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Date: Fri, 6 May 2016 22:35:20 +0100
From: Peter Stephenson <p.w.stephenson@ntlworld.com>
To: Zsh hackers list <zsh-workers@zsh.org>
Subject: Re: Weird issue with pipeviewer and multiple pipes
Message-ID: <20160506223520.34b3e3c4@ntlworld.com>
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References: <ufaa8k6ei8t.fsf@epithumia.math.uh.edu>
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On Tue, 3 May 2016 20:56:14 -0700
Bart Schaefer <schaefer@brasslantern.com> wrote:
>On Tue, May 3, 2016 at 6:15 PM, Jaron L Tibbitts III <tibbs@math.uh.edu> wrote:
> >
> > [2]  + 11459 done                    echo 1 |
> >        11461 suspended (tty output)  pv -l -s $(echo 1) |
> >        11462 interrupt               cat
> 
> I don't know why the $(echo) makes any
> difference to it receiving the TTOU in the first place.

Actually, it looks like This Can't Possibly Happen, since $(echo 1) is
over and done with by the time the pv is started; we've got the output,
closed the fd, and waited for the process to finish (by PID).  So there
is some weird lingering side effect.
 
> All of these also avoid the problem:
> 
>     echo 1 | { trap '' TTOU ; pv -p -s $(echo 1) } | cat
>     echo 1 | pv -p -s $(echo 1) 2>/dev/tty | cat
>     echo 1 | { x=$(echo 1); pv -p -s $x } | cat

Also, a substitution of the form $(<file) doesn't do it, either.  That's
probably not surprising as there's no extra process there, but it does
leave not that much code in getoutput() to be causing it.  I tried
commenting out entersubsh() to see if the terminal handling in there
maede a difference, but it didn't.  In fact, even pruning down
the behaviour in the child to simply printing something didn't
have any effect.

pws