Add modules

modules/environment/links.nix

@@ -0,0 +1,60 @@
+# Licensed under GNU Lesser General Public License v3 or later, see COPYING.
+# Copyright (c) 2019 Alexander Sosedkin and other contributors, see AUTHORS.
+
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.environment;
+in
+
+{
+
+  ###### interface
+
+  options = {
+
+    environment = {
+      binSh = mkOption {
+        type = types.str;
+        readOnly = true;
+        description = "Path to /bin/sh executable.";
+      };
+
+      usrBinEnv = mkOption {
+        type = types.str;
+        readOnly = true;
+        description = "Path to /usr/bin/env executable.";
+      };
+    };
+
+  };
+
+
+  ###### implementation
+
+  config = {
+
+    build.activation = {
+      linkBinSh = ''
+        $DRY_RUN_CMD mkdir $VERBOSE_ARG --parents /bin
+        $DRY_RUN_CMD ln $VERBOSE_ARG --symbolic --force ${cfg.binSh} /bin/.sh.tmp
+        $DRY_RUN_CMD mv $VERBOSE_ARG /bin/.sh.tmp /bin/sh
+      '';
+
+      linkUsrBinEnv = ''
+        $DRY_RUN_CMD mkdir $VERBOSE_ARG --parents /usr/bin
+        $DRY_RUN_CMD ln $VERBOSE_ARG --symbolic --force ${cfg.usrBinEnv} /usr/bin/.env.tmp
+        $DRY_RUN_CMD mv $VERBOSE_ARG /usr/bin/.env.tmp /usr/bin/env
+      '';
+    };
+
+    environment = {
+      binSh = "${pkgs.bashInteractive}/bin/sh";
+      usrBinEnv = "${pkgs.coreutils}/bin/env";
+    };
+
+  };
+
+}