copy can be used to copy a file in PHP.

PHP is typically being run as the apache or www-data user, thus the apache or www-data user will need to have permission to copy the file. exec can be used to run the whoami command to determine if PHP is being run as apache or www-data.

<?php
  echo exec('whoami');
?>

And getcwd will return your present working directory.

<?php
  echo getcwd();
?>

For example, let's say you want to make a copy of the /var/www/html/foo.php file on a Linux system. In this example, the www-data user has rwx (read, write, execute) permissions to the foo.php, so the www-data user should be able to make a copy of the the foo.php file. The apache or www-data user will also need to have permission to the directory where the new file will reside.

~]$ ls -ld /var/www/html
drwxr-xr-x. 2 www-data  www-data  6 Feb  5 07:59 /var/www/html

Here is how you would make a copy of /var/www/html/foo.php.

copy("/var/www/html/foo.php", "/var/www/html/bar.php");

It's probably also a good idea to use the file_exists function to first ensure the file exists.

$current_file = ""/var/www/html/foo.php";
$new_file = "/var/www/html/bar.php";

if (!file_exists($current_file)) {
  if (!copy($current_file, $new_file)) {
    echo "failed to copy $current_file to $new_file <br />";
  }
}