URL Slugs in PHP (with UTF-8 and Transliteration Support)

url_slug.php

<?php
/**
 * Create a web friendly URL slug from a string.
 * 
 * Although supported, transliteration is discouraged because
 *     1) most web browsers support UTF-8 characters in URLs
 *     2) transliteration causes a loss of information
 *
 * @author Sean Murphy <[email protected]>
 * @copyright Copyright 2012 Sean Murphy. All rights reserved.
 * @license http://creativecommons.org/publicdomain/zero/1.0/
 *
 * @param string $str
 * @param array $options
 * @return string
 */
function url_slug($str, $options = array()) {
	// Make sure string is in UTF-8 and strip invalid UTF-8 characters
	$str = mb_convert_encoding((string)$str, 'UTF-8', mb_list_encodings());
	
	$defaults = array(
		'delimiter' => '-',
		'limit' => null,
		'lowercase' => true,
		'replacements' => array(),
		'transliterate' => false,
	);
	
	// Merge options
	$options = array_merge($defaults, $options);
	
	$char_map = array(
		// Latin
		'À' => 'A', 'Á' => 'A', 'Â' => 'A', 'Ã' => 'A', 'Ä' => 'A', 'Å' => 'A', 'Æ' => 'AE', 'Ç' => 'C', 
		'È' => 'E', 'É' => 'E', 'Ê' => 'E', 'Ë' => 'E', 'Ì' => 'I', 'Í' => 'I', 'Î' => 'I', 'Ï' => 'I', 
		'Ð' => 'D', 'Ñ' => 'N', 'Ò' => 'O', 'Ó' => 'O', 'Ô' => 'O', 'Õ' => 'O', 'Ö' => 'O', 'Ő' => 'O', 
		'Ø' => 'O', 'Ù' => 'U', 'Ú' => 'U', 'Û' => 'U', 'Ü' => 'U', 'Ű' => 'U', 'Ý' => 'Y', 'Þ' => 'TH', 
		'ß' => 'ss', 
		'à' => 'a', 'á' => 'a', 'â' => 'a', 'ã' => 'a', 'ä' => 'a', 'å' => 'a', 'æ' => 'ae', 'ç' => 'c', 
		'è' => 'e', 'é' => 'e', 'ê' => 'e', 'ë' => 'e', 'ì' => 'i', 'í' => 'i', 'î' => 'i', 'ï' => 'i', 
		'ð' => 'd', 'ñ' => 'n', 'ò' => 'o', 'ó' => 'o', 'ô' => 'o', 'õ' => 'o', 'ö' => 'o', 'ő' => 'o', 
		'ø' => 'o', 'ù' => 'u', 'ú' => 'u', 'û' => 'u', 'ü' => 'u', 'ű' => 'u', 'ý' => 'y', 'þ' => 'th', 
		'ÿ' => 'y',

		// Latin symbols
		'©' => '(c)',

		// Greek
		'Α' => 'A', 'Β' => 'B', 'Γ' => 'G', 'Δ' => 'D', 'Ε' => 'E', 'Ζ' => 'Z', 'Η' => 'H', 'Θ' => '8',
		'Ι' => 'I', 'Κ' => 'K', 'Λ' => 'L', 'Μ' => 'M', 'Ν' => 'N', 'Ξ' => '3', 'Ο' => 'O', 'Π' => 'P',
		'Ρ' => 'R', 'Σ' => 'S', 'Τ' => 'T', 'Υ' => 'Y', 'Φ' => 'F', 'Χ' => 'X', 'Ψ' => 'PS', 'Ω' => 'W',
		'Ά' => 'A', 'Έ' => 'E', 'Ί' => 'I', 'Ό' => 'O', 'Ύ' => 'Y', 'Ή' => 'H', 'Ώ' => 'W', 'Ϊ' => 'I',
		'Ϋ' => 'Y',
		'α' => 'a', 'β' => 'b', 'γ' => 'g', 'δ' => 'd', 'ε' => 'e', 'ζ' => 'z', 'η' => 'h', 'θ' => '8',
		'ι' => 'i', 'κ' => 'k', 'λ' => 'l', 'μ' => 'm', 'ν' => 'n', 'ξ' => '3', 'ο' => 'o', 'π' => 'p',
		'ρ' => 'r', 'σ' => 's', 'τ' => 't', 'υ' => 'y', 'φ' => 'f', 'χ' => 'x', 'ψ' => 'ps', 'ω' => 'w',
		'ά' => 'a', 'έ' => 'e', 'ί' => 'i', 'ό' => 'o', 'ύ' => 'y', 'ή' => 'h', 'ώ' => 'w', 'ς' => 's',
		'ϊ' => 'i', 'ΰ' => 'y', 'ϋ' => 'y', 'ΐ' => 'i',

		// Turkish
		'Ş' => 'S', 'İ' => 'I', 'Ç' => 'C', 'Ü' => 'U', 'Ö' => 'O', 'Ğ' => 'G',
		'ş' => 's', 'ı' => 'i', 'ç' => 'c', 'ü' => 'u', 'ö' => 'o', 'ğ' => 'g', 

		// Russian
		'А' => 'A', 'Б' => 'B', 'В' => 'V', 'Г' => 'G', 'Д' => 'D', 'Е' => 'E', 'Ё' => 'Yo', 'Ж' => 'Zh',
		'З' => 'Z', 'И' => 'I', 'Й' => 'J', 'К' => 'K', 'Л' => 'L', 'М' => 'M', 'Н' => 'N', 'О' => 'O',
		'П' => 'P', 'Р' => 'R', 'С' => 'S', 'Т' => 'T', 'У' => 'U', 'Ф' => 'F', 'Х' => 'H', 'Ц' => 'C',
		'Ч' => 'Ch', 'Ш' => 'Sh', 'Щ' => 'Sh', 'Ъ' => '', 'Ы' => 'Y', 'Ь' => '', 'Э' => 'E', 'Ю' => 'Yu',
		'Я' => 'Ya',
		'а' => 'a', 'б' => 'b', 'в' => 'v', 'г' => 'g', 'д' => 'd', 'е' => 'e', 'ё' => 'yo', 'ж' => 'zh',
		'з' => 'z', 'и' => 'i', 'й' => 'j', 'к' => 'k', 'л' => 'l', 'м' => 'm', 'н' => 'n', 'о' => 'o',
		'п' => 'p', 'р' => 'r', 'с' => 's', 'т' => 't', 'у' => 'u', 'ф' => 'f', 'х' => 'h', 'ц' => 'c',
		'ч' => 'ch', 'ш' => 'sh', 'щ' => 'sh', 'ъ' => '', 'ы' => 'y', 'ь' => '', 'э' => 'e', 'ю' => 'yu',
		'я' => 'ya',

		// Ukrainian
		'Є' => 'Ye', 'І' => 'I', 'Ї' => 'Yi', 'Ґ' => 'G',
		'є' => 'ye', 'і' => 'i', 'ї' => 'yi', 'ґ' => 'g',

		// Czech
		'Č' => 'C', 'Ď' => 'D', 'Ě' => 'E', 'Ň' => 'N', 'Ř' => 'R', 'Š' => 'S', 'Ť' => 'T', 'Ů' => 'U', 
		'Ž' => 'Z', 
		'č' => 'c', 'ď' => 'd', 'ě' => 'e', 'ň' => 'n', 'ř' => 'r', 'š' => 's', 'ť' => 't', 'ů' => 'u',
		'ž' => 'z', 

		// Polish
		'Ą' => 'A', 'Ć' => 'C', 'Ę' => 'e', 'Ł' => 'L', 'Ń' => 'N', 'Ó' => 'o', 'Ś' => 'S', 'Ź' => 'Z', 
		'Ż' => 'Z', 
		'ą' => 'a', 'ć' => 'c', 'ę' => 'e', 'ł' => 'l', 'ń' => 'n', 'ó' => 'o', 'ś' => 's', 'ź' => 'z',
		'ż' => 'z',

		// Latvian
		'Ā' => 'A', 'Č' => 'C', 'Ē' => 'E', 'Ģ' => 'G', 'Ī' => 'i', 'Ķ' => 'k', 'Ļ' => 'L', 'Ņ' => 'N', 
		'Š' => 'S', 'Ū' => 'u', 'Ž' => 'Z',
		'ā' => 'a', 'č' => 'c', 'ē' => 'e', 'ģ' => 'g', 'ī' => 'i', 'ķ' => 'k', 'ļ' => 'l', 'ņ' => 'n',
		'š' => 's', 'ū' => 'u', 'ž' => 'z'
	);
	
	// Make custom replacements
	$str = preg_replace(array_keys($options['replacements']), $options['replacements'], $str);
	
	// Transliterate characters to ASCII
	if ($options['transliterate']) {
		$str = str_replace(array_keys($char_map), $char_map, $str);
	}
	
	// Replace non-alphanumeric characters with our delimiter
	$str = preg_replace('/[^\p{L}\p{Nd}]+/u', $options['delimiter'], $str);
	
	// Remove duplicate delimiters
	$str = preg_replace('/(' . preg_quote($options['delimiter'], '/') . '){2,}/', '$1', $str);
	
	// Truncate slug to max. characters
	$str = mb_substr($str, 0, ($options['limit'] ? $options['limit'] : mb_strlen($str, 'UTF-8')), 'UTF-8');
	
	// Remove delimiter from ends
	$str = trim($str, $options['delimiter']);
	
	return $options['lowercase'] ? mb_strtolower($str, 'UTF-8') : $str;
}
?>

url_slug_demo.php

<?php
include('url_slug.php');
header('Content-type: text/plain; charset=utf-8');

// Basic usage
echo "This is an example string. Nothing fancy." . "\n";
echo url_slug("This is an example string. Nothing fancy.") . "\n\n";

// Example using French with unwanted characters ('?)
echo "Qu'en est-il français? Ça marche alors?" . "\n";
echo url_slug("Qu'en est-il français? Ça marche alors?") . "\n\n";

// Example using transliteration
echo "Что делать, если я не хочу, UTF-8?" . "\n";
echo url_slug("Что делать, если я не хочу, UTF-8?", array('transliterate' => true)) . "\n\n";

// Example using transliteration on an unsupported language
echo "מה אם אני לא רוצה UTF-8 תווים?" . "\n";
echo url_slug("מה אם אני לא רוצה UTF-8 תווים?", array('transliterate' => true)) . "\n\n";

// Some other options
echo "This is an Example String. What's Going to Happen to Me?" . "\n";
echo url_slug(
	"This is an Example String. What's Going to Happen to Me?", 
	array(
		'delimiter' => '_',
		'limit' => 40,
		'lowercase' => false,
		'replacements' => array(
			'/\b(an)\b/i' => 'a',
			'/\b(example)\b/i' => 'Test'
		)
	)
);

/*
Output:

This is an example string. Nothing fancy.
this-is-an-example-string-nothing-fancy

Qu'en est-il français? Ça marche alors?
qu-en-est-il-français-ça-marche-alors

Что делать, если я не хочу, UTF-8?
chto-delat-esli-ya-ne-hochu-utf-8

מה אם אני לא רוצה UTF-8 תווים?
מה-אם-אני-לא-רוצה-utf-8-תווים

This is an Example String. What's Going to Happen to Me?
This_is_a_Test_String_What_s_Going_to_Ha
*/
?>

Cool, I like how it keeps most UTF-8 characters so it works internationally. I want to remind everyone reading this that UTF-8 characters aren't allowed in HTTP message headers (Body is fine of course), which includes the HTTP method and DOCUMENT PATH line. So, when sending an HTTP message with a URL path that contains non-ASCII special UTF-8 characters, or when doing a Location: redirect header, please be sure to properly URL encode the data.

Example:

GET /cookbook/recipes/Что-делать.html HTTP/1.1
Host: www.rebol.net
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:88.0) Gecko/20100101 Firefox/88.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: https://www.google.com/

That looks like a typical GET request. What's wrong? The GET line includes non-ASCII characters: Что-делать.html. The correct Request should be:

GET /cookbook/recipes/%D0%A7%D1%82%D0%BE-%D0%B4%D0%B5%D0%BB%D0%B0%D1%82%D1%8C.html HTTP/1.1
Host: www.rebol.net
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:88.0) Gecko/20100101 Firefox/88.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: https://www.google.com/

Though in general, I would recommend only using plain ASCII in URLs for maximum compatibility, but sometimes it cannot be avoided.

For HTTP responses, be sure to also use plain ASCII only:

HTTP/1.1 301 Moved Permanently
Server: nginx
Date: Tue, 18 May 2021 22:52:47 GMT
Content-Type: text/html
Content-Length: 162
Connection: keep-alive
Location: https://www.tumblr.com/%D0%A7%D1%82%D0%BE-%D0%B4%D0%B5%D0%BB%D0%B0%D1%82%D1%8C.html
 
<html>
<head><title>301 Moved Permanently</title></head>
<body>
<center><h1>301 Moved Permanently</h1></center>
<hr><center>nginx</center>
</body>
</html>

Notice the Location: header on the Response does not include any UTF-8 characters.

Some browsers and systems will fudge it and allow this, but others will be strict and deny accepting the Request or Response.

I was using this but noticed it does not work for all inputs.

Example:

$str = "Ruka";

function url_slug($str, $options = array()) {

 $str = mb_convert_encoding((string)$str, 'UTF-8', mb_list_encodings());
return $str;

}

Returns empty str

Looks like it breaks in PHP 8.1 and above.

https://3v4l.org/ckLNs#v8.1.0

For PHP 8.1 and above, you need to change line 19 to
$str = mb_convert_encoding((string)$str, 'UTF-8');