change my sql prompt

I want to use my username and my SID as a Prompt, and here is a condition, that I m using my single Oracle Home for the two databases both are on the 10g, and here what I needed
1- when I login to the database it asks for the database name like "Enter the database name Prod1 - ?
2- then it checks from which database I have logged in like from Prod1 or Prod2 and then it shows me the sql command prompt like "username@prod1>"

I am using my glogin.sql file for login to the database. Is any body have a solution to edit my glogin.sql file for doing all these task.
Thanks for ur support

If you are using 10g or above put the folowing in your glogin.sql file.

set sqlprompt "_USER'@'_CONNECT_IDENTIFIER _PRIVILEGE> "