主要代码

function getSystem(){   
    $sys = $_SERVER['HTTP_USER_AGENT'];   
    if(stripos($sys, "NT 6.1"))
        $os = "Windows 7";   
    elseif(stripos($sys, "NT 6.0"))   
        $os = "Windows Vista";   
    elseif(stripos($sys, "NT 5.1"))   
        $os = "Windows XP";   
    elseif(stripos($sys, "NT 5.2"))   
        $os = "Windows Server 2003";   
    elseif(stripos($sys, "NT 5"))   
        $os = "Windows 2000";   
    elseif(stripos($sys, "NT 4.9"))   
        $os = "Windows ME";   
    elseif(stripos($sys, "NT 4"))   
        $os = "Windows NT 4.0";   
    elseif(stripos($sys, "98"))   
        $os = "Windows 98";   
    elseif(stripos($sys, "95"))   
        $os = "Windows 95";   
    elseif(stripos($sys, "Mac"))   
        $os = "Mac";   
    elseif(stripos($sys, "Linux"))   
        $os = "Linux";   
    elseif(stripos($sys, "Unix"))   
        $os = "Unix";   
    elseif(stripos($sys, "FreeBSD"))   
        $os = "FreeBSD";   
    elseif(stripos($sys, "SunOS"))   
        $os = "SunOS";   
    elseif(stripos($sys, "BeOS"))   
        $os = "BeOS";   
    elseif(stripos($sys, "OS/2"))   
        $os = "OS/2";   
    elseif(stripos($sys, "PC"))   
        $os = "Macintosh";   
    elseif(stripos($sys, "AIX"))   
        $os = "AIX";   
    else  
        $os = "未知操作系统";   
    return $os;   
}  

调用代码

$system = getSystem();
echo "操作系统为".$system;