PHP program causes hard disk space usage to skyrocket

This program instantly caused the CPU and memory of my computer to skyrocket. When I saw the hard disk space used, it also increased. Now I am at a loss. I can’t find the hard disk space being used? I can't restore the previous hard disk space size. I am a beginner in PHP. I hope you can give me some advice? Help is needed! ! !

$filename="/home/wanbo/test/file/test.txt";
if(file_exists($filename))echo "the file is there.";
else echo "there isn't such a file";
$myfile=fopen($filename,"a+");
fwrite($myfile,"hello,world");
while(!feof($myfile))
{
  $mychar=fgetc( $myfile);
echo $mychar;
}
fclose($myfile);
?>

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