init

default.nix

@@ -0,0 +1,61 @@
+{
+  pkgs,
+  stdenv ? pkgs.stdenv,
+  packages ? [ ],
+  shellHook ? "",
+  ...
+}@vars:
+let
+  lib = pkgs.lib;
+  cleanVars = lib.removeAttrs vars [
+    "pkgs"
+    "packages"
+    "shellHook"
+    "stdenv"
+  ];
+  exported = lib.concatStringsSep "\n" (lib.mapAttrsToList (n: v: "export ${n}=${v}") cleanVars);
+  script = ''
+    #! /usr/bin/env bash
+    ${exported}
+    ${shellHook}
+  '';
+in
+stdenv.mkDerivation {
+  name = "cass-shell";
+  preferLocalBuild = true;
+
+  nativeBuildInputs =
+    with pkgs;
+    [
+      coreutils
+    ]
+    ++ packages;
+
+  buildCommand = ''
+    # unset all nix-related variables
+    unset SHELL configureFlags mesonFlags shell depsHostHost STRINGS depsTargetTarget stdenv \
+      builder PWD SOURCE_DATE_EPOCH enableParallelInstalling CXX TEMPDIR system HOST_PATH \
+      enableParallelBuilding doInstallCheck buildCommandPath enableParallelChecking LS_COLORS \
+      depsTargetTargetPropagated cmakeFlakes outputs TMPDIR LD READELF doCheck \
+      depsBuildBuild SIZE propagatedNativeBuildInputs strictDeps AR AS TEMP SHLVL NM \
+      patches passAsFile buildInputs SSL_CERT_FILE depsBuildTarget OBJCOPY STRIP TMP OBJDUMP propagatedBuildInputs \
+      CC __ETC_PROFILE_SOURCED depsBuildTargetPropagated depsBuildBuildPropagated CONFIG_SHELL __structuredAttrs \
+      RANLIB nativeBuildInputs name depsHostHostPropagated TEST TZ HOME GZIP_NO_TIMESTAMPS \
+      cmakeFlags TERM buildCommand preferLocalBuild _
+    unset "''${!NIX_@}"
+    # create export commands for the rest
+    envs="$(env | sed 's/^/export /' -)"
+    # assemble script
+    printf '${script}' > $out
+    echo "$envs" >> $out 
+    echo 'exec $SHELL' >> $out
+    # required here
+    sed -i 's/^export out=.*$//' $out
+    # inserted by env cmd
+    sed -i 's/^export _=.*$//' $out
+    # append to user's current path
+    sed -i '/^export PATH=/ s/$/:\$PATH/' $out
+    chmod +x $out
+  '';
+
+}

flake.nix

@@ -0,0 +1,7 @@
+{
+  outputs =
+    { self }:
+    {
+      mkShell = { pkgs, ... }@vars: import ./default.nix vars;
+    };
+}