CLI Application with OTP - application:start/2 doesn't work

I completely rely on the OTP principles. That’s why I use applications, gen_server and stuff overall and it works for me very well. There is only one issue with CLI applications:

If all code is started with applications and application:start/2 is supposed to start a supervisor than it doesn’t work in this case. One application is meant to be the main controller of the CLI application that only calls server functions.

Following solutions don’t work:

  • run the controller in start/2 and stop the whole program/release(?) with init:stop(). This will raise bad return value ok from almmain_app:start(normal, [])
  • manually patch the boot script to eval code to start the controller in a separate module
  • use rebar3 to provide an additional entry point. At least I couldn’t find any configuration option

I am curious if OTP is only used for pure server applications.

If you want to do CLI applications, try escripts (with argparse for processing arguments).

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Hallo acema,

I am also very new to elixir and CLI applications.

This is what I found on how to run an application and provide a needed Supervisor:

defmodule Hello do
use Application
def start(_type, _args) do
IO.puts(“Hello elixir”)
Supervisor.start_link(, strategy: :one_for_one)

Erlang is fine-ish for CLI tools, I’ve written a number of them. You can use escripts or just shell wrappers that run the code with erl -noshell -pa ... -run .... A few years ago I had to work around escript crash dumps going to the wrong output (stdout instead of stderr) but that’s fixed now.
As to OTP principles, I use gen_servers where apppropriate but not supervisors, and therefore not full-on stateful applications (they’re all library applications). A compiler say has little use for supervising the process holding lexer state.