title: General way for getting all parents of specified commit
body: <p>Is there a <em>general</em>* way to get all commit's parents in a <em>pure</em>** git way?</p>
  
  <p>Yep, parents of merge commit could be parsed from <code>git show</code> command, and parent of simple commit could be get with <code>$HASH^</code>-like stuff. But in my opinion it is ugly and clumsy.</p>
  
  <p>So, what I want is:</p>
  
  <pre><code>$&gt; git parents $NON_MERGE_COMMIT_HASH
  HASH1
  
  $&gt; git parents $MERGE_COMMIT_HASH
  HASH1
  HASH2
  ...
  </code></pre>
  
  <hr>
  
  <p><em>general</em>* - single command for non-merge commits and merge commits.</p>
  
  <p><em>pure</em>** - simple git command without any parsing of output. I.e. for getting current branch name <code>git rev-parse --abbrev-ref HEAD</code> is a pure command and <code>git branch</code> is not.</p>