Terminal setup, teardown and the handful of ANSI sequences the runtime needs.

Getting keys one at a time

Putting the terminal in raw mode is not enough. When the BEAM finds a usable terminal it starts its own line editor (prim_tty), which reads stdin, echoes what you type and hands the reader a whole line once you press Enter — no matter what stty says. So raw mode is asked for the way OTP intends: :shell.start_interactive({:noshell, :raw}), which switches that driver into raw mode and delivers each character as it is typed.

That path needs a VM started with -noshell, which is how mix run and release start scripts run. Where it is not available — inside IEx, or on OTP older than 26.2 — we fall back to stty against /dev/tty, which is enough when the BEAM has not claimed the terminal (no TERM, output redirected).

Ctrl-C

In raw mode prim_tty still treats byte 3 as the emulator break, popping the BREAK menu over the UI. The VM flag +Bc makes it a normal byte instead, so the runtime can act on it. Pass it however the application starts:

elixir --erl "+Bc" -S mix run --no-halt
ELIXIR_ERL_OPTIONS="+Bc" mix run --no-halt

In a release, put +Bc on a line of its own in rel/vm.args.eex.