In case "proving" that I know how to use this simple program helps, the following lines are equivalent, but the second one does not contain the GNUism '-s':
LC_ALL=C sort -r -s -k 1.3,1.4 grep -F -n '' | LC_ALL=C sort -t : -k 2.3r,2.4r -k 1n | cut -d : -f 2-
