Add a metabox displaying a shortcode with the current posts ID

metabox-shortcode.php

function shortcode_output() {
    global $post;

   // Get the data
   $id = $post->ID;

   // Echo out the field
   echo '<input type="text" name="_id" value="[elab_gallery id=' . $id . ']" class="widefat" readonly />';
  }

 function ve_custom_meta_boxes() {
    add_meta_box('corporate_gallery_id', 'GALLERY SHORTCODE<br><small>This shortcode is unique to this gallery.</small>', 'shortcode_output', 'post', 'side', 'high');
   }
   add_action('add_meta_boxes', 've_custom_meta_boxes');