$str1='abcde';
$str2='eda';
print "Test 1: strait set\n";
$diff1=$str1=~tr/$str2//;
$diff2=$str1=~tr/eda//;
print "   diff1=$diff1, diff2=$diff2\n";
print "Test 2: complement set\n";
$diff1=$str1=~tr/$str2//c;
$diff2=$str1=~tr/eda//c;
print "   diff1=$diff1, diff2=$diff2\n";