Novice question - capitalise function return Options

[will.birch]

Hi guys/gals

Really novice to this but trying my best.

All I want to do is capitalise the return of the function to then be replaced in the wordpress shortcode.
What am I missing here!

CODE

// Page Title Shortcode - page_title
function page_title_sc( ){
    return get_the_title();
}
$titleupper = strtoupper('page_title_sc');
add_shortcode( 'page_title', $titleupper );