.\"***************************************************************************
-.\" Copyright (c) 1998-2006,2010 Free Software Foundation, Inc. *
+.\" Copyright 2018-2023,2024 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 *
.\" authorization. *
.\"***************************************************************************
.\"
-.\" $Id: clear.1,v 1.8 2010/12/04 18:36:44 tom Exp $
-.TH @CLEAR@ 1 ""
-.ds n 5
+.\" $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"
+.ie \n(.g \{\
+.ds `` \(lq
+.ds '' \(rq
+.ds ' \(aq
+.\}
+.el \{\
+.ie t .ds `` ``
+.el .ds `` ""
+.ie t .ds '' ''
+.el .ds '' ""
+.ie t .ds ' \(aq
+.el .ds ' '
+.\}
+.
+.de bP
+.ie n .IP \(bu 4
+.el .IP \(bu 2
+..
+.
.SH NAME
-\fB@CLEAR@\fR \- clear the terminal screen
+\fB\%@CLEAR@\fP \-
+clear the terminal screen
.SH SYNOPSIS
-\fB@CLEAR@\fR
-.br
+.B @CLEAR@
+.RB [ \-x ]
+.RB [ \-T\ \c
+.IR terminal-type ]
+.PP
+.B "@CLEAR@ \-V"
.SH DESCRIPTION
-\fB@CLEAR@\fR clears your screen if this is possible. It looks in the
-environment for the terminal type and then in the \fBterminfo\fR database to
-figure out how to clear the screen.
+\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
-\fB@CLEAR@\fR ignores any command-line parameters that may be present.
-.SH SEE ALSO
-\fB@TPUT@\fR(1), \fBterminfo\fR(\*n)
+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
-This describes \fBncurses\fR
-version @NCURSES_MAJOR@.@NCURSES_MINOR@ (patch @NCURSES_PATCH@).
+.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)
projects / ncurses.git / blobdiff