MD5 Lookup Table Generator

lookup.rb

#!/usr/bin/ruby
require 'digest/md5'  # Hashing strings to MD5
if ARGV[0] != '-i' || ARGV[2] != '-o' || ARGV[3].nil?
  puts "Syntax Error!"
  puts "Usage: ruby lookup.rb -i <input file> -o <output file>"
else
  input_file = ARGV[1]
  if File.exist?(input_file)
    output_file = ARGV[3]
    text = File.open(input_file).read
    text.gsub!(/\r\n?/, "\n")
    text.each_line do |line|
      line.strip!
      hash = Digest::MD5.hexdigest(line)
      write = "#{hash}:#{line}" # Place hash first in case 'line' contains a semicolon
      File.open(output_file, 'a+') {|f| f.write(write+"\r\n")}
    end
  else
    puts "The input file: #{input_file} is invalid, check your syntax and try again!"
  end
end