>   Using the :ruby header arg.
>
> * lisp/ob-ruby.el (org-babel-execute:ruby): Locally set
>   `org-babel-ruby-command' using a header argument.
>
> TINYCHANGE
> ---
>  lisp/ob-ruby.el | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/lisp/ob-ruby.el b/lisp/ob-ruby.el
> index 669c2eabf..80870c6c0 100644
> --- a/lisp/ob-ruby.el
> +++ b/lisp/ob-ruby.el
> @@ -74,6 +74,9 @@ This function is called by `org-babel-execute-src-block'."
>  		   (cdr (assq :session params))))
>           (result-params (cdr (assq :result-params params)))
>           (result-type (cdr (assq :result-type params)))
> +	 (org-babel-ruby-command
> +	  (or (cdr (assq :ruby params))
> +	      org-babel-ruby-command))
>           (full-body (org-babel-expand-body:generic
>  		     body params (org-babel-variable-assignments:ruby params)))
>           (result (if (member "xmp" result-params)

Thanks, this is a much needed change.  But currently it is limited only
to non-session code execution.  Here is an additional patch that also
supports the same feature for session code execution as well:

ob-ruby.el: allow specification of session ruby command w/header arg

* lisp/ob-ruby.el (org-babel-ruby-initiate-session): Use a header argument
to get ruby command.