in reply to Nested LOOP in HTML::Template

You want the hash element to be an array of hashes. Use [] to create an anonymous arrayref of hashes out of @inner, then push onto @outer.

use strict;
use Data::Dumper;

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

__DATA__
data01
data02
data11
data12

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Output: 
$VAR1 = [
          {
            'INNER' => [
                         {
                           'DATA' => 'data01'
                         },
                         {
                           'DATA' => 'data02'
                         }
                       ]
          },
          {
            'INNER' => [
                         {
                           'DATA' => 'data11'
                         },
                         {
                           'DATA' => 'data12'
                         }
                       ]
          }
        ];

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