title: Subtract two variables in unix
body: <p>This is my script which I am running on UNIX(AIX):</p>
  
  <pre><code>$MON date +"%m"
  echo 'expr $MON - 2'
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>04
  expr $MON - 2
  </code></pre>
  
  <p>I just want to subtract 2 from my current month and display .</p>