A hash in scalar context

 my %f = 1 .. 4;
 my $o = %f;
die $o;
__END__
2/8 at - line 3.
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You want to take a reference, you want  $HOH{1} = \%hash1;

Or all in one step

my %HOH = (
    1 => {
        key1 => 'value1',
        key2 => 'value2',
        key3 => 'value3',
    },
    2 => {
        key1 => 'value1',
        key2 => 'value2',
        key3 => 'value3',
    },
);
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You want to read Tutorials► Data Types and Variables► Data Type: Hash► references quick reference