9. The Minibuffer

The minibuffer is where Emacs commands read complicated arguments (anything more a single number). We call it the “minibuffer” because it's a special-purpose buffer with a small amount of screen space. Minibuffer arguments can be file names, buffer names, Lisp function names, Emacs command names, Lisp expressions, and many other things—whatever the command wants to read. You can use the usual Emacs editing commands in the minibuffer to edit the argument text.

When the minibuffer is in use, it appears in the echo area, with a cursor. The minibuffer display starts with a prompt in a distinct color; it says what kind of input is expected and how it will be used. Often the prompt is derived from the name of the command that is reading the argument. The prompt normally ends with a colon.

Sometimes a default argument appears in the prompt, inside parentheses before the colon. The default will be used as the argument value if you just type <RET>. For example, commands that read buffer names show a buffer name as the default. You can type <RET> to operate on that default buffer.

The simplest way to enter a minibuffer argument is to type the text, then <RET> to exit the minibuffer. You can cancel the minibuffer, and the command that wants the argument, by typing C-g.

Since the minibuffer appears in the echo area, it can conflict with other uses of the echo area. Here is how Emacs handles such conflicts:

• An error occurs while the minibuffer is active.

  The error message hides the minibuffer for a few seconds, or until you type something. Then the minibuffer comes back.

• A command such as C-x = needs to display a message in the echo area.

  The message hides the minibuffer for a few seconds, or until you type something. Then the minibuffer comes back.

• Keystrokes don't echo while the minibuffer is in use.