Re: OT: Why is my result empty?

[AnomalousMonk]

Slightly OT, but if you have a lot of such character-for-character translation to do (a bio-app?), consider using  tr/// instead of  s/// (pattern substitution) for faster operation (see  tr/// in Quote-Like Operators in perlop):

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