If you've set -o vi, then when you're editing a command line: esc to get into command mode. v (just the letter v) will open the current command line in a vi o

If you've set -o vi, then when you're editing a command line: esc to get into command mode. v (just the letter v) will open the current command line in a vi or vim session (depending on your default editor). Now vim to your heart's content. :wq will get you out of the vi/vim session, and execute whatever you did in your vi/vim session.