title: Regex in KornShell
body: <p>I am trying to check whether a variable is exactly two numbers but I can not seem to figure it out.</p>
  
  <p>How do you do check regular expressions (regex) in KornShell (ksh)?</p>
  
  <p>I have tried:</p>
  
  <pre><code>if [[ $month =~ "[0-9]{2}" ]]
  if [[ $month = _[0-9]{2}_ ]]
  </code></pre>
  
  <p>I have not been able to find any docs on it.</p>
  
  <p>Any insight?</p>