Vi(m)
Vi (often referred to as ex-vi or nvi) is a command-line text editor. Vim (vi iMproved) is an extended version, that many people use as an entire IDE. vi and vim share the same basic commands and keyboard bindings, so if you just learn the basics, you’ll be fine no matter what kind of ancient or modern system you log in to.
Fair warning: vim is complicated and has a relatively steep learning curve. It’ll probably take a few weeks of spare time studying and experimenting to get comfortable with it – comparable to setting up your first Linux web server or writing your first 500-line program.
The wonderful thing about learning vim is that you can use it locally on your laptop or remotely on a server that has no GUI, and the editing experience is the same – beautifully efficient – in both places. To use it effectively, both a shift in mindset and an understanding of its vocabulary (the commands and modes we’ll get into) are important...