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.\"***************************************************************************
.\" Copyright (c) 1998-2016,2017 Free Software Foundation, Inc. *
.\" *
.\" Permission is hereby granted, free of charge, to any person obtaining a *
.\" copy of this software and associated documentation files (the *
.\" "Software"), to deal in the Software without restriction, including *
.\" without limitation the rights to use, copy, modify, merge, publish, *
.\" distribute, distribute with modifications, sublicense, and/or sell *
.\" copies of the Software, and to permit persons to whom the Software is *
.\" furnished to do so, subject to the following conditions: *
.\" *
.\" The above copyright notice and this permission notice shall be included *
.\" in all copies or substantial portions of the Software. *
.\" *
.\" THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS *
.\" OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF *
.\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. *
.\" IN NO EVENT SHALL THE ABOVE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, *
.\" DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR *
.\" OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR *
.\" THE USE OR OTHER DEALINGS IN THE SOFTWARE. *
.\" *
.\" Except as contained in this notice, the name(s) of the above copyright *
.\" holders shall not be used in advertising or otherwise to promote the *
.\" sale, use or other dealings in this Software without prior written *
.\" authorization. *
.\"***************************************************************************
.\"
.\" $Id: clear.1,v 1.19 2017/11/18 23:51:59 tom Exp $
.TH clear 1 ""
.\" these would be fallbacks for DS/DE,
.\" but groff changed the meaning of the macros.
.de NS
.ie n .sp
.el .sp .5
.ie n .in +4
.el .in +2
.nf
.ft C \" Courier
..
.de NE
.fi
.ft R
.in -4
..
.ie \n(.g .ds `` \(lq
.el .ds `` ``
.ie \n(.g .ds '' \(rq
.el .ds '' ''
.de bP
.ie n .IP \(bu 4
.el .IP \(bu 2
..
.ds n 5
.SH NAME
\fBclear\fR \- clear the terminal screen
.SH SYNOPSIS
\fBclear\fR [\fB\-T\fR\fItype\fR] [\fB\-V\fP] [\fB\-x\fP]
.br
.SH DESCRIPTION
\fBclear\fR clears your screen if this is possible,
including its scrollback buffer (if the extended \*(``E3\*('' capability is defined).
\fBclear\fR looks in the environment for the terminal type
given by the environment variable \fBTERM\fP,
and then in the
\fBterminfo\fR database to determine how to clear the screen.
.PP
\fBclear\fR writes to the standard output.
You can redirect the standard output to a file (which prevents
\fBclear\fR from actually clearing the screen),
and later \fBcat\fP the file to the screen, clearing it at that point.
.SH OPTIONS
.PP
.TP 5
.B \-T \fItype\fP
indicates the \fItype\fR of terminal.
Normally this option is
unnecessary, because the default is taken from the environment
variable \fBTERM\fR.
If \fB\-T\fR is specified, then the shell
variables \fBLINES\fR and \fBCOLUMNS\fR will also be ignored.
.TP
.B \-V
reports the version of ncurses which was used in this program, and exits.
The options are as follows:
.TP
.B \-x
do not attempt to clear the terminal's scrollback buffer
using the extended \*(``E3\*('' capability.
.SH HISTORY
A \fBclear\fP command appeared in 2.79BSD dated February 24, 1979.
Later that was provided in Unix 8th edition (1985).
.PP
AT&T adapted a different BSD program (\fBtset\fP) to make
a new command (\fBtput\fP),
and used this to replace the \fBclear\fP command with a shell script
which calls \fBtput clear\fP, e.g.,
.NS
/usr/bin/tput ${1:+-T$1} clear 2> /dev/null
exit
.NE
.PP
In 1989, when Keith Bostic revised the BSD \fBtput\fP command
to make it similar to the AT&T \fBtput\fP,
he added a shell script for the \fBclear\fP command:
.NS
exec tput clear
.NE
.PP
The remainder of the script in each case is a copyright notice.
.PP
The ncurses \fBclear\fP command began in 1995 by adapting the original
BSD \fBclear\fP command (with terminfo, of course).
.PP
The \fBE3\fP extension came later:
.bP
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
.NS
printf '\\033[2J'
.NE
.IP
one could clear the \fIscrollback\fP using
.NS
printf '\\033[\fB3\fPJ'
.NE
.IP
This is documented in \fIXTerm Control Sequences\fP as a feature originating
with xterm.
.bP
A few other terminal developers adopted the feature, e.g., 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.
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.
.bP
Again, a few other terminal developers adopted the feature. But the
next relevant step was a change to the \fBclear\fP program in 2013
to incorporate this extension.
.bP
In 2013, the \fBE3\fP extension was overlooked in \fBtput\fP with
the \*(``clear\*('' parameter.
That was addressed in 2016 by reorganizing \fBtput\fP to share
its logic with \fBclear\fP and \fBtset\fP.
.SH 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.
.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 \fBtput\fP as \fBclear\fP.
.SH SEE ALSO
\fBtput\fR(1), \fBterminfo\fR(\*n)
.PP
This describes \fBncurses\fR
version 6.1 (patch 20180317).
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