Subj : Re: redirection of stdout.
To   : Jasen.Betts@xspamp42.f531.n640.z3.f
From : Charles Dye
Date : Wed Mar 20 2002 08:48 pm

From: raster@highfiber.com (Charles Dye)

On Wed, 20 Mar 2002 08:00:29 GMT,
Jasen.Betts@xspamp42.f531.n640.z3.fidonet.org wrote:

>Hi All.
>
>(4dos/msdos:)
>
>is there a way (using 4dos) to detect from inside a batch file if stdout
>has been redirected (to a file/pipe).

I don't see any good way to do it using only internal 4DOS functions.  But it's 
trivial for an external program to check the status of its stdout handle, which 
it inherits from 4DOS. This same general approach would also work under 
COMMAND.COM.


@echo off

rem  REDIR.BTM
rem  Checks for redirection of the stdout handle

if (%@search[chkredir.com]) ne () goto :already

text | debug > nul
a 100
mov bx,1           ; handle 1 = stdout
mov ax,4400        ; ioctl Get Device Data function
int 21             ; call DOS
and al,82          ; does handle refer to the
cmp al,82          ; standard output device?
jne 113            ; if not, branch ahead
mov ax,4c00        ; stdout not redirected,
int 21             ; exit with errorlevel 0
mov ax,4c01        ; stdout was redirected,
int 21             ; exit with errorlevel 1

r cx
18
n chkredir.com
w
q
endtext

:already

chkredir.com
echoerr The stdout stream was %@if[%?==0,not ,]redirected.


--
Charles Dye     raster@highfiber.com

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