where was mention of what creates NUL files?

g ggrimes@nc.rr.com
Thu Jun 27 18:35:00 GMT 2013

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.
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.

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!

Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple

More information about the Cygwin mailing list