title: BASH script usage/help convention
body: <p>What is the convention for showing the usage of a bash script ?
  Below is the help output for my script</p>
  
  <pre><code>Usage: my_script [options] [PORT]
  
  Options:
      --help      print help and exit
      --version   print version and exit
  </code></pre>
  
  <p>Am i right in thinking that [ ] means optional </p>
  
  <p>How do I signify an optional argument and a mandatory argument ? </p>