PHP读取文件的第1行后删除此行数据

<?php
header(‘Content-Type: text/html; charset=utf-8’);

$fn = "1.txt";
$f= fopen($fn, "r");
$line = fgets($f);
ob_start();
fpassthru($f);
fclose($f);
file_put_contents($fn, ob_get_clean() );

echo $line;

?>