title: Invalid active developer path on MAC OS X after installing Ruby
body: <p>I get this error:</p>
  
  <p><code>xcrun: error: invalid active developer path (/Applications/Xcode.app), missing xcrun at: /Applications/Xcode.app/usr/bin/xcrun</code></p>
  
  <p>This <a href="https://stackoverflow.com/questions/14334708/xcrun-cant-find-xcode-path">solution</a> works, but the error occurs again after closing my terminal and reopening it; I then have to run the same commands every time I open a new terminal window.</p>
  
  <p>How can I apply these changes such that they will save after closing the terminal window out?</p>