How do i know a mac needs to restart?

Is there a way to figure out from a script whether a Mac needs to reboot? A file, the presence or contents of which i could monitor perhaps?

I'm looking for an equivalent to the file /var/run/reboot-required found on my Ubuntu boxen. My use case would be to centrally monitor my servers (and perhaps laptops) using Puppet, collectd or... well, something.

~llaurén