Need to connect to an oracle database?
Download Oracle SQLcl
https://www.oracle.com/tools/downloads/sqlcl-downloads.html
Extract the zip
Login using this command
> SQL username@//server:1521/databasename
Show what user you are
SQL> show user
Now check what version of oracle you're on
SQL> select BANNER from v$version;
Display the instance you're on
SQL> select INSTANCE_NAME, HOST_NAME, VERSION from v$instance;
Check what database you're connected to
SQL> select name from V$database;
List all user accounts
SQL> select * from all_users;