https://bugzilla.wikimedia.org/show_bug.cgi?id=55151
--- Comment #1 from Kunal Mehta (Legoktm) legoktm.wikipedia@gmail.com --- Data that can be used for further processing ('pipe') should be sent to stdout. All messages that are only relevant for the user should be sent to stderr. Errors should not be detected by checking if anything was written to stderr, but by checking the return value (which will be non-zero if an error occurred).
Basically, this is a well-known cron problem. See, for instance, http://habilis.net/cronic/