Run query every 5 minutes

Please find the below query:

select count(*) from v$session;

This has to be run on the database every 5 minutes. What is the right way to achieve this? The query has to be run every 5 minutes on the same sql*plus screen. Instead of pressing "/" every minute, I wanted to understand if there is a way. Database/Server details:

SQL> select * from v$version;
Oracle8i Enterprise Edition Release 8.1.7.4.0 - 64bit Production

SQL> !uname -a
HP-UX ap12121 B.11.11 U 9000/800 ap12121 unlimited-user license