- clear clears your screen if this is possible, including its scrollback
- buffer (if the extended "E3" capability is defined). clear looks in
- the environment for the terminal type given by the environment variable
- TERM, and then in the terminfo database to determine how to clear the
- screen.
+ clear clears your terminal's screen and its scrollback buffer, if any.
+ clear retrieves the terminal type from the environment variable TERM,
+ then consults the terminfo terminal capability database entry for that
+ type to determine how to perform these actions.
- clear writes to the standard output. You can redirect the standard
- output to a file (which prevents clear from actually clearing the
- screen), and later cat 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 user-defined
+ capability, applying an extension mechanism introduced in ncurses 5.0
+ (1999).
- -Ttype
- indicates the type of terminal. Normally this option is unneces-
- sary, because the default is taken from the environment variable
- TERM. If -T is specified, then the shell variables LINES and COL-
- UMNS will also be ignored.
+ clear recognizes the following options.
+
+ -Ttype produces instructions suitable for the terminal type.
+ Normally, this option is unnecessary, because the terminal
+ type is inferred from the environment variable TERM. If this
+ option is specified, clear ignores the environment variables
+ LINES and COLUMNS as well.
+
+ -V reports the version of ncurses associated with this program
+ and exits with a successful status.
+
+ -x prevents clear from attempting to clear the scrollback buffer.
+
- -V reports the version of ncurses which was used in this program, and
- exits. The options are as follows:
+
+ Neither IEEE Std 1003.1/The Open Group Base Specifications Issue 7
+ (POSIX.1-2008) nor X/Open Curses Issue 7 documents clear.
- -x do not attempt to clear the terminal's scrollback buffer using the
- extended "E3" capability.
+ The latter documents tput, which could be used to replace this utility
+ either via a shell script or by an alias (such as a symbolic link) to
+ run tput as clear.
- A clear command appeared in 2.79BSD dated February 24, 1979. Later
- that was provided in Unix 8th edition (1985).
+ A clear command using the termcap database and library appeared in 2BSD
+ (1979). Eighth Edition Unix (1985) later included it.
- AT&T adapted a different BSD program (tset) to make a new command
- (tput), and used this to replace the clear command with a shell script
- which calls tputclear, e.g.,
+ The commercial Unix arm of AT&T adapted a different BSD program (tset)
+ to make a new command, tput, and replaced the clear program with a
+ shell script that called "tputclear".
/usr/bin/tput ${1:+-T$1} clear 2> /dev/null
exit
- In 1989, when Keith Bostic revised the BSD tput command to make it sim-
- ilar to the AT&T tput, he added a shell script for the clear command:
+ In 1989, when Keith Bostic revised the BSD tput command to make it
+ similar to AT&T's tput, he added a clear shell script as well.
exec tput clear
The remainder of the script in each case is a copyright notice.
- The ncurses clear command began in 1995 by adapting the original BSD
- clear command (with terminfo, of course).
-
- The E3 extension came later:
+ In 1995, ncurses's clear began by adapting BSD's original clear command
+ to use terminfo. The E3 extension came later.
- o In June 1999, xterm provided an extension to the standard control
+ o 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 scrollback using
+ one could clear the scrollback buffer as well by using
printf '\033[3J'
- This is documented in XTermControlSequences as a feature origi-
- nating with xterm.
+ instead. "XTerm Control Sequences" documents this feature as
+ originating with xterm.
- o A few other terminal developers adopted the feature, e.g., PuTTY in
- 2006.
+ o A few other terminal emulators adopted it, such as PuTTY in 2006.
- o 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.
+ o 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 xterm, although that program was cited in the Red Hat bug
+ report (#683733) motivating the feature.
- o Again, a few other terminal developers adopted the feature. But
- the next relevant step was a change to the clear program in 2013 to
- incorporate this extension.
+ o Subsequently, more terminal developers adopted the feature. The
+ next relevant step was to change the ncursesclear program in 2013
+ to incorporate this extension.
- o In 2013, the E3 extension was overlooked in tput with the "clear"
- parameter. That was addressed in 2016 by reorganizing tput to
- share its logic with clear and tset.
-
-
-
- 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 tput, which could be used to replace this utility
- either via a shell script or by an alias (such as a symbolic link) to
- run tput as clear.
+ o In 2013, the E3 capability was not exercised by "tputclear". That
+ oversight was addressed in 2016 by reorganizing tput to share its
+ logic with clear and tset.