title: How can I show lines in common (reverse diff)?
body: <p>I have a series of text files for which I'd like to know the lines in common rather than the lines which are different between them. Command line Unix or Windows is fine.</p>
  <p>File <em>foo</em>:</p>
  <pre><code>linux-vdso.so.1 =&gt;  (0x00007fffccffe000)
  libvlc.so.2 =&gt; /usr/lib/libvlc.so.2 (0x00007f0dc4b0b000)
  libvlccore.so.0 =&gt; /usr/lib/libvlccore.so.0 (0x00007f0dc483f000)
  libc.so.6 =&gt; /lib/libc.so.6 (0x00007f0dc44cd000)
  </code></pre>
  <p>File <em>bar</em>:</p>
  <pre><code>libkdeui.so.5 =&gt; /usr/lib/libkdeui.so.5 (0x00007f716ae22000)
  libkio.so.5 =&gt; /usr/lib/libkio.so.5 (0x00007f716a96d000)
  linux-vdso.so.1 =&gt;  (0x00007fffccffe000)
  </code></pre>
  <p>So, given these two files above, the output of the desired utility would be akin to <code>file1:line_number, file2:line_number == matching text</code> (just a suggestion; I really don't care what the syntax is):</p>
  <pre><code>foo:1, bar:3 == linux-vdso.so.1 =&gt;  (0x00007fffccffe000)
  </code></pre>