Emacs Lisp: Overview of Coding Emacs Lisp

By Xah Lee. Date: . Last updated: .

In emacs, you can program it using the embedded language (called Emacs Lisp, or elisp) so that you can have custom functions to insert texts, templates, process files, or, many other features of emacs such as write a file manager, chat client, email reader, etc.

Two Parts of Emacs Lisp Programing

Programing emacs lisp can be divided into 2 major parts.

  1. Text Processing
  2. Major Mode (non-text-processing)

First part of programing emacs is about text processing. This is easier and most useful for programers. You can write your own commands to help you manipulate text, refactor code, process log files, etc.

The second part of programing emacs is about writing a Major Mode or Minor Mode, such as creating a file manager, special mode for a programing language, a web browser, chat bot, tetris game, etc.

Example of Simple Elisp Functions for Text Processing

Emacs provides functions for text manipulation. For example:

Cursor Position

;; current cursor position is called “point”.
;; Left of first char in buffer is 1
;; This returns the current cursor position
(point)

;; returns the position of the beginning/end of region (selection)
(region-beginning)
(region-end)

;; position for beginning/ending of current line
(line-beginning-position)
(line-end-position)

;; returns the position for the beginning/end of buffer, taking account of narrow-to-region
(point-min)
(point-max)

Try this. Type

(point)

in a buffer. Then, Evaluate Emacs Lisp Code

The result is current cursor position.

Move Cursor, Search Text

;; move cursor to position 39
(goto-char 39)

;; move cursor by 4 chars
(forward-char 4)
(backward-char 4)

;; move cursor to the location of a string
;; returns the new position
(search-forward "some") ; to end of “some”
(search-backward "some") ; to beginning of “some”

;; move cursor to the location matched by a regex
;; returns the new position
(re-search-forward "[0-9]") ; digit
(re-search-backward "[0-9]")

;; move cursor to the first char that's not “a to z”
;; Returns the distance traveled.
(skip-chars-forward "a-z")
(skip-chars-backward "a-z")

Delete, Insert, Change, Text

;; delete 9 chars starting at current cursor pos
(delete-char 9)

;; deleting text from pos 3 to 10
(delete-region 3 10)

;; insert string at current cursor position
(insert "i ♥ cats")

;; get the string from pos 71 to 300
(setq x (buffer-substring 71 300))

;; capitalize letters in a region
(capitalize-region 71 300)

String

;; length
(length "abc")
; returns 3

;; substring
(substring "abcdefg" 3 4)
; returns "d"

;; change a given string using regex
(replace-regexp-in-string "[0-9]" "X" "abc123")
;; returns "abcXXX"

Buffer

;; return the name of current buffer
(buffer-name)

;; return the full path of current file
(buffer-file-name)

;; switch to the buffer named xyz
(set-buffer "xyz")

;; save current buffer
(save-buffer)

;; close a buffer named xyz
(kill-buffer "xyz")

;; temporarily sets a buffer as current to work with
(with-current-buffer "xyz"
  ;; do something here. delete/insert text, etc.
)

File

;; open a file (in a buffer)
(find-file "~/")

;; same as “Save As”.
(write-file path)

;; insert file into current position
(insert-file-contents path)

;; append a text block to file
(append-to-file start-pos end-pos path)

;; renaming file
(rename-file file-name new-name)

;; copying file
(copy-file old-name new-name)

;; deleting file
(delete-file file-name)

;; get dir path
(file-name-directory full-path)

;; get filename part
(file-name-nondirectory full-path)

;; get filename's suffix
(file-name-extension file-name)

;; get filename sans suffix
(file-name-sans-extension file-name)

Simple Examples of Emacs Lisp Code

Programing a Major/Minor Mode

For example, all of the following major modes are written in elisp:

Tasks of writing a mode is more complex, because it involves understanding many of emacs's systems: keyboard input event, display (windows and fonts), user interface (menu, windows, scroll bar, tool bar), major/minor mode's structure, coloring text, package structure, etc.

You should have some experience doing text processing in elisp before writing a major mode.