title: How I can add variable in the node-red exec/unix command node
body: <p>I wanted to add some variable value (ex. test=test value) at the end of a file with a Unix command. For I wanted to add test value at the end of FILE_NAME.txt. So FILE_NAME.txt would contain test value </p>
  
  <pre><code>nano FILE_NAME.txt
  </code></pre>
  
  <p>will show string > 'test value' inside FILE_NAME.txt</p>
  
  <pre><code>sudo sed -i -e \$aVARIABLE(VAR_VALUE) /etc/FILE_NAME.txt
  </code></pre>
  
  <p>I tried similar with a node-red text input field node connected to the input of exec node. But didn't work.</p>
  
  <p>Any help would be appreciated. Thanks. </p>