nixos-build: construct NIXOS_CONFIG and NIX_PATH

bin/nixos-build

@@ -6,24 +6,19 @@ set -euf
 
 host=$1
 
-#target=root@$host
-
-pubkeys=$config_root/pubkeys
-nixpkgs=$nixpkgs_root/$host
-nixos_config=$config_root/modules/$host
-secrets_nix=$secrets_root/$host/nix
-secrets_rsync=$secrets_root/$host/rsync
+NIXOS_CONFIG=$config_root/modules/$host
+export NIXOS_CONFIG
 
 # Notice how host's NIX_PATH is used to prefetch nixpkgs.
-NIXOS_CONFIG=$nixos_config \
-  prefetch nixpkgs tmp/nixpkgs/$host
+prefetch nixpkgs "$nixpkgs_root/$host"
 
-nix-build \
-    -I "$nixpkgs" \
-    -I pubkeys="$pubkeys" \
-    -I nixos-config="$nixos_config" \
-    -I retiolum-hosts="$retiolum_hosts" \
-    -I secrets="$secrets_nix" \
+NIX_PATH=$nixpkgs_root/$host
+NIX_PATH=$NIX_PATH:secrets=$secrets_root/$host/nix
+NIX_PATH=$NIX_PATH:pubkeys=$config_root/pubkeys
+NIX_PATH=$NIX_PATH:retiolum-hosts=$retiolum_hosts
+export NIX_PATH
+
+exec nix-build \
   -A system \
   --no-out-link \
   '<nixos>'