Diff two email lists and find new and missing email

email_list_diff.rb

# Diff two email lists and find new and missing emails
# To use, call file and pass in an original list and updated list
# eg. ruby email_list_diff.rb ~/original_list.txt ~/updated_list.txt

original_list = File.readlines(ARGV[0])
updated_list = File.readlines(ARGV[1])

def find_unique_emails(list_01, list_02)
  # given two email lists, find all emails
  # in list_01 that are not in list_02
  unique_emails = []

  list_01.each do |email|

    # Create an array of any matched emails
    matches = list_02.select { |line| line[/#{email.chomp}/i] }
    
    if matches.empty?
      # if no matches, it's a unique email
      puts email
      unique_emails.push(email)
    end
  end
  
  return unique_emails
end

puts "Finding new emails ... "
new_emails = find_unique_emails(updated_list, original_list)
puts "#{new_emails.count} emails added"

puts "Finding missing emails ..."
removed_emails = find_unique_emails(original_list, updated_list)
puts "#{removed_emails.count} emails removed"