如果浏览器和操作系统标头为空，则重定向

A particular page is getting hit by someone using a block of IPs. Interestingly their headers are showing no information on their operating system or browser. How would I go about redirecting users that do not have browser or OS information in their http headers?

Is there an easy way to do this with some php?

I agree with the comment from Colin Morelli:

Bad idea. Many people have browser extensions that hide the User-Agent header because they're concerned about privacy.

However, if you want to do it, it's easy enough:

if (!isset($_SERVER['HTTP_USER_AGENT']) {
    // Redirect here.
    header('Location: http://example.com');
    exit;
}