I haven't found a great solution yet. Here is some information that can help:

* Apparently there is a [solution](http://ubuntuforums.org/showthread.php?t=893467) for Ubuntu on MacBooks. 

* [Lab Tick](http://www.makeuseof.com/tag/control-your-macbook-keyboard-lights-with-lab-tick/) runs on OS X but unfortunately not command-line (nor open source).

* [`brightness`](https://github.com/nriley/brightness) is free software to control the display brightness.

This turns off automatic backlight in low light:

    defaults write com.apple.BezelServices kDim -bool false

This turns off keyboard illumination when computer is not used for 1 second:

    defaults write com.apple.BezelServices kDimTime -int 1

But ideally I would just turn off the illumination under all circumstances. And I haven't found a CLI solution for that - yet.