Programming PHP

Quoting for regular expressions
The preg_quote( ) function creates a regular expression that matches only a given
string:
$re = preg_quote(string [, delimiter ]);
Every character in string that has special meaning inside a regular expression (e.g., *
or $) is prefaced with a backslash:
echo preg_quote('$5.00 (five bucks)');
\$5\.00 \(five bucks\)
The optional second argument is an extra character to be quoted. Usually, you pass
your regular expression delimiter here:
$to_find = '/usr/local/etc/rsync.conf';
$re = preg_quote($filename, '/');
if (preg_match("/$re", $filename)) {
// found it!
}
Differences from Perl Regular Expressions
Although very similar, PHP’s implementation of Perl-style regular expressions has a
few minor differences from actual Perl regular expressions:
• The null character (ASCII 0) is not allowed as a literal character within a pattern
string. You can reference it in other ways, however (\000, \x00, etc.).
• The \E, \G, \L, \l, \Q, \u, and \U options are not supported.
• The (?{ some perl code }) construct is not supported.
• The /D, /G, /U, /u, /A, and /X modifiers are supported.
• The vertical tab \v counts as a whitespace character.
• Lookahead and lookbehind assertions cannot be repeated using *, +, or ?.
• Parenthesized submatches within negative assertions are not remembered.
• Alternation branches within a lookbehind assertion can be of different lengths.
Perl-Compatible Regular Expressions | 115
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