Heh... This is funny because what I'm writing is a Nagios plugin, or more accurately, a bunch of plugins.

I've got a home-made protocol for sharing info about a host. It shares a lot of different stuff, like disk usage, what version of dhcpd am I running, or whatever I want. That means my disk-usage nagios plugin will have the exact same user interface, data gathering interface and data output interface as my correct-version-of-dhcpd plugin. The only difference is the bit that checks disk usage, or checks the dhcpd version.

So, I'm thinking I'll write a script that handles the user interface (command args etc...), data gathering interface (getting data from my home-brew info server) and data output (nagios style output). The pass/fail logic will be handled by plugins.