$ ls [0-9][0-9][0-9][0-9]1004 1005 1006 1009 1010 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026
$ ls [0-9]{4}ls: cannot access [0-9]{4}: No such file or directory