Re: 'wait' in command group in pipeline fails to recognize child process

[Martin Jambon]

On 6/22/21 4:31 AM, Greg Wooledge wrote:
> On Tue, Jun 22, 2021 at 02:42:40AM -0700, Martin Jambon wrote:
> > I ran into something that looks like a bug to me, although I'm not super
> > familiar curly-brace command groups.
> >
> > Bash version: latest from GitHub mirror (commit ce23728: Bash-5.1 patch 7)
> >
> > Minimal repro:
> >
> >    $ sleep 1 & { wait $!; } | cat
> >    [1] 665454
> >    bash: wait: pid 665454 is not a child of this shell
> >
> > I was expecting a success, just like we get without the pipeline:
>
> A pipeline creates two or more subshells, one for each command in the
> pipeline.  Therefore, your wait command is running in a different
> process than the one which created the sleep background job.
>
> The curly braces are irrelevant here.
>
> unicorn:~$ sleep 1 & wait "$!"|cat
> [1] 1290127
> bash: wait: pid 1290127 is not a child of this shell

Thank you! Now I know that a subshell is not a shell, $$ being the 
process ID of the shell, not of the subshell.