vi Mode
While the Readline library does not have a full set of vi editing
functions, it does contain enough to allow simple editing of the line.
In order to switch interactively between GNU Emacs and vi
editing modes, use the command M-C-j (toggle-editing-mode).
When you enter a line in vi mode, you are already placed in `insertion'
mode, as if you had typed an `i'. Pressing ESC switches you into
`edit' mode, where you can edit the text of the line with the standard
vi movement keys, move to previous history lines with `k', and following
lines with `j', and so forth.