title: Case reading input parameters being specific letters or any number
body: <p>I'm trying to convert a bunch of if/elses in case statement, but I'm having problem to set this rules:</p>
  
  <pre><code>./overload.sh k --&gt; input valid (already done)
  ./overload.sh c --&gt; input valid (already done)
  ./overload.sh (any range of number) --&gt; input valid (dont know how to do)
  ./overload.sh (exception) --&gt; input invalid and error message (already done)
  </code></pre>
  
  <p>I don't know how to make case understand that is to accept any number as a valid option or k or c, and any other input is an exception.</p>