Re: Weird set -u error

[Greg Wooledge <greg@wooledge.org>]

On Sat, Aug 27, 2022 at 09:52:11AM -0400, Greg Wooledge wrote:
> I also can't explain this (still inside the ssh localhost session):
> 
> 
> unicorn:~$ (bash -c 'declare -p PS1')
> declare -- PS1="\\h:\\w\\\$ "
> unicorn:~$ (bash -cu 'declare -p PS1')
> /etc/bash.bashrc: line 7: PS1: unbound variable
> /etc/bash.bashrc: line 1: declare: PS1: not found
> 
> 
> Why would adding the -u option change whether PS1 gets unset?  Not a clue.

It turns out, this is a bit of an illusion.  It's not -u causing PS1 to
be unset.  bash -c unsets PS1 (because it's launching a non-interactive
shell) -- but since it's inside an ssh session and has shell_level < 2,
it *also* reads the startup files.

In the first example above, reading the startup files succeeds, because
there is no -u.

In the second example above, reading the startup files fails, because
of -u.  Thus, PS1 remains unset.  The part of the startup files that
would have set PS1 never gets executed.

I believe all of the behaviors have been explained now.