Get all files in folder recursively

get_recursive_files_array.php

<?php
function get_recursive_files_array( $dir, $files = null ) {

	$files_in_folder = scandir( $dir );
	$files           = ( null === $files ) ? array() : $files;

	foreach ( $files_in_folder as $file ) {
		if ( ! is_dir( $dir . $file ) ) {
			$files[] = $dir . $file;

		} elseif ( '..' !== $file && '.' !== $file ) {

			$files = get_recursive_files_array( $dir . $file . '/' );
		}
	}

	return $files;
}