Hello guys ineed a php expert please

"iknow may not work or stupid idea"

but imade a web app but with 2 forms and 2 codes one for mobile and one for pc or laptop.. so how ido if statement with the guest os to the right path imade * if viewing from mobile iwant him to go http://ift.tt/2w5q8hz if from pc or lap www.site.com/pc *

<?php
$mobileOS=idk
if ($guest = $mobileOS) {
header('location: /mobile');
} else {
header('location: /pc');
?>

note:bootstrap doesn't work because iwant to change the whole site into 2 pathes

(sorry for bad english)