require HTTP::Request;
 $request = HTTP::Request->new(GET => "http://www.example.com/" . $file_name);

 $ua = LWP::UserAgent->new;
 $response = $ua->request($request);
 if ($response->is_success) {
        print "File exists on web server\n";
    }
    else {
        print "File does not exist on web server.\n";
    }