.\" -*- mode: troff; coding: utf-8 -*-
.TH "nix-build" "1" ""
.SH Name
\fCnix-build\fR - build a Nix expression
.SH Synopsis
\fCnix-build\fR [\fIpaths…\fR]
[\fC--arg\fR \fIname\fR \fIvalue\fR]
[\fC--argstr\fR \fIname\fR \fIvalue\fR]
[{\fC--attr\fR | \fC-A\fR} \fIattrPath\fR]
[\fC--no-out-link\fR]
[\fC--dry-run\fR]
[{\fC--out-link\fR | \fC-o\fR} \fIoutlink\fR]
.SH Description
The \fCnix-build\fR command builds the derivations described by the Nix
expressions in \fIpaths\fR. If the build succeeds, it places a symlink to
the result in the current directory. The symlink is called \fCresult\fR. If
there are multiple Nix expressions, or the Nix expressions evaluate to
multiple derivations, multiple sequentially numbered symlinks are
created (\fCresult\fR, \fCresult-2\fR, and so on).
.PP
If no \fIpaths\fR are specified, then \fCnix-build\fR will use \fCdefault.nix\fR in
the current directory, if it exists.
.PP
If an element of \fIpaths\fR starts with \fChttp://\fR or \fChttps://\fR, 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 \fCdefault.nix\fR.
.PP
\fCnix-build\fR is essentially a wrapper around
\fB\fCnix-instantiate\fR\fR (\fInix-instantiate.md\fR) (to translate a high-level Nix
expression to a low-level store derivation) and \fB\fCnix-store
--realise\fR\fR (\fInix-store.md#operation---realise\fR) (to build the store
derivation).
.RS
.PP
\fBWarning\fR
.PP
The result of the build is automatically registered as a root of the
Nix garbage collector. This root disappears automatically when the
\fCresult\fR symlink is deleted or renamed. So don’t rename the symlink.
.RE
.SH Options
All options not listed here are passed to \fCnix-store
--realise\fR, except for \fC--arg\fR and \fC--attr\fR / \fC-A\fR which are passed to
\fCnix-instantiate\fR.
.IP "\(bu" 2
\fC--no-out-link\fR
.br
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 \fCnix-store
--gc\fR.
.IP "\(bu" 2
\fC--dry-run\fR
.br
Show what store paths would be built or downloaded.
.IP "\(bu" 2
\fC--out-link\fR / \fC-o\fR \fIoutlink\fR
.br
Change the name of the symlink to the output path created from
\fCresult\fR to \fIoutlink\fR.
.LP
The following common options are supported:
.SH Examples
.LP
.EX
$ nix-build '<nixpkgs>' -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
.EE
.PP
If a derivation has multiple outputs, \fCnix-build\fR will build the default
(first) output. You can also build all outputs:
.LP
.EX
$ nix-build '<nixpkgs>' -A openssl.all
.EE
.PP
This will create a symlink for each output named \fCresult-outputname\fR.
The suffix is omitted if the output name is \fCout\fR. So if \fCopenssl\fR has
outputs \fCout\fR, \fCbin\fR and \fCman\fR, \fCnix-build\fR will create symlinks
\fCresult\fR, \fCresult-bin\fR and \fCresult-man\fR. It’s also possible to build a
specific output:
.LP
.EX
$ nix-build '<nixpkgs>' -A openssl.man
.EE
.PP
This will create a symlink \fCresult-man\fR.
.PP
Build a Nix expression given on the command line:
.LP
.EX
$ nix-build -E 'with import <nixpkgs> { }; runCommand \(dqfoo\(dq { } \(dqecho bar > $out\(dq'
$ cat ./result
bar
.EE
.PP
Build the GNU Hello package from the latest revision of the master
branch of Nixpkgs:
.LP
.EX
$ nix-build https://github.com/NixOS/nixpkgs/archive/master.tar.gz -A hello
.EE