WhatInstalls2.sh

#!/bin/bash

# Find out what caused the given package to installed,
# i.e. what other package pulled it in as a dependency.

# Usage: ./WhatInstalls.sh package-name

set -e
depending_pkgs_file="$(mktemp)"
recommending_pkgs_file="$(mktemp)"
installed_pkgs_file="$(mktemp)"

apt-rdepends -r "$1" | grep ':' | cut -d ' ' -f 5 | sort -u > "$depending_pkgs_file"
apt-rdepends -r --follow='Depends,Recommends' "$1" | grep ':' | cut -d ' ' -f 5 | sort -u > "$recommending_pkgs_file"
dpkg --get-selections | cut -f 1 | sort -u > "$installed_pkgs_file"

# Filter out packages that were installed as a dependency for another package
depending_pkgs_filtered="$(comm -12 "$depending_pkgs_file" "$installed_pkgs_file")"
recommending_pkgs_prefiltered="$(comm -12 "$recommending_pkgs_file" "$installed_pkgs_file")"
# Filter out strictly dependent packages from recommending pkgs list
recommending_pkgs_filtered="$(echo "$recommending_pkgs_prefiltered" | comm -23 - "$depending_pkgs_file")"

[ -n "$depending_pkgs_filtered" ] && echo "### The following manually installed packages depend on $1: ###
$depending_pkgs_filtered"

[ -n "$recommending_pkgs_filtered" ] && echo "### The following manually installed packages pull it in as a recommendation: ###
$recommending_pkgs_filtered"

rm "$depending_pkgs_file" "$recommending_pkgs_file" "$installed_pkgs_file"