As a command

$ fibs 10
1
1
2
3
5
8
13
21
34
55

As a library

require 'fibs'
p Fibs.(10)
#=> [1, 1, 2, ..., 55]

Or

require 'fibs'
p Fibs.new(1, 1).take(10)
#=> [1, 1, 2, ..., 55]

Or

require 'fibs'
Fibs.new(1, 1).each do |x|
  ...
end