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> Warning
> This program is experimental and its interface is subject to change.

# Name

`nix` - a tool for reproducible and declarative configuration management

# Synopsis

`nix` [option...] subcommand

where subcommand is one of the following:

Help commands:

- `nix help` - show help about `nix` or a particular subcommand
- `nix help-stores` - show help about store types and their settings

Main commands:

- `nix build` - build a derivation or fetch a store path
- `nix develop` - run a bash shell that provides the build environment of a derivation
- `nix flake` - manage Nix flakes
- `nix profile` - manage Nix profiles
- `nix run` - run a Nix application
- `nix search` - search for packages

Main commands:

- `nix repl` - start an interactive environment for evaluating Nix expressions

Infrequently used commands:

- `nix bundle` - bundle an application so that it works outside of the Nix store
- `nix copy` - copy paths between Nix stores
- `nix edit` - open the Nix expression of a Nix package in $EDITOR
- `nix eval` - evaluate a Nix expression
- `nix fmt` - reformat your code in the standard style
- `nix formatter` - build or run the formatter
- `nix log` - show the build log of the specified packages or paths, if available
- `nix path-info` - query information about store paths
- `nix registry` - manage the flake registry
- `nix why-depends` - show why a package has another package in its closure

Utility/scripting commands:

- `nix config` - manipulate the Nix configuration
- `nix daemon` - daemon to perform store operations on behalf of non-root clients
- `nix derivation` - Work with derivations, Nix's notion of a build plan.
- `nix env` - manipulate the process environment
- `nix hash` - compute and convert cryptographic hashes
- `nix key` - generate and convert Nix signing keys
- `nix nar` - create or inspect NAR files
- `nix print-dev-env` - print shell code that can be sourced by bash to reproduce the build environment of a derivation
- `nix realisation` - manipulate a Nix realisation
- `nix store` - manipulate a Nix store

Commands for upgrading or troubleshooting your Nix installation:

- `nix upgrade-nix` - upgrade Nix to the latest stable version

# Examples

- Create a new flake:

      # nix flake new hello
      # cd hello

- Build the flake in the current directory:

      # nix build
      # ./result/bin/hello
      Hello, world!

- Run the flake in the current directory:

      # nix run
      Hello, world!

- Start a development shell for hacking on this flake:

      # nix develop
      # unpackPhase
      # cd hello-*
      # configurePhase
      # buildPhase
      # ./hello
      Hello, world!
      # installPhase
      # ../outputs/out/bin/hello
      Hello, world!

# Description

Nix is a tool for building software, configurations and other artifacts in a reproducible and declarative way. For more information, see the Nix homepage or the Nix manual.

# Installables

> Warning
> Installables are part of the unstable `nix-command` experimental feature, and subject to change without notice.

Many `nix` subcommands operate on one or more installables. These are command line arguments that represent something that can be realised in the Nix store.

The following types of installable are supported by most commands:

- Flake output attribute (experimental)
  - This is the default
- Store path
  - This is assumed if the argument is a Nix store path or a symlink to a Nix store path
- Nix file, optionally qualified by an attribute path
  - Specified with `--file`/`-f`
- Nix expression, optionally qualified by an attribute path
  - Specified with `--expr`

For most commands, if no installable is specified, `.` is assumed. That is, Nix will operate on the default flake output attribute of the flake in the current directory.

### Flake output attribute

> Warning
> Flake output attribute installables depend on both the `flakes` and `nix-command` experimental features, and subject to change without notice.

Example: `nixpkgs#hello`

These have the form flakeref[`#`attrpath], where flakeref is a flake reference and attrpath is an optional attribute path. For more information on flakes, see the `nix flake` manual page. Flake references are most commonly a flake identifier in the flake registry (e.g. `nixpkgs`), or a raw path (e.g. `/path/to/my-flake` or `.` or `../foo`), or a full URL (e.g. `github:nixos/nixpkgs` or `path:.`)

When the flake reference is a raw path (a path without any URL scheme), it is interpreted as a `path:` or `git+file:` url in the following way:

- If the path is within a Git repository, then the url will be of the form `git+file://[GIT_REPO_ROOT]?dir=[RELATIVE_FLAKE_DIR_PATH]` where `GIT_REPO_ROOT` is the path to the root of the git repository, and `RELATIVE_FLAKE_DIR_PATH` is the path (relative to the directory root) of the closest parent of the given path that contains a `flake.nix` within the git repository. If no such directory exists, then Nix will error-out.

  Note that the search will only include files indexed by git. In particular, files which are matched by `.gitignore` or have never been `git add`-ed will not be available in the flake. If this is undesirable, specify `path:<directory>` explicitly;

  For example, if `/foo/bar` is a git repository with the following structure:

      .
      └── baz
          ├── blah
          │   └── file.txt
          └── flake.nix

  Then `/foo/bar/baz/blah` will resolve to `git+file:///foo/bar?dir=baz`

- If the supplied path is not a git repository, then the url will have the form `path:FLAKE_DIR_PATH` where `FLAKE_DIR_PATH` is the closest parent of the supplied path that contains a `flake.nix` file (within the same file-system). If no such directory exists, then Nix will error-out.

  For example, if `/foo/bar/flake.nix` exists, then `/foo/bar/baz/` will resolve to `path:/foo/bar`

If attrpath is omitted, Nix tries some default values; for most subcommands, the default is `packages.`system`.default` (e.g. `packages.x86_64-linux.default`), but some subcommands have other defaults. If attrpath is specified, attrpath is interpreted as relative to one or more prefixes; for most subcommands, these are `packages.`system, `legacyPackages.*system*` and the empty prefix. Thus, on `x86_64-linux` `nix build nixpkgs#hello` will try to build the attributes `packages.x86_64-linux.hello`, `legacyPackages.x86_64-linux.hello` and `hello`.

If attrpath begins with `.` then no prefixes or defaults are attempted. This allows the form flakeref[`#.`attrpath], such as `github:NixOS/nixpkgs#.lib.fakeSha256` to avoid a search of `packages.*system*.lib.fakeSha256`

### Store path

Example: `/nix/store/v5sv61sszx301i0x6xysaqzla09nksnd-hello-2.10`

These are paths inside the Nix store, or symlinks that resolve to a path in the Nix store.

A store derivation is also addressed by store path.

Example: `/nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv`

If you want to refer to an output path of that store derivation, add the output name preceded by a caret (`^`).

Example: `/nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv^out`

All outputs can be referred to at once with the special syntax `^*`.

Example: `/nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv^*`

### Nix file

Example: `--file /path/to/nixpkgs hello`

When the option `-f` / `--file` path [attrpath...] is given, installables are interpreted as the value of the expression in the Nix file at path. If attribute paths are provided, commands will operate on the corresponding values accessible at these paths. The Nix expression in that file, or any selected attribute, must evaluate to a derivation.

### Nix expression

Example: `--expr 'import <nixpkgs> {}' hello`

When the option `--expr` expression [attrpath...] is given, installables are interpreted as the value of the of the Nix expression. If attribute paths are provided, commands will operate on the corresponding values accessible at these paths. The Nix expression, or any selected attribute, must evaluate to a derivation.

You may need to specify `--impure` if the expression references impure inputs (such as `<nixpkgs>`).

## Derivation output selection

Derivations can have multiple outputs, each corresponding to a different store path. For instance, a package can have a `bin` output that contains programs, and a `dev` output that provides development artifacts like C/C++ header files. The outputs on which `nix` commands operate are determined as follows:

- You can explicitly specify the desired outputs using the syntax installable`^`output1`,`...`,`outputN — that is, a caret followed immediately by a comma-separated list of derivation outputs to select. For installables specified as Flake output attributes or Store paths, the output is specified in the same argument:

  For example, you can obtain the `dev` and `static` outputs of the `glibc` package:

      # nix build 'nixpkgs#glibc^dev,static'
      # ls ./result-dev/include/ ./result-static/lib/
      …

  and likewise, using a store path to a "drv" file to specify the derivation:

      # nix build '/nix/store/gzaflydcr6sb3567hap9q6srzx8ggdgg-glibc-2.33-78.drv^dev,static'
      …

  For `--expr` and `-f`/`--file`, the derivation output is specified as part of the attribute path:

      $ nix build -f '<nixpkgs>' 'glibc^dev,static'
      $ nix build --impure --expr 'import <nixpkgs> { }' 'glibc^dev,static'

  This syntax is the same even if the actual attribute path is empty:

      $ nix build --impure --expr 'let pkgs = import <nixpkgs> { }; in pkgs.glibc' '^dev,static'

- You can also specify that all outputs should be used using the syntax installable`^*`. For example, the following shows the size of all outputs of the `glibc` package in the binary cache:

      # nix path-info --closure-size --eval-store auto --store https://cache.nixos.org 'nixpkgs#glibc^*'
      /nix/store/g02b1lpbddhymmcjb923kf0l7s9nww58-glibc-2.33-123                 33208200
      /nix/store/851dp95qqiisjifi639r0zzg5l465ny4-glibc-2.33-123-bin             36142896
      /nix/store/kdgs3q6r7xdff1p7a9hnjr43xw2404z7-glibc-2.33-123-debug          155787312
      /nix/store/n4xa8h6pbmqmwnq0mmsz08l38abb06zc-glibc-2.33-123-static          42488328
      /nix/store/q6580lr01jpcsqs4r5arlh4ki2c1m9rv-glibc-2.33-123-dev             44200560

  and likewise, using a store path to a "drv" file to specify the derivation:

      # nix path-info --closure-size '/nix/store/gzaflydcr6sb3567hap9q6srzx8ggdgg-glibc-2.33-78.drv^*'
      …

- If you didn't specify the desired outputs, but the derivation has an attribute `meta.outputsToInstall`, Nix will use those outputs. For example, since the package `nixpkgs#libxml2` has this attribute:

      # nix eval 'nixpkgs#libxml2.meta.outputsToInstall'
      [ "bin" "man" ]

  a command like `nix shell nixpkgs#libxml2` will provide only those two outputs by default.

  Note that a store derivation (given by its `.drv` file store path) doesn't have any attributes like `meta`, and thus this case doesn't apply to it.

- Otherwise, Nix will use all outputs of the derivation.

# Nix stores

Most `nix` subcommands operate on a Nix store. The various store types are documented in the Store Types section of the manual.

The same information is also available from the `nix help-stores` command.

# Shebang interpreter

The `nix` command can be used as a `#!` interpreter. Arguments to Nix can be passed on subsequent lines in the script.

Verbatim strings may be passed in double backtick (````) quotes. Sequences of n backticks of 3 or longer are parsed as n-1 literal backticks. A single space before the closing ```` is ignored if present.

`--file` and `--expr` resolve relative paths based on the script location.

Examples:

    #!/usr/bin/env nix
    #! nix shell --file ``<nixpkgs>`` hello cowsay --command bash

    hello | cowsay

or with flakes:

    #!/usr/bin/env nix
    #! nix shell nixpkgs#bash nixpkgs#hello nixpkgs#cowsay --command bash

    hello | cowsay

or with an expression:

    #! /usr/bin/env nix
    #! nix shell --impure --expr ``
    #! nix with (import (builtins.getFlake "nixpkgs") {});
    #! nix terraform.withPlugins (plugins: [ plugins.openstack ])
    #! nix ``
    #! nix --command bash

    terraform "$@"

or with cascading interpreters. Note that the `#! nix` lines don't need to follow after the first line, to accommodate other interpreters.

    #!/usr/bin/env nix
    //! ```cargo
    //! [dependencies]
    //! time = "0.1.25"
    //! ```
    /*
    #!nix shell nixpkgs#rustc nixpkgs#rust-script nixpkgs#cargo --command rust-script
    */
    fn main() {
        for argument in std::env::args().skip(1) {
            println!("{}", argument);
        };
        println!("{}", std::env::var("HOME").expect(""));
        println!("{}", time::now().rfc822z());
    }
    // vim: ft=rust

# Options

## Logging-related options

- `--debug`

  Set the logging verbosity level to 'debug'.

- `--log-format` format

  Set the format of log output; one of `raw`, `internal-json`, `bar` or `bar-with-logs`.

- `--print-build-logs` / `-L`

  Print full build logs on standard error.

- `--quiet`

  Decrease the logging verbosity level.

- `--verbose` / `-v`

  Increase the logging verbosity level.

## Miscellaneous global options

- `--help`

  Show usage information.

- `--offline`

  Disable substituters and consider all previously downloaded files up-to-date.

- `--option` name value

  Set the Nix configuration setting name to value (overriding `nix.conf`).

- `--refresh`

  Consider all previously downloaded files out-of-date.

- `--version`

  Show version information.

> Note

> See `man nix.conf` for overriding configuration settings with command line flags.