[oracle@data ~]$ echo $ORACLE_SID
ORCL
[oracle@data ~]$ sqlplsus orcl_user@ORCL
-bash: sqlplsus: command not found
[oracle@data ~]$ sqlplus orcl_user@ORCL

SQL*Plus: Release 10.2.0.1.0 - Production on Wed Oct 17 09:29:16 2007

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

Enter password:
ERROR:
ORA-12154: TNS:could not resolve the connect identifier specified


Enter user-name: