6. The Minibuffer

The minibuffer is the facility used by XEmacs commands to read arguments more complicated than a single number. Minibuffer arguments can be file names, buffer names, Lisp function names, XEmacs command names, Lisp expressions, and many other things, depending on the command reading the argument. You can use the usual XEmacs editing commands in the minibuffer to edit the argument text.

When the minibuffer is in use, it appears in the echo area, and the cursor moves there. The beginning of the minibuffer line displays a prompt which says what kind of input you should supply and how it will be used. Often this prompt is derived from the name of the command that the argument is for. The prompt normally ends with a colon.

Sometimes a default argument appears in parentheses after the colon; it, too, is part of the prompt. The default is used as the argument value if you enter an empty argument (e.g., by just typing <RET>). For example, commands that read buffer names always show a default, which is the name of the buffer that will be used if you type just <RET>.

The simplest way to enter a minibuffer argument is to type the text you want, terminated by <RET> which exits the minibuffer. You can cancel the command that wants the argument, and get out of the minibuffer, by typing C-g.

Since the minibuffer uses the screen space of the echo area, it can conflict with other ways XEmacs customarily uses the echo area. One can avoid such a conflict as described in (lispref)Customizing Message Display section ‘Customizing Message Display’ in The XEmacs Lisp Reference Manual. Here is how XEmacs handles such conflicts by default:

• If a command gets an error while you are in the minibuffer, this does not cancel the minibuffer. However, the echo area is needed for the error message and therefore the minibuffer itself is hidden for a while. It comes back after a few seconds, or as soon as you type anything.
• If in the minibuffer you use a command whose purpose is to print a message in the echo area, such as C-x =, the message is printed normally, and the minibuffer is hidden for a while. It comes back after a few seconds, or as soon as you type anything.
• Echoing of keystrokes does not take place while the minibuffer is in use.

6.1 Minibuffers for File Names

Sometimes the minibuffer starts out with text in it. For example, when you are supposed to give a file name, the minibuffer starts out containing the default directory, which ends with a slash. This is to inform you which directory the file will be found in if you do not specify a directory.

For example, the minibuffer might start out with these contents:

Find File: /u2/emacs/src/

where ‘Find File: ’ is the prompt. Typing buffer.c specifies the file ‘/u2/emacs/src/buffer.c’. To find files in nearby directories, use ..; thus, if you type ../lisp/simple.el, you will get the file named ‘/u2/emacs/lisp/simple.el’. Alternatively, you can kill with M-<DEL> the directory names you don’t want (see section Words).

If you don’t want any of the default, you can kill it with C-a C-k. But you don’t need to kill the default; you can simply ignore it. Insert an absolute file name, one starting with a slash or a tilde, after the default directory. For example, to specify the file ‘/etc/termcap’, just insert that name, giving these minibuffer contents:

Find File: /u2/emacs/src//etc/termcap

XEmacs gives a special meaning to a double slash (which is not normally a useful thing to write): it means, “ignore everything before the second slash in the pair.” Thus, ‘/u2/emacs/src/’ is ignored in the example above, and you get the file ‘/etc/termcap’.

If you set insert-default-directory to nil, the default directory is not inserted in the minibuffer. This way, the minibuffer starts out empty. But the name you type, if relative, is still interpreted with respect to the same default directory.

6.2 Editing in the Minibuffer

The minibuffer is an XEmacs buffer (albeit a peculiar one), and the usual XEmacs commands are available for editing the text of an argument you are entering.

Since <RET> in the minibuffer is defined to exit the minibuffer, you can’t use it to insert a newline in the minibuffer. To do that, type C-o or C-q C-j. (Recall that a newline is really the character control-J.)

The minibuffer has its own window which always has space on the screen but acts as if it were not there when the minibuffer is not in use. When the minibuffer is in use, its window is just like the others; you can switch to another window with C-x o, edit text in other windows and perhaps even visit more files, before returning to the minibuffer to submit the argument. You can kill text in another window, return to the minibuffer window, and then yank the text to use it in the argument. See section Multiple Windows.

There are some restrictions on the use of the minibuffer window, however. You cannot switch buffers in it—the minibuffer and its window are permanently attached. Also, you cannot split or kill the minibuffer window. But you can make it taller in the normal fashion with C-x ^. If you enable Resize-Minibuffer mode, then the minibuffer window expands vertically as necessary to hold the text that you put in the minibuffer. Use M-x resize-minibuffer-mode to enable or disable this minor mode (see section Minor Modes).

If while in the minibuffer you issue a command that displays help text of any sort in another window, you can use the C-M-v command while in the minibuffer to scroll the help text. This lasts until you exit the minibuffer. This feature is especially useful if a completing minibuffer gives you a list of possible completions. See section Using Other Windows.

If the variable minibuffer-confirm-incomplete is t, you are asked for confirmation if there is no known completion for the text you typed. For example, if you attempted to visit a non-existent file, the minibuffer might read:

        Find File: chocolate_bar.c [no completions, confirm]

If you press Return again, that confirms the filename. Otherwise, you can continue editing it.

XEmacs supports recursive use of the minibuffer. However, it is easy to do this by accident (because of autorepeating keyboards, for example) and get confused. Therefore, most XEmacs commands that use the minibuffer refuse to operate if the minibuffer window is selected. If the minibuffer is active but you have switched to a different window, recursive use of the minibuffer is allowed—if you know enough to try to do this, you probably will not get confused.

If you set the variable enable-recursive-minibuffers to a non-nil, recursive use of the minibuffer is always allowed.

6.3 Completion

For certain kinds of arguments, you can use completion to enter the argument value. Completion means that you type part of the argument, then XEmacs visibly fills in the rest, or as much as can be determined from the part you have typed.

When completion is available, certain keys—<TAB>, <RET>, and <SPC>—are rebound to complete the text present in the minibuffer into a longer string that it stands for, by matching it against a set of completion alternatives provided by the command reading the argument. ? is defined to display a list of possible completions of what you have inserted.

For example, when M-x uses the minibuffer to read the name of a command, it provides a list of all available XEmacs command names to complete against. The completion keys match the text in the minibuffer against all the command names, find any additional name characters implied by the ones already present in the minibuffer, and add those characters to the ones you have given. This is what makes it possible to type M-x inse <SPC> b <RET> instead of M-x insert-buffer <RET> (for example).

Case is normally significant in completion because it is significant in most of the names that you can complete (buffer names, file names and command names). Thus, ‘fo’ does not complete to ‘Foo’. When you are completing a name in which case does not matter, case may be ignored for completion’s sake if specified by program.

When a completion list is displayed, the completions will highlight as you move the mouse over them. Clicking the middle mouse button on any highlighted completion will “select” it just as if you had typed it in and hit <RET>.

6.3.1 Completion Example

A concrete example may help here. If you type M-x au <TAB>, the <TAB> looks for alternatives (in this case, command names) that start with ‘au’. There are several, including auto-fill-mode and auto-save-mode—but they are all the same as far as auto, so the ‘au’ in the minibuffer changes to ‘auto’.

If you type <TAB> again immediately, there are multiple possibilities for the very next character—it could be any of ‘c-’—so no more characters are added; instead, <TAB> displays a list of all possible completions in another window.

If you go on to type -f <TAB>, this <TAB> sees ‘auto-f’. The only command name starting this way is auto-fill-mode, so completion fills in the rest of that. You now have ‘auto-fill-mode’ in the minibuffer after typing just au <TAB> f <TAB>. Note that <TAB> has this effect because in the minibuffer it is bound to the command minibuffer-complete when completion is available.

6.3.2 Completion Commands

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

<TAB>

Complete the text in the minibuffer as much as possible (minibuffer-complete).

<SPC>

Complete the minibuffer text, but don’t go beyond one word (minibuffer-complete-word).

<RET>

Submit the text in the minibuffer as the argument, possibly completing first as described below (minibuffer-complete-and-exit).

?

Print a list of all possible completions of the text in the minibuffer (minibuffer-list-completions).

<button2>

Select the highlighted text under the mouse as a minibuffer response. When the minibuffer is being used to prompt the user for a completion, any valid completions which are visible on the screen will be highlighted when the mouse moves over them. Clicking <button2> will select the highlighted completion and exit the minibuffer. (minibuf-select-highlighted-completion).

<SPC> completes much like <TAB>, but never goes beyond 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 stops completing after ‘fill-’. This gives ‘auto-fill-’. Another <SPC> at this point completes all the way to ‘auto-fill-mode’. <SPC> in the minibuffer when completion is available runs the command minibuffer-complete-word.

Here are some commands you can use to choose a completion from a window that displays a list of completions:

button2up

Clicking mouse button 2 on a completion in the list of possible completions chooses that completion (mouse-choose-completion). You normally use this command while point is in the minibuffer; but you must click in the list of completions, not in the minibuffer itself.

<PRIOR>

M-v

Typing <PRIOR> or 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. (Selecting that window in the usual ways has the same effect, but this way is more convenient.)

<RET>

Typing <RET> 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 windows to the window that shows the list of completions.

<RIGHT>

<TAB>

C-f

Typing the right-arrow key <RIGHT>, <TAB> or C-f in the completion list buffer moves point to the following completion (next-list-mode-item).

<LEFT>

C-b

Typing the left-arrow key <LEFT> or C-b in the completion list buffer moves point toward the beginning of the buffer, to the previous completion (previous-list-mode-item).

6.3.3 Strict Completion

There are three different ways that <RET> can work in completing minibuffers, depending on how the argument will be used.

• Strict completion is used when it is meaningless to give any argument except one of the known alternatives. For example, when C-x k reads the name of a buffer to kill, it is meaningless to give anything but the name of an existing buffer. In strict completion, <RET> refuses to exit if the text in the minibuffer does not complete to an exact match.
• Cautious completion is similar to strict completion, except that <RET> exits only if the text was an exact match already, not needing completion. If the text is not an exact match, <RET> does not exit, but it does complete the text. If it completes to an exact match, a second <RET> will exit.

  Cautious completion is used for reading file names for files that must already exist.

• Permissive completion is used when any string whatever is meaningful, and the list of completion alternatives is just a guide. For example, when C-x C-f reads the name of a file to visit, any file name is allowed, in case you want to create a file. In permissive completion, <RET> takes the text in the minibuffer exactly as given, without completing it.

The completion commands display a list of all possible completions in a window whenever there is more than one possibility for the very next character. Also, typing ? explicitly requests such a list. If the list of completions is long, you can scroll it with C-M-v (see section Using Other Windows).

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.

6.4 Minibuffer History

Every argument that you enter with the minibuffer is saved on a minibuffer history list so that you can use it again later in another argument. Special commands load the text of an earlier argument in the minibuffer. They discard the old minibuffer contents, so you can think of them as moving through the history of previous arguments.

<UP>

M-p

Move to the next earlier argument string saved in the minibuffer history (previous-history-element).

<DOWN>

M-n

Move to the next later argument string saved in the minibuffer history (next-history-element).

M-r regexp <RET>

Move to an earlier saved argument in the minibuffer history that has a match for regexp (previous-matching-history-element).

M-s regexp <RET>

Move to a later saved argument in the minibuffer history that has a match for regexp (next-matching-history-element).

The simplest way to reuse the saved arguments in the history list is to move through the history list one element at a time. While in the minibuffer, use M-p or up-arrow (previous-history-element) to “move to” the next earlier minibuffer input, and use M-n or down-arrow (next-history-element) to “move to” the next later input.

The previous input that you fetch from the history entirely replaces the contents of the minibuffer. To use it as the argument, exit the minibuffer as usual with <RET>. You can also edit the text before you reuse it; this does not change the history element that you “moved” to, but your new argument does go at the end of the history list in its own right.

For many minibuffer arguments there is a “default” value. In some cases, the minibuffer history commands know the default value. Then you can insert the default value into the minibuffer as text by using M-n to move “into the future” in the history.

There are also commands to search forward or backward through the history; they search for history elements that match a regular expression that you specify with the minibuffer. M-r (previous-matching-history-element) searches older elements in the history, while M-s (next-matching-history-element) searches newer elements. By special dispensation, these commands can use the minibuffer to read their arguments even though you are already in the minibuffer when you issue them. As with incremental searching, an uppercase letter in the regular expression makes the search case-sensitive (see section Searching and Case).

All uses of the minibuffer record your input on a history list, but there are separate history lists for different kinds of arguments. For example, there is a list for file names, used by all the commands that read file names.

There are several other very specific history lists, including one for command names read by M-x, one for buffer names, one for arguments of commands like query-replace, and one for compilation commands read by compile. Finally, there is one “miscellaneous” history list that most minibuffer arguments use.

6.5 Repeating Minibuffer Commands

Every command that uses the minibuffer at least once is recorded on a special history list, together with the values of its arguments, so that you can repeat the entire command. In particular, every use of M-x is recorded there, since M-x uses the minibuffer to read the command name.

C-x <ESC> <ESC>

Re-execute a recent minibuffer command (repeat-complex-command).

M-p

Within C-x <ESC> <ESC>, move to previous recorded command (previous-history-element).

M-n

Within C-x <ESC> <ESC>, move to the next (more recent) recorded command (next-history-element).

M-x list-command-history

Display the entire command history, showing all the commands C-x <ESC> <ESC> can repeat, most recent first.

C-x <ESC> <ESC> is used to re-execute a recent minibuffer-using command. With no argument, it repeats the last such command. A numeric argument specifies which command to repeat; one means the last one, and larger numbers specify earlier ones.

C-x <ESC> <ESC> works by turning the previous command into a Lisp expression and then entering a minibuffer initialized with the text for that expression. If you type just <RET>, the command is repeated as before. You can also change the command by editing the Lisp expression. Whatever expression you finally submit is what will be executed. The repeated command is added to the front of the command history unless it is identical to the most recently executed command already there.

Even if you don’t understand Lisp syntax, it will probably be obvious which command is displayed for repetition. If you do not change the text, you can be sure the command will repeat exactly as before.

If you are in the minibuffer for C-x <ESC> <ESC> and the command shown to you is not the one you want to repeat, you can move around the list of previous commands using M-n and M-p. M-p replaces the contents of the minibuffer with the next earlier recorded command, and M-n replaces it with the next later command. After finding the desired previous command, you can edit its expression and then resubmit it by typing <RET>. Any editing you have done on the command to be repeated is lost if you use M-n or M-p.

M-n and M-p are specially defined within C-x <ESC> <ESC> to run the commands previous-history-element and next-history-element.

The list of previous commands using the minibuffer is stored as a Lisp list in the variable command-history. Each element of the list is a Lisp expression which describes one command and its arguments. Lisp programs can reexecute a command by feeding the corresponding command-history element to eval.

This document was generated by Aidan Kehoe on December 27, 2016 using texi2html 1.82.