#!/bin/bash
for d in ./*; do
    if [ -d "$d" ]; then
        f=${d:2}
        cd "$d"
        echo ${f}.mp3
        # find all mp3s, sort them (e.g. 100 after 99, not after 10),
        # get only filenames, handle spaces, and pass list to mp3cat
        find  . -iname "*.mp3" -exec basename {} \; | sort -h | xargs -d '\n' mp3cat -c 1 -o "${f}.mp3"
#        mp3cat -c 1 ./*.mp3 -o "${f}.mp3"
        mv "${f}.mp3" ../
        cd ..
    fi
done