require 'fileutils'

20.times do |n|
  FileUtils.touch "f#{n}.txt"
end

p Dir["f*.txt"].sort
# => ["f0.txt", "f1.txt", "f10.txt", "f11.txt", ..., "f2.txt", "f3.txt", ...]

class Array
  def human_sort
    sort_by { |item| item.to_s.split(/(\d+)/).map { |e| [e.to_i, e] } }
  end
end

p Dir["f*.txt"].human_sort
# => ["f0.txt", "f1.txt", "f2.txt", "f3.txt", "f4.txt", "f5.txt", "f6.txt", ...]