Thanks, Graham. So here's what Peter (and I) need to do, assuming that
you moved the LilyPond app off your desktop and into the Applications
folder:
1) Open a new terminal window.
2) Type:
nano
3) In the program that opens, type <Ctrl>R. Type
.profile
and hit <Enter>.
You'll probably get a message: ".profile" not found, which is fine. If
that's what happened, skip to step (6)
4) Look in the file that loaded and see if it has a line that begins:
export PATH=
If it doesn't, then go on to step (6).
5) Move the cursor to the end of line that begins:
export PATH=
and add this to the end of it:
:/Applications/LilyPond.app/Contents/Resources/bin
Make sure to hit <Return> at the end of that line, and make sure not
to add any spaces before the colon, which has to be there. My line
looks like this:
export PATH=/opt/local/bin:/opt/local/sbin:/Applications/
LilyPond.app/Contents/Resources/bin
(It's all on one line, with a space between export and PATH, like
this: "export PATH"
Upper and lower case makes a difference!
Now skip to step (7)
6) Type:
export PATH=$PATH:/Applications/LilyPond.app/Contents/Resources/bin
7) Type <Ctrl>O (that's a letter o, not a numeral 0). When it prompts
with "File to save", type:
.profile
and hit <Enter>. If it asks if it's OK to overwrite, you should be
able to say "Yes" safely if you followed the instructions above. Note
that I am NOT responsible if, instead of doing anything useful, your
computer does something catastrophic, or just quits working the way
you want it to. It shouldn't happen, but I make no guarantees.
8) Type <Ctrl>X, which closes the editor.
9) Type:
exit
and hit <Enter>
10) Close the terminal window.
11) Open a new terminal window and see if lilypond-book works now.