title: Show sha1 only with git log
body: <p>I want to write a Bash script that loops over the sha1s of commits output by an invocation of <code>git log</code>. However, <code>git log</code> gives me much more output than I want:</p>
  
  <pre><code>commit 0375602ba2017ba8750a58e934b41153faee6fcb
  Author: Mark Amery &lt;markamery@notmyrealemail.com&gt;
  Date:   Wed Jan 1 21:35:07 2014 +0000
  
      Yet another commit message
  
      This one even has newlines.
  
  commit 4390ee9f4428c84bdbeb2fed0a461099a6c81b39
  Author: Mark Amery &lt;markamery@notmyrealemail.com&gt;
  Date:   Wed Jan 1 21:30:19 2014 +0000
  
      Second commit message.
  
  commit bff53bfbc56485c4c1007b0884bb1c0d61a1cf71
  Author: Mark Amery &lt;markamery@notmyrealemail.com&gt;
  Date:   Wed Jan 1 21:28:27 2014 +0000
  
      First commit message.
  </code></pre>
  
  <p>How can I get <code>git log</code> to just output sha1s so that I can loop over them conveniently?</p>