How can I find out which OS I am running in Emacs?

I开发者_JAVA百科s there an Elisp command which can return "Mac", "Windows", "linux", etc??

system-type is a variable defined in `C source code'. Its value is gnu/linux

Documentation: The value is a symbol indicating the type of operating system you are using. Special values:

  `gnu'          compiled for a GNU Hurd system.
  `gnu/linux'    compiled for a GNU/Linux system.
  `gnu/kfreebsd' compiled for a GNU system with a FreeBSD kernel.
  `darwin'       compiled for Darwin (GNU-Darwin, Mac OS X, ...).
  `ms-dos'       compiled as an MS-DOS application.
  `windows-nt'   compiled as a native W32 application.
  `cygwin'       compiled using the Cygwin library.

Anything else (in Emacs 23.1, the possibilities are: aix, berkeley-unix, hpux, irix, lynxos 3.0.1, usg-unix-v) indicates some sort of Unix system.