What are the best practices for handling user input and form data in PHP to ensure security and data integrity?

To ensure security and data integrity when handling user input and form data in PHP, it is important to sanitize and validate all input data before processing it. This can help prevent SQL injection, cross-site scripting (XSS) attacks, and other security vulnerabilities. Using PHP functions like htmlspecialchars() and filter_var() can help sanitize input, while validating input against expected formats can help ensure data integrity.

// Sanitize user input using htmlspecialchars()
$name = htmlspecialchars($_POST['name']);
$email = htmlspecialchars($_POST['email']);

// Validate email input using filter_var()
if (filter_var($email, FILTER_VALIDATE_EMAIL)) {
    // Process the input data
} else {
    // Handle invalid email input
}