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Full Discussion: File descriptors, redirecting output, and stdout
Top Forums Shell Programming and Scripting File descriptors, redirecting output, and stdout Post 302675703 by Corona688 on Monday 23rd of July 2012 12:07:51 PM
Old 07-23-2012
Instead of redirecting to 3 and 4 and using 'print -u4', you could've redirected stdout and stderr themselves. with 'exec 1>' and 'exec 2>' respectively, and not modified your print commands at all.

Of course, since you seem to wish to preserve stdout/stderr now, it'd be better to keep stdout/err as is.

A redirection can't cause something to print twice. If you want to print twice, you have to print twice. You can make a function to do so, however, simplifying things for you.

Code:
function output
{
        print "$@" >&3
        [ ! -z "$DEBUG" ] && print "$@"
}

function debug
{
        print "$@" >&4
        [ ! -z "$DEBUG" ] && print "$@" >&2
}

If you want to see the output appear on the screen, run it like DEBUG=1 ./myscript

or export the DEBUG variable in your shell or profile.
Last edited by Corona688; 07-23-2012 at 01:13 PM..
This User Gave Thanks to Corona688 For This Post:
Michael_K
 

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LEARN ABOUT DEBIAN

dpipe

DPIPE(1)						      General Commands Manual							  DPIPE(1)

NAME

       dpipe - bi-directional pipe command

SYNOPSIS

       dpipe [ command [ args ] ] = [ command [ args ] ]
       dpipe [ command [ args ] ] = [ command [ args ] ] [ = [ command [ args ] ] ] ...

DESCRIPTION

       dpipe  is  a  general tool to run two commands diverting the standard output of the first command into the standard input of the second and
       vice-versa.  It is the bi-directional extension of the | (pipe) syntax used by all the shells.  The = has been chosen as a metaphor of  two
       parallel  communication	lines  between	the commands.  It is also possible to concatenate several tools. Intermediate programs communicate
       using standard input and standard output with the preceding tool and alternate standard input and  output  (respectively  file  descriptors
       number  3  and  4) towards the following tool.  If an intermediate tool should process only the data flowing in one direction use { or } as
       suffix for the preceding = and prefix of the following one.
       This tool has been written as a tool for the Virtual Distributed Ethernet.

EXAMPLE

       dpipe a = b
       processes a and b are bidirectionally connected: stdin of a is connected to stdout of b and vice-versa
       dpipe a = b = c
       a and b are connected as above. Alternate stdin of b is connected to stdout of c and alternate stdout of b to stdin of c
       dpipe a =} b }= c
       This is a cycle of pipes: stdout of a is connected to stdin of b, stdout of b with stdin of c, and stdout of c to stdin of a
       dpipe a =} b }={ c {= d = e
       all the notations can be mixed together.  this is a -> b -> d -> c and back to a; alternate ports of d are connected to e

OPTIONS

       no options.

NOTICE

       Virtual Distributed Ethernet is not related in any way with www.vde.com ("Verband der Elektrotechnik, Elektronik  und  Informationstechnik"
       i.e. the German "Association for Electrical, Electronic & Information Technologies").

SEE ALSO

       vde_switch(1), vde_plug(1), vde_plug2tap(1), vdeq(1).  wirefilter(1).

AUTHOR

       VDE is a project by Renzo Davoli <renzo@cs.unibo.it>.

Virtual Distributed Ethernet					 December 6, 2006							  DPIPE(1)
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