#!/usr/bin/perl
use strict;
use warnings;
#psudo code from here on
# open the file with categories 
# read the categories in (probably to a hash where the key is the category and the value 0)
# close the categories file (you have your hash, you don't need to read from the file anymore)
# open the file with 3000k entries
# read the file line by line
# for each line read
#    trim to the first 8 characters
#    look for that value in the hash keys
#    increment the value of the hash key that is matched if any
# you now have a hash with category as the key, and the number found as the value
# you should be able to figure out how to find the top 100 values and print out the key and value for each of them or store them to file