[SOLVED] Terminal commands

I am going to create a dual boot of Kubuntu 16.04 & 18.04 and would like to have an almost identical setup and would like to install the same terminal commands I have in the already installed Kubuntu 16.04, such as ‘alien’ which is not a standard command.

How can I list all the available commands in terminal?

compgen -c | sort

Thanks Mark.
I never knew that there were so many terminal commands, including extra ones installed afterwards.