Whitelisting alpha-numerical characters to create friendly URL strings (slugs)

Published 4 months ago under PHP, Regular Expressions

You may have noticed the tidy URLs on this site used to link to each article. This is done by  turning each article title into a URL-friendly string, which is then used a unique key in my articles database. Many blogging systems do this as standard, but what if (like me) you prefer to build your own solutions?

What we want to do is turn this article title:
Whitelisting alpha-numerical characters to create friendly URL strings (slugs)
into a URL-friendly string:
whitelisting-alpha-numerical-characters-to-create-friendly-url-strings-slugs

And here's my function:

1: function strSEO($str) {
2:
3:    $str = preg_replace("/&#x[a-z0-9]{4};/i", "", $str);
4:    $str = html_entity_decode($str, ENT_QUOTES);
5:    $str = strtolower($str);
6:    $str = preg_replace("/[^a-z0-9\s]/i", "", $str);
7:    $str = (ereg_replace(" +", "-", trim($str));    
8:    return $str;
9:
10: };

Line 3: removes any unicode entity names.
Line 4: converts any HTML entities into their characters - for example & becomes &.
Line 5: turns string to lower-case.
Line 6: removes any character which isn't alpha-numeric or a space.
Line 7: trims the beginning and end of string, and replaces spaces with hyphens. Note that multiple consecutive spaces are only replaced with one hyphen.