clear(1) - phpMan

clear(1) General Commands Manual clear(1)

NAME
clear - clear the terminal screen

SYNOPSIS
clear [-Ttype] [-V] [-x]

DESCRIPTION
clear clears your screen if this is possible, including its scrollback buffer (if the ex-
tended "E3" capability is defined). clear looks in the environment for the terminal type
given by the environment variable TERM, and then in the terminfo database to determine how
to clear the screen.

clear writes to the standard output. You can redirect the standard output to a file
(which prevents clear from actually clearing the screen), and later cat the file to the
screen, clearing it at that point.

OPTIONS
-T type
indicates the type of terminal. Normally this option is unnecessary, because the de-
fault is taken from the environment variable TERM. If -T is specified, then the
shell variables LINES and COLUMNS will also be ignored.

-V reports the version of ncurses which was used in this program, and exits. The op-
tions are as follows:

-x do not attempt to clear the terminal's scrollback buffer using the extended "E3" ca-
pability.

HISTORY
A clear command appeared in 2.79BSD dated February 24, 1979. Later that was provided in
Unix 8th edition (1985).

AT&T adapted a different BSD program (tset) to make a new command (tput), and used this to
replace the clear command with a shell script which calls tput clear, e.g.,

/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 the AT&T
tput, he added a shell script for the clear command:

exec tput clear

The remainder of the script in each case is a copyright notice.

The ncurses clear command began in 1995 by adapting the original BSD clear command (with
terminfo, of course).

The E3 extension came later:

o In June 1999, xterm provided an extension to the standard control sequence for clear-
ing the screen. Rather than clearing just the visible part of the screen using

printf '\033[2J'

one could clear the scrollback using

printf '\033[3J'

This is documented in XTerm Control Sequences as a feature originating with xterm.

o A few other terminal developers adopted the feature, e.g., 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. The Linux change, part of the 3.0 release,
did not mention xterm, although it was cited in the Red Hat bug report (#683733) which
led to the change.

o Again, a few other terminal developers adopted the feature. But the next relevant
step was a change to the clear program in 2013 to incorporate this extension.

o In 2013, the E3 extension was overlooked in tput with the "clear" parameter. That was
addressed in 2016 by reorganizing tput to share its logic with clear and tset.

PORTABILITY
Neither IEEE Std 1003.1/The Open Group Base Specifications Issue 7 (POSIX.1-2008) nor
X/Open Curses Issue 7 documents tset or reset.

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.