Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!tut.cis.ohio-state.edu!pt.cs.cmu.edu!b.gp.cs.cmu.edu!Ralf.Brown@B.GP.CS.CMU.EDU
From: Ralf.Brown@B.GP.CS.CMU.EDU
Newsgroups: comp.sys.ibm.pc
Subject: Re: Redirect > nul affects procomm, why?
Message-ID: <24c315e7@ralf>
Date: 18 Jul 89 11:35:03 GMT
Sender: ralf@b.gp.cs.cmu.edu
Organization: Carnegie Mellon University School of Computer Science
Lines: 25
In-Reply-To: <277@gvlv2.GVL.Unisys.COM>

In article <277@gvlv2.GVL.Unisys.COM>, kleonard@gvlv2.GVL.Unisys.COM (Ken Leonard) wrote:
}* 1.  What exactly is the "nul" ?
}well, "nul" is not-a-file, or file-to-nowhere, or ignore-all-write-calls,
}depending on which version of what level of whose port of DOS you have.

All versions of DOS 2 and up that I am aware of have a NUL character device
that simply returns success on all write calls, and returns zero bytes on any
read calls.  Under DOS 1.x, an explicit check was made for a number of devices
(since there were no device drivers yet), one of them being NUL.  If NUL was
selected, DOS simply threw away the output.

Interestingly enough, the NUL device is not replaceable, since DOS hangs it
onto the front of the device driver chain after CONFIG.SYS runs (so the
built-in NUL is always the first device in the chain--that's how programs
which trace the device chain are able to find the chain).

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