Get a list of all packages installed on a system, triple-hashed on apt source url, release, and repo

get_package_by_repo.rb

require 'json'

# Collect the url, release, and repo immediately following the first
# line beginning with ` *** `, which indicates the installed instance of
# the package.
get_repo = %r{\n +\*\*\* +.*?\n +[0-9]+ +([^ ]+) +([^ /]+)/([^ ]+) .* Packages}m

# Get a list of all packages apt knows about.
packages = `apt list --installed | sed -e 's,/.*$,,'`.strip.split("\n")

all = {}

packages.each do |package|
  get_repo =~ `apt-cache policy #{package}`

  all[$1] = {} unless all.key? $1
  all[$1][$2] = {} unless all[$1].key? $2
  all[$1][$2][$3] = [] unless all[$1][$2].key? $3

  all[$1][$2][$3] << package
end

puts JSON.pretty_generate(all)