from the PHP UK list, Keith Young
When using PCRE (Perl Compatible Regular Expressions) you need to surround the expression to be evaluated with a delimiter.

$regexp=’/www./’;
$regexp=’!www.!’;
$regexp=’~www.~’;

The above are all equivalent… Most people use // as the delimiters.

There is one more “problem” in the PCRE you wrote.  The “.” in a PCRE denotes ANY character.  So if you had “wwwx” it would match.  To force the “.” to evaulate as a period you need to escape it:

$regexp=’/www\\./’;

More information about PCRE and how to use it (in PHP) is available on the PHP website (I find the pattern syntax page to be the one I reference more often – link below):

http://www.php.net/manual/en/pcre.pattern.syntax.php

One last point.  If you are doing a straight replace that doesn’t require any level of complexity to the pattern matching, then as someone else suggested, using str_replace is a better solution, since it is much easier on the PHP engine.  This is more noticable in situations where the replacement will occur multiple times (like in
loops and such).