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clear 1

clear(1)                                                              clear(1)




NAME

       clear - clear the terminal screen


SYNOPSIS

       clear [-Ttype] [-V] [-x]


DESCRIPTION

       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  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.


OPTIONS

       -T type
            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.

       -V   reports the version of ncurses which was used in this program, and
            exits.  The options are as follows:

       -x   do not attempt to clear the terminal's scrollback buffer using the
            extended "E3" capability.


HISTORY

       A  clear  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  (tset)  to  make  a  new  command
       (tput),  and used this to replace the clear command with a shell script
       which calls tput clear, e.g.,

           /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:

           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:

       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

               printf '\033[3J'

           This is documented in XTerm Control Sequences as a  feature  origi-
           nating with xterm.

       o   A few other terminal developers adopted the feature, e.g., 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   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   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.


PORTABILITY

       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.


SEE ALSO

       tput(1), terminfo(5)

       This describes ncurses version 6.0 (patch 20171125).



                                                                      clear(1)