How can PHP developers securely handle user input in forms to prevent vulnerabilities?

PHP developers can securely handle user input in forms by using functions like htmlspecialchars() to prevent cross-site scripting attacks. They should also validate and sanitize input data before processing it to prevent SQL injection attacks. Additionally, using prepared statements when interacting with databases can help prevent these vulnerabilities.

// Example of handling user input in a form securely
$user_input = $_POST['user_input'];

// Sanitize the input
$sanitized_input = htmlspecialchars($user_input);

// Validate the input
if (strlen($sanitized_input) > 0) {
    // Process the input data
    // For example, save it to a database
} else {
    // Handle invalid input
    echo "Invalid input";
}