Script to view and count number of sessions to the database

REM: Script to view and count number of sessions to the database
REM: NOTE: PLEASE TEST THIS SCRIPT BEFORE USE.
REM: Author will not be responsible for any damage that may be cause by this script.
REM:*****************************************

set pages 100
set lines 3000

col machine format a25
col username format a15
col program format a25
break on 1;

set heading off;
select
'Sessions on database '|| d.name ||' having instance name '|| i.instance_name
from v$database d,v$instance i;
set heading on;

compute sum label 'Total Sessions' of sessions on 1
select
1,username,machine,program,count(*) sessions
from v$session
group by username,machine,program
order by username,sessions desc;