nixpkgs/doc/stdenv.xml
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<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xml:id="chap-stdenv">
<title>The Standard Environment</title>
<para>The standard build environment in the Nix Packages collection
provides an environment for building Unix packages that does a lot of
common build tasks automatically. In fact, for Unix packages that use
the standard <literal>./configure; make; make install</literal> build
interface, you dont need to write a build script at all; the standard
environment does everything automatically. If
<literal>stdenv</literal> doesnt do what you need automatically, you
can easily customise or override the various build phases.</para>
<section xml:id="sec-using-stdenv"><title>Using
<literal>stdenv</literal></title>
<para>To build a package with the standard environment, you use the
function <varname>stdenv.mkDerivation</varname>, instead of the
primitive built-in function <varname>derivation</varname>, e.g.
<programlisting>
stdenv.mkDerivation {
name = "libfoo-1.2.3";
src = fetchurl {
url = http://example.org/libfoo-1.2.3.tar.bz2;
md5 = "e1ec107956b6ddcb0b8b0679367e9ac9";
};
}</programlisting>
(<varname>stdenv</varname> needs to be in scope, so if you write this
in a separate Nix expression from
<filename>pkgs/all-packages.nix</filename>, you need to pass it as a
function argument.) Specifying a <varname>name</varname> and a
<varname>src</varname> is the absolute minimum you need to do. Many
packages have dependencies that are not provided in the standard
environment. Its usually sufficient to specify those dependencies in
the <varname>buildInputs</varname> attribute:
<programlisting>
stdenv.mkDerivation {
name = "libfoo-1.2.3";
...
buildInputs = [libbar perl ncurses];
}</programlisting>
This attribute ensures that the <filename>bin</filename>
subdirectories of these packages appear in the <envar>PATH</envar>
environment variable during the build, that their
<filename>include</filename> subdirectories are searched by the C
compiler, and so on. (See <xref linkend="ssec-setup-hooks"/> for
details.)</para>
<para>Often it is necessary to override or modify some aspect of the
build. To make this easier, the standard environment breaks the
package build into a number of <emphasis>phases</emphasis>, all of
which can be overridden or modified individually: unpacking the
sources, applying patches, configuring, building, and installing.
(There are some others; see <xref linkend="sec-stdenv-phases"/>.)
For instance, a package that doesnt supply a makefile but instead has
to be compiled “manually” could be handled like this:
<programlisting>
stdenv.mkDerivation {
name = "fnord-4.5";
...
buildPhase = ''
gcc foo.c -o foo
'';
installPhase = ''
mkdir -p $out/bin
cp foo $out/bin
'';
}</programlisting>
(Note the use of <literal>''</literal>-style string literals, which
are very convenient for large multi-line script fragments because they
dont need escaping of <literal>"</literal> and <literal>\</literal>,
and because indentation is intelligently removed.)</para>
<para>There are many other attributes to customise the build. These
are listed in <xref linkend="ssec-stdenv-attributes"/>.</para>
<para>While the standard environment provides a generic builder, you
can still supply your own build script:
<programlisting>
stdenv.mkDerivation {
name = "libfoo-1.2.3";
...
builder = ./builder.sh;
}</programlisting>
where the builder can do anything it wants, but typically starts with
<programlisting>
source $stdenv/setup
</programlisting>
to let <literal>stdenv</literal> set up the environment (e.g., process
the <varname>buildInputs</varname>). If you want, you can still use
<literal>stdenv</literal>s generic builder:
<programlisting>
source $stdenv/setup
buildPhase() {
echo "... this is my custom build phase ..."
gcc foo.c -o foo
}
installPhase() {
mkdir -p $out/bin
cp foo $out/bin
}
genericBuild
</programlisting>
</para>
</section>
<section xml:id="sec-tools-of-stdenv"><title>Tools provided by
<literal>stdenv</literal></title>
<para>The standard environment provides the following packages:
<itemizedlist>
<listitem><para>The GNU C Compiler, configured with C and C++
support.</para></listitem>
<listitem><para>GNU coreutils (contains a few dozen standard Unix
commands).</para></listitem>
<listitem><para>GNU findutils (contains
<command>find</command>).</para></listitem>
<listitem><para>GNU diffutils (contains <command>diff</command>,
<command>cmp</command>).</para></listitem>
<listitem><para>GNU <command>sed</command>.</para></listitem>
<listitem><para>GNU <command>grep</command>.</para></listitem>
<listitem><para>GNU <command>awk</command>.</para></listitem>
<listitem><para>GNU <command>tar</command>.</para></listitem>
<listitem><para><command>gzip</command>, <command>bzip2</command>
and <command>xz</command>.</para></listitem>
<listitem><para>GNU Make. It has been patched to provide
<quote>nested</quote> output that can be fed into the
<command>nix-log2xml</command> command and
<command>log2html</command> stylesheet to create a structured,
readable output of the build steps performed by
Make.</para></listitem>
<listitem><para>Bash. This is the shell used for all builders in
the Nix Packages collection. Not using <command>/bin/sh</command>
removes a large source of portability problems.</para></listitem>
<listitem><para>The <command>patch</command>
command.</para></listitem>
</itemizedlist>
</para>
<para>On Linux, <literal>stdenv</literal> also includes the
<command>patchelf</command> utility.</para>
</section>
<section xml:id="ssec-stdenv-attributes"><title>Attributes</title>
<variablelist>
<title>Variables affecting <literal>stdenv</literal>
initialisation</title>
<varlistentry>
<term><varname>NIX_DEBUG</varname></term>
<listitem><para>If set, <literal>stdenv</literal> will print some
debug information during the build. In particular, the
<command>gcc</command> and <command>ld</command> wrapper scripts
will print out the complete command line passed to the wrapped
tools.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>buildInputs</varname></term>
<listitem><para>A list of dependencies used by
<literal>stdenv</literal> to set up the environment for the build.
For each dependency <replaceable>dir</replaceable>, the directory
<filename><replaceable>dir</replaceable>/bin</filename>, if it
exists, is added to the <envar>PATH</envar> environment variable.
Other environment variables are also set up via a pluggable
mechanism. For instance, if <varname>buildInputs</varname>
contains Perl, then the <filename>lib/site_perl</filename>
subdirectory of each input is added to the <envar>PERL5LIB</envar>
environment variable. See <xref linkend="ssec-setup-hooks"/> for
details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>propagatedBuildInputs</varname></term>
<listitem><para>Like <varname>buildInputs</varname>, but these
dependencies are <emphasis>propagated</emphasis>: that is, the
dependencies listed here are added to the
<varname>buildInputs</varname> of any package that uses
<emphasis>this</emphasis> package as a dependency. So if package
Y has <literal>propagatedBuildInputs = [X]</literal>, and package
Z has <literal>buildInputs = [Y]</literal>, then package X will
appear in Zs build environment automatically.</para></listitem>
</varlistentry>
</variablelist>
<variablelist>
<title>Variables affecting build properties</title>
<varlistentry>
<term><varname>enableParallelBuilding</varname></term>
<listitem><para>If set, <literal>stdenv</literal> will pass specific
flags to <literal>make</literal> and other build tools to enable
parallel building with up to <literal>build-cores</literal>
workers.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>preferLocalBuild</varname></term>
<listitem><para>If set, specifies that the package is so lightweight
in terms of build operations (e.g. write a text file from a Nix string
to the store) that there's no need to look for it in binary caches --
it's faster to just build it locally. It also tells Hydra and other
facilities that this package doesn't need to be exported in binary
caches (noone would use it, after all).</para></listitem>
</varlistentry>
</variablelist>
<variablelist>
<title>Special variables</title>
<varlistentry>
<term><varname>passthru</varname></term>
<listitem><para>This is an attribute set which can be filled with arbitrary
values. For example:
<programlisting>
passthru = {
foo = "bar";
baz = {
value1 = 4;
value2 = 5;
};
}
</programlisting>
</para>
<para>Values inside it are not passed to the builder, so you can change
them without triggering a rebuild. However, they can be accessed outside of a
derivation directly, as if they were set inside a derivation itself, e.g.
<literal>hello.baz.value1</literal>. We don't specify any usage or
schema of <literal>passthru</literal> - it is meant for values that would be
useful outside the derivation in other parts of a Nix expression (e.g. in other
derivations). An example would be to convey some specific dependency of your
derivation which contains a program with plugins support. Later, others who
make derivations with plugins can use passed-through dependency to ensure that
their plugin would be binary-compatible with built program.</para></listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="sec-stdenv-phases"><title>Phases</title>
<para>The generic builder has a number of <emphasis>phases</emphasis>.
Package builds are split into phases to make it easier to override
specific parts of the build (e.g., unpacking the sources or installing
the binaries). Furthermore, it allows a nicer presentation of build
logs in the Nix build farm.</para>
<para>Each phase can be overridden in its entirety either by setting
the environment variable
<varname><replaceable>name</replaceable>Phase</varname> to a string
containing some shell commands to be executed, or by redefining the
shell function
<varname><replaceable>name</replaceable>Phase</varname>. The former
is convenient to override a phase from the derivation, while the
latter is convenient from a build script.</para>
<section xml:id="ssec-controlling-phases"><title>Controlling
phases</title>
<para>There are a number of variables that control what phases are
executed and in what order:
<variablelist>
<title>Variables affecting phase control</title>
<varlistentry>
<term><varname>phases</varname></term>
<listitem>
<para>Specifies the phases. You can change the order in which
phases are executed, or add new phases, by setting this
variable. If its not set, the default value is used, which is
<literal>$prePhases unpackPhase patchPhase $preConfigurePhases
configurePhase $preBuildPhases buildPhase checkPhase
$preInstallPhases installPhase fixupPhase $preDistPhases
distPhase $postPhases</literal>.
</para>
<para>Usually, if you just want to add a few phases, its more
convenient to set one of the variables below (such as
<varname>preInstallPhases</varname>), as you then dont specify
all the normal phases.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>prePhases</varname></term>
<listitem>
<para>Additional phases executed before any of the default phases.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>preConfigurePhases</varname></term>
<listitem>
<para>Additional phases executed just before the configure phase.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>preBuildPhases</varname></term>
<listitem>
<para>Additional phases executed just before the build phase.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>preInstallPhases</varname></term>
<listitem>
<para>Additional phases executed just before the install phase.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>preFixupPhases</varname></term>
<listitem>
<para>Additional phases executed just before the fixup phase.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>preDistPhases</varname></term>
<listitem>
<para>Additional phases executed just before the distribution phase.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>postPhases</varname></term>
<listitem>
<para>Additional phases executed after any of the default
phases.</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</section>
<section xml:id="ssec-unpack-phase"><title>The unpack phase</title>
<para>The unpack phase is responsible for unpacking the source code of
the package. The default implementation of
<function>unpackPhase</function> unpacks the source files listed in
the <envar>src</envar> environment variable to the current directory.
It supports the following files by default:
<variablelist>
<varlistentry>
<term>Tar files</term>
<listitem><para>These can optionally be compressed using
<command>gzip</command> (<filename>.tar.gz</filename>,
<filename>.tgz</filename> or <filename>.tar.Z</filename>),
<command>bzip2</command> (<filename>.tar.bz2</filename> or
<filename>.tbz2</filename>) or <command>xz</command>
(<filename>.tar.xz</filename> or
<filename>.tar.lzma</filename>).</para></listitem>
</varlistentry>
<varlistentry>
<term>Zip files</term>
<listitem><para>Zip files are unpacked using
<command>unzip</command>. However, <command>unzip</command> is
not in the standard environment, so you should add it to
<varname>buildInputs</varname> yourself.</para></listitem>
</varlistentry>
<varlistentry>
<term>Directories in the Nix store</term>
<listitem><para>These are simply copied to the current directory.
The hash part of the file name is stripped,
e.g. <filename>/nix/store/1wydxgby13cz...-my-sources</filename>
would be copied to
<filename>my-sources</filename>.</para></listitem>
</varlistentry>
</variablelist>
Additional file types can be supported by setting the
<varname>unpackCmd</varname> variable (see below).</para>
<para></para>
<variablelist>
<title>Variables controlling the unpack phase</title>
<varlistentry>
<term><varname>srcs</varname> / <varname>src</varname></term>
<listitem><para>The list of source files or directories to be
unpacked or copied. One of these must be set.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>sourceRoot</varname></term>
<listitem><para>After running <function>unpackPhase</function>,
the generic builder changes the current directory to the directory
created by unpacking the sources. If there are multiple source
directories, you should set <varname>sourceRoot</varname> to the
name of the intended directory.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>setSourceRoot</varname></term>
<listitem><para>Alternatively to setting
<varname>sourceRoot</varname>, you can set
<varname>setSourceRoot</varname> to a shell command to be
evaluated by the unpack phase after the sources have been
unpacked. This command must set
<varname>sourceRoot</varname>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>preUnpack</varname></term>
<listitem><para>Hook executed at the start of the unpack
phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>postUnpack</varname></term>
<listitem><para>Hook executed at the end of the unpack
phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>dontMakeSourcesWritable</varname></term>
<listitem><para>If set to <literal>1</literal>, the unpacked
sources are <emphasis>not</emphasis> made
writable. By default, they are made writable to prevent problems
with read-only sources. For example, copied store directories
would be read-only without this.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>unpackCmd</varname></term>
<listitem><para>The unpack phase evaluates the string
<literal>$unpackCmd</literal> for any unrecognised file. The path
to the current source file is contained in the
<varname>curSrc</varname> variable.</para></listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="ssec-patch-phase"><title>The patch phase</title>
<para>The patch phase applies the list of patches defined in the
<varname>patches</varname> variable.</para>
<variablelist>
<title>Variables controlling the patch phase</title>
<varlistentry>
<term><varname>patches</varname></term>
<listitem><para>The list of patches. They must be in the format
accepted by the <command>patch</command> command, and may
optionally be compressed using <command>gzip</command>
(<filename>.gz</filename>), <command>bzip2</command>
(<filename>.bz2</filename>) or <command>xz</command>
(<filename>.xz</filename>).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>patchFlags</varname></term>
<listitem><para>Flags to be passed to <command>patch</command>.
If not set, the argument <option>-p1</option> is used, which
causes the leading directory component to be stripped from the
file names in each patch.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>prePatch</varname></term>
<listitem><para>Hook executed at the start of the patch
phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>postPatch</varname></term>
<listitem><para>Hook executed at the end of the patch
phase.</para></listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="ssec-configure-phase"><title>The configure phase</title>
<para>The configure phase prepares the source tree for building. The
default <function>configurePhase</function> runs
<filename>./configure</filename> (typically an Autoconf-generated
script) if it exists.</para>
<variablelist>
<title>Variables controlling the configure phase</title>
<varlistentry>
<term><varname>configureScript</varname></term>
<listitem><para>The name of the configure script. It defaults to
<filename>./configure</filename> if it exists; otherwise, the
configure phase is skipped. This can actually be a command (like
<literal>perl ./Configure.pl</literal>).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>configureFlags</varname></term>
<listitem><para>Additional arguments passed to the configure
script.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>configureFlagsArray</varname></term>
<listitem><para>A shell array containing additional arguments
passed to the configure script. You must use this instead of
<varname>configureFlags</varname> if the arguments contain
spaces.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>dontAddPrefix</varname></term>
<listitem><para>By default, the flag
<literal>--prefix=$prefix</literal> is added to the configure
flags. If this is undesirable, set this variable to
true.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>prefix</varname></term>
<listitem><para>The prefix under which the package must be
installed, passed via the <option>--prefix</option> option to the
configure script. It defaults to
<option>$out</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>dontAddDisableDepTrack</varname></term>
<listitem><para>By default, the flag
<literal>--disable-dependency-tracking</literal> is added to the
configure flags to speed up Automake-based builds. If this is
undesirable, set this variable to true.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>dontFixLibtool</varname></term>
<listitem><para>By default, the configure phase applies some
special hackery to all files called <filename>ltmain.sh</filename>
before running the configure script in order to improve the purity
of Libtool-based packages<footnote><para>It clears the
<varname>sys_lib_<replaceable>*</replaceable>search_path</varname>
variables in the Libtool script to prevent Libtool from using
libraries in <filename>/usr/lib</filename> and
such.</para></footnote>. If this is undesirable, set this
variable to true.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>dontDisableStatic</varname></term>
<listitem><para>By default, when the configure script has
<option>--enable-static</option>, the option
<option>--disable-static</option> is added to the configure flags.</para>
<para>If this is undesirable, set this variable to
true.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>preConfigure</varname></term>
<listitem><para>Hook executed at the start of the configure
phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>postConfigure</varname></term>
<listitem><para>Hook executed at the end of the configure
phase.</para></listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="build-phase"><title>The build phase</title>
<para>The build phase is responsible for actually building the package
(e.g. compiling it). The default <function>buildPhase</function>
simply calls <command>make</command> if a file named
<filename>Makefile</filename>, <filename>makefile</filename> or
<filename>GNUmakefile</filename> exists in the current directory (or
the <varname>makefile</varname> is explicitly set); otherwise it does
nothing.</para>
<variablelist>
<title>Variables controlling the build phase</title>
<varlistentry>
<term><varname>dontBuild</varname></term>
<listitem><para>Set to true to skip the build phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>makefile</varname></term>
<listitem><para>The file name of the Makefile.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>makeFlags</varname></term>
<listitem><para>Additional flags passed to
<command>make</command>. These flags are also used by the default
install and check phase. For setting make flags specific to the
build phase, use <varname>buildFlags</varname> (see
below).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>makeFlagsArray</varname></term>
<listitem><para>A shell array containing additional arguments
passed to <command>make</command>. You must use this instead of
<varname>makeFlags</varname> if the arguments contain
spaces, e.g.
<programlisting>
makeFlagsArray=(CFLAGS="-O0 -g" LDFLAGS="-lfoo -lbar")
</programlisting>
Note that shell arrays cannot be passed through environment
variables, so you cannot set <varname>makeFlagsArray</varname> in
a derivation attribute (because those are passed through
environment variables): you have to define them in shell
code.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>buildFlags</varname> / <varname>buildFlagsArray</varname></term>
<listitem><para>Additional flags passed to
<command>make</command>. Like <varname>makeFlags</varname> and
<varname>makeFlagsArray</varname>, but only used by the build
phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>preBuild</varname></term>
<listitem><para>Hook executed at the start of the build
phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>postBuild</varname></term>
<listitem><para>Hook executed at the end of the build
phase.</para></listitem>
</varlistentry>
</variablelist>
<para>
You can set flags for <command>make</command> through the
<varname>makeFlags</varname> variable.</para>
<para>Before and after running <command>make</command>, the hooks
<varname>preBuild</varname> and <varname>postBuild</varname> are
called, respectively.</para>
</section>
<section xml:id="ssec-check-phase"><title>The check phase</title>
<para>The check phase checks whether the package was built correctly
by running its test suite. The default
<function>checkPhase</function> calls <command>make check</command>,
but only if the <varname>doCheck</varname> variable is enabled.</para>
<variablelist>
<title>Variables controlling the check phase</title>
<varlistentry>
<term><varname>doCheck</varname></term>
<listitem><para>If set to a non-empty string, the check phase is
executed, otherwise it is skipped (default). Thus you should set
<programlisting>
doCheck = true;</programlisting>
in the derivation to enable checks.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>makeFlags</varname> /
<varname>makeFlagsArray</varname> /
<varname>makefile</varname></term>
<listitem><para>See the build phase for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>checkTarget</varname></term>
<listitem><para>The make target that runs the tests. Defaults to
<literal>check</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>checkFlags</varname> / <varname>checkFlagsArray</varname></term>
<listitem><para>Additional flags passed to
<command>make</command>. Like <varname>makeFlags</varname> and
<varname>makeFlagsArray</varname>, but only used by the check
phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>preCheck</varname></term>
<listitem><para>Hook executed at the start of the check
phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>postCheck</varname></term>
<listitem><para>Hook executed at the end of the check
phase.</para></listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="ssec-install-phase"><title>The install phase</title>
<para>The install phase is responsible for installing the package in
the Nix store under <envar>out</envar>. The default
<function>installPhase</function> creates the directory
<literal>$out</literal> and calls <command>make
install</command>.</para>
<variablelist>
<title>Variables controlling the install phase</title>
<varlistentry>
<term><varname>makeFlags</varname> /
<varname>makeFlagsArray</varname> /
<varname>makefile</varname></term>
<listitem><para>See the build phase for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>installTargets</varname></term>
<listitem><para>The make targets that perform the installation.
Defaults to <literal>install</literal>. Example:
<programlisting>
installTargets = "install-bin install-doc";</programlisting>
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>installFlags</varname> / <varname>installFlagsArray</varname></term>
<listitem><para>Additional flags passed to
<command>make</command>. Like <varname>makeFlags</varname> and
<varname>makeFlagsArray</varname>, but only used by the install
phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>preInstall</varname></term>
<listitem><para>Hook executed at the start of the install
phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>postInstall</varname></term>
<listitem><para>Hook executed at the end of the install
phase.</para></listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="ssec-fixup-phase"><title>The fixup phase</title>
<para>The fixup phase performs some (Nix-specific) post-processing
actions on the files installed under <filename>$out</filename> by the
install phase. The default <function>fixupPhase</function> does the
following:
<itemizedlist>
<listitem><para>It moves the <filename>man/</filename>,
<filename>doc/</filename> and <filename>info/</filename>
subdirectories of <envar>$out</envar> to
<filename>share/</filename>.</para></listitem>
<listitem><para>It strips libraries and executables of debug
information.</para></listitem>
<listitem><para>On Linux, it applies the <command>patchelf</command>
command to ELF executables and libraries to remove unused
directories from the <literal>RPATH</literal> in order to prevent
unnecessary runtime dependencies.</para></listitem>
<listitem><para>It rewrites the interpreter paths of shell scripts
to paths found in <envar>PATH</envar>. E.g.,
<filename>/usr/bin/perl</filename> will be rewritten to
<filename>/nix/store/<replaceable>some-perl</replaceable>/bin/perl</filename>
found in <envar>PATH</envar>.</para></listitem>
</itemizedlist>
</para>
<variablelist>
<title>Variables controlling the fixup phase</title>
<varlistentry>
<term><varname>dontStrip</varname></term>
<listitem><para>If set, libraries and executables are not
stripped. By default, they are.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>dontMoveSbin</varname></term>
<listitem><para>If set, files in <filename>$out/sbin</filename> are not moved
to <filename>$out/bin</filename>. By default, they are.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>stripAllList</varname></term>
<listitem><para>List of directories to search for libraries and
executables from which <emphasis>all</emphasis> symbols should be
stripped. By default, its empty. Stripping all symbols is
risky, since it may remove not just debug symbols but also ELF
information necessary for normal execution.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>stripAllFlags</varname></term>
<listitem><para>Flags passed to the <command>strip</command>
command applied to the files in the directories listed in
<varname>stripAllList</varname>. Defaults to <option>-s</option>
(i.e. <option>--strip-all</option>).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>stripDebugList</varname></term>
<listitem><para>List of directories to search for libraries and
executables from which only debugging-related symbols should be
stripped. It defaults to <literal>lib bin
sbin</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>stripDebugFlags</varname></term>
<listitem><para>Flags passed to the <command>strip</command>
command applied to the files in the directories listed in
<varname>stripDebugList</varname>. Defaults to
<option>-S</option>
(i.e. <option>--strip-debug</option>).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>dontPatchELF</varname></term>
<listitem><para>If set, the <command>patchelf</command> command is
not used to remove unnecessary <literal>RPATH</literal> entries.
Only applies to Linux.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>dontPatchShebangs</varname></term>
<listitem><para>If set, scripts starting with
<literal>#!</literal> do not have their interpreter paths
rewritten to paths in the Nix store.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>forceShare</varname></term>
<listitem><para>The list of directories that must be moved from
<filename>$out</filename> to <filename>$out/share</filename>.
Defaults to <literal>man doc info</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>setupHook</varname></term>
<listitem><para>A package can export a <link
linkend="ssec-setup-hooks">setup hook</link> by setting this
variable. The setup hook, if defined, is copied to
<filename>$out/nix-support/setup-hook</filename>. Environment
variables are then substituted in it using <function
linkend="fun-substituteAll">substituteAll</function>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>preFixup</varname></term>
<listitem><para>Hook executed at the start of the fixup
phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>postFixup</varname></term>
<listitem><para>Hook executed at the end of the fixup
phase.</para></listitem>
</varlistentry>
<varlistentry xml:id="stdenv-separateDebugInfo">
<term><varname>separateDebugInfo</varname></term>
<listitem><para>If set to <literal>true</literal>, the standard
environment will enable debug information in C/C++ builds. After
installation, the debug information will be separated from the
executables and stored in the output named
<literal>debug</literal>. (This output is enabled automatically;
you dont need to set the <varname>outputs</varname> attribute
explicitly.) To be precise, the debug information is stored in
<filename><replaceable>debug</replaceable>/lib/debug/.build-id/<replaceable>XX</replaceable>/<replaceable>YYYY…</replaceable></filename>,
where <replaceable>XXYYYY…</replaceable> is the <replaceable>build
ID</replaceable> of the binary — a SHA-1 hash of the contents of
the binary. Debuggers like GDB use the build ID to look up the
separated debug information.</para>
<para>For example, with GDB, you can add
<programlisting>
set debug-file-directory ~/.nix-profile/lib/debug
</programlisting>
to <filename>~/.gdbinit</filename>. GDB will then be able to find
debug information installed via <literal>nix-env
-i</literal>.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="ssec-distribution-phase"><title>The distribution
phase</title>
<para>The distribution phase is intended to produce a source
distribution of the package. The default
<function>distPhase</function> first calls <command>make
dist</command>, then it copies the resulting source tarballs to
<filename>$out/tarballs/</filename>. This phase is only executed if
the attribute <varname>doDist</varname> is set.</para>
<variablelist>
<title>Variables controlling the distribution phase</title>
<varlistentry>
<term><varname>distTarget</varname></term>
<listitem><para>The make target that produces the distribution.
Defaults to <literal>dist</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>distFlags</varname> / <varname>distFlagsArray</varname></term>
<listitem><para>Additional flags passed to
<command>make</command>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>tarballs</varname></term>
<listitem><para>The names of the source distribution files to be
copied to <filename>$out/tarballs/</filename>. It can contain
shell wildcards. The default is
<filename>*.tar.gz</filename>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>dontCopyDist</varname></term>
<listitem><para>If set, no files are copied to
<filename>$out/tarballs/</filename>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>preDist</varname></term>
<listitem><para>Hook executed at the start of the distribution
phase.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>postDist</varname></term>
<listitem><para>Hook executed at the end of the distribution
phase.</para></listitem>
</varlistentry>
</variablelist>
</section>
</section>
<section xml:id="ssec-stdenv-functions"><title>Shell functions</title>
<para>The standard environment provides a number of useful
functions.</para>
<variablelist>
<varlistentry xml:id='fun-substitute'>
<term><function>substitute</function>
<replaceable>infile</replaceable>
<replaceable>outfile</replaceable>
<replaceable>subs</replaceable></term>
<listitem>
<para>Performs string substitution on the contents of
<replaceable>infile</replaceable>, writing the result to
<replaceable>outfile</replaceable>. The substitutions in
<replaceable>subs</replaceable> are of the following form:
<variablelist>
<varlistentry>
<term><option>--replace</option>
<replaceable>s1</replaceable>
<replaceable>s2</replaceable></term>
<listitem><para>Replace every occurence of the string
<replaceable>s1</replaceable> by
<replaceable>s2</replaceable>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--subst-var</option>
<replaceable>varName</replaceable></term>
<listitem><para>Replace every occurence of
<literal>@<replaceable>varName</replaceable>@</literal> by
the contents of the environment variable
<replaceable>varName</replaceable>. This is useful for
generating files from templates, using
<literal>@<replaceable>...</replaceable>@</literal> in the
template as placeholders.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--subst-var-by</option>
<replaceable>varName</replaceable>
<replaceable>s</replaceable></term>
<listitem><para>Replace every occurence of
<literal>@<replaceable>varName</replaceable>@</literal> by
the string <replaceable>s</replaceable>.</para></listitem>
</varlistentry>
</variablelist>
</para>
<para>Example:
<programlisting>
substitute ./foo.in ./foo.out \
--replace /usr/bin/bar $bar/bin/bar \
--replace "a string containing spaces" "some other text" \
--subst-var someVar
</programlisting>
</para>
<para><function>substitute</function> is implemented using the
<command
xlink:href="http://replace.richardlloyd.org.uk/">replace</command>
command. Unlike with the <command>sed</command> command, you
dont have to worry about escaping special characters. It
supports performing substitutions on binary files (such as
executables), though there youll probably want to make sure
that the replacement string is as long as the replaced
string.</para>
</listitem>
</varlistentry>
<varlistentry xml:id='fun-substituteInPlace'>
<term><function>substituteInPlace</function>
<replaceable>file</replaceable>
<replaceable>subs</replaceable></term>
<listitem><para>Like <function>substitute</function>, but performs
the substitutions in place on the file
<replaceable>file</replaceable>.</para></listitem>
</varlistentry>
<varlistentry xml:id='fun-substituteAll'>
<term><function>substituteAll</function>
<replaceable>infile</replaceable>
<replaceable>outfile</replaceable></term>
<listitem><para>Replaces every occurence of
<literal>@<replaceable>varName</replaceable>@</literal>, where
<replaceable>varName</replaceable> is any environment variable, in
<replaceable>infile</replaceable>, writing the result to
<replaceable>outfile</replaceable>. For instance, if
<replaceable>infile</replaceable> has the contents
<programlisting>
#! @bash@/bin/sh
PATH=@coreutils@/bin
echo @foo@
</programlisting>
and the environment contains
<literal>bash=/nix/store/bmwp0q28cf21...-bash-3.2-p39</literal>
and
<literal>coreutils=/nix/store/68afga4khv0w...-coreutils-6.12</literal>,
but does not contain the variable <varname>foo</varname>, then the
output will be
<programlisting>
#! /nix/store/bmwp0q28cf21...-bash-3.2-p39/bin/sh
PATH=/nix/store/68afga4khv0w...-coreutils-6.12/bin
echo @foo@
</programlisting>
That is, no substitution is performed for undefined variables.</para>
<para>Environment variables that start with an uppercase letter or an
underscore are filtered out,
to prevent global variables (like <literal>HOME</literal>) or private
variables (like <literal>__ETC_PROFILE_DONE</literal>) from accidentally
getting substituted.
The variables also have to be valid bash “names”, as
defined in the bash manpage (alphanumeric or <literal>_</literal>,
must not start with a number).</para>
</listitem>
</varlistentry>
<varlistentry xml:id='fun-substituteAllInPlace'>
<term><function>substituteAllInPlace</function>
<replaceable>file</replaceable></term>
<listitem><para>Like <function>substituteAll</function>, but performs
the substitutions in place on the file
<replaceable>file</replaceable>.</para></listitem>
</varlistentry>
<varlistentry xml:id='fun-stripHash'>
<term><function>stripHash</function>
<replaceable>path</replaceable></term>
<listitem><para>Strips the directory and hash part of a store
path, storing the name part in the environment variable
<literal>strippedName</literal>. For example:
<programlisting>
stripHash "/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24"
# prints coreutils-8.24
echo $strippedName
</programlisting>
If you wish to store the result in another variable, then the
following idiom may be useful:
<programlisting>
name="/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24"
someVar=$(stripHash $name; echo $strippedName)
</programlisting>
</para></listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="ssec-setup-hooks"><title>Package setup hooks</title>
<para>The following packages provide a setup hook:
<variablelist>
<varlistentry>
<term>GCC wrapper</term>
<listitem><para>Adds the <filename>include</filename> subdirectory
of each build input to the <envar>NIX_CFLAGS_COMPILE</envar>
environment variable, and the <filename>lib</filename> and
<filename>lib64</filename> subdirectories to
<envar>NIX_LDFLAGS</envar>.</para></listitem>
</varlistentry>
<varlistentry>
<term>Perl</term>
<listitem><para>Adds the <filename>lib/site_perl</filename> subdirectory
of each build input to the <envar>PERL5LIB</envar>
environment variable.</para></listitem>
</varlistentry>
<varlistentry>
<term>Python</term>
<listitem><para>Adds the
<filename>lib/${python.libPrefix}/site-packages</filename> subdirectory of
each build input to the <envar>PYTHONPATH</envar> environment
variable.</para></listitem>
</varlistentry>
<varlistentry>
<term>pkg-config</term>
<listitem><para>Adds the <filename>lib/pkgconfig</filename> and
<filename>share/pkgconfig</filename> subdirectories of each
build input to the <envar>PKG_CONFIG_PATH</envar> environment
variable.</para></listitem>
</varlistentry>
<varlistentry>
<term>Automake</term>
<listitem><para>Adds the <filename>share/aclocal</filename>
subdirectory of each build input to the <envar>ACLOCAL_PATH</envar>
environment variable.</para></listitem>
</varlistentry>
<varlistentry>
<term>Autoconf</term>
<listitem><para>The <varname>autoreconfHook</varname> derivation adds
<varname>autoreconfPhase</varname>, which runs autoreconf, libtoolize and
automake, essentially preparing the configure script in autotools-based
builds.</para></listitem>
</varlistentry>
<varlistentry>
<term>libxml2</term>
<listitem><para>Adds every file named
<filename>catalog.xml</filename> found under the
<filename>xml/dtd</filename> and <filename>xml/xsl</filename>
subdirectories of each build input to the
<envar>XML_CATALOG_FILES</envar> environment
variable.</para></listitem>
</varlistentry>
<varlistentry>
<term>teTeX / TeX Live</term>
<listitem><para>Adds the <filename>share/texmf-nix</filename>
subdirectory of each build input to the <envar>TEXINPUTS</envar>
environment variable.</para></listitem>
</varlistentry>
<varlistentry>
<term>Qt 4</term>
<listitem><para>Sets the <envar>QTDIR</envar> environment variable
to Qts path.</para></listitem>
</varlistentry>
<varlistentry>
<term>gdk-pixbuf</term>
<listitem><para>Exports <envar>GDK_PIXBUF_MODULE_FILE</envar>
environment variable the the builder. Add librsvg package
to <varname>buildInputs</varname> to get svg support.</para></listitem>
</varlistentry>
<varlistentry>
<term>GHC</term>
<listitem><para>Creates a temporary package database and registers
every Haskell build input in it (TODO: how?).</para></listitem>
</varlistentry>
<varlistentry>
<term>GStreamer</term>
<listitem><para>Adds the
GStreamer plugins subdirectory of
each build input to the <envar>GST_PLUGIN_SYSTEM_PATH_1_0</envar> or
<envar>GST_PLUGIN_SYSTEM_PATH</envar> environment variable.</para></listitem>
</varlistentry>
</variablelist>
</para>
</section>
<section xml:id="sec-purity-in-nixpkgs"><title>Purity in Nixpkgs</title>
<para>[measures taken to prevent dependencies on packages outside the
store, and what you can do to prevent them]</para>
<para>GCC doesn't search in locations such as
<filename>/usr/include</filename>. In fact, attempts to add such
directories through the <option>-I</option> flag are filtered out.
Likewise, the linker (from GNU binutils) doesn't search in standard
locations such as <filename>/usr/lib</filename>. Programs built on
Linux are linked against a GNU C Library that likewise doesn't search
in the default system locations.</para>
</section>
</chapter>