How to run sqlplus

To run sqlplus you need 3 env var set. Set them as follows if they are not set already. ( you can check if they are set by doing "echo $ORACLE_SID" for example to see if your SID is set. )

export ORACLE_HOME=<your Oracle Home>
export PATH=%ORACLE_HOME%\bin;%PATH%
export ORACLE_SID=<your SID>

Then run the following at the command line to start sqlplus.
sqlplus /nolog

This starts sqlplus with no user logged in.