#!/usr/bin/perl
use strict; use warnings;
use YAML::XS;
use Data::Dumper;

my $data;
{local $/;$data = <DATA>};

print Dumper Load $data;

__DATA__
---
key1: &id01
  subkey_a: asdf
  subkey_b: qwer
key2:
  <<: *id01
  subkey_a: foo
  subkey_c: bar
...

##</code><code>##

$VAR1 = {
          'key2' => {
                    'subkey_a' => 'foo',
                    'subkey_c' => 'bar',
                    '<<' => {
                            'subkey_b' => 'qwer',
                            'subkey_a' => 'asdf'
                          }
                  },
          'key1' => $VAR1->{'key2'}{'<<'}
        };


##</code><code>##

#!/usr/bin/perl
use strict; use warnings;
use YAML::XS;
use Data::Dumper;
my $data;
{local $/;$data = <DATA>};
print Dumper mergekeys( Load $data );

sub mergekeys
{
    my ($ref) = @_;
    my $type = ref $ref;
    if ($type eq 'HASH')
    {
        my $tmphref = $ref->{'<<'};
        if ($tmphref)
        {
            die "Merge key does not support merging non-hashmaps"
                unless (ref $tmphref eq 'HASH');
            my %tmphash = %$tmphref;
            delete $ref->{'<<'};
            %$ref = (%tmphash, %$ref);
        }
        mergekeys($_) for (values %$ref);
    }
    elsif ($type eq 'ARRAY')
    {
        mergekeys($_) for (@$ref);
    }
    return $ref;
}

##</code><code>##

$VAR1 = {
          'key2' => {
                    'subkey_b' => 'qwer',
                    'subkey_a' => 'foo',
                    'subkey_c' => 'bar'
                  },
          'key1' => {
                    'subkey_b' => 'qwer',
                    'subkey_a' => 'asdf'
                  }
        };


##</code><code>##

@_=qw;
Just another Perl hacker,;
;$_=q=print
"@_"= and eval;