Byte order mark

Byte order mark (BOM, 位元組順序記號, 部分編輯器稱為「簽名」)

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."

Run sql on sqlfiddle.com or Download the Sql file directly.

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

If the column `id` was only allowed integer in column value, you can use the following sql query to find the records contains BOM:

SELECT * 
FROM `articles`
WHERE HEX(`id`) REGEXP '[^0-9]+'

PHP way

PHP code:

$string = "1234567890";
echo $string . " NOT contains BOM --> after str2hex: " . str2hex($string) . PHP_EOL;

$string = "\xEF\xBB\xBF" . "1234567890";
echo $string . " contains BOM  --> after str2hex: " . str2hex($string) . PHP_EOL;

function str2hex($string) {
	$hexstr = unpack('H*', $string);
	return array_shift($hexstr);
}

Result:

1234567890 NOT contains BOM --> after str2hex: 31323334353637383930
1234567890 contains BOM  --> after str2hex: efbbbf31323334353637383930

Excel way

Using the CODE function to check the "numeric code for the first character in a text string".

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