Info Catalog emacs: Hooks emacs: Variables emacs: File Variables

emacs: Locals

 
 51.2.3 Local Variables
 ----------------------
 
 ‘M-x make-local-variable <RET> VAR <RET>’
      Make variable VAR have a local value in the current buffer.
 ‘M-x kill-local-variable <RET> VAR <RET>’
      Make variable VAR use its global value in the current buffer.
 ‘M-x make-variable-buffer-local <RET> VAR <RET>’
      Mark variable VAR so that setting it will make it local to the
      buffer that is current at that time.
 
    Almost any variable can be made “local” to a specific Emacs buffer.
 This means that its value in that buffer is independent of its value in
 other buffers.  A few variables are always local in every buffer.  Every
 other Emacs variable has a “global” value which is in effect in all
 buffers that have not made the variable local.
 
    ‘M-x make-local-variable’ reads the name of a variable and makes it
 local to the current buffer.  Changing its value subsequently in this
 buffer will not affect others, and changes in its global value will not
 affect this buffer.
 
    ‘M-x make-variable-buffer-local’ marks a variable so it will become
 local automatically whenever it is set.  More precisely, once a variable
 has been marked in this way, the usual ways of setting the variable
 automatically do ‘make-local-variable’ first.  We call such variables
 “per-buffer” variables.  Many variables in Emacs are normally
 per-buffer; the variable’s document string tells you when this is so.  A
 per-buffer variable’s global value is normally never effective in any
 buffer, but it still has a meaning: it is the initial value of the
 variable for each new buffer.
 
    Major modes (Major Modes) always make variables local to the
 buffer before setting the variables.  This is why changing major modes
 in one buffer has no effect on other buffers.  Minor modes also work by
 setting variables—normally, each minor mode has one controlling variable
 which is non-‘nil’ when the mode is enabled (Minor Modes).  For
 many minor modes, the controlling variable is per buffer, and thus
 always buffer-local.  Otherwise, you can make it local in a specific
 buffer like any other variable.
 
    A few variables cannot be local to a buffer because they are always
 local to each display instead (Multiple Displays).  If you try
 to make one of these variables buffer-local, you’ll get an error
 message.
 
    ‘M-x kill-local-variable’ makes a specified variable cease to be
 local to the current buffer.  The global value of the variable
 henceforth is in effect in this buffer.  Setting the major mode kills
 all the local variables of the buffer except for a few variables
 specially marked as “permanent locals”.
 
    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
 construct ‘setq-default’.  This construct is used just like ‘setq’, but
 it sets variables’ global values instead of their local values (if any).
 When the current buffer does have a local value, the new global value
 may not be visible until you switch to another buffer.  Here is an
 example:
 
      (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’.
 
    Lisp programs can use ‘default-value’ to look at a variable’s default
 value.  This function takes a symbol as argument and returns its default
 value.  The argument is evaluated; usually you must quote it explicitly.
 For example, here’s how to obtain the default value of ‘fill-column’:
 
      (default-value 'fill-column)
 

Info Catalog emacs: Hooks emacs: Variables emacs: File Variables