The sqlplus executable isn't in your PATH specification. Make sure that in your environment the following variables are correctly set:
Code:
ORACLE_HOME
ORACLE_SID
PATH (must include $ORACLE_HOME/bin)
Then you can connect with sqlplus.
Sourcing the oraenv like invinzin21 said could be a starting point, but I think that oraenv doesn't set the PATH variable for you.
Otherwise, you must provide the full path to the sqlplus executable:
Code:
$ORACLE_HOME/bin/sqlplus user/pass
