Yes - if you execute 'mco rpc bar' from a cron job as a specific role user.

Your stdin is not a tty, and you don't have any input - in that case you want to fall back to the default discovery method.

However, I've realised that I can just check if STDIN.eof? also - if there is no TTY on stdin but data, we can assume we should use the discovery plugin (and break if there is no useful data - e.g. empty array), whilst also doing the non-interactive default discovery case correctly.