load environment variables from a per-directory rc file, reset to default upon entering any directory which doesn't have a .dirrc owned by your current user

gistfile1.sh

# source each directory's .dirrc for project-specific environment variables
function cd () {
  builtin cd "$@"
  if [[ $PWD == $HOME* ]]; then
    DIRPATH=( $(pwd) )

    i=$((${#DIRPATH[@]} - 1))
    while [ -O ${DIRPATH[$i]} ]; do
      DIRPATH=("${DIRPATH[$i]}/.." "${DIRPATH[@]}")
    done

    for d in ${DIRPATH[@]}; do
      [ -O "$d/.dirrc" ] && source "$d/.dirrc"
    done
  else
    source ~/.bashrc
  fi
  return 0
}