title: why "git show --name-only --pretty=format:" could show only names of affected files
body: <p>From git documentation,  <code>git show --name-only</code> Show only names of changed files. But with command <code>git show --name-only</code>, it outputs other info like commit id and and author and commit messages, etc. </p>
  
  <p>And I also know <code>--pretty=format:&lt;format&gt;</code> could format the output, but why given empty <code>&lt;format&gt;</code>, the output filters out other info when only using <code>git show --name-only</code>?</p>
  
  <p>Edited:</p>
  
  <p>With exact command <code>git show --name-only --pretty=format:</code>(nothing after colon), the output is exactly the lines of changed files. My question is more about why given no format it outputs such result?</p>