title: The meaning of ${BASH_SOURCE-$0}?
body: <p>I saw this shell script in Zookeeper <code>zkClear.sh</code>.</p>
  <pre><code>ZOOBIN=&quot;${BASH_SOURCE-$0}&quot;
  </code></pre>
  <p>Can anyone tell me the meaning of this script?
  Thanks.</p>