title: How to calculate variable in Upstart script and use it?
body: <p>Is where any way to achieve this?</p>
  
  <p>Some details:</p>
  
  <p>I am trying to create log file for gunicorn with datetime in name.</p>
  
  <p>Something like that, but it isn't works properly:</p>
  
  <pre><code>chdir /home/mypath
  script
     log_file=./err_$(date +"%d_%m_%Y_%T").log
     exec gunicorn --error-logfile $log_file
  end script
  </code></pre>
  
  <p>This approach fails too:</p>
  
  <pre><code>exec gunicorn --error-logfile ./err_$(date +"%d_%m_%Y_%T").log
  </code></pre>