title: In linux shell, how to copy all files/subdirs into subdir, except the subdir itself?
body: <p>Say I have this directory structure</p>
  <pre><code>/path/topdir
  /path/topdir/subdir1
  /path/topdir/subdir2
  /path/topdir/subdir3
  /path/topdir/file1.txt
  /path/topdir/file2.txt
  /path/topdir/file3.txt
  </code></pre>
  <p>What's a 1-liner shell command (not awk nor perl, etc., strictly shell) to copy everything in <code>topdir</code> into <code>subdir3</code>, except <code>subdir3</code> itself?</p>