title: Explain uses of these common env variables: HTTP_PROXY, HTTPS_PROXY, & NO_PROXY?
body: <p>Can someone explain the purpose and effective usage of these three environment variables?</p>
  
  <p>Is there a common convention when using them?</p>
  
  <p>What happens if I set all of them at the same time? Is this application specific (I assume it is, but are there best practices?).</p>
  
  <p>I see this as a pretty good "long form" answer. I don't know much about these variables or where to find more information about them and would love more information.</p>