From: Bart Schaefer <schaefer@brasslantern.com>
To: zsh-users@zsh.org
Subject: Re: multios doesn't work with 2>&1
Date: Sun, 27 Oct 2013 10:01:37 -0700 [thread overview]
Message-ID: <131027100137.ZM4100@torch.brasslantern.com> (raw)
In-Reply-To: <20131027145917.GA5509@localhost.localdomain>
On Oct 27, 10:59pm, Han Pingtian wrote:
}
} According to the zsh guide's "2.5.8 `Go faster' options for power
} users", page 44:
}
} % echo foo 2>&1 >/dev/null | sed 's/foo/bar/'
}
} should output "bar" if multios has been set. But it outputs nothing
Hmm, looks like this has been broken for a LONG time.
If I back out workers/20666 (Jan 2005), then this example works again.
Note that
% print -u2 foo 2>&1 >/dev/null | sed 's/foo/bar/'
does print "bar", so the problem is that the original fd 1 is directed
to /dev/null while the multio fd created by 2>&1 is is directed to the
pipe. You can see the reasoning for this in the "references" thread
going back from http://www.zsh.org/mla/workers/2005/msg00026.html
The workaround is to either explicitly add the original stdout to the
multio:
% echo foo 2>&1 >&1 >/dev/null | sed 's/foo/bar/'
Or to make sure the multio isn't created until the pipe is seen:
% { echo foo 2>&1 } >/dev/null | sed 's/foo/bar/'
If there's a way to fix the original complaint (that >&- doesn't really
close the descriptor when a multio is involved, so unnecessary multios
result) without the above example remaining broken, I may need some help
to find it.
Otherwise we have to decide whether to revert to the pre-2005 behavior,
or document around it.
prev parent reply other threads:[~2013-10-27 17:01 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-27 14:59 Han Pingtian
2013-10-27 17:01 ` Bart Schaefer [this message]
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