+++ /dev/null
-<html>
-<head>
-<title>pcrecompat specification</title>
-</head>
-<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
-<h1>pcrecompat man page</h1>
-<p>
-Return to the <a href="index.html">PCRE index page</a>.
-</p>
-<p>
-This page is part of the PCRE HTML documentation. It was generated automatically
-from the original man page. If there is any nonsense in it, please consult the
-man page, in case the conversion went wrong.
-<br>
-<br><b>
-DIFFERENCES BETWEEN PCRE AND PERL
-</b><br>
-<P>
-This document describes the differences in the ways that PCRE and Perl handle
-regular expressions. The differences described here are with respect to Perl
-5.10.
-</P>
-<P>
-1. PCRE has only a subset of Perl's UTF-8 and Unicode support. Details of what
-it does have are given in the
-<a href="pcre.html#utf8support">section on UTF-8 support</a>
-in the main
-<a href="pcre.html"><b>pcre</b></a>
-page.
-</P>
-<P>
-2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl permits
-them, but they do not mean what you might think. For example, (?!a){3} does
-not assert that the next three characters are not "a". It just asserts that the
-next character is not "a" three times.
-</P>
-<P>
-3. Capturing subpatterns that occur inside negative lookahead assertions are
-counted, but their entries in the offsets vector are never set. Perl sets its
-numerical variables from any such patterns that are matched before the
-assertion fails to match something (thereby succeeding), but only if the
-negative lookahead assertion contains just one branch.
-</P>
-<P>
-4. Though binary zero characters are supported in the subject string, they are
-not allowed in a pattern string because it is passed as a normal C string,
-terminated by zero. The escape sequence \0 can be used in the pattern to
-represent a binary zero.
-</P>
-<P>
-5. The following Perl escape sequences are not supported: \l, \u, \L,
-\U, and \N. In fact these are implemented by Perl's general string-handling
-and are not part of its pattern matching engine. If any of these are
-encountered by PCRE, an error is generated.
-</P>
-<P>
-6. The Perl escape sequences \p, \P, and \X are supported only if PCRE is
-built with Unicode character property support. The properties that can be
-tested with \p and \P are limited to the general category properties such as
-Lu and Nd, script names such as Greek or Han, and the derived properties Any
-and L&. PCRE does support the Cs (surrogate) property, which Perl does not; the
-Perl documentation says "Because Perl hides the need for the user to understand
-the internal representation of Unicode characters, there is no need to
-implement the somewhat messy concept of surrogates."
-</P>
-<P>
-7. PCRE does support the \Q...\E escape for quoting substrings. Characters in
-between are treated as literals. This is slightly different from Perl in that $
-and @ are also handled as literals inside the quotes. In Perl, they cause
-variable interpolation (but of course PCRE does not have variables). Note the
-following examples:
-<pre>
- Pattern PCRE matches Perl matches
-
- \Qabc$xyz\E abc$xyz abc followed by the contents of $xyz
- \Qabc\$xyz\E abc\$xyz abc\$xyz
- \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
-</pre>
-The \Q...\E sequence is recognized both inside and outside character classes.
-</P>
-<P>
-8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
-constructions. However, there is support for recursive patterns. This is not
-available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE "callout"
-feature allows an external function to be called during pattern matching. See
-the
-<a href="pcrecallout.html"><b>pcrecallout</b></a>
-documentation for details.
-</P>
-<P>
-9. Subpatterns that are called recursively or as "subroutines" are always
-treated as atomic groups in PCRE. This is like Python, but unlike Perl. There
-is a discussion of an example that explains this in more detail in the
-<a href="pcrepattern.html#recursiondifference">section on recursion differences from Perl</a>
-in the
-<a href="pcrepattern.html"><b>pcrepattern</b></a>
-page.
-</P>
-<P>
-10. There are some differences that are concerned with the settings of captured
-strings when part of a pattern is repeated. For example, matching "aba" against
-the pattern /^(a(b)?)+$/ in Perl leaves $2 unset, but in PCRE it is set to "b".
-</P>
-<P>
-11. PCRE does support Perl 5.10's backtracking verbs (*ACCEPT), (*FAIL), (*F),
-(*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in the forms without an
-argument. PCRE does not support (*MARK).
-</P>
-<P>
-12. PCRE's handling of duplicate subpattern numbers and duplicate subpattern
-names is not as general as Perl's. This is a consequence of the fact the PCRE
-works internally just with numbers, using an external table to translate
-between numbers and names. In particular, a pattern such as (?|(?<a>A)|(?<b)B),
-where the two capturing parentheses have the same number but different names,
-is not supported, and causes an error at compile time. If it were allowed, it
-would not be possible to distinguish which parentheses matched, because both
-names map to capturing subpattern number 1. To avoid this confusing situation,
-an error is given at compile time.
-</P>
-<P>
-13. PCRE provides some extensions to the Perl regular expression facilities.
-Perl 5.10 includes new features that are not in earlier versions of Perl, some
-of which (such as named parentheses) have been in PCRE for some time. This list
-is with respect to Perl 5.10:
-<br>
-<br>
-(a) Although lookbehind assertions in PCRE must match fixed length strings,
-each alternative branch of a lookbehind assertion can match a different length
-of string. Perl requires them all to have the same length.
-<br>
-<br>
-(b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
-meta-character matches only at the very end of the string.
-<br>
-<br>
-(c) If PCRE_EXTRA is set, a backslash followed by a letter with no special
-meaning is faulted. Otherwise, like Perl, the backslash is quietly ignored.
-(Perl can be made to issue a warning.)
-<br>
-<br>
-(d) If PCRE_UNGREEDY is set, the greediness of the repetition quantifiers is
-inverted, that is, by default they are not greedy, but if followed by a
-question mark they are.
-<br>
-<br>
-(e) PCRE_ANCHORED can be used at matching time to force a pattern to be tried
-only at the first matching position in the subject string.
-<br>
-<br>
-(f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, and
-PCRE_NO_AUTO_CAPTURE options for <b>pcre_exec()</b> have no Perl equivalents.
-<br>
-<br>
-(g) The \R escape sequence can be restricted to match only CR, LF, or CRLF
-by the PCRE_BSR_ANYCRLF option.
-<br>
-<br>
-(h) The callout facility is PCRE-specific.
-<br>
-<br>
-(i) The partial matching facility is PCRE-specific.
-<br>
-<br>
-(j) Patterns compiled by PCRE can be saved and re-used at a later time, even on
-different hosts that have the other endianness.
-<br>
-<br>
-(k) The alternative matching function (<b>pcre_dfa_exec()</b>) matches in a
-different way and is not Perl-compatible.
-<br>
-<br>
-(l) PCRE recognizes some special sequences such as (*CR) at the start of
-a pattern that set overall options that cannot be changed within the pattern.
-</P>
-<br><b>
-AUTHOR
-</b><br>
-<P>
-Philip Hazel
-<br>
-University Computing Service
-<br>
-Cambridge CB2 3QH, England.
-<br>
-</P>
-<br><b>
-REVISION
-</b><br>
-<P>
-Last updated: 04 October 2009
-<br>
-Copyright © 1997-2009 University of Cambridge.
-<br>
-<p>
-Return to the <a href="index.html">PCRE index page</a>.
-</p>
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