What are some common methods for validating user input, such as postal codes, in PHP?

Validating user input, such as postal codes, is essential to ensure data integrity and security in PHP applications. Common methods for validating postal codes include using regular expressions to match the expected format of the postal code, using built-in PHP functions like `preg_match()` to validate the input, or using third-party libraries for more complex validation rules.

// Example of validating a postal code using a regular expression
$postalCode = "12345"; // User input
$pattern = "/^\d{5}$/"; // Regular expression pattern for a 5-digit postal code
if (preg_match($pattern, $postalCode)) {
    echo "Postal code is valid";
} else {
    echo "Invalid postal code";
}