title: Difference between single dash and double dash in argparse
body: <p>Does anyone know what is the main difference between specifying an argparse agument with a single dash <code>-r</code> and a double dash <code>--r</code>?</p>
  
  <p>I came across <a href="http://argparsejl.readthedocs.org/en/latest/argparse.html#the-parse-args-function" rel="noreferrer">this</a> Julia language argparse which classifies them as short and long but doesn't say exactly why you would use one over the other.</p>