Open shell in current Flake to evaluate a variable:
nix repl .
For example evaluate a nixosConfiguration variable:
nix eval .#nixosConfigurations.<hostname>.config.networking.firewall.enable
Run a shell with a specific package:
# Open a new shell:
nix-shell -p octodns
# Run a specific command:
nix-shell -p octodns --run "octodns-sync --config-file=./config/production.yaml"