How to run a shell script in nagios repeatedly



I am interested in using nagios.
My problem is :
I would like to execute a shell script program in nagios repeatedly with some time period.
I don’t want to keep this script(what ever i required for execute) in /etc/crontab file.I would like to run a script with nagios only.

I am using Nagios 2.6, plugins are 1.4.0.

Please help me to solve this problem,Give detailed information on how to overcome this problem.