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diff --git a/external-libs/pcre/doc/pcrecompat.3 b/external-libs/pcre/doc/pcrecompat.3 deleted file mode 100644 index e358f607..00000000 --- a/external-libs/pcre/doc/pcrecompat.3 +++ /dev/null @@ -1,107 +0,0 @@ -.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 <a href="pcre.html#utf8support"> -.\" </a> -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. |