Learn Vim
Modal, keyboard-driven text editor available on almost every Unix machine
Vim is a modal text editor: instead of holding modifier keys, you switch between modes and compose short commands like 'delete inside quotes'. It is installed on nearly every server, its keybindings are available in most IDEs, and fluent Vim users edit text remarkably fast.
How deep do you want to go?
1. EssentialsRead and write simple code, do the everyday basics
2. PracticalUse it productively at work, with the usual idioms
3. AdvancedThe less common features, performance and trade-offs
4. ExpertInternals and the edge cases experts know