Assuming you have your counts in a hash, say %code_count (with code as the keys), then

use strict;
use warnings;

my %code_count = (
                  a => 5,
                  b => 4,
                  c =>10,
                  d => 1,
                  e => 2,
                  f => 17,
                 );

print "$_ $code_count{$_}\n"
    for (sort { $code_count{$b} <=> $code_count{$a} } keys %code_count
+ )[0..4];
__DATA__
f 17
c 10
a 5
b 4
e 2
[download]

will work. This sorts the hash by value (in largest-first order), and uses a slice to pull off the top five.

Updated: Added sample data and output.