ed(1) is a very old, line-oriented editor.  I think that ex(1) is similar,
though I don't really use it.

vi(1) is a screen-oriented, keystroke-interactive editor.  It requires a
rather more capable display than does ed.  (vi likes to move the cursor
around your screen.  ed can work on anything that supports lines of ASCII
text.)


As I understand it, vi was originally written as a more interactive/nicer
interface to the ed editor.  I believe that we have both ed and ex because
ed is kept minimalist for /bin.  On the other hand, NetBSD's vi is built
on top of ex (or is actually the same binary?).  vi requires shared
libraries, so you don't want that in /bin.  (^&


As I said, you can use ed just about anywhere.


  ``I probably don't know what I'm talking about.'' --rauch@math.rice.edu