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Message-ID: <51CC8B0C.9070809@cornell.edu>
Date: Thu, 27 Jun 2013 14:57:16 -0400
From: Ken Brown <kbrown AT cornell DOT edu>
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To: cygwin AT cygwin DOT com
Subject: Re: where was mention of what creates NUL files?
References: <4C93A171 DOT 4040402 AT fgm DOT com> <loom DOT 20130626T202645-269 AT post DOT gmane DOT org>
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On 6/26/2013 2:53 PM, g wrote:
>
>
>
> 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.

I can't reproduce this with Cygwin emacs.  You must be using native 
Windows emacs.

> 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

Just to be clear, users of Cygwin emacs should *not* do this.

Ken

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