Editing files

Sooner or later you need to change a file, not just read it: a setting, a note, a script. On a server there's no mouse and no window, so you use an editor that runs inside the terminal. The easiest is nano, which is on almost every system.

nano notes.txt opens the file, or starts a new, empty one with that name. Type and move with the arrow keys as you'd expect. The bottom two lines list the shortcuts, where ^ means Ctrl: ^O is Ctrl+O.

$ nano notes.txt
  (edit the text, then)
  Ctrl+O, Enter    save ("write Out"), keeping the name
  Ctrl+X           exit; it asks first if there are unsaved changes

A few more keys cover most jobs: Ctrl+W searches ("where is"), Ctrl+K cuts the whole line the cursor is on, and Ctrl+U pastes it back. To edit a system file you don't own, like /etc/hosts, open the editor with sudo: sudo nano /etc/hosts. (The next course explains owners and sudo.)

Some commands open an editor for you, for example when you edit a schedule of jobs. They use whatever the EDITOR setting names, and on many systems that's vim. Vim starts in a mode where keys are commands, not text, which traps a lot of people. To get out: press Esc, then type :q! and Enter to quit without saving, or :wq and Enter to save and quit.

Whichever editor you use, save before you test a change. A file that's open in the editor but not saved hasn't changed on disk yet.