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!cmd = repeat last usage of that command

!!enter which is 3 buttons where as up-arrow enter is the same thing.

!! is more useful than you think. It's substitute last command here, not just up-arrow enter.

See sudo !!.

By the way, recently discovered you can get some of these shortcuts in all input boxes by activating “emacs shortcuts” inside of gnome-tweaks! Was one of the final blockers for getting me from Mac to Linux

Yes! I use c-u to clear the line all the time.

And <c-w> clears the previous word :) Also <c-y> pastes the line/word back in (so you cant think of it like cut-copy).

You can also use the more standard Home/End/Ctrl+Left/Ctrl+Right to do all of the above. Much easier to remember and works in any other editor also.