Generating random strings in Ruby

randstr.rb

#!/usr/local/bin/ruby
# coding: utf-8

require 'securerandom'

def rand_str(chars, length)
  length.times.map {
    chars[SecureRandom.random_number(chars.length)]
  }.join('')
end

if $0 == __FILE__
  require 'optparse'
  option = OptionParser.new
  chars = []
  length = 20
  specified = 1
  option.on('-A', '--capltal-alphabets') { |opt| chars.concat  ('A'..'Z').to_a if opt }
  option.on('-a', '--small-alphabets') { |opt| chars.concat ('a'..'z').to_a if opt }
  option.on('-n', '--numeric') { |opt| chars.concat ('0'..'9').to_a if opt }
  option.on('-h', '--hiragana') { |opt| chars.concat ('あ'..'ん').to_a if opt }
  option.on('-k', '--katakana') { |opt| chars.concat ('ア'..'ン').to_a if opt }
  option.on('-p', '--printable') { |opt| chars.concat ('!'..'~').to_a if opt }
  option.on('-l LENGTH', '--length=LENGTH') { |val| length = val.to_i if val }
  option.on('-t TIMES', '--times=TIMES') { |val| specified = val.to_i if val }
  option.parse ARGV

  chars = ('!'..'~').to_a if chars.empty?

  specified.times { puts rand_str(chars, length) }
end