I use the code to detect HDD or USB. Hope this solution will helpfull.
hard_disks=`lsblk --nodeps -no name,type,tran | grep "disk" | grep -v "usb" | grep -Eo '^[^ ]+'`count_disk=`echo $hard_disks |grep -o '' | wc -l`if [ $count_disk -ne 0 ]; then hard_disks=`lsblk --nodeps -no name,type,tran | grep "disk" | grep -v "usb" | grep -Eo '^[^ ]+' | sed ':a;N;$!ba;s/\n/,/g'`fiusb=`lsblk --nodeps -no name,type,tran | grep "usb" | grep -Eo '^[^ ]+'`