Ruby HMAC verifier (See related posts)

#!/usr/bin/env ruby
#
#  Created by Jon (exabrial+hmacruby@gmail.com) on 2006-11-04.
#  Copyright (c) 2006. All rights reserved.
#  Released under MIT License

require 'openssl'
require "getopt/std"
include OpenSSL
include Digest

def printhelp
  help=<<end
Purpose: Provides HMAC-SHA1 of a file or string. Text passwords are SHA1 hashed.
Usage: hmac.rb ["string to digest"] [-f (pathtofile)] [-k (pathtokeyfile)]
Options:
  -f (pathtofile) digests a file instead of a string
  -k (pathtokeyfile) does not prompt for key and uses the specified file as a key instead.
end
  puts help
  exit
end

if ARGV.size < 1
  printhelp
elsif ARGV.size==1
  @plaintext=ARGV.shift
else
  begin
    opt = Getopt::Std.getopts("f:k:")
  rescue Getopt::StdError
    printhelp
  end
  
  if opt["f"]
    @plaintext=File.read(opt["f"])
  end
  if opt["k"]
    @key=File.read(opt["k"])
  end
  
  printhelp if (!@plaintext&&!@key)
end

def getkey
  return @key if @key
  print "Please type your key then push enter:"
  return SHA1.new(gets()).to_s
end

def main
  hmacd=HMAC.new(getkey(), SHA1.new)
  hmacd.update(@plaintext)
  puts hmacd.to_s
end

main