I want all possible three letter sets for a string. Scan does this:
irb>
>>"abcdefghijkl".scan(...)
# >> abc
# >> def
# >> ghi
# >> jkl

But I need:
# >> abc
# >> bcd
# >> cde
# >> def
etc.

I used to know the secret spell, but forgot it. Does anyone know how
to do this with regular expression--basically need to force the index
to advance one position rather than to the end of a match before
starting the next attempt.
Thanks in advance,
Tim