builder1.sh

source $stdenv/setup

echo test1 > $out
export FOO=BAR
echo "FOO from d1 is: $FOO"

builder2.sh

source $stdenv/setup
echo "FOO is: $FOO" | tee $out

default.nix

let
  pkgs = import <nixpkgs> {};
in

let
  d1 = derivation {
    inherit (pkgs) stdenv;
    name = "d1";
    src = ./.;
    system = builtins.currentSystem;
    builder = ./builder1.sh;
    buildInputs = [pkgs.python];
  };

  d2 = derivation {
    inherit (pkgs) stdenv;
    name = "d2";
    src = ./.;
    system = builtins.currentSystem;
    builder = ./builder2.sh;
    buildInputs = [d1];
  };
in

d2

output.log

$ nix-build default.nix
these derivations will be built:
  /nix/store/vgjnvg6sw4gpq5ngvamnrvi3v6sgb2kw-d1.drv
  /nix/store/4a00ylk9d2br5z4lcqzccnplxs4srqhc-d2.drv
building path(s) ‘/nix/store/n61rcbzw49i7v5kf7sgrlw0q6rqnj7iy-d1’

while setting up the build environment: executing ‘/nix/store/ffliclfpnpkjllxbn96awgmb7wasid44-builder1.sh’: Exec format error
builder for ‘/nix/store/vgjnvg6sw4gpq5ngvamnrvi3v6sgb2kw-d1.drv’ failed with exit code 1
cannot build derivation ‘/nix/store/4a00ylk9d2br5z4lcqzccnplxs4srqhc-d2.drv’: 1 dependencies couldn't be built
error: build of ‘/nix/store/4a00ylk9d2br5z4lcqzccnplxs4srqhc-d2.drv’ failed