virtualenv-auto-activate-auto-deactivate with support for existing custom PROMPT_COMMAND

virtualenv-auto-activate.sh

#!/bin/bash

_virtualenv_auto_activate() {
      if [ -e ".env" ]; then
          # Check to see if already activated to avoid redundant activating
          if [ "$VIRTUAL_ENV" = "" ]; then
              source .env/bin/activate
           fi
     else
       if [ "$VIRTUAL_ENV" != "" ]; then
         deactivate
       fi
     fi
   }

export PROMPT_COMMAND="_virtualenv_auto_activate; $PROMPT_COMMAND"