Sometimes I justify text in emacs using C-u 70 M-x fill-region.

I would like to have a function in my .emacs file that has a parameter so that I can use a shortcut to call the function instead of having to do C-u 70 fill-region. I would have 2 shortcuts, one uses the default 70 and another asks for a parameter.

I'm very new to emacs programming but I've been using emacs for a while now. If there is a solution for this, could you please explain how to do it?

  • You say that you want 2 shortcuts. Does that mean that you want key commands to be bound to the functions? If so, which key commands?
    – N.N.
    Dec 13, 2012 at 11:26

1 Answer 1


If you prefix a function with C-h f you can read documentation for it. If you do it for fill-region it shows, among other things:

The `fill-column' variable controls the width.

And if you check the Emacs manual on Fill commands you can read:

The maximum line width for filling is specified by the buffer-local variable fill-column. The default value (see Locals) is 70. The easiest way to set fill-column in the current buffer is to use the command C-x f (set-fill-column). With a numeric argument, it uses that as the new fill column. With just C-u as argument, it sets fill-column to the current horizontal position of point.

This explains how C-u 70 M-x fill-region works. It also shows that the width to fill with can be set via C-x f. Thus, it may not be necessary to write a function that asks for a parameter, i.e. you could use C-x f and fill-region instead.

If you still want new functions to do this you can use the following:

(defun fill-region-ask-width (fill-width)
  "Asks for a width and fills the region to it"
  (interactive "nFill region to column: ")
  (fill-region-width fill-width))

(defun fill-region-width-70 ()
  "Fills the region with width 70"
  (fill-region-width 70))

(defun fill-region-width (fill-width)
  "Fills the region with the given width"
  (set-fill-column fill-width)
  (fill-region (region-beginning) (region-end)))

The functions are explained by their doc strings but here are some more notes:

  • fill-region-ask-width takes one argument which it gets by asking the user and it treats that number as an integer (n) and passes it to fill-region-prompt-width.
  • fill-region-width-70 merely has a hard-coded number that it passes to fill-region-prompt-width.
  • fill-region-width is a helper function to modularize what the other two functions have in common. It is not defined as interactive so it is not possible to call via M-x. It sets fill-column to the given argument and fills the region`.

For learning how to write Emacs functions and binding them to keys see Learn Elisp For Emacs: Lesson 4-2 - Adding Custom Functions To Emacs.

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