# Running code when a script exits

**URL:** <https://forum.elixirforum.com/t/running-code-when-a-script-exits/32340>\
**Category:** Questions\
**Tags:** mix-run\
**Created:** [June 14, 2020, 6:08am UTC](https://forum.elixirforum.com/t/running-code-when-a-script-exits/32340 "2020-06-14T06:08:30Z")\
**Posts on this page:** 1\
**Showing post:** 12

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**Author:** ![fxn](https://forum.elixirforum.com/user_avatar/forum.elixirforum.com/fxn/32/20274_2.png) [@fxn](https://forum.elixirforum.com/u/fxn)\
**Post date:** [June 15, 2020, 10:10am UTC](https://forum.elixirforum.com/t/running-code-when-a-script-exits/32340/12 "2020-06-15T10:10:31Z")

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### Temporary hack

Thanks @rvirding! That makes sense. Since Ctrl-G does not trigger a signal, I guess someone needs to be monitoring standard input to do something about it.

By now, I am moving on with a dirty solution, which is to monitor a file:

```elixir
defmodule Halter do
  @halter "halt"

  def run(on_halt) do
    if File.exists?(@halter) do
      File.rm(@halter)
      on_halt.()
      System.stop()
    else
      Process.sleep(1000)
      run(on_halt)
    end
  end
end

Halter.run(fn -> IO.puts("done") end)

```

You leave the script running, and `touch halt` whenever you want it to stop. Enough for my purposes right now.

That solution prints these noisy traces, so it is definitely not clean:

```plaintext
** (exit) exited in: GenServer.call(Mix.ProjectStack, {:get_stack, #Function<10.12591541/1 in Mix.ProjectStack.peek/0>}, :infinity)
    ** (EXIT) no process: the process is not alive or there's no process currently associated with the given name, possibly because its application isn't started
    (elixir 1.10.3) lib/gen_server.ex:1013: GenServer.call/3

```

`System.at_exit/1` is not invoked (that is why `run/1` above receives a callback), I do not know why.

### Is this a missing feature?

Not being able to do this easily surprises to me. It is a fundamental aspect of Erlang/OTP that you start applications and, symmetrically, shut them down orderly.

So, given that `mix run` starts the application by default, you’d expect that there would be interface to shut it down too, no? @josevalim is there a technical reason this is not in place? Or is it something that could be contributed?

---

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