6.3.4 Completion Options

When completion is done on file names, certain file names are usually ignored. The variable completion-ignored-extensions contains a list of strings; a file whose name ends in any of those strings is ignored as a possible completion. The standard value of this variable has several elements including ".o", ".elc", ".dvi" and "~". The effect is that, for example, ‘foo’ can complete to ‘foo.c’ even though ‘foo.o’ exists as well. However, if all the possible completions end in “ignored” strings, then they are not ignored. Ignored extensions do not apply to lists of completions—those always mention all possible completions.

If a completion command finds the next character is undetermined, it automatically displays a list of all possible completions. If the variable completion-auto-help is set to nil, this does not happen, and you must type ? to display the possible completions.

If the variable minibuffer-confirm-incomplete is set to t, then in contexts where completing-read allows answers that are not valid completions, an extra RET must be typed to confirm the response. This is helpful for catching typos.

Icomplete mode presents a constantly-updated display that tells you what completions are available for the text you’ve entered so far. The command to enable or disable this minor mode is M-x icomplete-mode.