362 lines
12 KiB
XML
362 lines
12 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xml:id="chap-stdenv">
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<title>The Standard Environment</title>
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<para>The standard build environment in the Nix Packages collection
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provides a environment for building Unix packages that does a lot of
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common build tasks automatically. In fact, for Unix packages that use
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the standard <literal>./configure; make; make install</literal> build
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interface, you don’t need to write a build script at all; the standard
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environment does everything automatically. If
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<literal>stdenv</literal> doesn’t do what you need automatically, you
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can easily customise or override the various build phases.</para>
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<section><title>Using <literal>stdenv</literal></title>
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<para>To build a package with the standard environment, you use the
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function <varname>stdenv.mkDerivation</varname>, instead of the
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primitive built-in function <varname>derivation</varname>, e.g.
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<programlisting>
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stdenv.mkDerivation {
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name = "libfoo-1.2.3";
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src = fetchurl {
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url = http://example.org/libfoo-1.2.3.tar.bz2;
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md5 = "e1ec107956b6ddcb0b8b0679367e9ac9";
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};
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}</programlisting>
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(<varname>stdenv</varname> needs to be in scope, so if you write this
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in a separate Nix expression from
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<filename>pkgs/all-packages.nix</filename>, you need to pass it as a
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function argument.) Specifying a <varname>name</varname> and a
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<varname>src</varname> is the absolute minimum you need to do. Many
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packages have dependencies that are not provided in the standard
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environment. It’s usually sufficient to specify those dependencies in
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the <varname>buildInputs</varname> attribute:
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<programlisting>
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stdenv.mkDerivation {
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name = "libfoo-1.2.3";
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...
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buildInputs = [libbar perl ncurses];
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}</programlisting>
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This attribute ensures that the <filename>bin</filename>
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subdirectories of these packages appear in the <envar>PATH</envar>
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environment variable during the build, that their
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<filename>include</filename> subdirectories are searched by the C
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compiler, and so on. (See <xref linkend="ssec-setup-hooks"/> for
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details.)</para>
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<para>Often it is necessary to override or modify some aspect of the
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build. To make this easier, the standard environment breaks the
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package build into a number of <emphasis>phases</emphasis>, all of
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which can be overriden or modified individually: unpacking the
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sources, applying patches, configuring, building, and installing.
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(There are some others; see <xref linkend="ssec-stdenv-phases"/>.)
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For instance, a package that doesn’t supply a makefile but instead has
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to be compiled “manually” could be handled like this:
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<programlisting>
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stdenv.mkDerivation {
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name = "fnord-4.5";
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...
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buildPhase = ''
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gcc foo.c -o foo
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'';
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installPhase = ''
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ensureDir $out/bin
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cp foo $out/bin
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'';
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}</programlisting>
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(Note the use of <literal>''</literal>-style string literals, which
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are very convenient for large multi-line script fragments because they
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don’t need escaping of <literal>"</literal> and <literal>\</literal>,
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and because indentation is intelligently removed.)</para>
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<para>There are many other attributes to customise the build. These
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are listed in <xref linkend="ssec-stdenv-attributes"/>.</para>
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<para>While the standard environment provides a generic builder, you
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can still supply your own build script:
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<programlisting>
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stdenv.mkDerivation {
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name = "libfoo-1.2.3";
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...
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builder = ./builder.sh;
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}</programlisting>
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where the builder can do anything it wants, but typically starts with
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<programlisting>
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source $stdenv/setup
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</programlisting>
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to let <literal>stdenv</literal> set up the environment (e.g., process
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the <varname>buildInputs</varname>). If you want, you can still use
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<literal>stdenv</literal>’s generic builder:
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<programlisting>
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source $stdenv/setup
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buildPhase() {
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echo "... this is my custom build phase ..."
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gcc foo.c -o foo
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}
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installPhase() {
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ensureDir $out/bin
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cp foo $out/bin
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}
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genericBuild
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</programlisting>
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</para>
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</section>
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<section><title>Tools provided by <literal>stdenv</literal></title>
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<para>The standard environment provides the following packages:
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<itemizedlist>
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<listitem><para>The GNU C Compiler, configured with C and C++
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support.</para></listitem>
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<listitem><para>GNU coreutils (contains a few dozen standard Unix
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commands).</para></listitem>
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<listitem><para>GNU findutils (contains
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<command>find</command>).</para></listitem>
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<listitem><para>GNU diffutils (contains <command>diff</command>,
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<command>cmp</command>).</para></listitem>
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<listitem><para>GNU <command>sed</command>.</para></listitem>
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<listitem><para>GNU <command>grep</command>.</para></listitem>
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<listitem><para>GNU <command>awk</command>.</para></listitem>
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<listitem><para>GNU <command>tar</command>.</para></listitem>
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<listitem><para><command>gzip</command> and
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<command>bzip2</command>.</para></listitem>
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<listitem><para>GNU Make. It has been patched to provide
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<quote>nested</quote> output that can be fed into the
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<command>nix-log2xml</command> command and
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<command>log2html</command> stylesheet to create a structured,
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readable output of the build steps performed by
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Make.</para></listitem>
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<listitem><para>Bash. This is the shell used for all builders in
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the Nix Packages collection. Not using <command>/bin/sh</command>
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removes a large source of portability problems.</para></listitem>
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<listitem><para>The <command>patch</command>
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command.</para></listitem>
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</itemizedlist>
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</para>
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<para>On Linux, <literal>stdenv</literal> also includes the
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<command>patchelf</command> utility.</para>
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</section>
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<section xml:id="ssec-stdenv-phases"><title>Build phases</title>
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<para>The generic builder has a number of <emphasis>phases</emphasis>.
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Each phase can be overriden in its entirety either by setting the
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environment variable
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<varname><replaceable>name</replaceable>Phase</varname> to a string
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containing some shell commands to be executed, or by redefining the
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shell function
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<varname><replaceable>name</replaceable>Phase</varname>. The former
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is convenient to override a phase from the derivation, while the
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latter is convenient from a build script.</para>
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<para>The phases are:
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<itemizedlist>
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<listitem>
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<para><function>unpackPhase</function> unpacks the source files
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listed in the <envar>src</envar> environment variable to the
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current directory. It supports <filename>tar</filename> files,
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optionally compressed with <command>gzip</command> or
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<command>bzip2</command>; Zip files (but note that the
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<command>unzip</command> command is not a part of the standard
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environment; you should add it as a build input yourself); and
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unpacked source trees (i.e., directories; they are copied
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verbatim). You can add support for other file types by setting
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the <varname>findUnpacker</varname> hook. This hook should set
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the variable <varname>unpackCmd</varname> to contain the command
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to be executed to unpack the file.</para>
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<para>After running <function>unpackPhase</function>, the generic
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builder changes the current directory to the directory created by
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unpacking the sources. If there are multiple source directories,
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you should set <varname>sourceRoot</varname> to the name of the
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intended directory.</para>
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<para>It also calls the hook <varname>postUnpack</varname> after
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unpacking.</para>
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</listitem>
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<listitem><para><function>patchPhase</function> calls the
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<command>patch</command> command with the <option>-p1</option>
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option (overridable via <envar>patchFlags</envar>) for each patch
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file listed in the <envar>patches</envar>
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variable.</para></listitem>
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<listitem>
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<para><function>configurePhase</function> runs the script called
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<filename>configure</filename> in the current directory with a
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<option>--prefix</option> set to the output path. You can add
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additional flags through the <varname>configureFlags</varname>
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variable. If <filename>configure</filename> does not exist,
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nothing happens.</para>
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<para>Before and after running <filename>configure</filename>, the
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hooks <varname>preConfigure</varname> and
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<varname>postConfigure</varname> are called, respectively.</para>
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</listitem>
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<listitem>
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<para><function>buildPhase</function> calls
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<command>make</command>. You can set flags for
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<command>make</command> through the <varname>makeFlags</varname>
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variable.</para>
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<para>Before and after running <command>make</command>, the hooks
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<varname>preBuild</varname> and <varname>postBuild</varname> are
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called, respectively.</para>
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</listitem>
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<listitem><para><function>checkPhase</function> calls <command>make
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check</command>, but only if the <varname>doCheck</varname> variable
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is set to <literal>1</literal>. Additional flags can be set through
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the <varname>checkFlags</varname> variable.</para></listitem>
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<listitem>
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<para><function>installPhase</function> calls <command>make
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install</command>. Additional flags can be set through the
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<varname>installFlags</varname> variable.</para>
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<para>Before and after running <command>make install</command>,
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the hooks <varname>preInstall</varname> and
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<varname>postInstall</varname> are called, respectively.</para>
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</listitem>
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<listitem>
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<para><function>fixupPhase</function> cleans up the
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installed files in various ways:
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<itemizedlist>
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<listitem><para>It moves the <filename>man/</filename>,
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<filename>doc/</filename> and <filename>info/</filename>
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subdirectories of <envar>$out</envar> to
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<filename>share/</filename>.</para></listitem>
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<listitem><para>It strips libraries and executables of debug
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information.</para></listitem>
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<listitem><para>On Linux, it applies the
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<command>patchelf</command> command to ELF executables and
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libraries to remove unused directories from the
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<literal>RPATH</literal> in order to prevent unnecessary
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dependencies.</para></listitem>
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<listitem><para>It rewrites the interpreter paths of shell
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scripts to paths found in <envar>PATH</envar>. E.g.,
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<filename>/usr/bin/perl</filename> will be rewritten to
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<filename>/nix/store/<replaceable>some-perl</replaceable>/bin/perl</filename>
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found in <envar>PATH</envar>.</para></listitem>
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</itemizedlist>
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</para>
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</listitem>
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<listitem>
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<para><function>distPhase</function> calls <command>make
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dist</command>, but only if the <varname>doDist</varname> variable
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is set to <literal>1</literal>. Additional flags can be set
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through the <varname>distFlags</varname> variable. The resulting
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tarball is copied to the <filename>/tarballs</filename>
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subdirectory of the output path.</para>
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<para>Before and after running <command>make dist</command>, the
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hooks <varname>preDist</varname> and <varname>postDist</varname>
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are called, respectively.</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>You can change the order in which phases are executed, or add
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new phases, by setting the <varname>phases</varname> variable. The
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default is <literal>patchPhase configurePhase buildPhase checkPhase
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installPhase distPhase</literal>.</para>
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</section>
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<section xml:id="ssec-stdenv-attributes"><title>Attributes</title>
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<para></para>
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</section>
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<section xml:id="ssec-setup-hooks"><title>Package setup hooks</title>
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<para></para>
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</section>
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<section><title>Purity in Nixpkgs</title>
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<para>[measures taken to prevent dependencies on packages outside the
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store, and what you can do to prevent them]</para>
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<para>GCC doesn't search in locations such as
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<filename>/usr/include</filename>. In fact, attempts to add such
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directories through the <option>-I</option> flag are filtered out.
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Likewise, the linker (from GNU binutils) doesn't search in standard
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locations such as <filename>/usr/lib</filename>. Programs built on
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Linux are linked against a GNU C Library that likewise doesn't search
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in the default system locations.</para>
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</section>
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</chapter>
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