Store file checksum in the extended attribute

csumattr.sh

#!/usr/bin/bash
#
# Set/check SHA256 file checksum stored in the file's extended attributes
#

csum_attr="user.sha256sum"
check_path="."
action=""

usage() {
	printf \
"Usage:
$0 -a|-c|-p|-r|-h  path

 -a   Add checksums to the files that do not have them yet
 -c   Compare the stored checksum with the SHA256 hash of the file
 -p   Print the stored SHA256 checksums
 -r   Remove the extended attribute from the files
 -h   Print this help

The SHA256 checksums are stored in the user.sha256sum extended file attribute.
If <path> is a directory it is traversed recursively.\n" >&2
}

check_file() {
	filename="$1"

	sum=$(getfattr --only-values -n $csum_attr "$filename" 2>/dev/null)
	if [[ $? == 0 ]]; then
		echo "$sum  $filename" | sha256sum -c 2>/dev/null
		if [[ $? != 0 ]]; then
			printf "$filename: Checksum mismatch\n" >&2
			err=3 # worst case of all: replace errorcode with 3
		fi
	else
		printf "$filename: Checksum attribute not found\n" >&2
		err=${err:-1} # prevent overwriting err
	fi
}

add_checksum() {
	filename="$1"

	getfattr -n $csum_attr "$filename"
	if [[ $? == 0 ]]; then
		printf "$filename: Checksum attribute found: Skipping\n" >&2
	else
		setfattr -n $csum_attr -v $(sha256sum "$filename" | cut -f 1 -n) "$filename"
	fi
}

remove_checksum() {
	filename="$1"

	printf "Removing sum from \'$filename\'\n"
	setfattr -x $csum_attr "$filename"
}

print_checksum() {
	filename="$1"

	sum=$(getfattr --only-values -n $csum_attr "$filename")
	if [[ $? == 0 ]]; then
		printf "$sum  $filename\n"
	fi
}

process_file() {
	filename="$1"
	
	case $action in
		"add")
			add_checksum "$filename"
			;;
		"check")
			check_file "$filename"
			;;
		"remove")
			remove_checksum "$filename"
			;;
		"print")
			print_checksum "$filename"
			;;
	esac

	return ${err:-0}
}

# main
while getopts "acvhdp" opt; do
	case $opt in
		a)
			action="add"
			;;
		c)
			action="check"
			;;
		d)
			action="remove"
			;;
		p)
			action="print"
			;;
		h)
			usage
			exit 0
			;;
		*)
			usage
			exit 1
			;;
	esac
done

if [[ -z $action ]]; then
	printf "The -a or -c option must be specified.\n\n" >&2
	usage
	exit 1
fi

shift $((OPTIND-1))
check_path=$1

if [[ -d $check_path ]]; then
	find $check_path -type f -print0 | while read -d $'\0' esc_file
	do
		process_file "$esc_file"
	done;
elif [[ -f $check_path ]]; then
	process_file "$check_path"
else
	printf "Error: file not found: $check_path\n" >&2
	exit 2
fi

# returns the error code from process_file