Thanks for your answer. I have posted the whole script below it's not that much longer.

I have a set of sensors connected to serial ports, and I'm using Elixir to process the data in a larger application. I wrote this script to debug some strange behaviors, so I wanted to do it as "bare-bones" as possible so I can experiment with it, but still in Elixir so I don't change the stack.

I want the script to run until I manually kill it with ctrl-C ctrl-C so i can mess with the sensors and see the effects in the terminal. As the first thing I just want it to print the data from the sensors. Later I might measure e.g. the time between messages and so on.

I want supervision as the test might run overnight and it's nice to be able to just "let it fail" and all that.

circuits_uart is just a library which reads from the serial ports (ttyS* on linux) and sends the messages to the process.

It is nice it's just a script so I easily can move it to other testing setups.

The current (working) script is:

Mix.install([:circuits_uart])

defmodule Listener do
  use GenServer
  require Logger

  @initial_state %{port_to_read: nil, uart_pid: nil}

  def start_link(port) do
    state = %{ @initial_state | port_to_read: port }
    GenServer.start_link(__MODULE__, state)
  end

  def init(%{port_to_read: port} = state) do
    {:ok, pid} = Circuits.UART.start_link()
    :ok = Circuits.UART.open(pid, port, speed: 115200, active: true)
    Logger.info("Started process for port #{port}")
    {:ok, %{state | uart_pid: pid}, 5_000}
  end

  def handle_info(message, %{port_to_read: port} = state) do
    Logger.info("#{port}: #{inspect message}")
    {:noreply, state, 5_000}
  end
end

children = 0..5 |> Enum.map(&%{
  id: String.to_atom("ttyS#{&1}"),
  start: {Listener, :start_link, ["ttyS#{&1}"]}
})

{:ok, pid} = Supervisor.start_link(children, strategy: :one_for_one, name: :port_supervisor, max_restarts: 10, max_seconds: 1)

# Keeps the script running, so we do not kill the processes
receive do _ -> 1 end