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revision 459 by ph10, Sun Oct 4 09:21:39 2009 UTC revision 596 by ph10, Mon May 2 10:47:52 2011 UTC
# Line 6  PCRE - Perl-compatible regular expressio Line 6  PCRE - Perl-compatible regular expressio
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 with respect to Perl  regular expressions. The differences described here are with respect to Perl
9  5.10.  versions 5.10 and above.
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 20  in the main Line 20  in the main
20  .\"  .\"
21  page.  page.
22  .P  .P
23  2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl permits  2. PCRE does not allow repeat quantifiers on assertions. Perl permits them, but
24  them, but they do not mean what you might think. For example, (?!a){3} does  they do not mean what you might think. For example, (?!a){3} does not assert
25  not assert that the next three characters are not "a". It just asserts that the  that the next three characters are not "a". It just asserts that the next
26  next character is not "a" three times.  character is not "a" three times.
27  .P  .P
28  3. Capturing subpatterns that occur inside negative lookahead assertions are  3. Capturing subpatterns that occur inside negative lookahead assertions are
29  counted, but their entries in the offsets vector are never set. Perl sets its  counted, but their entries in the offsets vector are never set. Perl sets its
# Line 77  the Line 77  the
77  documentation for details.  documentation for details.
78  .P  .P
79  9. Subpatterns that are called recursively or as "subroutines" are always  9. Subpatterns that are called recursively or as "subroutines" are always
80  treated as atomic groups in PCRE. This is like Python, but unlike Perl. There  treated as atomic groups in PCRE. This is like Python, but unlike Perl. There
81  is a discussion of an example that explains this in more detail in the  is a discussion of an example that explains this in more detail in the
82  .\" HTML <a href="pcrepattern.html#recursiondifference">  .\" HTML <a href="pcrepattern.html#recursiondifference">
83  .\" </a>  .\" </a>
# Line 93  page. Line 93  page.
93  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
94  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".
95  .P  .P
96  11. PCRE does support Perl 5.10's backtracking verbs (*ACCEPT), (*FAIL), (*F),  11. PCRE's handling of duplicate subpattern numbers and duplicate subpattern
 (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in the forms without an  
 argument. PCRE does not support (*MARK).  
 .P  
 12. PCRE's handling of duplicate subpattern numbers and duplicate subpattern  
97  names is not as general as Perl's. This is a consequence of the fact the PCRE  names is not as general as Perl's. This is a consequence of the fact the PCRE
98  works internally just with numbers, using an external table to translate  works internally just with numbers, using an external table to translate
99  between numbers and names. In particular, a pattern such as (?|(?<a>A)|(?<b)B),  between numbers and names. In particular, a pattern such as (?|(?<a>A)|(?<b)B),
# Line 107  would not be possible to distinguish whi Line 103  would not be possible to distinguish whi
103  names map to capturing subpattern number 1. To avoid this confusing situation,  names map to capturing subpattern number 1. To avoid this confusing situation,
104  an error is given at compile time.  an error is given at compile time.
105  .P  .P
106    12. Perl recognizes comments in some places that PCRE doesn't, for example,
107    between the ( and ? at the start of a subpattern.
108    .P
109  13. PCRE provides some extensions to the Perl regular expression facilities.  13. PCRE provides some extensions to the Perl regular expression facilities.
110  Perl 5.10 includes new features that are not in earlier versions of Perl, some  Perl 5.10 includes new features that are not in earlier versions of Perl, some
111  of which (such as named parentheses) have been in PCRE for some time. This list  of which (such as named parentheses) have been in PCRE for some time. This list
# Line 164  Cambridge CB2 3QH, England. Line 163  Cambridge CB2 3QH, England.
163  .rs  .rs
164  .sp  .sp
165  .nf  .nf
166  Last updated: 04 October 2009  Last updated: 02 May 2011
167  Copyright (c) 1997-2009 University of Cambridge.  Copyright (c) 1997-2011 University of Cambridge.
168  .fi  .fi

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