What are the best practices for handling user input from a form in PHP?

When handling user input from a form in PHP, it is crucial to sanitize and validate the data to prevent security vulnerabilities such as SQL injection or cross-site scripting attacks. Use functions like htmlspecialchars() to sanitize input and filter_input() to validate input against specific criteria like email or URL format. Additionally, always use prepared statements when interacting with a database to prevent SQL injection attacks. 

// Sanitize and validate user input from a form
$user_input = $_POST['user_input'];

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

// Validate input
if (filter_var($sanitized_input, FILTER_VALIDATE_EMAIL)) {
    // Input is a valid email address
    // Proceed with further processing
} else {
    // Invalid input, handle accordingly
}

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