[tim]$ /usr/bin/tac test.txt
six
five
four
three
two
one
[tim]$ /usr/bin/tac --separator=blah test.txt
one
two
three
four
five
six
The output of the first command makes sense, but I think that the second run should print in the reverse order (and should have the separator, although I could be misreading the man page)
Tim