Long story short, I've written a simple BASH script to control the brightness of a non-Apple external monitor using
ddcctl. It works, with a couple hacks.
It would be really cool if I could display a notification when the script is called, so the end user can be aware what the current setting is relative to min/max. I just found out about AppleScript's
display notification function, which is cool—but the notifications don't go away on their own. I also found this essay on BezelServices, which is also neat—but I'm trying to do simple scripting, not creating an entire application.