Subj : Re: redirection of stdout.
To   : Winston.Smith@xspamp0.f120.n323.z1.
From : Charles Dye
Date : Sun Mar 24 2002 06:42 pm

From: raster@highfiber.com (Charles Dye)

On Mon, 25 Mar 2002 00:01:06 GMT,
Winston.Smith@xspamp0.f120.n323.z1.fidonet.org wrote:

>>> (4dos/msdos:)  is there a way (using 4dos) to detect from inside a
>>> batch file if stdout has been redirected (to a file/pipe).
>
>WS> Under MS-DOS using a pipe creates a temporary file in your
>WS> designated temporary directory that uses three dollar/currency
>WS> signs as a naming convention. It would be fairly easy to scan for
>WS> that.
>
>-> so how do I access the name?
>
>I believe it is <disk-letter>:<temp-path><wildcard>.$$$
>  for example,
>     C:\TMP\*.$$$
>  or
>     C:\WINDOWS\TEMP\*.$$$
>
>...but I haven't tried to crash MS-DOS I/O in a while, now.

You can see the filenames created by a pipe with:

   dir /a /od %temp | list

The temporary file created by the pipe will be the last one listed.  On *my* 
system, these files end in .000 not .$$$.  I do not know whether there is any 
circumstance where 4DOS would use .$$$, or a different numeric suffix such as 
..002. Current versions of COMMAND.COM create temporary files with no extension 
at all.

At any rate, the presence of such a file doesn't necessarily tell you anything 
about the state of the current shell.  A .000 file *might* indicate that the 
current shell is emulating a pipe.  Or it might be a different shell in a 
separate DOS box, or a temp file left over from a system crash last Thursday, 
or a temp file created by some other program....

--
Charles Dye     raster@highfiber.com

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