php continuously writes strings to a file

php Continuously writes a string in a file

php /*Continuously writes a string in the header of the file hello.txt Write a line of "hello world" string, the code is required to be complete*/

The PHP code is as follows:

<?php

//fopen，指定文件位置和模式，hello.txt指的就是当前目录下的hello.txt文件，如果在当前目录下的test文件夹下,就应该是test/hello.text,&#39;r&#39;指的是用只读的方式打开，指针（光标）放在文件头，
$fp=fopen(&#39;hello.txt&#39;,&#39;r&#39;);
//定义要写入的字符串,"\n"是换行的意思，如果没有换行,可以吧"\n"替换成"\r\n";
$str=&#39;hello!&#39;."\n";
//filesize(&#39;hello.txt&#39;)，获得次文件的大小字节，那么这一行的意思是读取hello.txt的内容，
//$str.=fread($fp,filesize(&#39;hello.txt&#39;)); 和$str = $str.fread($fp,filesize(&#39;hello.txt&#39;));是等同的
$str.=fread($fp,filesize(&#39;hello.txt&#39;));
//关闭$fp句柄，就是把内存占用和句柄释放掉
fclose($fp);
//不解释
$fp1=fopen(&#39;hello.txt&#39;,&#39;w&#39;);
//用fwrite向hello.txt写入$str，结束是我建议再次调用fclose，避免内存占用
fwrite($fp1,$str);
?>

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