HUD Overlay functionality as a script.

Does anyone know how I can simulate this as a command-line tool?

The easiest would be do use the btt:// url scheme:

open "btt://trigger_action/?json={\"BTTPredefinedActionType\" : 254, \"BTTHUDActionConfiguration\" : \"{\\\"BTTActionHUDDetail\\\":\\\"sub-test\\\",\\\"BTTActionHUDTitle\\\":\\\"title-test\\\",\\\"BTTActionHUDDuration\\\":1,\\\"BTTActionHUDBackground\\\":\\\"34.428670, 38.720695, 38.720066, 213.662109\\\",\\\"BTTActionHUDSlideDirection\\\":0}\"}"

It looks a bit weird because of the escaping. Copy &. paste the whole thing into terminal

Thanks for the reply. Though I don't understand how pasting this in the terminal will trigger the HUD Overlay. Am I missing something?

I'm trying to play with this at the moment. But not quite sure how to make it work either...

The command I pasted should trigger the HUD while BTT is running - does this not work for you?