Sqlplus prompt

$ORACLE_HOME/sqlplus/admin/glogin.sql

Method 1:
-- Default for XQUERY
COLUMN result_plus_xquery HEADING 'Result Sequence'

-- Default for pagesize
set pagesize 1000
-- Default Instance name in SQLPROMPT
set termout off
define iname=idle
column instance_name new_value iname
select instance_name from v$instance;
set sqlprompt "&iname> "
set termout on

Method 2:
SET SQLPROMPT "&_user'@'&_connect_identifier>"