Bootstrapping a chroot on the Steam Deck

steamdeck-chroot.sh

#!/bin/bash
# Largely adapted from https://www.reddit.com/r/SteamDeck/comments/xgslv9/howto_installing_pacman_packages_in_userspace/

if [ -z "$1" ] || [ -z "$2" ]; then
    echo "Usage: $0 <chrootdir> <command>"
    echo ""
    echo "Possible commands:"
    echo "  init           - initialize an empty directory as a chroot"
    echo "  pacman [args]  - use the host pacman to manage packages within the chroot"
    echo "  chroot         - calls arch-chroot on the chroot"
    echo "  venv           - runs an interactive host shell using the chroot's binaries and libraries"
    echo "  run <command>  - runs the given command on the host using the chroot's binaries and libaries"
    exit 1
fi

if [ "$EUID" -ne 0 ] && [ "$2" != "venv" ] && [ "$2" != "run" ]; then
    echo "Please run as root"
    exit 2
fi

USERROOT="$1"
if [ ! -d "$USERROOT" ]; then
    echo "Root dir doesn't exist"
    exit 3
fi

PACMAN_CONF="$USERROOT/etc/pacman.conf"
GPGDIR="$USERROOT/etc/pacman.d/gnupg"
DBPATH="$USERROOT/usr/lib/holo/pacmandb"
CACHEDIR="$USERROOT/var/cache/pacman/pkg"

mkdir -p "$USERROOT/etc"
mkdir -p "$GPGDIR"
mkdir -p "$USERROOT/usr/lib/holo/pacmandb"
mkdir -p "$USERROOT/var/lib/pacman"
mkdir -p "$CACHEDIR"

if [ "$2" == "init" ]; then
    cp /etc/pacman.conf "$USERROOT/etc/pacman.conf"
    sed -i 's/^CheckSpace/#CheckSpace/g' "$USERROOT/etc/pacman.conf"
    cp /etc/pacman.d/mirrorlist "$USERROOT/etc/pacman.d"
    pacman-key --gpgdir "$GPGDIR" --conf "$PACMAN_CONF" --init
    pacman-key --gpgdir "$GPGDIR" --conf "$PACMAN_CONF" --populate
elif [ "$2" == "pacman" ]; then
    shift 2
    pacman -r "$USERROOT" --gpgdir "$GPGDIR" --dbpath "$DBPATH" --cachedir "$CACHEDIR" "$@"
elif [ "$2" == "chroot" ]; then
    arch-chroot "$USERROOT"
elif [ "$2" == "venv" ]; then
    export PATH=$PATH:"$USERROOT/usr/bin"
    export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:"$USERROOT/lib":"$USERROOT/lib32"
    echo "Entering venv..."
    exec bash -i
elif [ "$2" == "run" ]; then
    shift 2
    export PATH=$PATH:"$USERROOT/usr/bin"
    export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:"$USERROOT/lib":"$USERROOT/lib32"
    cmd="$1"
    shift
    "$cmd" "$@"
fi