Editing Byte order mark (section)

== How to see Byte order mark ==
=== MySQL way ===
Using [https://www.w3resource.com/mysql/string-functions/mysql-hex-function.php MySQL HEX() function] "returns a string representation of a hexadecimal value of a decimal or string value specified as an argument." 


[http://sqlfiddle.com/#!9/5b46b0/1/0 Run sql on sqlfiddle.com] or Download the [https://drive.google.com/file/d/1TSjaK0q7f-ypxP-S_5SX18TlNvUW4yRJ/view?usp=sharing Sql file] directly.
<pre>
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`;
</pre>

<table border="1" class="wikitable" >
<tr>
<th>HEX(id)</th>
<th>id</th>
<th>notes</th>
</tr>

<tr>
<td>31323334353637383930</td>
<td>1234567890</td>
<td>UTF-8 without BOM</td>
</tr>
<tr>

<tr>
<td>EFBBBF31323334353637383930</td>
<td>1234567890</td>
<td>UTF-8 with BOM</td>
</tr>
<tr>

</table>


If the column {{kbd | key=`id`}} was only allowed integer in column value, you can use the following sql query to find the records contains BOM:
<pre>
SELECT * 
FROM `articles`
WHERE HEX(`id`) REGEXP '[^0-9]+'
</pre>

=== PHP way ===
PHP code<ref>[https://stackoverflow.com/questions/14674834/php-convert-string-to-hex-and-hex-to-string PHP convert string to hex and hex to string - Stack Overflow]</ref><ref>[https://www.w3schools.com/php/func_misc_unpack.asp PHP unpack() Function]</ref><ref>[https://stackoverflow.com/questions/10290849/how-to-remove-multiple-utf-8-bom-sequences-before-doctype php - How to remove multiple UTF-8 BOM sequences before "<!DOCTYPE>"? - Stack Overflow]</ref>:
<pre>

$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);
}

</pre>

Result:
<pre>
1234567890 NOT contains BOM --> after str2hex: 31323334353637383930
1234567890 contains BOM  --> after str2hex: efbbbf31323334353637383930
</pre>

=== Excel / Google sheet way ===
Using the [https://support.office.com/en-us/article/code-function-c32b692b-2ed0-4a04-bdd9-75640144b928 CODE function] to check the "numeric code for the first character in a text string". If the cell {{kbd | key=A1}} contains BOM, 
* {{kbd | key=<nowiki>=CODE(A1)</nowiki>}} returns {{kbd | key=63}} on Excel 2016 of {{Win}}<ref>[http://www.asciitable.com/ Ascii Table - ASCII character codes and html, octal, hex and decimal chart conversion]</ref>
* {{kbd | key=<nowiki>=CODE(A1)</nowiki>}} returns {{kbd | key=95}} on Excel 2016 of {{Mac}}
* {{kbd | key=<nowiki>=CODE(A1)</nowiki>}} returns {{kbd | key=65279}} or other numeric value e.g. {{kbd | key=28201}} on Google sheet

=== BASH command ===
Check if a UTF-8 encoded file contains a BOM. The first line result of {{kbd | key=hexdump}} mentioning ef bb bf indicates it contains a BOM

<pre>
% hexdump -n 3 -C filename

00000000  ef bb bf                                          |...|
00000003
</pre>

=== File command ===
Using [https://en.wikipedia.org/wiki/File_(command) file (command)]: {{kbd | key=<nowiki>file filename.txt</nowiki>}} on {{Linux}}, {{Mac}}<ref>[https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man1/file.1.html file(1) Mac OS X Manual Page]</ref> & Cygwin on {{Win}}. See details on [[Text file encoding]]

=== Hex editor ===
Using Hext editor to open the text file. [https://zh.wikipedia.org/wiki/%E4%BD%8D%E5%85%83%E7%B5%84%E9%A0%86%E5%BA%8F%E8%A8%98%E8%99%9F 位元組順序記號 - 維基百科，自由的百科全書]