EXTRA_BACKUP_OPTS with variables not works.

[terryzwt]

I want backup drupal database and ignore cache_* tables to reduce the backup size.
I'm using EXTRA_BACKUP_OPTS for add extra --ingore-tables with variable $db, but it does not works. The backup SQL file still including the cache_* tables.

If I'm using --ignore-table=dsf.watchdog without ${db} variable, it works.
I have also tried DB_NAME variable, but still not works.
Here are 2 issues:

1. How I can do this with dynamic db name?
2. I want to dump only the data structure append to the backup SQL,How to do this? I'm tring the pre/post scripts but looks can't do this. Here is the example scripts FYI.

special_tables=$(mysql -h $DB_HOST -P$DB_PORT -u$DB_USER -p$DB_PASS -N -e "SELECT GROUP_CONCAT(table_name SEPARATOR ' ') FROM information_schema.tables WHERE table_schema='$DB_NAME' AND (table_name LIKE 'cache%'  OR table_name = 'watchdog') AND table_type = 'BASE TABLE'")
mysqldump --single-transaction -h $DB_HOST -P$DB_PORT -u$DB_USER -p$DB_PASS $DB_NAME --no-data $special_tables >> $FILE_NAME

Here it the example docker-compose.yml

services:
  db-backup-v4-mariadb:
    image: tiredofit/db-backup:4.1.9
    container_name: db-backup-v4-mariadb
    restart: always
    volumes:
     - ./backups:/backup
    environment:
     - MODE=MANUAL
     - MANUAL_RUN_FOREVER=FALSE
     - CONTAINER_ENABLE_SCHEDULING=FALSE
     - DEFAULT_FILESYSTEM_PATH=/backup
     - DEFAULT_MYSQL_CLIENT=mariadb
     - DEBUG_MODE=TRUE
     - DEFAULT_LOG_LEVEL=debug
     - EXTRA_BACKUP_OPTS=--ignore-table=$${db}.cache_advagg --ignore-table=$${db}.cache_bootstrap --ignore-table=$${db}.cache_config --ignore-table=$${db}.cache_container --ignore-table=$${db}.cache_data --ignore-table=$${db}.cache_default --ignore-table=$${db}.cache_discovery --ignore-table=$${db}.cache_dynamic_page_cache --ignore-table=$${db}.cache_entity --ignore-table=$${db}.cache_file_mdm --ignore-table=$${db}.cache_jsonapi_normalizations --ignore-table=$${db}.cache_menu --ignore-table=$${db}.cache_page --ignore-table=$${db}.cache_render --ignore-table=$${db}.cache_rest --ignore-table=$${db}.cache_schema_metatag_cache --ignore-table=$${db}.cache_toolbar --ignore-table=$${db}.cachetags  --ignore-table=dsf.watchdog
     - DB_TYPE=mysql
     - DB_HOST=mariadb
     - DB_USER=root
     - DB_PASS=password
     - ROTATE_OPTIONS=--daily=7 --weekly=4 --monthly=3 --prefer-recent
     - DB_DUMP_BY_SCHEMA=true
     #- SINGLE_DATABASE=true
     #- RUN_ONCE=true
     #- DB_DUMP_CRON="20, 2, * * *"
     - DB_NAME=dsf
     - DB_NAMES_EXCLUDE="information_schema performance_schema sys mysql"
     - DB_DUMP_FREQ=1440
     - DB_DUMP_BEGIN=1308
     - DB_DUMP_DEBUG=true