title: For "git diff" is there a -U<infinity> option to show the whole file?
body: <p>I need to generate a full-context git diff programmatically for a web ui.</p>
  
  <p>A CLI for generating a full-context diff was covered in questions: </p>
  
  <ul>
  <li><a href="https://stackoverflow.com/questions/13627598/how-to-get-git-diff-with-full-context">How to get git diff with full context?</a> </li>
  <li><a href="https://stackoverflow.com/questions/27238258/git-show-whole-file-changes">Git show whole file changes</a></li>
  </ul>
  
  <p>The prevalent answer is something like <code>git diff -U99999</code></p>
  
  <p>With a <code>-U / --unified</code> option with a ridiculously high threshold (e.g. 999,999), doing <code>git diff -U999999</code>:</p>
  
  <ol>
  <li>Makes me suspect that there could be a performance hit</li>
  <li>Even worse, it's a correctness issue if my file is larger than 1M lines</li>
  </ol>
  
  <p>Is there a -U option to show the whole file?</p>