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revision 75 by nigel, Sat Feb 24 21:40:37 2007 UTC revision 87 by nigel, Sat Feb 24 21:41:21 2007 UTC
# Line 23  man page, in case the conversion went wr Line 23  man page, in case the conversion went wr
23  <P>  <P>
24  The PCRE library is a set of functions that implement regular expression  The PCRE library is a set of functions that implement regular expression
25  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
26  differences. The current implementation of PCRE (release 5.x) corresponds  differences. The current implementation of PCRE (release 6.x) corresponds
27  approximately with Perl 5.8, including support for UTF-8 encoded strings and  approximately with Perl 5.8, including support for UTF-8 encoded strings and
28  Unicode general category properties. However, this support has to be explicitly  Unicode general category properties. However, this support has to be explicitly
29  enabled; it is not the default.  enabled; it is not the default.
30  </P>  </P>
31  <P>  <P>
32    In addition to the Perl-compatible matching function, PCRE also contains an
33    alternative matching function that matches the same compiled patterns in a
34    different way. In certain circumstances, the alternative function has some
35    advantages. For a discussion of the two matching algorithms, see the
36    <a href="pcrematching.html"><b>pcrematching</b></a>
37    page.
38    </P>
39    <P>
40  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
41  written wrappers and interfaces of various kinds. A C++ class is included in  written wrappers and interfaces of various kinds. In particular, Google Inc.
42  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
43  primary FTP site, which is:  PCRE distribution. The
44    <a href="pcrecpp.html"><b>pcrecpp</b></a>
45    page has details of this interface. Other people's contributions can be found
46    in the <i>Contrib</i> directory at the primary FTP site, which is:
47  <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>
48  </P>  </P>
49  <P>  <P>
# Line 53  available. The features themselves are d Line 64  available. The features themselves are d
64  page. Documentation about building PCRE for various operating systems can be  page. Documentation about building PCRE for various operating systems can be
65  found in the <b>README</b> file in the source distribution.  found in the <b>README</b> file in the source distribution.
66  </P>  </P>
67    <P>
68    The library contains a number of undocumented internal functions and data
69    tables that are used by more than one of the exported external functions, but
70    which are not intended for use by external callers. Their names all begin with
71    "_pcre_", which hopefully will not provoke any name clashes. In some
72    environments, it is possible to control which external symbols are exported
73    when a shared library is built, and in these cases the undocumented symbols are
74    not exported.
75    </P>
76  <br><a name="SEC2" href="#TOC1">USER DOCUMENTATION</a><br>  <br><a name="SEC2" href="#TOC1">USER DOCUMENTATION</a><br>
77  <P>  <P>
78  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 82  all the sections are concatenated, for e
82  follows:  follows:
83  <pre>  <pre>
84    pcre              this document    pcre              this document
85    pcreapi           details of PCRE's native API    pcreapi           details of PCRE's native C API
86    pcrebuild         options for building PCRE    pcrebuild         options for building PCRE
87    pcrecallout       details of the callout feature    pcrecallout       details of the callout feature
88    pcrecompat        discussion of Perl compatibility    pcrecompat        discussion of Perl compatibility
89      pcrecpp           details of the C++ wrapper
90    pcregrep          description of the <b>pcregrep</b> command    pcregrep          description of the <b>pcregrep</b> command
91      pcrematching      discussion of the two matching algorithms
92    pcrepartial       details of the partial matching facility    pcrepartial       details of the partial matching facility
93    pcrepattern       syntax and semantics of supported regular expressions    pcrepattern       syntax and semantics of supported regular expressions
94    pcreperform       discussion of performance issues    pcreperform       discussion of performance issues
95    pcreposix         the POSIX-compatible API    pcreposix         the POSIX-compatible C API
96    pcreprecompile    details of saving and re-using precompiled patterns    pcreprecompile    details of saving and re-using precompiled patterns
97    pcresample        discussion of the sample program    pcresample        discussion of the sample program
98    pcretest          description of the <b>pcretest</b> testing command    pcretest          description of the <b>pcretest</b> testing command
99  </pre>  </pre>
100  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
101  library function, listing its arguments and results.  C library function, listing its arguments and results.
102  </P>  </P>
103  <br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>  <br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>
104  <P>  <P>
# Line 104  subpatterns, assertions, and other types Line 126  subpatterns, assertions, and other types
126  </P>  </P>
127  <P>  <P>
128  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
129  integer variable can hold. However, PCRE uses recursion to handle subpatterns  integer variable can hold. However, when using the traditional matching
130  and indefinite repetition. This means that the available stack space may limit  function, PCRE uses recursion to handle subpatterns and indefinite repetition.
131  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
132    string that can be processed by certain patterns.
133  <a name="utf8support"></a></P>  <a name="utf8support"></a></P>
134  <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>
135  <P>  <P>
# Line 133  If PCRE is built with Unicode character Line 156  If PCRE is built with Unicode character
156  support), the escape sequences \p{..}, \P{..}, and \X are supported.  support), the escape sequences \p{..}, \P{..}, and \X are supported.
157  The available properties that can be tested are limited to the general  The available properties that can be tested are limited to the general
158  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
159  number. A full list is given in the  number, the Unicode script names such as Arabic or Han, and the derived
160    properties Any and L&. A full list is given in the
161  <a href="pcrepattern.html"><b>pcrepattern</b></a>  <a href="pcrepattern.html"><b>pcrepattern</b></a>
162  documentation. The PCRE library is increased in size by about 90K when Unicode  documentation. Only the short names for properties are supported. For example,
163  property support is included.  \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported.
164    Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
165    compatibility with Perl 5.6. PCRE does not support this.
166  </P>  </P>
167  <P>  <P>
168  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 180  PCRE when PCRE_NO_UTF8_CHECK is set, the
180  may crash.  may crash.
181  </P>  </P>
182  <P>  <P>
183  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
184  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.  
185  </P>  </P>
186  <P>  <P>
187  3. The original hexadecimal escape sequence, \xhh, matches a two-byte UTF-8  3. Repeat quantifiers apply to complete UTF-8 characters, not to individual
 character if the value is greater than 127.  
 </P>  
 <P>  
 4. Repeat quantifiers apply to complete UTF-8 characters, not to individual  
188  bytes, for example: \x{100}{3}.  bytes, for example: \x{100}{3}.
189  </P>  </P>
190  <P>  <P>
191  5. The dot metacharacter matches one UTF-8 character instead of a single byte.  4. The dot metacharacter matches one UTF-8 character instead of a single byte.
192  </P>  </P>
193  <P>  <P>
194  6. The escape sequence \C can be used to match a single byte in UTF-8 mode,  5. The escape sequence \C can be used to match a single byte in UTF-8 mode,
195  but its use can lead to some strange effects.  but its use can lead to some strange effects. This facility is not available in
196    the alternative matching function, <b>pcre_dfa_exec()</b>.
197  </P>  </P>
198  <P>  <P>
199  7. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly  6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
200  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
201  digits, spaces, or word characters remain the same set as before, all with  digits, spaces, or word characters remain the same set as before, all with
202  values less than 256. This remains true even when PCRE includes Unicode  values less than 256. This remains true even when PCRE includes Unicode
# Line 186  cases. If you really want to test for a Line 205  cases. If you really want to test for a
205  must use Unicode property tests such as \p{Nd}.  must use Unicode property tests such as \p{Nd}.
206  </P>  </P>
207  <P>  <P>
208  8. Similarly, characters that match the POSIX named character classes are all  7. Similarly, characters that match the POSIX named character classes are all
209  low-valued characters.  low-valued characters.
210  </P>  </P>
211  <P>  <P>
212  9. Case-insensitive matching applies only to characters whose values are less  8. Case-insensitive matching applies only to characters whose values are less
213  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
214  property support is available, PCRE still uses its own character tables when  property support is available, PCRE still uses its own character tables when
215  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.
216  The Unicode property information is used only for characters with higher  The Unicode property information is used only for characters with higher
217  values.  values. Even when Unicode property support is available, PCRE supports
218    case-insensitive matching only when there is a one-to-one mapping between a
219    letter's cases. There are a small number of many-to-one mappings in Unicode;
220    these are not supported by PCRE.
221  </P>  </P>
222  <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>  <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
223  <P>  <P>
224  Philip Hazel &#60;ph10@cam.ac.uk&#62;  Philip Hazel
225  <br>  <br>
226  University Computing Service,  University Computing Service,
227  <br>  <br>
228  Cambridge CB2 3QG, England.  Cambridge CB2 3QG, England.
229    </P>
230    <P>
231    Putting an actual email address here seems to have been a spam magnet, so I've
232    taken it away. If you want to email me, use my initial and surname, separated
233    by a dot, at the domain ucs.cam.ac.uk.
234    Last updated: 24 January 2006
235  <br>  <br>
236  Phone: +44 1223 334714  Copyright &copy; 1997-2006 University of Cambridge.
 Last updated: 09 September 2004  
 <br>  
 Copyright &copy; 1997-2004 University of Cambridge.  
237  <p>  <p>
238  Return to the <a href="index.html">PCRE index page</a>.  Return to the <a href="index.html">PCRE index page</a>.
239  </p>  </p>

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