anchor.diff:  
           # Subscribe the root user to the NixOS channel by default.
           if [ "$USER" = root -a ! -e $HOME/.nix-channels ]; then
  -            echo "creating $HOME/.nix-channels with nixos-unstable subscription" >&2
               echo "http://nixos.org/channels/nixos-unstable nixos" > $HOME/.nix-channels
           fi
   
  
positive.code: 
          # Set up a default Nix expression from which to install stuff.
          if [ ! -e $HOME/.nix-defexpr -o -L $HOME/.nix-defexpr ]; then
              echo "creating $HOME/.nix-defexpr" >&2
              rm -f $HOME/.nix-defexpr
              mkdir $HOME/.nix-defexpr
              if [ "$USER" != root ]; then
  
negative.code:         fi
  
          if ! test -L $HOME/.nix-profile; then
              if test "$USER" != root; then
                  ln -s $NIX_USER_PROFILE_DIR/profile $HOME/.nix-profile
              else
  