Because YAML has a particular format, delineated with the "---", you will have to add a top level key that contains the contents you desire. When You decode, you will have to deference the hash key that this corresponds to. For example:
--- This: top level mapping is: - a - YAML - document
will decode to a hash that looks like:
my $yaml_hash_ref = { This => 'top level mapping', is => ['a', 'yaml', 'document'] };
Therefore, if you want "%This" to be your hash variable, you need to do this:
my %This = %{$yaml_hash_ref->{This}};
If you want the whole structure, you just use whatever YAML::decode gives you, i.e., YAML's encode doesn't take into account the name of your variable containing the data structure to convert to YAML. Similarly, decode returns a data structure reference (scalar, array, or hash) depending on how complex (e.g., hash references contain all non-trivial data structures implied by the YAML).

In reply to Re^3: Problem using YAML by perlfan
in thread Problem using YAML by Pazzeo

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