There is only so much you can do to make this portable to other database platforms such as Oracle. Reason is that Oracle handles things like databases and schemas much differently than mySQL.

In Oracle you will need to connect to each database/instance as a user/schema with DBA privileges and submit a query to list all of the users/schemas. Without an existing account and an existing database you won't get very far.

Actually, if you only wanted a list of databases/instances you could load and parse the /etc/oratab file. This file contains a list of all oracle databases on the host, along with their respective ORACLE_HOME locations, and whether or not they should startup or shutdown automatically. This would give you your database list but you'd still have to connect as a user to get a user list.

HTH