salt/pillars/envs.sls

{%- set envs=salt.cmd.shell('ls /srv/salt/').split('\n') -%}
envs:
{%- if envs is not none -%}
  {%- for env in envs %}
  - {{env}}
  {%- endfor -%}
{%- else -%}
  - prod
{%- endif -%}