What is the purpose of using regular expressions in PHP, and what are the potential pitfalls when using them?

Regular expressions in PHP are used to search, match, and manipulate text based on patterns. They are powerful tools for string manipulation and validation. However, when using regular expressions, it's important to be careful with complex patterns as they can be difficult to read and maintain. Additionally, improper use of regular expressions can lead to performance issues and security vulnerabilities.

// Example of using regular expressions in PHP to validate an email address
$email = "example@example.com";

if (preg_match("/^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/", $email)) {
    echo "Email address is valid.";
} else {
    echo "Email address is not valid.";
}