vi is the classic screen-editing program for Unix. A number of enhanced versions exist, including nvi , vim, vile, and elvis. On Linux, the vi command is usually a link to one of these programs. The Emacs editor, covered in Chapter 10, has several vi modes that allow you to use the same commands covered in this chapter.
The vi editor operates in two modes, command mode and insert mode. The dual mode makes vi an attractive editor for users who separate text entry from editing. For users who edit as they type, the modeless editing of emacs can be more comfortable.
vi is based on an older line editor called ex . A user can invoke powerful editing capabilities within vi by typing a colon ( :), entering an ex command, and pressing the Return key. Furthermore, you can place ex commands in a startup file called ~/.exrc, which vi reads at the beginning of your editing session. Because ex commands are still an important part of vi, they are also described in this chapter.
One of the most common versions of vi found on Linux systems is Bram Moolenaar’s Vi IMproved, or vim . On some Linux distributions, vim is the default version of vi and runs when you invoke vi. vim changes some of the basic features of vi, most notoriously changing the undo key to support multiple levels of undo. While seasoned users of vi find vim’s changes disturbing, those new to vi find vim’s extensive features attractive.
Fully documenting vim is beyond the scope of this chapter, ...