add output diffs

Signed-off-by: ahuston-0 <aliceghuston@gmail.com>

utils/eval-to-drv.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env nix
+#! nix shell nixpkgs#bash nixpkgs#gnugrep --command bash
+
+# diffs each derivation
+
+set -x
+set -v
+set -e
+
+if [ "$#" -ne 2 ]; then
+    echo "$0 (pre|post)"
+fi
+
+script_path=$(dirname "$(readlink -f $0)")
+parent_path=$(dirname "$script_path")
+out_path="$parent_path/$1-drv"
+
+
+drv=$(nix flake check --verbose 2> >(grep -P -o "derivation evaluated to (/nix/store/.*\.drv)" | grep -P -o "/nix/store/.*\.drv"))
+
+echo "$drv" > "$out_path"