Path: utzoo!attcan!uunet!mcvax!hp4nl!botter!star.cs.vu.nl!maart
From: maart@cs.vu.nl (Maarten Litmaath)
Newsgroups: comp.unix.questions
Subject: Re: clearing the terminal screen
Keywords: setenv clear vt100
Message-ID: <1817@solo10.cs.vu.nl>
Date: 15 Dec 88 21:39:43 GMT
References: <7007@batcomputer.tn.cornell.edu>
Distribution: comp
Organization: V.U. Informatica, Amsterdam, the Netherlands
Lines: 39

lynch@batcomputer.tn.cornell.edu (Tim Lynch) writes:


\I'm having a problem setting an environmental variable to speed up
\screen clearing. If I'm working from a hp terminal the following works:

\  % setenv CLEAR `clear`
\  % echo $CLEAR            # (and the screen is cleared)

\But, if I'm working from a vt100, issuing echo $CLEAR does nothing.
\Furthermore, echo $CLEAR | wc shows that CLEAR is of length zero.
\The terminfo for the vt100 appears ok because I can issue:

\  % clear

The escape code clearing a VT100 screen, contains some magic characters:

	^[[;H^[[2J	(^[ = escape)

The magic characters are `[', `;' and another `['. The `[' character is used
to match filenames, like:

	% echo *.[ch]	# echo all C source + include files

The escape code above doesn't contain a corresponding ']', so csh should have
said:
	Missing ].

(Of course if csh's syntax/parser were right, it wouldn't have parsed the
output of the backquote command at all.)
It's a bug indeed; there's no standard output, because the backquote command
ultimately fails, and csh simply forgets to issue an error message (on stderr).
Solution:

	% setenv	CLEAR	"`clear`"
	% echo "$CLEAR"		# you'll want to put this in an alias
-- 
fcntl(fd, F_SETFL, FNDELAY):          |Maarten Litmaath @ VU Amsterdam:
      let's go weepin' in the corner! |maart@cs.vu.nl, mcvax!botter!maart