title: Using grep and awk together
body: <p>I have a file (A.txt) with 4 columns of numbers and another file with 3 columns of numbers (B.txt). I need to solve the following problems:</p>
  <ol>
  <li><p>Find all lines in A.txt whose 3rd column has a number that appears any where in the 3rd column of B.txt.</p>
  </li>
  <li><p>Assume that I have many files like A.txt in a directory and I need to run this for every file in that directory.</p>
  </li>
  </ol>
  <p>How do I do this?</p>