Elisp: Determine OS, Emacs Version, Machine Host Name

The following are useful for setting up emacs init file on different machines.

Get Operating System Type

Here's how to find out what operating system emacs is running on.

;; check OS type
(cond
 ((string-equal system-type "windows-nt") ; Microsoft Windows
  (progn
    (message "Microsoft Windows")))
 ((string-equal system-type "darwin") ; Mac OS X
  (progn
    (message "Mac OS X")))
 ((string-equal system-type "gnu/linux") ; linux
  (progn
    (message "Linux"))))

Get Emacs Version

The following variables returns emacs version number.

• emacs-version (a dotted string)
• emacs-major-version (a integer type)
• emacs-minor-version (a integer type)

;; full emacs version number. A string.
emacs-version
;; sample value: "24.5.1"

;; A integer, emacs major version number.
emacs-major-version
;; sample value: 24

;; A integer, emacs minor version number.
emacs-minor-version
;; sample value: 5

Compare Version String

• version=
• version<
• version<=

;; check emacs version
(if (version< emacs-version "24.4")
    (message "is before 24.4")
  (message "is 24.4 or after"))

Get Host Name, User Name, Init File Path

Here's some other useful elisp function or variable to determine machine name (host name), user name, emacs init path.

• system-name → returns the host name.
• user-login-name → returns user login name.
• user-emacs-directory → init file dir.
• user-init-file → init file path.

For detail, see:

• (info "(elisp) User Identification")
• (info "(elisp) System Environment")

Check If a Package is Loaded

See: Elisp: Check If a {function, variable, feature} is Defined/Loaded.