title: homebrew/core is a shallow clone in Fish shell
body: <p>I tried to install something using <code>brew install</code> and this thing pops up</p>
  
  <pre><code>Warning: homebrew/core is shallow clone. To get complete history run:
    git -C "$(brew --repo homebrew/core)" fetch --unshallow
  </code></pre>
  
  <p>and when I copied that thing to make it run, this happens</p>
  
  <pre><code>fish: $(...) is not supported. In fish, please use '(brew)'.
  git -C "$(brew --repo homebrew/core)" fetch --unshallow
          ^
  </code></pre>
  
  <p>What does it means and how can I fix these things? Is there's a workaround to ignore or fix?</p>
  
  <p>Additional information about my workstation:</p>
  
  <ul>
  <li>MacOS Mojave</li>
  <li>Homebrew version 2.0.2</li>
  <li>Does run <code>brew doctor</code> and it shows up as no problem</li>
  <li>Using Fish shell (of course I do)</li>
  </ul>
  
  <hr>
  
  <p><strong>Update 1 :</strong>
  It looks like I am an idiot leaving the <code>$</code> there. 
  I did try to fix it with you guys suggestions, and this what happened.</p>
  
  <p>Removing the <code>$</code> from the command, like so</p>
  
  <pre><code>git -C "(brew --repo homebrew/core)" fetch --unshallow
  </code></pre>
  
  <p>and this happens</p>
  
  <pre><code>fatal: cannot change to '(brew --repo homebrew/core)': No such file or directory
  </code></pre>
  
  <hr>
  
  <p><strong>Update 2 :</strong>
  Also, @VonC asked me did <code>brew --repo homebrew/core</code> path exists by asking me to run these following line</p>
  
  <pre><code>brew --repo homebrew/core
  </code></pre>
  
  <p>and it comes up as this</p>
  
  <pre><code>/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core
  </code></pre>
  
  <p>which indicates that the repository path is still valid and ready to use</p>