9C4

9C4.rb

(1..9).each do |i1|
  (2..9).each do |i2|
    (3..9).each do |i3|
      (4..9).each do |i4|
        if i1 < i2 && i2 < i3 && i3 < i4
          print("#{i1}#{i2}#{i3}#{i4}\n")
        end
      end
    end
  end
end

run.sh

ruby 9C4.rb | wc -l #=> 126