PHP readfile() how to handle return value - php

Question

I'm learning PHP so this is the question for education purposes. Since I can't find an answer in tutorials I use, would be nice from you to make it clear for me.
So, imagine we have a file "text.txt" and content is:
"Hello World!"
The following PHP script:
<?php
echo readfile("text.txt");
?>
Will output "Hello World!12" - I can't think of any cases when such an output can be useful, but I found that if I don't want to see the file length at the end, I've to omit "echo":
<?php
readfile("text.txt");
?>
The output will be "Hello World!". This is a way better, but manual says: "Returns the number of bytes read from the file.", so my question is - How am I supposed to get the file length using the readfile() function? According to my logic it "returns" the file content but I feel like I didn't get something right. Please help me to figure this out.

Answer 1

So you want to read the size of a file using readfile()? Sure, but this function also outputs the file. No biggie, we have something we can use in this situation: output buffering.
<?php
ob_start();
$length = readfile("text.txt");
// the content of the file isn't lost as well, and you can manipulate it
$content = ob_get_clean();
echo $length;
?>

Answer 2

readfile is not used to get file size or file content the way you write. It is typically used to send a file to the client. For example, suppose that you have created a pdf file in your web application after the client submit a form or clicked some link. Sometimes you can direct them to the file directly, but sometimes you dont want that for some reasons(security etc.). This way you can do this:
How it is ment to be used.
$filepath = "../files/test.pdf";
header("Content-Description: File Transfer");
header("Content-Type: application/pdf; charset=UTF-8");
header("Content-Disposition: inline; filename='test.pdf'");
header("Content-Transfer-Encoding: binary");
header("Content-Length: " . filesize($filepath));
readfile($filepath);
exit;
An example for which you may use it.
$filepath = "../files/test.pdf";
ob_start();
$filesize = readfile($filepath);
$content = ob_get_clean();
header("Content-Description: File Transfer");
header("Content-Type: application/pdf; charset=UTF-8");
header("Content-Disposition: inline; filename='test.pdf'");
header("Content-Transfer-Encoding: binary");
header("Content-Length: " . $filesize );
echo $content;
exit;
So, here you output the file content in addition to the correct headers so that the browser will identify it as a pdf file and open it.