thesis: guixsd should provide /usr/bin/env

[Andy Wingo]

Hi!

I think GuixSD should follow NixOS's lead and provide /usr/bin/env.  The
reason is to support scripts that can run either on GuixSD or on some
other system.  For example instead of:

  #!/bin/bash

we can do

  #!/usr/bin/env bash

So we just need /usr/bin/env in the root and nothing else.

Alternately, I am not sure if this would work but we could make a form
of "guix environment" which populates a profile that is mounted at /usr
in a container.  That would allow many more non-Guix tools to run.

WDYT?

Andy