Gets the currently booted nixos generation

current_booted_gen.sh

#!/usr/bin/env bash
# based on https://github.com/NixOS/nixpkgs/issues/163936#issuecomment-1069797072
resolvesTo=`cat /proc/cmdline | sed -n 's/^.*init=\(.*\)\/init.*$/\1/p'`
directory="/nix/var/nix/profiles/"

for symlink in "$directory"/*; do
  if [ -L "$symlink" ]; then
    resolved_path=$(readlink -f "$symlink")

    if [ "$resolved_path" == "$resolvesTo" ]; then
      echo "Current booted generation:" `basename $symlink`
    fi
  fi
done