Re: Coproc within coproc supported?

[Chet Ramey]

On 11/17/22 5:43 AM, Tadeus Prastowo wrote:

> It is, and so I would like thank you very much for keeping Bash in a
> good shape for so many years.  I really appreciate it.  Despite using
> Bash since 2005 when I knew the GNU project for the very first time, I
> have appreciated its high-level programming capabilities only recently
> when I have to orchestrate many third-party programs to work in
> unison.  I find that Bash is indeed an efficient language when it
> comes to a system-wide process management that must be afforded using
> only BusyBox and the Linux kernel.

Thanks.

> > > Is it true that the intention of the statement in the man page is that
> > > at most one coprocess exists for every concurrently running Bash
> > > process where $$ expands to the same PID?
> >
> > No. Coprocs are process-based.
>
> In that case, why does Bash 4.3.48 when executing the following lines
> issues the coproc-exists warning despite the fact that if I understand
> it correctly, the (...)-construct creates a new process?
>
> coproc sleep 1
> echo $$, $BASHPID, $COPROC_PID >&2
> (coproc sleep 1; echo $$, $BASHPID, $COPROC_PID >&2; wait)
> wait

A (subshell) is an exact copy of the parent shell, so it inherits the
coproc. It just won't be able to write or read to the coproc, and can't
wait for a coproc it inherits, since the subshell is not the coproc
process's parent.

--
``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/