In (info "(coreutils) join invocation") ‘-a FILE-NUMBER’ Print a line for each unpairable line in file FILE-NUMBER (either ‘1’ or ‘2’), in addition to the normal output.
OK but say if we can use both: -a 1 -a 2? (Answer: yes) And if so how to tell which lines are from which file (Answer: by their content only). ‘-v FILE-NUMBER’ Print a line for each unpairable line in file FILE-NUMBER (either ‘1’ or ‘2’), instead of the normal output. OK but say if we can use both: -v 1 -v 2? And if so how to tell which lines are from which file. And in fact give an example to show what lines -a and -v are talking about!