nix-realize-in-build.nix

with import <nixpkgs> {};
let nixBin = "${pkgs.nix}/bin"; in
runCommand "foo" {}
''
    set -e
    datadir="${pkgs.nix}/share"
    export TEST_ROOT=$(pwd)/test-tmp
    export NIX_BUILD_HOOK=
    export NIX_CONF_DIR=$TEST_ROOT/etc
    export NIX_DB_DIR=$TEST_ROOT/db
    export NIX_LOCALSTATE_DIR=$TEST_ROOT/var
    export NIX_LOG_DIR=$TEST_ROOT/var/log/nix
    export NIX_MANIFESTS_DIR=$TEST_ROOT/var/nix/manifests
    export NIX_STATE_DIR=$TEST_ROOT/var/nix
    export NIX_STORE_DIR=$TEST_ROOT/store
    export PAGER=cat
    cacheDir=$TEST_ROOT/binary-cache
    ${nix}/bin/nix-store --init

    cat > drv.nix <<EOF
    derivation {
      name = "foo";
      system = ${pkgs.lib.strings.escapeNixString system};
      # /bin/sh is magically accessible to nix,
      # it is added to the build sandbox (with all runtime deps).
      builder = "/bin/sh";
      args = [ "-c" "echo $love && echo foo > \$out" ];
    }
    EOF

    ${nixBin}/nix-instantiate drv.nix > drv
    output=$(${nixBin}/nix-store --realize $(<drv))

    touch $out
''