Install and run nix from the home directory using proot

homedir_install.sh

#!/bin/bash

proot_url=https://proot.gitlab.io/proot/bin/proot
bindir=${XDG_DATA_HOME:-$HOME/.local/share}/../bin
scriptdir="$(cd "$(dirname "$0")" && pwd -P)"
PATH=$bindir:$PATH

set -euo pipefail

mkdir -p "$bindir"
if ! command -v proot >/dev/null 2>&1; then
    wget -O "$bindir/proot" "$proot_url"
    chmod +x "$bindir/proot"
fi

if ! [ -e ~/.config/nix/nix.conf ]; then
    mkdir -p ~/.config/nix
    cat >~/.config/nix/nix.conf <<END
experimental-features = nix-command flakes
sandbox = false
END
fi

unset NIX_PATH

mkdir -p ~/.nix
proot -b "$HOME/.nix:/nix" bash -c "curl -L https://nixos.org/nix/install | sh"

{
    echo "#!/usr/bin/env bash"
    echo
    echo "proot -b \"\$HOME/.nix:/nix\" bash -c 'for i in ~/.nix-profile/etc/profile.d/*.sh; do if [ -e "\$i" ]; then . "\$i"; fi; done && \"\$@\"' - \"\$@\""
} >"$bindir/nixrun"
chmod +x "$bindir/nixrun"

cp -av "$scriptdir/nixwrap" "$bindir/nixwrap"
"$bindir/nixwrap"

nixwrap

#!/bin/bash

set -euo pipefail

scriptdir="$(cd "$(dirname "$0")" && pwd -P)"
PATH="$scriptdir:$PATH"

bins="$(mktemp -t "${0##*/}.XXXXXX")"
trap 'rm -f "$bins"' EXIT INT TERM
shims="$(mktemp -t "${0##*/}.XXXXXX")"
trap 'rm -f "$bins" "$shims"' EXIT INT TERM

if [ -L ~/.nix-profile ]; then
    nixrun find ~/.nix-profile/bin -type l -printf '%f\n' 2>/dev/null | sort >>"$bins" || :
fi
if [ -e ~/.nix/shims ]; then
    find ~/.nix/shims -type l -printf '%f\n' | sort >>"$shims" || :
fi

mkdir -p ~/.nix/shims
if ! [ -f ~/.nix/shims/nixrun-wrap ]; then
    rm -f ~/.nix/shims/nixrun-wrap
    cat >~/.nix/shims/nixrun-wrap <<END
#!/bin/sh

nixrun "\$(basename "\$0")" "\$@"
END
    chmod +x ~/.nix/shims/nixrun-wrap
fi
comm -13 "$bins" "$shims" | sed -e "s#^#$HOME/.nix/shims/#" | tr '\n' '\0' | xargs -0 rm -fv
comm -23 "$bins" "$shims" | tr '\n' '\0' | xargs -0 -I "{}" ln -sfv ./nixrun-wrap ~/.nix/shims/"{}"