bug#53355: guix shell --check: confusing error message

[Chris Marusich]

Hi Ludo,

Ludovic Courtès <ludo@gnu.org> writes:

> So you confirm that a single “echo” is not enough, right?

I didn't test one specifically. It might work with just one, but it did
work with three.  If we want to proceed with the "echo" approach, let me
know and I'll test just one echo to see if that is reliable enough.

> Perhaps we should unroll the ‘for’ loop for portability, to be on the
> safe side.  Initially I tested with Bash, Zsh, and Fish:
>
>   https://issues.guix.gnu.org/51285#0-lineno49
>
> I think Fish has a very non-POSIX syntax, hence the suggestion to avoid
> ‘for’.

I see.  Yes, I'll do that if we decide to go with the echo-based
approach.

> I realized that setting PS1 could interfere with the logic below that
> checks for PS1.  And since it doesn’t seem to help, perhaps we can
> remove “PS1=;”?

I recall that I tried removing PS1, and I still had trouble.  I believe
it was because even if we unset PS1 as the very first command we do, the
original prompt is still printed.  Foreign distros usually set PS1 to
something, and whatever that is will be printed before we have a chance
to input any commands.  It's hard to avoid that in general.

> Thoughts?

One alternative method I tried successfully in a variety of shells was
to use shell redirection (see attached).  I like this approach.
However, this will only work in shells that support redirection.  I
recall testing with bash, ash (busybox's shell), dash, zsh, fish, ksh,
and csh.  I recall that only csh failed, since it doesn't support
redirection.

I personally like the attached patch better than what I proposed
earlier.  The earlier patch just echoes a few times.  Presumably, it
only works because the PS1 prompt is likely (but not guaranteed) to be
emitted before the last of the echo commands finishes printing.  I'd
rather just control the desired output and ignore PS1 entirely, and that
is what the attached patch accomplishes using FDs.  However, if support
for shells without redirection is a requirement, then maybe the original
hack (echo a few times) is OK, or perhaps we need something else.

How would you like to proceed?  Is it OK to rely on shell redirection?

-- 
Chris

PGP: https://savannah.gnu.org/people/viewgpg.php?user_id=106836

0001-environment-Prevent-PS1-from-clobbering-output-in-ch.patch
Description: [PATCH] environment: Prevent PS1 from clobbering output in 'check'.

signature.asc
Description: PGP signature