A session creates a file in a temporary directory on the server where registered session variables and their session id are stored. This data will be available to all pages on the site amid that visit.

The area of the temporary record is controlled by a setting in the php.ini document called session.save_path.

At the point when a session is begun following things happen -

1. PHP first makes two duplicates of one of a kind session id for that particular session of the client which is an arbitrary string of 32 hexadecimal numbers, for example, 3c7foj34c3jjhkyepop2fc937e3443.
2. One copy of unique session id automatically sent to the user?s computer for the sake of synchronization in future ahead, and one copy is being maintained at server side till the session is running.
3. Whenever you want to access the page of website or web app, then session id of the current user will be associated with the HTTP header, and that will be compared by the session id which is being maintained at the server. After completing the comparison process, you can easily access the page of the website or web app
4. A session ends when the user closes the browser, or after leaving the site, the server will terminate the session after a predetermined period, commonly 30 minutes duration.

PHP session_start() function is used to start the session. It starts new or resumes the current session. It returns the current session if the session is created already. If the session is not available, it creates and returns new sessions.

The main difference between session and cookie is that cookies are stored on user's computer in the text file format while sessions are stored on the server side.

Cookies can't hold multiple variables, on the other hand, Session can hold multiple variables.

You can manually set an expiry for a cookie, while session only remains active as long as browser is open.

PHP fopen() function is used to open file or URL and returns resource. It accepts two arguments: $filename and $mode.

Syntax:

PHP provides various functions to read data from the file. Different functions allow you to read all file data, read data line by line, and read data character by character.

PHP file read functions are given below:

• fread()
• fgets()
• fgetc()

PHP fwrite() and fputs() functions are used to write data into file. To write data into a file, you need to use w, r+, w+, x, x+, c or c+ mode.

The unlink() function is used to delete a file in PHP.

You should just run the PHP command line interface (CLI) and specify the file name of the script to be executed as follows.

The move_uploaded_file() function is used to upload file in PHP.