Path: utzoo!attcan!uunet!lll-winken!lll-ncis!oodis01!uplherc!esunix!bpendlet
From: bpendlet@esunix.UUCP (Bob Pendleton)
Newsgroups: comp.arch
Subject: Re: Shells everywhere (was Re: Cobol Data Corporation Cyber 180 ...)
Message-ID: <1185@esunix.UUCP>
Date: 13 Jan 89 15:46:57 GMT
References: <10847@tekecs.TEK.COM>
Organization: Evans & Sutherland, Salt Lake City, Utah
Lines: 45

From article <10847@tekecs.TEK.COM>, by andrew@frip.gwd.tek.com (Andrew Klossner):
> []
> 
> 	"It should be possible to write a shell for almost any usable
> 	computer ..."
> 
> A shell requires that the system supply fork() and exec(), or perhaps
> start_task() (fork and exec combined) system services, or something
> analogous and reasonably efficient.  

Well... sort of. Anyone remember Exec-8 on the Univac 1100 series? I
saw a shell on an 1108 that worked by creating a file consisting of
the commands needed to run a program and a command to restart the
shell. The shell would then @ADD the file to its input stream and
terminate so that the commands in the file would be executed.

Analogous to fork() and exec()? I don't think so. Reasonably
efficient? No. Did it work? Yes. Was it a shell? Yes.

> 
> MSDOS is also a single tasking system (today, at least), but you can
> write a shell for it by slipping a few tentacles into the (unprotected)
> kernel.  

Wouldn't it just be easier to write a shell as a replacement for
COMMAND.COM?

A program running under MSDOS can load another program into unused
memory, start it running and be awakened when the program terminates.
Check out the SHELL verb under MSBasic or spawn under TurboC 2.0 for
examples. This ability makes it possible to write quite a reasonable
shell under MSDOS.

Check out "Software Tools" by Kernighan & Plauger(SP?) for more
information on how to write a shell for OSs that don't support UNIX
system calls.

I can't comment on Tops-10, but I'm pretty sure there were shells on
Tenex and Tops-20.

			Bob P.
-- 
              Bob Pendleton, speaking only for myself.
UUCP Address:  decwrl!esunix!bpendlet or utah-cs!esunix!bpendlet

		Reality is what you make of it.