The vi editor, part 1: modes, moving, saving

Sooner or later you will be on a machine with no graphical editor, no nano, and a config file that needs one line changed. vi will be there; it has been part of Unix since 1976 and POSIX requires it. The BusyBox vi in this VM is a compact version with the essential commands, which is exactly the subset worth learning first. Nothing here is hard, but one idea takes getting used to: modes.

Two modes

In command mode, which is where vi starts, every key is an instruction: j moves down, x deletes a character, : opens a prompt at the bottom for longer commands. In insert mode, keys type text, like any editor. You enter insert mode with i (insert before the cursor), a (append after it), o (open a new line below) or O (open one above). You leave it with Esc. When in doubt, press Esc; pressing it in command mode is harmless.

The typical confusion is typing text while still in command mode: letters do odd things and the file seems to change at random. The fix is always the same: Esc, then u to undo the last change, then i and type again. BusyBox vi shows - Insert - in the bottom line while you are inserting; glance at it when unsure.

Moving around

Saving and quitting

Colon commands are typed in command mode and end with Enter. :w writes (saves) the file, :q quits, :wq does both, and ZZ (two capital letters, no colon) is a shortcut for :wq. If you have unsaved changes, :q refuses; :q! quits anyway and throws the changes away, which is the escape hatch when you have made a mess. :w newname saves a copy under another name.

~% vi notes.txt          # opens (or creates) the file, in command mode
i                        # enter insert mode
hello from vi            # type the text
<Esc>                    # back to command mode
:wq                      # write and quit
~% cat notes.txt
hello from vi
~% vi notes.txt
G                        # jump to the last line
o                        # open a line below and start inserting
second line<Esc>
:wq
~% cat notes.txt
hello from vi
second line

A few more command-mode keys you will want immediately: x deletes the character under the cursor, dd deletes the whole line, u undoes, and . repeats the last change. The next lesson covers editing properly, including search and replace; for now, practise opening a file, typing a line or two, and saving.