how to assign separate folder for each user........

[asheesh]

hi
I am using XAMPP for linux . i have created a web page for uploading assignments. there are so many student who upload assignments. to upload assignment student have to go through a login page consisting of ID and PASSWORD. after this file uploading page comes to upload the file.
now problem is: I want to save these files in separate folder,i.e., for each user there is folder at server in which his/her file must be stored.HOW i did it in PHP