The following perl command, found at
http://www.perlmonks.org/?node_id=324749 and slightly modified to suit the
situation, will print the grades found in the CSV file to the terminal:

    perl -l -a -F, -n -e 'print $F[3]' example.txt

Ideally, there would be a command to pick out the top five values and only
print those, but I'm not proficient enough in perl to know how to do
that, so in this case the user is left to read through and pick out those
values themselves. Anyone else got an idea?