Quickly check if a derivation is reproducible

r13y.sh

#! /usr/bin/env nix-shell
#! nix-shell -i bash --pure -p diffoscope nix
#  shellcheck shell=bash

set -eo pipefail

if [[ -z "$1" ]]; then
  cat <<EOF
usage:
  ./r13y.sh -A some.attribute

  ./r13y.sh /path/to/some.drv

EOF
  exit 1
elif [[ "$1" == "-A" ]]; then
  DERIV=$(nix-instantiate --quiet --quiet -A "$2")
else
  DERIV="$1"
fi

echo "Building derivation \"$DERIV\"..."

nix-build "$DERIV"

echo "Checking derivation \"$DERIV\"..."

if ! OUT=$(nix-build "$DERIV" --check --keep-failed |& tail -1); then
  A=$(cut -d ' ' -f9 <<< "$OUT")
  B=$(cut -d ' ' -f12 <<< "$OUT")

  diffoscope "${A//\'/}" "${B//\'/}"
fi

echo "Seems reproducible!"