PHP rename（）函数：Literal Strings和。 变量

I'm currently trying to have my website automatically move a file from the root directory where it is created into another folder to help with organization. I'm using the PHP rename() function and I can get it to work with literal strings but when I try using the variable name I get the error

PHP Warning: rename() expects parameter 1 to be a valid path, resource given in...

My code works when I use,

$txt = "Additional Comments: ".$_POST['additionalComments']."
";
fwrite($myfile, $txt);      
fclose($myfile);
rename('Leadership_Review2.txt', 'Leadership_Review/Leadership_Review2.txt');

However, when I use

$txt = "Additional Comments: ".$_POST['additionalComments']."
";
fwrite($myfile, $txt);      
fclose($myfile);
$mydir = "Leadership_Review/";
rename($myfile, $mydir.$myfile);

I get the error mentioned above. It would be a lot more useful if I could use the variable name instead of having the literal string. Any help understanding rename or where I am going wrong would be greatly appreciated. Thanks!

PHP rename(oldpath,newpath) need full relative path of both "oldpath" and "newpath". For Example,

<?php 
$oldpath = "/public_html/images";
$newpath = "/public_html/pictures";

rename($oldpath,$newpath);
?>

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