Load pillar files in the top file based on the grain

gistfile1.txt

base:
  # For each directory that can have pillar files
  {% for root in opts['pillar_roots']['base'] -%}
  # Set a variable to the path to check
  {% set mygrain_sls = '{0}/{1}.sls'.format(root, grains['mygrain']) -%}
  # Check to see if the file exists, if so, include that pillar file.
  {% if salt['file.file_exists'](mygrain_sls) %}
  'service_group:{{ grains["mygrain"] }}':
    - match: grain
    - {{ grains['mygrain'] }}
  {% endif %}
  {% endfor -%}