title: get variables substituted when I cat a file
body: <p>Is it possible, in a clean way to get the variable values when I cat a file, instead of the variable names, as written in the file. It's hard to explain, but here goes a simple example:</p>
  
  <pre><code>$ cat &lt;&lt;EOF
  $HOME
  EOF
  /home/myself
  </code></pre>
  
  <p>cat returns /home/myself because it is already expanded by the shell.</p>
  
  <pre><code>$ echo \$HOME &gt;/tmp/home
  $ cat /tmp/home
  $HOME
  </code></pre>
  
  <p>cat simply reads the file, I want $HOME to be expanded here somehow by cat, because the file will contain variable names (not like HOME=/home/myself)</p>
  
  <p>My question is if this is possible somehow, otherwise I will have to write some dirty code.</p>
  
  <p>EDIT: they are big xml files containing</p>
  
  <pre><code>&lt;checkbox active="$value"&gt;
  </code></pre>
  
  <p>true or false</p>