Writing a module

An Eshell module is defined the same as any other library but with two additional requirements: first, the module’s source file should be named em-name.el; second, the module must define an autoloaded Customize group (see Customization in The Emacs Lisp Reference Manual) with eshell-module as the parent group. In order to properly autoload this group, you should wrap its definition with progn as follows:

;;;###autoload
(progn
(defgroup eshell-my-module nil
  "My module lets you do very cool things in Eshell."
  :tag "My module"
  :group 'eshell-module))

Even if you don’t have any Customize options in your module, you should still define the group so that Eshell can include your module in the Customize interface for eshell-modules-list.