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To:	cygwin AT cygwin DOT com
From:	g <ggrimes AT nc DOT rr DOT com>
Subject:	Re: where was mention of what creates NUL files?
Date:	Wed, 26 Jun 2013 18:53:21 +0000 (UTC)
Lines:	41
Message-ID:	<loom.20130626T202645-269@post.gmane.org>
References:	<4C93A171 DOT 4040402 AT fgm DOT com>
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Daniel Barclay <daniel <at> fgm.com> writes:

> 
> Does anyone recall a mention of what in CygWin (or possibly Emacs) creates
> files with a simple name of "NUL"?
> 
> Thanks,
> Daniel
> 
> 


This has been driving me nuts for years. Finally tracked it down.
These are created by emacs' man.el code when you get a man page.
Reproduce: 
In emacs, do:
    M-x man <ret>
    <enter anything, valid ('ls') or not>
Now, you'll see a NUL file in the directory.

Root cause:
construction of the 'man' command that is passed to the shell includes:
(concat " %s 2>" null-device)

The variable `null-device' is platform specific and defaults to a pure-copy
of "/dev/null" which, apparently, becomes "NUL" on windows.

It is a defvar in files.el and 'set' again in dos-w32.el.

Resolution:
In your .emacs file, do:

   (require 'dos-w32) ;; load this first to avoid it undo'ing the next line
   (setq null-device "c:/tmp/emacs-dev-null.txt") ;; set to anything

Happy days!




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