rm fades.txt
rm files.txt
rm mix.sh

ITER=0
NEXT=1
for i in `ls -v *.wav`
do
echo "[0$ITER][$NEXT]acrossfade=ns=5:o=1:c1=tri:c2=tri[0$NEXT];" >> fades.txt
printf '\-i %s ' $i >> files.txt
ITER=$(expr $ITER + 1)
NEXT=$(expr $NEXT + 1)
done

printf "ffmpeg " >> mix.sh
cat files.txt >> mix.sh
printf " -filter_complex \"" >> mix.sh
cat fades.txt >> mix.sh
echo '\" out.wav' >> mix.sh