There are three basic modes of vi:

Command mode

This is the default when you enter vi. In command mode,

most letters, or short sequences of letters, that you type

will be interpreted as commands, without explicitly

pressing Enter . If you press Esc when you're in command

mode, your terminal will beep at you. This is a very good

way to tell when you're in command mode.

Insert mode

In insert mode, whatever you type is inserted in the file

at the cursor position. Type a (lowercase letter a, for

append) to enter insert mode from command mode; press Esc

to end insert mode, and return to command mode.

Line mode

Use line mode to enter line oriented commands. To enter

line mode from command mode, type a colon ( : ). Your

cursor moves to the bottom of the screen, by a colon

prompt. Type a line mode command, then press Enter. Any

sensible command from the Unix line editor ex will work,

and a few are good to know about. These commands are

indicated in this handout by a colon in front of the

command. Each time you use a line mode command, you must

type a colon to enter line mode, then type the command by

the colon prompt at the bottom of the screen, then press

Enter when you finish typing the command. (The search

commands starting with / and ? work similarly.