How can including external files in PHP affect the scope of variables and functions, and what precautions should be taken to ensure proper functionality?

Including external files in PHP can affect the scope of variables and functions by introducing them into the global scope of the script. To prevent conflicts and ensure proper functionality, it's important to use include_once or require_once to avoid redeclaring functions or variables. Additionally, using namespaces and properly organizing code can help isolate variables and functions to prevent unintended interactions. 

// Example of including an external file with proper precautions
require_once 'external_file.php';

// Code within external_file.php
namespace MyNamespace;

function myFunction() {
    // Function code here
}

Keywords

PHP include require scope variables

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