doc: Write "Building from the Command Line".

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Ludovic Courtès 2011-10-12 14:20:02 +00:00
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@ -353,15 +353,66 @@ in
</section>
<section>
<title>Building on the Command Line</title>
<title>Building from the Command Line</title>
Overigens zijn die helemaal niet Hydra-specifiek, je kunt ze gewoon vanaf de
command line bouwen, bijv. als je een patchelf checkout hebt (met een nixpkgs
checkout in ../nixpkgs):
<para>
It is often useful to test a build recipe, for instance before
it is actually used by Hydra, when testing changes, or when
debugging a build issue. Since build recipes for Hydra jobsets
are just plain Nix expressions, they can be evaluated using the
standard Nix tools.
</para>
<para>
To evaluate the <varname>tarball</varname> jobset of <xref
linkend='ex-hello' />, just run:
<screen>
$ nix-build release.nix -A rpm_fedora10i386
$ nix-build release.nix -A tarball
</screen>
However, doing this with <xref linkend='ex-hello' /> as is will
probably yield an error like this:
<screen>
error: cannot auto-call a function that has an argument without a default value (`nixpkgs')
</screen>
This is because no value was specified for the
<varname>nixpkgs</varname> argument of the Nix expression.
</para>
<para>
This is fixed by providing a default value for that argument in
the Nix expression, which will allow <command>nix-build</command>
to auto-call the function: instfead of writing <literal>{ nixpkgs
}:</literal>, we now write <literal>{ nixpkgs ? &lt;nixpkgs&gt;
}:</literal>. What it means is that, by default, the
<varname>nixpkgs</varname> variable will be bound to the absolute
path of any <filename>nixpkgs</filename> file found in the Nix
search path. Similarly, a default value for
<varname>helloSrc</varname> needs to be provided.
</para>
<para>
Thus, assuming a checkout of Nixpkgs is available under
<filename>$HOME/src/nixpkgs</filename>, the
<varname>tarball</varname> jobset can now be evaluated by running:
<screen>
$ nix-build -I ~/src release.nix -A tarball
</screen>
Similarly, the <varname>build</varname> jobset can be evaluated:
<screen>
$ nix-build -I ~/src release.nix -A build
</screen>
The <varname>build</varname> job reuses the result of the
<varname>tarball</varname> job, rebuilding it only if it needs to.
</para>
</section>
</chapter>