system.el

;; check OS type
(cond
 ((string-equal system-type "windows-nt")
  (progn
    (message "Windows Worst System operative") )
  )
 ((string-equal system-type "darwin")
  (progn
    (message "Mac OS")
    )
  )
 ((string-equal system-type "gnu/linux")
  (progn
    (message "Linux") )
  )
 ((string-equal system-type "berkeley-unix")
  (progn
    (message "Freebsd") )
    )
 )