my @df_k = split(/\n/, `df -k`);

shift(@df_k); # Remove header.

my @sorted_by_drive =
   sort { $a->[5] cmp $b->[5] }
      map { [ split(/\s+/, $_, 6) ] }
         @df_k;


use Data::Dumper ();
print(Data::Dumper->Dump(
   [    \@sorted_by_drive   ],
   [qw(  $sorted_by_drive  )],
));