title: How to list all Linux environment variables including LD_LIBRARY_PATH
body: <p>How to list all the environment variables in Linux?</p>
  
  <p>When I type the command <code>env</code> or <code>printenv</code> it gives me lots of variables, but some variables like <code>LD_LIBRARY_PATH</code> and <code>PKG_CONFIG</code> don't show up in this list.</p>
  
  <p>I want to type a command that list all the environment variables including this variables (<code>LD_LIBRARY_PATH</code> and <code>PKG_CONFIG</code>)</p>