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From: james@bigtex.UUCP
Newsgroups: comp.unix.questions
Subject: Re: SHL LAYERS
Message-ID: <391@bigtex.uucp>
Date: Sat, 24-Jan-87 00:35:40 EST
Article-I.D.: bigtex.391
Posted: Sat Jan 24 00:35:40 1987
Date-Received: Mon, 26-Jan-87 01:54:43 EST
References: <1324@cadovax.UUCP> <5528@brl-smoke.ARPA> <380@oblio.UUCP> <5547@brl-smoke.ARPA>
Sender: james@bigtex.uucp
Reply-To: james@bigtex.UUCP (James Van Artsdalen)
Organization: F.B.N. Software, Austin TX
Lines: 22

IN article <5547@brl-smoke.ARPA>, gwyn@brl.arpa (Doug Gwyn) wrote:
> Is there some significant drawback other than the ones I had
> noted?

Well, the obvious problem with System V layers is that there isn't any
practical way to use them.  The "shl" program is not a shell, and cannot be
used as such, and AT&T's Bourne shell does not support layers.  One has to
run the shl program after logging in, and every time you use ^Z, you go back
to this shl program, not to a shell.  I have to wonder why AT&T bothered with
layering if it wasn't worth the trouble of modifying a shell to use it.
Perhaps one day the Korn shell will use it.

The other obvious problem is the fact you noted: there is no way to communicate
layers activity to programs such as vi and so forth.  Screen oriented programs
really do need to know when to repaint the screen, and as far as I know there
is no way under System V for vi to find out when to redraw.

If anyone knows of a practical way to use shl I'd be interested in hearing
about it, but in the meantime I see no reason to link it into the kernel.
-- 
James R. Van Artsdalen   ...!ut-sally!utastro!bigtex!james   "Live Free or Die"
(512)-328-0282