c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = 'xxxDxUxxDDxxUUxDUDxUDUx';
 print qq{'$s'};
 ;;
 $s =~ tr/DU/M/;
 print qq{'$s'};
"
'xxxDxUxxDDxxUUxDUDxUDUx'
'xxxMxMxxMMxxMMxMMMxMMMx'