pcrecompat specification

From 582b500cd996c96054615870fd13d6ab0ea77428 Mon Sep 17 00:00:00 2001 From: Jay Berkenbilt Date: Sat, 10 Oct 2009 15:10:05 +0000 Subject: start integrating windows port git-svn-id: svn+q:///qpdf/trunk@757 71b93d88-0707-0410-a8cf-f5a4172ac649 --- external-libs/pcre/doc/html/pcrecompat.html | 136 ++++++++++++++++++++++++++++ 1 file changed, 136 insertions(+) create mode 100644 external-libs/pcre/doc/html/pcrecompat.html (limited to 'external-libs/pcre/doc/html/pcrecompat.html') diff --git a/external-libs/pcre/doc/html/pcrecompat.html b/external-libs/pcre/doc/html/pcrecompat.html new file mode 100644 index 00000000..1ec22038 --- /dev/null +++ b/external-libs/pcre/doc/html/pcrecompat.html @@ -0,0 +1,136 @@ + + +pcrecompat specification + + +This HTML document has been 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.
+

DIFFERENCES FROM PERL +

+
DIFFERENCES FROM PERL
+

+This document describes the differences in the ways that PCRE and Perl handle +regular expressions. The differences described here are with respect to Perl +5.8. +

+1. PCRE does not have full UTF-8 support. Details of what it does have are +given in the +section on UTF-8 support +in the main +pcre +page. +

+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. +

+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. +

+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. +

+5. The following Perl escape sequences are not supported: \l, \u, \L, +\U, \P, \p, \N, and \X. 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. +

+6. 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: +

+    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
+

+The \Q...\E sequence is recognized both inside and outside character classes. +

+7. Fairly obviously, PCRE does not support the (?{code}) and (?p{code}) +constructions. However, there is some experimental support for recursive +patterns using the non-Perl items (?R), (?number) and (?P>name). Also, the PCRE +"callout" feature allows an external function to be called during pattern +matching. +

+8. 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". +

+9. PCRE provides some extensions to the Perl regular expression facilities: +

+(a) Although lookbehind assertions 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. +

+(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. +

+© If PCRE_EXTRA is set, a backslash followed by a letter with no special +meaning is faulted. +

+(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. +

+(e) PCRE_ANCHORED can be used to force a pattern to be tried only at the first +matching position in the subject string. +

+(f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAPTURE +options for pcre_exec() have no Perl equivalents. +

+(g) The (?R), (?number), and (?P>name) constructs allows for recursive pattern +matching (Perl can do this using the (?p{code}) construct, which PCRE cannot +support.) +

+(h) PCRE supports named capturing substrings, using the Python syntax. +

+(i) PCRE supports the possessive quantifier "++" syntax, taken from Sun's Java +package. +

+(j) The (R) condition, for testing recursion, is a PCRE extension. +

+(k) The callout facility is PCRE-specific. +