How to redirect stderr to a pipe and stdout to a file?

How to redirect stderr to a pipe and stdout to a file?

[Haakon Riiser]

In bash, I could always do

  $ ls INVALID . 2>&1 >/dev/null | less

to send stderr:

  ls: INVALID: No such file or directory

to the less buffer and stdout to /dev/null.  When I use the
same command in zsh 4.0.6, _both_ stderr and stdout is sent
to less.  If I remove "| less" from the command, it works as it
should:  stdout is discarded and stderr is sent to the terminal.
I've looked through the chapter on redirection in zshmisc(1),
but I couldn't find an answer.  (Of course, that doesn't mean
it's not there. :-)

Thanks in advance for any help.

-- 
 Haakon

Re: How to redirect stderr to a pipe and stdout to a file?

[Erik Trulsson]

On Sun, Jun 15, 2003 at 02:50:30PM +0200, Haakon Riiser wrote:
> In bash, I could always do
> 
>   $ ls INVALID . 2>&1 >/dev/null | less
> 
> to send stderr:
> 
>   ls: INVALID: No such file or directory
> 
> to the less buffer and stdout to /dev/null.  When I use the
> same command in zsh 4.0.6, _both_ stderr and stdout is sent
> to less.  If I remove "| less" from the command, it works as it
> should:  stdout is discarded and stderr is sent to the terminal.
> I've looked through the chapter on redirection in zshmisc(1),
> but I couldn't find an answer.  (Of course, that doesn't mean
> it's not there. :-)
> 
> Thanks in advance for any help.

I don't know what the real answer is, but a workaround (which should
also work in bash) is to execute the first command in a subshell, i.e:

( ls INVALID . 2>&1 >/dev/null ) | less



-- 
<Insert your favourite quote here.>
Erik Trulsson
ertr1013@student.uu.se

Re: How to redirect stderr to a pipe and stdout to a file?

[Pavol Juhas]

On Sun, Jun 15, 2003 at 02:50:30PM +0200, Haakon Riiser wrote:
> In bash, I could always do
> 
>   $ ls INVALID . 2>&1 >/dev/null | less
> 
> to send stderr:
> 
>   ls: INVALID: No such file or directory
> to the less buffer and stdout to /dev/null.  When I use the
> same command in zsh 4.0.6, _both_ stderr and stdout is sent
> to less.  If I remove "| less" from the command, it works as it
> should:  stdout is discarded and stderr is sent to the terminal.
...

You need to 
    setopt no_multios
and the redirection would work as expected.  For explanation
see the MULTIOS section in zshmisc(1).

HTH,

Pavol

Re: How to redirect stderr to a pipe and stdout to a file?

[Bart Schaefer]

On Jun 15, 12:11pm, Pavol Juhas wrote:
} Subject: Re: How to redirect stderr to a pipe and stdout to a file?
}
} On Sun, Jun 15, 2003 at 02:50:30PM +0200, Haakon Riiser wrote:
} > 
} >   $ ls INVALID . 2>&1 >/dev/null | less
} 
} You need to 
}     setopt no_multios

Multios are applied at the "pipeline" level of shell grammar, so you can
also prevent the effects by introducing any complex structure; easiest is
just to wrap the first command in { } like so:

    % { ls INVALID . 2>&1 >/dev/null } | less