GNU Emacs Manual - Examining

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### 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's value is 75

    Documentation:
    *Column beyond which automatic line-wrapping should happen.
    Automatically becomes buffer-local when set in any fashion.

The star at the beginning of the documentation indicates that this variable is a user option. `C-h v` is not restricted to user options; it allows any variable name.

The most convenient way to set a specific user option 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. 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.

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