Generate /etc/shadow Hash Under Ruby

unix_passwd.rb

#!/usr/bin/env ruby
require 'unix_crypt'
require 'io/console'
require 'optparse'

#####
#
# Script for generating a users password hash defaults to SHA512.  Will prompt for password twice
# to make sure that it has been entered correctly.
# 
# Requires https://github.com/mogest/unix-crypt
# or 
# gem install unix-crypt
#
# Created by Robert Hernandez
#
#####

# Get the option flags that are passed in
optparse = OptionParser.new do |opts|
  opts.banner = "Usage: %s [SHA512 (default), SHA256, MD5, DES]" % File.basename(__FILE__)
  opts.on( '-h', '--help', 'Display this screen' ) do
    puts opts
    exit
  end
end

# Remove ARGV and parse commandline flags
optparse.parse!

# Get the algorithm value from ARGV
if ARGV.size == 0
  hash_alg = 'SHA512'
elsif ARGV.size == 1
  hash_alg = ARGV[0].upcase
elsif ARGV.size > 1
  puts optparse
  abort
end

build_string = "UnixCrypt::%s" % hash_alg
hash = nil
while true
  print "Enter Password: "
  password = STDIN.noecho(&:gets).chomp
  puts
  hash_tmp = eval(build_string).build(password,
                                      if hash.nil? then hash
                                      elsif hash_alg == 'DES' then hash[0..1]
                                      else hash.split('$')[2] end) # Assumes defualt rounds
  if hash_tmp == hash
    puts hash
    break
  else
    hash = hash_tmp
    next
  end
end