Vim

From Chaehyun

다중 라인 코멘트 (multi line comment)

Select your lines with VISUAL BLOCK (CTRL-V), then press I to insert before all highlighted lines. Next type your comment character, # (for python, shell, etc). Last press ESC.

I forget not frequently used, but helpful VIM commands from time to time. Why not blog it?

You can alternatively select your lines with VISUAL LINE (SHIFT-V), then type : s/^/#