Shutdown all running Vagrant boxes

That's pretty sweet. Although I've not ever used the $F array. Is that a file arguments array of some kind?

$F is a predefined variable when you run ruby -a. here's more documentation on ruby predefined variables:
http://www.tutorialspoint.com/ruby/ruby_predefined_variables.htm

That might be a good protip on it's own! :D

More UNIX-ly variant:

vagrant global-status | awk '$3 == "running"{print $4}' | xargs -I '{}' sh -c 'cd "$1" && vagrant halt'

At first I liked this, but a quick check by running "vagrant global-status" when I had two separate Vagrant directories running one instance each shows only one instance. This is on OSX Yosemite (10.10), VirtualBox 4.3.18r96516 and Vagrant 1.6.5.