https://invisible-island.net/ncurses/man/
clear(1) User commands clear(1)
clear - clear the terminal screen
clear [-x] [-T terminal-type]
clear -V
clear clears your terminal's screen and its scrollback buffer, if any.
clear retrieves the terminal type from the environment variable TERM,
then consults the terminfo terminal capability database entry for that
type to determine how to perform these actions.
The capabilities to clear the screen and scrollback buffer are named
"clear" and "E3", respectively. The latter is a user-defined
capability, applying an extension mechanism introduced in ncurses 5.0
(1999).
clear recognizes the following options.
-T type produces instructions suitable for the terminal type.
Normally, this option is unnecessary, because the terminal
type is inferred from the environment variable TERM. If this
option is specified, clear ignores the environment variables
LINES and COLUMNS as well.
-V reports the version of ncurses associated with this program
and exits with a successful status.
-x prevents clear from attempting to clear the scrollback buffer.
Neither IEEE Std 1003.1/The Open Group Base Specifications Issue 7
(POSIX.1-2008) nor X/Open Curses Issue 7 documents clear.
The latter documents tput, which could be used to replace this utility
either via a shell script or by an alias (such as a symbolic link) to
run tput as clear.
A clear command using the termcap database and library appeared in 2BSD
(1979). Eighth Edition Unix (1985) later included it.
The commercial Unix arm of AT&T adapted a different BSD program (tset)
to make a new command, tput, and replaced the clear program with a
shell script that called "tput clear".
/usr/bin/tput ${1:+-T$1} clear 2> /dev/null
exit
In 1989, when Keith Bostic revised the BSD tput command to make it
similar to AT&T's tput, he added a clear shell script as well.
exec tput clear
The remainder of the script in each case is a copyright notice.
In 1995, ncurses's clear began by adapting BSD's original clear command
to use terminfo. The E3 extension came later.
o In June 1999, xterm provided an extension to the standard control
sequence for clearing the screen. Rather than clearing just the
visible part of the screen using
printf '\033[2J'
one could clear the scrollback buffer as well by using
printf '\033[3J'
instead. "XTerm Control Sequences" documents this feature as
originating with xterm.
o A few other terminal emulators adopted it, such as PuTTY in 2006.
o In April 2011, a Red Hat developer submitted a patch to the Linux
kernel, modifying its console driver to do the same thing.
Documentation of this change, appearing in Linux 3.0, did not
mention xterm, although that program was cited in the Red Hat bug
report (#683733) motivating the feature.
o Subsequently, more terminal developers adopted the feature. The
next relevant step was to change the ncurses clear program in 2013
to incorporate this extension.
o In 2013, the E3 capability was not exercised by "tput clear". That
oversight was addressed in 2016 by reorganizing tput to share its
logic with clear and tset.
tput(1), xterm(1), terminfo(5)
ncurses 6.5 2024-03-16 clear(1)