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- * Copyright (c) 1998-2010,2013 Free Software Foundation, Inc. *
+ * Copyright (c) 1998-2016,2017 Free Software Foundation, Inc. *
* *
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* copy of this software and associated documentation files (the *
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- * @Id: clear.1,v 1.10 2013/06/22 22:22:11 tom Exp @
+ * @Id: clear.1,v 1.18 2017/10/07 21:30:17 tom Exp @
+ * these would be fallbacks for DS/DE,
+ * but groff changed the meaning of the macros.
-->
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<H1 class="no-header">clear 1</H1>
<PRE>
-<STRONG><A HREF="clear.1.html">clear(1)</A></STRONG> <STRONG><A HREF="clear.1.html">clear(1)</A></STRONG>
+<STRONG><A HREF="clear.1.html">clear(1)</A></STRONG>
<STRONG><A HREF="clear.1.html">clear(1)</A></STRONG>
</PRE><H2><a name="h2-SYNOPSIS">SYNOPSIS</a></H2><PRE>
- <STRONG>clear</STRONG>
+ <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 and then in the <STRONG>terminfo</STRONG> database to determine how to
- clear the screen.
+ <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> ignores any command-line parameters that may be
- present.
+ <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 6.0 (patch 20160521).
+ This describes <STRONG>ncurses</STRONG> version 6.0 (patch 20171007).
- <STRONG><A HREF="clear.1.html">clear(1)</A></STRONG>
+
<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>
</div>
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