add writeFennelScript function, make ifwait use it

pkgs/ifwait/default.nix

@@ -1,34 +1,13 @@
 {
   luaSmall
 , netlink-lua
-, stdenv
-, makeWrapper
+, writeFennelScript
+, runCommand
 }:
 let
   lua = luaSmall;
   netlink = netlink-lua.override {inherit lua;};
-  fennel = lua.pkgs.fennel;
-in stdenv.mkDerivation rec {
-  pname = "ifwait";
-  version = "1";
-  phases = [ "installPhase" ];
-
-  buildInputs = [ lua netlink ];
-  nativeBuildInputs = [ makeWrapper fennel ];
-
-  LUA_CPATH = "${netlink}/lib/lua/${lua.luaversion}/\?.so"; # for nix-shell
-
-  installPhase = ''
-    mkdir -p $out/bin $out/lib
-    fennel --compile  ${./ifwait.fnl} > $out/lib/${pname}.lua
-
-    makeWrapper ${lua}/bin/lua $out/bin/${pname} \
-      --prefix LUA_CPATH ";" ${netlink}/lib/lua/${lua.luaversion}/\?.so \
-      --add-flags $out/lib/${pname}.lua
-    # makeWrapper adds a shebang for bash
-    sed -i -e '1c#!/bin/sh' $out/bin/${pname}
-  '';
-}
-
-# to use fennel.view,
-#  --prefix LUA_PATH ";" ${fennel}/share/lua/5.2/\?.lua \
+in runCommand "ifwait" {} ''
+  mkdir -p $out/bin
+  cp -p ${writeFennelScript "ifwait" [netlink] ./ifwait.fnl} $out/bin/ifwait
+''