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In article <1990Oct8.165133.17187@cti-software.nl>, pim@cti-software.nl (Pim Zandbergen) writes:
|> 
|> How can one redirect stderr to a command while leaving stdout unaffected ?


For csh and bash try       (command > temp1) >& temp2
For sh                      command 2> temp

somebody else will have to handle ksh.

     Richard Coleman
     G.E. Simulation & Control Systems
     coleman@sunny.dab.ge.com

In article <6133@ge-dab.GE.COM>, coleman@sunny.DAB.GE.COM (Richard Coleman) writes:
|> In article <1990Oct8.165133.17187@cti-software.nl>, pim@cti-software.nl (Pim Zandbergen) writes:
|> |> How can one redirect stderr to a command while leaving stdout unaffected ?
|> For csh and bash try       (command > temp1) >& temp2
|> For sh                      command 2> temp

  The original poster asked how to redirect to a *command*.  You've shown how
to redirect to a *file*.

  In csh, one possible way to do it (when working at a tty) would be:

    (program > /dev/tty) |& command

A similar approach will work in sh (and probably ksh), although there's
probably some better way to do it with various hideous file descriptor
reassignments (I don't use the bourne shell a lot, so I don't qualify to
invent hideous file descriptor reassignments :-):

    (program > /dev/tty) 2>&1 | command

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In article <1990Oct8.204053.15797@athena.mit.edu> jik@athena.mit.edu (Jonathan I. Kamens) writes:
>|> |> How can one redirect stderr to a command while leaving stdout unaffected ?
>A similar approach will work in sh (and probably ksh), although there's
>probably some better way to do it with various hideous file descriptor
>reassignments (I don't use the bourne shell a lot, so I don't qualify to
>invent hideous file descriptor reassignments :-):
>
>    (program > /dev/tty) 2>&1 | command

They're not that hideous!

In bash, sh, and (I'm fairly sure) ksh, you can do this and avoid the
subshell:

program 2>&1 >/dev/tty | command

--
     Are you nervy?  Irritable?  Depressed?  Tired of life?  Keep it up!

In article <1990Oct8.165133.17187@cti-software.nl> pim@cti-software.nl (Pim Zandbergen) writes:
>
>How can one redirect stderr to a command while leaving stdout unaffected ?

Assuming you are asking this because you are using the c-shell (that doesn't
support 2>) I will point you toward the comp.unix.questions FAQ posting 
(just posted in the last week) question number 16.


-- 
Conor P. Cahill            (703)430-9247        Virtual Technologies, Inc.,
uunet!virtech!cpcahil                           46030 Manekin Plaza, Suite 160
                                                Sterling, VA 22170 

In article <6133@ge-dab.GE.COM> coleman@sunny.DAB.GE.COM (Richard Coleman) writes:
>
>-- 
>In article <1990Oct8.165133.17187@cti-software.nl>, pim@cti-software.nl (Pim Zandbergen) writes:
>|> 
>|> How can one redirect stderr to a command while leaving stdout unaffected ?
		^^^^^^^^	^^^^^^^^^^^^
>
>
>For csh and bash try       (command > temp1) >& temp2
>For sh                      command 2> temp
>
>somebody else will have to handle ksh.
>

The question was how to redirect to a command, not a file.  You might think
that something like 2| would work, but it doesn't (at least in sh, I have
no ksh to try it on).

I have tried several permutations of re-ordering file descriptors and trying
to use new ones with the _exec- builtin but have had no success yet.

Bob McGowan  (standard disclaimer, these are my own ...)
Product Support, Wyse Technology, San Jose, CA
..!uunet!wyse!bob
bob@wyse.com

In article <1990Oct8.204053.15797@athena.mit.edu> jik@athena.mit.edu (Jonathan I. Kamens) writes:
>   In csh, one possible way to do it (when working at a tty) would be:

But who said there's a tty around? What if Pim wanted to pipe his output
through yet another command?

> A similar approach will work in sh (and probably ksh), although there's
> probably some better way to do it with various hideous file descriptor
> reassignments (I don't use the bourne shell a lot, so I don't qualify to
> invent hideous file descriptor reassignments :-):

I use the bourne shell a lot, so I guess I qualify. It isn't too
hideous, though, if you write it clearly:

  ( exec 5>&1; exec 1>&2; exec 2>&5; foo ) | err-processor

Even you :-) should be able to recognize the swap idiom there. Start
from basic constructs like this and soon you'll be piping stdout and
stderr through separate commands. Someday you may even learn to use
multitee... [grin]

---Dan

In article <1990Oct8.165133.17187@cti-software.nl>, pim@cti-software.nl (Pim Zandbergen) writes:
> 
> How can one redirect stderr to a command while leaving stdout unaffected ?

The real solution in sh and ksh is to exchange stdout and stderr:

	command_1 3>&1 1>&2 2>&3 3>&- | command_2

Well, some comments may be needed :-)
   (a)	3>&1	File descriptor 3 now is an 'alias' for 1 (original stdout)
   (b)	1>&2	File descr. 1 now is an 'alias' for 2 (original stderr)
   (c)	2>&3	File descr. 2 now is an 'alias' for 3 which still is an alias
		for the original stdout
   (d)	3>&-	File descr. 3 is closed as it is no longer needed

Net effect:
	File descriptor 1 (stdout) is connected to the original stderr (b)
	File descriptor 2 (stderr) is connected to the original stdout (c)

For C writers amongst you:
	3>&1 will probably be implemented as
		close(3);	/* To ensure 3 is free */
		fcntl(1, F_DUPFD, 3);	/* Returns lowest possible   */
					/* 'dup'ed file descr. >= 3  */


  /-------------------------------------------------------+
 /  Henk Keller                         AT Computing bv   |
|   Teleph.: +31 80 566880              P.O. Box 1428     |
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|                                                         |
|                    -- do not fold --                    |
+---------------------------------------------------------+

In article <3207@idunno.Princeton.EDU> pfalstad@flower.Princeton.EDU (Paul John Falstad) writes:
>In article <1990Oct8.204053.15797@athena.mit.edu> jik@athena.mit.edu (Jonathan I. Kamens) writes:
>>|> |> How can one redirect stderr to a command while leaving stdout unaffected ?
>
>In bash, sh, and (I'm fairly sure) ksh, you can do this and avoid the
>subshell:
>
>program 2>&1 >/dev/tty | command

In sh, file descriptor re-directions are evaluated left to right, so you can
even swap stdout & stderr with a little care & avoid /dev/tty if you want:

program 3>&2 2>&1 >&3 | command

I think this should work in ksh, but doesn't seem to in my version - a buglet?
I can't speak for bash as I don't use it.
-- 
Rick Jones			The definition of atomic:
Tetra Ltd.				from the Greek meaning "indivisible"
Maidenhead, Berks, UK		So what is:
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In article <668@atcmpe.atcmp.nl>,
	henk@atcmp.nl (Henk M. Keller) writes:
)In article <1990Oct8.165133.17187@cti-software.nl>,
)	pim@cti-software.nl (Pim Zandbergen) writes:
)> 
)> How can one redirect stderr to a command while leaving stdout unaffected ?
)
)The real solution in sh and ksh is to exchange stdout and stderr:
)
)	command_1 3>&1 1>&2 2>&3 3>&- | command_2

But that still does _not_ answer Pim's question!
He said: `... while leaving stdout _unaffected_' (emphasis added).
In Henk's example stdout is dup(2)ed to stderr.

So:
	exec 3>&1
	command_1 2>&1 1>&3 3>&- | command_2 3>&-
	exec 3>&-

Or:
	3>&1 (command_1 2>&1 1>&3 3>&- | command_2 3>&-)

	# yes Virginia, that's correct

Don't forget to close the extra descriptor, or you'll get screwed one day.
--
            "the C shell is flakier than a snowstorm."  (Guy Harris)

In article <668@atcmpe.atcmp.nl> henk@atcmp.nl (Henk M. Keller) writes:
> 	3>&1 will probably be implemented as
> 		close(3);	/* To ensure 3 is free */
> 		fcntl(1, F_DUPFD, 3);	/* Returns lowest possible   */
> 					/* 'dup'ed file descr. >= 3  */

Or dup2(1,3).

---Dan

In article <3002@wyse.wyse.com> bob@wyse.UUCP (Bob McGowen x4312 dept208) writes:
>In article <1990Oct8.165133.17187@cti-software.nl>, pim@cti-software.nl writes:
>> How can one redirect stderr to a command while leaving stdout unaffected ?
>The question was how to redirect to a command, not a file.  You might think
>that something like 2| would work, but it doesn't (at least in sh, I have
>no ksh to try it on).
>
>I have tried several permutations of re-ordering file descriptors and trying
>to use new ones with the _exec- builtin but have had no success yet.

Just thought I'd take a stab at it.  There may be a better way.
I use Korn Shell.

$ echo now is the time > xx
$ rm -f zz
$ ( cat zz xx 2>&1 1>&3 | od -c ) 3>&1
now is the time
0000000   c   a   t   :       c   a   n   n   o   t       o   p   e   n
0000020       z   z  \n
0000024

Paul Chamberlain | I do NOT represent IBM.     tif@doorstop, sc30661 at ausvm6
512/838-7008     | ...!cs.utexas.edu!ibmaus!auschs!doorstop.austin.ibm.com!tif

In article <1990Oct8.165133.17187@cti-software.nl>, pim@cti-software.nl (Pim Zandbergen) writes:
> 
> How can one redirect stderr to a command while leaving stdout unaffected ?

I'm not 100% sure but logically this should work.

command1 2>tempfile &
tail -f tempfile | command2

the only problem I think would be that the tail -f would never end.


another solution:
again I'm not sure but here goes:

command1 2|command2



I have not tried either of these .  let me know if they work.

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