This is the first in a series about using the "command line" in Linux. It is also about knowing when to use a gui instead. But before going into any of that we need to understand what is meant by a "command line" application. You'll find that as we explore that idea, a lot of things that are not really true 'cli' (command line interface) apps arguably count as cli, including menu driven console based apps and even gui apps. This will be controversial. Let's start with some basic definitions. If anyone has any problems with any of the following just let me know. Consider this a first draft subject to revision!