title: bash process data from two files
body: <p>file1:</p>
  
  <pre><code>456
  445
  2323
  </code></pre>
  
  <p>file2:</p>
  
  <pre><code>433
  456
  323
  </code></pre>
  
  <p>I want get the deficit of the data in the two files and output to output.txt, that is:</p>
  
  <pre><code>23
  -11
  2000
  </code></pre>
  
  <p>How do I realize this? thank you.</p>