(somewhat OT:) lilypond calling bash script questions

[Urs Liska]

Please excuse if I post a linux question here, but I'd prefer not to 
have to find a dedicated forum and subscribe there first ...

I have a project with more than two dozens of lilypond scores. For 
several reasons I have them in individual files which I can't \include 
in a master file.
I would like to write a script that allows me to compile all .ly files 
in one run.
For this I need the following which I didn't find through Google:
How can I sequentially cd to all subdirectories that start with a number?
What I want is to do

cd 01_01_...
lilypond *.ly
cd ..
cd 01_02_...
..

in a form like

for dir in [get me all directories starting with a number]
do
cd $dir
lilypond *.ly
cd ..
done

This _has_ to be absolutely simple, but I didn't manage do find out how 
so far.

Many thanks for any assistance.
Urs