Add multiple file extensions to major modes

add-to-mode.el

;; Instead of this
(add-to-list 'auto-mode-alist '("\\.rake$" . ruby-mode))
(add-to-list 'auto-mode-alist '("\\.gemspec$" . ruby-mode))
(add-to-list 'auto-mode-alist '("\\.ru$" . ruby-mode))
(add-to-list 'auto-mode-alist '("Rakefile$" . ruby-mode))
(add-to-list 'auto-mode-alist '("Gemfile$" . ruby-mode))
(add-to-list 'auto-mode-alist '("Capfile$" . ruby-mode))
(add-to-list 'auto-mode-alist '("Vagrantfile$" . ruby-mode))


;; maybe try this:

(defun add-to-mode (mode &rest files)
  (dolist (file files)
    (add-to-list 'auto-mode-alist
                 (cons file mode))))

(add-to-mode 'ruby-mode
             "\\.rake$"
             "\\.gemspec$"
             "\\.ru$"
             "\\(Cap\\|Gem\\|Rake\\|Vagrant\\)file$"
             "^\\.irbrc$")