Save processes in cache and save at once in a text file - php

Question

I use the following code to get the size of the files in a folder. As you can see, to save the size of a file in a text file, you have to open and close the text file from the hard drive each time. I want to first store all the information in cache (RAM) and then at once in a text file. Do you think this will speed things up? Do you have an idea and code to do this?
<?php
$dir = 'img/';
foreach (glob($dir."*.png") as $filename) {
$filesize = 'File Size: '.round((filesize($filename)/1024/1024),2).' MB';
echo $filesize."</br>";
fwrite(fopen("result.txt", "a"), $filesize."\n");
fclose("result.txt");
}
?>

Answer 1

<?php
$dir = 'img/';
$result='';
foreach (glob($dir."*.png") as $filename)
{
$filesize = 'File Size: '.round((filesize($filename)/1024/1024),2).' MB';
echo $filesize."</br>";
$result.=$filesize."\n";
}
fwrite(fopen("result.txt", "a"), $result."\n");
fclose("result.txt");
?>
This way you saving all content to $result and write content to file once after all sizes checked.