Re: the exquisite pain of signal handling in shell scripts

[Ralph Corderoy]

Hi Branden,

> > > It seems like the main difference between our signal handlers is that
> > > you do not reset the handler, and rely on exiting with a status
> > > greater than 127 to notify the shell that the process was killed with
> > > a signal.  I'm not sure that is reliable, or supposed to be.
> > 
> > Do you mean distinguish these two cases from a shell script using `$?'?
> > 
> >     $ sh -c 'kill $$'; echo $?
> >     Terminated
> >     143
> >     $ sh -c 'exit 143'; echo $?
> >     143
> >     $
>
> Yes.
...
> I suppose that in practice it may be that bit 7 of wstatus is
> typically the bit returned by the WIFSIGNALED() macro, but I wouldn't
> want to stake my life on it.
>
> The more of the Austin Group's time I see taken up with bizarre
> implementation differences in the shell, the more paranoid and less
> certain I get about what is reliable.

Scripts shouldn't use exit $n where n>=126 unless it's for one of the
reasons given in
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_21_18
which includes n>128 for signal n-128.

-- 
Cheers, Ralph.