my $str = "aaa authentication login\x0d\n ssid Rich\x0d\n authentication open\x0d\n authentication shared \x0d\n";
    
   my $authentication;  

   while ($str =~/authentication (\S+)/){
      $authentication = $authentiction. $1. " ";            
   }

   # At the end of the while loop
   # $authentication should have the value 
   # $authentication = open shared