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From: levy@TTRDC.UUCP
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Message-ID: <8603092107.AA10233@ucbvax.berkeley.edu>
Date: Sun, 9-Mar-86 16:07:48 EST
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Posted: Sun Mar  9 16:07:48 1986
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Subject: Re: Keyboards, ^S, ^Q, and ESC
In-reply-to: article <12187370727.27.JBS@DEEP-THOUGHT.MIT.EDU>

Lemme put in my two cents worth on ESC.

ESC is used in the Unix [whazzat you say?  Ever hear of that user friendly
interactive OS developed by AT&T?] screen editor 'vi' as a means of leaving
insert-text mode and re-entering command mode.  Yet, vi is quite capable
of understanding special-key sequences beginning with ESC, even though
hitting ESC in command mode by itself just sounds the bell (or flashes the
screen if the terminal is thus capable).  I bet you all wonder how vi can
make this distinction.  Well, it's simple.  vi waits for a short period after
getting an ESC to see what else it gets right afterward.  If the ESC was immed-
iately followed by the rest of a special-key sequence, vi obeys it.  If  the
ESC is NOT followed by the remainder of a special-key sequence, or something
else which should be valid in command mode, during that wait, vi beeps or
flashes to indicate an error.  By this means, vi can not only distinguish a
bare ESC, it can distinguish a bare character of ANY kind that happens to
start off some weird terminal's idea of a special-key sequence.  (vi uses
termcap, or more recently, terminfo, terminal descriptions which I believe
are the most flexible in the world in terms of the terminals which can be
accommodated.  Try THAT with EDT or most other VMS-bound screen editors :-).
--
 -------------------------------    Disclaimer:  The views contained herein are
|       dan levy | yvel nad      |  my own and are not at all those of my em-
|         an engihacker @        |  ployer or the administrator of any computer
| at&t computer systems division |  upon which I may hack.
|        skokie, illinois        |
 --------------------------------   Path: ..!{akgua,homxb,ihnp4,ltuxa,mvuxa,
						vax135}!ttrdc!levy