How to sort,uniq and display line that appear more than X times

Question

I have a file like this:

80.13.178.2
80.13.178.2
80.13.178.2
80.13.178.2
80.13.178.1
80.13.178.3
80.13.178.3
80.13.178.3
80.13.178.4
80.13.178.4
80.13.178.7
         


        

Answer 1

With pure awk:

awk '{a[$0]++}END{for(i in a){if(a[i] > 2){print i}}}' a.txt 

It iterates over the file and counts the occurances of every IP. At the end of the file it outputs every IP which occurs more than 2 times.