PHP Sessions

To store information about, or change settings for a user session use a PHP session variable. Session variables hold information about one single user, and are available to all pages in one application.
Working with an application is much like a Session. But there is one problem on the internet. The web server does not know who you are and what you do because the HTTP address doesn't maintain state.
A PHP session allows you to store user information on the server for later use. However this information is temporary and will be deleted after the user has left the website. For permanent storage you should to store the data in a database.
UID is a unique id which is created by session. Sessions store variables based on this UID.

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