Remove all non-alphanumeric characters using preg_replace

How can I remove all non alphanumeric characters from a string in PHP?

This is the code, that I'm currently using:

$url = preg_replace('/\s+/', '', $string);

It only replaces blank spaces.

$url = preg_replace('/[^\da-z]/i', '', $string);

At first take this is how I'd do it

$str = 'qwerty!@#$@#$^@#$Hello%#$';

$outcome = preg_replace("/[^a-zA-Z0-9]/", "", $str);

var_dump($outcome);
//string(11) "qwertyHello"

Hope this helps!

Not sure why no-one else has suggested this, but this seems to be the simplest regex:

preg_replace("/\W|_/", "", $string)

You can see it in action here, too: http://phpfiddle.org/lite/code/0sg-314

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