How to Clear Shell Console

shellterminal

Is there a way to clear up what is displayed on the shell console (in ubuntu linux) in just a single key or two? When I get flood of lines from grep and that exceeds the height of the window, I want to quickly scroll back to the position where I typed the command after the prompt. I can do so if I had opened a fresh terminal before I type the command, and just go to the initial position. But if keep using the same terminal window, I have to manually find the position. Ctrl+l is not an answer because it just scrolls, and the contents of the terminal remains. I cannot use less because the colored output of grep does not show up in color.

Best Answer

The

reset

command, which is part of ncurses, and is located in the ncurses-bin package on Debian, will completely clear the console. Is that what you want?

Brief summary of reset from the man page:

reset sets cooked and echo modes, turns off cbreak and raw modes, turns on new-line translation and resets any unset special characters to their default values before doing terminal initialization the same way as tset.

As discussed in https://superuser.com/questions/122911/bash-reset-and-clear-commands, and as pointed out by Erik in Shell console clearing, clear will just clear the screen, reset will (as bignose put it), "reset your terminal when it gets messed up by control sequences". Personally, I'm good at messing up my terminal, and when I clear it, I'm not looking to get anything back that was there before, so I just use reset. But ymmv.

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The terminals listed hints that the behavior is seen with Linux: The clues are in the manual page for wall (Solaris for instance is different):

wall displays a message, or the contents of a file, or otherwise its standard input, on the terminals of all currently logged in users.

Some sessions, such as wdm, that have in the beginning of utmp(5) ut_type data a ':' character will not get the message from wall. This is done to avoid write errors.

That is, wall uses the utmp data, looks for terminals in use (i.e., logged-in users), and writes to the associated device. Each line in the output of w shows a (possible) terminal, recorded by the terminal in the utmp file. For instance, I am ssh'd into a server and running screen while at the same time I logged into a console. Just for completeness, I ran xterm using the -ls (login-shell) option. Here is the output of w:

$ w
 19:53:15 up  4:08,  5 users,  load average: 0.00, 0.01, 0.05
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
tom      tty2                      19:48    5:11   0.04s  0.02s -tcsh
tom      pts/0    michener:S.0     15:51   13:18   0.35s  0.24s ssh -X thomas@b
tom      pts/2    michener:S.1     16:34    2.00s  0.14s  0.00s sh -c w
tom      pts/4    michener:S.3     15:52    3:59m  0.12s  0.00s /bin/sh /users/
tom      pts/3    localhost:10.0   19:53    7.00s  0.03s  0.03s -tcsh

and running wall writes to each of those TTY devices.

However, if the terminal does not write to the utmp file, it will not be listed — and wall will ignore it.

Now, some programs may have the feature compiled-in, but lack privileges to change it. That is why some programs are run with setgid to the "utmp" group. Other programs (such as xterm — or gnome-terminal) may use an external program that updates utmp on their behalf.

With gnome-terminal, the feature has been deprecated due to the mindset of the gnome developers that (a) users run on a local machine, where gdm handles login, and (b) consequently there's no distinction worth bothering about between login shells and non-login shells. That makes for some interesting bug reports:

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