title: Math expression in IF clause with Linux shell
body: <p>I want to use math expression in IF clause - something like this: </p>
  
  <pre><code>         #!/bin/sh
  
           now=`date +%H%M`
  
           if [ $now % 5 -gt 0 ] ; then
             exit
           fi
  
           perl ...
  </code></pre>
  
  <p>What is a correct <strong>syntax</strong> for that?</p>