X-Git-Url: https://ncurses.scripts.mit.edu/?p=ncurses.git;a=blobdiff_plain;f=man%2Fclear.1;h=16914dbb96ca8e5132ebdc958eb2306535dadc7f;hp=31d0f93e05b9c68a841fe75443e4537546d903c4;hb=cd142df6d9934f1bda19f5b968cc666291be5072;hpb=f70db18a0c3c6a828d8a5999be37239f01c9d98a;ds=sidebyside

diff --git a/man/clear.1 b/man/clear.1
index 31d0f93e..16914dbb 100644
--- a/man/clear.1
+++ b/man/clear.1
@@ -1,5 +1,5 @@
 .\"***************************************************************************
-.\" Copyright (c) 1998-2000,2006 Free Software Foundation, Inc.              *
+.\" 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            *
@@ -26,28 +26,133 @@
 .\" authorization.                                                           *
 .\"***************************************************************************
 .\"
-.\" $Id: clear.1,v 1.6 2006/12/24 18:07:53 tom Exp $
+.\" $Id: clear.1,v 1.18 2017/10/07 21:30:17 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
+.IP \(bu 4
+..
 .ds n 5
 .SH NAME
-\fB@CLEAR@\fR - clear the terminal screen
+\fB@CLEAR@\fR \- clear the terminal screen
 .SH SYNOPSIS
-\fB@CLEAR@\fR
+\fB@CLEAR@\fR [\fB\-T\fR\fItype\fR] [\fB\-V\fP] [\fB\-x\fP]
 .br
 .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@\fR clears your screen if this is possible,
+including its scrollback buffer (if the extended \*(``E3\*('' capability is defined).
+\fB@CLEAR@\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
-\fB@CLEAR@\fR ignores any command-line parameters that may be present.
+\fB@CLEAR@\fR writes to the standard output.
+You can redirect the standard output to a file (which prevents
+\fB@CLEAR@\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 \fB@TPUT@\fP with
+the \*(``clear\*('' parameter.
+That was addressed in 2016 by reorganizing \fB@TPUT@\fP to share
+its logic with \fB@CLEAR@\fP and \fB@TSET@\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 \fB@TPUT@\fP as \fB@CLEAR@\fP.
 .SH SEE ALSO
 \fB@TPUT@\fR(1), \fBterminfo\fR(\*n)
 .PP
 This describes \fBncurses\fR
 version @NCURSES_MAJOR@.@NCURSES_MINOR@ (patch @NCURSES_PATCH@).
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