show source code of a html file.php

This script shows the (html) source code of a html-file  :

<form action="thisfile.php?action=showsource" method='post'>
<input type="text" name="urlx" value="http://localhost/filename.html" size="50">
<INPUT TYPE="submit" VALUE="GO">
</form>
<?php
switch ($action)
{
case "showsource" :
show_source("$urlx");
break;
}
?>