8.3.2 Completion Commands

Here is a list of the completion commands defined in the minibuffer when completion is allowed.

<TAB>

Complete the text in the minibuffer as much as possible; if unable to complete, display a list of possible completions (minibuffer-complete).

<SPC>

Complete up to one word from the minibuffer text before point (minibuffer-complete-word). <SPC> for completion is not available when entering a file name, since file names often include spaces.

<RET>

Submit the text in the minibuffer as the argument, possibly completing first as described in the next node (minibuffer-complete-and-exit). See Strict Completion.

?

Display a list of possible completions of the text before point (minibuffer-completion-help).

<TAB> (minibuffer-complete) is the most fundamental completion command. It searches for all possible completion alternatives that match the existing minibuffer text, and attempts to complete as much as it can. The matching of completion alternatives to the minibuffer text is performed according to somewhat intricate rules, which are designed so that plausible completions are offered under most circumstances. A valid completion alternative must satisfy the following criteria:

• The minibuffer text before point must be the same as the beginning of the completion alternative. If there is any minibuffer text after point, it must be a substring of the remainder of the completion alternative.
• If no completion alternative satisfies the above rules, try using partial completion rules: divide the minibuffer text into words separated by hyphens or spaces, and complete each word separately. Thus, when completing command names, ‘em-l-m’ completes to ‘emacs-lisp-mode’.
• If there is still no completion alternative, try the first rule again, but ignore the minibuffer text after point (i.e., don't try matching it).

When performing these comparisons, a ‘*’ in the minibuffer text acts as a wildcard—it matches any character at the corresponding position in the completion alternative.

<SPC> (minibuffer-complete-word) completes like <TAB>, but only up to the next hyphen or space. If you have ‘auto-f’ in the minibuffer and type <SPC>, it finds that the completion is ‘auto-fill-mode’, but it only inserts ‘ill-’, giving ‘auto-fill-’. Another <SPC> at this point completes all the way to ‘auto-fill-mode’.

If <TAB> or <SPC> is unable to complete, it displays a list of possible completions (if there are any) in a separate window. You can choose a completion from this list using the following commands:

Mouse-1

Mouse-2

Clicking mouse button 1 or 2 on a completion possibility chooses that completion (mouse-choose-completion).

M-v

<PageUp>

<prior>

Typing M-v, while in the minibuffer, selects the window showing the completion list buffer (switch-to-completions). This paves the way for using the commands below. Typing <PageUp> or <prior> does the same, as does selecting that window in other ways.

<RET>

Typing <RET>, while in the completion list buffer, chooses the completion that point is in or next to (choose-completion). To use this command, you must first switch to the completion list window.

<Right>

Typing the right-arrow key <Right>, while in the completion list buffer, moves point to the following completion possibility (next-completion).

<Left>

Typing the left-arrow key <Left>, while in the completion list buffer, moves point to the previous completion possibility (previous-completion).