WPYoda

If you can write and run some PHP code then…

<?php

$copyFrom = '/public_html/.../oldTheme/file.php';
$copyTo = '/public_html/.../newTheme/file.php';

if(!copy($copyFrom, $copyTo)){
    echo 'copy failed';
}

?>

You didn’t write a PHP class, but if you had, this is how you’d access it.

<?php

// This is a PHP class.
class myClass
{
    public $variable1 = 1;

    public function sayHi(){
        return 'hi';
    }

}

// This is how you create an instance your class.
$object = new myClass;

// This is how you call a function inside of your class.
echo $object->sayHi();

?>