If you are working with subdomains, it can be difficult to use segment conditionals or assigned variables for different purposes.
Here is a different way, using the path.php document that should be in the root of your domain folder as well as in the subdomain folder.
In the first path.php document you put
$global_vars = array(
"my_site" => "s1"
); // Last entry must not include the comma at the end
In the second path.php document (in the subdomain) you simply change “s1” so “s2” and so forth.
Then, you make a conditional where you need it. Below is an example of how to change the title of the document depending if you’re on you main domain or on your subdomain:
<title>
{if my_site == 's1' AND segment_1 == ""}
Welcome to my domain
{if:else my_site == 's2' AND segment_1 == ""}
Welcome to my subdomain
{/if}
</title>
This solution was created by Robin Sowell in response to a forum question.