if($cgi->http('HTTP_REFERER')){

        print "<p>Testing, there was a referer: ".$cgi->http('HTTP_REF
+ERER')."</p>";

    }else{

        print "<p>Testing, there was <b>no</b> referer</p>";

    }
[download]

Note that the correct spelling is "referrer". That is how it should be spelled in English text, despite the unfortunate misspelling in the HTTP standard that we are all stuck with forever.