title: What does the '$' mean in command line commands?
body: <p>I often find command line commands starting with <em>dollar signs</em> in instructions to install many things. For example to install <strong>Ruby</strong> in <strong>Ubuntu</strong>, the website says to use the following command:</p>
  
  <pre><code>$ sudo apt-get install ruby-full
  </code></pre>
  
  <p>What does the <code>$</code> represent?</p>