#!/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
...