using 'printf' in a script in terminal window

[Mike McNally]

I'm running Linux, and yes I was talking about the console, not an X terminal
emulator.

Note that the only way for "printf" to clear the screen reliably would be for
it to do exactly the same thing that "clear" does. (Key word there is
"reliably.")

I won't defend the status quo as representing a state of perfection of course.
Back in the 70's the real-world day-to-day problem that was the ridiculous
variation in ASCII terminal capabilities was insane.  At least nowadays the
vast majority of "terminals" in use are xterm (or whatever-term). Still, there
are surprisingly many variations even of that animal (though I suspect that
most of them more-or-less behave like xterm, which itself is mostly like a
VT-100 or VT-something, I think).

On Sat, Nov 21, 2009 at 2:47 PM, Jerry <gesbbb at yahoo.com> wrote:
> On Sat, 21 Nov 2009 12:26:44 -0600
> Mike McNally <emmecinque at gmail.com> replied:
>
>> On Sat, Nov 21, 2009 at 12:13 PM, Jerry <gesbbb at yahoo.com> wrote:
>> > On Sat, 21 Nov 2009 11:26:09 -0600
>> > Mike McNally <emmecinque at gmail.com> replied:
>> >
>> >
>> >> On Sat, Nov 21, 2009 at 11:14 AM, Jerry <gesbbb at yahoo.com> wrote:
>> >> > On Sat, 21 Nov 2009 13:32:48 +0100
>> >> > Mike Massonnet <mmassonnet at gmail.com> replied:
>> >> >
>> >> >> I tested it on Terminal, Konsole, and finally xterm, none of
>> >> >> those clear the screen. And if xterm isn't doing pretty much
>> >> >> nobody does it.
>> >> >>
>> >> >> Why don't you use `clear'?
>> >> >
>> >> > This would appear to be a "by design" feature; although I cannot
>> >> > fathom why. Using 'clear' is fine as long as the script is not
>> >> > used via CRON. 'Clear' produces strange output with scripts run
>> >> > via CRON. I know that there are ways to program around that;
>> >> > however, it does complicate things. I prefer the "KISS" approach.
>> >> >
>> >> > Although it probably would not make any appreciable difference, I
>> >> > might appeal to the developers to change this behavior.
>> >> >
>> >> There's no truly standard character sequence that clears a terminal
>> >> display, and there never has been. The '\f' code is a "form feed",
>> >> which is a printer control to feed out paper up to the next page
>> >> perforation.
>> >>
>> >> Most "terminal" programs (xterm et al) emulate old DEC VT-100
>> >> terminals, which did not clear the screen in response to a form
>> >> feed character, as far as I know.
>> >
>> > I am not familiar with how it worked historically. I do know that
>> > there is a very real difference between how the printf "\f" command
>> > works at a console and how it works within Terminal, xterm, etc. If
>> > this was Microsoft, I might expect the left hand to be ignorant of
>> > what the right hand is doing. Here, I would expect better.
>> >
>> > The bottom line is that this greatly inhibits my ability to fully
>> > test scripts that I develop.
>
>> Well that's why there's such a thing as the "clear" program: it
>> figures out what sort of terminal you're printing to and what sort of
>> special character sequence will cause the screen to be cleared, and
>> it sends that out.
>>
>> When you're doing standard printing out to any sort of "tty" device in
>> Linux, with any window manager or desktop, the basic facts are the
>> same: the software behaves pretty much exactly the same way it would
>> have behaved 25 years ago when it would have been sending character
>> through an RS-232 device to a *real* VT-100 (or ADM-3A or PE550 or
>> any of the other zillion types of terminals, each with its own
>> proprietary set of control codes).
>>
>> If the console tty emulator interprets the form-feed character to mean
>> that the screen should be cleared, that's great. The problem is that
>> that's just one tty emulator out of many.
>>
>> Also, for what it's worth, using "printf" to echo out a '\f'
>> character doesn't cause my console screen to clear. It seems to be
>> treated like a linefeed character.
>
> Out of morbid curiosity, what OS are you using? I have only tried on a
> few other than FreeBSD; however, they all seem to work the same.
> Obviously, that is at the console and not in an "X" session. So far, it
> never works in "X".
>
> As I stated previously, 'clear' causes a problem when used in
> conjunction with CRON. While I can, and have, circumvented the problem,
> I prefer not to have to.
>
>
> --
> Jerry
> gesbbb at yahoo.com
>
> |::::=======
> |::::=======
> |===========
> |===========
> |
>
> It is difficult to soar with the eagles when you work with turkeys.
>
> _______________________________________________
> Xfce mailing list
> Xfce at xfce.org
> http://foo-projects.org/mailman/listinfo/xfce
> http://www.xfce.org
>



-- 
Turtle, turtle, on the ground,
Pink and shiny, turn around.