To comment/uncomment a line in emacs, add this to your ~/.emacs

;; comment line
(defun comment-or-uncomment-region-or-line ()
    "Comments or uncomments the region or the current line if there's no active region."
    (interactive)
    (let (beg end)
        (if (region-active-p)
            (setq beg (region-beginning) end (region-end))
            (setq beg (line-beginning-position) end (line-end-position)))
        (comment-or-uncomment-region beg end)
        ;(next-line)
	))
(global-set-key (kbd "M-#") 'comment-or-uncomment-region-or-line)

(courtesy of Gerstmann on StackOverflow)