Why vi?

vi (and its modern variant vim) is installed on essentially every Unix-like system. When you SSH into a stripped-down server with no GUI, vi is often your only editor. It is modal — keys behave differently in different modes — which feels alien at first but is extremely fast once internalized.

The Three Modes

1. Command (Normal) mode — the default when vi opens. Keys are commands: dd deletes a line, yy copies, p pastes, /pat searches.
2. Insert mode — entered with i, I, a, A, o or O. Now keys insert text. Press Esc to leave.
3. Ex / Last-line mode — entered by typing : in command mode. Used for file operations: :w save, :q quit, :wq save & quit, :q! discard, :set number show line numbers.

Essential Command-mode Keys

Writing a Shell Script in vi

1. vi hello.sh — opens a new file in command mode.
2. Press i to enter insert mode and type:

#!/bin/bash echo "Hello, $USER!" date

1. Press Esc to return to command mode.
2. Type :wq and press Enter to save and quit.
3. Make it executable and run it:

chmod +x hello.sh ./hello.sh

Common Beginner Pitfalls

• Typing into command mode and seeing nothing happen — you forgot i.
• Stuck in vi — press Esc then :q! to quit without saving.
• Garbled file — use u to undo. Vim allows many levels of undo.

Summary

• vi has three modes: Command, Insert, and Ex.
• Always return to command mode with Esc before issuing a save/quit command.
• A shell script written in vi is just a text file with #!/bin/bash and execute permission.