In my last blog I gave you a small introduction into the term "Reverse Shell". I described it as: "A Reverse Shell is where your target machine creates a connection to your machine, after which you get a shell on the target machine in which you can execute system commands." It is similar to SSH, but without any encryption and the connection is created the other way around (from target to you, instead of you to the target).

The first function in Clojure returns the first item of a collection. The next function returns a new sequence with all elements after the first element from a collection. Clojure adds some utility methods to combine first and next with different combinations. We can use the function ffirst which is will return the first element of the first element of a collection and the nfirst function to get the next elements from the first element of a collection. We can use the function fnext to get the first element of the next elements of a collection and the function nnext to get the next elements of the next elements of a collection.

In the following example we use the ffirst, nfirst, fnext and nnext: