diff -ur v4/bk.py v5/bk.py
--- v4/bk.py	2018-06-07 09:50:49.000000000 +0900
+++ v5/bk.py	2018-06-17 22:46:22.000000000 +0900
@@ -13,9 +13,21 @@
 
 exists = lambda path: os.path.exists(path)
 
+def qt(s):
+	q1 = "'"
+	q2 = '"'
+	has1 = q1 in s
+	has2 = q2 in s
+	if has1 and has2:
+		# danger ...
+		s = s.replace(q2, q1+q1)
+	if has1:
+		return '"{}"'.format(s)
+	return "'{}'".format(s)
+
 def mkdir_if_not(path):
 	if not exists(path):
-		exec_cmd( "mkdir -p '{}'".format(path) )
+		exec_cmd( "mkdir -p {}".format( qt(path) ) )
 
 def yaml_load(fname, def_val):
 	v = def_val
@@ -40,7 +52,7 @@
 def add_db_if_not(db, path):
 	if path in db:
 		return
-	s = exec_cmd( "find '{}' -type f -or -type l".format(path) )
+	s = exec_cmd( "find {} -type f -or -type l".format( qt(path) ) )
 	s = s.decode()
 	if not s:
 		return
@@ -77,7 +89,7 @@
 	return (lst, rm_lst)
 
 def get_disk_free(path):
-	s = exec_cmd( "df -k '{}'".format(path) )
+	s = exec_cmd( "df -k {}".format( qt(path) ) )
 	s = s.decode()
 	lst = s.strip().split('\n')
 	lst = list( map( lambda s: s.split(), lst ) )
@@ -92,16 +104,16 @@
 		i += 1
 	return str(v) + ( ut[i-1] if i > 0 else '' )
 
-rm = lambda p, d: exec_cmd( "rm -f '{}'".format( os.path.join(d, p) ) )
+rm = lambda p, d: exec_cmd( "rm -f {}".format( qt( os.path.join(d, p) ) ) )
 
-tar_cp = lambda p, s, d: exec_cmd( "tar cf - -C '{}' '{}' | tar xf - -C '{}'".format(s, p, d) )
+tar_cp = lambda p, s, d: exec_cmd( "tar cf - -C {} {} | tar xf - -C {}".format( qt(s), qt(p), qt(d) ) )
 
 def cp(p, s, d):
 	(dn, fn) = os.path.split(p)
 	d_dn = os.path.join(d, dn)
 	mkdir_if_not(d_dn)
 	s_p = os.path.join(s, p)
-	exec_cmd( "cp -p '{}' '{}'".format(s_p, d_dn) )
+	exec_cmd( "cp -p {} {}".format( qt(s_p), qt(d_dn) ) )
 
 def backup(db, s, d, lst, rm_lst):
 	db_s = db.get(s, {})