I noticed from your code, I was very unfair to while/each because I lack value assignment with foreach/keys test function. When I change Benchmark test function from

    foreach my $k (keys %h){
    }
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Look at the code again carefully. When the command line argument -M2=pairs the code run for the for / keys test is:

else {
    if( $M2 eq 'pairs' ) {
        for my $k ( keys %hash ) {
            my $v = $hash{ $k };
            ++$count;
        }
    }
[download]

Ie. This is equivalent to the while / each case for -M2=pairs of:

if( $M1 eq 'each' ) {
    if( $M2 eq 'pairs' ) {
        while( my( $k, $v ) = each %hash ) {
            ++$count;
        }
    }
[download]

To perform the test for both cases where only the keys are accessed, use a command line argument of -M2=keysonly (or any value other than pairs). The code that gets run for two methods in this case are:

    else {
        while( my $k = each %hash ) {
            ++$count;
        }
    }
[download]

and

    else {
        for my $k ( keys %hash ) {
            ++$count;
        }
    }
[download]

Again, equivalent code.

Thanks for confirming my premise.