Few things I noticed in the code

One of the problem I face when using this plugin is that if the links ends with a ‘/’ at the end then wordpress redirects to 404. So I was checking the code shorten-url.php -> redirect_404() [line number 845].

I have added a fix for the backslash, let me know if its correct.
What I am doing is checking if the last element is blank then remove it from the array ‘param’.

function redirect_404() {
		global $post;
		global $wpdb;
		$table_name = $this->table_name;

		if(is_404()) {
			$param = explode("/", $_SERVER['REQUEST_URI']) ; 

			// Fixed by Ahmed, if there is a slash at the end.
			if( count( $param ) > 2 ) {
				$last_elem = array_pop( $param );
				if( $last_elem != '' )
					$param[] = $last_elem;
			}
			// End fix
			if (preg_match("/^([a-zA-Z0-9_.-])*$/",$param[count($param)-1],$matches)==1) {
				$select = "SELECT id_post FROM {$table_name} WHERE short_url='".$param[count($param)-1]."'" ;
				$temp_id = $wpdb->get_var( $select ) ;
				if (($temp_id==null)||($temp_id===false)) {
					return ;
				} else if (is_numeric($temp_id)) {
					if ($temp_id==0) {
						$select = "SELECT url_externe FROM {$table_name} WHERE short_url='".$param[count($param)-1]."'" ;
						$temp_url = $wpdb->get_var( $select ) ;
						$wpdb->query("UPDATE {$table_name} SET nb_hits = IFNULL(nb_hits, 0) + 1 WHERE short_url='".$param[count($param)-1]."'") ;
						header("HTTP/1.1 301 Moved Permanently");
						$temp_url = str_replace("&", "&", $temp_url);
						header("Location: ".$temp_url );
						exit();
					} else {
						$wpdb->query("UPDATE {$table_name} SET nb_hits = IFNULL(nb_hits, 0) + 1 WHERE id_post=".$temp_id) ;
						header("HTTP/1.1 301 Moved Permanently");
						//$temp_url = str_replace("&", "&", $temp_url); -- Why is this line added ? -Ahmed
						header("Location: ".get_permalink($temp_id));
						exit();
					}
				}
			}
		}
	}

What I am not trying to understand is this piece of code,
preg_match("/^([a-zA-Z0-9_.-])*$/",$param[count($param)-1],$matches)

When a blank is passed as the second argument, then it return 1, I think it should return FALSE.

Thanks

https://wordpress.org/plugins/shorten-url/