pfSense

When running svc status for an unknown service you get:

root: pfSsh.php playback svc status unknown
/bin/pgrep -anx ''pgrep: Cannot compile regular expression `' (empty (sub)expression)

Service unknown is stopped.

Two issue here really:
- is_process_running generates an error when $process is "". This is addressed by the attached patch
- svc probably should return something like "Unknown service: unknown".