What is the purpose of the include_once function in PHP?

The include_once function is used to include and run a specified file during the execution of the current script. It inserts the content of the specified file into the current script, allowing it to include other PHP files, HTML files, text files, and so on.

Unlike the include function, the include_once function checks if the file has already been included before including it. If it has been included before, it will not include it again, preventing errors caused by including the same file multiple times.

The syntax for using the include_once function is as follows:
include_once ‘filename.php’;

In this case, ‘filename.php’ is the path and name of the file to be included.