use strict;
use Data::Dumper;

my @outer = ();
my @inner = ();
my $n = 0;
while (<DATA>) {
	chomp;
	push @inner, { DATA => $_ };
	if ($n == 1) {
		push @outer, { 'INNER' => @inner };
		@inner = ();
		$n = 0;
	} else { $n++; }
}
print Dumper(\@outer);

__DATA__
data01
data02
data11
data12