How can a PHP developer ensure that their code adheres to best practices regarding file inclusion and security?

To ensure that PHP code adheres to best practices regarding file inclusion and security, developers should avoid using user input directly in file inclusion functions to prevent directory traversal attacks. Instead, they should sanitize and validate user input before including files. Additionally, developers should use absolute file paths rather than relative paths to include files securely.

// Sanitize and validate user input before including files
$user_input = filter_input(INPUT_POST, 'file', FILTER_SANITIZE_STRING);
$allowed_files = ['file1.php', 'file2.php', 'file3.php'];

if (in_array($user_input, $allowed_files)) {
    include_once('/path/to/secure/directory/' . $user_input);
}