anchor.diff:  
         runCommand "nix-binary-tarball-${version}"
           { exportReferencesGraph = [ "closure1" toplevel "closure2" cacert ];
  -          buildInputs = [ perl shellcheck ];
  +          buildInputs = [ perl ] ++ lib.optional (system != "aarch64-linux") shellcheck;
             meta.description = "Distribution-independent Nix bootstrap binaries for ${system}";
           }
           ''
  
positive.code: { nix ? builtins.fetchGit ./.
  , nixpkgs ? fetchTarball channel:nixos-17.09
  , officialRelease ? false
  , systems ? [ "x86_64-linux" "i686-linux" "x86_64-darwin" "aarch64-linux" ]
  }:
  
negative.code:             --subst-var-by nix ${toplevel} \
              --subst-var-by cacert ${cacert}
  
            if type -p shellcheck; then
              shellcheck -e SC1090 $TMPDIR/install
              shellcheck -e SC1091,SC2002 $TMPDIR/install-darwin-multi-user
            fi
  
            chmod +x $TMPDIR/install
            chmod +x $TMPDIR/install-darwin-multi-user
  