Eshell is a command shell implemented entirely in Emacs Lisp.

Put the expression below into your ~/.emacs.

;; You can run eshell by M-x eshell
(require 'eshell-auto)
;; Use pcomplete with shell-mode 
(require 'pcmpl-auto)
(add-hook 'shell-mode-hook 'pcomplete-shell-setup)

WWW: http://emacswiki.org/johnw/eshell.html