title: Why doesn't grep work if a file is not specified?
body: <p>I have some problem with the Linux grep command, it don't work !!!</p>
  
  <p>I am trying the following test on my Ubuntu system:</p>
  
  <ol>
  <li><p>I have create the following folder: <code>/home/andrea/Scrivania/prova</code></p></li>
  <li><p>Inside this folder I have created a txt file named prova.txt and inside this file I have write the string <code>test</code> and I have save it</p></li>
  <li><p>In the shell I have first access the folder <code>/home/andrea/Scrivania/prova</code> and so I have launched the grep command in the following way:</p>
  
  <pre><code>~/Scrivania/prova$ grep test
  </code></pre></li>
  </ol>
  
  <p>The problem is that the cursor continues to blink endlessly and cannot find NOTHING! Why? What is the problem?</p>