Vi/Vim Essentials

vi is the text editor you can count on: almost every Linux and Unix system has it, including minimal servers and containers with no other editor. Most systems ship Vim ("vi improved"), which runs when you type vi. You don't need to master it. You need enough to open a config file, change it, save and get out. This note covers that core.

Modes#

Vi is a modal editor. The same key does different things depending on the mode. This is the one idea that makes vi make sense.

If you're unsure which mode you're in, press Esc. That always brings you back to Normal mode.

Open, save and quit#

The first thing most people need is a way out, so start with saving and quitting. vi filename opens a file. If it doesn't exist, vi creates it when you first save. All save and quit commands start with : and end with Enter.

Entering Insert mode#

To change the file, you switch from Normal mode to Insert mode. Several keys do that, each at a different spot. Press Esc when you finish typing.

A saves a step: it jumps to the end of the line and enters Insert mode at once.

Moving around#

Back in Normal mode, you move the cursor to the next spot you want to edit. Arrow keys work in Vim, but these Normal-mode keys are faster once learned.

Deleting#

The movement keys matter beyond moving, because Vim reuses them as motions in other commands. Delete commands combine d with a motion, and the motion says how far to delete.

dG and dgg both include the current line. A number before most commands repeats it, so 5x deletes five characters.

Copy, cut and paste#

Copying follows the same pattern as deleting. Vi calls copying yank. Anything you delete or yank goes into a register (a clipboard slot), so d works as cut.

To move a line, press dd, move the cursor, then press p. To duplicate a line, press yy then p.

Search and replace#

In a long config file, searching is faster than moving line by line. Search from Normal mode, and replace with a :s command.

% means "every line". g means "every match on the line", not only the first.

Saving a file that needs root#

One situation catches almost everyone. You open /etc/hosts, make changes, and :w fails with a permission error because you didn't start Vim with sudo. You can save from inside Vim without losing your edits.

:w !sudo tee % > /dev/null

Each part has a job:

• :w !cmd sends the buffer to a shell command's stdin, instead of writing the file.
• sudo tee runs tee as root. tee writes its stdin to the file it is given.
• % expands to the current file's name.
• > /dev/null hides tee's copy of the file on the screen.

Vim then sees that the file changed on disk and asks what to do. Press L to load the saved version, or O to keep the buffer. This works in Vim. Neovim can't show the sudo password prompt this way. Next time, open system files with sudoedit /etc/hosts.

Key takeaways#

• Vi has modes. Esc always returns to Normal mode.
• :w saves, :q quits, :wq does both, :q! quits without saving.
• i, a, A and o enter Insert mode at different spots.
• d plus a motion deletes: dd a line, dw a word, dG to the end, dgg to the top.
• yy copies, p pastes, u undoes.
• /word searches; :%s/old/new/g replaces in the whole file.