PHP 判断客户端是IOS还是Android

<?php
if(strpos($_SERVER['HTTP_USER_AGENT'], 'iPhone')||strpos($_SERVER['HTTP_USER_AGENT'], 'iPad')){
    echo 'systerm is IOS';
}else if(strpos($_SERVER['HTTP_USER_AGENT'], 'Android')){
    echo 'systerm is Android';
}else{
    echo 'systerm is other';
}
?>