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57.3.1 Examining and Setting Variables

C-h v var <RET>

Display the value and documentation of variable var (describe-variable).

M-x set-variable <RET> var <RET> value <RET>

Change the value of variable var to value.

To examine the value of a single variable, use C-h v (describe-variable), which reads a variable name using the minibuffer, with completion. It displays both the value and the documentation of the variable. For example,

 
C-h v fill-column <RET>

displays something like this:

 
fill-column is a variable defined in `C source code'.
fill-column's value is 70
Local in buffer custom.texi; global value is 70
Automatically becomes buffer-local when set in any fashion.

This variable is safe to use as a file local variable only if its value
satisfies the predicate `integerp'.

Documentation:
*Column beyond which automatic line-wrapping should happen.
Interactively, you can set the buffer local value using C-x f.

You can customize this variable.

The line that says you can customize the variable indicates that this variable is a user option. (The star also indicates this, but it is an obsolete indicator that may eventually disappear.) C-h v is not restricted to user options; it allows any variable name.

The most convenient way to set a specific user option variable is with M-x set-variable. This reads the variable name with the minibuffer (with completion), and then reads a Lisp expression for the new value using the minibuffer a second time (you can insert the old value into the minibuffer for editing via M-n). For example,

 
M-x set-variable <RET> fill-column <RET> 75 <RET>

sets fill-column to 75.

M-x set-variable is limited to user option variables, but you can set any variable with a Lisp expression, using the function setq. Here is a setq expression to set fill-column:

 
(setq fill-column 75)

To execute an expression like this one, go to the ‘*scratch*’ buffer, type in the expression, and then type C-j. See section Lisp Interaction Buffers.

Setting variables, like all means of customizing Emacs except where otherwise stated, affects only the current Emacs session. The only way to alter the variable in future sessions is to put something in the ‘~/.emacs’ file to set it those sessions (see section The Init File, ‘~/.emacs).


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