Андрей

//echo '<pre>';print_r($_SERVER);echo '</pre>';
if((empty($_SERVER['DOCUMENT_URI']) || $_SERVER['DOCUMENT_URI']=='/index.php')&&
	empty($_SERVER['QUERY_STRING'])){
}else{
	echo '<button type="button" class="btn btn-link" onclick="history.back()">
	<i class="glyphicon	glyphicon-arrow-left"></i><span>Назад</span></button>';
}