title: How can I require an optional Perl module if installed?
body: <p>I have Perl code which relies on <code>Term::ReadKey</code> to get the terminal width. My installation is missing this module, so I want to provide a default if the module isn't present rather than throw an exception.</p>
  <p>How can I conditionally use an optional module, without knowing ahead of time whether it is available.</p>
  <pre><code># but only if the module is installed and exists
  use Term::ReadKey;
  ...
  </code></pre>
  <p>How can I accomplish this?</p>