Input is lost with erl -noshell -eval "shell:start_interactive()."

[josevalim]

When the shell is started interactively (because it has to be started by Elixir, rebar3, or something else), any previous input is lost (i.e. not read as part of the shell). It can be reproduced with these two scripts (save them to a file, chmod +x FILE, and run them):

Working script

#!/usr/bin/expect
spawn erl
send "\"Hello World\".\n"
interact

The script above will send "Hello world" to the shell.

Non-working script

#!/usr/bin/expect
spawn erl -noshell -eval "shell:start_interactive()."
send "\"Hello World\".\n"
interact

The script above will not send "Hello world" to the shell.

Expected behavior

Perhaps it makes sense to read any buffered input when starting the shell? I am also fine if this is expected somehow, but I thought I would report.

Affected versions

Erlang/OTP 26. Note this works fine if I use -user but I think starting the shell interactively is a better experience. :)

Thank you.

[garazdawi]

You need to use -noinput in such scenarios. The -noshell option is for when you want to start a system without a shell and then use io:read or something like that to get the data.

[josevalim]

I am not sure if that's always possible. I assume, for example, rebar3 starts with -noshell because a task may need to read some input, but particular commands such as rebar3 shell may start the shell.

Feel free to close this anyway, if it is not worth it though. I just need to know the plan so I can document it. :)

[garazdawi]

If you need to read input then you can do shell:start_interactive(noshell) after the system was started with -noinput.

[josevalim]

Got it, thank you!