Sorry - I don't think that I made myself very clear:
Yes I can use vi to edit files, but what I was asking was -
Is it possible to use vi commands to edit whatever is typed on the command line and more usefully to use the search facility to find a command from the history?
For example on SCO I can use
<esc> /sqlplus <return>
to scroll back [using <n>] through all commands in the history that have "sqlplus" in them.
Does this make more sense?