Setups

This is what finally worked for me. Thanks to Orm Finnendahl:

Install emacs: http://emacsformacosx.com

Install LilyPond:

http://www.lilypond.org/index.de.html

For absolute beginners: open your terminal. Go to /Applications/Utilities/Terminal.app




Lilypond emacs-Setup OS X

At first add LilyPond to your PATH:
Open Terminal

sudo touch ~/.bash_profile

Open .bash-profile in your favorite editor and fill in:
export PATH="/Applications/LilyPond.app/Contents/Resources/bin:$PATH"

Save

control with echo $PATH

Now you can start LilyPond by typing "lilypond" in your terminal.

CD to /Applications/LilyPond.app/Contents/Resources/share/emacs/site-lisp

Type:

sudo ln -s /Applications/LilyPond.app/Contents/Resources/share/emacs/site-lisp /Applications/Emacs.app/Contents/Resources/site-lisp

Now we have to edit lilypond-mode.el. Right click on the LilyPond.app. Show packages: navigate to Applications/LilyPond.app/Contents/Resources/share/emacs/site-lisp

Open lilypond-mode.el in emacs
type M-g-g
Go to line 335 and change (defcustom LilyPond-lilypond-command
change to
(defcustom LilyPond-lilypond-command "/Applications/LilyPond.app/Contents/Resources/bin/lilypond"
"Command used to compile LY files."
:group 'LilyPond
:type 'string)

We want to use our Preview.App for PS-Files, so change the above lines, too.

(defcustom LilyPond-ps-command " /Applications/Preview.app/Contents/MacOS/Preview --watch"
"Command used to display PS files."

:group 'LilyPond
:type 'string)

The same is with our standard PDF-Viewer, we choose Safari for URL-Handling.

(defcustom LilyPond-pdf-command "/Applications/Safari.app/Contents/MacOS/Safari“
"Command used to display PDF files."

:group 'LilyPond
:type 'string)

/* not yet working as expected

Change MIDI

(defcustom LilyPond-midi-command "open"
"Command used to play MIDI files."

Change MIDI-Player to Logic Pro X.



(defcustom LilyPond-all-midi-command "/Applications/Logic\ Pro\ X.app/Contents/MacOS/Logic\ Pro\ X -ia"
"Command used to play MIDI files."

:group 'LilyPond
:type 'string) */

save with M-x-s

on a Mac now type alt-shift-:

type
(find-file user-init-file)

standard lilypond.mode-config-suggestions do not use .ily-files, so I modified them too. Copy and Paste the following to your .emacs

in emacs type C-y

(setq load-path (append (list (expand-file-name"/Applications/LilyPond.app/Contents/Resources/share/emacs/site-lisp")) load-path))
(autoload 'LilyPond-mode "lilypond-mode" "LilyPond Editing Mode" t)
(add-to-list 'auto-mode-alist '("\\.ly$" . LilyPond-mode))
(add-to-list 'auto-mode-alist '("\\.ily$" . LilyPond-mode))
(add-to-list 'auto-mode-alist '("\\.lytex$" . LilyPond-mode))
(add-hook 'LilyPond-mode-hook (lambda () (turn-on-font-lock)))

(setq locale-coding-system 'utf-8)
(set-terminal-coding-system 'utf-8)
(set-keyboard-coding-system 'utf-8)
(set-selection-coding-system 'utf-8)
(prefer-coding-system 'utf-8)

restart emacs

You are done

Open a LilyPond-file in emacs and you'll see!