Many of the utilities in Ubuntu Linux use a text editor to allow you to edit configuration options and files. An example of this is using the crontab command, which allows you to edit your cron jobs using the default editor.
From wikipedia: vi is a screen-oriented text editor written by Bill Joy in 1976 for an early BSD release. The name vi is derived from the shortest unambiguous abbreviation for the command visual in ex; the command in question switches the line editor ex to visual mode. Current releases of vi are free and open source software, usually released under permissive free software licenses> such as the BSD License. vi is the commandline text editor of choice (well, not if you ask the emacs crowd), but the reason for it’s widespread use is that it can fit on a floppy disk to aid system recovery. It is a power editor with many options to navigate and manipulate text and we’ll covers the basics here.
Download the Cheat Sheet: vicheatsheet.pdf (source )