[erlang-questions] Starting EShell via code

[Fred Hebert]

Gonna answer both emails at once here.

On Saturday, September 20, 2014, James Hague <james.hague@REDACTED> wrote:
> Under OS X Mavericks and Erlang/OTP 17 I can start a working EShell easily
> enough from code, but some keys don't behave the same as the default shell:
> no tab completion, no arrow key movement.
>
> What am I missing?
>

How are you starting things? Usually, tab completion and arrow movement
is done through a ping pong between edlin.erl and group.erl:

https://github.com/blackberry/Erlang-OTP/blob/master/lib/stdlib/src/edlin.erl
https://github.com/blackberry/Erlang-OTP/blob/master/lib/kernel/src/group.erl

The input and display of a few characters that are broken can be due to
having used the old shell (which didn't handle these and was implemented
in user.erl, an older and rarely used version of the shell:
https://github.com/blackberry/Erlang-OTP/blob/master/lib/kernel/src/user.erl)

I tried to document the general structure of the Erlang shell in
http://ferd.ca/repl-a-bit-more-and-less-than-that.html.

You can read my response to José below where I do mention a way that
appears to work decently to programatically start a shell.

On 09/20, José Valim wrote:
> Afaik there is no easy way to *correctly* start the shell after the
> VM boots because the user and group processes have already been registered.
> You always get a limited version of the shell.
> 

This can be specified by some special trickery by starting with -nouser,
which will start no shell, no user, etc. and then having to substitute
in your own mechanisms to try and handle it with the special file
descriptor {fd, 0, 1} (stdio, stdout) and {fd, 2, 2} (stderr), and
moving them around.

The problem there is that things may also depend on the tty program
being around.

Something similar is done with 'rebar shell' as a command, which
nevertheless hijacks the current IO stuff by killing it, and taking over
talking with the tty program -- though these are somewhat constrained by
virtue of running in an escript:
https://github.com/rebar/rebar/blob/master/src/rebar_shell.erl

That stuff still leaves a few things a bit wonky here and there from
what I've seen using it, but generally seems to do an okay job.


Regards,
Fred.