Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!husc6!bloom-beacon!tut.cis.ohio-state.edu!osu-cis!att!ihuxy!vg55611
From: vg55611@ihuxy.ATT.COM (Gopal)
Newsgroups: comp.sys.ibm.pc
Subject: Re: MS-DOS puzzle #1
Message-ID: <2936@ihuxy.ATT.COM>
Date: 22 Apr 89 19:09:36 GMT
References: <6893@bsu-cs.bsu.edu>
Reply-To: vg55611@ihuxy.UUCP (55421-Gopal,V.P.)
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 31

In article <6893@bsu-cs.bsu.edu> dhesi@bsu-cs.bsu.edu (Rahul Dhesi) writes:

>     Question:  Why does COMMAND.COM allow redirection of standard
>     input and standard output, but not standard error?

I think the question really should be - why does MS-DOS allow stdin/stdout
redirection but not stderr ?  Command.com simply goes through DOS to do
the redirection (by playing with the filehandles etc.)

>     Answer:  MS-DOS, unlike UNIX, doesn't have a fork() system call;
>     therefore the MS-DOS command interpreter, unlike the
>     UNIX shell, can't redirect standard error.

I don't think MS-DOS has stderr defined.  I think at one point, a very early
point (DOS 1.00 ?), it didn't even have stdin and stdout defined, you only
had keyboard / display services.  Later, stdin and stdout were defined, and
the keyboard/display services were mapped to these.  At that time, they
could have added stderr services, but they didn't.

If application programs and compilers seem to have stderr, I am quite sure
that it is because they bypass DOS and use BIOS to write to the display
directly.

>THE PUZZLE.  Does the above make any sense?  If it does, why?  If it
>does not, what is the real answer to the question?

Venu P. Gopal
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