pkgs.writeAshScript is similar to writeShellScript but busybox

overlay.nix

@@ -3,6 +3,8 @@ final: prev: {
   s6-init-files = final.callPackage ./pkgs/s6-init-files {};
   strace = prev.strace.override { libunwind = null; };
   liminix = final.callPackage ./pkgs/liminix-tools {};
+  writeAshScript = final.callPackage ./pkgs/write-ash-script {};
+
   pppoe = prev.rpPPPoE.overrideAttrs (o: {
     # use newer rp-pppoe, it builds cleanly
     src = final.fetchFromGitHub {

pkgs/write-ash-script/default.nix

@@ -0,0 +1,14 @@
+{
+  busybox
+, writeScript
+, lib
+}
+: name : { runtimeInputs ? [] } : text : writeScript name ''
+#!${busybox}/bin/sh
+set -o errexit
+set -o nounset
+set -o pipefail
+
+export PATH="${lib.makeBinPath ([ busybox ] ++ runtimeInputs)}:$PATH"
+${text}
+''