use Benchmark qw(cmpthese);
use 5.010;

cmpthese(-2, {
    shift => sub {
        my @array = (1..10)x10000;
        my $item = shift @array;
    },
    index => sub {
        my @array = (1..10)x10000;
        my $item = $array[0];
    },
});

cmpthese(-2, {
    inside => sub {
        my $x = 0;

        while ($x < 5) {
            my $val = $x + 2;  #repeatedly declaring a new variable?

            say $val;
            $x++;
        }
    },
    outside => sub {
        my ($x, $val);
        $x = 0;

        while ($x < 5) {
            $val = $x + 2;  #same old variable every time

            say $val;
            $x++;
        }
    },
});

##</code><code>##

        Rate index shift
index 62.6/s    --   -1%
shift 63.1/s    1%    --

##</code><code>##

            Rate  inside outside
inside  132994/s      --     -9%
outside 146050/s     10%      --