According to the Supervisor docs, you can access environment variables in the command by prefixing ENV_ like: %(ENV_YOUR_VAR)s
http://supervisord.org/configuration.html#environment-variables
String expressions are evaluated against a dictionary containing the keys group_name, host_node_name, process_num, program_name, here (the directory of the supervisord config file), and all supervisord’s environment variables prefixed with ENV_.
However, according to this commit: https://github.com/Supervisor/supervisor/commit/2d6ca34582a8a07a5dd96ae45ef62cd58a459f4f this feature was added after version 3.2.