Hittade lösningen:
<?
function linkURL($web) {
$web = preg_replace("/(?<=^|\s)(www\.([-a-zA-Z0-9_]+\.)*[-a-zA-Z0-9_]+\.[-a-zA-Z0-9_]{2,6}(\/[^\s]*)*)(?=\s|$)/", "http://$1", $web);
$search = "/(?<=^|\s)(http:\/\/|https:\/\/|ftp:\/\/)(([-a-zA-Z0-9_]+\.)*[-a-zA-Z0-9_]+\.[-a-zA-Z0-9_]{2,6}(\/[^\s]*)*)(?=\s|$)/";
$replace = "<a href=\"$1$2\" target='_blank'>$2</a>";
$web = preg_replace($search, $replace, $web);
return $web;
}
?>
och så anropar jag den bara med linkURL(sträng);