On Sat, Oct 12, 2024 at 21:43:39 -0400, Karl Vogel wrote:
> >> In previous messages:
> >
> > system('systemctl', '--quiet', [...] , @start_units) == 0
> > or die("Could not execute systemctl: $!");
> >
> > Could not execute systemctl: at /usr/bin/deb-systemd-invoke line 148.
>
> See the ":" followed by two spaces? Unlike systemctl, well-behaved
> programs set "errno" when they puke, and that setting is turned into
> a more-or-less useful error message like "Permission denied".
> "$!" would have held that message.
I don't think this is correct. A *function* can set errno (a global
variable in C), in addition to returning a value. A process can't,
unless there has been some major change to the Unix process model that
I've missed.
A failing process can return an exit status greater than 0 to indicate
that something has gone awry, but that's it. There's no other mechanism
available (that I know of) to pass information back to the parent
process. The closest thing would be that the parent can detect whether
the child was killed by a signal, which is not relevant here.
