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revision 99 by ph10, Tue Mar 6 12:27:42 2007 UTC revision 453 by ph10, Fri Sep 18 19:12:35 2009 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 mainly with respect to  regular expressions. The differences described here are mainly with respect to
9  Perl 5.8, though PCRE version 7.0 contains some features that are expected to  Perl 5.8, though PCRE versions 7.0 and later contain some features that are
10  be in the forthcoming Perl 5.10.  in Perl 5.10.
11  .P  .P
12  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
13  it does have are given in the  it does have are given in the
# Line 46  encountered by PCRE, an error is generat Line 46  encountered by PCRE, an error is generat
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, script names such as Greek or Han, and the derived properties Any  Lu and Nd, script names such as Greek or Han, and the derived properties Any
49  and L&.  and L&. PCRE does support the Cs (surrogate) property, which Perl does not; the
50    Perl documentation says "Because Perl hides the need for the user to understand
51    the internal representation of Unicode characters, there is no need to
52    implement the somewhat messy concept of surrogates."
53  .P  .P
54  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
55  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 66  The \eQ...\eE sequence is recognized bot Line 69  The \eQ...\eE sequence is recognized bot
69  .P  .P
70  8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})  8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
71  constructions. However, there is support for recursive patterns. This is not  constructions. However, there is support for recursive patterns. This is not
72  available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE "callout"  available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE "callout"
73  feature allows an external function to be called during pattern matching. See  feature allows an external function to be called during pattern matching. See
74  the  the
75  .\" HREF  .\" HREF
# Line 75  the Line 78  the
78  documentation for details.  documentation for details.
79  .P  .P
80  9. Subpatterns that are called recursively or as "subroutines" are always  9. Subpatterns that are called recursively or as "subroutines" are always
81  treated as atomic groups in PCRE. This is like Python, but unlike Perl.  treated as atomic groups in PCRE. This is like Python, but unlike Perl. There
82    is a discussion of an example that explains this in more detail in the
83    .\" HTML <a href="pcrepattern.html#recursiondifference">
84    .\" </a>
85    section on recursion differences from Perl
86    .\"
87    in the
88    .\" HREF
89    \fBpcrecompat\fP
90    .\"
91    page.
92  .P  .P
93  10. There are some differences that are concerned with the settings of captured  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  11. PCRE provides some extensions to the Perl regular expression facilities.  11. PCRE does support Perl 5.10's backtracking verbs (*ACCEPT), (*FAIL), (*F),
98    (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in the forms without an
99    argument. PCRE does not support (*MARK).
100    .P
101    12. PCRE provides some extensions to the Perl regular expression facilities.
102  Perl 5.10 will include new features that are not in earlier versions, some of  Perl 5.10 will include new features that are not in earlier versions, some of
103  which (such as named parentheses) have been in PCRE for some time. This list is  which (such as named parentheses) have been in PCRE for some time. This list is
104  with respect to Perl 5.10:  with respect to Perl 5.10:
# Line 94  string. Perl requires them all to have t Line 111  string. Perl requires them all to have t
111  meta-character matches only at the very end of the string.  meta-character matches only at the very end of the string.
112  .sp  .sp
113  (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
114  meaning is faulted. Otherwise, like Perl, the backslash is ignored. (Perl can  meaning is faulted. Otherwise, like Perl, the backslash is quietly ignored.
115  be made to issue a warning.)  (Perl can be made to issue a warning.)
116  .sp  .sp
117  (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
118  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 104  question mark they are. Line 121  question mark they are.
121  (e) PCRE_ANCHORED can be used at matching time to force a pattern to be tried  (e) PCRE_ANCHORED can be used at matching time to force a pattern to be tried
122  only at the first matching position in the subject string.  only at the first matching position in the subject string.
123  .sp  .sp
124  (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAPTURE  (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, and
125  options for \fBpcre_exec()\fP have no Perl equivalents.  PCRE_NO_AUTO_CAPTURE options for \fBpcre_exec()\fP have no Perl equivalents.
126  .sp  .sp
127  (g) The callout facility is PCRE-specific.  (g) The \eR escape sequence can be restricted to match only CR, LF, or CRLF
128    by the PCRE_BSR_ANYCRLF option.
129  .sp  .sp
130  (h) The partial matching facility is PCRE-specific.  (h) The callout facility is PCRE-specific.
131  .sp  .sp
132  (i) Patterns compiled by PCRE can be saved and re-used at a later time, even on  (i) The partial matching facility is PCRE-specific.
133    .sp
134    (j) Patterns compiled by PCRE can be saved and re-used at a later time, even on
135  different hosts that have the other endianness.  different hosts that have the other endianness.
136  .sp  .sp
137  (j) The alternative matching function (\fBpcre_dfa_exec()\fP) matches in a  (k) The alternative matching function (\fBpcre_dfa_exec()\fP) matches in a
138  different way and is not Perl-compatible.  different way and is not Perl-compatible.
139    .sp
140    (l) PCRE recognizes some special sequences such as (*CR) at the start of
141    a pattern that set overall options that cannot be changed within the pattern.
142  .  .
143  .  .
144  .SH AUTHOR  .SH AUTHOR
# Line 132  Cambridge CB2 3QH, England. Line 155  Cambridge CB2 3QH, England.
155  .rs  .rs
156  .sp  .sp
157  .nf  .nf
158  Last updated: 06 March 2007  Last updated: 18 September 2009
159  Copyright (c) 1997-2007 University of Cambridge.  Copyright (c) 1997-2009 University of Cambridge.
160  .fi  .fi

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