`clear` ( 1 )

очистить экран терминала (clear the terminal screen)

Имя (Name)

@CLEAR@ - clear the terminal screen

Синопсис (Synopsis)

@CLEAR@ [-Ttype] [-V] [-x]

Описание (Description)

@CLEAR@ clears your screen if this is possible, including its scrollback buffer (if the extended '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.

Параметры (Options)

-T type
            indicates the type of terminal.  Normally this option is
            unnecessary, because the default 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 options are as follows:

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

История (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:

• 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 using

printf '\033[3J'

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

• A few other terminal developers adopted the feature, e.g., PuTTY in 2006.

• 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.

• 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.

• 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@.

Портативность (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@.

Смотри также (See also)

@TPUT@(1), terminfo(5)

This describes ncurses version @NCURSES_MAJOR@.@NCURSES_MINOR@ (patch @NCURSES_PATCH@).

Исходный текст на man7.org

clear ( 1 )