How can PHP developers ensure that their code is robust and error-free when dealing with external input like command line arguments?

When dealing with external input like command line arguments in PHP, developers can ensure their code is robust and error-free by validating and sanitizing the input before using it in their code. This can help prevent security vulnerabilities such as SQL injection or code injection attacks. One way to achieve this is by using PHP's built-in functions like filter_var() to validate input and htmlspecialchars() to sanitize input before processing it.

// Validate and sanitize command line arguments
if(isset($argv[1])) {
    $arg = filter_var($argv[1], FILTER_SANITIZE_STRING);
    
    // Use the sanitized input in your code
    echo "Command line argument: " . $arg;
} else {
    echo "No command line argument provided.";
}