Byte order mark

Byte order mark (BOM, 位元組順序記號)

How to see Byte order mark

MySQL way

Using MySQL HEX() function "returns a string representation of a hexadecimal value of a decimal or string value specified as an argument."

Sql file

CREATE TABLE `articles` (
  `id` varchar(50) NOT NULL,
  `notes` text NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO `articles` (`id`, `notes`) VALUES
('1234567890', 'no BOM'),
('1234567890', 'BOM');

ALTER TABLE `articles`
  ADD UNIQUE KEY `id` (`id`) USING BTREE;

SELECT HEX(id), id, notes FROM articles;

HEX(id)	id	notes
31323334353637383930	1234567890	no BOM
EFBBBF31323334353637383930	1234567890	BOM

File command way

Using file (command): file filename.txt on Linux , macOS & Cygwin on Win

File content	Example result returned by file command
File contains BOM	UTF-8 Unicode (with BOM) text
File NOT contains BOM	UTF-8 Unicode text