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revision 453 by ph10, Fri Sep 18 19:12:35 2009 UTC revision 457 by ph10, Sat Oct 3 16:24:08 2009 UTC
# Line 5  PCRE - Perl-compatible regular expressio Line 5  PCRE - Perl-compatible regular expressio
5  .rs  .rs
6  .sp  .sp
7  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
8  regular expressions. The differences described here are mainly with respect to  regular expressions. The differences described here are with respect to Perl
9  Perl 5.8, though PCRE versions 7.0 and later contain some features that are  5.10.
 in Perl 5.10.  
10  .P  .P
11  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
12  it does have are given in the  it does have are given in the
# Line 86  section on recursion differences from Pe Line 85  section on recursion differences from Pe
85  .\"  .\"
86  in the  in the
87  .\" HREF  .\" HREF
88  \fBpcrecompat\fP  \fBpcrepattern\fP
89  .\"  .\"
90  page.  page.
91  .P  .P
# Line 98  the pattern /^(a(b)?)+$/ in Perl leaves Line 97  the pattern /^(a(b)?)+$/ in Perl leaves
97  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in the forms without an  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in the forms without an
98  argument. PCRE does not support (*MARK).  argument. PCRE does not support (*MARK).
99  .P  .P
100  12. PCRE provides some extensions to the Perl regular expression facilities.  12. PCRE's handling of duplicate subpattern numbers and duplicate subpattern
101  Perl 5.10 will include new features that are not in earlier versions, some of  names is not as general as Perl's. This is a consequence of the fact the PCRE
102  which (such as named parentheses) have been in PCRE for some time. This list is  works internally just with numbers, using an external table to translate
103  with respect to Perl 5.10:  between numbers and names. The following are some specific differences:
104  .sp  .sp
105  (a) Although lookbehind assertions must match fixed length strings, each  (a) A pattern such as (?|(?<a>A)|(?<b)B), where the two capturing
106  alternative branch of a lookbehind assertion can match a different length of  parentheses have the same number but different names, is not supported, and
107  string. Perl requires them all to have the same length.  causes an error at compile time. If it were allowed, it would not be possible
108    to distinguish which parentheses matched, because both names map to capturing
109    subpattern number 1. To avoid this confusing situation, an error is given at
110    compile time.
111    .sp
112    (b) A condition test for a subpattern with a name that is duplicated gives
113    unpredictable results. For example, when the pattern
114    (?:(?<a>A)|(?<a>B))(?('a')...|...) is compiled (the PCRE_DUPNAMES option is
115    required), the condition test (?('a') is set to test whether subpattern 1 has
116    matched, ignoring subpattern 2, even though it has the same name.
117    .P
118    13. PCRE provides some extensions to the Perl regular expression facilities.
119    Perl 5.10 includes new features that are not in earlier versions of Perl, some
120    of which (such as named parentheses) have been in PCRE for some time. This list
121    is with respect to Perl 5.10:
122    .sp
123    (a) Although lookbehind assertions in PCRE must match fixed length strings,
124    each alternative branch of a lookbehind assertion can match a different length
125    of string. Perl requires them all to have the same length.
126  .sp  .sp
127  (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $  (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
128  meta-character matches only at the very end of the string.  meta-character matches only at the very end of the string.
# Line 155  Cambridge CB2 3QH, England. Line 172  Cambridge CB2 3QH, England.
172  .rs  .rs
173  .sp  .sp
174  .nf  .nf
175  Last updated: 18 September 2009  Last updated: 03 October 2009
176  Copyright (c) 1997-2009 University of Cambridge.  Copyright (c) 1997-2009 University of Cambridge.
177  .fi  .fi

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