If you don't receive oath letter before oath, go to the oath and they will be able to reprint a copy of the oath letter for you. You'll still be able to complete oath if you've already been scheduled but never received oath letter.
Thank you very much for all your help,
I have another question. Iam planning to travel to Tunisia in north Africa right after the ceremony. Can I apply for my U.S passport at the U.S embassy in Tunisia ? Do you think it is possible ?