title: Fish equivalent of bash $(command) notation
body: <p>I am currently trying out the fish shell instead of using bash. One type of notation I'm having trouble learning the fish-equivalent notation for is <code>$(command)</code>, similar to how it is described in <a href="https://stackoverflow.com/questions/4708549/shell-programming-whats-the-difference-between-command-and-command">this SOF post</a>. How do I write this using fish? Keep in mind that I could use backslash characters around the command I want to evaluate, but the linked post and other posts discourage this because it is an old style of evaluating commands.</p>
  
  <p>Specifically, this is the bash command I want to convert to fish syntax (for initializing <em>rbenv</em> during startup of the shell):</p>
  
  <pre><code>eval "$(rbenv init -)"
  </code></pre>