Re: Debian bug #822605: SIGPIPE not handled in "echo >", terminates shell

[Chet Ramey]

On 3/22/24 2:02 AM, Gioele Barabucci wrote:

> > > For various reasons. First of all, because it confuses users (there are 
> > > various bug reports in Debian for this specific issue).
> > >
> > > More technically, because non-builtin commands are treated differently, 
> > > for example /bin/echo (from <https://bugs.debian.org/423207>):
> >
> > There's been a fair amount of (inconclusive) discussion on the POSIX
> > mailing list about this issue at various points, but not enough reason
> > to change the way bash has always behaved.
>
> Dear Chet, thanks you for your reply. Do you have a link or two to these 
> discussions that I can add to the Debian bug reports to explain why they 
> will be marked as "wontfix"?

The one I can find looking quickly is 
https://www.austingroupbugs.net/view.php?id=789; that one lasted for years.

which is a discussion about `pipefail' but includes comments about setting
SIGPIPE to SIG_IGN with trap if you don't want it to affect the exit
status.

There was also a May, 2016 discussion, but I don't know where the austin-
group mail archives are kept. That one was inconclusive, but did note that
there are a number of pieces of state that can cause differing behavior
when a builtin is executed (e.g., resource limits).

If you want to insulate a script against this, there are various ways to
discover whether or not a utility is a builtin (e.g., type) and to make
sure you always run something external (e.g., full pathnames or enable
to disable the builtin).

> > For example, there is plenty of code that expects the shell to exit when
> > you hit it with, say, a SIGHUP while it's executing a builtin, or if you
> > hit a non-interactive shell with a SIGTERM during a builtin, because that's
> > how shells have always behaved.
>
> I'd argue (but I assume it has already been done in the aforementioned 
> discussions) that the SIGPIPE comes from a command being run in a pipeline 
> provided by the user, while these other signals come from an "external" 
> source (the user? other programs?).

There's no real difference. The shell gets a signal and either handles it
or does not. From the script's perspective, it doesn't matter what
originates it.

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/

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