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revision 79 by nigel, Sat Feb 24 21:40:52 2007 UTC revision 181 by ph10, Wed Jun 13 14:55:18 2007 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 with respect to Perl  regular expressions. The differences described here are mainly with respect to
9  5.8.  Perl 5.8, though PCRE versions 7.0 and later contain some features that are
10    expected to be in the forthcoming Perl 5.10.
11  .P  .P
12  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
13  given in the  it does have are given in the
14  .\" HTML <a href="pcre.html#utf8support">  .\" HTML <a href="pcre.html#utf8support">
15  .\" </a>  .\" </a>
16  section on UTF-8 support  section on UTF-8 support
# Line 44  encountered by PCRE, an error is generat Line 45  encountered by PCRE, an error is generat
45  6. The Perl escape sequences \ep, \eP, and \eX are supported only if PCRE is  6. The Perl escape sequences \ep, \eP, and \eX are supported only if PCRE is
46  built with Unicode character property support. The properties that can be  built with Unicode character property support. The properties that can be
47  tested with \ep and \eP are limited to the general category properties such as  tested with \ep and \eP are limited to the general category properties such as
48  Lu and Nd.  Lu and Nd, script names such as Greek or Han, and the derived properties Any
49    and L&.
50  .P  .P
51  7. PCRE does support the \eQ...\eE escape for quoting substrings. Characters in  7. PCRE does support the \eQ...\eE escape for quoting substrings. Characters in
52  between are treated as literals. This is slightly different from Perl in that $  between are treated as literals. This is slightly different from Perl in that $
# Line 62  following examples: Line 64  following examples:
64  .sp  .sp
65  The \eQ...\eE sequence is recognized both inside and outside character classes.  The \eQ...\eE sequence is recognized both inside and outside character classes.
66  .P  .P
67  8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})  8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
68  constructions. However, there is support for recursive patterns using the  constructions. However, there is support for recursive patterns. This is not
69  non-Perl items (?R), (?number), and (?P>name). Also, the PCRE "callout" feature  available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE "callout"
70  allows an external function to be called during pattern matching. See the  feature allows an external function to be called during pattern matching. See
71    the
72  .\" HREF  .\" HREF
73  \fBpcrecallout\fP  \fBpcrecallout\fP
74  .\"  .\"
75  documentation for details.  documentation for details.
76  .P  .P
77  9. There are some differences that are concerned with the settings of captured  9. Subpatterns that are called recursively or as "subroutines" are always
78    treated as atomic groups in PCRE. This is like Python, but unlike Perl.
79    .P
80    10. There are some differences that are concerned with the settings of captured
81  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
82  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".
83  .P  .P
84  10. PCRE provides some extensions to the Perl regular expression facilities:  11. PCRE provides some extensions to the Perl regular expression facilities.
85    Perl 5.10 will include new features that are not in earlier versions, some of
86    which (such as named parentheses) have been in PCRE for some time. This list is
87    with respect to Perl 5.10:
88  .sp  .sp
89  (a) Although lookbehind assertions must match fixed length strings, each  (a) Although lookbehind assertions must match fixed length strings, each
90  alternative branch of a lookbehind assertion can match a different length of  alternative branch of a lookbehind assertion can match a different length of
# Line 85  string. Perl requires them all to have t Line 94  string. Perl requires them all to have t
94  meta-character matches only at the very end of the string.  meta-character matches only at the very end of the string.
95  .sp  .sp
96  (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
97  meaning is faulted.  meaning is faulted. Otherwise, like Perl, the backslash is quietly ignored.
98    (Perl can be made to issue a warning.)
99  .sp  .sp
100  (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
101  inverted, that is, by default they are not greedy, but if followed by a  inverted, that is, by default they are not greedy, but if followed by a
# Line 97  only at the first matching position in t Line 107  only at the first matching position in t
107  (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAPTURE  (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAPTURE
108  options for \fBpcre_exec()\fP have no Perl equivalents.  options for \fBpcre_exec()\fP have no Perl equivalents.
109  .sp  .sp
110  (g) The (?R), (?number), and (?P>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.)  
 .sp  
 (h) PCRE supports named capturing substrings, using the Python syntax.  
 .sp  
 (i) PCRE supports the possessive quantifier "++" syntax, taken from Sun's Java  
 package.  
 .sp  
 (j) The (R) condition, for testing recursion, is a PCRE extension.  
 .sp  
 (k) The callout facility is PCRE-specific.  
111  .sp  .sp
112  (l) The partial matching facility is PCRE-specific.  (h) The partial matching facility is PCRE-specific.
113  .sp  .sp
114  (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
115  different hosts that have the other endianness.  different hosts that have the other endianness.
116  .sp  .sp
117  (n) The alternative matching function (\fBpcre_dfa_exec()\fP) matches in a  (j) The alternative matching function (\fBpcre_dfa_exec()\fP) matches in a
118  different way and is not Perl-compatible.  different way and is not Perl-compatible.
119  .P  .
120  .in 0  .
121  Last updated: 28 February 2005  .SH AUTHOR
122  .br  .rs
123  Copyright (c) 1997-2005 University of Cambridge.  .sp
124    .nf
125    Philip Hazel
126    University Computing Service
127    Cambridge CB2 3QH, England.
128    .fi
129    .
130    .
131    .SH REVISION
132    .rs
133    .sp
134    .nf
135    Last updated: 13 June 2007
136    Copyright (c) 1997-2007 University of Cambridge.
137    .fi

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