.EL File Format

Introduction

An .el file holds Emacs Lisp, the dialect of Lisp built into the GNU Emacs text editor. Most of Emacs is written in it, and so are its extensions and packages. A user’s own settings, in init.el, are Emacs Lisp too.

Emacs can byte-compile an .el file to a .elc file, and versions built with native compilation produce .eln files as well. The .el file stays the source that people read and edit.

Structure

An Emacs Lisp file is plain text, usually UTF-8, made of parenthesised forms that are evaluated in turn. Comments start with ; and run to the end of the line. By convention, the number of semicolons shows the level of a comment. Emacs also reads the first line for file-local settings between -*- marks. The setting lexical-binding: t turns on lexical scope, which new code is expected to use.

A library follows a set layout: a first line naming the file and describing it, a header of comment lines such as Author:, Version: and Package-Requires:, a ;;; Commentary: part and a ;;; Code: part. It ends with (provide 'name), which lets (require 'name) load it, and a closing comment. Package tools read these headers. Functions are defined with defun and user settings with defcustom, and a function that can be run with a keystroke or M-x contains (interactive).

;;; greet.el --- Say hello  -*- lexical-binding: t; -*-

;; Author: A. Example
;; Version: 1.0

;;; Commentary:

;; A small example library.

;;; Code:

(defun greet (name)
  "Show a greeting for NAME."
  (interactive "sName: ")
  (message "Hello, %s" name))

(provide 'greet)
;;; greet.el ends here

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