c:\@Work\Perl>perl -wMstrict -le
"my $s = 'xxx aBc yyy dE zzz';
 print qq{\$s: '$s'};
 ;;
 print qq{\$1: '$1'} if $s =~ s{ ([AaBbCcDdEe]+) }{XXX}xmsg;
   print qq{\$s: '$s'};
  "
$s: 'xxx aBc yyy dE zzz'
$1: 'dE'
$s: 'xxx XXX yyy XXX zzz'