calling user variables from a template

How would I go about called something like $post[username] from a row in a database and still have it work for each user. When I tryed last all that came up was $post[username]

Example: I put this into a database

<center>$post[username]</center>

then I call it from the database using $postusername

Would I have to use eval for that? I think I have to just want to make sure.

Thanks for your time.

Edit: I posted the wrong word for the title :\