Remove first 3 characters and last 1 character from all mp3 files in all subdirectory

In base directory i have folders like this:

1
2
3
4
5
10
110

so in each of them i have files like

  0010011.mp3  0010031.mp3  0010051.mp3  0010071.mp3  0010021.mp3  0010041.mp3  0010061.mp3

so i want to remove first 3 characters and last 1 character so files will look like this

 001.mp3   003.mp3   005.mp3   007.mp3   002.mp3   004.mp3  006.mp3

i tried this

for file in ??????*; do echo mv $file `echo $file | cut -c4-`; done

also this is not working in subdirectories it is just if files are in base directory

Answer

You may use this while loop:

cd /base/dir

while IFS= read -rd '' file; do
   echo mv "$file" "$(sed -E 's~(.*/).{3}(.+)..~12.~' <<< "$file")"
done < <(find . -type f -print0)

Once you’re satisfied with the results, remove echo before mv command.