gistfile1.txt

---
:backends:
  - yaml
:yaml:
  :datadir: /tmp/hiera
:hierarchy:
  - "roles/%{::hostname}"
  
=>> tree /tmp/hiera
/tmp/hiera
└── roles
    └── test.yaml
    
=>> hiera --config hiera.yaml somefact hostname=test
nil

 =>> cat /tmp/hiera/roles/test.yaml
somefact: test

=>> hiera --debug --config /tmp/hiera.yaml somefact hostname=test
DEBUG: 2014-05-05 12:26:51 -0600: Hiera YAML backend starting
DEBUG: 2014-05-05 12:26:51 -0600: Looking up somefact in YAML backend
nil