Manual:CheckUsernames.php/en

Details
checkUsernames.php file is a maintenance script that is used to check that all usernames in the database ( table) are actually valid. Existing usernames can become invalid if   is altered or if  is changed.

Options
checkUsernames.php does not accept any option.

Usage
In case invalid usernames are found, the script returns the user_id and the username for each of the affected users.