What is the function of the code snippet using ereg in this PHP forum thread?

The issue in this PHP forum thread is related to validating a user's input against a regular expression pattern using the `ereg` function. To solve this issue, we can update the code snippet to use the `preg_match` function instead, as `ereg` is deprecated in PHP 5.3.0 and removed in PHP 7.0.0.

// Original code snippet using ereg
if (ereg("^[a-zA-Z0-9]+$", $input)) {
    // Valid input
} else {
    // Invalid input
}

// Updated code snippet using preg_match
if (preg_match("/^[a-zA-Z0-9]+$/", $input)) {
    // Valid input
} else {
    // Invalid input
}