Automatically link Twitter names to Twitter URL in blog posts and comments (functions.php)

gistfile1.php

<?php

//* DO NOT include the opening PHP tag

//* Automatically link Twitter names to Twitter URL
function twtreplace($content) {
	$twtreplace = preg_replace('/([^a-zA-Z0-9-_&])@([0-9a-zA-Z_]+)/',"$1<a href=\"http://twitter.com/$2\" target=\"_blank\" rel=\"nofollow\">@$2</a>",$content);
	return $twtreplace;
}

add_filter('the_content', 'twtreplace');   
add_filter('comment_text', 'twtreplace');