if backup of shadow file does not exist:
  a) copy shadow file to backup name
  b) exit
else 
  a) read in shadow file into a hash 
         userid => encrypted password
  b) read in backup shadow file into a hash
         userid => encrypted password
  c) loop through shadow hash
      1) push userid into changed array if 
         password fields do not match
      2) push userid into new id array if 
         userid does not exist in backup hash
  d) copy present file into backup file
  e) email results