How to determine operating system in elisp?

Question

How do I programmatically determine which OS Emacs is running under in ELisp?

I would like to run different code in .emacs depending on the OS.

Answer 1

Now there is also Linux Subsystem for Windows (bash under Windows 10) where system-type is gnu/linux. To detect this system type use:

(if
    (string-match "Microsoft"
         (with-temp-buffer (shell-command "uname -r" t)
                           (goto-char (point-max))
                           (delete-char -1)
                           (buffer-string)))
    (message "Running under Linux subsystem for Windows")
    (message "Not running under Linux subsystem for Windows")
  )