Are there any specific guidelines or recommendations for calling external PHP files within a main script to achieve specific functionalities?

When calling external PHP files within a main script to achieve specific functionalities, it is recommended to use include or require functions in PHP. These functions allow you to include the contents of a PHP file into another PHP file, enabling you to reuse code and modularize your application.

// Include an external PHP file to achieve specific functionality
require 'external_file.php';