System.stop(1) does not return code to shell


I am developing an escript and want to return the code 1 to the shell in case of an error, so if my tool gets automated, the automation scripts can detect an error based on the returned code.

So, to keep it simply, we return right from the main function of my escript entrypoint module:

  def main(_args) do

Then after I run my generated escript:

$ echo $?

Am I right that there should be a 1 instead of a 0?

Here it works from IEx:

$ iex
Erlang/OTP 21 [erts-10.0] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe]

Interactive Elixir (1.8.0-dev) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> System.stop(1)
$ echo $?

So it may be a bug with escripts in Erlang/OTP? I would try to build a minimal erlang escript and see if you can reproduce it there. If so, that’s the bug. :slight_smile: System.stop(1) is init:stop(1) in Erlang.

How do you build and run that escript? Are you using a shell wrapper around it?

Can you perhaps provide a minimal project in GitHub that reproduces the issue? I never experienced any problems.

Yes, seems to fail in the erlang escript too:

~/Private/Code/Tests/erlang_escript_test$ cat escript_test
%% -*- erlang -*-
%%! -smp enable -sname factorial -mnesia debug verbose
main(_) ->
    io:format("simple example\n"),
~/Private/Code/Tests/erlang_escript_test$ ./escript_test
simple example
~/Private/Code/Tests/erlang_escript_test$ echo $?

I tried with…

defmodule Excript.CLI do
  def main(args \\ []) do
    {opts, _, _} = OptionParser.parse(args, switches: [halt: :boolean])
    if opts[:halt], do: System.halt(1), else: System.stop(1)

…and could definitely reproduce the error, see:

$ ./excript --halt
$ echo $?
$ ./excript
$ echo $?

As @Phillipp says… it’s an issue with erlang escripts.

1 Like

It’s actually already reported since 2014 :man_facepalming:

Ha, that’s a shame. I Just checked, System.halt(1) does work properly but it does not carefully shut down the VM. I assume it won’t cause any troubles in my case, but we can’t be sure about it.

Usually it is fine for escripts and sometimes even desired for faster shutdown. The difference is that System.halt() does not shutdown the applications supervision trees one by one. It just halts the system.


You can always manually shut down parts that need to be shut down cleanly before calling it though (just don’t shut down the kernel before you get a chance to call halt). :slight_smile: