title: How to execute Perl qx function with variable
body: <p>How do I get Perl's <code>qx</code> function to execute with my <code>$opt</code> variable?</p>
  
  <p>Before (works):</p>
  
  <pre><code>my @df_output = qx (df -k /tmp);
  </code></pre>
  
  <p>I want to use either <code>-k</code>, <code>-g</code>, or <code>-H</code>:</p>
  
  <pre><code>my @df_output = qx (df -$opt /tmp);
  </code></pre>