title: test for an argument being a 5 digit integer
body: <p>I want to test whether or not an argument in my <code>bash</code> script is a 5 digit integer.</p>
  
  <pre><code>if [ "$1" == [0-9][0-9][0-9][0-9][0-9] ]; then
      echo "first arg is 5 digits"
  else
      echo "not 5 digits"
  </code></pre>
  
  <p>This does not work for me, is there an easier way to do this i.e. using the <code>expr</code> function?</p>