Can shortcodes be used in php?

I want to have a search box appear in the header of the site only when Subscribers are logged in.

I thought perhaps to use the membership level shortcode (as outlined on page 22 of the Membership plugin documentation) to protect the search form so it would only display when a logged-in Subscriber viewed it... but need to know how to make the shortcode operate in a PHP file.

I tried this in the header.php file:

[level-subscriber-full-access]<?php get_search_form(); ?>[/level-subscriber-full-access]

But this didn't work (I didn't really expect it to, but figured I had to start somewhere).

Is this possible, and how is it done?