WordPress Shortcode Output Buffer

gistfile1.txt

/**
 * Sample Shortcode
 * @since 1.0.0
 *
 * @param	null
 * @return	string	Site URL
 */
function jb_sample_shortcode( $atts ) {
	ob_start(); ?>
	<!-- hello world -->
	<?php $output_string = ob_get_contents();
	ob_end_clean();
	return $output_string;

	return $output;
}
add_shortcode( 'sample_shortcode','jb_sample_shortcode' );