forked from lix-project/lix
200 lines
7 KiB
Markdown
200 lines
7 KiB
Markdown
R""(
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# Examples
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* Create a new flake:
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```console
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# nix flake new hello
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# cd hello
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```
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* Build the flake in the current directory:
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```console
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# nix build
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# ./result/bin/hello
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Hello, world!
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```
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* Run the flake in the current directory:
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```console
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# nix run
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Hello, world!
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```
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* Start a development shell for hacking on this flake:
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```console
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# nix develop
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# unpackPhase
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# cd hello-*
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# configurePhase
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# buildPhase
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# ./hello
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Hello, world!
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# installPhase
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# ../outputs/out/bin/hello
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Hello, world!
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```
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# Description
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Nix is a tool for building software, configurations and other
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artifacts in a reproducible and declarative way. For more information,
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see the [Nix homepage](https://nixos.org/) or the [Nix
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manual](https://nixos.org/manual/nix/stable/).
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# Installables
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Many `nix` subcommands operate on one or more *installables*. These are
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command line arguments that represent something that can be built in
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the Nix store. Here are the recognised types of installables:
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* **Flake output attributes**: `nixpkgs#hello`
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These have the form *flakeref*[`#`*attrpath*], where *flakeref* is a
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flake reference and *attrpath* is an optional attribute path. For
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more information on flakes, see [the `nix flake` manual
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page](./nix3-flake.md). Flake references are most commonly a flake
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identifier in the flake registry (e.g. `nixpkgs`), or a raw path
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(e.g. `/path/to/my-flake` or `.` or `../foo`), or a full URL
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(e.g. `github:nixos/nixpkgs` or `path:.`)
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When the flake reference is a raw path (a path without any URL
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scheme), it is interpreted as a `path:` or `git+file:` url in the following
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way:
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- If the path is within a Git repository, then the url will be of the form
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`git+file://[GIT_REPO_ROOT]?dir=[RELATIVE_FLAKE_DIR_PATH]`
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where `GIT_REPO_ROOT` is the path to the root of the git repository,
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and `RELATIVE_FLAKE_DIR_PATH` is the path (relative to the directory
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root) of the closest parent of the given path that contains a `flake.nix` within
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the git repository.
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If no such directory exists, then Nix will error-out.
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Note that the search will only include files indexed by git. In particular, files
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which are matched by `.gitignore` or have never been `git add`-ed will not be
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available in the flake. If this is undesirable, specify `path:<directory>` explicitly;
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For example, if `/foo/bar` is a git repository with the following structure:
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```
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.
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└── baz
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├── blah
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│ └── file.txt
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└── flake.nix
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```
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Then `/foo/bar/baz/blah` will resolve to `git+file:///foo/bar?dir=baz`
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- If the supplied path is not a git repository, then the url will have the form
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`path:FLAKE_DIR_PATH` where `FLAKE_DIR_PATH` is the closest parent
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of the supplied path that contains a `flake.nix` file (within the same file-system).
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If no such directory exists, then Nix will error-out.
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For example, if `/foo/bar/flake.nix` exists, then `/foo/bar/baz/` will resolve to
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`path:/foo/bar`
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If *attrpath* is omitted, Nix tries some default values; for most
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subcommands, the default is `packages.`*system*`.default`
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(e.g. `packages.x86_64-linux.default`), but some subcommands have
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other defaults. If *attrpath* *is* specified, *attrpath* is
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interpreted as relative to one or more prefixes; for most
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subcommands, these are `packages.`*system*,
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`legacyPackages.*system*` and the empty prefix. Thus, on
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`x86_64-linux` `nix build nixpkgs#hello` will try to build the
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attributes `packages.x86_64-linux.hello`,
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`legacyPackages.x86_64-linux.hello` and `hello`.
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* **Store paths**: `/nix/store/v5sv61sszx301i0x6xysaqzla09nksnd-hello-2.10`
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These are paths inside the Nix store, or symlinks that resolve to a
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path in the Nix store.
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* **Store derivations**: `/nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv`
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Store derivations are store paths with extension `.drv` and are a
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low-level representation of a build-time dependency graph used
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internally by Nix. By default, if you pass a store derivation to a
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`nix` subcommand, it will operate on the *output paths* of the
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derivation. For example, `nix path-info` prints information about
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the output paths:
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```console
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# nix path-info --json /nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv
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[{"path":"/nix/store/v5sv61sszx301i0x6xysaqzla09nksnd-hello-2.10",…}]
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```
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If you want to operate on the store derivation itself, pass the
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`--derivation` flag.
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* **Nix attributes**: `--file /path/to/nixpkgs hello`
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When the `-f` / `--file` *path* option is given, installables are
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interpreted as attribute paths referencing a value returned by
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evaluating the Nix file *path*.
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* **Nix expressions**: `--expr '(import <nixpkgs> {}).hello.overrideDerivation (prev: { name = "my-hello"; })'`.
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When the `--expr` option is given, all installables are interpreted
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as Nix expressions. You may need to specify `--impure` if the
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expression references impure inputs (such as `<nixpkgs>`).
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For most commands, if no installable is specified, the default is `.`,
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i.e. Nix will operate on the default flake output attribute of the
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flake in the current directory.
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## Derivation output selection
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Derivations can have multiple outputs, each corresponding to a
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different store path. For instance, a package can have a `bin` output
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that contains programs, and a `dev` output that provides development
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artifacts like C/C++ header files. The outputs on which `nix` commands
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operate are determined as follows:
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* You can explicitly specify the desired outputs using the syntax
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*installable*`^`*output1*`,`*...*`,`*outputN*. For example, you can
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obtain the `dev` and `static` outputs of the `glibc` package:
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```console
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# nix build 'nixpkgs#glibc^dev,static'
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# ls ./result-dev/include/ ./result-static/lib/
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…
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```
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* You can also specify that *all* outputs should be used using the
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syntax *installable*`^*`. For example, the following shows the size
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of all outputs of the `glibc` package in the binary cache:
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```console
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# nix path-info -S --eval-store auto --store https://cache.nixos.org 'nixpkgs#glibc^*'
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/nix/store/g02b1lpbddhymmcjb923kf0l7s9nww58-glibc-2.33-123 33208200
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/nix/store/851dp95qqiisjifi639r0zzg5l465ny4-glibc-2.33-123-bin 36142896
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/nix/store/kdgs3q6r7xdff1p7a9hnjr43xw2404z7-glibc-2.33-123-debug 155787312
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/nix/store/n4xa8h6pbmqmwnq0mmsz08l38abb06zc-glibc-2.33-123-static 42488328
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/nix/store/q6580lr01jpcsqs4r5arlh4ki2c1m9rv-glibc-2.33-123-dev 44200560
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```
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* If you didn't specify the desired outputs, but the derivation has an
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attribute `meta.outputsToInstall`, Nix will use those outputs. For
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example, since the package `nixpkgs#libxml2` has this attribute:
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```console
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# nix eval 'nixpkgs#libxml2.meta.outputsToInstall'
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[ "bin" "man" ]
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```
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a command like `nix shell nixpkgs#libxml2` will provide only those
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two outputs by default.
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* Otherwise, Nix will use all outputs of the derivation.
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# Nix stores
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Most `nix` subcommands operate on a *Nix store*.
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TODO: list store types, options
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)""
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