* sale, use or other dealings in this Software without prior written *
* authorization. *
****************************************************************************
- * @Id: clear.1,v 1.38 2023/09/16 23:39:05 tom Exp @
- * these would be fallbacks for DS/DE,
- * but groff changed the meaning of the macros.
+ * @Id: clear.1,v 1.40 2023/10/01 22:12:38 tom Exp @
+ * https://minnie.tuhs.org/cgi-bin/utree.pl?file=2BSD/src/clear.c
+ * https://minnie.tuhs.org/cgi-bin/utree.pl?file=Net2/usr/src/usr.bin/\
+ * tput/clear.sh
-->
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-<TITLE>clear 1 2023-09-16 ncurses 6.4 User commands</TITLE>
+<TITLE>clear 1 2023-10-01 ncurses 6.4 User commands</TITLE>
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-<H1 class="no-header">clear 1 2023-09-16 ncurses 6.4 User commands</H1>
+<H1 class="no-header">clear 1 2023-10-01 ncurses 6.4 User commands</H1>
<PRE>
<STRONG><A HREF="clear.1.html">clear(1)</A></STRONG> User commands <STRONG><A HREF="clear.1.html">clear(1)</A></STRONG>
</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>]
+ <STRONG>clear</STRONG> [<STRONG>-x</STRONG>] [<STRONG>-T</STRONG> <EM>type</EM>]
+
+ <STRONG>clear</STRONG> <STRONG>-V</STRONG>
</PRE><H2><a name="h2-DESCRIPTION">DESCRIPTION</a></H2><PRE>
- <STRONG>clear</STRONG> clears your terminal's screen if this is possible, including the
- terminal's 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> clears your terminal's screen and its scrollback buffer, if any.
+ <STRONG>clear</STRONG> retrieves the terminal type from the environment variable <STRONG>TERM</STRONG>,
+ then consults the <EM>terminfo</EM> terminal capability database entry for that
+ type to determine how to perform these actions.
- <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.
+ The capabilities to clear the screen and scrollback buffer are named
+ "clear" and "E3", respectively. The latter is a <EM>user-defined</EM>
+ <EM>capability</EM>, applying an extension mechanism introduced in <EM>ncurses</EM> 5.0
+ (1999).
</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
- unnecessary, 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>COLUMNS</STRONG> will also be ignored.
+ <STRONG>clear</STRONG> recognizes the following options.
+
+ <STRONG>-T</STRONG> <EM>type</EM> produces instructions suitable for the terminal <EM>type</EM>.
+ Normally, this option is unnecessary, because the terminal
+ type is inferred from the environment variable <STRONG>TERM</STRONG>. If this
+ option is specified, <STRONG>clear</STRONG> ignores the environment variables
+ <STRONG>LINES</STRONG> and <STRONG>COLUMNS</STRONG> as well.
- <STRONG>-V</STRONG> reports the version of ncurses which was used in this program, and
- exits. The options are as follows:
+ <STRONG>-V</STRONG> reports the version of <EM>ncurses</EM> associated with this program
+ and exits with a successful status.
- <STRONG>-x</STRONG> do not attempt to clear the terminal's scrollback buffer using the
- extended "E3" capability.
+ <STRONG>-x</STRONG> prevents <STRONG>clear</STRONG> from attempting to clear the scrollback buffer.
</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).
+ A <STRONG>clear</STRONG> command using the <EM>termcap</EM> database and library appeared in 2BSD
+ (1979). Eighth Edition Unix (1985) later included it.
- 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.,
+ The commercial Unix arm of AT&T adapted a different BSD program (<STRONG>tset</STRONG>)
+ to make a new command, <STRONG>tput</STRONG>, and replaced the <STRONG>clear</STRONG> program with a
+ shell script that called "<STRONG>tput</STRONG> <STRONG>clear</STRONG>".
/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
- similar to the AT&T <STRONG>tput</STRONG>, he added a shell script for the <STRONG>clear</STRONG>
- command:
+ In 1989, when Keith Bostic revised the BSD <STRONG>tput</STRONG> command to make it
+ similar to AT&T's <STRONG>tput</STRONG>, he added a <STRONG>clear</STRONG> shell script as well.
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).
+ In 1995, <EM>ncurses</EM>'s <STRONG>clear</STRONG> began by adapting BSD's original <STRONG>clear</STRONG> command
+ to use <EM>terminfo</EM>. The <STRONG>E3</STRONG> extension came later.
- The <STRONG>E3</STRONG> extension came later:
-
- <STRONG>o</STRONG> In June 1999, <STRONG>xterm</STRONG> provided an extension to the standard control
+ <STRONG>o</STRONG> In June 1999, <EM>xterm</EM> 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
+ one could clear the scrollback buffer using
printf '\033[<STRONG>3</STRONG>J'
- This is documented in <EM>XTerm</EM> <EM>Control</EM> <EM>Sequences</EM> as a feature
- originating with <STRONG>xterm</STRONG>.
+ "XTerm Control Sequences" documents this feature as originating
+ with <EM>xterm</EM>.
- <STRONG>o</STRONG> A few other terminal developers adopted the feature, e.g., PuTTY in
- 2006.
+ <STRONG>o</STRONG> A few other terminal emulators adopted it, such as 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 <STRONG>xterm</STRONG>,
- although it was cited in the Red Hat bug report (#683733) which led
- to the change.
+ <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.
+ Documentation of this change, appearing in Linux 3.0, did not
+ mention <EM>xterm</EM>, although that program was cited in the Red Hat bug
+ report (#683733) motivating the feature.
- <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> Subsequently, more terminal developers adopted the feature. The
+ next relevant step was to change the <EM>ncurses</EM> <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>.
+ <STRONG>o</STRONG> In 2013, the <STRONG>E3</STRONG> capability was not exercised by "<STRONG>tput</STRONG> <STRONG>clear</STRONG>". That
+ oversight 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.
+ (POSIX.1-2008) nor X/Open Curses Issue 7 documents <STRONG>tset</STRONG> or <STRONG>reset</STRONG>.
- 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
+ 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>xterm(1)</STRONG>, <STRONG><A HREF="terminfo.5.html">terminfo(5)</A></STRONG>.
-
- This describes <STRONG>ncurses</STRONG> version 6.4 (patch 20230923).
+ <STRONG><A HREF="tput.1.html">tput(1)</A></STRONG>, <STRONG>xterm(1)</STRONG>, <STRONG><A HREF="terminfo.5.html">terminfo(5)</A></STRONG>
-ncurses 6.4 2023-
09-16 <STRONG><A HREF="clear.1.html">clear(1)</A></STRONG>
+ncurses 6.4 2023-
10-01 <STRONG><A HREF="clear.1.html">clear(1)</A></STRONG>
</PRE>
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