mirror of
https://github.com/privatevoid-net/nix-super.git
synced 2024-12-02 02:16:15 +02:00
114 lines
4.1 KiB
XML
114 lines
4.1 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
|
|
xmlns:xlink="http://www.w3.org/1999/xlink"
|
|
xmlns:xi="http://www.w3.org/2001/XInclude"
|
|
version="5.0"
|
|
xml:id='sec-build-script'>
|
|
|
|
<title>Build Script</title>
|
|
|
|
<para>Here is the builder referenced
|
|
from Hello's Nix expression (stored in
|
|
<filename>pkgs/applications/misc/hello/ex-1/builder.sh</filename>):</para>
|
|
|
|
<programlisting>
|
|
source $stdenv/setup ①
|
|
|
|
PATH=$perl/bin:$PATH ②
|
|
|
|
tar xvfz $src ③
|
|
cd hello-*
|
|
./configure --prefix=$out ④
|
|
make ⑤
|
|
make install</programlisting>
|
|
|
|
<para>The builder can actually be made a lot shorter by using the
|
|
<emphasis>generic builder</emphasis> functions provided by
|
|
<varname>stdenv</varname>, but here we write out the build steps to
|
|
elucidate what a builder does. It performs the following
|
|
steps:</para>
|
|
|
|
<orderedlist>
|
|
|
|
<listitem>
|
|
|
|
<para>When Nix runs a builder, it initially completely clears the
|
|
environment (except for the attributes declared in the
|
|
derivation). This is done to prevent undeclared inputs from being
|
|
used in the build process. If for example the
|
|
<literal>PATH</literal> contained <filename>/usr/bin</filename>,
|
|
then you might accidentally use
|
|
<filename>/usr/bin/gcc</filename>.</para>
|
|
|
|
<para>So the first step is to set up the environment. This is
|
|
done by calling the <filename>setup</filename> script of the
|
|
standard environment. The environment variable
|
|
<literal>stdenv</literal> points to the location of the standard
|
|
environment being used. (It wasn't specified explicitly as an
|
|
attribute in <xref linkend='ex-hello-nix' />, but
|
|
<varname>mkDerivation</varname> adds it automatically.)</para>
|
|
|
|
</listitem>
|
|
|
|
<listitem>
|
|
|
|
<para>Since Hello needs Perl, we have to make sure that Perl is in
|
|
the <literal>PATH</literal>. The <literal>perl</literal> environment
|
|
variable points to the location of the Perl package (since it
|
|
was passed in as an attribute to the derivation), so
|
|
<filename><emphasis>$perl</emphasis>/bin</filename> is the
|
|
directory containing the Perl interpreter.</para>
|
|
|
|
</listitem>
|
|
|
|
<listitem>
|
|
|
|
<para>Now we have to unpack the sources. The
|
|
<varname>src</varname> attribute was bound to the result of
|
|
fetching the Hello source tarball from the network, so the
|
|
<literal>src</literal> environment variable points to the location in
|
|
the Nix store to which the tarball was downloaded. After
|
|
unpacking, we <command>cd</command> to the resulting source
|
|
directory.</para>
|
|
|
|
<para>The whole build is performed in a temporary directory
|
|
created in <varname>/tmp</varname>, by the way. This directory is
|
|
removed after the builder finishes, so there is no need to clean
|
|
up the sources afterwards. Also, the temporary directory is
|
|
always newly created, so you don't have to worry about files from
|
|
previous builds interfering with the current build.</para>
|
|
|
|
</listitem>
|
|
|
|
<listitem>
|
|
|
|
<para>GNU Hello is a typical Autoconf-based package, so we first
|
|
have to run its <filename>configure</filename> script. In Nix
|
|
every package is stored in a separate location in the Nix store,
|
|
for instance
|
|
<filename>/nix/store/9a54ba97fb71b65fda531012d0443ce2-hello-2.1.1</filename>.
|
|
Nix computes this path by cryptographically hashing all attributes
|
|
of the derivation. The path is passed to the builder through the
|
|
<literal>out</literal> environment variable. So here we give
|
|
<filename>configure</filename> the parameter
|
|
<literal>--prefix=$out</literal> to cause Hello to be installed in
|
|
the expected location.</para>
|
|
|
|
</listitem>
|
|
|
|
<listitem>
|
|
|
|
<para>Finally we build Hello (<literal>make</literal>) and install
|
|
it into the location specified by <literal>out</literal>
|
|
(<literal>make install</literal>).</para>
|
|
|
|
</listitem>
|
|
|
|
</orderedlist>
|
|
|
|
<para>If you are wondering about the absence of error checking on the
|
|
result of various commands called in the builder: this is because the
|
|
shell script is evaluated with Bash's <option>-e</option> option,
|
|
which causes the script to be aborted if any command fails without an
|
|
error check.</para>
|
|
|
|
</section>
|