function to mount and decrpyt one of the USB disks in a list

crypted_backup_usb.sh

#!/bin/bash
check_backup_disk() {
  local -a EXTERNAL_DISK_PATHS=(
    "/dev/disk/by-id/usb-SOME_EXTERNAL_USB_XXXXXXXXXXXXXXX-0:0"
    "/dev/disk/by-id/usb-SOME_External_USB_3.0_XXXXXXXXXXXXXX-0:0"
  )
  CURRENT_DISK=""

  for path in "${EXTERNAL_DISK_PATHS[@]}"; do
    if [[ -e "$path" ]]; then
      CURRENT_DISK=$(basename "$path")
      break
    fi
  done
}

mount_external_backup_disks() {  
    if [ -n "$CURRENT_DISK" ]; then
        echo "Current Disk : $CURRENT_DISK" 
        echo "Decrytp $CURRENT_DISK-part2"
        echo "Activate LVM volume_backup (root,home,swap)"
        echo "mount /dev/volume_backup/root to /mnt/backup"
        echo "mount /dev/volume_backup/home to /mnt/backup/home"
        echo "mount $CURRENT_DISK-part1 to /mnt/backup/boot"
    else
        echo "NO External Disk Present : STOPPING"
    fi
}

close_external_backup_disks() {
    if [ -n "$CURRENT_DISK" ]; then
        echo "Current Disk : $CURRENT_DISK" 
        echo "Umount everything under /mnt/backup"
        echo "Deactivate volume_backup"
        echo "Close encrypted partition"
    else
        echo "NO External Disk Present : STOPPING"
    fi
}

rsync_backup(){
if [[ -d "/mnt/backup" && -d "/mnt/backup/boot" && -d "/mnt/backup/home" && -n "$CURRENT_DISK" ]]; then
    echo "Current Disk : $CURRENT_DISK" 
    echo "sync everything BUT /boot to $CURRENT_DISK"
    echo sudo rsync -aAXHl           --delete --info=progress2 --human-readable --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*","/lost+found","/boot"} / /mnt/backup/  
    echo sudo rsync -aAXHl --inplace --delete --info=progress2 --human-readable --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*","/lost+found"} /boot/ /mnt/backup/boot
    echo "copy local backuped systemd-boot entries and fstab to backup disk"
    echo sudo cp $CURRENT_DISK/boot/loader/entries/*conf /mnt/backup/boot/loader/entries/
    echo sudo cp $CURRENT_DISK/etc/fstab /mnt/backup/etc/
else
  # Actions to perform if any path does not exist or CURRENT_DISK is empty
  if [ ! -d "/mnt/backup" ]; then
    echo "/mnt/backup does not exist."
  fi
  if [ ! -d "/mnt/backup/boot" ]; then
    echo "/mnt/backup/boot does not exist."
  fi
  if [ ! -d "/mnt/backup/home" ]; then
    echo "/mnt/backup/home does not exist."
  fi
  if [ -z "$CURRENT_DISK" ]; then
    echo "CURRENT_DISK is empty."
  fi
fi
}