title: To understand the practical use of Grep's option -H in different situations
body: <p>This question is based on <a href="https://stackoverflow.com/questions/1121776/to-understand-xargs-better/1121897#1121897">this answer</a>.</p>
  
  <p><strong>Why do you get the same output from the both commands?</strong></p>
  
  <p><strong>Command A</strong></p>
  
  <pre><code>$sudo grep muel *                                                             /tmp
  masi:muel
  </code></pre>
  
  <p><strong>Command B</strong></p>
  
  <pre><code>$sudo grep -H muel *                                                          /tmp
  masi:muel
  </code></pre>
  
  <p>Rob's comment suggests me that <em>Command A</em> should not give me <code>masi:</code>, but only <code>muel</code>.</p>
  
  <p>In short, <strong>what is the practical purpose of <code>-H</code>?</strong></p>