Get custom posts with certain ids in a custom loop using a shortcode

If you use comma separated id’s in the shortcode like "112,93,34,91", you can make use of the explode function to make an array out of the string, like the following:

extract(shortcode_atts(array(
    'ids' => ''
), $atts));

$id_array = explode(',', $ids); 

Then you just have to use 'post__in' => $id_array