Nix Expression for Running Rails Apps

rails.nix

with (import <nixpkgs> {});

stdenv.mkDerivation {
  name = "717-app";
  buildInputs = [ libiconv openssl ruby21 postgresql git nodejs ];
  src = "/src/717";
  builder = builtins.toFile "builder.sh" ''
    set -e
    source $stdenv/setup

    export GEM_HOME=$out/.gems
    export HOME=$out
    export PATH=$out/.gems/bin:$PATH
    export ICONV=/nix/store/3j8ixbc22mrz5bsb1jlchmiza8ahmpks-libiconv-1.13.1


    echo "Performing setup in $src with ICONV $ICONV"
    (cd $src &&
      gem install --no-user-install --no-http-proxy --no-document bundler &&
      bundle config build.nokogiri --with-iconv-dir=$ICONV &&
      bundle install --path=.gems &&
      npm install)
  '';

  shellHook = ''
    export PGDATA=/var/srv/pg
    export GEM_HOME=$out/.gems
    export PATH=$out/.gems/bin:$PATH

    if [ ! -d $PGDATA ]; then
      initdb
    fi

    if [ $autostart-postgres ]; then
      pg_ctl -D $PGDATA -l $src/log/pg.log start
      trap 'pg_ctl -D $PGDATA stop' EXIT
    fi

  '';

  system  = "x86_64-darwin";
}

To get it semi-working I had to change ruby21 to ruby_2_1. It seems that you hard coded the PGDATA to some root directory. I haven't tried doing it somewhere else but is this required? I haven't tried running it with sudo (because I have another postgres installed)