$inp = '"foo[1].bar.baz[0]", value: 123';

$inp =~ /^"(.*?)", value: (.*)$/;
my $layout = $1; my $data = $2;
while ($layout =~ s/(\[(\d+)\]|\.?(\w+))$//) {
    if ($3) { $data = { $3 => $data }; }
    else { $data = [ (undef) x $2, $data ]; }
}

print $data->{'foo'}->[1]->{'bar'}->{'baz'}->[0];
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