How to shut down VirtualBox / Vagrant from CLI

So you need to stop one or more running VirtualBox instances that you may have started and are hanging around. Here are a few helpful commands:

List all running machines (returns name and UUID)
VBoxManage list runningvms

Stop running VMs by "hibernating" them (recommended to avoid data loss)
VBoxManage controlvm <name|uuid> savestate

Poweroff running VMs (not recommended because we may lose data in the guest)
VBoxManage controlvm <name|uuid> poweroff

Use ACPI in an ACPI-aware guest OS (preferable to poweroff for graceful shutdown of guests)
VBoxManage controlv m <name|uuid> acpipowerbutton

How to repair Homebrew after OS X upgrade

I was getting the following error when running brew after the latest upgrade to OS X (El Capitan).

 /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby: bad interpreter: No such file or directory

I couldn't even run brew update - arg.

This is what I did to correct the issue - git to the rescue!

cd /usr/local/Library

git pull origin master

git pull will throw an error if you have changes in the directory (/usr/local/Library). If so, you'll have to fetch the master branch and perform a hard reset.

git fetch --all

git reset --hard origin/master

You should be able to now use brew again - hurrah!

Note: in the event you installed Homebrew as a non-root user, you'll need to cd to /Users/non-root-user-rname/homebrew/Library instead of /usr/local/Library.