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/pcrecompat.3 | 107 ++++++++++++++++++++++++++++++++++++ 1 file changed, 107 insertions(+) create mode 100644 external-libs/pcre/doc/pcrecompat.3 (limited to 'external-libs/pcre/doc/pcrecompat.3') diff --git a/external-libs/pcre/doc/pcrecompat.3 b/external-libs/pcre/doc/pcrecompat.3 new file mode 100644 index 00000000..e358f607 --- /dev/null +++ b/external-libs/pcre/doc/pcrecompat.3 @@ -0,0 +1,107 @@ +.TH PCRE 3 +.SH NAME +PCRE - Perl-compatible regular expressions +.SH DIFFERENCES FROM PERL +.rs +.sp +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 +.\" HTML +.\" +section on UTF-8 support +.\" +in the main +.\" HREF +\fBpcre\fR +.\" +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. + +(c) 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 \fBpcre_exec()\fR 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. + +.in 0 +Last updated: 09 December 2003 +.br +Copyright (c) 1997-2003 University of Cambridge. -- cgit v1.2.3-54-g00ecf