Learning GNU Emacs, 3rd Edition

Completion

We saw an example of Emacs's completion facility in Chapter 1. Completion is more than just a feature: it is a general principle in the design of Emacs. It can be articulated as follows:

If you have to type in the name of something, and that name is one of a finite number of possibilities, Emacs should figure out what you mean after the smallest possible number of keystrokes.

In other words, you can type in the shortest unambiguous prefix and tell Emacs to figure out the rest of the name. By "shortest unambiguous prefix," we mean "enough of the name, starting from the beginning, to distinguish it from the other possibilities." Several important things in Emacs have names that are chosen from a finite number of possibilities, including the following:

• Commands

• Files in a given directory

• Buffers

• Emacs variables

Most of the time, completion is available when you are prompted for a name of something in the minibuffer. While you are typing in the name, you can use three keys to tell Emacs to help complete it for you: Tab, Space, and question mark (?). Their functions are shown in Table 14-5.

Table 14-5. Completion keys

Keystroke	Action
Tab	Completes the name as far as possible.
Space	Completes the name out to the next punctuation character.
?	Lists the choices at this point in a *Completions* window.

You will probably find Tab to be the most useful.

As a running example, assume you have typed C-x C-f to visit a file, and the file you want to visit is a C program called ...