setup-eshell.el

(require 'eshell)

(defun eshell-other-window (&optional arg)
  "Create an interactive Eshell buffer.
The buffer used for Eshell sessions is determined by the value of
`eshell-buffer-name'.  If there is already an Eshell session active in
that buffer, Emacs will simply switch to it.  Otherwise, a new session
will begin.  A numeric prefix arg (as in `C-u 42 M-x eshell RET')
switches to the session with that number, creating it if necessary.  A
nonnumeric prefix arg means to create a new session.  Returns the
buffer selected (or created)."
  (interactive "P")
  (cl-assert eshell-buffer-name)
  (let ((buf (cond ((numberp arg)
		    (get-buffer-create (format "%s<%d>"
					       eshell-buffer-name
					       arg)))
		   (arg
		    (generate-new-buffer eshell-buffer-name))
		   (t
		    (get-buffer-create eshell-buffer-name)))))
    (cl-assert (and buf (buffer-live-p buf)))
    (pop-to-buffer buf)
    (unless (eq major-mode 'eshell-mode)
      (eshell-mode))
    buf))