9.1. Conceptual Overview

vi is the classic screen-editing program for Unix. A number of enhanced versions exist, including nvi, vim, vile, and elvis. On GNU/Linux systems, the vi command is usually one of these programs (either a copy or a link). The Emacs editor, covered in Chapter 8, has several vi modes that allow you to use many of 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. However, vim supports both ways of editing, through the insertmode option and the evim command for invoking vim.

vi is based on an older line editor called ex. (ex, in turn, was developed by Bill Joy at the University of California, Berkeley, from the primordial Unix line editor, ed.) A user can invoke powerful editing capabilities within vi by typing a colon (:), entering an ex command, and pressing the ENTER 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 such an important part of vi, they are also described in this chapter.

One of the most common versions of vi found on GNU/Linux systems is Bram Moolenaar's Vi IMproved, or vim. On some GNU/Linux distributions, vim is the default version of vi and runs when you invoke vi. vim offers many extra features, and optionally changes some of the basic features of vi, most notoriously changing the undo command to support multiple levels of undo.

Fully documenting vim is beyond the scope of this chapter, but we do cover some of its most commonly used options and features. Beyond what we cover here, vim offers enhanced support to programmers through an integrated build and debugging process, syntax highlighting, extended ctags support, and support for Perl and Python, as well as GUI fonts and menus, function key mapping, independent mapping for each mode, and more. Fortunately, vim comes with a powerful internal help system that you can use to learn more about the things that we just couldn't fit into this chapter. See http://www.vim.org/ for more information.