title: Using double brackets gives -bash: conditional binary operator expected
body: <p>Why does this doesn't work</p>
  
  <pre><code>if [[ screen -ls | grep -q "Hello" ]];
   then 
      echo "Hello"; 
  fi
  </code></pre>
  
  <p>It gives the errors</p>
  
  <pre><code>-bash: unexpected token `|', conditional binary operator expected
  -bash: syntax error near `-ls'
  </code></pre>
  
  <p>But this works</p>
  
  <pre><code>if screen -ls | grep -q "Hello";
   then 
      echo "Hello"; 
  fi
  </code></pre>
  
  <p>Shouldn't it be the other way around? How can I fix the double brackets.</p>