--- /dev/null
+.\"***************************************************************************
+.\" Copyright 2018-2021,2022 Thomas E. Dickey *
+.\" Copyright 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 1.1 2024/04/27 15:05:55 jmc 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
+.ie n .in -4
+.el .in -2
+..
+.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\fP \- clear the terminal screen
+.SH SYNOPSIS
+\fBclear\fR [\fB\-T\fItype\fR] [\fB\-V\fR] [\fB\-x\fR]
+.br
+.SH DESCRIPTION
+\fBclear\fP clears your terminal's screen if this is possible,
+including the terminal's scrollback buffer
+(if the extended \*(``E3\*('' capability is defined).
+\fBclear\fP looks in the environment for the terminal type
+given by the environment variable \fBTERM\fP,
+and then in the
+\fBterminfo\fP database to determine how to clear the screen.
+.PP
+\fBclear\fP writes to the standard output.
+You can redirect the standard output to a file (which prevents
+\fBclear\fP 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\fP of terminal.
+Normally this option is
+unnecessary, because the default is taken from the environment
+variable \fBTERM\fP.
+If \fB\-T\fP is specified, then the shell
+variables \fBLINES\fP and \fBCOLUMNS\fP 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, \fBxterm\fP 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 \fBxterm\fP.
+.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 \fBxterm\fP,
+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\fP(1), \fBterminfo\fP(\*n), \fBxterm\fP(1).
+.PP
+This describes \fBncurses\fP
+version 6.4 (patch 20221231).
projects / openbsd / commitdiff