diff -ur v9/fsyn.py v10/fsyn.py
--- v9/fsyn.py	2020-05-05 12:24:53.000000000 +0900
+++ v10/fsyn.py	2020-05-06 14:49:02.000000000 +0900
@@ -32,6 +32,10 @@
 		cmd = 'rm -rf ' + path
 		cmd_call( cmd )
 
+def clear_dir(dir_path):
+	cmd = '( cd {} ; ls -A | xargs rm -rf )'.format( dir_path )
+	cmd_call( cmd )
+
 cut_tail_sla = lambda path: path[ : -1 ] if path[-1] == '/' else path
 
 
@@ -253,8 +257,7 @@
 		show_ids( ids, 'next' )
 
 	def ckout_org():
-		cmd = '( cd {} ; ls -A | xargs rm -rf )'.format( dir_path )
-		cmd_call( cmd )
+		clear_dir( dir_path )
 
 		targ_id = 'org'
 		fn = id_fn( targ_id, 'update.tgz' )
@@ -371,6 +374,71 @@
 					msg = k + ':\n' + to_str( lst, pre='  ' )
 					dbg.out( msg )
 
+	def curr_backup_new():
+		( DIR, BASE ) = os.path.split( dir_path )
+
+		bak_id = get_curr()
+		tmp_dir = cmd_ut.mk_tmp_dir( '/tmp/fsyn_diff_' )
+		cmd = 'tar czf {}/{} -C {} {}'.format( tmp_dir, 'bak.tgz', DIR, BASE )
+		cmd_call( cmd )
+
+		def restore():
+			clear_dir( dir_path )
+			cmd = 'tar xzf {}/{} -C {}'.format( tmp_dir, 'bak.tgz', DIR )
+			cmd_call( cmd )
+			cmd_ut.rm_rf( tmp_dir )
+			set_curr( bak_id )
+
+		return empty.new( locals() )
+
+	def ckout_force(id):
+		if id == 'now':
+			return True
+
+		id = alias_cnv( id )
+		if not path_exists( path_join( fsyn_path(), id ) ):
+			return False
+
+		curr_cmp = get_curr_cmp()
+		if not curr_cmp.same: # dirty
+			ckout_org()
+		ckout( id )
+		return True
+
+	def curr_copy(dir_, name):
+		( DIR, BASE ) = os.path.split( dir_path )
+		cmd = 'tar cf - -C {} {} | tar xf - -C {}'.format( DIR, BASE, dir_ )
+		cmd_call( cmd )
+		cmd = '( cd {} ; mv {} {} )'.format( dir_, BASE, name )
+		cmd_call( cmd )
+
+	def diff_inner(a, b, curr_backup):
+		tmp_dir = curr_backup.tmp_dir
+
+		if not ckout_force( b ):
+			return
+		curr_copy( tmp_dir, 'b' )
+
+		if not ckout_force( a ):
+			return
+		curr_copy( tmp_dir, 'a' )
+
+		cmd = '( cd {} ; diff -urN a b )'.format( tmp_dir )
+		cmd_ut.call_show( cmd )
+
+	def diff(*args):
+		a = get_curr()
+		b = 'now'
+		args = list( args )
+		if args:
+			a = args.pop( 0 )
+		if args:
+			b = args.pop( 0 )
+
+		curr_backup = curr_backup_new()
+		diff_inner( a, b, curr_backup )
+		curr_backup.restore()
+
 	def fix_link(id):
 		link = get_link( id )
 		e = empty.new()
@@ -674,6 +742,7 @@
 		arg.cmd_new( 'next', comment='show next ids' ),
 		arg.cmd_new( 'checkout', [ 'id' ], comment='alias is used instead of id' ),
 		arg.cmd_new( 'check', comment='show dirty' ),
+		arg.cmd_new( 'diff' ),
 		arg.cmd_new( 'fixlink', comment='fix link info' ),
 		arg.cmd_new( 'push', [ 'to_path' ] ),
 		arg.cmd_new( 'pull', [ 'from_path' ] ),
@@ -687,8 +756,13 @@
 	if cmd.name == 'clone':
 		clone( cmd, dir_path )
 	else:
+		add_rest = [ 'diff' ]
+
 		fsyn = fsyn_new( dir_path )
 
 		func = getattr( fsyn, cmd.name )
-		func( *cmd.args )
+		args = cmd.args
+		if cmd.name in add_rest:
+			args = args + cmd.a.get_av()
+		func( *args )
 # EOF