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revision 87 by nigel, Sat Feb 24 21:41:21 2007 UTC revision 96 by nigel, Fri Mar 2 13:10:43 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 6.x) corresponds  differences. (Certain features that appeared in Python and PCRE before they
27  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.  
28  </P>  </P>
29  <P>  <P>
30  In addition to the Perl-compatible matching function, PCRE also contains an  The current implementation of PCRE (release 7.x) corresponds approximately with
31    Perl 5.10, including support for UTF-8 encoded strings and Unicode general
32    category properties. However, UTF-8 and Unicode support has to be explicitly
33    enabled; it is not the default. The Unicode tables correspond to Unicode
34    release 5.0.0.
35    </P>
36    <P>
37    In addition to the Perl-compatible matching function, PCRE contains an
38  alternative matching function that matches the same compiled patterns in a  alternative matching function that matches the same compiled patterns in a
39  different way. In certain circumstances, the alternative function has some  different way. In certain circumstances, the alternative function has some
40  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 100  follows:
100    pcreposix         the POSIX-compatible C API    pcreposix         the POSIX-compatible C API
101    pcreprecompile    details of saving and re-using precompiled patterns    pcreprecompile    details of saving and re-using precompiled patterns
102    pcresample        discussion of the sample program    pcresample        discussion of the sample program
103      pcrestack         discussion of stack usage
104    pcretest          description of the <b>pcretest</b> testing command    pcretest          description of the <b>pcretest</b> testing command
105  </pre>  </pre>
106  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 119  internal linkage size of 3 or 4 (see the
119  distribution and the  distribution and the
120  <a href="pcrebuild.html"><b>pcrebuild</b></a>  <a href="pcrebuild.html"><b>pcrebuild</b></a>
121  documentation for details). In these cases the limit is substantially larger.  documentation for details). In these cases the limit is substantially larger.
122  However, the speed of execution will be slower.  However, the speed of execution is slower.
123    </P>
124    <P>
125    All values in repeating quantifiers must be less than 65536. The maximum
126    compiled length of subpattern with an explicit repeat count is 30000 bytes. The
127    maximum number of capturing subpatterns is 65535.
128  </P>  </P>
129  <P>  <P>
130  All values in repeating quantifiers must be less than 65536.  There is no limit to the number of parenthesized subpatterns, but there can be
131  The maximum number of capturing subpatterns is 65535.  no more than 65535 capturing subpatterns.
132  </P>  </P>
133  <P>  <P>
134  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
135  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.  
136  </P>  </P>
137  <P>  <P>
138  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
139  integer variable can hold. However, when using the traditional matching  integer variable can hold. However, when using the traditional matching
140  function, PCRE uses recursion to handle subpatterns and indefinite repetition.  function, PCRE uses recursion to handle subpatterns and indefinite repetition.
141  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
142  string that can be processed by certain patterns.  string that can be processed by certain patterns. For a discussion of stack
143    issues, see the
144    <a href="pcrestack.html"><b>pcrestack</b></a>
145    documentation.
146  <a name="utf8support"></a></P>  <a name="utf8support"></a></P>
147  <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>
148  <P>  <P>
# Line 149  instead of just strings of bytes. Line 162  instead of just strings of bytes.
162  <P>  <P>
163  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
164  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
165  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.
166  </P>  </P>
167  <P>  <P>
168  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
# Line 184  may crash. Line 197  may crash.
197  UTF-8 character if the value is greater than 127.  UTF-8 character if the value is greater than 127.
198  </P>  </P>
199  <P>  <P>
200  3. Repeat quantifiers apply to complete UTF-8 characters, not to individual  3. Octal numbers up to \777 are recognized, and match two-byte UTF-8
201    characters for values greater than \177.
202    </P>
203    <P>
204    4. Repeat quantifiers apply to complete UTF-8 characters, not to individual
205  bytes, for example: \x{100}{3}.  bytes, for example: \x{100}{3}.
206  </P>  </P>
207  <P>  <P>
208  4. 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  <P>  <P>
211  5. 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,
212  but its use can lead to some strange effects. This facility is not available in  but its use can lead to some strange effects. This facility is not available in
213  the alternative matching function, <b>pcre_dfa_exec()</b>.  the alternative matching function, <b>pcre_dfa_exec()</b>.
214  </P>  </P>
215  <P>  <P>
216  6. 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
217  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
218  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
219  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 205  cases. If you really want to test for a Line 222  cases. If you really want to test for a
222  must use Unicode property tests such as \p{Nd}.  must use Unicode property tests such as \p{Nd}.
223  </P>  </P>
224  <P>  <P>
225  7. Similarly, characters that match the POSIX named character classes are all  8. Similarly, characters that match the POSIX named character classes are all
226  low-valued characters.  low-valued characters.
227  </P>  </P>
228  <P>  <P>
229  8. Case-insensitive matching applies only to characters whose values are less  9. Case-insensitive matching applies only to characters whose values are less
230  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
231  property support is available, PCRE still uses its own character tables when  property support is available, PCRE still uses its own character tables when
232  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.
# Line 225  Philip Hazel Line 242  Philip Hazel
242  <br>  <br>
243  University Computing Service,  University Computing Service,
244  <br>  <br>
245  Cambridge CB2 3QG, England.  Cambridge CB2 3QH, England.
246  </P>  </P>
247  <P>  <P>
248  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
249  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
250  by a dot, at the domain ucs.cam.ac.uk.  by a dot, at the domain ucs.cam.ac.uk.
251  Last updated: 24 January 2006  Last updated: 23 November 2006
252  <br>  <br>
253  Copyright &copy; 1997-2006 University of Cambridge.  Copyright &copy; 1997-2006 University of Cambridge.
254  <p>  <p>
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