php怎么post换行

<?php
$str=$_POST['name1'].'-'.$_POST['phone1'].'-'.$_POST['address'].'-'.$_POST['express'];
echo $str."<br>";
$fp=fopen("b.txt","a+");
fwrite($fp,$str);//写入
fclose($fp);//关闭
?>

$str=$_POST['name1'].'-'.$_POST['phone1'].'-'.$_POST['address'].'-'.$_POST['express']."
";