#!/bin/bash

BACKUP_DIR=bkup; export BACKUP_DIR
REZIP_DIR=done; export REZIP_DIR

for file in *.zip
do
 # backup_dir exists
 if [ -e $BACKUP_DIR ]
 then
   cp "$file" $BACKUP_DIR
 fi
 unzip -j "$file"
 rm -f "$file"
 zip -mq "$file" *.mp3 *.cdg *.MP3 *.CDG *.Mp3 *.Cdg
 rm -f *.mp3 *.cdg *.MP3 *.CDG *.Mp3 *.Cdg
 mv "$file" $REZIP_DIR
done