Display message if URL redirect - php

Question

I have a primary domain (example.com) with WordPress installed. A simple domain re-direct from example.com to example-usa.com has been put in place from the hosting control panel.
My client would like a simple welcome message displaying to anyone that has come from example-usa.com.
To achieve this, I opted for the following PHP:
<?php
$host = $_SERVER['HTTP_HOST'];
if ($host == "example-usa.com" or $host == "www.example-usa.com") {
echo '<header><h1>USA Message</h1>';
}
else {
echo '<header><h1>Normal welcome message</h1>';
}
?>
Unfortunately, when the user arrives to the site, the usa domain disappears from the browser URL bar and is replaced with the primary domain. This means my PHP isn't kicking in as it should.
Is there another way I can achieve this? I'd rather not use a plugin or location service.
It's important to note that there are two re-direct options from the clients domain registrar (123-reg). I've currently picked the 301 option as this is a permanent re-direct. I can however, pick a 302 direction which will introduce an iFrame.

Answer 1

I don't think you'll be able to do this with a redirect in your hosting. Your best bet would be to handle the redirect in your code and set a cookie before you do the redirect. Then on the destination side you can check for that cookie before you show the message.

Answer 2

HTTP_HOST contains the current domain, you can use the HTTP_REFERER to check the previous domain. This one will match with your 'usa' domain after the redirect.

Answer 3

Try this:
<?php
$host = parse_url(get_home_url(), PHP_URL_HOST); // will return 'example-usa.com'
if ($host == "example-usa.com" or $host == "www.example-usa.com") {
echo '<header><h1>USA Message</h1>';
}
else {
echo '<header><h1>Normal welcome message</h1>';
}
exit;
?>

Answer 4

Try this. Since you are redirecting user you will need to look at referrer URL^
if (strpos($_SERVER["HTTP_REFERER"], 'example-usa.com') !== false) {
echo 'Welcome to example.com';
}