title: Grep strings containing two or more words
body: <p>I have three strings</p>
  
  <pre><code>strA="a b mam am"
  strB="a b a"
  strC="a b a c"
  </code></pre>
  
  <p>and I want to grep strings containing two or more words "a", so <code>strA</code> shouldn't return anything, while <code>strB</code> and <code>strC</code> should.</p>
  
  <p>I tried this command: <code>echo "a b a" | grep  "a *a"</code> but why isn't it working?</p>