title: Git equivalent of hg add + hg diff?
body: <p>I've recently started using git after having gotten used to mercurial.</p>
  
  <p>In mercurial, if I <code>hg add</code> some files, then <code>hg diff</code>, I get a patch which I can then apply, theoretically, with a simple <code>patch -p1</code> and get the exact same local copy.</p>
  
  <p>Now, with git, things are different: You <code>git diff</code> before you <code>git add</code>. But how can I make <code>git diff</code> also cover all of the untracked files, like <code>hg diff</code> after <code>hg add</code>ing?</p>