use strict;

my $datafields = 3;
my $item_no    = 2;
my @records;

# read from DATA - any filehandle will do . . .
foreach my $line (<DATA>) {
   chomp $line;
   push @records, [ split(/\s+/,$line,$datafields) ];
}

=comment
 now @records looks like this:
 @records = (
    ['foo','gabba','12'],
    ['bar','hey','2'],
    ['baz','gabba','38']
 );
 the elements in []'s are array references

 now store the array references based on the order
 of the 3rd element, which is a number - numbers
 are compared with the <=> operator, strings are
 comparted with the cmp operator - $a and $b are
 magic variables that contain the two items being
 compared - if you want ascending order, compare
 $a to $b - for descencing order, compare $b to $a
=cut

my @sorted = sort { $b->[$item_no] <=> $a->[$item_no] } @records;

=comment
 that's it! now print out the results - the tricky part
 is that @sorted is a list of list REFERENCES, so we need
 to do some extra work to de-reference them
=cut

foreach my $line (@sorted) {
   print join(', ', @$line), "\n";
}

=comment
 the following would normally be found in a data file.
 i originally delimited these values with tabs, but they
 will probably turn into spaces when you copy and paste
 that's why i used /\s+/ instead of /\t/ in split above
=cut

__DATA__
foo     gabba     12
bar     hey       2
baz     gabba     38