OpenWrt flash script that only preserves ssh key

flash.sh

#!/usr/bin/env bash

usage() {
        echo "Usage: $0 -f <file> <hostname>"
        exit 1
}

file=""

while getopts "f:h" opt; do
        case ${opt} in
        f)
                file=${OPTARG}
                ;;
        h)
                usage
                ;;
        *)
                usage
                ;;
        esac
done

shift $((OPTIND - 1))

# Get the hostname from the remaining arguments
if [ $# -lt 1 ]; then
        echo "Error: Hostname argument is required."
        usage
fi
hostname=$1

if [ -z "$file" ]; then
        echo "Error: -f flag requires a file argument."
        usage
fi

filebase=$(basename "${file}")

script=$(cat <<ENDSSH
#!/usr/bin/env sh
TMPFILE="\$(mktemp -u)"

echo -e "\e[31mBacking up SSH keys...\$TMPFILE\e[0m"
tar cvzf "\$TMPFILE" /etc/dropbear/*

echo -e "\e[31mBacked up to \$TMPFILE\e[0m"

SHASUM="\$(sha256sum /tmp/${filebase} | cut -d " " -f 1 )"
echo -e "\n\e[31msha256sum for ${filebase} is \$SHASUM. \e[0m"


read -rp "Do you want to proceed? (y/n): " yn
if [[ "\$yn" != "y" ]]; then
  echo "Operation aborted."
  exit 1
fi

sysupgrade -f "\$TMPFILE" /tmp/${filebase}
ENDSSH
)

scp -O "$file" root@"${hostname}":/tmp

echo "$script" | ssh root@"$hostname" "cat > /tmp/upgrscript.sh && chmod +x /tmp/upgrscript.sh"
ssh -tt root@"${hostname}" "/tmp/upgrscript.sh"