16.9.2 Creating and Deleting Buffer-Local Bindings

Command: make-local-variable variable

This function creates a buffer-local binding in the current buffer for variable (a symbol). Other buffers are not affected. The value returned is variable.

The buffer-local value of variable starts out as the same value variable previously had. If variable was void, it remains void.

;; In buffer ‘b1’:
(setq foo 5)                ; Affects all buffers.
     ⇒ 5

(make-local-variable 'foo)  ; Now it is local in ‘b1’.
     ⇒ foo

foo                         ; That did not change
     ⇒ 5                   ;   the value.

(setq foo 6)                ; Change the value
     ⇒ 6                   ;   in ‘b1’.

foo
     ⇒ 6

;; In buffer ‘b2’, the value hasn’t changed.
(save-excursion
  (set-buffer "b2")
  foo)
     ⇒ 5

Making a variable buffer-local within a let-binding for that variable does not work. This is because let does not distinguish between different kinds of bindings; it knows only which variable the binding was made for.

Please note: do not use make-local-variable for a hook variable. Instead, use make-local-hook. See Hooks.

Command: make-variable-buffer-local variable

This function marks variable (a symbol) automatically buffer-local, so that any subsequent attempt to set it will make it local to the current buffer at the time.

The value returned is variable.

Function: local-variable-p variable buffer &optional after-set

This returns t if variable is buffer-local in buffer buffer; else nil.

If optional third arg after-set is non-nil, return t if symbol would be buffer-local after it is set, regardless of whether it is so presently.

A nil value for buffer is not the same as (current-buffer), but means "no buffer". Specifically:

If buffer is nil and after-set is nil, a return value of t indicates that the variable is one of the special built-in variables that is always buffer-local. (This includes buffer-file-name, buffer-read-only, buffer-undo-list, and others.)

If buffer is nil and after-set is t, a return value of t indicates that the variable has had make-variable-buffer-local applied to it.

Function: buffer-local-variables &optional buffer

This function returns a list describing the buffer-local variables in buffer buffer. It returns an association list (see Association Lists) in which each association contains one buffer-local variable and its value. When a buffer-local variable is void in buffer, then it appears directly in the resulting list. If buffer is omitted, the current buffer is used.

(make-local-variable 'foobar)
(makunbound 'foobar)
(make-local-variable 'bind-me)
(setq bind-me 69)

(setq lcl (buffer-local-variables))
    ;; First, built-in variables local in all buffers:
⇒ ((mark-active . nil)
    (buffer-undo-list nil)
    (mode-name . "Fundamental")
    …

    ;; Next, non-built-in local variables.
    ;; This one is local and void:
    foobar
    ;; This one is local and nonvoid:
    (bind-me . 69))

Note that storing new values into the CDRs of cons cells in this list does not change the local values of the variables.

Command: kill-local-variable variable

This function deletes the buffer-local binding (if any) for variable (a symbol) in the current buffer. As a result, the global (default) binding of variable becomes visible in this buffer. Usually this results in a change in the value of variable, since the global value is usually different from the buffer-local value just eliminated.

If you kill the local binding of a variable that automatically becomes local when set, this makes the global value visible in the current buffer. However, if you set the variable again, that will once again create a local binding for it.

kill-local-variable returns variable.

This function is a command because it is sometimes useful to kill one buffer-local variable interactively, just as it is useful to create buffer-local variables interactively.

Function: kill-all-local-variables

This function eliminates all the buffer-local variable bindings of the current buffer except for variables marked as “permanent”. As a result, the buffer will see the default values of most variables.

This function also resets certain other information pertaining to the buffer: it sets the local keymap to nil, the syntax table to the value of standard-syntax-table, and the abbrev table to the value of fundamental-mode-abbrev-table.

Every major mode command begins by calling this function, which has the effect of switching to Fundamental mode and erasing most of the effects of the previous major mode. To ensure that this does its job, the variables that major modes set should not be marked permanent.

kill-all-local-variables returns nil.

A local variable is permanent if the variable name (a symbol) has a permanent-local property that is non-nil. Permanent locals are appropriate for data pertaining to where the file came from or how to save it, rather than with how to edit the contents.