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* @Id: clear.1,v 1.23 2020/02/02 23:34:34 tom Exp @
* these would be fallbacks for DS/DE,
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<H1 class="no-header">clear 1</H1>
<PRE>
<STRONG><A HREF="clear.1.html">clear(1)</A></STRONG> General Commands Manual <STRONG><A HREF="clear.1.html">clear(1)</A></STRONG>
</PRE><H2><a name="h2-NAME">NAME</a></H2><PRE>
<STRONG>clear</STRONG> - clear the terminal screen
</PRE><H2><a name="h2-SYNOPSIS">SYNOPSIS</a></H2><PRE>
<STRONG>clear</STRONG> [<STRONG>-T</STRONG><EM>type</EM>] [<STRONG>-V</STRONG>] [<STRONG>-x</STRONG>]
</PRE><H2><a name="h2-DESCRIPTION">DESCRIPTION</a></H2><PRE>
<STRONG>clear</STRONG> clears your screen if this is possible, including its scrollback
buffer (if the extended "E3" capability is defined). <STRONG>clear</STRONG> looks in
the environment for the terminal type given by the environment variable
<STRONG>TERM</STRONG>, and then in the <STRONG>terminfo</STRONG> database to determine how to clear the
screen.
<STRONG>clear</STRONG> writes to the standard output. You can redirect the standard
output to a file (which prevents <STRONG>clear</STRONG> from actually clearing the
screen), and later <STRONG>cat</STRONG> the file to the screen, clearing it at that
point.
</PRE><H2><a name="h2-OPTIONS">OPTIONS</a></H2><PRE>
<STRONG>-T</STRONG> <EM>type</EM>
indicates the <EM>type</EM> of terminal. Normally this option is unneces-
sary, because the default is taken from the environment variable
<STRONG>TERM</STRONG>. If <STRONG>-T</STRONG> is specified, then the shell variables <STRONG>LINES</STRONG> and <STRONG>COL-</STRONG>
<STRONG>UMNS</STRONG> will also be ignored.
<STRONG>-V</STRONG> reports the version of ncurses which was used in this program, and
exits. The options are as follows:
<STRONG>-x</STRONG> do not attempt to clear the terminal's scrollback buffer using the
extended "E3" capability.
</PRE><H2><a name="h2-HISTORY">HISTORY</a></H2><PRE>
A <STRONG>clear</STRONG> command appeared in 2.79BSD dated February 24, 1979. Later
that was provided in Unix 8th edition (1985).
AT&T adapted a different BSD program (<STRONG>tset</STRONG>) to make a new command
(<STRONG>tput</STRONG>), and used this to replace the <STRONG>clear</STRONG> command with a shell script
which calls <STRONG>tput</STRONG> <STRONG>clear</STRONG>, e.g.,
/usr/bin/tput ${1:+-T$1} clear 2> /dev/null
exit
In 1989, when Keith Bostic revised the BSD <STRONG>tput</STRONG> command to make it sim-
ilar to the AT&T <STRONG>tput</STRONG>, he added a shell script for the <STRONG>clear</STRONG> command:
exec tput clear
The remainder of the script in each case is a copyright notice.
The ncurses <STRONG>clear</STRONG> command began in 1995 by adapting the original BSD
<STRONG>clear</STRONG> command (with terminfo, of course).
The <STRONG>E3</STRONG> extension came later:
<STRONG>o</STRONG> 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
printf '\033[2J'
one could clear the <EM>scrollback</EM> using
printf '\033[<STRONG>3</STRONG>J'
This is documented in <EM>XTerm</EM> <EM>Control</EM> <EM>Sequences</EM> as a feature origi-
nating with xterm.
<STRONG>o</STRONG> A few other terminal developers adopted the feature, e.g., PuTTY in
2006.
<STRONG>o</STRONG> 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.
<STRONG>o</STRONG> Again, a few other terminal developers adopted the feature. But
the next relevant step was a change to the <STRONG>clear</STRONG> program in 2013 to
incorporate this extension.
<STRONG>o</STRONG> In 2013, the <STRONG>E3</STRONG> extension was overlooked in <STRONG>tput</STRONG> with the "clear"
parameter. That was addressed in 2016 by reorganizing <STRONG>tput</STRONG> to
share its logic with <STRONG>clear</STRONG> and <STRONG>tset</STRONG>.
</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
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.
The latter documents <STRONG>tput</STRONG>, which could be used to replace this utility
either via a shell script or by an alias (such as a symbolic link) to
run <STRONG>tput</STRONG> as <STRONG>clear</STRONG>.
</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>
<STRONG><A HREF="tput.1.html">tput(1)</A></STRONG>, <STRONG><A HREF="terminfo.5.html">terminfo(5)</A></STRONG>
This describes <STRONG>ncurses</STRONG> version 6.2 (patch 20200212).
<STRONG><A HREF="clear.1.html">clear(1)</A></STRONG>
</PRE>
<div class="nav">
<ul>
<li><a href="#h2-NAME">NAME</a></li>
<li><a href="#h2-SYNOPSIS">SYNOPSIS</a></li>
<li><a href="#h2-DESCRIPTION">DESCRIPTION</a></li>
<li><a href="#h2-OPTIONS">OPTIONS</a></li>
<li><a href="#h2-HISTORY">HISTORY</a></li>
<li><a href="#h2-PORTABILITY">PORTABILITY</a></li>
<li><a href="#h2-SEE-ALSO">SEE ALSO</a></li>
</ul>
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