fix/src/nix/build.md

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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 GNU Hello and print the resulting store path.

  # nix build nixpkgs#hello --print-out-paths
  /nix/store/v5sv61sszx301i0x6xysaqzla09nksnd-hello-2.10
  

• 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).

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