diff --git a/overlays/rolling_datasets/bin/roll_dataset b/overlays/rolling_datasets/bin/roll_dataset
index 2ba7cfc..ff79d01 100644
--- a/overlays/rolling_datasets/bin/roll_dataset
+++ b/overlays/rolling_datasets/bin/roll_dataset
@@ -4,7 +4,7 @@ source @out@/share/functions/get_old_datasets
 
 export "PATH=$PATH:@runtimePath@"
 
-if [[ "$#" != 3 ]] ; then
+if [[ "$#" != 2 ]] ; then
     echo "This script requires precisely 2 arguments!"
     exit 1
 fi
@@ -21,7 +21,7 @@ zfs rollback "$dataset@blank" && echo "rollback complete"
 
 while IFS="\n" read gen
 do
-    printf "$gen < $(("$generation" - "$to_keep")) => "
+    printf -- "$gen < $(("$generation" - "$to_keep")) => "
     if [ "$gen" -lt "$(("$generation" - "$to_keep"))" ]; then
         zfs destroy -r "$dataset/$gen"
         echo "destroyed"
diff --git a/overlays/rolling_datasets/default.nix b/overlays/rolling_datasets/default.nix
index aded02a..34c07ad 100644
--- a/overlays/rolling_datasets/default.nix
+++ b/overlays/rolling_datasets/default.nix
@@ -1,50 +1,27 @@
-{ inputs, ... }:
+{ inputs, lib, ... }:
+let
+  inherit (lib)
+    filterAttrs
+    mapAttrsToList
+    concatStringsSep
+    ;
+in
 {
   flake.overlays.rolling_datasets =
     final: prev:
     let
-      writeTextFile =
-        { name # the name of the derivation
-        , text
-        , executable ? false # run chmod +x ?
-        , destination ? ""   # relative path appended to $out eg "/bin/foo"
-        , checkPhase ? ""    # syntax checks, e.g. for scripts
-        , env ? {}
-        }:
-        final.runCommand name
-          ({ inherit text executable;
-            passAsFile = [ "text" ];
-            # Pointless to do this on a remote machine.
-            preferLocalBuild = true;
-            allowSubstitutes = false;
-          } // env)
-          ''
-            n=$out${destination}
-            mkdir -p "$(dirname "$n")"
-
-            if [ -e "$textPath" ]; then
-              mv "$textPath" "$n"
-            else
-              echo -n "$text" > "$n"
-            fi
-
-            ${checkPhase}
-
-            (test -n "$executable" && chmod +x "$n") || true
-          '';
-      writeShellScriptBin = name : text : env :
-        writeTextFile {
-          inherit name;
-          executable = true;
-          destination = "/bin/${name}";
-          text = ''
-            #!${final.runtimeShell}
-            ${text}
+        writeShellScript = name: text:
+          prev.writeTextFile {
+            inherit name;
+            executable = true;
+            text = ''
+              #!/bin/sh
+              ${text}
             '';
-          checkPhase = ''
-            ${final.stdenv.shell} -n $out/bin/${name}
-          '';
-        };
+            checkPhase = ''
+              ${prev.stdenv.shellDryRun} "$target"
+            '';
+          };
     in
       {
         rolling_datasets =
@@ -56,11 +33,14 @@
             export runtimeShell=${prev.runtimeShell} \
                    runtimePath=${prev.lib.makeBinPath (with prev; [ utillinux zfs ])}
 
-            for binary in ${./bin}/* ; do
-              output_binary="$out/bin/$(basename "$binary")"
+            ${concatStringsSep "\n" (mapAttrsToList (name: _: ''
+            {
+              binary=${writeShellScript name (builtins.readFile (./. + "/bin/${name}"))}
+              output_binary="$out/bin/${name}"
               substituteAll "$binary" "$output_binary"
               chmod +x "$output_binary"
-            done
+            }
+            '') (filterAttrs (_: v: v == "regular") (builtins.readDir ./bin)))}
 
             for function in ${./functions}/* ; do
               substituteAll "$function" "$out/share/functions/$(basename "$function")"