In what ways can regular expressions in PHP be utilized for string validation purposes?

Regular expressions in PHP can be utilized for string validation purposes by defining patterns that the input string must adhere to. This can be useful for validating email addresses, phone numbers, passwords, or any other specific format required. By using regular expressions, developers can easily check if the input string matches the desired pattern, ensuring data integrity and security.

// Validate email address using regular expression
$email = "example@example.com";
if (preg_match("/^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/", $email)) {
    echo "Email address is valid.";
} else {
    echo "Invalid email address.";
}