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Re: implicit redirection of background within pipeline

From: Martin Kealey
Subject: Re: implicit redirection of background within pipeline
Date: Wed, 13 Jan 2016 13:20:02 +1300 (NZDT)
User-agent: Alpine 2.00 (DEB 1167 2008-08-23)

On Mon, 11 Jan 2016, Chet Ramey wrote:
> "The standard input for an asynchronous list, before any explicit
> redirections are performed, shall be considered to be assigned to a file
> that has the same properties as /dev/null."

I thought the (only) point of that to avoid a background job reading the tty
in an environment that lacked job control.

The standard is actually a bit vague; under "Compound Commands" it mentions
that "Each redirection will apply to all the commands within the compound
command that do not explicitly override that redirection" but it fails to
mention that this applies to pipes as well; so I submit that it is a
reasonable interpretation that a pipe on an outer block counts as an
(explicit) redirection for the purpose of reading the "Asynchronous Lists"
sub section.

What do other shells do? Ksh? Dash? Zsh?


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