I often find myself performing operations on single column CSV files to perform tasks such as merging member id lists, or email addresses, counting unique entries, finding duplicates etc.

By applying some set theory (remember that from math class) and some standard linux/unix command line tools, almost any operation I have ever wanted to achieve in this vain is possible. And I have found a post, over at Linux By Examples that provides a simple list of operations and examples of how to achieve them on text files using sort and uniq.