$storePath = `nix-store --add "$uri"`
            or die "cannot copy path $uri to the Nix store.\n";

        if ( $uri =~ /^\// ) {
            $storePath = `nix-store --add "$uri"`
                or die "cannot copy path $uri to the Nix store.\n";
        } else {
            $storePath = `PRINT_PATH=1 nix-prefetch-url "$uri" | tail -n 1`
                or die "cannot fetch $uri to the Nix store.\n";
        }