You can install babushka on your system, no matter what state it's in, using babushka.me/up. That's a script that knows enough to install ruby if required (babushka's only runtime dependency), and then download a temporary babushka that knows how to do the proper install.
New Macs have curl, stock Ubuntu has wget.
bash -c "`curl -L babushka.me/up`"bash -c "`wget -O - babushka.me/up`"It's the perfect way to get started on a new server, or on your new laptop, since it can literally be the first command you run on the machine.
If you'd prefer to install manually or just check out the code, check the github page for the repo URL.