apt-tree

#!/bin/bash -u
#
# Show package dependency tree
# Inspired by https://gist.github.com/damphat/6214499
#
# Copyright (C) 2021 Rodrigo Silva (MestreLion) <linux@rodrigosilva.com>
# License: GPLv3 or later, at your choice. See <http://www.gnu.org/licenses/gpl>
#------------------------------------------------------------------------------

usage() {
	if [[ "${1:-}" ]]; then exec >&2; fi
	cat <<-USAGE
	Usage: $myname [options] PACKAGE
	USAGE
	if [[ "${1:-}" ]] ; then
		cat <<- USAGE
		Try '$myname --help' for more information.
		USAGE
		exit 1
	fi
	cat <<-USAGE

	Show package dependency tree

	Options:
	  -h|--help     - show this page.

	Other options are passed to 'apt-rdepends', for example:
	  -r|--reverse  - show packages that depend on the specified one

	Suggested bash-completion:
	  complete -F _comp_pkg_names apt-tree
	USAGE
	exit 0
}

exists()  { type "$@" >/dev/null 2>&1; }
argerr()  { printf "%s: %s\n" "$myname" "${1:-error}" >&2; usage 1; }
invalid() { argerr "invalid ${2:-option}: ${1:-}"; }
missing() { argerr "missing ${1:+$1 }argument${2:+ from $2}."; }

#------------------------------------------------------------------------------

myname=${0##*/}
opts=()
args=()
package=

# Pre-parse for -h|--help, ignoring if after '--'
for arg in "$@"; do
	if [[ "$arg" == '--' ]]; then break; fi
	if [[ "$arg" == "-h" || "$arg" == "--help" ]]; then usage; fi
done
while (($#)); do
	case "$1" in
	-*) opts+=( "$1" );;
	* ) args+=( "$1" );;
	--) shift; break;;
	esac
	shift || break
done
args+=("$@")
case ${#args[@]} in
	0) missing PACKAGE;;
	1) package=${args[0]}; if [[ -z "$package" ]]; then missing PACKAGE; fi;;
	*) invalid "${args[1]}" argument;;
esac

#------------------------------------------------------------------------------

if ! exists apt-rdepends; then
	echo "Installing pre-requisite apt-rdepends"
	sudo apt install apt-rdepends  # not the same output as `apt rdepends`!
fi

#------------------------------------------------------------------------------

declare -gA dep=()
declare -gA num=()
pkgs=:

parse_deps() {
	local root=$1
	local pkg
	local category name version
	while read category name version; do
		if [[ "$category" == "P" ]];  then
			pkg=$name
			dep["$pkg"]=""
			num["$pkg"]=0
		else
			dep["$pkg"]="${dep["$pkg"]} ${name}"
			num["$pkg"]=$((${num["$pkg"]} + 1))
		fi
	done < <(
		apt-rdepends "${opts[@]}" "$root" |
		# mark 'P' for package, 'D' for dependency
		sed -E 's/^/P\t/; s/^P?\t? +[^:]+: /D\t/; s/ \(([^)]+)\)/\t\1/'
	)
	walk_deps "$root"
}

walk_deps() {
	local root=$1
	local level=${2:-0}
	local last=${3:-0}
	local prefix=${4:-}
	local T1= T2=
	local pkg
	local i=0

	# mark packages already printed to avoid circular dependencies
	local dupe=; if [[ "$pkgs" == *:${root}:* ]]; then dupe=*; fi

	if ((level++)); then
		T1=' │  '; if ((last)); then T1='    '; fi
		T2=' ├─ '; if ((last)); then T2=' ╰─ '; fi
	fi
	echo "${prefix}${T2}${root}${dupe}"

	# Do not print children of duplicates, otherwise add it to the "list"
	if [[ "$dupe" ]]; then return; fi

	pkgs=${pkgs}${root}:
	prefix="${prefix}${T1}"
	for pkg in ${dep[$root]:1}; do
		walk_deps "$pkg" $level $((++i == num[$root])) "$prefix"
	done
}

parse_deps "$package"