#!/bin/bash
all=($(< packages.txt sed 's/#.*//' | xargs printf -- '%s\n' | sort -u))
grps=($(printf -- '%s\n' "${all[@]}" | sed -n 's/^g://p'))
pkgs=($(printf -- '%s\n' "${all[@]}" | sed -n 's/^p://p'))

echo ' => In packages.txt, but not installed'
comm -13 \
    <(pacman -Qq|sort -u) \
    <({ pacman -Qgq -- "${grps[@]}"; printf '%s\n' "${pkgs[@]}"; }|sort -u) |
sed 's|^|  -> |'

echo ' => Installed explicitly, but not in packages.txt'
comm -23 \
    <(pacman -Qetq|sort -u) \
    <({ pacman -Qgq -- "${grps[@]}"; printf '%s\n' "${pkgs[@]}"; }|sort -u) |
sed 's|^|  -> |'

echo ' => Installed as dependencies, but only optionally needed'
comm -23 \
     <(pacman -Qdttq|sort -u) \
     <(pacman -Qdtq |sort -u) |
sed 's|^|  -> |'

echo ' => Installed as dependencies, but no longer needed'
pacman -Qdtq|sort -u |sed 's|^|  -> |'