Convert hyphen to underscore in permalinks

Question

I would like to use underscore in my permalinks instead of hyphen.

Current permalink:

www.example.com/2013/01/hello-this-is-a-test-post/

Desired permalink

www.example.com/2013/01/hello_this_is_a_test_post/

I have tried some solutions mentioned here in stacexchange. But they were not working.

Answer 1

Toscho advised me like this.

Google treats - as word separator, but not _. You will hurt yourself. :)

He was 100% true. Here is an article that explains it. So I dropped the idea.

But if you still looking for a solution here is the answer.

Answered by this stackoverflow user

Hunt down the following file: wp-includes/formatting.php

Jump down to the sanitize_title_with_dashes function. You'll find this section of code inside:

$title = strtolower($title);
$title = preg_replace('/&.+?;/', '', $title); // kill entities
$title = str_replace('.', '-', $title);
$title = preg_replace('/[^%a-z0-9 _-]/', '', $title);
$title = preg_replace('/\s+/', '-', $title);
$title = preg_replace('|-+|', '-', $title);
$title = trim($title, '-');

Swap out all of the dashes/hyphens (-) for underscores (_) like so:

$title = strtolower($title);
$title = preg_replace('/&.+?;/', '', $title); // kill entities
$title = str_replace('.', '_', $title);
$title = preg_replace('/[^%a-z0-9 _-]/', '', $title);
$title = preg_replace('/\s+/', '_', $title);
$title = preg_replace('|-+|', '_', $title);
$title = trim($title, '_');

Note that any posts you've created before this change, and rely on the %postname% permalink structure tag, will be broken.

In that case you'll need to go back and republish those post so the dashes are swapped out for the underscores. Or just write yourself a little SQL to replace them.