title: Show only changed lines with diff, not newly added lines
body: <p>I'm curious if there is a way to get only changed lines with diff, not the newly added lines?</p>
  
  <p>I mean, let's say I have two files file1 and file2. </p>
  
  <p>file1 is:</p>
  
  <pre><code>abc=123
  def=234
  klm=10.10
  xyz=6666
  </code></pre>
  
  <p>file2 is:</p>
  
  <pre><code>abc+=123
  def=234
  klm=10.101
  xyz=666
  stackoverflow=1000
  superuser=2000
  wtf=911
  </code></pre>
  
  <p>what I want is giving a command like <code>diff &lt;parameters&gt; file1 file2</code> and getting an output like</p>
  
  <pre><code>- abc=123
  + abc+=123
  - klm=10.10
  + klm=10.101
  - xyz=6666
  + xyz=666
  </code></pre>
  
  <p>Such output is welcomed too:</p>
  
  <pre><code>- abc=123
  + abc+=123
    def=234
  - klm=10.10
  + klm=10.101
  - xyz=6666
  + xyz=666
  </code></pre>
  
  <p>I don't want the</p>
  
  <pre><code>stackoverflow=1000
  superuser=2000
  wtf=911
  </code></pre>
  
  <p>lines in the output.</p>
  
  <p>Is there a way to get this functionality with the parameters of diff in Linux?</p>