laravel4 CSV帮助路由

I have a button and when I click that button the data should be opened in csv format

 public function get_textfile() {

            $table = Campaign::all();
                $file = fopen('file.csv', 'w');
                foreach ($table as $row) {
                    fputcsv($file, $row);
                }
                fclose($file);


            header("Content-type: text/csv");  
            header("Cache-Control: no-store, no-cache");  
            header('Content-Disposition: attachment;   filename="campaign.csv"');
            header("Expires: 0");




               // return Redirect::to('');

            }

the above code is there in my controller ...

my button is in view (i have problem in routing how to route ?)

<a href= {{ URL::to('?????' ); }} "" class="btn btn-large btn-success">Export CSV file</a>

Can anyone please do explain the process ?

{{URL::action('YourController@get_txtfile')}}

That should work I believe.