title: Replace a text with a variable
body: <p>How can I do this?</p>
  
  <pre><code>sed -i 's/wiki_host/$host_name/g' /root/bin/sync
  </code></pre>
  
  <p>It will replace <code>wiki_host</code> with the text <code>$host_name</code>.
  But I want to replace it with the content of the variable..</p>
  
  <p>I tried it with</p>
  
  <pre><code>sed -i 's/wiki_host/${host_name}/g' /root/bin/sync
  </code></pre>
  
  <p>It doesn't work either.</p>