Converts multiple mp3 to one single mp3

MultiMP3s-to-1MP3

#!/bin/bash

for d in */ ; do
    mp3PATH=$PWD/"$d"
    OUTDIR=$(basename "${mp3PATH//\'}")

    echo $mp3PATH $OUTDIR

    if [ -d "$mp3PATH" ]; then

        for d2 in "$mp3PATH"*; do
            MIN_BITRATE=$(soxi -B "$d2"/*.mp3 | grep -o -E '[0-9]+' | sort -n | head -1)
            echo "Min bitrate: " $MIN_BITRATE

            if [ $MIN_BITRATE -lt 160 ]; then
                BITRATE=128
            elif [ $MIN_BITRATE -lt 192 ]; then
                BITRATE=160
            elif [ $MIN_BITRATE -lt 224 ]; then
                BITRATE=192
            elif [ $MIN_BITRATE -lt 256 ]; then
                BITRATE=224
            elif [ $MIN_BITRATE -lt 320 ]; then
                BITRATE=256
            else
                BITRATE=320
            fi

            # BITRATE=256 # STATICALLY DEFINED

            echo "Bitrate for sox -C: " $BITRATE

            OUTFILE=$(basename "${d2//\'}")

            OUT_DIR=/home/your-outdir/"$OUTDIR"
            [ -d "$OUT_DIR" ] || mkdir "$OUT_DIR"
            echo $OUT_DIR

            # Add files info
            echo -n > "$OUT_DIR"/"$OUTFILE"_info.txt

            for f in "$d2"/*.{mp3,Mp3,MP3,mP3}; do
                if [ -f "$f" ]; then
                    BF=$(basename "$f")
                    E=$(soxi -d "$f")
                    echo "$BF | $E" >> "$OUT_DIR"/"$OUTFILE"_info.txt
                fi

                if [ ! -f "$f".wav ]; then
                    echo "$f"
                    ffmpeg -i "$f" -ar 44100 "$f".wav >/dev/null 2>&1
                fi
            done

	    for f in "$d2"/*.flac; do
                if [ -f "$f" ]; then
                    BF=$(basename "$f")
                    E=$(soxi -d "$f")
                    echo "$BF | $E" >> "$OUT_DIR"/"$OUTFILE"_info.txt
                fi

                if [ ! -f "$f".wav ]; then
                    echo "$f"
                    ffmpeg -i "$f" "$f".wav >/dev/null 2>&1
                fi
            done

            WAV="$d2"/*.wav

            sox "$WAV" -C $BITRATE "$OUT_DIR"/"$OUTFILE"_"$BITRATE"k.mp3

            echo "Removing partial WAV files..."
            rm "$d2"/*.wav

        done

    fi
done