How can PHP be used to validate form fields before submitting data?

To validate form fields before submitting data in PHP, you can use conditional statements to check if the input meets certain criteria such as being non-empty, within a specific range, or matching a certain pattern. This can help prevent users from submitting incorrect or malicious data to your application.

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $name = $_POST["name"];
    $email = $_POST["email"];
    
    if (empty($name) || empty($email)) {
        echo "Please fill out all required fields.";
    } else {
        // Process the form data
    }
}