nix build

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

# Name

`nix build` - build a derivation or fetch a store path

# Synopsis

`nix build` [option...] installables...

# Examples

- Build the default package from the flake in the current directory:

      # nix build

- Build and run GNU Hello from the `nixpkgs` flake:

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

- Build GNU Hello and Cowsay, leaving two result symlinks:

      # nix build nixpkgs#hello nixpkgs#cowsay
      # ls -l result*
      lrwxrwxrwx 1 … result -> /nix/store/v5sv61sszx301i0x6xysaqzla09nksnd-hello-2.10
      lrwxrwxrwx 1 … result-1 -> /nix/store/rkfrm0z6x6jmi7d3gsmma4j53h15mg33-cowsay-3.03+dfsg2

- Build a specific output:

      # nix build nixpkgs#glibc.dev
      # ls -ld ./result-dev
      lrwxrwxrwx 1 … ./result-dev -> /nix/store/dkm3gwl0xrx0wrw6zi5x3px3lpgjhlw4-glibc-2.32-dev

- Build attribute `build.x86_64-linux` from (non-flake) Nix expression `release.nix`:

      # nix build -f release.nix build.x86_64-linux

- Build a NixOS system configuration from a flake, and make a profile point to the result:

      # nix build --profile /nix/var/nix/profiles/system \
          ~/my-configurations#nixosConfigurations.machine.config.system.build.toplevel

  (This is essentially what `nixos-rebuild` does.)

- Build an expression specified on the command line:

      # nix build --impure --expr \
          'with import <nixpkgs> {};
           runCommand "foo" {
             buildInputs = [ hello ];
           }
           "hello > $out"'
      # cat ./result
      Hello, world!

  Note that `--impure` is needed because we're using `<nixpkgs>`, which relies on the `$NIX_PATH` environment variable.

- Fetch a store path from the configured substituters, if it doesn't already exist:

      # nix build /nix/store/rkfrm0z6x6jmi7d3gsmma4j53h15mg33-cowsay-3.03+dfsg2

# Description

`nix build` builds the specified installables. Installables that resolve to derivations are built (or substituted if possible). Store path installables are substituted.

Unless `--no-link` is specified, after a successful build, it creates symlinks to the store paths of the installables. These symlinks have the prefix `./result` by default; this can be overridden using the `--out-link` option. Each symlink has a suffix `-<N>-<outname>`, where N is the index of the installable (with the left-most installable having index 0), and outname is the symbolic derivation output name (e.g. `bin`, `dev` or `lib`). `-<N>` is omitted if N = 0, and `-<outname>` is omitted if outname = `out` (denoting the default output).

# Options

- `--dry-run`
  Show what this command would do without doing it.

- `--json`
  Produce output in JSON format, suitable for consumption by another program.

- `--no-link`
  Do not create symlinks to the build results.

- `--out-link` / `-o` path
  Use path as prefix for the symlinks to the build results. It defaults to `result`.

- `--profile` path
  The profile to update.

- `--rebuild`
  Rebuild an already built package and compare the result to the existing store paths.

Common evaluation options:

- `--arg` name expr
  Pass the value expr as the argument name to Nix functions.

- `--argstr` name string
  Pass the string string as the argument name to Nix functions.

- `--eval-store` store-url
  The Nix store to use for evaluations.

- `--impure`
  Allow access to mutable paths and repositories.

- `--include` / `-I` path
  Add path to the list of locations used to look up `<...>` file names.

- `--override-flake` original-ref resolved-ref
  Override the flake registries, redirecting original-ref to resolved-ref.

Common flake-related options:

- `--commit-lock-file`
  Commit changes to the flake's lock file.

- `--inputs-from` flake-url
  Use the inputs of the specified flake as registry entries.

- `--no-registries`
  Don't allow lookups in the flake registries. This option is deprecated; use `--no-use-registries`.

- `--no-update-lock-file`
  Do not allow any updates to the flake's lock file.

- `--no-write-lock-file`
  Do not write the flake's newly generated lock file.

- `--override-input` input-path flake-url
  Override a specific flake input (e.g. `dwarffs/nixpkgs`). This implies `--no-write-lock-file`.

- `--recreate-lock-file`
  Recreate the flake's lock file from scratch.

- `--update-input` input-path
  Update a specific flake input (ignoring its previous entry in the lock file).

Options that change the interpretation of installables:

- `--derivation`
  Operate on the store derivation rather than its outputs.

- `--expr` expr
  Interpret installables as attribute paths relative to the Nix expression expr.

- `--file` / `-f` file
  Interpret installables as attribute paths relative to the Nix expression stored in file. If file is the character -, then a Nix expression will be read from standard input.