Important built-in functions for PHP learning

1. require_once () function

This function contains and executes the specified file during script execution, similar to the Require statement, except that if the code in the file is already contained, it will not be included again.

The require_once () function guarantees that, during script execution, for cases where the same file is included more than once, you want to make sure that it contains one time to avoid function redefinition, variable re-assignment, and so on.

As with the include () function, this function returns True if it executes successfully.

Also, we should note that the behavior of require_once () and include_once () may not be expected in a case-insensitive operating system like window.