Note: chgrp() is aware of the actual filesystem.
So you need to check it by using file_exists() function or...
(PHP 4, PHP 5, PHP 7)
chgrp — Changes file group
Attempts to change the group of the file filename
to group.
Only the superuser may change the group of a file arbitrarily; other users may change the group of a file to any group of which that user is a member.
filenamePath to the file.
groupA group name or number.
Returns TRUE on success or FALSE on failure.
Example #1 Changing a file's group
<?php
$filename = 'shared_file.txt';
$format = "%s's Group ID @ %s: %d\n";
printf($format, $filename, date('r'), filegroup($filename));
chgrp($filename, 8);
clearstatcache(); // do not cache filegroup() results
printf($format, $filename, date('r'), filegroup($filename));
?>
Note: This function will not work on remote files as the file to be examined must be accessible via the server's filesystem.
Note: When safe mode is enabled, PHP checks whether the files or directories being operated upon have the same UID (owner) as the script that is being executed.
Note: chgrp() is aware of the actual filesystem.
So you need to check it by using file_exists() function or...