Keyboard shortcut to store typed command and clean the line

After you've used CTRL-U you can use CTRL-Y to paste back what you've erased. It works after erasing a word or a number of words with CTRL-W too.

Note this way you don't really need to copy anything to the clipboard or select it with the mouse - CTRL-U actually yanks the line to a separate clipboard, so to speak.

Add a '#' to the beginning of your current line. Hit enter to add the comment to your history. Execute the prerequisite command. Go up to the previous command and delete the #.

This was recently asked and discussed over on SE's Unix & Linux site. My answer explained that if you use zsh as your shell, you can use the push-line feature to stash your command-in-progress away, run something else, then your first command will come back and you can finish it. In .zshrc:

bindkey '^L' push-line

Then use Ctrl+L to suspend the current command and come back to it after running something else.

Several other answers were given including settings for how to do something similar in bash and some customized versions of this builtin in zsh.