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revision 91 by nigel, Sat Feb 24 21:41:34 2007 UTC revision 93 by nigel, Sat Feb 24 21:41:42 2007 UTC
# Line 17  DIFFERENCES BETWEEN PCRE AND PERL Line 17  DIFFERENCES BETWEEN PCRE AND PERL
17  </b><br>  </b><br>
18  <P>  <P>
19  This document describes the differences in the ways that PCRE and Perl handle  This document describes the differences in the ways that PCRE and Perl handle
20  regular expressions. The differences described here are with respect to Perl  regular expressions. The differences described here are mainly with respect to
21  5.8.  Perl 5.8, though PCRE version 7.0 contains some features that are expected to
22    be in the forthcoming Perl 5.10.
23  </P>  </P>
24  <P>  <P>
25  1. PCRE has only a subset of Perl's UTF-8 and Unicode support. Details of what  1. PCRE has only a subset of Perl's UTF-8 and Unicode support. Details of what
# Line 76  following examples: Line 77  following examples:
77  The \Q...\E sequence is recognized both inside and outside character classes.  The \Q...\E sequence is recognized both inside and outside character classes.
78  </P>  </P>
79  <P>  <P>
80  8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})  8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
81  constructions. However, there is support for recursive patterns using the  constructions. However, there is support for recursive patterns. This is not
82  non-Perl items (?R), (?number), and (?P&#62;name). Also, the PCRE "callout" feature  available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE "callout"
83  allows an external function to be called during pattern matching. See the  feature allows an external function to be called during pattern matching. See
84    the
85  <a href="pcrecallout.html"><b>pcrecallout</b></a>  <a href="pcrecallout.html"><b>pcrecallout</b></a>
86  documentation for details.  documentation for details.
87  </P>  </P>
88  <P>  <P>
89  9. There are some differences that are concerned with the settings of captured  9. Subpatterns that are called recursively or as "subroutines" are always
90    treated as atomic groups in PCRE. This is like Python, but unlike Perl.
91    </P>
92    <P>
93    10. There are some differences that are concerned with the settings of captured
94  strings when part of a pattern is repeated. For example, matching "aba" against  strings when part of a pattern is repeated. For example, matching "aba" against
95  the pattern /^(a(b)?)+$/ in Perl leaves $2 unset, but in PCRE it is set to "b".  the pattern /^(a(b)?)+$/ in Perl leaves $2 unset, but in PCRE it is set to "b".
96  </P>  </P>
97  <P>  <P>
98  10. PCRE provides some extensions to the Perl regular expression facilities:  11. PCRE provides some extensions to the Perl regular expression facilities.
99    Perl 5.10 will include new features that are not in earlier versions, some of
100    which (such as named parentheses) have been in PCRE for some time. This list is
101    with respect to Perl 5.10:
102  <br>  <br>
103  <br>  <br>
104  (a) Although lookbehind assertions must match fixed length strings, each  (a) Although lookbehind assertions must match fixed length strings, each
# Line 119  only at the first matching position in t Line 128  only at the first matching position in t
128  options for <b>pcre_exec()</b> have no Perl equivalents.  options for <b>pcre_exec()</b> have no Perl equivalents.
129  <br>  <br>
130  <br>  <br>
131  (g) The (?R), (?number), and (?P&#62;name) constructs allows for recursive pattern  (g) The callout facility is PCRE-specific.
 matching (Perl can do this using the (?p{code}) construct, which PCRE cannot  
 support.)  
 <br>  
 <br>  
 (h) PCRE supports named capturing substrings, using the Python syntax.  
 <br>  
 <br>  
 (i) PCRE supports the possessive quantifier "++" syntax, taken from Sun's Java  
 package.  
 <br>  
 <br>  
 (j) The (R) condition, for testing recursion, is a PCRE extension.  
 <br>  
 <br>  
 (k) The callout facility is PCRE-specific.  
132  <br>  <br>
133  <br>  <br>
134  (l) The partial matching facility is PCRE-specific.  (h) The partial matching facility is PCRE-specific.
135  <br>  <br>
136  <br>  <br>
137  (m) Patterns compiled by PCRE can be saved and re-used at a later time, even on  (i) Patterns compiled by PCRE can be saved and re-used at a later time, even on
138  different hosts that have the other endianness.  different hosts that have the other endianness.
139  <br>  <br>
140  <br>  <br>
141  (n) The alternative matching function (<b>pcre_dfa_exec()</b>) matches in a  (j) The alternative matching function (<b>pcre_dfa_exec()</b>) matches in a
142  different way and is not Perl-compatible.  different way and is not Perl-compatible.
143  </P>  </P>
144  <P>  <P>
145  Last updated: 06 June 2006  Last updated: 28 November 2006
146  <br>  <br>
147  Copyright &copy; 1997-2006 University of Cambridge.  Copyright &copy; 1997-2006 University of Cambridge.
148  <p>  <p>

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