title: Find the difference between two files
body: <p>I have the following situation:</p>
  
  <p>The file1.dat is like:</p>
  
  <pre><code>1 2
  1 3
  1 4
  2 1
  </code></pre>
  
  <p>and the file2.dat is like:</p>
  
  <pre><code>1 2
  2 1
  2 3
  3 4
  </code></pre>
  
  <p>I want to find the differences between the second file from the first. I tried wit <code>grep -v -f file1 file2</code> but my real files are bigger than this two and when I tried with it the shell never ended is work. </p>
  
  <p>The result should be:</p>
  
  <pre><code>2 3
  3 4
  </code></pre>
  
  <p>The files are sorted and they have the same number of elements. Any way to find a solution with awk?</p>