CVS update: php3/doc/functions

Date: Saturday June 12, 1999 @ 18:00 Author: andrey Update of /repository/php3/doc/functions In directory php:/tmp/cvs-serv22468 Modified Files: pcre.sgml Log Message: Started adding secions from PCRE manpage. Index: php3/doc/functions/pcre.sgml diff -u php3/doc/functions/pcre.sgml:1.10 php3/doc/functions/pcre.sgml:1.11 --- php3/doc/functions/pcre.sgml:1.10 Fri Jun 11 13:20:19 1999 +++ php3/doc/functions/pcre.sgml Sat Jun 12 18:00:46 1999 @@ -455,6 +455,107 @@ </blockquote> </refsect1> </refentry> + + <refentry id="pattern.options"> + <refnamediv> + <refname>Pattern Syntax</refname> + <refpurpose>describes PCRE regex syntax</refpurpose> + </refnamediv> + <refsect1> + <title>Description</title> + <literallayout> + The PCRE library is a set of functions that implement regular + expression pattern matching using the same syntax and semantics + as Perl 5, with just a few differences (see below). The current + implementation corresponds to Perl 5.005. + </literallayout> + + <refsect1> + <title>Differences from Perl</title> + <literallayout> + The differences described here are with respect to Perl + 5.005. + + 1. By default, a whitespace character is any character that + the C library function isspace() recognizes, though it is + possible to compile PCRE with alternative character type + tables. Normally isspace() matches space, formfeed, newline, + carriage return, horizontal tab, and vertical tab. Perl 5 no + longer includes vertical tab in its set of whitespace char- + acters. The \v escape that was in the Perl documentation for + a long time was never in fact recognized. However, the char- + acter itself was treated as whitespace at least up to 5.002. + In 5.004 and 5.005 it does not match \s. + + 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 looka- + head assertions are counted, but their entries in the + offsets vector are never set. Perl sets its numerical vari- + ables 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 sub- + ject 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, \E, \Q. In fact these are implemented by + Perl's general string-handling and are not part of its pat- + tern matching engine. + + 6. The Perl \G assertion is not supported as it is not + relevant to single pattern matches. + + 7. Fairly obviously, PCRE does not support the (?{code}) + construction. + + 8. There are at the time of writing some oddities in Perl + 5.005_02 concerned with the settings of captured strings + when part of a pattern is repeated. For example, matching + "aba" against the pattern /^(a(b)?)+$/ sets $2 to the value + "b", but matching "aabbaa" against /^(aa(bb)?)+$/ leaves $2 + unset. However, if the pattern is changed to + /^(aa(b(b))?)+$/ then $2 (and $3) get set. + + In Perl 5.004 $2 is set in both cases, and that is also true + of PCRE. If in the future Perl changes to a consistent state + that is different, PCRE may change to follow. + + 9. Another as yet unresolved discrepancy is that in Perl + 5.005_02 the pattern /^(a)?(?(1)a|b)+$/ matches the string + "a", whereas in PCRE it does not. However, in both Perl and + PCRE /^(a)?a/ matched against "a" leaves $1 unset. + + 10. 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 5.005 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 repeti- + tion quantifiers is inverted, that is, by default they are + not greedy, but if followed by a question mark they are. + </literallayout> + </refsect1> + </refentry> </reference> <!-- Keep this comment at the end of the file