Как подружить if else с командой sha256sum

function hammerhead-M4B30Z {
	local M4B30Z="hammerhead-m4b30z-factory-625c027b.zip"

	if [ ! -e "${M4B30Z}" ]; then
		show_info 'Download Factory Images...'
		wget https://dl.google.com/dl/android/aosp/hammerhead-m4b30z-factory-625c027b.zip || exit 1
	fi

	# Check sha256
	# sha256sum -c ... || exit 1
	
	# Extract
	show_info 'Extraction Factory Images...'
	unzip hammerhead-m4b30z*.zip

	# Install
	show_info 'Install Factory Images...'
	cd hammerhead-m4b30z
	./flash-all.sh

	# Timeout
	sleep 5

	# Back
	cd -

	# Cleanup and finish
	rm -rf hammerhead-m4b30z*

	# Done
	show_success 'Done.'
	whiptail --title "Finished" --msgbox "Installation complete." 8 78
	images
}

625c027b21afe6de7c3d0de66e3a42000269dd00c2ef9a5347007734537f3ea2

touch SHA256SUM
echo "625c027b21afe6de7c3d0de66e3a42000269dd00c2ef9a5347007734537f3ea2 *hammerhead-m4b30z-factory-625c027b.zip" >> SHA256SUM
sha256sum -c SHA256SUM || exit 1

echo "625c027b21afe6de7c3d0de66e3a42000269dd00c2ef9a5347007734537f3ea2 hammerhead-m4b30z-factory-625c027b.zip" | sha256sum -c

...

fatal() {
 xc=$1 ; shift ; echo $@ 1>&2 ; exit $xc
}

checksum() {
 test "$1" = 625c027b21afe6de7c3d0de66e3a42000269dd00c2ef9a5347007734537f3ea2
}

...

    M4B30ZU="https://dl.google.com/dl/android/aosp/hammerhead-m4b30z-factory-625c027b.zip"
    M4B30Z="${M4B30ZU##*/}"

...

    wget "$M4B30ZU"
fi

checksum $( sha256sum "$M4B30Z" ) || fatal 29 File checksum failed

...