Determine OS X keyboard layout (“input source”) in the terminal/a script?

Question

I would like to determine the OS X keyboard layout (or \"input source\" as OS X calls it) from the terminal so that I can show it in places like the tmux status bar.

Answer 1

This question led to the creation of the keyboardSwitcher CLI Tool: https://github.com/Lutzifer/keyboardSwitcher

Though similar to the already mentioned https://github.com/myshov/xkbswitch-macosx this has additional features, e.g. the list of Layouts is not hardcoded and thus can also support third party layouts (e.g. Logitech) and supports installation via homebrew.