66 Character lines without regex

If you're interested in exploring an answer that doesn't use RegEx, try
something like:

a = "Your string goes here"
d = 66
Array(0..a.length/d).collect {|j| a[j*d..(j+1)*d-1]}.join("\n")

The RegEx is likely faster, but this uses the Array Constructor,
.collect and .join so it might be an interesting learning exercise. The
first part generates an array of numbers based on the number of chunks
(a.length/d). The collect gathers the substrings in to an array. The
body of the collect generates substrings by ranges on the original
string, and the join puts it back together with '\n' separators.

from @RickH at stackoverflow