of  the first three conventions is used by at least one operating
972           system as its standard newline sequence. When PCRE is built, a  default
973           can  be  specified.  The default default is LF, which is the Unix stan-
974           dard. When PCRE is run, the default can be overridden,  either  when  a
975           pattern is compiled, or when it is matched.
976    
977           At compile time, the newline convention can be specified by the options
978           argument of pcre_compile(), or it can be specified by special  text  at
979           the start of the pattern itself; this overrides any other settings. See
980           the pcrepattern page for details of the special character sequences.
981    
982           In the PCRE documentation the word "newline" is used to mean "the char-
983           acter  or pair of characters that indicate a line break". The choice of
984           newline convention affects the handling of  the  dot,  circumflex,  and
985           dollar metacharacters, the handling of #-comments in /x mode, and, when
986           CRLF is a recognized line ending sequence, the match position  advance-
987           ment for a non-anchored pattern. There is more detail about this in the
988           section on pcre_exec() options below.
989    
990           The choice of newline convention does not affect the interpretation  of
991           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
992           which is controlled in a similar way, but by separate options.
993    
994    
995  MULTITHREADING  MULTITHREADING
996    
997         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
998         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
999         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1000         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
1001    
1002         The  compiled form of a regular expression is not altered during match-         The compiled form of a regular expression is not altered during  match-
1003         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
1004         at once.         at once.
1005    
1006    
1007    SAVING PRECOMPILED PATTERNS FOR LATER USE
1008    
1009           The compiled form of a regular expression can be saved and re-used at a
1010           later  time,  possibly by a different program, and even on a host other
1011           than the one on which  it  was  compiled.  Details  are  given  in  the
1012           pcreprecompile  documentation.  However, compiling a regular expression
1013           with one version of PCRE for use with a different version is not  guar-
1014           anteed to work and may cause crashes.
1015    
1016    
1017  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
1018    
1019         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
# Line 486  CHECKING BUILD-TIME OPTIONS Line 1033  CHECKING BUILD-TIME OPTIONS
1033         The  output is an integer that is set to one if UTF-8 support is avail-         The  output is an integer that is set to one if UTF-8 support is avail-
1034         able; otherwise it is set to zero.         able; otherwise it is set to zero.
1035    
1036             PCRE_CONFIG_UNICODE_PROPERTIES
1037    
1038           The output is an integer that is set to  one  if  support  for  Unicode
1039           character properties is available; otherwise it is set to zero.
1040    
1041           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1042    
1043         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
1044         used  for the newline character. It is either linefeed (10) or carriage         sequence that is recognized as meaning "newline". The four values  that
1045         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,
1046         operating system.         and -1 for ANY. The default should normally be  the  standard  sequence
1047           for your operating system.
1048    
1049             PCRE_CONFIG_BSR
1050    
1051           The output is an integer whose value indicates what character sequences
1052           the \R escape sequence matches by default. A value of 0 means  that  \R
1053           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1054           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1055           tern is compiled or matched.
1056    
1057           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1058    
# Line 514  CHECKING BUILD-TIME OPTIONS Line 1075  CHECKING BUILD-TIME OPTIONS
1075         internal  matching  function  calls in a pcre_exec() execution. Further         internal  matching  function  calls in a pcre_exec() execution. Further
1076         details are given with pcre_exec() below.         details are given with pcre_exec() below.
1077    
1078             PCRE_CONFIG_MATCH_LIMIT_RECURSION
1079    
1080           The output is an integer that gives the default limit for the depth  of
1081           recursion  when calling the internal matching function in a pcre_exec()
1082           execution. Further details are given with pcre_exec() below.
1083    
1084           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1085    
1086         The output is an integer that is set to one if  internal  recursion  is         The output is an integer that is set to one if internal recursion  when
1087         implemented  by recursive function calls that use the stack to remember         running pcre_exec() is implemented by recursive function calls that use
1088         their state. This is the usual way that PCRE is compiled. The output is         the stack to remember their state. This is the usual way that  PCRE  is
1089         zero  if PCRE was compiled to use blocks of data on the heap instead of         compiled. The output is zero if PCRE was compiled to use blocks of data
1090         recursive  function  calls.  In  this   case,   pcre_stack_malloc   and         on the  heap  instead  of  recursive  function  calls.  In  this  case,
1091         pcre_stack_free  are  called  to manage memory blocks on the heap, thus         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
1092         avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1093    
1094    
1095  COMPILING A PATTERN  COMPILING A PATTERN
# Line 531  COMPILING A PATTERN Line 1098  COMPILING A PATTERN
1098              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
1099              const unsigned char *tableptr);              const unsigned char *tableptr);
1100    
1101           pcre *pcre_compile2(const char *pattern, int options,
1102                int *errorcodeptr,
1103                const char **errptr, int *erroffset,
1104                const unsigned char *tableptr);
1105    
1106         The function pcre_compile() is called to  compile  a  pattern  into  an         Either of the functions pcre_compile() or pcre_compile2() can be called
1107         internal  form.  The pattern is a C string terminated by a binary zero,         to compile a pattern into an internal form. The only difference between
1108         and is passed in the argument pattern. A pointer to a single  block  of         the two interfaces is that pcre_compile2() has an additional  argument,
1109         memory  that is obtained via pcre_malloc is returned. This contains the         errorcodeptr, via which a numerical error code can be returned.
1110         compiled code and related data.  The  pcre  type  is  defined  for  the  
1111         returned  block;  this  is a typedef for a structure whose contents are         The pattern is a C string terminated by a binary zero, and is passed in
1112         not externally defined. It is up to the caller to free the memory  when         the pattern argument. A pointer to a single block  of  memory  that  is
1113         it is no longer required.         obtained  via  pcre_malloc is returned. This contains the compiled code
1114           and related data. The pcre type is defined for the returned block; this
1115           is a typedef for a structure whose contents are not externally defined.
1116           It is up to the caller to free the memory (via pcre_free) when it is no
1117           longer required.
1118    
1119         Although  the compiled code of a PCRE regex is relocatable, that is, it         Although  the compiled code of a PCRE regex is relocatable, that is, it
1120         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
1121         fully relocatable, because it contains a copy of the tableptr argument,         fully  relocatable, because it may contain a copy of the tableptr argu-
1122         which is an address (see below).         ment, which is an address (see below).
1123    
1124         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
1125         tion.  It  should  be  zero  if  no  options  are required. Some of the         pilation.  It  should be zero if no options are required. The available
1126         options, in particular, those that are compatible with Perl,  can  also         options are described below. Some of them, in  particular,  those  that
1127         be  set and unset from within the pattern (see the detailed description         are  compatible  with  Perl,  can also be set and unset from within the
1128         of regular expressions in the  pcrepattern  documentation).  For  these         pattern (see the detailed description  in  the  pcrepattern  documenta-
1129         options,  the  contents of the options argument specifies their initial         tion).  For  these options, the contents of the options argument speci-
1130         settings at the start of compilation and execution.  The  PCRE_ANCHORED         fies their initial settings at the start of compilation and  execution.
1131         option can be set at the time of matching as well as at compile time.         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time
1132           of matching as well as at compile time.
1133    
1134         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1135         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1136         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
1137         sage. 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
1138         the  error  was  discovered  is  placed  in  the variable pointed to by         try to free it. The offset from the start of the pattern to the charac-
1139         erroffset, which must not be NULL. If it  is,  an  immediate  error  is         ter where the error was discovered is placed in the variable pointed to
1140           by erroffset, which must not be NULL. If it is, an immediate  error  is
1141         given.         given.
1142    
1143         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1144         character tables which are built when it is compiled, using the default         codeptr argument is not NULL, a non-zero error code number is  returned
1145         C  locale.  Otherwise,  tableptr  must  be  the  result  of  a  call to         via  this argument in the event of an error. This is in addition to the
1146         pcre_maketables(). See the section on locale support below.         textual error message. Error codes and messages are listed below.
1147    
1148           If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1149           character  tables  that  are  built  when  PCRE  is compiled, using the
1150           default C locale. Otherwise, tableptr must be an address  that  is  the
1151           result  of  a  call to pcre_maketables(). This value is stored with the
1152           compiled pattern, and used again by pcre_exec(), unless  another  table
1153           pointer is passed to it. For more discussion, see the section on locale
1154           support below.
1155    
1156         This code fragment shows a typical straightforward  call  to  pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1157         pile():         pile():
# Line 581  COMPILING A PATTERN Line 1166  COMPILING A PATTERN
1166             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1167             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1168    
1169         The following option bits are defined:         The  following  names  for option bits are defined in the pcre.h header
1170           file:
1171    
1172           PCRE_ANCHORED           PCRE_ANCHORED
1173    
1174         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
1175         is constrained to match only at the first matching point in the  string         is  constrained to match only at the first matching point in the string
1176         which is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1177         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1178         only way to do it in Perl.         only way to do it in Perl.
1179    
1180             PCRE_AUTO_CALLOUT
1181    
1182           If this bit is set, pcre_compile() automatically inserts callout items,
1183           all  with  number  255, before each pattern item. For discussion of the
1184           callout facility, see the pcrecallout documentation.
1185    
1186             PCRE_BSR_ANYCRLF
1187             PCRE_BSR_UNICODE
1188    
1189           These options (which are mutually exclusive) control what the \R escape
1190           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1191           or to match any Unicode newline sequence. The default is specified when
1192           PCRE is built. It can be overridden from within the pattern, or by set-
1193           ting an option when a compiled pattern is matched.
1194    
1195           PCRE_CASELESS           PCRE_CASELESS
1196    
1197         If  this  bit is set, letters in the pattern match both upper and lower         If this bit is set, letters in the pattern match both upper  and  lower
1198         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1199         changed within a pattern by a (?i) option setting.         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1200           always  understands the concept of case for characters whose values are
1201           less than 128, so caseless matching is always possible. For  characters
1202           with  higher  values,  the concept of case is supported if PCRE is com-
1203           piled with Unicode property support, but not otherwise. If you want  to
1204           use  caseless  matching  for  characters 128 and above, you must ensure
1205           that PCRE is compiled with Unicode property support  as  well  as  with
1206           UTF-8 support.
1207    
1208           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1209    
1210         If  this bit is set, a dollar metacharacter in the pattern matches only         If  this bit is set, a dollar metacharacter in the pattern matches only
1211         at the end of the subject string. Without this option,  a  dollar  also         at the end of the subject string. Without this option,  a  dollar  also
1212         matches  immediately before the final character if it is a newline (but         matches  immediately before a newline at the end of the string (but not
1213         not before any  other  newlines).  The  PCRE_DOLLAR_ENDONLY  option  is         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1214         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
1215         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1216    
1217           PCRE_DOTALL           PCRE_DOTALL
1218    
1219         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharater in the pattern matches all char-
1220         acters,  including  newlines.  Without  it, newlines are excluded. This         acters,  including  those that indicate newline. Without it, a dot does
1221         option is equivalent to Perl's /s option, and it can be changed  within         not match when the current position is at a  newline.  This  option  is
1222         a  pattern  by  a  (?s)  option  setting. A negative class such as [^a]         equivalent  to Perl's /s option, and it can be changed within a pattern
1223         always matches a newline character, independent of the setting of  this         by a (?s) option setting. A negative class such as [^a] always  matches
1224         option.         newline characters, independent of the setting of this option.
1225    
1226             PCRE_DUPNAMES
1227    
1228           If  this  bit is set, names used to identify capturing subpatterns need
1229           not be unique. This can be helpful for certain types of pattern when it
1230           is  known  that  only  one instance of the named subpattern can ever be
1231           matched. There are more details of named subpatterns  below;  see  also
1232           the pcrepattern documentation.
1233    
1234           PCRE_EXTENDED           PCRE_EXTENDED
1235    
1236         If  this  bit  is  set,  whitespace  data characters in the pattern are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1237         totally ignored except  when  escaped  or  inside  a  character  class.         totally ignored except when escaped or inside a character class. White-
1238         Whitespace  does  not  include the VT character (code 11). In addition,         space does not include the VT character (code 11). In addition, charac-
1239         characters between an unescaped # outside a  character  class  and  the         ters between an unescaped # outside a character class and the next new-
1240         next newline character, inclusive, are also ignored. This is equivalent         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1241         to 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-
1242         option setting.         ting.
1243    
1244         This  option  makes  it possible to include comments inside complicated         This  option  makes  it possible to include comments inside complicated
1245         patterns.  Note, however, that this applies only  to  data  characters.         patterns.  Note, however, that this applies only  to  data  characters.
# Line 639  COMPILING A PATTERN Line 1255  COMPILING A PATTERN
1255         letter that has no special meaning  causes  an  error,  thus  reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1256         these  combinations  for  future  expansion.  By default, as in Perl, a         these  combinations  for  future  expansion.  By default, as in Perl, a
1257         backslash followed by a letter with no special meaning is treated as  a         backslash followed by a letter with no special meaning is treated as  a
1258         literal.  There  are  at  present  no other features controlled by this         literal.  (Perl can, however, be persuaded to give a warning for this.)
1259         option. It can also be set by a (?X) option setting within a pattern.         There are at present no other features controlled by  this  option.  It
1260           can also be set by a (?X) option setting within a pattern.
1261    
1262             PCRE_FIRSTLINE
1263    
1264           If  this  option  is  set,  an  unanchored pattern is required to match
1265           before or at the first  newline  in  the  subject  string,  though  the
1266           matched text may continue over the newline.
1267    
1268             PCRE_JAVASCRIPT_COMPAT
1269    
1270           If this option is set, PCRE's behaviour is changed in some ways so that
1271           it is compatible with JavaScript rather than Perl. The changes  are  as
1272           follows:
1273    
1274           (1)  A  lone  closing square bracket in a pattern causes a compile-time
1275           error, because this is illegal in JavaScript (by default it is  treated
1276           as a data character). Thus, the pattern AB]CD becomes illegal when this
1277           option is set.
1278    
1279           (2) At run time, a back reference to an unset subpattern group  matches
1280           an  empty  string (by default this causes the current matching alterna-
1281           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1282           set  (assuming  it can find an "a" in the subject), whereas it fails by
1283           default, for Perl compatibility.
1284    
1285           PCRE_MULTILINE           PCRE_MULTILINE
1286    
1287         By default, PCRE treats the subject string as consisting  of  a  single         By default, PCRE treats the subject string as consisting  of  a  single
1288         "line"  of  characters (even if it actually contains several newlines).         line  of characters (even if it actually contains newlines). The "start
1289         The "start of line" metacharacter (^) matches only at the start of  the         of line" metacharacter (^) matches only at the  start  of  the  string,
1290         string,  while  the "end of line" metacharacter ($) matches only at the         while  the  "end  of line" metacharacter ($) matches only at the end of
1291         end of the string, or before a terminating  newline  (unless  PCRE_DOL-         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1292         LAR_ENDONLY is set). This is the same as Perl.         is set). This is the same as Perl.
1293    
1294         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"
1295         constructs match immediately following or immediately before  any  new-         constructs match immediately following or immediately  before  internal
1296         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
1297         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
1298         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-
1299         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,
1300         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1301    
1302             PCRE_NEWLINE_CR
1303             PCRE_NEWLINE_LF
1304             PCRE_NEWLINE_CRLF
1305             PCRE_NEWLINE_ANYCRLF
1306             PCRE_NEWLINE_ANY
1307    
1308           These  options  override the default newline definition that was chosen
1309           when PCRE was built. Setting the first or the second specifies  that  a
1310           newline  is  indicated  by a single character (CR or LF, respectively).
1311           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1312           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1313           that any of the three preceding sequences should be recognized. Setting
1314           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1315           recognized. The Unicode newline sequences are the three just mentioned,
1316           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1317           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1318           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1319           UTF-8 mode.
1320    
1321           The newline setting in the  options  word  uses  three  bits  that  are
1322           treated as a number, giving eight possibilities. Currently only six are
1323           used (default plus the five values above). This means that if  you  set
1324           more  than one newline option, the combination may or may not be sensi-
1325           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1326           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1327           cause an error.
1328    
1329           The only time that a line break is specially recognized when  compiling
1330           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1331           character class is encountered. This indicates  a  comment  that  lasts
1332           until  after the next line break sequence. In other circumstances, line
1333           break  sequences  are  treated  as  literal  data,   except   that   in
1334           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1335           and are therefore ignored.
1336    
1337           The newline option that is set at compile time becomes the default that
1338           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1339    
1340           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1341    
1342         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-
1343         theses in the pattern. Any opening parenthesis that is not followed  by         theses  in the pattern. Any opening parenthesis that is not followed by
1344         ?  behaves as if it were followed by ?: but named parentheses can still         ? behaves as if it were followed by ?: but named parentheses can  still
1345         be used for capturing (and they acquire  numbers  in  the  usual  way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1346         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1347    
1348           PCRE_UNGREEDY           PCRE_UNGREEDY
1349    
1350         This  option  inverts  the "greediness" of the quantifiers so that they         This option inverts the "greediness" of the quantifiers  so  that  they
1351         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
1352         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
1353         within the pattern.         within the pattern.
1354    
1355           PCRE_UTF8           PCRE_UTF8
1356    
1357         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
1358         strings  of  UTF-8 characters instead of single-byte character strings.         strings of UTF-8 characters instead of single-byte  character  strings.
1359         However, it is available only if PCRE has been built to  include  UTF-8         However,  it is available only when PCRE is built to include UTF-8 sup-
1360         support.  If  not, the use of this option provokes an error. Details of         port. If not, the use of this option provokes an error. Details of  how
1361         how this option changes the behaviour of PCRE are given in the  section         this  option  changes the behaviour of PCRE are given in the section on
1362         on UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1363    
1364           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1365    
1366         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1367         automatically checked. If an invalid UTF-8 sequence of bytes is  found,         automatically  checked.  There  is  a  discussion about the validity of
1368         pcre_compile()  returns an error. If you already know that your pattern         UTF-8 strings in the main pcre page. If an invalid  UTF-8  sequence  of
1369         is valid, and you want to skip this check for performance reasons,  you         bytes  is  found,  pcre_compile() returns an error. If you already know
1370         can  set  the  PCRE_NO_UTF8_CHECK option. When it is set, the effect of         that your pattern is valid, and you want to skip this check for perfor-
1371         passing an invalid UTF-8 string as a pattern is undefined. It may cause         mance  reasons,  you  can set the PCRE_NO_UTF8_CHECK option. When it is
1372         your  program  to  crash.  Note that there is a similar option for sup-         set, the effect of passing an invalid UTF-8  string  as  a  pattern  is
1373         pressing the checking of subject strings passed to pcre_exec().         undefined.  It  may  cause your program to crash. Note that this option
1374           can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1375           UTF-8 validity checking of subject strings.
1376    
1377    
1378    COMPILATION ERROR CODES
1379    
1380           The  following  table  lists  the  error  codes than may be returned by
1381           pcre_compile2(), along with the error messages that may be returned  by
1382           both  compiling functions. As PCRE has developed, some error codes have
1383           fallen out of use. To avoid confusion, they have not been re-used.
1384    
1385              0  no error
1386              1  \ at end of pattern
1387              2  \c at end of pattern
1388              3  unrecognized character follows \
1389              4  numbers out of order in {} quantifier
1390              5  number too big in {} quantifier
1391              6  missing terminating ] for character class
1392              7  invalid escape sequence in character class
1393              8  range out of order in character class
1394              9  nothing to repeat
1395             10  [this code is not in use]
1396             11  internal error: unexpected repeat
1397             12  unrecognized character after (? or (?-
1398             13  POSIX named classes are supported only within a class
1399             14  missing )
1400             15  reference to non-existent subpattern
1401             16  erroffset passed as NULL
1402             17  unknown option bit(s) set
1403             18  missing ) after comment
1404             19  [this code is not in use]
1405             20  regular expression is too large
1406             21  failed to get memory
1407             22  unmatched parentheses
1408             23  internal error: code overflow
1409             24  unrecognized character after (?<
1410             25  lookbehind assertion is not fixed length
1411             26  malformed number or name after (?(
1412             27  conditional group contains more than two branches
1413             28  assertion expected after (?(
1414             29  (?R or (?[+-]digits must be followed by )
1415             30  unknown POSIX class name
1416             31  POSIX collating elements are not supported
1417             32  this version of PCRE is not compiled with PCRE_UTF8 support
1418             33  [this code is not in use]
1419             34  character value in \x{...} sequence is too large
1420             35  invalid condition (?(0)
1421             36  \C not allowed in lookbehind assertion
1422             37  PCRE does not support \L, \l, \N, \U, or \u
1423             38  number after (?C is > 255
1424             39  closing ) for (?C expected
1425             40  recursive call could loop indefinitely
1426             41  unrecognized character after (?P
1427             42  syntax error in subpattern name (missing terminator)
1428             43  two named subpatterns have the same name
1429             44  invalid UTF-8 string
1430             45  support for \P, \p, and \X has not been compiled
1431             46  malformed \P or \p sequence
1432             47  unknown property name after \P or \p
1433             48  subpattern name is too long (maximum 32 characters)
1434             49  too many named subpatterns (maximum 10000)
1435             50  [this code is not in use]
1436             51  octal value is greater than \377 (not in UTF-8 mode)
1437             52  internal error: overran compiling workspace
1438             53  internal  error:  previously-checked  referenced  subpattern  not
1439           found
1440             54  DEFINE group contains more than one branch
1441             55  repeating a DEFINE group is not allowed
1442             56  inconsistent NEWLINE options
1443             57  \g is not followed by a braced, angle-bracketed, or quoted
1444                   name/number or by a plain number
1445             58  a numbered reference must not be zero
1446             59  (*VERB) with an argument is not supported
1447             60  (*VERB) not recognized
1448             61  number is too big
1449             62  subpattern name expected
1450             63  digit expected after (?+
1451             64  ] is an invalid data character in JavaScript compatibility mode
1452    
1453           The  numbers  32  and 10000 in errors 48 and 49 are defaults; different
1454           values may be used if the limits were changed when PCRE was built.
1455    
1456    
1457  STUDYING A PATTERN  STUDYING A PATTERN
1458    
1459         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1460              const char **errptr);              const char **errptr);
1461    
1462         When a pattern is going to be used several times, it is worth  spending         If a compiled pattern is going to be used several times,  it  is  worth
1463         more  time  analyzing it in order to speed up the time taken for match-         spending more time analyzing it in order to speed up the time taken for
1464         ing. The function pcre_study() takes a pointer to a compiled pattern as         matching. The function pcre_study() takes a pointer to a compiled  pat-
1465         its first argument. If studing the pattern produces additional informa-         tern as its first argument. If studying the pattern produces additional
1466         tion that will help speed up matching, pcre_study() returns  a  pointer         information that will help speed up matching,  pcre_study()  returns  a
1467         to  a  pcre_extra  block,  in  which the study_data field points to the         pointer  to a pcre_extra block, in which the study_data field points to
1468         results of the study.         the results of the study.
1469    
1470         The returned value from  a  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1471         pcre_exec().  However,  the pcre_extra block also contains other fields         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1472         that can be set by the caller before the block  is  passed;  these  are         that can be set by the caller before the block  is  passed;  these  are
1473         described  below.  If  studying  the pattern does not produce any addi-         described below in the section on matching a pattern.
        tional information, pcre_study() returns NULL. In that circumstance, if  
        the  calling  program  wants  to  pass  some  of  the  other  fields to  
        pcre_exec(), it must set up its own pcre_extra block.  
1474    
1475         The second argument contains option bits. At present,  no  options  are         If  studying  the  pattern  does not produce any additional information
1476         defined for pcre_study(), and this argument should always be zero.         pcre_study() returns NULL. In that circumstance, if the calling program
1477           wants  to  pass  any of the other fields to pcre_exec(), it must set up
1478           its own pcre_extra block.
1479    
1480           The second argument of pcre_study() contains option bits.  At  present,
1481           no options are defined, and this argument should always be zero.
1482    
1483         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.
1484         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1485         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
1486         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
1487         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
1488           after calling pcre_study(), to be sure that it has run successfully.
1489    
1490         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1491    
# Line 735  STUDYING A PATTERN Line 1496  STUDYING A PATTERN
1496             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1497    
1498         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1499         that do not have a single fixed starting character. A bitmap of  possi-         that  do not have a single fixed starting character. A bitmap of possi-
1500         ble starting characters is created.         ble starting bytes is created.
1501    
1502    
1503  LOCALE SUPPORT  LOCALE SUPPORT
1504    
1505         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1506         letters, digits, or whatever, by reference to a  set  of  tables.  When         letters,  digits, or whatever, by reference to a set of tables, indexed
1507         running  in UTF-8 mode, this applies only to characters with codes less         by character value. When running in UTF-8 mode, this  applies  only  to
1508         than 256. The library contains a default set of tables that is  created         characters  with  codes  less than 128. Higher-valued codes never match
1509         in  the  default  C locale when PCRE is compiled. This is used when the         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
1510         final argument of pcre_compile() is NULL, and is  sufficient  for  many         with  Unicode  character property support. The use of locales with Uni-
1511         applications.         code is discouraged. If you are handling characters with codes  greater
1512           than  128, you should either use UTF-8 and Unicode, or use locales, but
1513         An alternative set of tables can, however, be supplied. Such tables are         not try to mix the two.
1514         built by calling the pcre_maketables() function,  which  has  no  argu-  
1515         ments,  in  the  relevant  locale.  The  result  can  then be passed to         PCRE contains an internal set of tables that are used  when  the  final
1516         pcre_compile() as often as necessary. For example,  to  build  and  use         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1517         tables that are appropriate for the French locale (where accented char-         applications.  Normally, the internal tables recognize only ASCII char-
1518         acters with codes greater than 128 are treated as letters), the follow-         acters. However, when PCRE is built, it is possible to cause the inter-
1519         ing code could be used:         nal tables to be rebuilt in the default "C" locale of the local system,
1520           which may cause them to be different.
1521    
1522           The  internal tables can always be overridden by tables supplied by the
1523           application that calls PCRE. These may be created in a different locale
1524           from  the  default.  As more and more applications change to using Uni-
1525           code, the need for this locale support is expected to die away.
1526    
1527           External tables are built by calling  the  pcre_maketables()  function,
1528           which  has no arguments, in the relevant locale. The result can then be
1529           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1530           example,  to  build  and use tables that are appropriate for the French
1531           locale (where accented characters with  values  greater  than  128  are
1532           treated as letters), the following code could be used:
1533    
1534           setlocale(LC_CTYPE, "fr");           setlocale(LC_CTYPE, "fr_FR");
1535           tables = pcre_maketables();           tables = pcre_maketables();
1536           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1537    
1538         The  tables  are  built in memory that is obtained via pcre_malloc. The         The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1539         pointer that is passed to pcre_compile is saved with the compiled  pat-         if you are using Windows, the name for the French locale is "french".
1540         tern, and the same tables are used via this pointer by pcre_study() and  
1541         pcre_exec(). Thus, for any single pattern,  compilation,  studying  and         When pcre_maketables() runs, the tables are built  in  memory  that  is
1542         matching  all  happen in the same locale, but different patterns can be         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1543         compiled in different locales. It is  the  caller's  responsibility  to         that the memory containing the tables remains available for as long  as
1544         ensure  that  the memory containing the tables remains available for as         it is needed.
1545         long as it is needed.  
1546           The pointer that is passed to pcre_compile() is saved with the compiled
1547           pattern, and the same tables are used via this pointer by  pcre_study()
1548           and normally also by pcre_exec(). Thus, by default, for any single pat-
1549           tern, compilation, studying and matching all happen in the same locale,
1550           but different patterns can be compiled in different locales.
1551    
1552           It  is  possible to pass a table pointer or NULL (indicating the use of
1553           the internal tables) to pcre_exec(). Although  not  intended  for  this
1554           purpose,  this facility could be used to match a pattern in a different
1555           locale from the one in which it was compiled. Passing table pointers at
1556           run time is discussed below in the section on matching a pattern.
1557    
1558    
1559  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
# Line 776  INFORMATION ABOUT A PATTERN Line 1561  INFORMATION ABOUT A PATTERN
1561         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1562              int what, void *where);              int what, void *where);
1563    
1564         The pcre_fullinfo() function returns information about a compiled  pat-         The  pcre_fullinfo() function returns information about a compiled pat-
1565         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1566         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1567    
1568         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1569         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
1570         the pattern was not studied. The third argument specifies  which  piece         the  pattern  was not studied. The third argument specifies which piece
1571         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
1572         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
1573         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1574    
1575           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 792  INFORMATION ABOUT A PATTERN Line 1577  INFORMATION ABOUT A PATTERN
1577           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1578           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1579    
1580         Here  is a typical call of pcre_fullinfo(), to obtain the length of the         The "magic number" is placed at the start of each compiled  pattern  as
1581         compiled pattern:         an  simple check against passing an arbitrary memory pointer. Here is a
1582           typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1583           pattern:
1584    
1585           int rc;           int rc;
1586           unsigned long int length;           size_t length;
1587           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1588             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1589             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1590             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1591             &length);         /* where to put the data */             &length);         /* where to put the data */
1592    
1593         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
1594         are as follows:         are as follows:
1595    
1596           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1597    
1598         Return  the  number  of  the highest back reference in the pattern. The         Return the number of the highest back reference  in  the  pattern.  The
1599         fourth argument should point to an int variable. Zero  is  returned  if         fourth  argument  should  point to an int variable. Zero is returned if
1600         there are no back references.         there are no back references.
1601    
1602           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1603    
1604         Return  the  number of capturing subpatterns in the pattern. The fourth         Return the number of capturing subpatterns in the pattern.  The  fourth
1605         argument should point to an int variable.         argument should point to an int variable.
1606    
1607             PCRE_INFO_DEFAULT_TABLES
1608    
1609           Return  a pointer to the internal default character tables within PCRE.
1610           The fourth argument should point to an unsigned char *  variable.  This
1611           information call is provided for internal use by the pcre_study() func-
1612           tion. External callers can cause PCRE to use  its  internal  tables  by
1613           passing a NULL table pointer.
1614    
1615           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1616    
1617         Return information about the first byte of any matched  string,  for  a         Return  information  about  the first byte of any matched string, for a
1618         non-anchored    pattern.    (This    option    used    to   be   called         non-anchored pattern. The fourth argument should point to an int  vari-
1619         PCRE_INFO_FIRSTCHAR; the old name is  still  recognized  for  backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1620         compatibility.)         is still recognized for backwards compatibility.)
1621    
1622         If  there  is  a  fixed  first  byte,  e.g.  from  a  pattern  such  as         If there is a fixed first byte, for example, from  a  pattern  such  as
1623         (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  
1624    
1625         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1626         branch starts with "^", or         branch starts with "^", or
# Line 846  INFORMATION ABOUT A PATTERN Line 1640  INFORMATION ABOUT A PATTERN
1640         returned. The fourth argument should point to an unsigned char *  vari-         returned. The fourth argument should point to an unsigned char *  vari-
1641         able.         able.
1642    
1643             PCRE_INFO_HASCRORLF
1644    
1645           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1646           characters, otherwise 0. The fourth argument should  point  to  an  int
1647           variable.  An explicit match is either a literal CR or LF character, or
1648           \r or \n.
1649    
1650             PCRE_INFO_JCHANGED
1651    
1652           Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1653           otherwise  0. The fourth argument should point to an int variable. (?J)
1654           and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1655    
1656           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1657    
1658         Return  the  value of the rightmost literal byte that must exist in any         Return the value of the rightmost literal byte that must exist  in  any
1659         matched string, other than at its  start,  if  such  a  byte  has  been         matched  string,  other  than  at  its  start,  if such a byte has been
1660         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1661         is no such byte, -1 is returned. For anchored patterns, a last  literal         is  no such byte, -1 is returned. For anchored patterns, a last literal
1662         byte  is  recorded only if it follows something of variable length. For         byte is recorded only if it follows something of variable  length.  For
1663         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1664         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1665    
# Line 860  INFORMATION ABOUT A PATTERN Line 1667  INFORMATION ABOUT A PATTERN
1667           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1668           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1669    
1670         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1671         ses. The names are just an additional way of identifying the  parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1672         ses,  which still acquire a number. A caller that wants to extract data         ses, which still acquire numbers. Several convenience functions such as
1673         from a named subpattern must convert the name to a number in  order  to         pcre_get_named_substring()  are  provided  for extracting captured sub-
1674         access  the  correct  pointers  in  the  output  vector (described with         strings by name. It is also possible to extract the data  directly,  by
1675         pcre_exec() below). In order to do this, it must first use these  three         first  converting  the  name to a number in order to access the correct
1676         values to obtain the name-to-number mapping table for the pattern.         pointers in the output vector (described with pcre_exec() below). To do
1677           the  conversion,  you  need  to  use  the  name-to-number map, which is
1678           described by these three values.
1679    
1680         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1681         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1682         of  each  entry;  both  of  these  return  an int value. The entry size         of each entry; both of these  return  an  int  value.  The  entry  size
1683         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1684         a  pointer  to  the  first  entry of the table (a pointer to char). The         a pointer to the first entry of the table  (a  pointer  to  char).  The
1685         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1686         sis,  most  significant byte first. The rest of the entry is the corre-         sis, most significant byte first. The rest of the entry is  the  corre-
1687         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1688         For  example,  consider  the following pattern (assume PCRE_EXTENDED is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1689         set, so white space - including newlines - is ignored):         theses  numbers.  For  example,  consider the following pattern (assume
1690           PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1691           (?P<date> (?P<year>(\d\d)?\d\d) -         ignored):
1692           (?P<month>\d\d) - (?P<day>\d\d) )  
1693             (?<date> (?<year>(\d\d)?\d\d) -
1694         There are four named subpatterns, so the table has  four  entries,  and           (?<month>\d\d) - (?<day>\d\d) )
1695         each  entry  in the table is eight bytes long. The table is as follows,  
1696         with non-printing bytes shows in hex, and undefined bytes shown as ??:         There  are  four  named subpatterns, so the table has four entries, and
1697           each entry in the table is eight bytes long. The table is  as  follows,
1698           with non-printing bytes shows in hexadecimal, and undefined bytes shown
1699           as ??:
1700    
1701           00 01 d  a  t  e  00 ??           00 01 d  a  t  e  00 ??
1702           00 05 d  a  y  00 ?? ??           00 05 d  a  y  00 ?? ??
1703           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1704           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1705    
1706         When writing code to extract data from named subpatterns, remember that         When writing code to extract data  from  named  subpatterns  using  the
1707         the length of each entry may be different for each compiled pattern.         name-to-number  map,  remember that the length of the entries is likely
1708           to be different for each compiled pattern.
1709    
1710             PCRE_INFO_OKPARTIAL
1711    
1712           Return 1 if the pattern can be used for partial matching, otherwise  0.
1713           The  fourth  argument  should point to an int variable. The pcrepartial
1714           documentation lists the restrictions that apply to patterns  when  par-
1715           tial matching is used.
1716    
1717           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1718    
1719         Return  a  copy of the options with which the pattern was compiled. The         Return  a  copy of the options with which the pattern was compiled. The
1720         fourth argument should point to an unsigned long  int  variable.  These         fourth argument should point to an unsigned long  int  variable.  These
1721         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1722         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1723           other  words,  they are the options that will be in force when matching
1724           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1725           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1726           and PCRE_EXTENDED.
1727    
1728         A pattern is automatically anchored by PCRE if  all  of  its  top-level         A pattern is automatically anchored by PCRE if  all  of  its  top-level
1729         alternatives begin with one of the following:         alternatives begin with one of the following:
# Line 922  INFORMATION ABOUT A PATTERN Line 1746  INFORMATION ABOUT A PATTERN
1746    
1747           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1748    
1749         Returns  the  size of the data block pointed to by the study_data field         Return the size of the data block pointed to by the study_data field in
1750         in a pcre_extra block. That is, it is the  value  that  was  passed  to         a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1751         pcre_malloc() when PCRE was getting memory into which to place the data         pcre_malloc() when PCRE was getting memory into which to place the data
1752         created by pcre_study(). The fourth argument should point to  a  size_t         created by pcre_study(). The fourth argument should point to  a  size_t
1753         variable.         variable.
# Line 951  OBSOLETE INFO FUNCTION Line 1775  OBSOLETE INFO FUNCTION
1775         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1776    
1777    
1778  MATCHING A PATTERN  REFERENCE COUNTS
1779    
1780           int pcre_refcount(pcre *code, int adjust);
1781    
1782           The  pcre_refcount()  function is used to maintain a reference count in
1783           the data block that contains a compiled pattern. It is provided for the
1784           benefit  of  applications  that  operate  in an object-oriented manner,
1785           where different parts of the application may be using the same compiled
1786           pattern, but you want to free the block when they are all done.
1787    
1788           When a pattern is compiled, the reference count field is initialized to
1789           zero.  It is changed only by calling this function, whose action is  to
1790           add  the  adjust  value  (which may be positive or negative) to it. The
1791           yield of the function is the new value. However, the value of the count
1792           is  constrained to lie between 0 and 65535, inclusive. If the new value
1793           is outside these limits, it is forced to the appropriate limit value.
1794    
1795           Except when it is zero, the reference count is not correctly  preserved
1796           if  a  pattern  is  compiled on one host and then transferred to a host
1797           whose byte-order is different. (This seems a highly unlikely scenario.)
1798    
1799    
1800    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1801    
1802         int pcre_exec(const pcre *code, const pcre_extra *extra,         int pcre_exec(const pcre *code, const pcre_extra *extra,
1803              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1804              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1805    
1806         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
1807         pre-compiled pattern, which is passed in the code argument. If the pat-         compiled pattern, which is passed in the code argument. If the  pattern
1808         tern  has been studied, the result of the study should be passed in the         has been studied, the result of the study should be passed in the extra
1809         extra argument.         argument. This function is the main matching facility of  the  library,
1810           and it operates in a Perl-like manner. For specialist use there is also
1811           an alternative matching function, which is described below in the  sec-
1812           tion about the pcre_dfa_exec() function.
1813    
1814           In  most applications, the pattern will have been compiled (and option-
1815           ally studied) in the same process that calls pcre_exec().  However,  it
1816           is possible to save compiled patterns and study data, and then use them
1817           later in different processes, possibly even on different hosts.  For  a
1818           discussion about this, see the pcreprecompile documentation.
1819    
1820         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
1821    
# Line 973  MATCHING A PATTERN Line 1828  MATCHING A PATTERN
1828             11,             /* the length of the subject string */             11,             /* the length of the subject string */
1829             0,              /* start at offset 0 in the subject */             0,              /* start at offset 0 in the subject */
1830             0,              /* default options */             0,              /* default options */
1831             ovector,        /* vector for substring information */             ovector,        /* vector of integers for substring information */
1832             30);            /* number of elements in the vector */             30);            /* number of elements (NOT size in bytes) */
1833    
1834       Extra data for pcre_exec()
1835    
1836         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
1837         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
1838         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-
1839         tional information in it. The fields in the block are as follows:         tional information in it. The pcre_extra block contains  the  following
1840           fields (not necessarily in this order):
1841    
1842           unsigned long int flags;           unsigned long int flags;
1843           void *study_data;           void *study_data;
1844           unsigned long int match_limit;           unsigned long int match_limit;
1845             unsigned long int match_limit_recursion;
1846           void *callout_data;           void *callout_data;
1847             const unsigned char *tables;
1848    
1849         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
1850         are set. The flag bits are:         are set. The flag bits are:
1851    
1852           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1853           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1854             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1855           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1856             PCRE_EXTRA_TABLES
1857    
1858         Other flag bits should be set to zero. The study_data field is  set  in         Other flag bits should be set to zero. The study_data field is  set  in
1859         the  pcre_extra  block  that is returned by pcre_study(), together with         the  pcre_extra  block  that is returned by pcre_study(), together with
1860         the appropriate flag bit. You should not set this yourself, but you can         the appropriate flag bit. You should not set this yourself, but you may
1861         add to the block by setting the other fields.         add  to  the  block by setting the other fields and their corresponding
1862           flag bits.
1863    
1864         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
1865         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
1866         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1867         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1868         repeats. Internally, PCRE uses a function called match() which it calls         repeats.
1869         repeatedly (sometimes recursively). The limit is imposed on the  number  
1870         of  times  this function is called during a match, which has the effect         Internally, PCRE uses a function called match() which it calls  repeat-
1871         of limiting the amount of recursion  and  backtracking  that  can  take         edly  (sometimes  recursively). The limit set by match_limit is imposed
1872         place.  For  patterns that are not anchored, the count starts from zero         on the number of times this function is called during  a  match,  which
1873           has  the  effect  of  limiting the amount of backtracking that can take
1874           place. For patterns that are not anchored, the count restarts from zero
1875         for each position in the subject string.         for each position in the subject string.
1876    
1877         The default limit for the library can be set when PCRE  is  built;  the         The  default  value  for  the  limit can be set when PCRE is built; the
1878         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1879         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1880         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra    block    in    which    match_limit    is    set,     and
1881         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is         PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1882         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1883    
1884         The  pcre_callout  field is used in conjunction with the "callout" fea-         The match_limit_recursion field is similar to match_limit, but  instead
1885           of limiting the total number of times that match() is called, it limits
1886           the depth of recursion. The recursion depth is a  smaller  number  than
1887           the  total number of calls, because not all calls to match() are recur-
1888           sive.  This limit is of use only if it is set smaller than match_limit.
1889    
1890           Limiting  the  recursion  depth  limits the amount of stack that can be
1891           used, or, when PCRE has been compiled to use memory on the heap instead
1892           of the stack, the amount of heap memory that can be used.
1893    
1894           The  default  value  for  match_limit_recursion can be set when PCRE is
1895           built; the default default  is  the  same  value  as  the  default  for
1896           match_limit.  You can override the default by suppling pcre_exec() with
1897           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1898           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1899           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1900    
1901           The pcre_callout field is used in conjunction with the  "callout"  fea-
1902         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1903    
1904         The PCRE_ANCHORED option can be passed in the options  argument,  whose         The  tables  field  is  used  to  pass  a  character  tables pointer to
1905         unused  bits  must  be zero. This limits pcre_exec() to matching at the         pcre_exec(); this overrides the value that is stored with the  compiled
1906         first matching position.  However,  if  a  pattern  was  compiled  with         pattern.  A  non-NULL value is stored with the compiled pattern only if
1907         PCRE_ANCHORED,  or turned out to be anchored by virtue of its contents,         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1908         it cannot be made unachored at matching time.         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1909           PCRE's internal tables to be used. This facility is  helpful  when  re-
1910         When PCRE_UTF8 was set at compile time, the validity of the subject  as         using  patterns  that  have been saved after compiling with an external
1911         a  UTF-8  string is automatically checked, and the value of startoffset         set of tables, because the external tables  might  be  at  a  different
1912         is also checked to ensure that it points to the start of a UTF-8  char-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1913         acter.  If  an  invalid  UTF-8  sequence of bytes is found, pcre_exec()         tion for a discussion of saving compiled patterns for later use.
1914         returns  the  error  PCRE_ERROR_BADUTF8.  If  startoffset  contains  an  
1915         invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.     Option bits for pcre_exec()
1916    
1917           The unused bits of the options argument for pcre_exec() must  be  zero.
1918           The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1919           PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1920           PCRE_PARTIAL.
1921    
1922         If  you  already  know that your subject is valid, and you want to skip           PCRE_ANCHORED
        these   checks   for   performance   reasons,   you   can    set    the  
        PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to  
        do this for the second and subsequent calls to pcre_exec() if  you  are  
        making  repeated  calls  to  find  all  the matches in a single subject  
        string. However, you should be  sure  that  the  value  of  startoffset  
        points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is  
        set, the effect of passing an invalid UTF-8 string as a subject,  or  a  
        value  of startoffset that does not point to the start of a UTF-8 char-  
        acter, is undefined. Your program may crash.  
1923    
1924         There are also three further options that can be set only  at  matching         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1925         time:         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1926           turned  out to be anchored by virtue of its contents, it cannot be made
1927           unachored at matching time.
1928    
1929             PCRE_BSR_ANYCRLF
1930             PCRE_BSR_UNICODE
1931    
1932           These options (which are mutually exclusive) control what the \R escape
1933           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1934           or to match any Unicode newline sequence. These  options  override  the
1935           choice that was made or defaulted when the pattern was compiled.
1936    
1937             PCRE_NEWLINE_CR
1938             PCRE_NEWLINE_LF
1939             PCRE_NEWLINE_CRLF
1940             PCRE_NEWLINE_ANYCRLF
1941             PCRE_NEWLINE_ANY
1942    
1943           These  options  override  the  newline  definition  that  was chosen or
1944           defaulted when the pattern was compiled. For details, see the  descrip-
1945           tion  of  pcre_compile()  above.  During  matching,  the newline choice
1946           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1947           ters.  It may also alter the way the match position is advanced after a
1948           match failure for an unanchored pattern.
1949    
1950           When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
1951           set,  and a match attempt for an unanchored pattern fails when the cur-
1952           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1953           explicit  matches  for  CR  or  LF  characters,  the  match position is
1954           advanced by two characters instead of one, in other words, to after the
1955           CRLF.
1956    
1957           The above rule is a compromise that makes the most common cases work as
1958           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1959           option is not set), it does not match the string "\r\nA" because, after
1960           failing at the start, it skips both the CR and the LF before  retrying.
1961           However,  the  pattern  [\r\n]A does match that string, because it con-
1962           tains an explicit CR or LF reference, and so advances only by one char-
1963           acter after the first failure.
1964    
1965           An explicit match for CR of LF is either a literal appearance of one of
1966           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1967           matches  such  as [^X] do not count, nor does \s (which includes CR and
1968           LF in the characters that it matches).
1969    
1970           Notwithstanding the above, anomalous effects may still occur when  CRLF
1971           is a valid newline sequence and explicit \r or \n escapes appear in the
1972           pattern.
1973    
1974           PCRE_NOTBOL           PCRE_NOTBOL
1975    
1976         The  first  character  of the string is not the beginning of a line, so         This option specifies that first character of the subject string is not
1977         the circumflex metacharacter should not match before it.  Setting  this         the  beginning  of  a  line, so the circumflex metacharacter should not
1978         without  PCRE_MULTILINE  (at  compile  time) causes circumflex never to         match before it. Setting this without PCRE_MULTILINE (at compile  time)
1979         match.         causes  circumflex  never to match. This option affects only the behav-
1980           iour of the circumflex metacharacter. It does not affect \A.
1981    
1982           PCRE_NOTEOL           PCRE_NOTEOL
1983    
1984         The end of the string is not the end of a line, so the dollar metachar-         This option specifies that the end of the subject string is not the end
1985         acter  should  not  match  it  nor (except in multiline mode) a newline         of  a line, so the dollar metacharacter should not match it nor (except
1986         immediately before it. Setting this without PCRE_MULTILINE (at  compile         in multiline mode) a newline immediately before it. Setting this  with-
1987         time) causes dollar never to match.         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1988           option affects only the behaviour of the dollar metacharacter. It  does
1989           not affect \Z or \z.
1990    
1991           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1992    
# Line 1078  MATCHING A PATTERN Line 2006  MATCHING A PATTERN
2006         cial case of a pattern match of the empty  string  within  its  split()         cial case of a pattern match of the empty  string  within  its  split()
2007         function,  and  when  using  the /g modifier. It is possible to emulate         function,  and  when  using  the /g modifier. It is possible to emulate
2008         Perl's behaviour after matching a null string by first trying the match         Perl's behaviour after matching a null string by first trying the match
2009         again at the same offset with PCRE_NOTEMPTY set, and then if that fails         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
2010         by advancing the starting offset (see below)  and  trying  an  ordinary         if that fails by advancing the starting offset (see below)  and  trying
2011         match again.         an ordinary match again. There is some code that demonstrates how to do
2012           this in the pcredemo.c sample program.
2013    
2014         The  subject string is passed to pcre_exec() as a pointer in subject, a           PCRE_NO_UTF8_CHECK
2015         length in length, and a starting byte offset in startoffset. Unlike the  
2016         pattern  string,  the  subject  may contain binary zero bytes. When the         When PCRE_UTF8 is set at compile time, the validity of the subject as a
2017         starting offset is zero, the search for a match starts at the beginning         UTF-8  string is automatically checked when pcre_exec() is subsequently
2018         of the subject, and this is by far the most common case.         called.  The value of startoffset is also checked  to  ensure  that  it
2019           points  to  the start of a UTF-8 character. There is a discussion about
2020         If the pattern was compiled with the PCRE_UTF8 option, the subject must         the validity of UTF-8 strings in the section on UTF-8  support  in  the
2021         be a sequence of bytes that is a valid UTF-8 string, and  the  starting         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2022         offset  must point to the beginning of a UTF-8 character. If an invalid         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2023         UTF-8 string or offset is passed, an error  (either  PCRE_ERROR_BADUTF8         tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2024         or   PCRE_ERROR_BADUTF8_OFFSET)   is   returned,   unless   the  option  
2025         PCRE_NO_UTF8_CHECK is set,  in  which  case  PCRE's  behaviour  is  not         If  you  already  know that your subject is valid, and you want to skip
2026         defined.         these   checks   for   performance   reasons,   you   can    set    the
2027           PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
2028           do this for the second and subsequent calls to pcre_exec() if  you  are
2029           making  repeated  calls  to  find  all  the matches in a single subject
2030           string. However, you should be  sure  that  the  value  of  startoffset
2031           points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
2032           set, the effect of passing an invalid UTF-8 string as a subject,  or  a
2033           value  of startoffset that does not point to the start of a UTF-8 char-
2034           acter, is undefined. Your program may crash.
2035    
2036             PCRE_PARTIAL
2037    
2038           This option turns on the  partial  matching  feature.  If  the  subject
2039           string  fails to match the pattern, but at some point during the match-
2040           ing process the end of the subject was reached (that  is,  the  subject
2041           partially  matches  the  pattern and the failure to match occurred only
2042           because there were not enough subject characters), pcre_exec()  returns
2043           PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
2044           used, there are restrictions on what may appear in the  pattern.  These
2045           are discussed in the pcrepartial documentation.
2046    
2047       The string to be matched by pcre_exec()
2048    
2049         A  non-zero  starting offset is useful when searching for another match         The  subject string is passed to pcre_exec() as a pointer in subject, a
2050         in the same subject by calling pcre_exec() again after a previous  suc-         length in length, and a starting byte offset in startoffset.  In  UTF-8
2051         cess.   Setting  startoffset differs from just passing over a shortened         mode,  the  byte  offset  must point to the start of a UTF-8 character.
2052         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         Unlike the pattern string, the subject may contain binary  zero  bytes.
2053           When  the starting offset is zero, the search for a match starts at the
2054           beginning of the subject, and this is by far the most common case.
2055    
2056           A non-zero starting offset is useful when searching for  another  match
2057           in  the same subject by calling pcre_exec() again after a previous suc-
2058           cess.  Setting startoffset differs from just passing over  a  shortened
2059           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2060         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2061    
2062           \Biss\B           \Biss\B
2063    
2064         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
2065         only if the current position in the subject is not  a  word  boundary.)         only  if  the  current position in the subject is not a word boundary.)
2066         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
2067         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
2068         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
2069         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
2070         to  be  a  word  boundary. However, if pcre_exec() is passed the entire         to be a word boundary. However, if pcre_exec()  is  passed  the  entire
2071         string again, but with startoffset  set  to  4,  it  finds  the  second         string again, but with startoffset set to 4, it finds the second occur-
2072         occurrence  of  "iss"  because  it  is able to look behind the starting         rence of "iss" because it is able to look behind the starting point  to
2073         point to discover that it is preceded by a letter.         discover that it is preceded by a letter.
2074    
2075         If a non-zero starting offset is passed when the pattern  is  anchored,         If  a  non-zero starting offset is passed when the pattern is anchored,
2076         one  attempt  to match at the given offset is tried. This can only suc-         one attempt to match at the given offset is made. This can only succeed
2077         ceed if the pattern does not require the match to be at  the  start  of         if  the  pattern  does  not require the match to be at the start of the
2078         the subject.         subject.
2079    
2080       How pcre_exec() returns captured substrings
2081    
2082         In  general, a pattern matches a certain portion of the subject, and in         In general, a pattern matches a certain portion of the subject, and  in
2083         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2084         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2085         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2086         subpattern"  is  used for a fragment of a pattern that picks out a sub-         subpattern" is used for a fragment of a pattern that picks out  a  sub-
2087         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2088         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2089    
2090         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of  integer
2091         offsets whose address is passed in ovector. The number of  elements  in         offsets  whose  address is passed in ovector. The number of elements in
2092         the vector is passed in ovecsize. The first two-thirds of the vector is         the vector is passed in ovecsize, which must be a non-negative  number.
2093         used to pass back captured substrings, each substring using a  pair  of         Note: this argument is NOT the size of ovector in bytes.
2094         integers.  The  remaining  third  of the vector is used as workspace by  
2095         pcre_exec() while matching capturing subpatterns, and is not  available         The  first  two-thirds of the vector is used to pass back captured sub-
2096         for  passing  back  information.  The  length passed in ovecsize should         strings, each substring using a pair of integers. The  remaining  third
2097         always be a multiple of three. If it is not, it is rounded down.         of  the  vector is used as workspace by pcre_exec() while matching cap-
2098           turing subpatterns, and is not available for passing back  information.
2099           The  length passed in ovecsize should always be a multiple of three. If
2100           it is not, it is rounded down.
2101    
2102         When a match has been successful, information about captured substrings         When a match is successful, information about  captured  substrings  is
2103         is returned in pairs of integers, starting at the beginning of ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2104         and continuing up to two-thirds of its length at the  most.  The  first         and continuing up to two-thirds of its length at the  most.  The  first
2105         element of a pair is set to the offset of the first character in a sub-         element of a pair is set to the offset of the first character in a sub-
2106         string, and the second is set to the  offset  of  the  first  character         string, and the second is set to the  offset  of  the  first  character
2107         after  the  end  of  a  substring. The first pair, ovector[0] and ovec-         after  the  end  of  a  substring. The first pair, ovector[0] and ovec-
2108         tor[1], identify the portion of  the  subject  string  matched  by  the         tor[1], identify the portion of  the  subject  string  matched  by  the
2109         entire  pattern.  The next pair is used for the first capturing subpat-         entire  pattern.  The next pair is used for the first capturing subpat-
2110         tern, and so on. The value returned by pcre_exec()  is  the  number  of         tern, and so on. The value returned by pcre_exec() is one more than the
2111         pairs  that  have  been set. If there are no capturing subpatterns, the         highest numbered pair that has been set. For example, if two substrings
2112         return value from a successful match is 1,  indicating  that  just  the         have been captured, the returned value is 3. If there are no  capturing
2113         first pair of offsets has been set.         subpatterns,  the return value from a successful match is 1, indicating
2114           that just the first pair of offsets has been set.
        Some  convenience  functions  are  provided for extracting the captured  
        substrings as separate strings. These are described  in  the  following  
        section.  
   
        It  is  possible  for  an capturing subpattern number n+1 to match some  
        part of the subject when subpattern n has not been  used  at  all.  For  
        example, if the string "abc" is matched against the pattern (a|(z))(bc)  
        subpatterns 1 and 3 are matched, but 2 is not. When this happens,  both  
        offset values corresponding to the unused subpattern are set to -1.  
2115    
2116         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2117         of the string that it matched that gets returned.         of the string that it matched that is returned.
2118    
2119         If the vector is too small to hold all the captured substrings,  it  is         If  the vector is too small to hold all the captured substring offsets,
2120         used as far as possible (up to two-thirds of its length), and the func-         it is used as far as possible (up to two-thirds of its length), and the
2121         tion returns a value of zero. In particular, if the  substring  offsets         function  returns a value of zero. In particular, if the substring off-
2122         are  not  of interest, pcre_exec() may be called with ovector passed as         sets are not of interest, pcre_exec() may be called with ovector passed
2123         NULL and ovecsize as zero. However, if the pattern contains back refer-         as  NULL  and  ovecsize  as zero. However, if the pattern contains back
2124         ences  and  the  ovector  isn't big enough to remember the related sub-         references and the ovector is not big enough to  remember  the  related
2125         strings, PCRE has to get additional memory  for  use  during  matching.         substrings,  PCRE has to get additional memory for use during matching.
2126         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
2127    
2128         Note  that  pcre_info() can be used to find out how many capturing sub-         The pcre_info() function can be used to find  out  how  many  capturing
2129         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns  there  are  in  a  compiled pattern. The smallest size for
2130         that  will  allow for n captured substrings, in addition to the offsets         ovector that will allow for n captured substrings, in addition  to  the
2131         of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
2132    
2133           It  is  possible for capturing subpattern number n+1 to match some part
2134           of the subject when subpattern n has not been used at all. For example,
2135           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
2136           return from the function is 4, and subpatterns 1 and 3 are matched, but
2137           2  is  not.  When  this happens, both values in the offset pairs corre-
2138           sponding to unused subpatterns are set to -1.
2139    
2140           Offset values that correspond to unused subpatterns at the end  of  the
2141           expression  are  also  set  to  -1. For example, if the string "abc" is
2142           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
2143           matched.  The  return  from the function is 2, because the highest used
2144           capturing subpattern number is 1. However, you can refer to the offsets
2145           for  the  second  and third capturing subpatterns if you wish (assuming
2146           the vector is large enough, of course).
2147    
2148           Some convenience functions are provided  for  extracting  the  captured
2149           substrings as separate strings. These are described below.
2150    
2151         If pcre_exec() fails, it returns a negative number. The  following  are     Error return values from pcre_exec()
2152    
2153           If  pcre_exec()  fails, it returns a negative number. The following are
2154         defined in the header file:         defined in the header file:
2155    
2156           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1186  MATCHING A PATTERN Line 2159  MATCHING A PATTERN
2159    
2160           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2161    
2162         Either  code  or  subject  was  passed as NULL, or ovector was NULL and         Either code or subject was passed as NULL,  or  ovector  was  NULL  and
2163         ovecsize was not zero.         ovecsize was not zero.
2164    
2165           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1195  MATCHING A PATTERN Line 2168  MATCHING A PATTERN
2168    
2169           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2170    
2171         PCRE stores a 4-byte "magic number" at the start of the compiled  code,         PCRE  stores a 4-byte "magic number" at the start of the compiled code,
2172         to  catch  the case when it is passed a junk pointer. This is the error         to catch the case when it is passed a junk pointer and to detect when a
2173         it gives when the magic number isn't present.         pattern that was compiled in an environment of one endianness is run in
2174           an environment with the other endianness. This is the error  that  PCRE
2175           gives when the magic number is not present.
2176    
2177           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2178    
2179         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2180         compiled  pattern.  This  error  could be caused by a bug in PCRE or by         compiled pattern. This error could be caused by a bug  in  PCRE  or  by
2181         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2182    
2183           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2184    
2185         If a pattern contains back references, but the ovector that  is  passed         If  a  pattern contains back references, but the ovector that is passed
2186         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2187         PCRE gets a block of memory at the start of matching to  use  for  this         PCRE  gets  a  block of memory at the start of matching to use for this
2188         purpose.  If the call via pcre_malloc() fails, this error is given. The         purpose. If the call via pcre_malloc() fails, this error is given.  The
2189         memory is freed at the end of matching.         memory is automatically freed at the end of matching.
2190    
2191           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2192    
2193         This error is used by the pcre_copy_substring(),  pcre_get_substring(),         This  error is used by the pcre_copy_substring(), pcre_get_substring(),
2194         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2195         returned by pcre_exec().         returned by pcre_exec().
2196    
2197           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2198    
2199         The recursion and backtracking limit, as specified by  the  match_limit         The  backtracking  limit,  as  specified  by the match_limit field in a
2200         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         pcre_extra structure (or defaulted) was reached.  See  the  description
2201         description above.         above.
2202    
2203           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2204    
2205         This error is never generated by pcre_exec() itself. It is provided for         This error is never generated by pcre_exec() itself. It is provided for
2206         use  by  callout functions that want to yield a distinctive error code.         use by callout functions that want to yield a distinctive  error  code.
2207         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2208    
2209           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2210    
2211         A string that contains an invalid UTF-8 byte sequence was passed  as  a         A  string  that contains an invalid UTF-8 byte sequence was passed as a
2212         subject.         subject.
2213    
2214           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2215    
2216         The UTF-8 byte sequence that was passed as a subject was valid, but the         The UTF-8 byte sequence that was passed as a subject was valid, but the
2217         value of startoffset did not point to the beginning of a UTF-8  charac-         value  of startoffset did not point to the beginning of a UTF-8 charac-
2218         ter.         ter.
2219    
2220             PCRE_ERROR_PARTIAL        (-12)
2221    
2222           The subject string did not match, but it did match partially.  See  the
2223           pcrepartial documentation for details of partial matching.
2224    
2225             PCRE_ERROR_BADPARTIAL     (-13)
2226    
2227           The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
2228           items that are not supported for partial matching. See the  pcrepartial
2229           documentation for details of partial matching.
2230    
2231             PCRE_ERROR_INTERNAL       (-14)
2232    
2233           An  unexpected  internal error has occurred. This error could be caused
2234           by a bug in PCRE or by overwriting of the compiled pattern.
2235    
2236             PCRE_ERROR_BADCOUNT       (-15)
2237    
2238           This error is given if the value of the ovecsize argument is  negative.
2239    
2240             PCRE_ERROR_RECURSIONLIMIT (-21)
2241    
2242           The internal recursion limit, as specified by the match_limit_recursion
2243           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2244           description above.
2245    
2246             PCRE_ERROR_BADNEWLINE     (-23)
2247    
2248           An invalid combination of PCRE_NEWLINE_xxx options was given.
2249    
2250           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2251    
2252    
2253  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2254    
# Line 1262  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2269  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2269         string_list() are provided for extracting captured substrings  as  new,         string_list() are provided for extracting captured substrings  as  new,
2270         separate,  zero-terminated strings. These functions identify substrings         separate,  zero-terminated strings. These functions identify substrings
2271         by number. The next section describes functions  for  extracting  named         by number. The next section describes functions  for  extracting  named
2272         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2273         extracted and has a further zero added on the end, but  the  result  is  
2274         not, of course, a C string.         A  substring that contains a binary zero is correctly extracted and has
2275           a further zero added on the end, but the result is not, of course, a  C
2276           string.   However,  you  can  process such a string by referring to the
2277           length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2278           string().  Unfortunately, the interface to pcre_get_substring_list() is
2279           not adequate for handling strings containing binary zeros, because  the
2280           end of the final string is not independently indicated.
2281    
2282         The  first  three  arguments  are the same for all three of these func-         The  first  three  arguments  are the same for all three of these func-
2283         tions: subject is the subject string which has just  been  successfully         tions: subject is the subject string that has  just  been  successfully
2284         matched, ovector is a pointer to the vector of integer offsets that was         matched, ovector is a pointer to the vector of integer offsets that was
2285         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2286         were  captured  by  the match, including the substring that matched the         were  captured  by  the match, including the substring that matched the
2287         entire regular expression. This is the value returned by  pcre_exec  if         entire regular expression. This is the value returned by pcre_exec() if
2288         it  is greater than zero. If pcre_exec() returned zero, indicating that         it  is greater than zero. If pcre_exec() returned zero, indicating that
2289         it ran out of space in ovector, the value passed as stringcount  should         it ran out of space in ovector, the value passed as stringcount  should
2290         be the size of the vector divided by three.         be the number of elements in the vector divided by three.
2291    
2292         The  functions pcre_copy_substring() and pcre_get_substring() extract a         The  functions pcre_copy_substring() and pcre_get_substring() extract a
2293         single substring, whose number is given as  stringnumber.  A  value  of         single substring, whose number is given as  stringnumber.  A  value  of
2294         zero  extracts  the  substring  that  matched the entire pattern, while         zero  extracts  the  substring that matched the entire pattern, whereas
2295         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2296         string(),  the  string  is  placed  in buffer, whose length is given by         string(),  the  string  is  placed  in buffer, whose length is given by
2297         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2298         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2299         The yield of the function is the length of the  string,  not  including         The yield of the function is the length of the  string,  not  including
2300         the terminating zero, or one of         the terminating zero, or one of these error codes:
2301    
2302           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2303    
# Line 1297  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2310  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2310    
2311         The pcre_get_substring_list()  function  extracts  all  available  sub-         The pcre_get_substring_list()  function  extracts  all  available  sub-
2312         strings  and  builds  a list of pointers to them. All this is done in a         strings  and  builds  a list of pointers to them. All this is done in a
2313         single block of memory which is obtained via pcre_malloc.  The  address         single block of memory that is obtained via pcre_malloc. The address of
2314         of the memory block is returned via listptr, which is also the start of         the  memory  block  is returned via listptr, which is also the start of
2315         the list of string pointers. The end of the list is marked  by  a  NULL         the list of string pointers. The end of the list is marked  by  a  NULL
2316         pointer. The yield of the function is zero if all went well, or         pointer.  The  yield  of  the function is zero if all went well, or the
2317           error code
2318    
2319           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2320    
2321         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2322    
2323         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2324         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2325         the  subject, but subpattern n has not been used at all, they return an         the subject, but subpattern n has not been used at all, they return  an
2326         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2327         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2328         tive for unset substrings.         tive for unset substrings.
2329    
2330         The    two    convenience    functions    pcre_free_substring()     and         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2331         pcre_free_substring_list() can be used to free the memory returned by a         string_list() can be used to free the memory  returned  by  a  previous
2332         previous call  of  pcre_get_substring()  or  pcre_get_substring_list(),         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2333         respectively. They do nothing more than call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2334         pcre_free, which of course could be called directly from a  C  program.         pcre_free,  which  of course could be called directly from a C program.
2335         However,  PCRE is used in some situations where it is linked via a spe-         However, PCRE is used in some situations where it is linked via a  spe-
2336         cial  interface  to  another  programming  language  which  cannot  use         cial   interface  to  another  programming  language  that  cannot  use
2337         pcre_free  directly;  it is for these cases that the functions are pro-         pcre_free directly; it is for these cases that the functions  are  pro-
2338         vided.         vided.
2339    
2340    
2341  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2342    
2343           int pcre_get_stringnumber(const pcre *code,
2344                const char *name);
2345    
2346         int pcre_copy_named_substring(const pcre *code,         int pcre_copy_named_substring(const pcre *code,
2347              const char *subject, int *ovector,              const char *subject, int *ovector,
2348              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2349              char *buffer, int buffersize);              char *buffer, int buffersize);
2350    
        int pcre_get_stringnumber(const pcre *code,  
             const char *name);  
   
2351         int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2352              const char *subject, int *ovector,              const char *subject, int *ovector,
2353              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2354              const char **stringptr);              const char **stringptr);
2355    
2356         To extract a substring by name, you first have to find associated  num-         To  extract a substring by name, you first have to find associated num-
2357         ber.  This  can  be  done by calling pcre_get_stringnumber(). The first         ber.  For example, for this pattern
2358         argument is the compiled pattern, and the second is the name. For exam-  
2359         ple, for this pattern           (a+)b(?<xxx>\d+)...
2360    
2361           ab(?<xxx>\d+)...         the number of the subpattern called "xxx" is 2. If the name is known to
2362           be unique (PCRE_DUPNAMES was not set), you can find the number from the
2363         the  number  of the subpattern called "xxx" is 1. Given the number, you         name by calling pcre_get_stringnumber(). The first argument is the com-
2364         can then extract the substring directly, or use one  of  the  functions         piled pattern, and the second is the name. The yield of the function is
2365         described  in the previous section. For convenience, there are also two         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2366         functions that do the whole job.         subpattern of that name.
2367    
2368         Most   of   the   arguments    of    pcre_copy_named_substring()    and         Given the number, you can extract the substring directly, or use one of
2369         pcre_get_named_substring() are the same as those for the functions that         the functions described in the previous section. For convenience, there
2370         extract by number, and so are not re-described here. There are just two         are also two functions that do the whole job.
2371         differences.  
2372           Most    of    the    arguments   of   pcre_copy_named_substring()   and
2373           pcre_get_named_substring() are the same  as  those  for  the  similarly
2374           named  functions  that extract by number. As these are described in the
2375           previous section, they are not re-described here. There  are  just  two
2376           differences:
2377    
2378         First,  instead  of a substring number, a substring name is given. Sec-         First,  instead  of a substring number, a substring name is given. Sec-
2379         ond, there is an extra argument, given at the start, which is a pointer         ond, there is an extra argument, given at the start, which is a pointer
# Line 1363  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2382  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2382    
2383         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2384         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2385         ate.         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2386           behaviour may not be what you want (see the next section).
2387    
 Last updated: 09 December 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2388    
2389  PCRE(3)                                                                PCRE(3)  DUPLICATE SUBPATTERN NAMES
2390    
2391           int pcre_get_stringtable_entries(const pcre *code,
2392                const char *name, char **first, char **last);
2393    
2394           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2395           subpatterns are not required to  be  unique.  Normally,  patterns  with
2396           duplicate  names  are such that in any one match, only one of the named
2397           subpatterns participates. An example is shown in the pcrepattern  docu-
2398           mentation.
2399    
2400           When    duplicates   are   present,   pcre_copy_named_substring()   and
2401           pcre_get_named_substring() return the first substring corresponding  to
2402           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2403           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2404           function  returns one of the numbers that are associated with the name,
2405           but it is not defined which it is.
2406    
2407           If you want to get full details of all captured substrings for a  given
2408           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2409           first argument is the compiled pattern, and the second is the name. The
2410           third  and  fourth  are  pointers to variables which are updated by the
2411           function. After it has run, they point to the first and last entries in
2412           the  name-to-number  table  for  the  given  name.  The function itself
2413           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2414           there  are none. The format of the table is described above in the sec-
2415           tion entitled Information about a  pattern.   Given  all  the  relevant
2416           entries  for the name, you can extract each of their numbers, and hence
2417           the captured data, if any.
2418    
2419    
2420    FINDING ALL POSSIBLE MATCHES
2421    
2422           The traditional matching function uses a  similar  algorithm  to  Perl,
2423           which stops when it finds the first match, starting at a given point in
2424           the subject. If you want to find all possible matches, or  the  longest
2425           possible  match,  consider using the alternative matching function (see
2426           below) instead. If you cannot use the alternative function,  but  still
2427           need  to  find all possible matches, you can kludge it up by making use
2428           of the callout facility, which is described in the pcrecallout documen-
2429           tation.
2430    
2431  NAME         What you have to do is to insert a callout right at the end of the pat-
2432         PCRE - Perl-compatible regular expressions         tern.  When your callout function is called, extract and save the  cur-
2433           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2434           backtrack and try other alternatives. Ultimately, when it runs  out  of
2435           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2436    
 PCRE CALLOUTS  
2437    
2438         int (*pcre_callout)(pcre_callout_block *);  MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2439    
2440         PCRE provides a feature called "callout", which is a means of temporar-         int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2441         ily passing control to the caller of PCRE  in  the  middle  of  pattern              const char *subject, int length, int startoffset,
2442         matching.  The  caller of PCRE provides an external function by putting              int options, int *ovector, int ovecsize,
2443         its entry point in the global variable pcre_callout. By  default,  this              int *workspace, int wscount);
        variable contains NULL, which disables all calling out.  
2444    
2445         Within  a  regular  expression,  (?C) indicates the points at which the         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2446         external function is to be called.  Different  callout  points  can  be         against a compiled pattern, using a matching algorithm that  scans  the
2447         identified  by  putting  a number less than 256 after the letter C. The         subject  string  just  once, and does not backtrack. This has different
2448         default value is zero.  For  example,  this  pattern  has  two  callout         characteristics to the normal algorithm, and  is  not  compatible  with
2449         points:         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2450           theless, there are times when this kind of matching can be useful.  For
2451           a discussion of the two matching algorithms, see the pcrematching docu-
2452           mentation.
2453    
2454           The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2455           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2456           ent way, and this is described below. The other  common  arguments  are
2457           used  in  the  same way as for pcre_exec(), so their description is not
2458           repeated here.
2459    
2460           The two additional arguments provide workspace for  the  function.  The
2461           workspace  vector  should  contain at least 20 elements. It is used for
2462           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2463           workspace  will  be  needed for patterns and subjects where there are a
2464           lot of potential matches.
2465    
2466           (?C1)abc(?C2)def         Here is an example of a simple call to pcre_dfa_exec():
2467    
2468         During matching, when PCRE reaches a callout point (and pcre_callout is           int rc;
2469         set), the external function is called. Its only argument is  a  pointer           int ovector[10];
2470         to a pcre_callout block. This contains the following variables:           int wspace[20];
2471             rc = pcre_dfa_exec(
2472               re,             /* result of pcre_compile() */
2473               NULL,           /* we didn't study the pattern */
2474               "some string",  /* the subject string */
2475               11,             /* the length of the subject string */
2476               0,              /* start at offset 0 in the subject */
2477               0,              /* default options */
2478               ovector,        /* vector of integers for substring information */
2479               10,             /* number of elements (NOT size in bytes) */
2480               wspace,         /* working space vector */
2481               20);            /* number of elements (NOT size in bytes) */
2482    
2483       Option bits for pcre_dfa_exec()
2484    
2485           The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2486           zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2487           LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2488           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2489           three of these are the same as for pcre_exec(), so their description is
2490           not repeated here.
2491    
2492             PCRE_PARTIAL
2493    
2494           This  has  the  same general effect as it does for pcre_exec(), but the
2495           details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2496           pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2497           PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2498           been no complete matches, but there is still at least one matching pos-
2499           sibility. The portion of the string that provided the partial match  is
2500           set as the first matching string.
2501    
2502             PCRE_DFA_SHORTEST
2503    
2504           Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2505           stop as soon as it has found one match. Because of the way the alterna-
2506           tive  algorithm  works, this is necessarily the shortest possible match
2507           at the first possible matching point in the subject string.
2508    
2509             PCRE_DFA_RESTART
2510    
2511           When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2512           returns  a  partial  match, it is possible to call it again, with addi-
2513           tional subject characters, and have it continue with  the  same  match.
2514           The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2515           workspace and wscount options must reference the same vector as  before
2516           because  data  about  the  match so far is left in them after a partial
2517           match. There is more discussion of this  facility  in  the  pcrepartial
2518           documentation.
2519    
2520       Successful returns from pcre_dfa_exec()
2521    
2522           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2523           string in the subject. Note, however, that all the matches from one run
2524           of  the  function  start  at the same point in the subject. The shorter
2525           matches are all initial substrings of the longer matches. For  example,
2526           if the pattern
2527    
2528             <.*>
2529    
2530           is matched against the string
2531    
2532             This is <something> <something else> <something further> no more
2533    
2534           the three matched strings are
2535    
2536             <something>
2537             <something> <something else>
2538             <something> <something else> <something further>
2539    
2540           On  success,  the  yield of the function is a number greater than zero,
2541           which is the number of matched substrings.  The  substrings  themselves
2542           are  returned  in  ovector. Each string uses two elements; the first is
2543           the offset to the start, and the second is the offset to  the  end.  In
2544           fact,  all  the  strings  have the same start offset. (Space could have
2545           been saved by giving this only once, but it was decided to retain  some
2546           compatibility  with  the  way pcre_exec() returns data, even though the
2547           meaning of the strings is different.)
2548    
2549           The strings are returned in reverse order of length; that is, the long-
2550           est  matching  string is given first. If there were too many matches to
2551           fit into ovector, the yield of the function is zero, and the vector  is
2552           filled with the longest matches.
2553    
2554       Error returns from pcre_dfa_exec()
2555    
2556           The  pcre_dfa_exec()  function returns a negative number when it fails.
2557           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2558           described  above.   There are in addition the following errors that are
2559           specific to pcre_dfa_exec():
2560    
2561             PCRE_ERROR_DFA_UITEM      (-16)
2562    
2563           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2564           tern  that  it  does not support, for instance, the use of \C or a back
2565           reference.
2566    
2567             PCRE_ERROR_DFA_UCOND      (-17)
2568    
2569           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2570           that  uses  a back reference for the condition, or a test for recursion
2571           in a specific group. These are not supported.
2572    
2573             PCRE_ERROR_DFA_UMLIMIT    (-18)
2574    
2575           This return is given if pcre_dfa_exec() is called with an  extra  block
2576           that contains a setting of the match_limit field. This is not supported
2577           (it is meaningless).
2578    
2579             PCRE_ERROR_DFA_WSSIZE     (-19)
2580    
2581           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2582           workspace vector.
2583    
2584             PCRE_ERROR_DFA_RECURSE    (-20)
2585    
2586           When  a  recursive subpattern is processed, the matching function calls
2587           itself recursively, using private vectors for  ovector  and  workspace.
2588           This  error  is  given  if  the output vector is not large enough. This
2589           should be extremely rare, as a vector of size 1000 is used.
2590    
2591    
2592    SEE ALSO
2593    
2594           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2595           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2596    
2597    
2598    AUTHOR
2599    
2600           Philip Hazel
2601           University Computing Service
2602           Cambridge CB2 3QH, England.
2603    
2604    
2605    REVISION
2606    
2607           Last updated: 12 April 2008
2608           Copyright (c) 1997-2008 University of Cambridge.
2609    ------------------------------------------------------------------------------
2610    
2611    
2612    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2613    
2614    
2615    NAME
2616           PCRE - Perl-compatible regular expressions
2617    
2618    
2619    PCRE CALLOUTS
2620    
2621           int (*pcre_callout)(pcre_callout_block *);
2622    
2623           PCRE provides a feature called "callout", which is a means of temporar-
2624           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2625           matching.  The  caller of PCRE provides an external function by putting
2626           its entry point in the global variable pcre_callout. By  default,  this
2627           variable contains NULL, which disables all calling out.
2628    
2629           Within  a  regular  expression,  (?C) indicates the points at which the
2630           external function is to be called.  Different  callout  points  can  be
2631           identified  by  putting  a number less than 256 after the letter C. The
2632           default value is zero.  For  example,  this  pattern  has  two  callout
2633           points:
2634    
2635             (?C1)abc(?C2)def
2636    
2637           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2638           called, PCRE automatically  inserts  callouts,  all  with  number  255,
2639           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2640           used with the pattern
2641    
2642             A(\d{2}|--)
2643    
2644           it is processed as if it were
2645    
2646           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2647    
2648           Notice that there is a callout before and after  each  parenthesis  and
2649           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2650           progress of pattern matching. The pcretest command has an  option  that
2651           sets  automatic callouts; when it is used, the output indicates how the
2652           pattern is matched. This is useful information when you are  trying  to
2653           optimize the performance of a particular pattern.
2654    
2655    
2656    MISSING CALLOUTS
2657    
2658           You  should  be  aware  that,  because of optimizations in the way PCRE
2659           matches patterns, callouts sometimes do not happen. For example, if the
2660           pattern is
2661    
2662             ab(?C4)cd
2663    
2664           PCRE knows that any matching string must contain the letter "d". If the
2665           subject string is "abyz", the lack of "d" means that  matching  doesn't
2666           ever  start,  and  the  callout is never reached. However, with "abyd",
2667           though the result is still no match, the callout is obeyed.
2668    
2669    
2670    THE CALLOUT INTERFACE
2671    
2672           During matching, when PCRE reaches a callout point, the external  func-
2673           tion  defined by pcre_callout is called (if it is set). This applies to
2674           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2675           only  argument  to  the callout function is a pointer to a pcre_callout
2676           block. This structure contains the following fields:
2677    
2678           int          version;           int          version;
2679           int          callout_number;           int          callout_number;
# Line 1408  PCRE CALLOUTS Line 2685  PCRE CALLOUTS
2685           int          capture_top;           int          capture_top;
2686           int          capture_last;           int          capture_last;
2687           void        *callout_data;           void        *callout_data;
2688             int          pattern_position;
2689             int          next_item_length;
2690    
2691         The  version  field  is an integer containing the version number of the         The version field is an integer containing the version  number  of  the
2692         block format. The current version  is  zero.  The  version  number  may         block  format. The initial version was 0; the current version is 1. The
2693         change  in  future if additional fields are added, but the intention is         version number will change again in future  if  additional  fields  are
2694         never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2695    
2696         The callout_number field contains the number of the  callout,  as  com-         The callout_number field contains the number of the  callout,  as  com-
2697         piled into the pattern (that is, the number after ?C).         piled  into  the pattern (that is, the number after ?C for manual call-
2698           outs, and 255 for automatically generated callouts).
2699    
2700         The  offset_vector field is a pointer to the vector of offsets that was         The offset_vector field is a pointer to the vector of offsets that  was
2701         passed by the caller to pcre_exec(). The contents can be  inspected  in         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2702         order  to extract substrings that have been matched so far, in the same         pcre_exec() is used, the contents can be inspected in order to  extract
2703         way as for extracting substrings after a match has completed.         substrings  that  have  been  matched  so  far,  in the same way as for
2704           extracting substrings after a match has completed. For  pcre_dfa_exec()
2705           this field is not useful.
2706    
2707         The subject and subject_length fields contain copies  the  values  that         The subject and subject_length fields contain copies of the values that
2708         were passed to pcre_exec().         were passed to pcre_exec().
2709    
2710         The  start_match  field contains the offset within the subject at which         The start_match field normally contains the offset within  the  subject
2711         the current match attempt started. If the pattern is not anchored,  the         at  which  the  current  match  attempt started. However, if the escape
2712         callout  function  may  be  called several times for different starting         sequence \K has been encountered, this value is changed to reflect  the
2713         points.         modified  starting  point.  If the pattern is not anchored, the callout
2714           function may be called several times from the same point in the pattern
2715           for different starting points in the subject.
2716    
2717         The current_position field contains the offset within  the  subject  of         The  current_position  field  contains the offset within the subject of
2718         the current match pointer.         the current match pointer.
2719    
2720         The  capture_top field contains one more than the number of the highest         When the pcre_exec() function is used, the capture_top  field  contains
2721         numbered  captured  substring  so  far.  If  no  substrings  have  been         one  more than the number of the highest numbered captured substring so
2722         captured, the value of capture_top is one.         far. If no substrings have been captured, the value of  capture_top  is
2723           one.  This  is always the case when pcre_dfa_exec() is used, because it
2724         The  capture_last  field  contains the number of the most recently cap-         does not support captured substrings.
2725         tured substring.  
2726           The capture_last field contains the number of the  most  recently  cap-
2727           tured  substring. If no substrings have been captured, its value is -1.
2728           This is always the case when pcre_dfa_exec() is used.
2729    
2730         The callout_data field contains a value that is passed  to  pcre_exec()         The callout_data field contains a value that is passed  to  pcre_exec()
2731         by  the  caller specifically so that it can be passed back in callouts.         or  pcre_dfa_exec() specifically so that it can be passed back in call-
2732         It is passed in the pcre_callout field of the  pcre_extra  data  struc-         outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2733         ture.  If  no  such  data  was  passed,  the value of callout_data in a         structure.  If  no such data was passed, the value of callout_data in a
2734         pcre_callout block is NULL. There is a description  of  the  pcre_extra         pcre_callout block is NULL. There is a description  of  the  pcre_extra
2735         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2736    
2737           The  pattern_position field is present from version 1 of the pcre_call-
2738           out structure. It contains the offset to the next item to be matched in
2739           the pattern string.
2740    
2741           The  next_item_length field is present from version 1 of the pcre_call-
2742           out structure. It contains the length of the next item to be matched in
2743           the  pattern  string. When the callout immediately precedes an alterna-
2744           tion bar, a closing parenthesis, or the end of the pattern, the  length
2745           is  zero.  When the callout precedes an opening parenthesis, the length
2746           is that of the entire subpattern.
2747    
2748           The pattern_position and next_item_length fields are intended  to  help
2749           in  distinguishing between different automatic callouts, which all have
2750           the same callout number. However, they are set for all callouts.
2751    
2752    
2753  RETURN VALUES  RETURN VALUES
2754    
2755         The callout function returns an integer. If the value is zero, matching         The external callout function returns an integer to PCRE. If the  value
2756         proceeds as normal. If the value is greater than zero,  matching  fails         is  zero,  matching  proceeds  as  normal. If the value is greater than
2757         at the current point, but backtracking to test other possibilities goes         zero, matching fails at the current point, but  the  testing  of  other
2758         ahead, just as if a lookahead assertion had failed.  If  the  value  is         matching possibilities goes ahead, just as if a lookahead assertion had
2759         less  than  zero,  the  match is abandoned, and pcre_exec() returns the         failed. If the value is less than zero, the  match  is  abandoned,  and
2760         value.         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2761    
2762         Negative  values  should  normally  be   chosen   from   the   set   of         Negative   values   should   normally   be   chosen  from  the  set  of
2763         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2764         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2765         reserved  for  use  by callout functions; it will never be used by PCRE         reserved for use by callout functions; it will never be  used  by  PCRE
2766         itself.         itself.
2767    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2768    
2769  PCRE(3)                                                                PCRE(3)  AUTHOR
2770    
2771           Philip Hazel
2772           University Computing Service
2773           Cambridge CB2 3QH, England.
2774    
2775    
2776    REVISION
2777    
2778           Last updated: 29 May 2007
2779           Copyright (c) 1997-2007 University of Cambridge.
2780    ------------------------------------------------------------------------------
2781    
2782    
2783    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2784    
2785    
2786  NAME  NAME
2787         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2788    
 DIFFERENCES FROM PERL  
2789    
2790         This  document describes the differences in the ways that PCRE and Perl  DIFFERENCES BETWEEN PCRE AND PERL
        handle regular expressions. The differences  described  here  are  with  
        respect to Perl 5.8.  
2791    
2792         1.  PCRE does not have full UTF-8 support. Details of what it does have         This  document describes the differences in the ways that PCRE and Perl
2793         are given in the section on UTF-8 support in the main pcre page.         handle regular expressions. The differences described here  are  mainly
2794           with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2795           some features that are expected to be in the forthcoming Perl 5.10.
2796    
2797           1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2798           of  what  it does have are given in the section on UTF-8 support in the
2799           main pcre page.
2800    
2801         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2802         permits  them,  but they do not mean what you might think. For example,         permits  them,  but they do not mean what you might think. For example,
# Line 1498  DIFFERENCES FROM PERL Line 2812  DIFFERENCES FROM PERL
2812    
2813         4. Though binary zero characters are supported in the  subject  string,         4. Though binary zero characters are supported in the  subject  string,
2814         they are not allowed in a pattern string because it is passed as a nor-         they are not allowed in a pattern string because it is passed as a nor-
2815         mal C string, terminated by zero. The escape sequence "\0" can be  used         mal C string, terminated by zero. The escape sequence \0 can be used in
2816         in the pattern to represent a binary zero.         the pattern to represent a binary zero.
2817    
2818         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2819         \U, \P, \p, \N, and \X. In fact these are implemented by Perl's general         \U, and \N. In fact these are implemented by Perl's general string-han-
2820         string-handling and are not part of its pattern matching engine. If any         dling  and are not part of its pattern matching engine. If any of these
2821         of these are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
2822    
2823           6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2824           is  built  with Unicode character property support. The properties that
2825           can be tested with \p and \P are limited to the general category  prop-
2826           erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2827           derived properties Any and L&.
2828    
2829         6. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2830         ters  in  between  are  treated as literals. This is slightly different         ters  in  between  are  treated as literals. This is slightly different
2831         from Perl in that $ and @ are  also  handled  as  literals  inside  the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2832         quotes.  In Perl, they cause variable interpolation (but of course PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
# Line 1522  DIFFERENCES FROM PERL Line 2842  DIFFERENCES FROM PERL
2842         The \Q...\E sequence is recognized both inside  and  outside  character         The \Q...\E sequence is recognized both inside  and  outside  character
2843         classes.         classes.
2844    
2845         7. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2846         constructions. However, there is some experimental support  for  recur-         constructions. However, there is support for recursive  patterns.  This
2847         sive  patterns  using the non-Perl items (?R), (?number) and (?P>name).         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2848         Also, the PCRE "callout" feature allows  an  external  function  to  be         "callout" feature allows an external function to be called during  pat-
2849         called during pattern matching.         tern matching. See the pcrecallout documentation for details.
2850    
2851           9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2852           always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2853           unlike Perl.
2854    
2855         8.  There  are some differences that are concerned with the settings of         10.  There are some differences that are concerned with the settings of
2856         captured strings when part of  a  pattern  is  repeated.  For  example,         captured strings when part of  a  pattern  is  repeated.  For  example,
2857         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2858         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2859    
2860         9. PCRE  provides  some  extensions  to  the  Perl  regular  expression         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2861         facilities:         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2862           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2863           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2864           ture group; this is different to Perl.
2865    
2866           12. PCRE provides some extensions to the Perl regular expression facil-
2867           ities.   Perl  5.10  will  include new features that are not in earlier
2868           versions, some of which (such as named parentheses) have been  in  PCRE
2869           for some time. This list is with respect to Perl 5.10:
2870    
2871         (a)  Although  lookbehind  assertions  must match fixed length strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2872         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
# Line 1544  DIFFERENCES FROM PERL Line 2876  DIFFERENCES FROM PERL
2876         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2877    
2878         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2879         cial meaning is faulted.         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2880           ignored.  (Perl can be made to issue a warning.)
2881    
2882         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2883         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
2884         lowed by a question mark they are.         lowed by a question mark they are.
2885    
2886         (e)  PCRE_ANCHORED  can  be used to force a pattern to be tried only at         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
2887         the first matching position in the subject string.         tried only at the first matching position in the subject string.
2888    
2889         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and  PCRE_NO_AUTO_CAP-         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2890         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2891    
2892         (g)  The (?R), (?number), and (?P>name) constructs allows for recursive         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2893         pattern matching (Perl can do  this  using  the  (?p{code})  construct,         CRLF by the PCRE_BSR_ANYCRLF option.
        which PCRE cannot support.)  
2894    
2895         (h)  PCRE supports named capturing substrings, using the Python syntax.         (h) The callout facility is PCRE-specific.
2896    
2897         (i) PCRE supports the possessive quantifier  "++"  syntax,  taken  from         (i) The partial matching facility is PCRE-specific.
        Sun's Java package.  
2898    
2899         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2900           even on different hosts that have the other endianness.
2901    
2902         (k) The callout facility is PCRE-specific.         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2903           different way and is not Perl-compatible.
2904    
2905  Last updated: 09 December 2003         (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2906  Copyright (c) 1997-2003 University of Cambridge.         of a pattern that set overall options that cannot be changed within the
2907  -----------------------------------------------------------------------------         pattern.
2908    
 PCRE(3)                                                                PCRE(3)  
2909    
2910    AUTHOR
2911    
2912           Philip Hazel
2913           University Computing Service
2914           Cambridge CB2 3QH, England.
2915    
2916    
2917    REVISION
2918    
2919           Last updated: 11 September 2007
2920           Copyright (c) 1997-2007 University of Cambridge.
2921    ------------------------------------------------------------------------------
2922    
2923    
2924    PCREPATTERN(3)                                                  PCREPATTERN(3)
2925    
2926    
2927  NAME  NAME
2928         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2929    
2930    
2931  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2932    
2933         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2934         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2935         documentation  and in a number of other books, some of which have copi-         tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
2936         ous examples. Jeffrey Friedl's "Mastering  Regular  Expressions",  pub-         semantics as closely as it can. PCRE  also  supports  some  alternative
2937         lished  by  O'Reilly, covers them in great detail. The description here         regular  expression  syntax (which does not conflict with the Perl syn-
2938         is intended as reference documentation.         tax) in order to provide some compatibility with regular expressions in
2939           Python, .NET, and Oniguruma.
2940         The basic operation of PCRE is on strings of bytes. However,  there  is  
2941         also  support for UTF-8 character strings. To use this support you must         Perl's  regular expressions are described in its own documentation, and
2942         build PCRE to include UTF-8 support, and then call pcre_compile()  with         regular expressions in general are covered in a number of  books,  some
2943         the  PCRE_UTF8  option.  How  this affects the pattern matching is men-         of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
2944         tioned in several places below. There is also a summary of  UTF-8  fea-         Expressions", published by  O'Reilly,  covers  regular  expressions  in
2945         tures in the section on UTF-8 support in the main pcre page.         great  detail.  This  description  of  PCRE's  regular  expressions  is
2946           intended as reference material.
2947    
2948           The original operation of PCRE was on strings of  one-byte  characters.
2949           However,  there is now also support for UTF-8 character strings. To use
2950           this, you must build PCRE to  include  UTF-8  support,  and  then  call
2951           pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern
2952           matching is mentioned in several places below. There is also a  summary
2953           of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
2954           page.
2955    
2956           The remainder of this document discusses the  patterns  that  are  sup-
2957           ported  by  PCRE when its main matching function, pcre_exec(), is used.
2958           From  release  6.0,   PCRE   offers   a   second   matching   function,
2959           pcre_dfa_exec(),  which matches using a different algorithm that is not
2960           Perl-compatible. Some of the features discussed below are not available
2961           when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2962           alternative function, and how it differs from the normal function,  are
2963           discussed in the pcrematching page.
2964    
2965    
2966    NEWLINE CONVENTIONS
2967    
2968           PCRE  supports five different conventions for indicating line breaks in
2969           strings: a single CR (carriage return) character, a  single  LF  (line-
2970           feed) character, the two-character sequence CRLF, any of the three pre-
2971           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2972           discussion  about newlines, and shows how to set the newline convention
2973           in the options arguments for the compiling and matching functions.
2974    
2975           It is also possible to specify a newline convention by starting a  pat-
2976           tern string with one of the following five sequences:
2977    
2978             (*CR)        carriage return
2979             (*LF)        linefeed
2980             (*CRLF)      carriage return, followed by linefeed
2981             (*ANYCRLF)   any of the three above
2982             (*ANY)       all Unicode newline sequences
2983    
2984           These override the default and the options given to pcre_compile(). For
2985           example, on a Unix system where LF is the default newline sequence, the
2986           pattern
2987    
2988             (*CR)a.b
2989    
2990           changes the convention to CR. That pattern matches "a\nb" because LF is
2991           no longer a newline. Note that these special settings,  which  are  not
2992           Perl-compatible,  are  recognized  only at the very start of a pattern,
2993           and that they must be in upper case.  If  more  than  one  of  them  is
2994           present, the last one is used.
2995    
2996           The  newline  convention  does  not  affect what the \R escape sequence
2997           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2998           compatibility.  However, this can be changed; see the description of \R
2999           in the section entitled "Newline sequences" below. A change of \R  set-
3000           ting can be combined with a change of newline convention.
3001    
3002    
3003    CHARACTERS AND METACHARACTERS
3004    
3005         A  regular  expression  is  a pattern that is matched against a subject         A  regular  expression  is  a pattern that is matched against a subject
3006         string from left to right. Most characters stand for  themselves  in  a         string from left to right. Most characters stand for  themselves  in  a
# Line 1603  PCRE REGULAR EXPRESSION DETAILS Line 3009  PCRE REGULAR EXPRESSION DETAILS
3009    
3010           The quick brown fox           The quick brown fox
3011    
3012         matches a portion of a subject string that is identical to itself.  The         matches a portion of a subject string that is identical to itself. When
3013         power of regular expressions comes from the ability to include alterna-         caseless  matching is specified (the PCRE_CASELESS option), letters are
3014         tives and repetitions in the pattern. These are encoded in the  pattern         matched independently of case. In UTF-8 mode, PCRE  always  understands
3015         by  the  use  of meta-characters, which do not stand for themselves but         the  concept  of case for characters whose values are less than 128, so
3016         instead are interpreted in some special way.         caseless matching is always possible. For characters with  higher  val-
3017           ues,  the concept of case is supported if PCRE is compiled with Unicode
3018         There are two different sets of meta-characters: those that are  recog-         property support, but not otherwise.   If  you  want  to  use  caseless
3019         nized  anywhere in the pattern except within square brackets, and those         matching  for  characters  128  and above, you must ensure that PCRE is
3020         that are recognized in square brackets. Outside  square  brackets,  the         compiled with Unicode property support as well as with UTF-8 support.
3021         meta-characters are as follows:  
3022           The power of regular expressions comes  from  the  ability  to  include
3023           alternatives  and  repetitions in the pattern. These are encoded in the
3024           pattern by the use of metacharacters, which do not stand for themselves
3025           but instead are interpreted in some special way.
3026    
3027           There  are  two different sets of metacharacters: those that are recog-
3028           nized anywhere in the pattern except within square brackets, and  those
3029           that  are  recognized  within square brackets. Outside square brackets,
3030           the metacharacters are as follows:
3031    
3032           \      general escape character with several uses           \      general escape character with several uses
3033           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 1630  PCRE REGULAR EXPRESSION DETAILS Line 3045  PCRE REGULAR EXPRESSION DETAILS
3045                  also "possessive quantifier"                  also "possessive quantifier"
3046           {      start min/max quantifier           {      start min/max quantifier
3047    
3048         Part  of  a  pattern  that is in square brackets is called a "character         Part of a pattern that is in square brackets  is  called  a  "character
3049         class". In a character class the only meta-characters are:         class". In a character class the only metacharacters are:
3050    
3051           \      general escape character           \      general escape character
3052           ^      negate the class, but only if the first character           ^      negate the class, but only if the first character
# Line 1640  PCRE REGULAR EXPRESSION DETAILS Line 3055  PCRE REGULAR EXPRESSION DETAILS
3055                    syntax)                    syntax)
3056           ]      terminates the character class           ]      terminates the character class
3057    
3058         The following sections describe the use of each of the meta-characters.         The  following sections describe the use of each of the metacharacters.
3059    
3060    
3061  BACKSLASH  BACKSLASH
3062    
3063         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
3064         a non-alphameric character, it takes  away  any  special  meaning  that         a  non-alphanumeric  character,  it takes away any special meaning that
3065         character  may  have.  This  use  of  backslash  as an escape character         character may have. This  use  of  backslash  as  an  escape  character
3066         applies both inside and outside character classes.         applies both inside and outside character classes.
3067    
3068         For example, if you want to match a * character, you write  \*  in  the         For  example,  if  you want to match a * character, you write \* in the
3069         pattern.   This  escaping  action  applies whether or not the following         pattern.  This escaping action applies whether  or  not  the  following
3070         character would otherwise be interpreted as a meta-character, so it  is         character  would  otherwise be interpreted as a metacharacter, so it is
3071         always  safe to precede a non-alphameric with backslash to specify that         always safe to precede a non-alphanumeric  with  backslash  to  specify
3072         it stands for itself. In particular, if you want to match a  backslash,         that  it stands for itself. In particular, if you want to match a back-
3073         you write \\.         slash, you write \\.
3074    
3075         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
3076         the pattern (other than in a character class) and characters between  a         the  pattern (other than in a character class) and characters between a
3077         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
3078         An escaping backslash can be used to include a whitespace or #  charac-         ing  backslash  can  be  used to include a whitespace or # character as
3079         ter as part of the pattern.         part of the pattern.
3080    
3081         If  you  want  to remove the special meaning from a sequence of charac-         If you want to remove the special meaning from a  sequence  of  charac-
3082         ters, you can do so by putting them between \Q and \E. This is  differ-         ters,  you can do so by putting them between \Q and \E. This is differ-
3083         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E
3084         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
3085         tion. Note the following examples:         tion. Note the following examples:
3086    
3087           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 1676  BACKSLASH Line 3091  BACKSLASH
3091           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3092           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3093    
3094         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
3095         classes.         classes.
3096    
3097       Non-printing characters
3098    
3099         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
3100         acters  in patterns in a visible manner. There is no restriction on the         acters in patterns in a visible manner. There is no restriction on  the
3101         appearance of non-printing characters, apart from the binary zero  that         appearance  of non-printing characters, apart from the binary zero that
3102         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates a pattern, but when a pattern  is  being  prepared  by  text
3103         editing, it is usually easier  to  use  one  of  the  following  escape         editing,  it  is  usually  easier  to  use  one of the following escape
3104         sequences than the binary character it represents:         sequences than the binary character it represents:
3105    
3106           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3107           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3108           \e        escape (hex 1B)           \e        escape (hex 1B)
3109           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3110           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3111           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3112           \t        tab (hex 09)           \t        tab (hex 09)
3113           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
3114           \xhh      character with hex code hh           \xhh      character with hex code hh
3115           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
3116    
3117         The  precise  effect of \cx is as follows: if x is a lower case letter,         The precise effect of \cx is as follows: if x is a lower  case  letter,
3118         it is converted to upper case. Then bit 6 of the character (hex 40)  is         it  is converted to upper case. Then bit 6 of the character (hex 40) is
3119         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;
3120         becomes hex 7B.         becomes hex 7B.
3121    
3122         After \x, from zero to two hexadecimal digits are read (letters can  be         After  \x, from zero to two hexadecimal digits are read (letters can be
3123         in  upper or lower case). In UTF-8 mode, any number of hexadecimal dig-         in upper or lower case). Any number of hexadecimal  digits  may  appear
3124         its may appear between \x{ and }, but the value of the  character  code         between  \x{  and  },  but the value of the character code must be less
3125         must  be  less  than  2**31  (that is, the maximum hexadecimal value is         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3126         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger
3127