RE: The euro symbol in emacs

[Drew Adams]

> (global-set-key (kbd "s-2") (lambda () (interactive)  (insert  ?€)))
> 
> That works fine for text buffers, but it does not work in the prompt
> area.

The prompt area is read-only, normally.  My crystal ball tells me that
you really mean "in the minibuffer", i.e., during input.

For that, try adding that binding to one or all of the minibuffer
keymaps.  It is probably enough to add it to only `minibuffer-local-map':

(define-key minibuffer-local-map (kbd "s-2")
                                 (lambda () (interactive) (insert ?€)))