symbolic links, aliases, cls clear

[Michael Paoli]

Floyd L. Davidson wrote:
> af.dingo at gmail.com wrote:
> >If I may recommend an alternative,
> >print "\033[H\033[J"
> Unfortunately, it is poor practice to hard code such sequences.
> Instead the proper sequence should be obtained from the
> appropriate database (TERMINFO or TERMCAP), and the easy way to
> do that is,
>    tput clear

Or clear(1), as also mentioned earlier.  Yes, definitely don't want to
hardcode the sequence.  Definitely do use the appropriate terminal
capabilities database (terminfo or termcap) in the appropriate manner
(e.g. clear(1) or tput clear will handle that in the simple case of
shell accessible means to clear the screen).

Most UNIX(/LINUX/BSD/...) implementations support a large number of
terminal types.  E.g. on my system, I check and find that there are
1470 unique terminal types (descriptions) supported - and that's not
including multiple aliases for the same terminal type/description (but
it does count distinct names/files which have differing
configurations, even if they are for the same terminal - such as
changing certain options or behavior of a terminal, or using the
terminal in distinct modes).  Among those terminal types on my system,
I find 154 distinct means of clearing the screen.  Just for
illustrative purposes, here are the top 10 I find, with count of how
many distinct types (descriptions) use that particular sequence:
    236         clear=\E[H\E[J,
    120         clear=^L,
    120         clear=\E[H\E[2J,
     64         clear=\EH\EJ,
     61         clear=\E[2J,
     42         clear=\E[H\E[J$<156>,
     38         clear=^Z,
     36         clear=\E[H\E[J$<50>,
     31         clear=\E[H\E[J$<40>,
     29         clear=\E[2J\E[H,
And of course, sending the wrong sequence (e.g. like trying some to
see what works) can be highly problematic - it can do very nasty
things to some terminals.  E.g. I own one terminal, which among
sequences it supports, is one which effectively says interpret the
following hexadecimal character pairs as bytes, load them into RAM,
and execute them - a relatively sure-fire way to crash the terminal if
it is sent garbage (I used to run into that and other problems with
some BBS systems that would presume everyone must be running something
ANSI capable or that it was safe to do other tests such as see if
certain sequences would render a blue square on one's screen).

references:
"system" call/function, in various programming languages
clear(1)
tput(1)
terminfo(5)
termcap(5)
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