Hook to change the site URL

I am working on a WP system that is supposed to be served by multiple domains. For example, foo.example.com and elpmaxe.com point to the same installation. But depending on the URL, the system will conditionally serve a different landing page.

The question is, how do I make the site_url() just return the current URL, NOT the URL value from the database.

Answers:

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Method 1

You can filter site_url using a filter – called site_url

The hook has the following signature:

apply_filters( 'site_url', string $url, string $path, string|null $scheme, int|null $blog_id )

You can use it like this:

add_filter( 'site_url', 'wpse_381006_custom_site_url', 10, 1 );

function wpse_381006_custom_site_url( $url ){
    if( is_admin() ) // you probably don't want this in admin side
        return $url;

    // for example, return the request_uri - but this is not a complete solution, you would need to work out what you return and in what conditions..
    return $_SERVER['REQUEST_URI'];

}

Reference: https://developer.wordpress.org/reference/hooks/site_url/

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