Question

I know you can change the frame size in the .emacs file with set-frame-width or (add-to-list 'default-frame-alist '(width . 80)) but how can I change the width after Emacs has started up (aside from dragging the edge of the frame)?

Answer 1

Well, go to the *scratch* buffer and use set-frame-width.

(set-frame-width (selected-frame) 100)  ;; ^J to execute. 

set-frame-width isn’t interactive, so you can’t run it with M-x but you could trivially write a set-frame-width-interactive, something like

(defun set-frame-width-interactive (arg)    (interactive 'p')    (set-frame-width (selected-frame) arg)) 

Now C-u 8 0 M-x set-frame-width-interactive will set the width to 80.

Is this what you’re trying to do?