Here is another script `getmp3.sh` that you can use to download .mp3 file from any youtube music video:

   #!/usr/bin/env bash
   echo "Downloading mp3 from $1"
   yt-dlp -x --audio-format mp3 "$1"

You'll need to install https://github.com/yt-dlp/yt-dlp#installation before you can use that. As you can see, the "script" is just so to add a options `-x` (extract audio) and `--audio-format mp3` to convert to mp3 in the end.