Joined: 06 Jun 2008 Posts: 8120 Location: East Dubuque, Illinois, USA
DSN=NULLFILE is a dummy data set. If you read from it you get end of file immediately. If you write to it, the data goes to the bit bucket immediately, so is lost forever.
An empty file may or may not get end of file immediately if you read from it (that depends on whether the file has been opened for output already or not). Data written to an empty file will be stored in the file and be available later.