[chef] How to tell if Chef is running?

[Noah Gibbs < >]

Is there a standard way to tell if your (ruby) code is being invoked 
(indirectly) by a Chef run?  In this specific case the code is executing in a 
RubyGems pre-install hook.

Semi-relatedly, Chef seems strongly aimed at being run to configure the 
machine, and then mostly not run again on the same node except to add more 
software.  For example, there aren't a lot of uninstall-based resources, I 
don't see an obvious way to "reverse" a cookbook, few cookbooks seem written 
to work incrementally or in stages, etc.  Is that pretty much how it's 
intended, or am I missing something?

To be fair, I haven't come up with a good scenario yet for why you'd want to 
run it on a more continuous basis (at least, not one where you couldn't do it 
better in some other way).  But it's odd because a lot of the individual 
resources seem to be kind of incremental in feel (specify how many backups to 
make, specify that you're syncing the git repository rather than just 
creating it, etc) -- almost as though they're meant for repeated use as a 
deployment tool, for instance.  But the cookbooks don't seem to be written 
the same way.  It's slightly confusing.