How do I search to see if a MySQL user exists on the system?
Thanks to @matthewh's answer I managed to compose a query that would work when searching through a large number of users: 

use mysql;
select  User, Host from  user where User like 'user%';


Note: &lt;user&gt; is whatever component of the username you need to search for, you may need a % on both sides if you don't know the start of the username, also &lt;> are merely to note the variable, don't include them in an actual query, unless the username includes &lt; or >.