implement writeBash with makeScriptWriter

pkgs/default.nix

@@ -164,13 +164,8 @@ pkgs: oldpkgs: {
          echo hello world
        ''
   */
-  writeBash = name: text:
+  writeBash = pkgs.makeScriptWriter {
-    assert (with types; either absolute-pathname filename).check name;
+    interpreter = "${pkgs.bash}/bin/bash";
-    pkgs.write (baseNameOf name) {
-      ${optionalString (types.absolute-pathname.check name) name} = {
-        executable = true;
-        text = "#! ${pkgs.bash}/bin/bash\n${text}";
-      };
   };
 
   writeBashBin = name: