php detect browser

if (preg_match("/(MSIE)[\/ ]?([0-9.]*)/", $_SERVER["HTTP_USER_AGENT"], $match))
{
    $browser['name'] = $match[1];
    $browser['version'] = $match[2];

    // IE 版本小於 8
    if((int)$browser['version'] <= 8)
    {  
        doSomething();                    
    }   

}

Reference :
How can I detect the browser with PHP or JavaScript? - Stack Overflow