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98 lines
3 KiB
XML
98 lines
3 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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version="5.0"
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xml:id='sec-generic-builder'>
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<title>Generic Builder Syntax</title>
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<para>Recall from <xref linkend='ex-hello-builder' /> that the builder
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looked something like this:
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<programlisting>
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PATH=$perl/bin:$PATH
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tar xvfz $src
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cd hello-*
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./configure --prefix=$out
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make
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make install</programlisting>
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The builders for almost all Unix packages look like this — set up some
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environment variables, unpack the sources, configure, build, and
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install. For this reason the standard environment provides some Bash
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functions that automate the build process. Here is what a builder
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using the generic build facilities looks like:</para>
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<programlisting>
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buildInputs="$perl" ①
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source $stdenv/setup ②
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genericBuild ③</programlisting>
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<para>Here is what each line means:
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<orderedlist>
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<listitem>
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<para>The <literal>buildInputs</literal> variable tells
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<filename>setup</filename> to use the indicated packages as
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<quote>inputs</quote>. This means that if a package provides a
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<filename>bin</filename> subdirectory, it's added to
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<literal>PATH</literal>; if it has a <filename>include</filename>
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subdirectory, it's added to GCC's header search path; and so
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on. (This is implemented in a modular way:
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<filename>setup</filename> tries to source the file
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<filename><emphasis>pkg</emphasis>/nix-support/setup-hook</filename>
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of all dependencies. These “setup hooks” can then set up whatever
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environment variables they want; for instance, the setup hook for
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Perl sets the <literal>PERL5LIB</literal> environment variable to
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contain the <filename>lib/site_perl</filename> directories of all
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inputs.)
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</para>
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</listitem>
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<listitem arearefs='ex-hello-builder2-co-2'>
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<para>The function <function>genericBuild</function> is defined in
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the file <literal>$stdenv/setup</literal>.</para>
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</listitem>
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<listitem arearefs='ex-hello-builder2-co-3'>
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<para>The final step calls the shell function
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<function>genericBuild</function>, which performs the steps that
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were done explicitly in <xref linkend='ex-hello-builder' />. The
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generic builder is smart enough to figure out whether to unpack
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the sources using <command>gzip</command>,
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<command>bzip2</command>, etc. It can be customised in many ways;
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see the Nixpkgs manual for details.</para>
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</listitem>
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</orderedlist>
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</para>
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<para>Discerning readers will note that the
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<literal>buildInputs</literal> could just as well have been set in the Nix
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expression, like this:
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<programlisting>
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buildInputs = [ perl ];</programlisting>
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The <varname>perl</varname> attribute can then be removed, and the
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builder becomes even shorter:
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<programlisting>
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source $stdenv/setup
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genericBuild</programlisting>
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In fact, <varname>mkDerivation</varname> provides a default builder
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that looks exactly like that, so it is actually possible to omit the
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builder for Hello entirely.</para>
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</section>
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