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8.4 KiB
HTML
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****************************************************************************
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* Copyright 2018-2024,2025 Thomas E. Dickey *
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* Copyright 1998-2016,2017 Free Software Foundation, Inc. *
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* @Id: clear.1,v 1.53 2025/04/05 21:56:26 tom Exp @
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-->
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
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<HTML>
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<HEAD>
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<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
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<meta name="generator" content="Manpage converted by man2html - see https://invisible-island.net/scripts/readme.html#others_scripts">
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<TITLE>clear 1 2025-04-05 ncurses 6.6 User commands</TITLE>
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<link rel="author" href="mailto:bug-ncurses@gnu.org">
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</HEAD>
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<BODY>
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<H1 class="no-header">clear 1 2025-04-05 ncurses 6.6 User commands</H1>
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<PRE>
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<STRONG><A HREF="clear.1.html">clear(1)</A></STRONG> User commands <STRONG><A HREF="clear.1.html">clear(1)</A></STRONG>
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</PRE><H2><a name="h2-NAME">NAME</a></H2><PRE>
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<STRONG>clear</STRONG> - clear the terminal screen
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</PRE><H2><a name="h2-SYNOPSIS">SYNOPSIS</a></H2><PRE>
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<STRONG>clear</STRONG> [<STRONG>-x</STRONG>] [<STRONG>-T</STRONG> <EM>terminal-type</EM>]
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<STRONG>clear</STRONG> <STRONG>-V</STRONG>
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</PRE><H2><a name="h2-DESCRIPTION">DESCRIPTION</a></H2><PRE>
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<STRONG>clear</STRONG> clears your terminal's screen and its scrollback buffer, if any.
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<STRONG>clear</STRONG> retrieves the terminal type from the environment variable <EM>TERM</EM>,
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then consults the <EM>terminfo</EM> terminal capability database entry for that
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type to determine how to perform these actions.
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The capabilities to clear the screen and scrollback buffer are named
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"clear" and "E3", respectively. The latter is a <EM>user-defined</EM>
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<EM>capability</EM>, applying an extension mechanism introduced in <EM>ncurses</EM> 5.0
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(1999).
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</PRE><H2><a name="h2-OPTIONS">OPTIONS</a></H2><PRE>
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<STRONG>clear</STRONG> recognizes the following options.
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<STRONG>-T</STRONG> <EM>type</EM> produces instructions suitable for the terminal <EM>type</EM>.
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Normally, this option is unnecessary, because the terminal
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type is inferred from the environment variable <EM>TERM</EM>. If this
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option is specified, <STRONG>clear</STRONG> ignores the environment variables
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<EM>LINES</EM> and <EM>COLUMNS</EM> as well.
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<STRONG>-V</STRONG> reports the version of <EM>ncurses</EM> associated with this program
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and exits with a successful status.
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<STRONG>-x</STRONG> prevents <STRONG>clear</STRONG> from attempting to clear the scrollback buffer.
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</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
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Neither IEEE Std 1003.1/The Open Group Base Specifications Issue 7
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(POSIX.1-2008) nor X/Open Curses Issue 7 documents <STRONG>clear</STRONG>.
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The latter documents <STRONG>tput</STRONG>, which could be used to replace this utility
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either via a shell script or by an alias (such as a symbolic link) to
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run <STRONG>tput</STRONG> as <STRONG>clear</STRONG>.
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</PRE><H2><a name="h2-HISTORY">HISTORY</a></H2><PRE>
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A <STRONG>clear</STRONG> command using the <EM>termcap</EM> database and library appeared in 2BSD
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(1979). Eighth Edition Unix (1985) later included it.
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The commercial Unix arm of AT&T adapted a different BSD program (<STRONG>tset</STRONG>)
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to make a new command, <STRONG>tput</STRONG>, and replaced the <STRONG>clear</STRONG> program with a
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shell script that called "<STRONG>tput</STRONG> <STRONG>clear</STRONG>".
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/usr/bin/tput ${1:+-T$1} clear 2> /dev/null
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exit
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In 1989, when Keith Bostic revised the BSD <STRONG>tput</STRONG> command to make it
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similar to AT&T's <STRONG>tput</STRONG>, he added a <STRONG>clear</STRONG> shell script as well.
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exec tput clear
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The remainder of the script in each case is a copyright notice.
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In 1995, <EM>ncurses</EM>'s <STRONG>clear</STRONG> began by adapting BSD's original <STRONG>clear</STRONG> command
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to use <EM>terminfo</EM>. The <STRONG>E3</STRONG> extension came later.
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<STRONG>o</STRONG> In June 1999, <EM>xterm</EM> provided an extension to the standard control
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sequence for clearing the screen. Rather than clearing just the
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visible part of the screen using
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printf '\033[2J'
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one could clear the scrollback buffer as well by using
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printf '\033[<STRONG>3</STRONG>J'
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instead. "XTerm Control Sequences" documents this feature as
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originating with <EM>xterm</EM>.
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<STRONG>o</STRONG> A few other terminal emulators adopted it, such as PuTTY in 2006.
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<STRONG>o</STRONG> In April 2011, a Red Hat developer submitted a patch to the Linux
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kernel, modifying its console driver to do the same thing.
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Documentation of this change, appearing in Linux 3.0, did not
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mention <EM>xterm</EM>, although that program was cited in the Red Hat bug
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report (#683733) motivating the feature.
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<STRONG>o</STRONG> Subsequently, more terminal developers adopted the feature. The
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next relevant step was to change the <EM>ncurses</EM> <STRONG>clear</STRONG> program in 2013
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to incorporate this extension.
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<STRONG>o</STRONG> In 2013, the <STRONG>E3</STRONG> capability was not exercised by "<STRONG>tput</STRONG> <STRONG>clear</STRONG>". That
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oversight was addressed in 2016 by reorganizing <STRONG>tput</STRONG> to share its
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logic with <STRONG>clear</STRONG> and <STRONG>tset</STRONG>.
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</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>
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<STRONG><A HREF="tput.1.html">tput(1)</A></STRONG>, <STRONG>xterm(1)</STRONG>, <STRONG><A HREF="terminfo.5.html">terminfo(5)</A></STRONG>
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ncurses 6.6 2025-04-05 <STRONG><A HREF="clear.1.html">clear(1)</A></STRONG>
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</PRE>
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<div class="nav">
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<ul>
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<li><a href="#h2-NAME">NAME</a></li>
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<li><a href="#h2-SYNOPSIS">SYNOPSIS</a></li>
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<li><a href="#h2-DESCRIPTION">DESCRIPTION</a></li>
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<li><a href="#h2-OPTIONS">OPTIONS</a></li>
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<li><a href="#h2-PORTABILITY">PORTABILITY</a></li>
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<li><a href="#h2-HISTORY">HISTORY</a></li>
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<li><a href="#h2-SEE-ALSO">SEE ALSO</a></li>
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</ul>
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</div>
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</BODY>
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</HTML>
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