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revision 83 by nigel, Sat Feb 24 21:41:06 2007 UTC revision 208 by ph10, Mon Aug 6 15:23:29 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 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 52  supported by PCRE are given in separate Line 58  supported by PCRE are given in separate
58  <a href="pcrepattern.html"><b>pcrepattern</b></a>  <a href="pcrepattern.html"><b>pcrepattern</b></a>
59  and  and
60  <a href="pcrecompat.html"><b>pcrecompat</b></a>  <a href="pcrecompat.html"><b>pcrecompat</b></a>
61  pages.  pages. There is a syntax summary in the
62    <a href="pcresyntax.html"><b>pcresyntax</b></a>
63    page.
64  </P>  </P>
65  <P>  <P>
66  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
# Line 82  all the sections are concatenated, for e Line 90  all the sections are concatenated, for e
90  follows:  follows:
91  <pre>  <pre>
92    pcre              this document    pcre              this document
93      pcre-config       show PCRE installation configuration information
94    pcreapi           details of PCRE's native C API    pcreapi           details of PCRE's native C API
95    pcrebuild         options for building PCRE    pcrebuild         options for building PCRE
96    pcrecallout       details of the callout feature    pcrecallout       details of the callout feature
# Line 91  follows: Line 100  follows:
100    pcrematching      discussion of the two matching algorithms    pcrematching      discussion of the two matching algorithms
101    pcrepartial       details of the partial matching facility    pcrepartial       details of the partial matching facility
102    pcrepattern       syntax and semantics of supported regular expressions    pcrepattern       syntax and semantics of supported regular expressions
103      pcresyntax        quick syntax reference
104    pcreperform       discussion of performance issues    pcreperform       discussion of performance issues
105    pcreposix         the POSIX-compatible C API    pcreposix         the POSIX-compatible C API
106    pcreprecompile    details of saving and re-using precompiled patterns    pcreprecompile    details of saving and re-using precompiled patterns
107    pcresample        discussion of the sample program    pcresample        discussion of the sample program
108      pcrestack         discussion of stack usage
109    pcretest          description of the <b>pcretest</b> testing command    pcretest          description of the <b>pcretest</b> testing command
110  </pre>  </pre>
111  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 124  internal linkage size of 3 or 4 (see the
124  distribution and the  distribution and the
125  <a href="pcrebuild.html"><b>pcrebuild</b></a>  <a href="pcrebuild.html"><b>pcrebuild</b></a>
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  <P>  <P>
130  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.  
131  </P>  </P>
132  <P>  <P>
133  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
134  depth of nesting of all kinds of parenthesized subpattern, including capturing  no more than 65535 capturing subpatterns.
135  subpatterns, assertions, and other types of subpattern, is 200.  </P>
136    <P>
137    The maximum length of name for a named subpattern is 32 characters, and the
138    maximum number of named subpatterns is 10000.
139  </P>  </P>
140  <P>  <P>
141  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
142  integer variable can hold. However, when using the traditional matching  integer variable can hold. However, when using the traditional matching
143  function, PCRE uses recursion to handle subpatterns and indefinite repetition.  function, PCRE uses recursion to handle subpatterns and indefinite repetition.
144  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
145  string that can be processed by certain patterns.  string that can be processed by certain patterns. For a discussion of stack
146    issues, see the
147    <a href="pcrestack.html"><b>pcrestack</b></a>
148    documentation.
149  <a name="utf8support"></a></P>  <a name="utf8support"></a></P>
150  <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>
151  <P>  <P>
# Line 149  instead of just strings of bytes. Line 165  instead of just strings of bytes.
165  <P>  <P>
166  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
167  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
168  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.
169  </P>  </P>
170  <P>  <P>
171  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
172  support), the escape sequences \p{..}, \P{..}, and \X are supported.  support), the escape sequences \p{..}, \P{..}, and \X are supported.
173  The available properties that can be tested are limited to the general  The available properties that can be tested are limited to the general
174  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
175  number. A full list is given in the  number, the Unicode script names such as Arabic or Han, and the derived
176    properties Any and L&. A full list is given in the
177  <a href="pcrepattern.html"><b>pcrepattern</b></a>  <a href="pcrepattern.html"><b>pcrepattern</b></a>
178  documentation. The PCRE library is increased in size by about 90K when Unicode  documentation. Only the short names for properties are supported. For example,
179  property support is included.  \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported.
180    Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
181    compatibility with Perl 5.6. PCRE does not support this.
182  </P>  </P>
183  <P>  <P>
184  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 196  PCRE when PCRE_NO_UTF8_CHECK is set, the
196  may crash.  may crash.
197  </P>  </P>
198  <P>  <P>
199  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
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: \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.  
201  </P>  </P>
202  <P>  <P>
203  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
204  character if the value is greater than 127.  characters for values greater than \177.
205  </P>  </P>
206  <P>  <P>
207  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 214  must use Unicode property tests such as Line 229  must use Unicode property tests such as
229  low-valued characters.  low-valued characters.
230  </P>  </P>
231  <P>  <P>
232  9. Case-insensitive matching applies only to characters whose values are less  9. However, the Perl 5.10 horizontal and vertical whitespace matching escapes
233    (\h, \H, \v, and \V) do match all the appropriate Unicode characters.
234    </P>
235    <P>
236    10. Case-insensitive matching applies only to characters whose values are less
237  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
238  property support is available, PCRE still uses its own character tables when  property support is available, PCRE still uses its own character tables when
239  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.
240  The Unicode property information is used only for characters with higher  The Unicode property information is used only for characters with higher
241  values.  values. Even when Unicode property support is available, PCRE supports
242    case-insensitive matching only when there is a one-to-one mapping between a
243    letter's cases. There are a small number of many-to-one mappings in Unicode;
244    these are not supported by PCRE.
245  </P>  </P>
246  <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>  <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
247  <P>  <P>
248  Philip Hazel  Philip Hazel
249  <br>  <br>
250  University Computing Service,  University Computing Service
251    <br>
252    Cambridge CB2 3QH, England.
253  <br>  <br>
 Cambridge CB2 3QG, England.  
254  </P>  </P>
255  <P>  <P>
256  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
257  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 two initials, followed by the
258  by a dot, at the domain ucs.cam.ac.uk.  two digits 10, at the domain cam.ac.uk.
259  Last updated: 07 March 2005  </P>
260    <br><a name="SEC6" href="#TOC1">REVISION</a><br>
261    <P>
262    Last updated: 06 August 2007
263    <br>
264    Copyright &copy; 1997-2007 University of Cambridge.
265  <br>  <br>
 Copyright &copy; 1997-2005 University of Cambridge.  
266  <p>  <p>
267  Return to the <a href="index.html">PCRE index page</a>.  Return to the <a href="index.html">PCRE index page</a>.
268  </p>  </p>

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