Where Goeth the Line-editing? (was Re: Strangeness in shell)

[Dave Shepperd]

>From article <13303 at bloom-beacon.MIT.EDU>, by jik at athena.mit.edu (Jonathan I. Kamens):
> 
> [stuff deleted]
>
>   In multics, it was possible to install a driver that lived at the
> gateway between the actual terminal and user processes.  This driver
> would intercept and process *all* input before sending it to the
> process.  Therefore, if you wrote a line-editing driver and installed
> it, it would work for *every* program on the system, without fail.
> There were, of course, ways to turn off the line-editing features for
> programs that needed character-by-character input.
> 

Actually, Un*x has this "feature" as well. At least, sort of. The
concept of line disciplines was developed to address this issue (or
other protocol handling requirements). Line discipline 0 is responsible
for doing the input editing you get when doing normal (such as echo,
backspace processing, line kill, signals, etc). It also does the stuff
such as adding extra cr's, lf's, null's or other things in the output
stream as so indicated by various stty flags. Line disciplines don't do
the job as neatly as is desired (a better idea, STREAMS, was invented
which does the job quite a bit better).

I wrote a command line editor using the line discipline mechanism on
Xenix (cuz that's what I had) and can say it's no picnic. I haven't
a clue whether it'll work on another flavor of Unix since I don't have
one (other than SCO/UNIX 3.2) and am not interested in getting one
just yet. Although I haven't brought up SCO/Unix 3.2 (it doesn't
have support for the Ethernet boards I have), from what I can
gather in its doc set, the line discipline mechanism is exactly the
same as on Xenix 2.3.2, so it ought to install and work without any
trouble (I'll believe it when I see it).

I've been using my editor for some months now as have all the other
Xenix users here and we have found it to be quite indispensible. None
of us understands why an interactive line editor hasn't been part
of the distribution of most flavors of Un*x for years.
-- 

Dave Shepperd.	    shepperd at dms.UUCP or weitek!dms!shepperd
Atari Games Corporation, Sycamore Drive, Milpitas CA 95035.
(Arcade Video Game Manufacturer, NOT Atari Corp. ST manufacturer).