Re: `jobs` shows output even when nothing has been started in the background

[Ajeet D'Souza]

Hey Chet,

Thanks for the quick reply. I have some follow-up questions:

   - Is there an elegant way I can start an external process without it
   showing up under jobs, even on affected versions? My current best idea
   is: (_="$(/bin/echo)"; jobs -l)
   - Is there an elegant way I can get the correct number of jobs, even on
   affected versions? My current best idea is to run jobs once before doing
   the count: (jobs &> /dev/null; jobs | wc -l)

I'm trying to keep the behaviour consistent across all versions of Bash.

Thanks,
Ajeet

On Wed, Jun 14, 2023 at 8:17 PM Chet Ramey <chet.ramey@case.edu> wrote:

> On 6/14/23 4:47 AM, Ajeet D'Souza wrote:
>
> > Bash Version: 5.2
> > Patch Level: 15
> > Release Status: release
> >
> > *Description:*
> > I apologize if this is not a bug, but I couldn't find any documentation
> > around this behaviour.
> >
> > In Bash, this does not produce any output:
> > /bin/echo; jobs -l
> >
> > But if you run it in a subshell, it does:
> > (/bin/echo; jobs -l) # output: [1]  42135 Done
> /bin/echo
> >
> > Similar problem if you put this into $PROMPT_COMMAND, although it does
> not
> > run in a subshell AFAIK:
> > PROMPT_COMMAND='/bin/echo; jobs -l' # output on every prompt: [1]  42135
> > Done                    /bin/echo
> >
> > This happens only for external processes, if you were to use the builtin
> > echo, it would not show any background process.
>
> Thanks for the report. I changed this back in late September, 2022 after
> a bug-bash discussion:
>
> https://lists.gnu.org/archive/html/bug-bash/2022-09/msg00067.html
>
> The original report was
>
> https://lists.gnu.org/archive/html/bug-bash/2022-07/msg00117.html
>
> The original (through bash-5.2) behavior was due to the subshell not
> notifying the user about the status of the completed foreground job,
> even though not running it in a subshell ignored foreground jobs. The
> fix was to remove terminated foreground jobs the shell would never notify
> the user about (foreground jobs not killed by a signal) from the jobs list.
>
> Chet
> --
> ``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/
>
>