$s='afdafd jjk   ddl';
echo preg_replace('/\s+/',',',$s);

------解决方案--------------------

	$str = preg_replace('#[\r\n]+#','<br>',$str);
	$str = preg_replace('#\s+#',',',$str);

------解决方案--------------------
echo preg_replace('/\s/i', '', file_get_contents('http://www.a744.com/text.txt'));