How to automatically detect and write to usb with variable spaces in its name

To get the right USB and it's path:

• noticed that the first USB plugged into my system is mounted on the /dev/sdb1 filesystem and the second is mounted on the /dev/sdc1 filesystem. I added a section to switch to /dev/sdc1 if udevadm info -q all -n "/dev/sdb" | grep "ID_BUS=usb" returned true.

• if diff between df --output=target | grep "/media/darren" before and after has "/media/darren" in it, that's presumably the new USB. USB is mounted.

• if udevadm info -q all -n "/dev/sdb" | grep "ID_BUS=usb is true then that device mounted on "/dev/sdb" is a usb device

• to get the path, and make sure I was grabbing the right one: df --output=source,avail,target | grep "$FILESYSTEM" | grep "$MOUNTPOINT" and some really nice awk

  udevadm info -q all -n "$FILESYSTEM" | grep "ID_BUS=usb" > $RESULT
  USB_ADDR="$BACKUP_DIR"/usb_addr.txt
  if grep "ID_BUS=usb" "$RESULT" ; then
      df --output=source,avail,target | grep "$FILESYSTEM" | grep "$MOUNTPOINT" > "$USB_ADDR"
      awk -i inplace '{$0=gensub(/s*S+/,"",1)}1' "$USB_ADDR"
      awk -i inplace '{$0=gensub(/s*S+/,"",1)}1' "$USB_ADDR"
      sed -i 's/^ *//' "$USB_ADDR"
  

Unfortunately diffing fails if other stuff is added or removed. But, at least it fails nicely if it grabs the wrong device when using the df filtered output and grepping for the filesystem and mountpoint.

Tried awk 'NR!=1{print $NF}' <(df)|sort. Still not great on bash expansions.

#!/bin/bash

if [ "$UID" -eq 0 ] ; then
        echo "Don't run this as root"
        exit 50
fi

#Create a backup file with the date as title in a backup directory
BACKUP_DIR="$HOME/backup"
DATE_OF_COPY=$(date --rfc-3339=date)
BACKUP_FILE="$BACKUP_DIR/$DATE_OF_COPY"

[ -d "$BACKUP_DIR" ] || mkdir -m 700 "$BACKUP_DIR"

#find all files recursively in $HOME directory
find -P $HOME >> "$BACKUP_FILE"

#use lzma to compress
xz -zk --format=auto --check=sha256 --threads=0 "$BACKUP_FILE"

#making files to use in operations of before and after usb is inserted info and diff between them
#this is part of how we will insure that we are writing to the correct device
BEFORE="$BACKUP_DIR"/before_usb.txt
AFTER="$BACKUP_DIR"/after_usb.txt
DIFFERENCE="$BACKUP_DIR"/difference.txt
#MOUNTPOINT=where computer mounts USBs by default
MOUNTPOINT="/media/darren"
FILESYSTEM="/dev/sdb"
RESULT="$BACKUP_DIR"/result.txt


#if there is something on the mountpoint before we plug in the usb, we want to know
#so the new device is written to
udevadm info -q all -n "$FILESYSTEM" | grep "ID_BUS=usb" > $RESULT
if grep "ID_BUS=usb" "$RESULT" ; then
        FILESYSTEM="/dev/sdc"
        echo $FILESYSTEM
fi        

df --output=target | grep $MOUNTPOINT > "$BEFORE"

read -p 'Enter USB or hard drive and press any button' ok

df --output=target | grep $MOUNTPOINT > "$AFTER"
#dif them to find the new one
diff "$BEFORE" "$AFTER" > "$DIFFERENCE"

# Look in mountpoint in the difference between the before and after df outputs
SEARCH_FOR_MOUNT=$(grep "$MOUNTPOINT" "$DIFFERENCE")

until [ "$SEARCH_FOR_MOUNT" ] ;
do
        df --output=target | grep $MOUNTPOINT > "$AFTER"
        diff "$BEFORE" "$AFTER" > "$DIFFERENCE"
        SEARCH_FOR_MOUNT=$(grep "$MOUNTPOINT" "$DIFFERENCE")

done
#check if new device plugged into filesystem is a USB
udevadm info -q all -n "$FILESYSTEM" | grep "ID_BUS=usb" > $RESULT
USB_ADDR="$BACKUP_DIR"/usb_addr.txt
if grep "ID_BUS=usb" "$RESULT" ; then
        df --output=source,avail,target | grep "$FILESYSTEM" | grep "$MOUNTPOINT" > "$USB_ADDR"
        awk -i inplace '{$0=gensub(/s*S+/,"",1)}1' "$USB_ADDR"
        awk -i inplace '{$0=gensub(/s*S+/,"",1)}1' "$USB_ADDR"
        sed -i 's/^ *//' "$USB_ADDR"

        if [ ! -s $USB_ADDR ] ; then
              echo "Error finding USB Address"
              exit 100


        ADDR=$(cat "$USB_ADDR")
        cp "$BACKUP_FILE.xz" "$ADDR"
        rm "$BACKUP_FILE" "$USB_ADDR" "$RESULT" "$BEFORE" "$AFTER" "$DIFFERENCE"

else
        echo "Device is not a USB"
        exit 52
fi

exit $?