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https://github.com/ryan4yin/nixos-and-flakes-book
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290 lines
10 KiB
Markdown
290 lines
10 KiB
Markdown
## Development Environments on NixOS
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NixOS's reproducibility makes it ideal for building development environments. However, if you're used to other distros, you may encounter problems because NixOS has its own logic. We'll explain this briefly below.
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On NixOS, it's recommended to only install common tools in the global environment, such as `git`, `vim`, `emacs`, `tmux`, `zsh`, etc. The development environment of each language should be an independent environment for each project.
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You should NOT install the development environment of each language in the global environment. The project environment should be completely isolated from each other and will not affect each other.
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In the following sections, we'll introduce how the development environment works in NixOS.
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### Creating a Development Environment
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We can create a development environment using `pkgs.mkShell { ... }` and open an interactive Bash shell of this development environment using `nix develop`.
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To see how `pkgs.mkShell` works, let's take a look at [its source code](https://github.com/NixOS/nixpkgs/blob/master/pkgs/build-support/mkshell/default.nix).
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```nix
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{ lib, stdenv, buildEnv }:
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# A special kind of derivation that is only meant to be consumed by the
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# nix-shell.
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{ name ? "nix-shell"
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, # a list of packages to add to the shell environment
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packages ? [ ]
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, # propagate all the inputs from the given derivations
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inputsFrom ? [ ]
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, buildInputs ? [ ]
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, nativeBuildInputs ? [ ]
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, propagatedBuildInputs ? [ ]
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, propagatedNativeBuildInputs ? [ ]
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, ...
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}@attrs:
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let
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mergeInputs = name:
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(attrs.${name} or [ ]) ++
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(lib.subtractLists inputsFrom (lib.flatten (lib.catAttrs name inputsFrom)));
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rest = builtins.removeAttrs attrs [
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"name"
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"packages"
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"inputsFrom"
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"buildInputs"
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"nativeBuildInputs"
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"propagatedBuildInputs"
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"propagatedNativeBuildInputs"
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"shellHook"
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];
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in
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stdenv.mkDerivation ({
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inherit name;
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buildInputs = mergeInputs "buildInputs";
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nativeBuildInputs = packages ++ (mergeInputs "nativeBuildInputs");
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propagatedBuildInputs = mergeInputs "propagatedBuildInputs";
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propagatedNativeBuildInputs = mergeInputs "propagatedNativeBuildInputs";
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shellHook = lib.concatStringsSep "\n" (lib.catAttrs "shellHook"
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(lib.reverseList inputsFrom ++ [ attrs ]));
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phases = [ "buildPhase" ];
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# ......
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# when distributed building is enabled, prefer to build locally
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preferLocalBuild = true;
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} // rest)
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```
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`pkgs.mkShell { ... }` is a special Derivation (Nix package). Its `name` `buildInputs` and other parameters are customizable, and `shellHook` is a special parameter that will be executed when `nix develop` enters the environment.
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Here is a `flake.nix` that defined a development environment with nodejs 18 installed:
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```nix
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{
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description = "A Nix-flake-based Node.js development environment";
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inputs = {
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nixpkgs.url = "github:nixos/nixpkgs/nixos-23.05";
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};
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outputs = { self , nixpkgs ,... }: let
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# system should match the system you are running on
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# system = "x86_64-linux";
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system = "x86_64-darwin";
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in {
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devShells."${system}".default = let
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pkgs = import nixpkgs {
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inherit system;
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overlays = [
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(self: super: rec {
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nodejs = super.nodejs-18_x;
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pnpm = super.nodePackages.pnpm;
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yarn = (super.yarn.override { inherit nodejs; });
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})
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];
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};
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in pkgs.mkShell {
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# create an environment with nodejs-18_x, pnpm, and yarn
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packages = with pkgs; [
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node2nix
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nodejs
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pnpm
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yarn
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];
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shellHook = ''
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echo "node `${pkgs.nodejs}/bin/node --version`"
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'';
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};
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};
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}
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```
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Create an empty folder, save the above configuration as `flake.nix`, and then execute `nix develop` (or more precisely, you can use `nix develop .#default`), you will find that you have entered a nodejs 18 development environment, you can use `node` `npm` `pnpm` `yarn` and other commands. And when you just entered, `shellHook` was also executed, outputting the current version of nodejs.
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### Enter the build environment of any Nix package
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Now let's take a look at `nix develop`, first read the help document output by `nix develop --help`:
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```
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Name
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nix develop - run a bash shell that provides the build environment of a derivation
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Synopsis
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nix develop [option...] installable
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# ......
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```
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It tells us that `nix develop` accepts a parameter `installable`, which means that we can enter the development environment of any installable Nix package through it, not just the environment created by `pkgs.mkShell`.
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By default, `nix develop` will try to use the following attributes in the flake outputs:
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- `devShells.<system>.default`
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- `packages.<system>.default`
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If we use `nix develop /path/to/flake#<name>` to specify the flake package address and flake output name, then `nix develop` will try the following attributes in the flake outputs:
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- `devShells.<system>.<name>`
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- `packages.<system>.<name>`
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- `legacyPackages.<system>.<name>`
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Now let's try it out. First, test it to confirm that We don't have `c++` `g++` and other compilation-related commands in the current environment:
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```shell
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ryan in 🌐 aquamarine in ~
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› c++
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c++: command not found
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ryan in 🌐 aquamarine in ~
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› g++
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g++: command not found
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```
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Then use `nix develop` to enter the build environment of the `hello` package in `nixpkgs`:
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```shell
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# login to the build environment of the package `hello`
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ryan in 🌐 aquamarine in ~
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› nix develop nixpkgs#hello
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ryan in 🌐 aquamarine in ~ via ❄️ impure (hello-2.12.1-env)
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› env | grep CXX
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CXX=g++
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ryan in 🌐 aquamarine in ~ via ❄️ impure (hello-2.12.1-env)
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› c++ --version
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g++ (GCC) 12.3.0
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Copyright (C) 2022 Free Software Foundation, Inc.
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This is free software; see the source for copying conditions. There is NO
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warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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ryan in 🌐 aquamarine in ~ via ❄️ impure (hello-2.12.1-env)
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› g++ --version
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g++ (GCC) 12.3.0
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Copyright (C) 2022 Free Software Foundation, Inc.
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This is free software; see the source for copying conditions. There is NO
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warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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```
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We can see that the `CXX` environment variable have been set, and the `c++` `g++` and other commands can be used normally now.
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In addition, we can also call every build phase of the `hello` package normally:
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> The default execution order of all build phases of a Nix package is: `$prePhases unpackPhase patchPhase $preConfigurePhases configurePhase $preBuildPhases buildPhase checkPhase $preInstallPhases installPhase fixupPhase installCheckPhase $preDistPhases distPhase $postPhases`
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```shell
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# unpack source code
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ryan in 🌐 aquamarine in /tmp/xxx via ❄️ impure (hello-2.12.1-env)
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› unpackPhase
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unpacking source archive /nix/store/pa10z4ngm0g83kx9mssrqzz30s84vq7k-hello-2.12.1.tar.gz
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source root is hello-2.12.1
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setting SOURCE_DATE_EPOCH to timestamp 1653865426 of file hello-2.12.1/ChangeLog
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ryan in 🌐 aquamarine in /tmp/xxx via ❄️ impure (hello-2.12.1-env)
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› ls
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hello-2.12.1
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ryan in 🌐 aquamarine in /tmp/xxx via ❄️ impure (hello-2.12.1-env)
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› cd hello-2.12.1/
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# generate Makefile
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ryan in 🌐 aquamarine in /tmp/xxx/hello-2.12.1 via ❄️ impure (hello-2.12.1-env)
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› configurePhase
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configure flags: --prefix=/tmp/xxx/outputs/out --prefix=/tmp/xxx/outputs/out
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checking for a BSD-compatible install... /nix/store/02dr9ymdqpkb75vf0v1z2l91z2q3izy9-coreutils-9.3/bin/install -c
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checking whether build environment is sane... yes
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checking for a thread-safe mkdir -p... /nix/store/02dr9ymdqpkb75vf0v1z2l91z2q3izy9-coreutils-9.3/bin/mkdir -p
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checking for gawk... gawk
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checking whether make sets $(MAKE)... yes
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checking whether make supports nested variables... yes
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checking for gcc... gcc
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# ......
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checking that generated files are newer than configure... done
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configure: creating ./config.status
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config.status: creating Makefile
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config.status: creating po/Makefile.in
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config.status: creating config.h
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config.status: config.h is unchanged
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config.status: executing depfiles commands
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config.status: executing po-directories commands
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config.status: creating po/POTFILES
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config.status: creating po/Makefile
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# build the package
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ryan in 🌐 aquamarine in /tmp/xxx/hello-2.12.1 via C v12.3.0-gcc via ❄️ impure (hello-2.12.1-env) took 2s
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› buildPhase
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build flags: SHELL=/run/current-system/sw/bin/bash
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make all-recursive
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make[1]: Entering directory '/tmp/xxx/hello-2.12.1'
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# ......
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ranlib lib/libhello.a
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gcc -g -O2 -o hello src/hello.o ./lib/libhello.a
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make[2]: Leaving directory '/tmp/xxx/hello-2.12.1'
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make[1]: Leaving directory '/tmp/xxx/hello-2.12.1'
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# run the built program
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ryan in 🌐 aquamarine in /tmp/xxx/hello-2.12.1 via C v12.3.0-gcc via ❄️ impure (hello-2.12.1-env)
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› ./hello
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Hello, world!
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```
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This usage is mainly used to debug the build process of a Nix package, or to execute some commands in the build environment of a Nix package.
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### `nix shell` & `nix run`
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Compare to `nix develop`, these two commands are much simpler and easier to understand.
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`nix shell` is used to enter an environment containing the specified Nix package and open an interactive shell for it:
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```shell
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# hello not exists
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› hello
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hello: command not found
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# enter an environment containing hello
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› nix shell nixpkgs#hello
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# now hello exists
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› hello
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Hello, world!
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```
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`nix run` is used to create an environment containing the specified installable and run the installable in it:
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```shell
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# hello not exists
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› hello
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hello: command not found
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# enter an environment containing hello 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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Because `nix run` will directly run the Nix package as an installable, the Nix package used as its parameter must be able to generate an executable program.
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According to the description of `nix run --help`, `nix run` will execute `<out>/bin/<name>`, where `<out>` is the root directory of a 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 name part of the value of the name attribute of the derivation.
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For instance, if name is set to `hello-1.10`, nix run will run $out/bin/hello.
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## References
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- [pkgs.mkShell - nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-pkgs-mkShell)
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- [A minimal nix-shell](https://fzakaria.com/2021/08/02/a-minimal-nix-shell.html)
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- [One too many shell, Clearing up with nix' shells nix shell and nix-shell - Yannik Sander](https://blog.ysndr.de/posts/guides/2021-12-01-nix-shells/)
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