Generate random passwords according to a given pattern

passgen.rb

#!/usr/bin/ruby
# Generate random passwords according to guidance in
# https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/458857/Password_guidance_-_simplifying_your_approach.pdf 
require 'securerandom'

module PassGen
  VOWELS     = %w{a i e o u}.map { |l| l.freeze }.freeze
  CONSONANTS = (('a'..'z').to_a - VOWELS).map { |l| l.freeze }.freeze
  SYMBOLS    = ['!', '$', '%', '^', '&', '*', '+', '-', '_', '?', '@', '#', '~', '.', ',', '=', '"', '\\', '/', '<', '>', ':', ';'].map { |l| l.freeze }.freeze

  module_function
  def vowel
    VOWELS[SecureRandom.random_number(VOWELS.size)]
  end
  
  def consonant
    CONSONANTS[SecureRandom.random_number(CONSONANTS.size)]
  end

  def number
    SecureRandom.random_number(10)
  end

  def symbol
    SYMBOLS[SecureRandom.random_number(SYMBOLS.size)]  
  end

  def password_from_pattern(pattern='cvc')
    pattern.downcase.gsub(/./) { |l|
      case l
      when 'c'
        consonant
      when 'v'
        vowel
      when 'n'
        number
      when 's'
        symbol  
      else
        l
      end  
    }    
  end

  def password(n = 4, pattern = 'cvc', join = '-')
    password_from_pattern(n.times.map { |_| pattern }.join(join))
  end
end

if $0 == __FILE__
require 'optparse'

Options = Struct.new(:pattern, :count)

class Parser
  def self.parse(options)
    args = Options.new("cvc-cvc-cvc-cvc", 1)

    opt_parser = OptionParser.new do |opts|
      opts.banner = "Usage: #{__FILE__} [options]"

      opts.on("-pPATTERN", "--pattern=PATTERN", "Pattern for generated passwords") do |pattern|
        args.pattern = pattern
      end

      opts.on("-cCOUNT", "--count=COUNT", "number of passwords to generate") do |c|
          args.count = c.to_i
      end

      opts.on("-h", "--help", "Prints this help") do
        puts opts
        exit
      end
    end

    opt_parser.parse!(options)
    return args
  end
end
options = Parser.parse ARGV

options.count.times do
  puts PassGen.password_from_pattern(options.pattern)
end

end