Writing GNU Emacs Extensions

Apropos

Before wrapping up this first example, let's discuss Emacs's most important on-line help facility, apropos. Suppose you're one of those who have both BS and DEL keys and think it's a good idea for BS to erase the character preceding the cursor and DEL to erase the character following the cursor. You know that delete-backward-char is the command that accomplishes the former, but you don't know which command achieves the latter. You strongly suspect that Emacs must have such a command. How do you find it?

The answer is to use the apropos command, which allows you to search all known variables and functions for a pattern you specify. Try this:^[7]

M-x apropos RET delete RET

The result is a buffer listing all the matches for "delete" among Emacs's variables and functions. If we search that buffer for occurrences of the word "character," we narrow the field down to

backward-delete-char
Command: Delete the previous N characters (following if N is negative).
backward-delete-char-untabify
Command: Delete characters backward, changing tabs into spaces.
delete-backward-char
Command: Delete the previous N characters (following if N is negative).
delete-char
Command: Delete the following N characters (previous if N is negative).

The function delete-char is the one we want.

(global-set-key "\C-?" 'delete-char)

(For historical reasons, the way to write the DEL character is CONTROL-question-mark.)

You may invoke apropos with a prefix argument. In Emacs, pressing C-u before executing a command is ...