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Written by Oleksandr Gavenko (AKA gavenkoa), compiled on 2024-04-01 from rev 052223c22317.



Packages for Emacs.

Getting help.

Installing Emacs.

Official build of GNU Emacs for Windows.
Official alpha build of GNU Emacs.
Clean GNU Emacs for Mac OS X.



Select one of:

(set 'variable value)
(setq variable value)
(defvar variable value "documentation")

or file local:

# Local variables:
# variable: value
# End:

Find variable/function/feature by name or value.

(apropos-value "PATT")
(apropos-variable "PATT")
(apropos-function "PATT")
(apropos-library "PATT")
(apropos-documentation "PATT")


Evaluating elisp expression on the fly.

Type M-: than lisp expression than type RET.

Or in any buffer place point at the end of lisp expression and type C-x C-e.

Or invoke elisp "shell" by M-x ielm.

What functions and variables Emacs load and from which files?

See value of variable load-history (by C-h v load-history RET):

(symbol-file 'scheme 'provide)        ; Who provide feature.
(symbol-file 'nxml-mode-hook 'defvar) ; Where variable defined.
(symbol-file 'message-send 'defun)    ; Where function defined.
(symbol-file 'scheme)  ; Look for symbol despite its type.
(locate-library "gnus.el")
(find-lisp-object-file-name 'c-mode (symbol-function 'c-mode))

Using edebug.

Execute M-x edebug-defun (also on C-u C-M-x) on defun in source code to enable debugging for desired function. When next time this function invoked you entered to its debugging (jumped to its source code).

To start debug execute code which used debugged function.

You can disable edebug on a function by evaluating the function again using C-M-x.

How debug func?

Use M-x debug-on-entry and M-x cancel-debug-on-entry to control which functions will enter the debugger when called. Next time that function loaded in debug-mode.

You can use (debug) in your function to automatically enter to debugger.

You can use (backtrace) to print a trace of Lisp function.

How debug ini file?

When your ini has a bug, or when you load external files that cause errors, the bug is often hard to find, because the Emacs Lisp reader does not know about line numbers and files - it just knows an error happened, and that's it.

Try run Emacs with --debug-init to see backtrace.

How debug long running command?

Remember Emacs elisp interpreter single threaded. To interrupt long running command press C-g. Sometime it should be typed several times.

On toggle-debug-on-quit or M-x debug-on-quit RET on C-g Emacs enter to debug mode.

Check if bug in ini file not in Emacs itself.

First run Emacs without loading anything:

$ emacs --no-init-file --no-site-file

or more shortly (as -Q imply -q, --no-site-file, and --no-splash together):

$ emacs -Q

If bug not reproduced bug lies in ini files!

Elisp debug tips.

  • Use a keyboard macro that moves forward one expression (sexp) and evaluates it.
  • Try C-x check-parens.

Enable debug mode (also on loading).

Set in source:

(setq debug-on-error t)

or invoke Emacs like:

$ emacs --debug-init

where --debug-init binds debug-on-error to t while loading the init file, and bypasses the condition-case which normally catches errors in the init file.

Call tree.

Before byte compiling file execute:

(setq byte-compile-generate-call-tree t)

Veiw buffer local variables.

(pp (buffer-local-variables))

Emacs profiling.


edebug allow save execution statistic on per line basis. As usual evaluate C-u M-S-x (or M-x edebug-defun) on top lovel functional form. Call code that uses examined function. On entry to edebug type c (edebug-continue-mode). After finishing evaluation place cursor to examined function form and evaluate M-x edebug-display-freq-count. Function be annotated with evaluation counts per line.


(benchmark-run 1 (revert-buffer))
(benchmark-run-compiled 1 (hi-lock-face-phrase-buffer "hello" 'hi-yellow))


Enter a prefix for M-x elp-instrument-package, perform action and see result by M-x elp-results. To perform new measurement don't forget to run M-x elp-reset-all.

Validating Elisp code

(byte-compile-file (buffer-file-name))



Sort and uniquify lines.

Select region, type C-u M-| sort -u RET.

With transient-mark-mode and delete-selection-mode enabled: select region, type M-| sort -u RET to replace selection with sorted and uniquified lines.

Determining running environment/platform.

Check variables:

window-system             - ``nil`` if in terminal, ``w32`` if native Windows build, ``x`` if under X Window
window-system-version     - for windows only
operating-system-release  - release of the operating system Emacs is running on
system-configuration      - like configuration triplet: cpu-manufacturer-os
system-name               - host name of the machine you are running on
system-type               - indicating the type of operating system you are using:
                            ``gnu`` (GNU Hurd),
                            ``gnu/kfreebsd``, ``berkeley-unix`` for (FreeBSD),
                            ``darwin`` (GNU-Darwin, Mac OS X),
dynamic-library-alist or deprecated image-library-alist
                          - alist of image types vs external libraries needed to display them

and check functions:

(fboundp ...)             - return t if SYMBOL's function definition is not void
(featurep ...)            - returns t if FEATURE is present in this Emacs
(display-graphic-p)       - return non-nil if DISPLAY is a graphic display; graphical
                            displays are those which are capable of displaying several
                            frames and several different fonts at once
(display-multi-font-p)    - same as ``display-graphic-p``
(display-multi-frame-p)   - same as ``display-graphic-p``
(display-color-p)         - return t if DISPLAY supports color
(display-images-p)        - return non-nil if DISPLAY can display images
(display-grayscale-p)     - return non-nil if frames on DISPLAY can display shades of gray
(display-mouse-p)         - return non-nil if DISPLAY has a mouse available
(display-popup-menus-p)   - return non-nil if popup menus are supported on DISPLAY
(display-selections-p)    - return non-nil if DISPLAY supports selections

Run those checks as below:

(when window-system ...)
(when (eq window-system 'x) ...)
(when (>= emacs-major-version 22) ...)
(when (fboundp '...) ...)
(when (featurep '...) ...)

Compiling emacs.


Get MSYS for POSIX shell and utilities . Get MinGW for GCC. Get Gnuwin32 for jpeg, ungif, tiff, xpm, png, zlib libraries.

Read emacs/nt/INSTALL:

$ cmd
$ cd emacs\nt
$ configure.bat --prefix %INST_ROOT% --with-gcc --cflags -I%GNUWIN32_ROOT%/include --ldflags -L%GNUWIN32_ROOT%/lib  --ldflags -lregex
$ make bootstrap
$ make info
$ make install


Elisp documentation.

;;; <file-name>.el --- <one-line-description>

;; Copyright (C) <years> <person>

;; Author: <person> <mail>
;; Maintainer: <person> <mail>
;; Created: <date>
;; Version: <version>
;; Keywords: <look for ``finder-by-keyword`` output, separate by comma>
;; URL: <file-location>

;;; Commentary:
;;; Code:
;;; <file-name> ends here



CheckDoc checks your EmacsLisp code for errors in documentation and style.

home page before including it into GNU Emacs

Installing Emacs.


$ apt-get install emacs

Emacs paths.

source-directory data-directory doc-directory exec-directory
invocation-directory trash-directory tutorial-directory user-emacs-directory

Emacs games.

hanoi hanoi-unix life pong tetris gomoku

Long lines.

(setq longlines-show-hard-newlines t)
(setq longlines-wrap-follows-window-size t)
(longlines-mode 1)

Printing Emacs structures.

(message "%S" '(a b 123 "hello" 'set))
(pp '(a b 123 "hello" 'set))
(prin1-to-string '(1 2))

(symbol-name 'f)
(symbol-value 'f)
(symbol-function 'f)
(symbol-plist 'f)

(local-variable-p var buffer)

File manager.


Describe the current list of spp macros.
List of C/C++ files that contain preprocessor macros for the C lexer.

Debugging C code.

-*- mode: grep; mode: auto-revert-tail; default-directory: "~/devel/proj" -*-

XML modes.


XSLT-process is a minor mode for GNU Emacs/XEmacs which transforms it into a powerful editor with XSLT processing and debugging capabilities.

The mode currently supports two Java XSLT processors:

  • Saxon - fully supported, including debugging capabilities.
  • Xalan - fully supported, including debugging capabilities.
home page

Useful program logging.

Put first line to your log file, you must replace default-directory to dir where you build program:

-*- mode: compilation-minor; mode: auto-revert-tail; default-directory: "~/devel/proj" -*-

Program must use one of supported by compilation-minor-mode (see compilation-error-regexp-alist), like:

printf(__FILE__ ":%d: %s\n", __LINE__, msg);  /* msg - user defined string */

or in second form (in this case line number included in format string, so easy searchable in debugger):

#define NUM2STR(x) STR(x)
#define STR(x) #x

printf(__FILE__ ":" NUM2STR(__LINE__) ": %s\n", msg);

Or some faster use grep-mode, but you restricted with GNU like error format:

-*- mode: grep; mode: auto-revert-tail; default-directory: "~/devel/proj" -*-

Edit HTML.


Get main development sources:

$ bzr init-repo --2a emacs
$ cd emacs
$ bzr branch http://bzr.savannah.gnu.org/r/emacs/trunk trunk
$ cd trunk
$ bzr bind http://bzr.savannah.gnu.org/r/emacs/trunk

To update with latest changes:

$ cd emacs/trunk
$ bzr update



[patch] fix bat-generic-mode highlighting pattern for CLI switch.

How report bug.

Visit http://debbugs.gnu.org or M-x report-emacs-bug.

Finding emacs packages.

Emacs Lisp Package Archive


ELPA goal is to make it simple to install, use, and upgrade Emacs Lisp packages.

Currently (2011-02-15) available such sources:

(setq package-archives '(("ELPA" . "http://tromey.com/elpa/")
                         ("gnu" . "http://elpa.gnu.org/packages/")
                         ("marmalade" . "http://marmalade-repo.org/packages/")
official GNU Emacs Lisp Package Archive
old Emacs Lisp Package Archive home page
how to contribute

Funny Emacs modes.

Minor mode for making identifiers likeThis readable.

Useful commands.

flush-lines keep-lines
C-x C-o
C-x l
locate-library find-library
features load-history