According to manual page and StackOverflow, when there is a match grep returns 'SUCCESS', so the logic of the 'if' code must be inverted. In addition, for better output readability, instead of "failure" the output may be "already added" as `transmission-remote` says "Invalid argument" when a torrent has the specific tracker included

The same behavior described in 04d5da1 applies here

Update tracker scripts `grep' behavior

avoid add trackers for private torrents