# Name `nix-build` - build a Nix expression # Synopsis `nix-build` [*paths…*] [`--arg` *name* *value*] [`--argstr` *name* *value*] [{`--attr` | `-A`} *attrPath*] [`--no-out-link`] [`--dry-run`] [{`--out-link` | `-o`} *outlink*] # Description The `nix-build` command builds the derivations described by the Nix expressions in *paths*. If the build succeeds, it places a symlink to the result in the current directory. The symlink is called `result`. If there are multiple Nix expressions, or the Nix expressions evaluate to multiple derivations, multiple sequentially numbered symlinks are created (`result`, `result-2`, and so on). If no *paths* are specified, then `nix-build` will use `default.nix` in the current directory, if it exists. If an element of *paths* starts with `http://` or `https://`, it is interpreted as the URL of a tarball that will be downloaded and unpacked to a temporary location. The tarball must include a single top-level directory containing at least a file named `default.nix`. `nix-build` is essentially a wrapper around [`nix-instantiate`](nix-instantiate.md) (to translate a high-level Nix expression to a low-level store derivation) and [`nix-store --realise`](nix-store.md#operation---realise) (to build the store derivation). > **Warning** > > The result of the build is automatically registered as a root of the > Nix garbage collector. This root disappears automatically when the > `result` symlink is deleted or renamed. So don’t rename the symlink. # Options All options not listed here are passed to `nix-store --realise`, except for `--arg` and `--attr` / `-A` which are passed to `nix-instantiate`. - `--no-out-link` Do not create a symlink to the output path. Note that as a result the output does not become a root of the garbage collector, and so might be deleted by `nix-store --gc`. - `--dry-run` Show what store paths would be built or downloaded. - `--out-link` / `-o` *outlink* Change the name of the symlink to the output path created from `result` to *outlink*. The following common options are supported: # Examples ```console $ nix-build '' -A firefox store derivation is /nix/store/qybprl8sz2lc...-firefox-1.5.0.7.drv /nix/store/d18hyl92g30l...-firefox-1.5.0.7 $ ls -l result lrwxrwxrwx ... result -> /nix/store/d18hyl92g30l...-firefox-1.5.0.7 $ ls ./result/bin/ firefox firefox-config ``` If a derivation has multiple outputs, `nix-build` will build the default (first) output. You can also build all outputs: ```console $ nix-build '' -A openssl.all ``` This will create a symlink for each output named `result-outputname`. The suffix is omitted if the output name is `out`. So if `openssl` has outputs `out`, `bin` and `man`, `nix-build` will create symlinks `result`, `result-bin` and `result-man`. It’s also possible to build a specific output: ```console $ nix-build '' -A openssl.man ``` This will create a symlink `result-man`. Build a Nix expression given on the command line: ```console $ nix-build -E 'with import { }; runCommand "foo" { } "echo bar > $out"' $ cat ./result bar ``` Build the GNU Hello package from the latest revision of the master branch of Nixpkgs: ```console $ nix-build https://github.com/NixOS/nixpkgs/archive/master.tar.gz -A hello ```