Learning GNU Emacs, 3rd Edition

Setting Emacs Variables

Now we will get into ways to affect Emacs' behavior—not just its user interface. The easiest way to do so is by setting variables that control various things. We already saw examples of this like auto-save-interval in Chapter 2. To set the value of a variable, use the setq function in your .emacs, as in:

(setq auto-save-interval 800)

Although auto-save-interval takes an integer (number) value, many Emacs variables take true or false values, called Boolean in computer parlance. In Emacs Lisp, t is the true value, and nil is the false value, although in most cases, anything other than nil is taken to mean true. Emacs variables can take other types of values, and here is how to specify them:

• Strings of characters are surrounded by double quotes. We saw examples of strings in the arguments to key binding commands earlier in this chapter.

• Characters are specified like strings but with a ? preceding them, and they are not surrounded by double quotes. Thus, ?x and ?\C-c are character values x and C-c, respectively.

• Symbols are given by a single quote followed by a symbol name—for example, 'never (see the variable version-control in Appendix A).

A list of useful Emacs variables, grouped by category, appears in Appendix A, with descriptions and default values. Emacs has more than 2,500 variables—many more than are covered in Appendix A. If there is something about Emacs that you want to customize, a variable probably controls the feature (especially if what you want ...