use strict;
use warnings;
use feature 'say';
use Time::HiRes 'time';

my $x = 'a' x 1e6;
my $y = 'b' . $x;

my $t = time;
$x =~ s/./$&-/g;
say time - $t;

$t = time;
$y =~ s/./$&-/g;
say time - $t;

say $^V;

__END__

12.7103209495544
0.850119113922119
v5.32.1

12.7171239852905
0.765337944030762
v5.28.2

0.345196962356567
0.314804077148438
v5.26.3