man/clear.1

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.\" $Id: clear.1,v 1.48 2024/03/16 15:35:01 tom Exp $
.TH @CLEAR@ 1 2024-03-16 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "User commands"
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.SH NAME
\fB\%@CLEAR@\fP \-
clear the terminal screen
.SH SYNOPSIS
.B @CLEAR@
.RB [ \-x ]
.RB [ \-T\ \c
.IR terminal-type ]
.PP
.B "@CLEAR@ \-V"
.SH DESCRIPTION
\fB\%@CLEAR@\fP clears your terminal's screen and its scrollback buffer,
if any.
\fB\%@CLEAR@\fP retrieves the terminal type from the environment
variable \fITERM\fP,
then consults the \fIterminfo\fP terminal capability database entry for
that type to determine how to perform these actions.
.PP
The capabilities to clear the screen and scrollback buffer are named
\*(``clear\*('' and \*(``E3\*('', respectively.
The latter is a \fIuser-defined capability\fP,
applying an extension mechanism introduced in \fI\%ncurses\fP 5.0
(1999).
.SH OPTIONS
\fB\%@CLEAR@\fP recognizes the following options.
.TP 9 \" "-T type" + 2n
.B \-T \fItype\fP
produces instructions suitable for the terminal \fItype\fP.
Normally,
this option is unnecessary,
because the terminal type is inferred from the environment variable
\fITERM\fP.
If this option is specified,
\fB\%@CLEAR@\fP ignores the environment variables \fILINES\fP and
\fI\%COLUMNS\fP as well.
.TP
.B \-V
reports the version of \fI\%ncurses\fP associated with this program and
exits with a successful status.
.TP
.B \-x
prevents \fB\%@CLEAR@\fP from attempting to clear the scrollback buffer.
.SH PORTABILITY
Neither IEEE Std 1003.1/The Open Group Base Specifications Issue 7
(POSIX.1-2008) nor X/Open Curses Issue 7 documents \fB\%@CLEAR@\fP.
.PP
The latter documents \fBtput\fP,
which could be used to replace this utility either via a shell script or
by an alias
(such as a symbolic link)
to run \fB\%@TPUT@\fP as \fB\%@CLEAR@\fP.
.SH HISTORY
A \fBclear\fP command using the \fItermcap\fP database and library
appeared in 2BSD (1979).
.\" https://minnie.tuhs.org/cgi-bin/utree.pl?file=2BSD/src/clear.c
Eighth Edition Unix (1985) later included it.
.PP
The commercial Unix arm of AT&T adapted a different BSD program
(\fBtset\fP) to make a new command,
\fBtput\fP,
and replaced the \fBclear\fP program with a shell script that called
\*(``\fBtput clear\fP\*(''.
.PP
.RS 4
.EX
/usr/bin/tput ${1:+\-T$1} clear 2> /dev/null
exit
.EE
.RE
.PP
In 1989, when Keith Bostic revised the BSD \fBtput\fP command
to make it similar to AT&T's \fBtput\fP,
he added a \fBclear\fP shell script as well.
.\" https://minnie.tuhs.org/cgi-bin/utree.pl?file=Net2/usr/src/usr.bin/\
.\"   tput/clear.sh
.PP
.RS 4
.EX
exec tput clear
.EE
.RE
.PP
The remainder of the script in each case is a copyright notice.
.PP
In 1995,
\fI\%ncurses\fP's \fBclear\fP began by adapting BSD's original
\fBclear\fP command to use \fIterminfo\fP.
The \fBE3\fP extension came later.
.bP
In June 1999, \fIxterm\fP provided an extension to the standard control
sequence for clearing the screen.
Rather than clearing just the visible part of the screen using
.RS 8
.PP
.EX
printf \*'\e033[2J\*'
.EE
.RE
.IP
one could clear the scrollback buffer as well by using
.RS 8
.PP
.EX
printf \*'\e033[\fB3\fPJ\*'
.EE
.RE
.IP
instead.
\*(``XTerm Control Sequences\fP\*('' documents this feature as
originating with \fIxterm\fP.
.bP
A few other terminal emulators adopted it,
such as PuTTY in 2006.
.bP
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 \fIxterm\fP,
although that program was cited in the Red Hat bug report (#683733)
motivating the feature.
.bP
Subsequently,
more terminal developers adopted the feature.
The next relevant step was to change the \fI\%ncurses\fP \fBclear\fP
program in 2013 to incorporate this extension.
.bP
In 2013,
the \fBE3\fP capability was not exercised by
\*(``\fB\%@TPUT@ clear\fP\*(''.
That oversight was addressed in 2016 by reorganizing \fB\%@TPUT@\fP to
share its logic with \fB\%@CLEAR@\fP and \fB\%@TSET@\fP.
.SH SEE ALSO
\fB\%@TPUT@\fP(1),
\fB\%xterm\fP(1),
\fB\%terminfo\fP(5)