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revision 83 by nigel, Sat Feb 24 21:41:06 2007 UTC revision 99 by ph10, Tue Mar 6 12:27:42 2007 UTC
# Line 7  Line 7 
7  <p>  <p>
8  Return to the <a href="index.html">PCRE index page</a>.  Return to the <a href="index.html">PCRE index page</a>.
9  </p>  </p>
10  <p>  <p>
11  This page is part of the PCRE HTML documentation. It was generated automatically  This page is part of the PCRE HTML documentation. It was generated automatically
12  from the original man page. If there is any nonsense in it, please consult the  from the original man page. If there is any nonsense in it, please consult the
13  man page, in case the conversion went wrong.  man page, in case the conversion went wrong.
14  <br>  <br>
15  <ul>  <ul>
16  <li><a name="TOC1" href="#SEC1">INTRODUCTION</a>  <li><a name="TOC1" href="#SEC1">INTRODUCTION</a>
17  <li><a name="TOC2" href="#SEC2">USER DOCUMENTATION</a>  <li><a name="TOC2" href="#SEC2">USER DOCUMENTATION</a>
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 6.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.)
 Unicode general category properties. However, this support has to be explicitly  
 enabled; it is not the default.  
29  </P>  </P>
30  <P>  <P>
31  In addition to the Perl-compatible matching function, PCRE also contains an  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  alternative matching function that matches the same compiled patterns in a
40  different way. In certain circumstances, the alternative function has some  different way. In certain circumstances, the alternative function has some
41  advantages. For a discussion of the two matching algorithms, see the  advantages. For a discussion of the two matching algorithms, see the
# Line 95  follows: Line 101  follows:
101    pcreposix         the POSIX-compatible C API    pcreposix         the POSIX-compatible C API
102    pcreprecompile    details of saving and re-using precompiled patterns    pcreprecompile    details of saving and re-using precompiled patterns
103    pcresample        discussion of the sample program    pcresample        discussion of the sample program
104      pcrestack         discussion of stack usage
105    pcretest          description of the <b>pcretest</b> testing command    pcretest          description of the <b>pcretest</b> testing command
106  </pre>  </pre>
107  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
# Line 113  internal linkage size of 3 or 4 (see the Line 120  internal linkage size of 3 or 4 (see the
120  distribution and the  distribution and the
121  <a href="pcrebuild.html"><b>pcrebuild</b></a>  <a href="pcrebuild.html"><b>pcrebuild</b></a>
122  documentation for details). In these cases the limit is substantially larger.  documentation for details). In these cases the limit is substantially larger.
123  However, the speed of execution will be slower.  However, the speed of execution is slower.
124    </P>
125    <P>
126    All values in repeating quantifiers must be less than 65536. The maximum
127    compiled length of subpattern with an explicit repeat count is 30000 bytes. The
128    maximum number of capturing subpatterns is 65535.
129  </P>  </P>
130  <P>  <P>
131  All values in repeating quantifiers must be less than 65536.  There is no limit to the number of parenthesized subpatterns, but there can be
132  The maximum number of capturing subpatterns is 65535.  no more than 65535 capturing subpatterns.
133  </P>  </P>
134  <P>  <P>
135  There is no limit to the number of non-capturing subpatterns, but the maximum  The maximum length of name for a named subpattern is 32 characters, and the
136  depth of nesting of all kinds of parenthesized subpattern, including capturing  maximum number of named subpatterns is 10000.
 subpatterns, assertions, and other types of subpattern, is 200.  
137  </P>  </P>
138  <P>  <P>
139  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
140  integer variable can hold. However, when using the traditional matching  integer variable can hold. However, when using the traditional matching
141  function, PCRE uses recursion to handle subpatterns and indefinite repetition.  function, PCRE uses recursion to handle subpatterns and indefinite repetition.
142  This means that the available stack space may limit the size of a subject  This means that the available stack space may limit the size of a subject
143  string that can be processed by certain patterns.  string that can be processed by certain patterns. For a discussion of stack
144    issues, see the
145    <a href="pcrestack.html"><b>pcrestack</b></a>
146    documentation.
147  <a name="utf8support"></a></P>  <a name="utf8support"></a></P>
148  <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>
149  <P>  <P>
# Line 149  instead of just strings of bytes. Line 163  instead of just strings of bytes.
163  <P>  <P>
164  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
165  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
166  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.
167  </P>  </P>
168  <P>  <P>
169  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
170  support), the escape sequences \p{..}, \P{..}, and \X are supported.  support), the escape sequences \p{..}, \P{..}, and \X are supported.
171  The available properties that can be tested are limited to the general  The available properties that can be tested are limited to the general
172  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
173  number. A full list is given in the  number, the Unicode script names such as Arabic or Han, and the derived
174    properties Any and L&. A full list is given in the
175  <a href="pcrepattern.html"><b>pcrepattern</b></a>  <a href="pcrepattern.html"><b>pcrepattern</b></a>
176  documentation. The PCRE library is increased in size by about 90K when Unicode  documentation. Only the short names for properties are supported. For example,
177  property support is included.  \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported.
178    Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
179    compatibility with Perl 5.6. PCRE does not support this.
180  </P>  </P>
181  <P>  <P>
182  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 177  PCRE when PCRE_NO_UTF8_CHECK is set, the Line 194  PCRE when PCRE_NO_UTF8_CHECK is set, the
194  may crash.  may crash.
195  </P>  </P>
196  <P>  <P>
197  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
198  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.  
199  </P>  </P>
200  <P>  <P>
201  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
202  character if the value is greater than 127.  characters for values greater than \177.
203  </P>  </P>
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
# Line 219  than 128, unless PCRE is built with Unic Line 232  than 128, unless PCRE is built with Unic
232  property support is available, PCRE still uses its own character tables when  property support is available, PCRE still uses its own character tables when
233  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.
234  The Unicode property information is used only for characters with higher  The Unicode property information is used only for characters with higher
235  values.  values. Even when Unicode property support is available, PCRE supports
236    case-insensitive matching only when there is a one-to-one mapping between a
237    letter's cases. There are a small number of many-to-one mappings in Unicode;
238    these are not supported by PCRE.
239  </P>  </P>
240  <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>  <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
241  <P>  <P>
242  Philip Hazel  Philip Hazel
243  <br>  <br>
244  University Computing Service,  University Computing Service
245    <br>
246    Cambridge CB2 3QH, England.
247  <br>  <br>
 Cambridge CB2 3QG, England.  
248  </P>  </P>
249  <P>  <P>
250  Putting an actual email address here seems to have been a spam magnet, so I've  Putting an actual email address here seems to have been a spam magnet, so I've
251  taken it away. If you want to email me, use my initial and surname, separated  taken it away. If you want to email me, use my initial and surname, separated
252  by a dot, at the domain ucs.cam.ac.uk.  by a dot, at the domain ucs.cam.ac.uk.
253  Last updated: 07 March 2005  </P>
254    <br><a name="SEC6" href="#TOC1">REVISION</a><br>
255    <P>
256    Last updated: 06 March 2007
257    <br>
258    Copyright &copy; 1997-2007 University of Cambridge.
259  <br>  <br>
 Copyright &copy; 1997-2005 University of Cambridge.  
260  <p>  <p>
261  Return to the <a href="index.html">PCRE index page</a>.  Return to the <a href="index.html">PCRE index page</a>.
262  </p>  </p>

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