27.2.4 Local Variables
Make a variable have a local value in the current buffer.
Make a variable use its global value in the current buffer.
Mark a variable so that setting it will make it local to the
buffer that is current at that time.
You can make any variable "local" to a specific Emacs buffer. This
means that the variable's value in that buffer is independent of its
value in other buffers. A few variables are always local in every
buffer. All other Emacs variables have a "global" value which is in
effect in all buffers that have not made the variable local.
Major modes always make the variables they set local to the buffer.
This is why changing major modes in one buffer has no effect on other
`M-x make-local-variable' reads the name of a variable and makes it
local to the current buffer. Further changes in this buffer will not
affect others, and changes in the global value will not affect this
`M-x make-variable-buffer-local' reads the name of a variable and
changes the future behavior of the variable so that it automatically
becomes local when it is set. More precisely, once you have marked a
variable in this way, the usual ways of setting the variable will
automatically invoke `make-local-variable' first. We call such
variables "per-buffer" variables.
Some important variables have been marked per-buffer already. They
include `abbrev-mode', `auto-fill-function', `case-fold-search',
`comment-column', `ctl-arrow', `fill-column', `fill-prefix',
`mode-line-format', `overwrite-mode', `selective-display-ellipses',
`selective-display', `tab-width', and `truncate-lines'. Some other
variables are always local in every buffer, but they are used for
Note: the variable `auto-fill-function' was formerly named
If you want a variable to cease to be local to the current buffer,
call `M-x kill-local-variable' and provide the name of a variable to
the prompt. The global value of the variable is again in effect in
this buffer. Setting the major mode kills all the local variables of
To set the global value of a variable, regardless of whether the
variable has a local value in the current buffer, you can use the Lisp
function `setq-default'. It works like `setq'. If there is a local
value in the current buffer, the local value is not affected by
`setq-default'; thus, the new global value may not be visible until you
switch to another buffer, as in the case of:
(setq-default fill-column 75)
`setq-default' is the only way to set the global value of a variable
that has been marked with `make-variable-buffer-local'.
Programs can look at a variable's default value with `default-value'.
This function takes a symbol as an argument and returns its default
value. The argument is evaluated; usually you must quote it
explicitly, as in the case of:
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