title: How to use heroku's ephemeral filesystem
body: <p>I'm using Python/Django on Heroku (Cedar Stack) and I've got a management command that I need to write that will pull a file out of an S3 bucket and process it.  I'm not sure I understand how to use the ephemeral filesystem.  Are there only certain directories that are writeable?  I found an other article that implied that there were only certain folders that were writable (but, it doesn't seem to apply to the Cedar stack).  I found this dev <a href="https://devcenter.heroku.com/articles/dynos#ephemeral-filesystem" rel="noreferrer">article</a> but it doesn't go into much detail (note: I do understand that it's just temporary.  I only need to unzip the file and process the file).  Can I just create a folder anywhere under the application's root?  And how would I get that?  It seems like I could probably just use $HOME.  I did a bit of testing by connecting to via</p>
  
  <pre><code>$ heroku run bash
  </code></pre>
  
  <p>and running:</p>
  
  <pre><code>$ echo #HOME
  </code></pre>
  
  <p>returns:</p>
  
  <p>/app</p>
  
  <p>and running:</p>
  
  <pre><code>$ mkdir $HOME/tmp
  </code></pre>
  
  <p>creates a folder in the app's root and gives with the same user and group as the other files and folders.</p>
  
  <p>So...  anything I'm missing here?  A better way to do it?  Is there an OS environment variable for this?  I've run "env" and I don't see a better one.</p>