Generate the difference in packages between two Debian-derived chroots.

chroot_package_diff

#!/usr/bin/env bash
set -e

# Validate the command-line arguments.
if [[ $# -ne 3 ]]; then
  echo "Usage: $0 [chroot1] [chroot2] [only_in_1,only_in_2,in_both]"
  exit 1
elif [[ ! -d "$1" ]]; then
  echo "$1 is not a directory."
  exit 1
elif [[ ! -d "$2" ]]; then
  echo "$2 is not a directory.";
  exit 1;
elif [[ "$3" != "only_in_1" && "$3" != "only_in_2" && "$3" != "in_both" ]]; then
  echo "$3 is invalid. Valid options are only_in_1, only_in_2, and in_both."
  exit 1
fi

# Get installed package lists from both chroots and compute their difference.
PKGS_1=$(sudo chroot "$1" /bin/bash -c "apt list --installed" 2>/dev/null | \
         tail +2 | awk 'BEGIN{FS="/"}{print $1}')
PKGS_2=$(sudo chroot "$2" /bin/bash -c "apt list --installed" 2>/dev/null | \
         tail +2 | awk 'BEGIN{FS="/"}{print $1}')
DIFF=$(diff --unified=999999 <(echo "$PKGS_1") <(echo "$PKGS_2") | tail +3)

# Produce the requested output type.
if [[ "$3" == "only_in_1" ]]; then
  echo "${DIFF}" | grep "^-" | cut -c2-
elif [[ "$3" == "only_in_2" ]]; then
  echo "${DIFF}" | grep "^+" | cut -c2-
elif [[ "$3" == "in_both" ]]; then
  echo "${DIFF}" | grep "^ " | cut -c2-
fi