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

Ruby has so many ways. :)

str, arr = "abcdefghijkl", []
3.times {|f| arr << str[f..f-3].split(//)}
p arr.transpose.map{|u| u.join}


Harry

-- 
A Look into Japanese Ruby List in English
http://www.kakueki.com/ruby/list.html