my $x = -2; 
my $y = 0; 
my $z = 1;

my $t = 1; 
for( $x,$y,$z){ $t = $t<<1 if $_; }

print "none set" if $t == 1;
print "only one set" if $t == 2;
print "more than 1 set" if $t > 2;