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revision 75 by nigel, Sat Feb 24 21:40:37 2007 UTC revision 182 by ph10, Wed Jun 13 15:09:54 2007 UTC
# Line 18  man page, in case the conversion went wr Line 18  man page, in case the conversion went wr
18  <li><a name="TOC3" href="#SEC3">LIMITATIONS</a>  <li><a name="TOC3" href="#SEC3">LIMITATIONS</a>
19  <li><a name="TOC4" href="#SEC4">UTF-8 AND UNICODE PROPERTY SUPPORT</a>  <li><a name="TOC4" href="#SEC4">UTF-8 AND UNICODE PROPERTY SUPPORT</a>
20  <li><a name="TOC5" href="#SEC5">AUTHOR</a>  <li><a name="TOC5" href="#SEC5">AUTHOR</a>
21    <li><a name="TOC6" href="#SEC6">REVISION</a>
22  </ul>  </ul>
23  <br><a name="SEC1" href="#TOC1">INTRODUCTION</a><br>  <br><a name="SEC1" href="#TOC1">INTRODUCTION</a><br>
24  <P>  <P>
25  The PCRE library is a set of functions that implement regular expression  The PCRE library is a set of functions that implement regular expression
26  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
27  differences. The current implementation of PCRE (release 5.x) corresponds  differences. (Certain features that appeared in Python and PCRE before they
28  approximately with Perl 5.8, including support for UTF-8 encoded strings and  appeared in Perl are also available using the Python syntax.)
29  Unicode general category properties. However, this support has to be explicitly  </P>
30  enabled; it is not the default.  <P>
31    The current implementation of PCRE (release 7.x) corresponds approximately with
32    Perl 5.10, including support for UTF-8 encoded strings and Unicode general
33    category properties. However, UTF-8 and Unicode support has to be explicitly
34    enabled; it is not the default. The Unicode tables correspond to Unicode
35    release 5.0.0.
36    </P>
37    <P>
38    In addition to the Perl-compatible matching function, PCRE contains an
39    alternative matching function that matches the same compiled patterns in a
40    different way. In certain circumstances, the alternative function has some
41    advantages. For a discussion of the two matching algorithms, see the
42    <a href="pcrematching.html"><b>pcrematching</b></a>
43    page.
44  </P>  </P>
45  <P>  <P>
46  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
47  written wrappers and interfaces of various kinds. A C++ class is included in  written wrappers and interfaces of various kinds. In particular, Google Inc.
48  these contributions, which can be found in the <i>Contrib</i> directory at the  have provided a comprehensive C++ wrapper. This is now included as part of the
49  primary FTP site, which is:  PCRE distribution. The
50    <a href="pcrecpp.html"><b>pcrecpp</b></a>
51    page has details of this interface. Other people's contributions can be found
52    in the <i>Contrib</i> directory at the primary FTP site, which is:
53  <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</a>  <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</a>
54  </P>  </P>
55  <P>  <P>
# Line 53  available. The features themselves are d Line 70  available. The features themselves are d
70  page. Documentation about building PCRE for various operating systems can be  page. Documentation about building PCRE for various operating systems can be
71  found in the <b>README</b> file in the source distribution.  found in the <b>README</b> file in the source distribution.
72  </P>  </P>
73    <P>
74    The library contains a number of undocumented internal functions and data
75    tables that are used by more than one of the exported external functions, but
76    which are not intended for use by external callers. Their names all begin with
77    "_pcre_", which hopefully will not provoke any name clashes. In some
78    environments, it is possible to control which external symbols are exported
79    when a shared library is built, and in these cases the undocumented symbols are
80    not exported.
81    </P>
82  <br><a name="SEC2" href="#TOC1">USER DOCUMENTATION</a><br>  <br><a name="SEC2" href="#TOC1">USER DOCUMENTATION</a><br>
83  <P>  <P>
84  The user documentation for PCRE comprises a number of different sections. In  The user documentation for PCRE comprises a number of different sections. In
# Line 62  all the sections are concatenated, for e Line 88  all the sections are concatenated, for e
88  follows:  follows:
89  <pre>  <pre>
90    pcre              this document    pcre              this document
91    pcreapi           details of PCRE's native API    pcre-config       show PCRE installation configuration information
92      pcreapi           details of PCRE's native C API
93    pcrebuild         options for building PCRE    pcrebuild         options for building PCRE
94    pcrecallout       details of the callout feature    pcrecallout       details of the callout feature
95    pcrecompat        discussion of Perl compatibility    pcrecompat        discussion of Perl compatibility
96      pcrecpp           details of the C++ wrapper
97    pcregrep          description of the <b>pcregrep</b> command    pcregrep          description of the <b>pcregrep</b> command
98      pcrematching      discussion of the two matching algorithms
99    pcrepartial       details of the partial matching facility    pcrepartial       details of the partial matching facility
100    pcrepattern       syntax and semantics of supported regular expressions    pcrepattern       syntax and semantics of supported regular expressions
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 <b>pcretest</b> testing command    pcretest          description of the <b>pcretest</b> testing command
107  </pre>  </pre>
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  </P>  </P>
111  <br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>  <br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>
112  <P>  <P>
# Line 91  internal linkage size of 3 or 4 (see the Line 121  internal linkage size of 3 or 4 (see the
121  distribution and the  distribution and the
122  <a href="pcrebuild.html"><b>pcrebuild</b></a>  <a href="pcrebuild.html"><b>pcrebuild</b></a>
123  documentation for details). In these cases the limit is substantially larger.  documentation for details). In these cases the limit is substantially larger.
124  However, the speed of execution will be slower.  However, the speed of execution is slower.
125  </P>  </P>
126  <P>  <P>
127  All values in repeating quantifiers must be less than 65536.  All values in repeating quantifiers must be less than 65536. The maximum
128  The maximum number of capturing subpatterns is 65535.  compiled length of subpattern with an explicit repeat count is 30000 bytes. The
129    maximum number of capturing subpatterns is 65535.
130  </P>  </P>
131  <P>  <P>
132  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
133  depth of nesting of all kinds of parenthesized subpattern, including capturing  no more than 65535 capturing subpatterns.
134  subpatterns, assertions, and other types of subpattern, is 200.  </P>
135    <P>
136    The maximum length of name for a named subpattern is 32 characters, and the
137    maximum number of named subpatterns is 10000.
138  </P>  </P>
139  <P>  <P>
140  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
141  integer variable can hold. However, PCRE uses recursion to handle subpatterns  integer variable can hold. However, when using the traditional matching
142  and indefinite repetition. This means that the available stack space may limit  function, PCRE uses recursion to handle subpatterns and indefinite repetition.
143  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
144    string that can be processed by certain patterns. For a discussion of stack
145    issues, see the
146    <a href="pcrestack.html"><b>pcrestack</b></a>
147    documentation.
148  <a name="utf8support"></a></P>  <a name="utf8support"></a></P>
149  <br><a name="SEC4" href="#TOC1">UTF-8 AND UNICODE PROPERTY SUPPORT</a><br>  <br><a name="SEC4" href="#TOC1">UTF-8 AND UNICODE PROPERTY SUPPORT</a><br>
150  <P>  <P>
# Line 126  instead of just strings of bytes. Line 164  instead of just strings of bytes.
164  <P>  <P>
165  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
166  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
167  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.
168  </P>  </P>
169  <P>  <P>
170  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
171  support), the escape sequences \p{..}, \P{..}, and \X are supported.  support), the escape sequences \p{..}, \P{..}, and \X are supported.
172  The available properties that can be tested are limited to the general  The available properties that can be tested are limited to the general
173  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
174  number. A full list is given in the  number, the Unicode script names such as Arabic or Han, and the derived
175    properties Any and L&. A full list is given in the
176  <a href="pcrepattern.html"><b>pcrepattern</b></a>  <a href="pcrepattern.html"><b>pcrepattern</b></a>
177  documentation. The PCRE library is increased in size by about 90K when Unicode  documentation. Only the short names for properties are supported. For example,
178  property support is included.  \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported.
179    Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
180    compatibility with Perl 5.6. PCRE does not support this.
181  </P>  </P>
182  <P>  <P>
183  The following comments apply when PCRE is running in UTF-8 mode:  The following comments apply when PCRE is running in UTF-8 mode:
# Line 154  PCRE when PCRE_NO_UTF8_CHECK is set, the Line 195  PCRE when PCRE_NO_UTF8_CHECK is set, the
195  may crash.  may crash.
196  </P>  </P>
197  <P>  <P>
198  2. In a pattern, the escape sequence \x{...}, where the contents of the braces  2. An unbraced hexadecimal escape sequence (such as \xb3) matches a two-byte
199  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: \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.  
200  </P>  </P>
201  <P>  <P>
202  3. The original hexadecimal escape sequence, \xhh, matches a two-byte UTF-8  3. Octal numbers up to \777 are recognized, and match two-byte UTF-8
203  character if the value is greater than 127.  characters for values greater than \177.
204  </P>  </P>
205  <P>  <P>
206  4. Repeat quantifiers apply to complete UTF-8 characters, not to individual  4. Repeat quantifiers apply to complete UTF-8 characters, not to individual
# Line 174  bytes, for example: \x{100}{3}. Line 211  bytes, for example: \x{100}{3}.
211  </P>  </P>
212  <P>  <P>
213  6. The escape sequence \C can be used to match a single byte in UTF-8 mode,  6. The escape sequence \C can be used to match a single byte in UTF-8 mode,
214  but its use can lead to some strange effects.  but its use can lead to some strange effects. This facility is not available in
215    the alternative matching function, <b>pcre_dfa_exec()</b>.
216  </P>  </P>
217  <P>  <P>
218  7. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly  7. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
# Line 190  must use Unicode property tests such as Line 228  must use Unicode property tests such as
228  low-valued characters.  low-valued characters.
229  </P>  </P>
230  <P>  <P>
231  9. Case-insensitive matching applies only to characters whose values are less  9. However, the Perl 5.10 horizontal and vertical whitespace matching escapes
232    (\h, \H, \v, and \V) do match all the appropriate Unicode characters.
233    </P>
234    <P>
235    10. Case-insensitive matching applies only to characters whose values are less
236  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
237  property support is available, PCRE still uses its own character tables when  property support is available, PCRE still uses its own character tables when
238  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.
239  The Unicode property information is used only for characters with higher  The Unicode property information is used only for characters with higher
240  values.  values. Even when Unicode property support is available, PCRE supports
241    case-insensitive matching only when there is a one-to-one mapping between a
242    letter's cases. There are a small number of many-to-one mappings in Unicode;
243    these are not supported by PCRE.
244  </P>  </P>
245  <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>  <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
246  <P>  <P>
247  Philip Hazel &#60;ph10@cam.ac.uk&#62;  Philip Hazel
248    <br>
249    University Computing Service
250  <br>  <br>
251  University Computing Service,  Cambridge CB2 3QH, England.
252  <br>  <br>
253  Cambridge CB2 3QG, England.  </P>
254    <P>
255    Putting an actual email address here seems to have been a spam magnet, so I've
256    taken it away. If you want to email me, use my two initials, followed by the
257    two digits 10, at the domain cam.ac.uk.
258    </P>
259    <br><a name="SEC6" href="#TOC1">REVISION</a><br>
260    <P>
261    Last updated: 13 June 2007
262  <br>  <br>
263  Phone: +44 1223 334714  Copyright &copy; 1997-2007 University of Cambridge.
 Last updated: 09 September 2004  
264  <br>  <br>
 Copyright &copy; 1997-2004 University of Cambridge.  
265  <p>  <p>
266  Return to the <a href="index.html">PCRE index page</a>.  Return to the <a href="index.html">PCRE index page</a>.
267  </p>  </p>

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