Append overlapping intro and outro audio to another audio file with sox and ffmpeg

intro-outro.sh

#!/bin/bash

IFS=$'\n'

IntroLen=9
OutroLen=12
OverlapLen=8

IntroSilenceLen=3
OutroSilenceLen=10

sox -n -r 44100 -c 1 IntroSilence.wav trim 0.0 $IntroSilenceLen
sox -n -r 44100 -c 1 OutroSilence.wav trim 0.0 $OutroSilenceLen


for FILE in *.mp3;
do
  
  echo $FILE
  ffmpeg -y -i $FILE -f ffmetadata metadata.txt
  FILEWAV=x${FILE%.mp3}.wav
  ffmpeg -y -i $FILE ${FILEWAV}
  CurrentAudioLength=`ffprobe -i $FILEWAV -show_entries format=duration -v quiet -of csv="p=0"` 
  echo "Current audio is $CurrentAudioLength seconds"
  SilenceTrackLen="$((${CurrentAudioLength%.*} - ${OverlapLen%.*}))"
  echo "Silence Track of $SilenceTrackLen seconds"
  sox -n -r 44100 -c 1 SilenceTrack.wav trim 0.0 $SilenceTrackLen
  echo 'Making Tracks'  
  sox IntroSilence.wav $FILEWAV OutroSilence.wav TrackA.wav
  sox intro.wav SilenceTrack.wav outro.wav TrackB.wav
  echo 'Merging'  
  ffmpeg -y -i TrackA.wav -i TrackB.wav -f ffmetadata -i metadata.txt -c copy -map_metadata 2 -filter_complex amerge -ac 1 -c:a libmp3lame -q:a 2 _${FILE}
  
done