How can we undo the clear command in Linux?

Question

clear clears the screen of the terminal.

Is there any command that can restore the original screen contents from before clear was run, effectively undoing that clear?

Answer 1

There is no direct opposite of the clear command, which clears a terminal screen.

However, some implementations of a command line terminal emulator offer a scroll-back buffer. This buffer may keep previous lines of output. For example, using these commands in mintty from Cygwin to generate text and then clear the screen I find that I am able to scroll back to the previous result. However, this is implemented purely as part of a terminal emulator and is unlikely to be accessible programmatically:

yes | head -n20 | nl     # Generate 20 lines of unique output
yes n | head -n20 | nl   # And some more

clear

After scroll-back

Answer 2

If using the tmux terminal emulator/multiplexer, you could define an undoable clear as:

clear() {
  tmux capture-pane -eb c &&
    tput sc &&
    command clear "$@"
}

And unclear as:

unclear() {
  tput home && tmux show-buffer -b c && tput rc
}

Where clear captures the contents of the screen into the c buffer and saves the cursor position before clearing and unclear dumps the contents of that buffer after having moved the cursor to the home position (top-left) and then restores the cursor position.

Answer 3

If you mean undo, then there is ★nothing. Except, you can go through the command history and re-run a command. If the command is idempotent, then you will get the same result.

Footnotes: ★ nothing unless you use some sort of logging system. This logging may be part of a terminal program, or separate. It is not part of the kernel called Linux.