Custom mktemp for Ruby

mktemp.rb

class Foo
  def mktemp(template)
    regex = /^([^X].*?)(X)(XXXXX)/

    unless m = regex.match(template)
      raise "Invalid template: #{template}"
    end

    chars  = ('a'..'z').to_a

    result = m.captures[0] + chars[rand(25)]
    5.times{ result << rand(9).to_s }

    result
  end
end

p Foo.new.mktemp("rb_file_temp_XXXXXX")