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Reply-To: zeil@cs.odu.edu
Subject: Re: how do i simulate a null character from the keyboard?
To: cygwin@cygwin.com
Cc: emallove@yahoo.com
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From: szeil@notesmail.cs.odu.edu
Date: Thu, 21 Feb 2002 13:08:13 -0500
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Ethan Mallove <emallove at yahoo dot com> wrote:
>
>  why is ctrl-d a logout command
>instead of NULL?
>
Because that's what ctrl-d is supposed to be for!

In the ASCII character code set, ctrl-d is defined as the EOT
signal, short for "End Of Transmission".  So Unix (and
consequently Cygwin) were just following the published
standard.

NUL would, in general, be a terrible choice for an OS to
adopt because NUL characters have perfectly useful
applications in serial data streams (e.g., as something
that you can insert into a stream to affect the timing
without altering the message).

ctrl-z, by the way, used as the terminator by MSDOS and other
early PC operating systems was an unintentionally humorous
choice. It's defined as the SUB character, used as
a placeholder to indicate the data lost during a garbled transmission.

Steve Z



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