@my_array = <DATA>;

use Benchmark ':all';


sub regex_method {
	my  $array = [@_];
	for (@$array) {
		next unless /^\d{6}\s*$/;  ## validate data
		s:(\d{2})(?!$):$1/:g;
	}
}

sub sprint_method {
	my $array = [@_];
	for (@$array) {
	   next unless /^\d{6}\s*$/;  ## validate data
	   $_ = sprintf "%d%d/%d%d/%d%d", split('',$_);
	}
}

sub unpack_method {
	my $array = [@_];
	for (@$array) {
		next unless /^\d{6}\s*$/;  ## validate data
		$_=join '/', unpack 'A2' x 3, $_ for @arr;
	}
}

cmpthese( 50000, {
	'regex'   => sub { regex_method(@my_array) },
	'sprintf' => sub { sprint_method(@my_array) },
	'unpack'  => sub { unpack_method(@my_array) },
});

__DATA__
010203
020304
012398
122399