entering subdomain from top level domain.

[seba@]

Hey,
I made a subdomain and I want to upload images and create folders in it from a php script that 's running on the main domain.

So here is the script:
/var/www/vhosts/{domain}/httpdocs/

and here is the subdomain:
/var/www/vhosts/{domain}/subdomains/{subdomain}/httpdocs/

But so how can I enter that subdomain from a script in the top level domain.

cause with mkdir('/var/www/vhosts/{domain}/subdomains/{subdomain}/httpdocs/{dir}');
it doesn't work.

Thx in advance,
seba