Output Control WP Shortcode

ocwps.php

<?php
add_shortcode( 'list-posts', 'smoney_list_posts' );

function smoney_list_posts($atts, $content = null) {
  extract( shortcode_atts( array(
				'numb' => 5,
					), $atts ) );

	if ( !is_page() ) {
		$out = 'This shortcode can only be used on a page';
		return $out;
	}

	$cats = get_the_category();
	$query_cats = array( );

	// fire output buffering to write cleaner code
	ob_start();

	// construct the query parameter for each category the page belongs to
	foreach ( $cats as $cat ) {
		$query_cats[] = $cat->term_id;
	}

	$args = array(
		'category__in' => $query_cats,
	);

	// run the query given the parameters
	$related_posts = new WP_Query( $args );
	?>	
	<?php if ( $related_posts->have_posts() ): ?>
		<h3> Related Posts</h3>
		<ul>
			<?php while ( $related_posts->have_posts() ): $related_posts->the_post(); ?>
				<li><a href="<?php the_permalink(); ?>"><?php the_title(); ?> </a></li>
			<?php endwhile; ?>
		</ul>
	<?php endif; ?>
	<?php
	// reset the query
	wp_reset_postdata();

	// get the ob contents
	$out = ob_get_contents();

	ob_end_clean();

	return do_shortcode( $out );
}