perl -wMstrict -e
"my %X = qw(a 1  b 2  c 3  z 9);  my %Y = qw(d 4  e 5  f 6  z 8);
 my %X_not_in_Y = %X;  my %Y_not_in_X = %Y;
 delete @X_not_in_Y{ keys %Y };  delete @Y_not_in_X{ keys %X };
 print qq(X not in Y: @{[ keys %X_not_in_Y ]} \n);
 print qq(Y not in X: @{[ keys %Y_not_in_X ]})"
X not in Y: c a b
Y not in X: e d f