Useful howto on bash Vi command line editing HERE.
>set -o vi
sets vi cmd line editing mode
It drops you into insert mode. Hitting Esc will get you into command mode like usual. Many vi editing commands work. Search (/foo) does not search the current command line. Instead it searches your bash history. Hitting ‘n’ after a search finds the next match as usual. The substitute cmd (s/foo/bar) does not work.
Hitting ‘v’ when in command mode opens up vi with your command line. Now you are in regular vi – the usual editing works. Once done editing ‘:wq’ will quit vi and execute the command.