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revision 75 by nigel, Sat Feb 24 21:40:37 2007 UTC revision 208 by ph10, Mon Aug 6 15:23:29 2007 UTC
# Line 6  PCRE - Perl-compatible regular expressio Line 6  PCRE - Perl-compatible regular expressio
6  .sp  .sp
7  The PCRE library is a set of functions that implement regular expression  The PCRE library is a set of functions that implement regular expression
8  pattern matching using the same syntax and semantics as Perl, with just a few  pattern matching using the same syntax and semantics as Perl, with just a few
9  differences. The current implementation of PCRE (release 5.x) corresponds  differences. (Certain features that appeared in Python and PCRE before they
10  approximately with Perl 5.8, including support for UTF-8 encoded strings and  appeared in Perl are also available using the Python syntax.)
11  Unicode general category properties. However, this support has to be explicitly  .P
12  enabled; it is not the default.  The current implementation of PCRE (release 7.x) corresponds approximately with
13    Perl 5.10, including support for UTF-8 encoded strings and Unicode general
14    category properties. However, UTF-8 and Unicode support has to be explicitly
15    enabled; it is not the default. The Unicode tables correspond to Unicode
16    release 5.0.0.
17    .P
18    In addition to the Perl-compatible matching function, PCRE contains an
19    alternative matching function that matches the same compiled patterns in a
20    different way. In certain circumstances, the alternative function has some
21    advantages. For a discussion of the two matching algorithms, see the
22    .\" HREF
23    \fBpcrematching\fP
24    .\"
25    page.
26  .P  .P
27  PCRE is written in C and released as a C library. A number of people have  PCRE is written in C and released as a C library. A number of people have
28  written wrappers and interfaces of various kinds. A C++ class is included in  written wrappers and interfaces of various kinds. In particular, Google Inc.
29  these contributions, which can be found in the \fIContrib\fR directory at the  have provided a comprehensive C++ wrapper. This is now included as part of the
30  primary FTP site, which is:  PCRE distribution. The
31    .\" HREF
32    \fBpcrecpp\fP
33    .\"
34    page has details of this interface. Other people's contributions can be found
35    in the \fIContrib\fR directory at the primary FTP site, which is:
36  .sp  .sp
37  .\" HTML <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">  .\" HTML <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">
38  .\" </a>  .\" </a>
# Line 29  and Line 47  and
47  .\" HREF  .\" HREF
48  \fBpcrecompat\fR  \fBpcrecompat\fR
49  .\"  .\"
50  pages.  pages. There is a syntax summary in the
51    .\" HREF
52    \fBpcresyntax\fR
53    .\"
54    page.
55  .P  .P
56  Some features of PCRE can be included, excluded, or changed when the library is  Some features of PCRE can be included, excluded, or changed when the library is
57  built. The  built. The
# Line 43  available. The features themselves are d Line 65  available. The features themselves are d
65  .\"  .\"
66  page. Documentation about building PCRE for various operating systems can be  page. Documentation about building PCRE for various operating systems can be
67  found in the \fBREADME\fP file in the source distribution.  found in the \fBREADME\fP file in the source distribution.
68    .P
69    The library contains a number of undocumented internal functions and data
70    tables that are used by more than one of the exported external functions, but
71    which are not intended for use by external callers. Their names all begin with
72    "_pcre_", which hopefully will not provoke any name clashes. In some
73    environments, it is possible to control which external symbols are exported
74    when a shared library is built, and in these cases the undocumented symbols are
75    not exported.
76  .  .
77  .  .
78  .SH "USER DOCUMENTATION"  .SH "USER DOCUMENTATION"
# Line 55  all the sections are concatenated, for e Line 85  all the sections are concatenated, for e
85  follows:  follows:
86  .sp  .sp
87    pcre              this document    pcre              this document
88    pcreapi           details of PCRE's native API    pcre-config       show PCRE installation configuration information
89      pcreapi           details of PCRE's native C API
90    pcrebuild         options for building PCRE    pcrebuild         options for building PCRE
91    pcrecallout       details of the callout feature    pcrecallout       details of the callout feature
92    pcrecompat        discussion of Perl compatibility    pcrecompat        discussion of Perl compatibility
93      pcrecpp           details of the C++ wrapper
94    pcregrep          description of the \fBpcregrep\fP command    pcregrep          description of the \fBpcregrep\fP command
95      pcrematching      discussion of the two matching algorithms
96    pcrepartial       details of the partial matching facility    pcrepartial       details of the partial matching facility
97  .\" JOIN  .\" JOIN
98    pcrepattern       syntax and semantics of supported    pcrepattern       syntax and semantics of supported
99                        regular expressions                        regular expressions
100      pcresyntax        quick syntax reference
101    pcreperform       discussion of performance issues    pcreperform       discussion of performance issues
102    pcreposix         the POSIX-compatible API    pcreposix         the POSIX-compatible C API
103    pcreprecompile    details of saving and re-using precompiled patterns    pcreprecompile    details of saving and re-using precompiled patterns
104    pcresample        discussion of the sample program    pcresample        discussion of the sample program
105      pcrestack         discussion of stack usage
106    pcretest          description of the \fBpcretest\fP testing command    pcretest          description of the \fBpcretest\fP testing command
107  .sp  .sp
108  In addition, in the "man" and HTML formats, there is a short page for each  In addition, in the "man" and HTML formats, there is a short page for each
109  library function, listing its arguments and results.  C library function, listing its arguments and results.
110  .  .
111  .  .
112  .SH LIMITATIONS  .SH LIMITATIONS
# Line 89  distribution and the Line 124  distribution and the
124  \fBpcrebuild\fP  \fBpcrebuild\fP
125  .\"  .\"
126  documentation for details). In these cases the limit is substantially larger.  documentation for details). In these cases the limit is substantially larger.
127  However, the speed of execution will be slower.  However, the speed of execution is slower.
128  .P  .P
129  All values in repeating quantifiers must be less than 65536.  All values in repeating quantifiers must be less than 65536.
 The maximum number of capturing subpatterns is 65535.  
130  .P  .P
131  There is no limit to the number of non-capturing subpatterns, but the maximum  There is no limit to the number of parenthesized subpatterns, but there can be
132  depth of nesting of all kinds of parenthesized subpattern, including capturing  no more than 65535 capturing subpatterns.
133  subpatterns, assertions, and other types of subpattern, is 200.  .P
134    The maximum length of name for a named subpattern is 32 characters, and the
135    maximum number of named subpatterns is 10000.
136  .P  .P
137  The maximum length of a subject string is the largest positive number that an  The maximum length of a subject string is the largest positive number that an
138  integer variable can hold. However, PCRE uses recursion to handle subpatterns  integer variable can hold. However, when using the traditional matching
139  and indefinite repetition. This means that the available stack space may limit  function, PCRE uses recursion to handle subpatterns and indefinite repetition.
140  the size of a subject string that can be processed by certain patterns.  This means that the available stack space may limit the size of a subject
141    string that can be processed by certain patterns. For a discussion of stack
142    issues, see the
143    .\" HREF
144    \fBpcrestack\fP
145    .\"
146    documentation.
147  .sp  .sp
148  .\" HTML <a name="utf8support"></a>  .\" HTML <a name="utf8support"></a>
149  .  .
# Line 125  instead of just strings of bytes. Line 167  instead of just strings of bytes.
167  .P  .P
168  If you compile PCRE with UTF-8 support, but do not use it at run time, the  If you compile PCRE with UTF-8 support, but do not use it at run time, the
169  library will be a bit bigger, but the additional run time overhead is limited  library will be a bit bigger, but the additional run time overhead is limited
170  to testing the PCRE_UTF8 flag in several places, so should not be very large.  to testing the PCRE_UTF8 flag occasionally, so should not be very big.
171  .P  .P
172  If PCRE is built with Unicode character property support (which implies UTF-8  If PCRE is built with Unicode character property support (which implies UTF-8
173  support), the escape sequences \ep{..}, \eP{..}, and \eX are supported.  support), the escape sequences \ep{..}, \eP{..}, and \eX are supported.
174  The available properties that can be tested are limited to the general  The available properties that can be tested are limited to the general
175  category properties such as Lu for an upper case letter or Nd for a decimal  category properties such as Lu for an upper case letter or Nd for a decimal
176  number. A full list is given in the  number, the Unicode script names such as Arabic or Han, and the derived
177    properties Any and L&. A full list is given in the
178  .\" HREF  .\" HREF
179  \fBpcrepattern\fP  \fBpcrepattern\fP
180  .\"  .\"
181  documentation. The PCRE library is increased in size by about 90K when Unicode  documentation. Only the short names for properties are supported. For example,
182  property support is included.  \ep{L} matches a letter. Its Perl synonym, \ep{Letter}, is not supported.
183    Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
184    compatibility with Perl 5.6. PCRE does not support this.
185  .P  .P
186  The following comments apply when PCRE is running in UTF-8 mode:  The following comments apply when PCRE is running in UTF-8 mode:
187  .P  .P
# Line 151  not diagnose an invalid UTF-8 string. If Line 196  not diagnose an invalid UTF-8 string. If
196  PCRE when PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  PCRE when PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program
197  may crash.  may crash.
198  .P  .P
199  2. In a pattern, the escape sequence \ex{...}, where the contents of the braces  2. An unbraced hexadecimal escape sequence (such as \exb3) matches a two-byte
200  is a string of hexadecimal digits, is interpreted as a UTF-8 character whose  UTF-8 character if the value is greater than 127.
 code number is the given hexadecimal number, for example: \ex{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.  
201  .P  .P
202  3. The original hexadecimal escape sequence, \exhh, matches a two-byte UTF-8  3. Octal numbers up to \e777 are recognized, and match two-byte UTF-8
203  character if the value is greater than 127.  characters for values greater than \e177.
204  .P  .P
205  4. Repeat quantifiers apply to complete UTF-8 characters, not to individual  4. Repeat quantifiers apply to complete UTF-8 characters, not to individual
206  bytes, for example: \ex{100}{3}.  bytes, for example: \ex{100}{3}.
# Line 167  bytes, for example: \ex{100}{3}. Line 208  bytes, for example: \ex{100}{3}.
208  5. The dot metacharacter matches one UTF-8 character instead of a single byte.  5. The dot metacharacter matches one UTF-8 character instead of a single byte.
209  .P  .P
210  6. The escape sequence \eC can be used to match a single byte in UTF-8 mode,  6. The escape sequence \eC can be used to match a single byte in UTF-8 mode,
211  but its use can lead to some strange effects.  but its use can lead to some strange effects. This facility is not available in
212    the alternative matching function, \fBpcre_dfa_exec()\fP.
213  .P  .P
214  7. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly  7. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly
215  test characters of any code value, but the characters that PCRE recognizes as  test characters of any code value, but the characters that PCRE recognizes as
# Line 180  must use Unicode property tests such as Line 222  must use Unicode property tests such as
222  8. Similarly, characters that match the POSIX named character classes are all  8. Similarly, characters that match the POSIX named character classes are all
223  low-valued characters.  low-valued characters.
224  .P  .P
225  9. Case-insensitive matching applies only to characters whose values are less  9. However, the Perl 5.10 horizontal and vertical whitespace matching escapes
226    (\eh, \eH, \ev, and \eV) do match all the appropriate Unicode characters.
227    .P
228    10. Case-insensitive matching applies only to characters whose values are less
229  than 128, unless PCRE is built with Unicode property support. Even when Unicode  than 128, unless PCRE is built with Unicode property support. Even when Unicode
230  property support is available, PCRE still uses its own character tables when  property support is available, PCRE still uses its own character tables when
231  checking the case of low-valued characters, so as not to degrade performance.  checking the case of low-valued characters, so as not to degrade performance.
232  The Unicode property information is used only for characters with higher  The Unicode property information is used only for characters with higher
233  values.  values. Even when Unicode property support is available, PCRE supports
234    case-insensitive matching only when there is a one-to-one mapping between a
235    letter's cases. There are a small number of many-to-one mappings in Unicode;
236    these are not supported by PCRE.
237    .
238  .  .
239  .SH AUTHOR  .SH AUTHOR
240  .rs  .rs
241  .sp  .sp
242  Philip Hazel <ph10@cam.ac.uk>  .nf
243  .br  Philip Hazel
244  University Computing Service,  University Computing Service
245  .br  Cambridge CB2 3QH, England.
246  Cambridge CB2 3QG, England.  .fi
247  .br  .P
248  Phone: +44 1223 334714  Putting an actual email address here seems to have been a spam magnet, so I've
249  .sp  taken it away. If you want to email me, use my two initials, followed by the
250  .in 0  two digits 10, at the domain cam.ac.uk.
251  Last updated: 09 September 2004  .
252  .br  .
253  Copyright (c) 1997-2004 University of Cambridge.  .SH REVISION
254    .rs
255    .sp
256    .nf
257    Last updated: 06 August 2007
258    Copyright (c) 1997-2007 University of Cambridge.
259    .fi

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