>perl -wMstrict -le
"my ($x, $y) = qw{abXcdYef pqXrsYtu};
 my $diff = $x ^ $y;
 $diff =~ tr{\x00-\xff}{=!};
 print $diff;
 print 'number of differences: ', $diff =~ tr{!}{!};
 my @i_diffs = do {
   my $i = 0;
   map   $_->[1],
   grep  $_->[0] eq '!',
   map   [ $_, $i++ ],
   split '',
   $diff;
   };
 print qq{differing positions: @i_diffs};
"
!!=!!=!!
number of differences: 6
differing positions: 0 1 3 4 6 7