How can preg_match be used to validate the format of a user-generated input in PHP?

To validate the format of a user-generated input in PHP, you can use the preg_match function to check if the input matches a specific pattern or regular expression. This can be useful for ensuring that user inputs such as email addresses, phone numbers, or other data follow a certain format. Example PHP code snippet: 

$user_input = $_POST['user_input']; // Get the user input from a form

// Define the pattern to match (e.g. email address format)
$pattern = '/^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/';

// Use preg_match to check if the user input matches the pattern
if (preg_match($pattern, $user_input)) {
    echo "Input is valid.";
} else {
    echo "Input is not valid.";
}

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