What security considerations should be taken into account when using PHP functions like check_mobile() and including external files in PHP scripts?

When using PHP functions like check_mobile() and including external files in PHP scripts, security considerations should be taken into account to prevent vulnerabilities such as code injection or unauthorized access. It is important to sanitize user input before using it in functions like check_mobile() to avoid potential exploits. Additionally, when including external files, make sure to validate and sanitize the file path to prevent directory traversal attacks.

// Sanitize user input before using it in check_mobile() function
$user_input = $_POST['user_input'];
$clean_input = filter_var($user_input, FILTER_SANITIZE_STRING);
$mobile_status = check_mobile($clean_input);

// Validate and sanitize file path before including external files
$file_path = $_GET['file_path'];
$clean_file_path = filter_var($file_path, FILTER_SANITIZE_URL);
if (strpos($clean_file_path, 'allowed_directory/') === 0) {
    include($clean_file_path);
} else {
    echo "Invalid file path";
}