Emacs

https://www.gnu.org/software/emacs

Manual: https://www.gnu.org/software/emacs/manual/html_node/emacs/index.html

Reference Cards: https://www.gnu.org/software/emacs/refcards/index.html

https://www.emacswiki.org

https://emacsrocks.com

.emacs file

You can use ~/.emacs, ~/.emacs.el, ~/.emacs.d/init.el and others.

• https://www.gnu.org/software/emacs/manual/html_node/efaq/Setting-up-a-customization-file.html
• https://stackoverflow.com/questions/19524627/where-is-my-emacs-file-on-mac-os-x
• https://www.gnu.org/software/emacs/manual/html_node/emacs/Init-File.html

Interesting comment (source):

I would recommend ~/.emacs.d/init.el, though, because that makes it easier to keep the whole Emacs configuration under version control.

Undo

C-x u

https://www.emacswiki.org/emacs/UndoCommands

Show line and column numbers

Go to your init file and add (setq column-number-mode t). From https://www.gnu.org/software/emacs/manual/html_node/efaq/Displaying-the-current-line-or-column.html

Note that this works on version >= 26.

• https://emacs.stackexchange.com/questions/278/how-do-i-display-line-numbers-in-emacs-not-in-the-mode-line
• https://www.emacswiki.org/emacs/LineNumbers