# where $inp = your file contents...

my ($sections, @lines, $key, $value, $p, %hash);
foreach (split(/\n\n+/, $inp)) {
    ($sections, @lines) = split(/\n/, $_);
    my %thash;
    foreach (@lines) {
        ($key, $value) = split(/: /, $_);
        if ($thash{$key}) {
            $p = $thash{$key};
            push(@$p, $value);
        }
        else {
            $p = [$value];
            $thash{$key} = $p;
        }
    }
    while ($sections =~ /{(.*?)}/g) {
        $hash{$1} = \%thash;
    }
}

print $hash{'section2'}->{'key2'}[0] . "\n";
print $hash{'section3'}->{'key2'}[0] . "\n";

$hash{'section2'}->{'key2'}[0] = 'value4_9';

print $hash{'section2'}->{'key2'}[0] . "\n";
print $hash{'section3'}->{'key2'}[0] . "\n";
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As you can see, the sections are just pointers to the actual data, so you can have unlimited section aliases without taking up a lot of space. To print all the contents of key2 in section2:

$key = $hash{'section2'}->{'key2'};
foreach (@$key) {
    print "$_\n";
}
[download]