Extracting specific bytes from raw udp data

I've a list of udp data and I wanted to extract specific bytes from Data in order to create a new column and then export that info in a CSV file. For example I need to get 4 bytes that belong to 003a - 003b - 003c - 003d in hex, unfortunately the slice operator [] only work by comparison. Then put that value in a column (I already know how to accomplish this). I've been trying with tshark but I can't get it! Is possible to do this withouth building a dissector?