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.sp |
.sp |
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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 |
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regular expressions. The differences described here are mainly with respect to |
regular expressions. The differences described here are mainly with respect to |
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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 |
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be in the forthcoming Perl 5.10. |
in Perl 5.10. |
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.P |
.P |
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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 |
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it does have are given in the |
it does have are given in the |
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built with Unicode character property support. The properties that can be |
built with Unicode character property support. The properties that can be |
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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 |
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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 |
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and L&. |
and L&. PCRE does support the Cs (surrogate) property, which Perl does not; the |
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Perl documentation says "Because Perl hides the need for the user to understand |
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the internal representation of Unicode characters, there is no need to |
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implement the somewhat messy concept of surrogates." |
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.P |
.P |
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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 |
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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 $ |
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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 |
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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". |
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.P |
.P |
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11. PCRE provides some extensions to the Perl regular expression facilities. |
11. PCRE does support Perl 5.10's backtracking verbs (*ACCEPT), (*FAIL), (*F), |
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(*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in the forms without an |
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argument. PCRE does not support (*MARK). |
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|
.P |
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12. PCRE provides some extensions to the Perl regular expression facilities. |
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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 |
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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 |
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with respect to Perl 5.10: |
with respect to Perl 5.10: |
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meta-character matches only at the very end of the string. |
meta-character matches only at the very end of the string. |
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.sp |
.sp |
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(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 |
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meaning is faulted. Otherwise, like Perl, the backslash is ignored. (Perl can |
meaning is faulted. Otherwise, like Perl, the backslash is quietly ignored. |
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be made to issue a warning.) |
(Perl can be made to issue a warning.) |
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.sp |
.sp |
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(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 |
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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 |
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(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 |
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only at the first matching position in the subject string. |
only at the first matching position in the subject string. |
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.sp |
.sp |
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(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 |
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options for \fBpcre_exec()\fP have no Perl equivalents. |
PCRE_NO_AUTO_CAPTURE options for \fBpcre_exec()\fP have no Perl equivalents. |
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|
.sp |
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(g) The \eR escape sequence can be restricted to match only CR, LF, or CRLF |
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|
by the PCRE_BSR_ANYCRLF option. |
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.sp |
.sp |
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(g) The callout facility is PCRE-specific. |
(h) The callout facility is PCRE-specific. |
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.sp |
.sp |
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(h) The partial matching facility is PCRE-specific. |
(i) The partial matching facility is PCRE-specific. |
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.sp |
.sp |
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(i) Patterns compiled by PCRE can be saved and re-used at a later time, even on |
(j) Patterns compiled by PCRE can be saved and re-used at a later time, even on |
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different hosts that have the other endianness. |
different hosts that have the other endianness. |
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.sp |
.sp |
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(j) The alternative matching function (\fBpcre_dfa_exec()\fP) matches in a |
(k) The alternative matching function (\fBpcre_dfa_exec()\fP) matches in a |
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different way and is not Perl-compatible. |
different way and is not Perl-compatible. |
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|
.sp |
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(l) PCRE recognizes some special sequences such as (*CR) at the start of |
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a pattern that set overall options that cannot be changed within the pattern. |
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. |
. |
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. |
. |
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.SH AUTHOR |
.SH AUTHOR |
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.rs |
.rs |
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.sp |
.sp |
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.nf |
.nf |
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Last updated: 06 March 2007 |
Last updated: 16 September 2009 |
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Copyright (c) 1997-2007 University of Cambridge. |
Copyright (c) 1997-2009 University of Cambridge. |
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.fi |
.fi |