Re: crashes when setting COLUMNS=0 or 1

[Peter Stephenson <Peter.Stephenson@xxxxxxx>]

On Tue, 26 Jun 2012 00:30:42 -0700
Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx> wrote:
> So, interesting side-effect:  If my patch for IPDEF5 is applied, then
> settings of COLUMNS and LINES get propagated through to the tty driver
> and can end up affecting the behavior of the parent shell (or anything
> else that's using the terminal where those values were changed), even
> after the shell where the assignments were made has exited.
> 
> E.g. (COLUMNS=20) in a subshell will change the tty driver which will
> signal the parent shell which will pick up the change and set its own
> column width to 20.  This is the only case I can think of where a
> parameter assigned in a subshell can behave this way.

That's not necessarily always a problem.  The parent is in case subject
to such changes asynchronously via SIGWINCH.  The fact that it's getting
the value a different way shouldn't make matters worse in general.

Where it's unhelpful is if you're setting COLUMNS not because anything
has changed but as a temporary trick for some utility that tests it and
truncates.  Then you wouldn't want the change to propagate back.

This is going to be niggling if it means these two have different
effects:

COLUMNS=20 ls
(export COLUMNS=20; ls)

since they look as if they ought to be similar.

Howeve, I'm not sure what can reasonably be done.  Restoring COLUMNS on
exit from a subshell doesn't seem a particularly clean thing to do, but
might work in most cases.

-- 
Peter Stephenson <pws@xxxxxxx>            Software Engineer
Tel: +44 (0)1223 692070                   Cambridge Silicon Radio Limited
Churchill House, Cambridge Business Park, Cowley Road, Cambridge, CB4 0WZ, UK


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