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revision 75 by nigel, Sat Feb 24 21:40:37 2007 UTC revision 231 by ph10, Tue Sep 11 11:15:33 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 versions 7.0 and later contain some features that are
22    expected to be in the forthcoming Perl 5.10.
23  </P>  </P>
24  <P>  <P>
25  1. PCRE does not have full UTF-8 support. Details of what it does have are  1. PCRE has only a subset of Perl's UTF-8 and Unicode support. Details of what
26  given in the  it does have are given in the
27  <a href="pcre.html#utf8support">section on UTF-8 support</a>  <a href="pcre.html#utf8support">section on UTF-8 support</a>
28  in the main  in the main
29  <a href="pcre.html"><b>pcre</b></a>  <a href="pcre.html"><b>pcre</b></a>
# Line 57  encountered by PCRE, an error is generat Line 58  encountered by PCRE, an error is generat
58  6. The Perl escape sequences \p, \P, and \X are supported only if PCRE is  6. The Perl escape sequences \p, \P, and \X are supported only if PCRE is
59  built with Unicode character property support. The properties that can be  built with Unicode character property support. The properties that can be
60  tested with \p and \P are limited to the general category properties such as  tested with \p and \P are limited to the general category properties such as
61  Lu and Nd.  Lu and Nd, script names such as Greek or Han, and the derived properties Any
62    and L&.
63  </P>  </P>
64  <P>  <P>
65  7. PCRE does support the \Q...\E escape for quoting substrings. Characters in  7. PCRE does support the \Q...\E escape for quoting substrings. Characters in
# Line 75  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 does support Perl 5.10's backtracking verbs (*ACCEPT), (*FAIL), (*F),
99    (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in the forms without an
100    argument. PCRE does not support (*MARK). If (*ACCEPT) is within capturing
101    parentheses, PCRE does not set that capture group; this is different to Perl.
102    </P>
103    <P>
104    12. PCRE provides some extensions to the Perl regular expression facilities.
105    Perl 5.10 will include new features that are not in earlier versions, some of
106    which (such as named parentheses) have been in PCRE for some time. This list is
107    with respect to Perl 5.10:
108  <br>  <br>
109  <br>  <br>
110  (a) Although lookbehind assertions must match fixed length strings, each  (a) Although lookbehind assertions must match fixed length strings, each
# Line 101  meta-character matches only at the very Line 117  meta-character matches only at the very
117  <br>  <br>
118  <br>  <br>
119  (c) If PCRE_EXTRA is set, a backslash followed by a letter with no special  (c) If PCRE_EXTRA is set, a backslash followed by a letter with no special
120  meaning is faulted.  meaning is faulted. Otherwise, like Perl, the backslash is quietly ignored.
121    (Perl can be made to issue a warning.)
122  <br>  <br>
123  <br>  <br>
124  (d) If PCRE_UNGREEDY is set, the greediness of the repetition quantifiers is  (d) If PCRE_UNGREEDY is set, the greediness of the repetition quantifiers is
# Line 117  only at the first matching position in t Line 134  only at the first matching position in t
134  options for <b>pcre_exec()</b> have no Perl equivalents.  options for <b>pcre_exec()</b> have no Perl equivalents.
135  <br>  <br>
136  <br>  <br>
137  (g) The (?R), (?number), and (?P&#62;name) constructs allows for recursive pattern  (g) The \R escape sequence can be restricted to match only CR, LF, or CRLF
138  matching (Perl can do this using the (?p{code}) construct, which PCRE cannot  by the PCRE_BSR_ANYCRLF option.
139  support.)  <br>
140  <br>  <br>
141    (h) The callout facility is PCRE-specific.
142  <br>  <br>
 (h) PCRE supports named capturing substrings, using the Python syntax.  
143  <br>  <br>
144    (i) The partial matching facility is PCRE-specific.
145  <br>  <br>
 (i) PCRE supports the possessive quantifier "++" syntax, taken from Sun's Java  
 package.  
146  <br>  <br>
147    (j) Patterns compiled by PCRE can be saved and re-used at a later time, even on
148    different hosts that have the other endianness.
149  <br>  <br>
 (j) The (R) condition, for testing recursion, is a PCRE extension.  
150  <br>  <br>
151    (k) The alternative matching function (<b>pcre_dfa_exec()</b>) matches in a
152    different way and is not Perl-compatible.
153  <br>  <br>
 (k) The callout facility is PCRE-specific.  
154  <br>  <br>
155    (l) PCRE recognizes some special sequences such as (*CR) at the start of
156    a pattern that set overall options that cannot be changed within the pattern.
157    </P>
158    <br><b>
159    AUTHOR
160    </b><br>
161    <P>
162    Philip Hazel
163  <br>  <br>
164  (l) The partial matching facility is PCRE-specific.  University Computing Service
165  <br>  <br>
166    Cambridge CB2 3QH, England.
167  <br>  <br>
 (m) Patterns compiled by PCRE can be saved and re-used at a later time, even on  
 different hosts that have the other endianness.  
168  </P>  </P>
169    <br><b>
170    REVISION
171    </b><br>
172  <P>  <P>
173  Last updated: 09 September 2004  Last updated: 11 September 2007
174    <br>
175    Copyright &copy; 1997-2007 University of Cambridge.
176  <br>  <br>
 Copyright &copy; 1997-2004 University of Cambridge.  
177  <p>  <p>
178  Return to the <a href="index.html">PCRE index page</a>.  Return to the <a href="index.html">PCRE index page</a>.
179  </p>  </p>
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