where a portion of the file is displayed on the terminal screen, and the cursor can be moved around the screen to indicate where you want to make changes. You can select which part of the file you want to have displayed. Screen editors are also called display editors, or visual editors . vi is one of the more popular screen editors that run on the UNIX system [7, p. 186].
This editor relies heavily on the cursor keys to move around. Again, only the basic commands will be introduced.
Once in vi, commands must be invoked for anything to happen.
These commands can be anything from :q to i to 
CTL-f
.
Following the philosophy of UNIX, vi assumes the user
knows what he/she is doing!!!
NOTE: if a command puts the user into a mode (input, append, replace), the escape key must be pressed to get OUT of that mode.
For more information on vi, see [7, pp. 264-310].