Looking at it closer, you may notice there is no built in way to get any "critical", "warning" or "ok" status back by setting limits. So even if we got the output we wanted, such as, "2% free" we could not be able to get a warning in nagios. All you would get is the output displayed. It would take a great deal of re-writing this script to get it to work as it should work. I'm not even sure what it is good for.
It might take a bit of work, but I'd just setup barebones nagios on each of the machines that you are interested in. That's what I did. It's easier for your "main" nagios machine to process 1000 passive checks, than 1000 active checks anyway.
I have nagios setup on several Solaris machines to check diskspace, cpu, Oracle tablespace free, 50 or more "is a process running" etc. It's well worth the effort and the guys at work just love what nagios is checking.