Lighttpd

i am able to redirect domain.com to www.domain.com but how can i make it so it doesn't add the file extention?

example:

$HTTP["host"] == "domain.com" {
url.redirect = ("/(.*)$" => "http://www.domain.com/$1")
}

but if i type: domain.com/file it redirects to www.domain.com/file.cgi
how can i get it to leave out the extension since it wasn't in the URL to begin with?

thanks