nix-shell -p nixUnstable
nix --version

nix shell
    github:edolstra/hello -c hello

nix build
    github:edolstra/dwarffs#checks.aarch64-linux.build
        extra flake-based syntax after #

    /path/to/my-flake#nixosConfigurations.container.config.system.build.toplevel
        https://www.tweag.io/blog/2020-07-31-nixos-flakes/
        here <container> is the name of configuration
        Note that "system.build.toplevel" is an internal NixOS option that evaluates to the "system" derivation
        that commands like nixos-rebuild, nixos-install and nixos-container build and activate.
        The symlink
            /run/current-system
        points to the output of this derivation.


nix registry
    add nixpkgs ~/my-nixpkgs
        add custom flakes registry
    add nixpkgs github:NixOS/nixpkgs/5272327b81ed355bbed5659b8d303cf2979b6953
        or pin it to the specific revision

nixos-rebuild
    switch --flake /path/to/my-flake#my-machine
    -v --flake .# switch

nixos-container
    update flake-test --flake /path/to/my-flake?rev=9190c396f4dcfc734e554768c53a81d1c231c6a7
    --no-allow-dirty

nix flake
    https://hydra.nixos.org/build/136801108/download/1/manual/command-ref/new-cli/nix3-flake.html
    init
        ... later
        git init && git add --all
        cat flake.nix

        # then 
        nix build [--override-inputs ...]
        # thich is exactly the same as
        nix build .#defaultPackages.x86_64-[linux|darwin]
        # then
        nix shell .#defaultPackages.x86_64-linux
        # then
        hello
        # or
        nix run [git+ssh://git@example.com/you/hello-flake.git]
        nix run github:balsoft/hello-flake

    info
        display "description string"

    list-inputs
        github:edolstra/dwarffs
            display flake inputs

    show
        github:edolstra/dwarffs
        or
        github:NixOS/hydra
            display flake outputs

    show templates
        list available templates
            https://github.com/NixOS/templates

    update
        --recreate-lock-file
            !!! really updates all the stuff
            https://www.reddit.com/r/NixOS/comments/k05pxk/nixosrebuild_upgrade_does_not_work_if_flakelock/
        --update-input home-manager
            update specific input (home-manager)
        --commit-lock-file
            commits the new lock file with a commit message that records the input change.
        --override-input <input-name> /path/to/my/<input-name>

    check -L
        --show-trace