title: How to use SED without a file with an env var?
body: <p>Is it possible to substitute a thing in env var with SED?</p>
  
  <pre><code>$ a='aoeua'
  $ sed 's@a@o@g' &lt;$a
  bash: aoeua: No such file or directory
  $ env|grep "SHELL"
  SHELL=/bin/bash
  </code></pre>
  
  <p>The output I want is</p>
  
  <pre><code>ooeuo
  </code></pre>
  
  <p>replacing each <code>a</code> in <code>'aoeua'</code> with <code>o</code>.</p>