gistfile1.txt

# Gets a list of files and/or directories to build a SHA-256 from their contents.
# Returns the SHA-256 hash if succeeded, otherwise an empty string.
sha256sum_from_files() {
	local files_in=${@:-}
	local files=""
	local shasum=""

	# Process the input files:
	#  - discard the files/directories that don't exist.
	#  - find the files if it is a directory
	for f in $files_in; do
		if [ -d "$f" ]; then
			files+=" $(find $f -type f)"
		elif [ -f "$f" ]; then
			files+=" $f"
		fi
	done
	# Return in case there is none input files.
	[ -n "$files" ] || return 0

	# Alphabetically sorting the files.
	files="$(echo $files | tr ' ' '\n' | LC_ALL=C sort -u)"
	# Concate the files and calculate a hash.
	shasum="$(cat $files | sha256sum -b)" || true
	if [ -n "$shasum" ];then
		# Return only the SHA field.
		echo $(awk '{ print $1 }' <<< $shasum)
	fi
}