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91 lines
3.4 KiB
Markdown
91 lines
3.4 KiB
Markdown
# Usage of the New CLI
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Once you have enabled the `nix-command` and `flakes` features, you can start using the new generation Nix command-line tools provided by [New Nix Commands][New Nix Commands].
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In this section, we will focus on two commands: `nix shell` and `nix run`.
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Other important commands like `nix build` will be discussed in detail in [`nix develop` & `pkgs.mkShell`](/development/intro.md)
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## `nix shell`
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The `nix shell` command allows you to enter an environment with the specified Nix package and opens an interactive shell within that environment:
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```shell
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# hello is not available
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› hello
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hello: command not found
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# Enter an environment with the 'hello' and `cowsay` package
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› nix shell nixpkgs#hello nixpkgs#cowsay
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# hello is now available
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› hello
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Hello, world!
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# ponysay is also available
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› cowsay "Hello, world!"
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_______
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< hello >
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-------
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\ ^__^
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\ (oo)\_______
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(__)\ )\/\
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||----w |
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```
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## `nix run`
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On the other hand, `nix run` creates an environment with the specified Nix package and directly runs that package within the environment (without installing it into the system environment):
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```shell
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# hello is not available
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› hello
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hello: command not found
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# Create an environment with the 'hello' package and run it
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› nix run nixpkgs#hello
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Hello, world!
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```
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Since `nix run` directly executes the Nix package, the package specified as the argument must generate an executable program.
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According to the `nix run --help` documentation, `nix run` executes the command `<out>/bin/<name>`, where `<out>` is the root directory of the derivation and `<name>` is selected in the following order:
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- The `meta.mainProgram` attribute of the derivation
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- The `pname` attribute of the derivation
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- The content of the `name` attribute of the derivation with the version number removed
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For example, in the case of the 'hello' package we tested earlier, `nix run` actually executes the program `$out/bin/hello`.
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Here are two more examples with detailed explanations of the relevant parameters:
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```bash
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# Explanation of the command:
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# `nixpkgs#ponysay` means the 'ponysay' package in the 'nixpkgs' flake.
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# `nixpkgs` is a flake registry id, and Nix will find the corresponding GitHub repository address
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# from <https://github.com/NixOS/flake-registry/blob/master/flake-registry.json>.
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# Therefore, this command creates a new environment, installs, and runs the 'ponysay' package provided by the 'nixpkgs' flake.
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# Note: It has been mentioned earlier that a Nix package is one of the outputs of a flake.
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echo "Hello Nix" | nix run "nixpkgs#ponysay"
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# This command has the same effect as the previous one, but it uses the complete flake URI instead of the flake registry id.
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echo "Hello Nix" | nix run "github:NixOS/nixpkgs/nixos-unstable#ponysay"
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```
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## Common Use Cases for `nix run` and `nix shell`
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These commands are commonly used for running programs temporarily. For example, if I want to clone my configuration repository using Git on a new NixOS host without Git installed, I can use the following command:
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```bash
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nix run nixpkgs#git clone git@github.com:ryan4yin/nix-config.git
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```
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Alternatively, I can use `nix shell` to enter an environment with Git and then run the `git clone` command:
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```bash
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nix shell nixpkgs#git
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git clone git@github.com:ryan4yin/nix-config.git
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```
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[New Nix Commands]: https://nixos.org/manual/nix/stable/command-ref/new-cli/nix.html
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