Replace directory in the middle of a filepath string

Question

$string = 'http://example.com/category/1/news/2134/'; // '1' is dynamic

How can I change 1 to any number I want?

Can't call parts of the string, its just a text-like variable.

It can be done with some true regex.

Answer 1

$string = preg_replace('~(?<=category/)[0-9]+(?=/news)~', '56', $string);

This replaces the number by 56.

This approach uses a regex with assertions.

Answer 2

$array = explode('/',$string);
$array[4] = '666';
$string = implode('/',$array);

[edit] @People downvoting, what seems to be the problem with this approach?