Detect whether a directory tree has changed (in bash, without diff)

does_command_change_files.sh

# hash_the_dir ()
#   Hash all the files in the given directory to produce one checksum.
#   (Useful for checking for any file's contents or name being changed.)
#   Parameter: directory
#   Output: md5sum of the names and contents of all the files, recursively.
hash_the_dir() {
	# The options below are to make the archive deterministic:
	# i.e. same files, same hash; not affected by metadata (like timestamps),
	# nor by any changes to the git repo, if present (like commits).
	local error="Error calling hash_the_dir"
	[ ${#} -eq 0 ] && {
		echo "$error: no arguments passed. Expected a directory." >&2
		return 1
	}
	[ -d "$1" ] || {
		echo "$error: '$1' is not a directory!" >&2
		return 1
	}
	tar --sort=name \
		--format=posix \
		--mtime='@0' \
		--owner=0 --group=0 --numeric-owner \
		--pax-option=delete=atime,delete=ctime \
		--exclude=.git \
		-cf - "$1" | md5sum | sed 's/  -$//'
}

# changes_files ()
#   Takes a command as an argument, executes it, and sees whether any
#   files in the current working directory are changed.
#   Parameter: command to execute
#   Exit value:
#     0 if any file under the cwd is changed/moved/added/deleted
#     1 if all the files are the same.
#   Depends on: hash_the_dir ()
changes_files() {
	local -r command="$*"
	local hash1
	local hash2

	hash1="$(hash_the_dir ".")" # snapshot before running command
	(
		# shellcheck disable=SC1090 # because can't static-check a variable command!
		. <(echo "$command")
	)
	hash2="$(hash_the_dir ".")" # snapshot after running command

	# if [[ "$hash1" == "$hash2" ]]; then
	if [ "$hash1" = "$hash2" ]; then
		return 1 # hashes matched, therefore nothing changed
	else
		return 0 # something changed between the two hashes
	fi
}