php: visitor log

check.php

$filename = 'log.txt';
                    $timestamp = date('l  d  F  Y   H:i:s');
                    $u_agent = $_SERVER['HTTP_USER_AGENT'];
        $ub = '';
        if(preg_match('/MSIE/i',$u_agent))
        {
            $ub = "Internet Explorer";
        }
        elseif(preg_match('/Firefox/i',$u_agent))
        {
            $ub = "Mozilla Firefox";
        }
        elseif(preg_match('/Safari/i',$u_agent))
        {
            $ub = "Apple Safari";
        }
        elseif(preg_match('/Chrome/i',$u_agent))
        {
            $ub = "Google Chrome";
        }
        elseif(preg_match('/Flock/i',$u_agent))
         {
            $ub = "Flock";
        }
        elseif(preg_match('/Opera/i',$u_agent))
        {
            $ub = "Opera";
        }
        elseif(preg_match('/Netscape/i',$u_agent))
        {
            $ub = "Netscape";
        } 
                    $log = $timestamp . '     ' . 'IPAddress:'. '  ' . $_SERVER['REMOTE_ADDR'] . '     ' . 'Referer:'. '  ' . $_SERVER['REQUEST_URI'] . '     ' . 'Browser:'. '  ' . $ub . '     ' . 'Username:'. '  ' .    $username;
                        

                    $stream = fopen("log.txt","a+");
                    fwrite($stream,$log ."\n");
                    fclose($stream);