example of code for http://stackoverflow.com/questions/9420270/how-to-define-an-alternate-command-for-emacs-eshell

test.el

(defun string-join-accum (joiner strings accum)
  (cond ((not strings) accum)
        ((not (cdr strings)) (concat accum (car strings)))
        (t (string-join-accum joiner (cdr strings)
                              (concat accum (car strings) joiner)))))

(defun string-join (joiner strings)
  (string-join-accum joiner strings ""))

(defun invoke-bash (command)
  (let ((invoke-bash-cmd (concat "bash -c \"" command " "
				 (string-join " " eshell-last-arguments) "\"")))
    (message invoke-bash-cmd)
    (throw 'eshell-replace-command (eshell-parse-command invoke-bash-cmd))))