my $string= ' ' x 2**19;
$string= '';

##</code><code>##

use Benchmark "cmpthese";

sub pre {
    my $str = " " x 2**19;
    $str = "";
    $str .= "aaaa" for 1..2**17;
}

sub std {
    my $str = "";
    $str .= "aaaa" for 1..2**17;
}

cmpthese( -1, {
    'pre' => 'pre()',
    'std' => 'std()'
});

##</code><code>##

      Rate pre std
pre 43.6/s  -- -7%
std 46.7/s  7%  --